naloxone and Disease-Models--Animal

Anxiety is the most prevalent brain disorder and a common cause of human disability. Animal models are critical for understanding anxiety pathogenesis and its pharmacotherapy. The zebrafish (Danio rerio) is increasingly utilized as a powerful model organism in anxiety research and anxiolytic drug screening. High similarity between human, rodent and zebrafish molecular targets implies shared signaling pathways involved in anxiety pathogenesis. However, mounting evidence shows that zebrafish behavior can be modulated by drugs beyond conventional anxiolytics or anxiogenics. Furthermore, these effects may differ from human and/or rodent responses, as such 'unconventional' drugs may affect zebrafish behavior despite having no such profiles (or exerting opposite effects) in humans or rodents. Here, we discuss the effects of several putative unconventional anxiotropic drugs (aspirin, lysergic acid diethylamide (LSD), nicotine, naloxone and naltrexone) and their potential mechanisms of action in zebrafish. Emphasizing the growing utility of zebrafish models in CNS drug discovery, such unconventional anxiety pharmacology may provide important, evolutionarily relevant insights into complex regulation of anxiety in biological systems. Albeit seemingly complicating direct translation from zebrafish into clinical phenotypes, this knowledge may instead foster the development of novel CNS drugs, eventually facilitating innovative treatment of patients based on novel 'unconventional' targets identified in fish models.

Topics: Animals; Anti-Anxiety Agents; Anxiety; Aspirin; Behavior, Animal; Disease Models, Animal; Humans; Lysergic Acid Diethylamide; Motor Activity; Naloxone; Naltrexone; Nicotine; Zebrafish

Although antagonist drugs are receiving increasing attention in the treatment of opioid withdrawal, the mechanisms of interaction of opiate agonists and antagonists remain largely to be investigated. We focused on the effects of very low quantities of opiate antagonists, following the clinical indication of their potential utility in detoxification. Upon reviewing the evidence on the administration of small doses of naloxone and naltrexone in the presence of agonist drugs, the effects of low-dose naltrexone during opiate administration and withdrawal are described. The application of a translational methodology allowed completing the clinical design with behavioral and cellular information obtained from a specifically developed animal model. The initial results indicate that low doses of naltrexone may help reducing the manifestation of opioid withdrawal, offer suggestions for further investigations and confirm the utility of a translational research approach to the clinical neurobiology of drug addiction.

Topics: Animals; Brain; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Humans; Naloxone; Naltrexone; Narcotic Antagonists; Narcotics; Opioid-Related Disorders; Substance Withdrawal Syndrome

Recent data support the view that neuropeptide mediators, in particular opioid peptides, participate in the control of hematopoiesis. The main arguments are: neuropeptides modulate the functions of lymphoid cells, macrophages and mature granulocytes; they control cell proliferation and differentiation in many tissues, particularly during embryogenesis; lymphoid cells, macrophages, polymorphonuclear granulocytes and bone marrow stromal elements express neuropeptide receptors; bone marrow cells produce opioid-like neuropeptides; the CD10/CALLA marker of lymphoid, myeloid and marrow stromal cells is an enzyme, endopeptidase, which cleaves- and thus activates/inactivates-opioid and other neuropeptides. We have shown that opioid peptides enkephalins, opioid antagonist naloxone, and the inhibitor of enkephalin-degrading endopeptidase, thiorphan, modulate the proliferation and differentiation of hematopoietic cells in clonal and long-term cultures of mouse bone marrow. The effects partly depended on the presence of the accessory hematopoietic elements, and followed a circadian pattern. The dose-responses were irregular, showed strain-dependent and individual variations, and apparently reflected the state of the activity of target cells, cellular interactions and simultaneous signals by other mediators. The enkephalins were shown to bind to specific (opioid) receptors on the target cells, and their signals to be transmitted to the cell interior by a cascade of secondary messengers including diacyl-glycerol (DAG), protein-kinase C (PKC) and Ca++ ions. Neuropeptide regulation of hematopoiesis might belong to a complex immuno-neuroendocrine network including melatonin.

Topics: Animals; Antibody Formation; Disease Models, Animal; Enkephalins; Hematopoiesis; Hematopoietic System; Immune System; In Vitro Techniques; Mice; Naloxone; Narcotic Antagonists; Neprilysin; Neuropeptides; Opioid Peptides

Topics: Animals; Antibodies; beta-Endorphin; Disease Models, Animal; Endorphins; Immunity, Cellular; Inflammation; Naloxone; Neuroimmunomodulation; Neurons, Afferent; Pain; Pain Threshold; Rats; Receptors, Opioid

Experimental studies in animal spinal cord injury models suggest that preservation of a relatively small number of spinal axons can support neurological recovery. The second National Acute Spinal Cord Injury Study (NASCIS 2) was the first clinical trial to demonstrate that a treatment given after injury can enhance neurological recovery. In this trial, patients treated with high-dose methylprednisolone within 8 hours of spinal cord injury recovered more sensory and motor function than did those treated with placebo. In addition to demonstrating the first effective pharmacological intervention in central nervous system injury, NASCIS 2 identified several critical issues that must be investigated in future preclinical and clinical research. These include drug dose, initiation time, and duration of treatment, as well as combination therapy and injury severity. Addressing these issues systematically will require more reproducible animal models and more accurate outcome measures.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Humans; Injury Severity Score; Methylprednisolone; Naloxone; Rats; Spinal Cord Injuries; Time Factors

Topics: Animals; Atropine; Cardiopulmonary Resuscitation; Disease Models, Animal; Epinephrine; Humans; Intubation, Intratracheal; Lidocaine; Naloxone; Pediatrics

1. Amygdaloid kindled seizures in rats produce postictal motor deficits, disruption of affective responding to sensory input, postictal explosiveness, and seizure suppression that may be similar to events following complex partial seizures in humans. 2. Preliminary 2DG studies in kindled rats indicate that postictal motor deficits may be mediated by the substantia nigra. Disruption of affective responding and postictal seizure suppression may be mediated by the hippocampus. 3. Data from the literature indicates that postictal motor deficits may be mediated by mu and kappa opioid receptors. The disruption of affective responding may be mediated primarily be delta and maybe also by kappa receptors. Postictal explosiveness may involve either a non-mu receptor or it may be a non-opioid effect. Kindling-induced postictal seizure suppression may be mediated by kappa receptors and perhaps also by mu receptors. 4. Mechanisms underlying postictal effects of complex partial seizures in humans are suggested by the data in this manuscript. New approaches to the treatment of these postictal events are also proposed.

Topics: Animals; Deoxyglucose; Disease Models, Animal; Endorphins; Epilepsy, Temporal Lobe; Limbic System; Motor Activity; Naloxone; Rats; Receptors, Opioid

Topics: Adrenal Cortex Hormones; Animals; Anti-Inflammatory Agents, Non-Steroidal; Cyclooxygenase Inhibitors; Disease Models, Animal; Drug Therapy, Combination; Endotoxins; Humans; Naloxone; Sepsis

Much of our knowledge about the CNS control of blood pressure is derived from animal studies using techniques such as intracerebroventricular administration of drugs, stereotactic ablation of specific brain nuclei, and biochemical analysis of these nuclei. These methods have identified numerous specific brain nuclei in the brain stem and a meshwork of interconnecting neurones involved in cardiovascular control. The main neurotransmitter involved is noradrenaline but recent interest has focused on several laterally situated nuclei which are capable of synthesizing adrenaline. Centrally acting antihypertensive drugs are thought to act by stimulating central alpha 2-adrenoceptors either by the parent drug itself (clonidine) or via the formation of an active metabolite (alpha-methyldopa). This leads to decreased peripheral sympathetic activity and a hypotensive response but the latter is often attained at the expense of central side-effects such as drowsiness or dry mouth. The mechanism of the antihypertensive effect of beta-blockers remains uncertain although the balance of evidence is against a central effect. The central administration of propranolol causes decreased peripheral sympathetic activity in animals, but plasma catecholamine levels are little altered by beta-blockers in man. In equipotent antihypertensive doses, central alpha-agonists cause a much greater reduction in plasma noradrenaline than beta-blockers.

Topics: Adrenergic beta-Antagonists; Animals; Antihypertensive Agents; Blood Pressure; Catecholamines; Clonidine; Disease Models, Animal; Ganglia, Sympathetic; Half-Life; Hypothalamus; Models, Neurological; Naloxone; Neurons; Nitroprusside; Norepinephrine; Phenylethanolamine N-Methyltransferase; Pressoreceptors; Propranolol; Rats; Rats, Inbred SHR; Receptors, Opioid; Reflex; Splanchnic Nerves; Thiophenes; Yohimbine

Naloxone has been used as a pharmacological tool to investigate the role of endorphins and opiate receptors in the cardiovascular pathophysiology of shock. It would appear that endorphins act on opiate receptors to contribute to the abnormalities found and that naloxone improves survival as well as cardiovascular function in shock. Preliminary studies in humans and the subhuman primate create cautious optimism regarding the clinical application of this information. Naloxone has served us well as a key to unlock the involvement of endorphins and opiate receptors in shock. However, further advances in our understanding may depend on the development and use of opiate receptor agonists and antagonists specific for the different opiate receptors described, each subserving different functions. Naloxone's disadvantage of increasing pain awareness may limit its clinical usefulness but might be overcome by using drugs that reverse the behavioral and neuroendocrine changes produced by beta-endorphin without altering pain relief. Thyrotropin-releasing hormone (TRH) is just such a "physiological" opiate antagonist which has been shown to increase MAP in experimental endotoxic and hemorrhagic shock [32].

Topics: Adrenal Cortex Hormones; Animals; Blood Pressure; Disease Models, Animal; Dogs; Endorphins; Hemodynamics; Horses; Humans; Macaca fascicularis; Naloxone; Narcotic Antagonists; Rats; Receptors, Opioid; Shock, Septic; Swine

Topics: Animals; Brain; Disease Models, Animal; Drug Interactions; Humans; Mice; Morphine; Morphine Dependence; Naloxone; Neurotransmitter Agents; Substance Withdrawal Syndrome; Time Factors

Experimental studies in animal spinal cord injury models suggest that preservation of a relatively small number of spinal axons can support neurological recovery. The second National Acute Spinal Cord Injury Study (NASCIS 2) was the first clinical trial to demonstrate that a treatment given after injury can enhance neurological recovery. In this trial, patients treated with high-dose methylprednisolone within 8 hours of spinal cord injury recovered more sensory and motor function than did those treated with placebo. In addition to demonstrating the first effective pharmacological intervention in central nervous system injury, NASCIS 2 identified several critical issues that must be investigated in future preclinical and clinical research. These include drug dose, initiation time, and duration of treatment, as well as combination therapy and injury severity. Addressing these issues systematically will require more reproducible animal models and more accurate outcome measures.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Humans; Injury Severity Score; Methylprednisolone; Naloxone; Rats; Spinal Cord Injuries; Time Factors

The abuse of oral formulations of prescription opioids has precipitated the current opioid epidemic. We developed an oral oxycodone consumption model consisting of a limited access (4 h) two-bottle choice drinking in the dark (TBC-DID) paradigm and quantified dependence with naloxone challenge using mice of both sexes. We also assessed neurobiological correlates of withdrawal and dependence elicited via oral oxycodone consumption using immunohistochemistry for DeltaFosB (ΔFosB), a transcription factor described as a molecular marker for drug addiction. Neither sex developed a preference for the oxycodone bottle, irrespective of oxycodone concentration, bottle position or prior water restriction. Mice that volitionally consumed oxycodone exhibited hyperlocomotion in an open field test and supraspinal but not spinally-mediated antinociception. Both sexes also developed robust, dose-dependent levels of opioid withdrawal that was precipitated by the opioid antagonist naloxone. Oral oxycodone consumption followed by naloxone challenge led to mesocorticolimbic region-dependent increases in the number of ΔFosB expressing cells. Naloxone-precipitated withdrawal jumps, but not the oxycodone bottle % preference, was positively correlated with the number of ΔFosB expressing cells specifically in the nucleus accumbens shell. Thus, limited access oral consumption of oxycodone produced physical dependence and increased ΔFosB expression despite the absence of opioid preference. Our TBC-DID paradigm allows for the study of oral opioid consumption in a simple, high-throughput manner and elucidates the underlying neurobiological substrates that accompany opioid-induced physical dependence.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Locomotion; Mice; Naloxone; Narcotic Antagonists; Nociception; Nucleus Accumbens; Opioid-Related Disorders; Oxycodone; Proto-Oncogene Proteins c-fos; Substance Withdrawal Syndrome

Ben-Cha-Moon-Yai (BMY) remedy used in Thai traditional medicine as an anti-inflammatory, analgesic, and antipyretic agent compromises five herbal root extracts of equal weights: Aegle marmelos (L.) Corrêa (AM), Oroxylum indicum (L.) Kurz (OI), Dimocarpus longan Lour. (DL), Dolichandrone serrulata (Wall. ex DC.) Seem. (DS), and Walsura trichostemon Miq. (WT).. To assess the anti-nociceptive and anti-inflammatory effects of the root extracts of all five species of BMY in experimental animal (mouse) models to ensure the rational use of herbal products in Thai traditional medicine.. Root extracts prepared by ethanol and water extraction were used for the biological assays in animal models at five dose levels: 25, 50,100,200 & 400 mg/kg. The anti-nociceptive activity was evaluated based on hot-plate latency, duration of paw licking induced by formalin, and abdominal writhing induced by acetic acid. Carrageenan- and prostaglandin-induced paw oedema models were used to determine the anti-inflammatory activity.. The oral administration of AM, DS and WT root extracts displayed significant analgesic effects in the hot-plate test, both phases (early and late) of formalin test and acetic-acid induced writhing test at different dose levels. OI and DL only produced significant analgesia in the late phase of the formalin test and writhing test. The pretreatment of animals with the non-selective opioid receptor antagonist naloxone, reverse AM, DS and WT induced-antinociceptive activity. In both carrageenan and prostaglandin-induced paw oedema tests, all five herbal plant root extracts significantly reduced paw oedema at 3 h or more at different dose levels. Rotarod test results showed no effects of five herbal plant root extracts on the balance and the motor coordination at the highest dose level evaluated (400 mg/kg).. The root extracts of AM, DS, and WT possess both central and peripheral anti-nociceptive properties, while OI and DL possess only peripheral analgesic properties. All five root extracts own anti-inflammatory properties, which might be due to their activity on the prostaglandin system. Altogether these findings ensure the rational use of BMY remedy in Thai traditional medicine.

Topics: Aegle; Animals; Anti-Inflammatory Agents; Disease Models, Animal; Dose-Response Relationship, Drug; Indomethacin; Male; Medicine, East Asian Traditional; Mice; Mice, Inbred ICR; Morphine; Naloxone; Nociception; Opioid Peptides; Pain Measurement; Plant Extracts; Plant Preparations; Plant Roots; Prostaglandins; Sapindaceae

Major depressive disorder (MDD) is a debilitating disease with a high worldwide prevalence. Despite its greater prevalence in women, male animals are used in most preclinical studies of depression even though there are many sex differences in key components of depression, such as stress responses and immune system functions. In the present study, we found that chronic restraint stress-induced depressive-like behaviors are quite similar in male and female mice, with both sexes displaying increased immobility time in the tail suspension test and reduced social interactions, and both sexes exhibited deficits in working and spatial memories. However, in contrast to the similar depressive-like behaviors developed by male and female mice in response to stress, they displayed different patterns of pro-inflammatory cytokine increases in the periphery and the brain, different changes in microglia, and different changes in the expression of Toll-like receptor 4 in response to stress. Treatment with (+)-naloxone, a Toll-like receptor 4 antagonist that previously demonstrated anti-depressant-like effects in male mice, was more efficacious in male than female mice in reducing the deleterious effects of stress, and its effects were not microbiome-mediated. Altogether, these results suggest differential mechanisms to consider in potential sex-specific treatments of depression.

Topics: Animals; Behavior, Animal; Cytokines; Depressive Disorder, Major; Disease Models, Animal; Female; Male; Mice; Naloxone; Stress, Psychological; Toll-Like Receptor 4

The current work examined the pharmacological potential of a selected flavanone derivative 2-hydroxyflavanone as a promising remedy for the treatment and management of pain. The selected flavanone derivative (2-HF) was evaluated for its analgesic and anti-inflammatory potentials following standard pharmacological protocols including hot plate, acetic acid-induced writhing and tail immersion tests. Naloxone and pentylenetetrazol were used to evaluate the potential implication of GABAergic and opioidergic mechanisms. The anti-inflammatory potential of 2-HF was confirmed using carrageenan-, serotonin- and histamine-induced paw edema models as well as a xylene-induced ear edema model. Furthermore, the anti-neuropathic potential of 2-HF was tested using a cisplatin-induced neuropathic pain model. Our sample, at the tested concentrations of 15, 30 and 45 mg kg

Topics: Analgesics; Animals; Anti-Inflammatory Agents; Cisplatin; Disease Models, Animal; Edema; Flavanones; Gabapentin; Hyperalgesia; Inflammation; Naloxone; Neuralgia; Pentylenetetrazole; Rodentia

Morphine is widely used in patients and has been reported to alter seizure threshold, but its role in the development of epilepsy is unknown. In this study, role of morphine administration in the development of epilepsy using the status epilepticus (SE) model was determined in rats.. Rats experiencing SE with lithium-pilocarpine (LiP) were randomized into four groups- saline, morphine low dose (5 mg/kg, s.c.), morphine high dose (5-20 mg/kg, s.c.), and naloxone (1 mg/kg, s.c.). Treatments were started 90 min after termination of SE and repeated twice daily for next three days. Rats were video monitored daily for 21 days to determine onset and frequency of spontaneous convulsive seizures (SS).. Morphine in low doses increased frequency of SS (1.51 ± 0.15 vs LiP 0.60 ± 0.12 seizures/rat/day, p-value = 0.0026) and seizures occurred during handling (SDH) (0.08 ± 0.02 vs LiP control 0.01 ± 0.01) (p-value = 0.0018). In high doses, no significant change in SS and SDH was found as compared to LiP. No effect of morphine on the onset of SS and percentage of rats experienced SS was found. No effect of naloxone per se was found on SS.. Morphine administration after SE does not affect epileptogenesis as no change in the onset of SS and percentage of rats experiencing SS was found. However, it might alter the susceptibility and frequency of SS. As no other study is available with a similar finding, it needs further evaluation.

Topics: Animals; Disease Models, Animal; Epilepsy; Lithium; Morphine; Naloxone; Pilocarpine; Rats; Seizures; Status Epilepticus

In this study, we investigated the effect of long-term administration of orexin receptor 1 (OXR1) antagonist on naloxone-precipitated morphine withdrawal symptoms and nociceptive behaviors in morphine-dependent rats.. Wistar rats received subcutaneous (s.c.) injections of morphine (6, 16, 26, 36, 46, 56, and 66 mg/kg, 2 ml/kg) at an interval of 24 h for 7 days. In chronic groups, the OXR1 antagonist, SB-334867 (20 mg/kg, i.p.), or its vehicle, was injected repetitively from postnatal day 1 (PND1)-PND23 and then for the following seven days before each morphine injection. Meanwhile, in acute groups, SB-334867, or its vehicle, was administered before each morphine injection. In groups of rats that were designated for withdrawal experiments, naloxone (2.5 mg/kg, i.p.) was administered after the last injection of morphine. In the formalin-induced pain, the effect of OXR1 inhibition on the antinociceptive effects of morphine was measured by injecting formalin after the final morphine injection.. Animals that received long-term SB-334867 administration before morphine injection demonstrated a significant reduction in chewing, defecation, diarrhea, grooming, teeth chattering, wet-dog shake, and writhing. Inhibiting OXR1 for a long time increased formalin-induced nociceptive behaviors in interphase and phase II of the formalin-induced pain.. Our results indicated that the inhibition of OXR1 significantly reduces the development of morphine dependence and behavioral signs elicited by the administration of naloxone in morphine-dependent rats. Furthermore, the prolonged blockade of OXR1 might be involved in formalin-induced nociceptive behaviors.

Topics: Animals; Behavior, Animal; Benzoxazoles; Disease Models, Animal; Morphine; Morphine Dependence; Naloxone; Naphthyridines; Narcotic Antagonists; Narcotics; Nociceptive Pain; Orexin Receptor Antagonists; Rats; Rats, Wistar; Substance Withdrawal Syndrome; Urea

Rotigotine-loaded microspheres (RoMS), a sustained-release formulation with a continuous release of rotigotine for more than 7 days in vivo, have been conducted a clinical trial for the treatment of Parkinson's disease (PD). Previous work from our laboratory showed that RoMS exerted an antinociceptive effect in rat models of inflammatory pain. The purpose of this study was to investigate the mechanisms of action underlying the antinociceptive effect of RoMS. A rat model of inflammatory pain was prepared by an intraplantar injection of carrageenan. The hot plate test and the Randall-Selitto test were used to evaluate the effect of domperidone (selective D

Topics: Analgesics; Animals; Carrageenan; Corpus Striatum; Disease Models, Animal; Domperidone; Dopamine; Dopamine Agents; Dopamine D2 Receptor Antagonists; Inflammation; Injections; Male; Microspheres; Naloxone; Narcotic Antagonists; Pain; Periaqueductal Gray; Rats, Sprague-Dawley; Receptors, Dopamine D2; Receptors, Dopamine D3; Stress, Mechanical; Temperature; Tetrahydronaphthalenes; Thiophenes

The jump is one of the common stereotyped behavior in rodents which can be found in certain types of disease models, such as addiction. It can be easily identified by the human eye. However, it is difficult to be tagged in real-time by manual operation, which limits the detailed exploration of its neural mechanisms with the new techniques, such as fiber photometry recording. Here we introduced an auto real-time jump tagging system (Art-JT system) to record the jump based on online monitoring the pressure changes of the floor in which the mouse is free exploring. Meanwhile, the Art-JT system can send the digital signal of the jump timing to the external device for tagging the events in the fiber photometry system. We tested it with the mice induced by Naloxone precipitated withdrawal jumping and found that it could accurately record the jump events and provide several detailed parameters of the jump. We also confirmed that the jump was correlated with the medial prefrontal cortex and primary motor cortex neuronal activities by combining the Art-JT system, GCaMP6 mice, and fiber photometry system. Our results suggested that the Art-JT system may be a powerful tool for recording and analyzing jumps efficiently and helping us to understand stereotyped behavior.

Topics: Animals; Behavior, Animal; Calcium; Disease Models, Animal; Male; Mice; Mice, Inbred C57BL; Movement; Naloxone; Neurons; Photometry; Prefrontal Cortex; Pressure; Stereotyped Behavior; Stimulation, Chemical; Substance Withdrawal Syndrome

Human prion diseases are fatal neurodegenerative disorders that include sporadic, infectious and genetic forms. Inherited Creutzfeldt-Jakob disease due to the E200K mutation of the prion protein-coding gene is the most common form of genetic prion disease. The phenotype resembles that of sporadic Creutzfeldt-Jakob disease at both the clinical and pathological levels, with a median disease duration of 4 months. To date, there is no available treatment for delaying the occurrence or slowing the progression of human prion diseases. Existing in vivo models do not allow high-throughput approaches that may facilitate the discovery of compounds targeting pathological assemblies of human prion protein or their effects on neuronal survival. Here, we generated a genetic model in the nematode Caenorhabditis elegans, which is devoid of any homologue of the prion protein, by expressing human prion protein with the E200K mutation in the mechanosensitive neuronal system. Expression of E200K prion protein induced a specific behavioural pattern and neurodegeneration of green fluorescent protein-expressing mechanosensitive neurons, in addition to the formation of intraneuronal inclusions associated with the accumulation of a protease-resistant form of the prion protein. We demonstrated that this experimental system is a powerful tool for investigating the efficacy of anti-prion compounds on both prion-induced neurodegeneration and prion protein misfolding, as well as in the context of human prion protein. Within a library of 320 compounds that have been approved for human use and cross the blood-brain barrier, we identified five molecules that were active against the aggregation of the E200K prion protein and the neurodegeneration it induced in transgenic animals. This model breaks a technological limitation in prion therapeutic research and provides a key tool to study the deleterious effects of misfolded prion protein in a well-described neuronal system.

Topics: Animals; Animals, Genetically Modified; Benzocaine; Brain; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Disease Models, Animal; Humans; Naloxone; Piroxicam; Prion Diseases; Prion Proteins; Protein Aggregation, Pathological; Tubulin

Recent studies suggest that lipids, including free fatty acids (FFAs), are necessary for proper μ opioid receptor (MOR) binding and that activation of opioid receptors (ORs) improves intestinal inflammation. The objective of the study was to investigate a possible interaction between the ORs and FFA receptors (FFARs) ligands in the colitis.. The potential synergistic effect of ORs and FFARs ligands was evaluated using mouse model of acute colitis induced by dextran sulfate sodium (DSS, 4%). Compounds were injected intraperitoneally (i.p.) once or twice daily at the doses of 0.01 or 0.02 mg/kg body weight (BW) (DAMGO-an MOR agonist), 0.3 mg/kg BW (DPDPE-a δ OR (DOR) agonist) and 1 mg/kg BW (naloxone-a non-selective OR antagonist, GLPG 0974-a FFAR2 antagonist, GSK 137647-a FFAR4 agonist and AH 7614-a FFAR4 antagonist) for 4 days.. Myeloperoxidase (MPO) activity was significantly decreased after DAMGO (0.02 mg/kg BW) and GSK 137647 (1 mg/kg BW) administration and co-administration as compared to DSS group.. Treatment with ligands of ORs and FFARs may affect the immune cells in the inflammation; however, no significant influence on the severity of colitis and no synergistic effect were observed.

Topics: Aniline Compounds; Animals; Butyrates; Colitis; Disease Models, Animal; Drug Synergism; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Inflammation; Ligands; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Peroxidase; Receptors, G-Protein-Coupled; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Sulfonamides; Thiophenes; Xanthenes

Topics: Animals; Conotoxins; Disease Models, Animal; Excitatory Amino Acid Antagonists; Hippocampus; Locomotion; Male; Mice; Morphine Dependence; Naloxone; Piperidines; Receptors, N-Methyl-D-Aspartate; Spatial Memory

The aim of this study was to investigate the therapeutic effect and possible mechanisms of tibial nerve stimulation (TNS) on visceral hypersensitivity in rats.. 1) The effects of TNS with five sets of parameters on visceral sensitivity in normal rats were evaluated by the assessment of abdominal electromyogram (EMG) and abdominal withdrawal reflex (AWR). 2) The effects and mechanisms of TNS with a special set of parameters (14 Hz, 330 μsec, and 40% motor threshold) were evaluated in acute visceral hypersensitivity rats induced by restraint stress and colonic hypersensitized rats induced by acetic acid during the neonatal stage assessed by the EMG, AWR, and the spectral analysis of heart rate variability derived from the electrocardiogram.. 1) In normal rats, TNS did not show any effect on the visceromotor reflex. 2) In rats with restraint stress-induced hypersensitivity, TNS with the special set of parameters reduced AWR scores and EMG responses to rectal distention at a pressure of 20-60 mmHg (p < 0.05, vs. baseline for both AWR and EMG). Concurrently, TNS increased vagal activity and decreased sympathetic activity (p < 0.03 for both). 3) Similar effects were noted on the EMG (p < 0.05, vs. baseline) and AWR (p < 0.05 vs. baseline) with acute and chronic TNS in rats with chronic colonic hypersensitivity and the effects were blocked by naloxone.. TNS with parameters of 14 Hz, 330 μsec, and 40% motor threshold is effective in improving visceral hypersensitivity in rodent models of colonic hypersensitivity via the modulation of autonomic and opioid mechanisms.

Topics: Analgesics, Opioid; Animals; Colon; Disease Models, Animal; Naloxone; Rats; Rats, Sprague-Dawley; Tibial Nerve

To investigate the effect of minocycline on morphine withdrawal symptoms.. We established a rat model of morphine dependence, then injected the animals with naloxone to induce withdrawal symptoms. Minocycline was injected into the midbrain periaqueductal gray and its effect on withdrawal symptoms and Ca. Minocycline inhibited withdrawal symptoms such as "wet dog" shakes, teeth chatter, and ptosis, perhaps by inhibiting the activation of microglia and the expression of CaMKII, Ras, and p-ERK. Minocycline had no effect on the behavior of control rats or on CaMKII, Ras, or p-ERK expression.. Minocycline alleviates morphine withdrawal symptoms by inhibiting the activation of microglia and downregulating the expression of CaMKII, Ras, and p-ERK.

Topics: Animals; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Disease Models, Animal; Down-Regulation; Humans; Male; MAP Kinase Signaling System; Microglia; Minocycline; Morphine; Naloxone; Periaqueductal Gray; ras Proteins; Rats; Substance Withdrawal Syndrome

Opioid use disorder is a growing concern in the United States. Mice were used to investigate the mechanisms involving opioid physical dependence and for evaluating medications for treating opioid use disorders. While there are many preclinical reports describing protocols for inducing physical dependence upon morphine, there are fewer preclinical reports describing more contemporary abused prescription opiates. The goal of this study was to characterize and validate a mouse model of oxycodone dependence. Male C57BL/6J mice were injected with saline or increasing doses of oxycodone (9-33 mg/kg) twice daily for 8 days. On the 9th day, mice were challenged with 1 mg/kg naloxone and observed for somatic signs. Mice were pretreated with oxycodone (17, 33, or 75 mg/kg) prior to withdrawal to determine if it could attenuate somatic withdrawal signs. Additional mouse groups were pretreated with 1 mg/kg clonidine. Lastly, we measured somatic signs for 6, 24, and 48 h post-withdrawal during spontaneous and precipitated withdrawal. Pretreating with oxycodone or clonidine dose-dependently prevented the emergence of withdrawal signs. Mice chronically treated with oxycodone exhibited more withdrawal signs than vehicle at 24 h after the final injection during spontaneous withdrawal. In contrast, mice that received repeated naloxone challenges showed peak withdrawal signs at 6 h, and withdrawal signs were significantly greater at all time points compared to vehicle. Reversal of withdrawal effects by positive controls, and establishing spontaneous and precipitated withdrawal paradigms, serve as validation of this model and provide a means to examine novel therapeutics to treat opioid withdrawal.

Topics: Analgesics; Analgesics, Opioid; Animals; Behavior, Animal; Clonidine; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Mice, Inbred C57BL; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Oxycodone; Substance Withdrawal Syndrome

There is a need to develop a novel analgesic for pain associated with interstitial cystitis/painful bladder syndrome (IC/PBS). The use of the conventional μ-opioid receptor agonists to manage IC/PBS pain is controversial due to adverse CNS effects. These effects are attenuated in benzylideneoxymorphone (BOM), a low-efficacy μ-opioid receptor agonist/δ-opioid receptor antagonist that attenuates thermal pain and is devoid of reinforcing effects. We hypothesize that BOM will inhibit bladder pain by attenuating responses of urinary bladder distension (UBD)-sensitive afferent fibers. Therefore, the effect of BOM was tested on responses of UBD-sensitive afferent fibers in L6 dorsal root from inflamed and non-inflamed bladder of rats. Immunohistochemical (IHC) examination reveals that following the induction of inflammation there were significant high expressions of μ, δ, and μ-δ heteromer receptors in DRG. BOM dose-dependently (1-10 mg/kg, i.v) attenuated mechanotransduction properties of these afferent fibers from inflamed but not from non-inflamed rats. In behavioral model of bladder pain, BOM significantly attenuated visceromotor responses (VMRs) to UBD only in inflamed group of rats when injected either systemically (10 mg/kg, i.v.) or locally into the bladder (0.1 ml of 10 mg/ml). Furthermore, oxymorphone (OXM), a high-efficacy μ-opioid receptor agonist, attenuated responses of mechanosensitive bladder afferent fibers and VMRs to UBD. Naloxone (10 mg/kg, i.v.) significantly reversed the inhibitory effects of BOM and OXM on responses of bladder afferent fibers and VMRs suggesting μ-opioid receptor-related analgesic effects of these compounds. The results reveal that a low-efficacy, bifunctional opioid-based compound can produce analgesia by attenuating mechanotransduction functions of afferent fibers innervating the urinary bladder.

Topics: Action Potentials; Afferent Pathways; Analgesics; Animals; Benzylidene Compounds; Cystitis, Interstitial; Disease Models, Animal; Lumbar Vertebrae; Mechanotransduction, Cellular; Naloxone; Narcotic Antagonists; Oxymorphone; Rats; Receptors, Opioid, delta; Receptors, Opioid, mu; Spinal Nerve Roots

Investigations have shown that the circadian rhythm can affect the mechanisms associated with drug dependence. In this regard, we sought to assess the negative consequence of morphine withdrawal syndrome on conditioned place aversion (CPA) and lateral paragigantocellularis (LPGi) neuronal activity in morphine-dependent rats during light (8:00-12:00) and dark (20:00-24:00) cycles. Male Wistar rats (250-300 g) were received 10 mg/kg morphine or its vehicle (Saline, 2 mL/kg/12 h, s.c.) in 13 consecutive days for behavioral assessment tests. Then, naloxone-induced conditioned place aversion and physical signs of withdrawal syndrome were evaluated during light and dark cycles. In contrast to the behavioral part, we performed in vivo extracellular single-unit recording for investigating the neural response of LPGi to naloxone in morphine-dependent rats on day 10 of morphine/saline exposure. Results showed that naloxone induced conditioned place aversion in both light and dark cycles, but the CPA score during the light cycle was larger. Moreover, the intensity of physical signs of morphine withdrawal syndrome was more severe during the light cycle (rest phase) compare to the dark one. In electrophysiological experiments, results indicated that naloxone evoked both excitatory and inhibitory responses in LPGi neurons and the incremental effect of naloxone on LPGi activity was stronger in the light cycle. Also, the neurons with the excitatory response exhibited higher baseline activity in the dark cycle, but the neurons with the inhibitory response showed higher baseline activity in the light cycle. Interestingly, the baseline firing rate of neurons recorded in the light cycle was significantly different in response (excitatory/inhibitory) -dependent manner. We concluded that naloxone-induced changes in LPGi cellular activity and behaviors of morphine-dependent rats can be affected by circadian rhythm and the internal clock.

Topics: Animals; Behavior, Animal; Circadian Rhythm; Conditioning, Classical; Disease Models, Animal; Electrophysiological Phenomena; Male; Medulla Oblongata; Morphine Dependence; Naloxone; Narcotic Antagonists; Neurons; Rats; Rats, Wistar; Substance Withdrawal Syndrome

The aim of this study was to evaluate the anti-inflammatory effects and underlying mechanism of naloxone on lipopolysaccharide- (LPS-) induced neuronal inflammation and microglial activation.. LPS-treated microglial BV-2 cells and mice were used to investigate the anti-inflammatory effects of naloxone.. The results showed that naloxone dose-dependently promoted cell proliferation in LPS-induced BV-2 cells, downregulated the expression of proinflammatory cytokines (TNF-. Naloxone prevented LPS-induced neuroinflammation and microglial activation partially through the KATP channel. These findings might highlight the potential of naloxone in neuroinflammation therapy.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Behavior, Animal; Cell Line; Cell Proliferation; Computational Biology; Disease Models, Animal; Inflammation; KATP Channels; Lipopolysaccharides; Mice; Mice, Inbred BALB C; Microglia; Naloxone; Narcotic Antagonists; Neurodegenerative Diseases

When Zika virus emerged as a public health emergency there were no drugs or vaccines approved for its prevention or treatment. We used a high-throughput screen for Zika virus protease inhibitors to identify several inhibitors of Zika virus infection. We expressed the NS2B-NS3 Zika virus protease and conducted a biochemical screen for small-molecule inhibitors. A quantitative structure-activity relationship model was employed to virtually screen ∼138,000 compounds, which increased the identification of active compounds, while decreasing screening time and resources. Candidate inhibitors were validated in several viral infection assays. Small molecules with favorable clinical profiles, especially the five-lipoxygenase-activating protein inhibitor, MK-591, inhibited the Zika virus protease and infection in neural stem cells. Members of the tetracycline family of antibiotics were more potent inhibitors of Zika virus infection than the protease, suggesting they may have multiple mechanisms of action. The most potent tetracycline, methacycline, reduced the amount of Zika virus present in the brain and the severity of Zika virus-induced motor deficits in an immunocompetent mouse model. As Food and Drug Administration-approved drugs, the tetracyclines could be quickly translated to the clinic. The compounds identified through our screening paradigm have the potential to be used as prophylactics for patients traveling to endemic regions or for the treatment of the neurological complications of Zika virus infection.

Topics: Animals; Antiviral Agents; Artificial Intelligence; Chlorocebus aethiops; Disease Models, Animal; Drug Evaluation, Preclinical; High-Throughput Screening Assays; Immunocompetence; Inhibitory Concentration 50; Methacycline; Mice, Inbred C57BL; Protease Inhibitors; Quantitative Structure-Activity Relationship; Small Molecule Libraries; Vero Cells; Zika Virus; Zika Virus Infection

It has been demonstrated that smoking is associated with an increase in postoperative and chronic pain. The changes in the pain-related neural pathways responsible for these effects are unknown. Additionally, the effects of nicotine withdrawal, resulting from smoking abstinence preoperatively, has not been evaluated in terms of its impact on pain sensation. In this study, an animal model has been used to assess these effects. A rat model of long-term nicotine exposure was used. Von Frey mechanical sensory tests were performed. Western Blot and immunohistological analysis were conducted on spinal cord samples. Mechanical sensory thresholds increased in the initial period (1-3 weeks), indicating hyposensitivity. Long-term (410 weeks) and under nicotine withdrawal, the mechanical sensory thresholds decreased, indicating hyperalgesia. During short-term nicotine exposure, glutamate decarboxylase 67 (GAD67), GAD65, and μ-opioid receptors (MOR) up-regulated. Beta-endorphins down-regulated. Increased γ -aminobutyric acid (GABA) and MOR appear responsible for the hyposensitivity since the GABA receptor antagonist, bicuculline and opioid receptor antagonist, naloxone decreased the mechanical thresholds of nicotine-induced hyposensitivity. In long-term nicotine exposure, the expression of GAD67, MOR, and GABA decreased. Baclofen, a derivative of GABA, reversed the hyperalgesia seen with nicotine withdrawal. Therefore, nicotine acts as an analgesic when used acutely or short-term. Long-term exposure or nicotine withdrawal (similar to smoking cessation) results in hyperalgesia. Nicotine appears to alter pain sensitivity by affecting the expression of GAD65, GAD67, MOR, endorphins, and GABA. This may partially explain the increased pain and opioid use seen in chronic smokers in the postoperative period.

Topics: Animals; Baclofen; Bicuculline; Disease Models, Animal; Down-Regulation; Endorphins; gamma-Aminobutyric Acid; Glutamate Decarboxylase; Hyperalgesia; Male; Naloxone; Nicotine; Pain Perception; Pain Threshold; Rats; Receptors, Opioid, mu; Spinal Cord; Substance Withdrawal Syndrome; Time Factors; Up-Regulation

The efficacy of each antidepressant available has been found equal to that of amitriptyline in double-blind studies. However, a few of them are being prescribed (at under-therapeutic doses) for sleep, in non-depressed persons, when there are relative contraindications for sedative-hypnotics. Following previous studies regarding the antinociceptive mechanisms of various antidepressants, we suggest that the involvement of the opioid system in some of the antidepressants' mechanism of action may contribute to these medications' use for the induction and maintenance of sleep. The mostly prescribed antidepressants for sleep are trazodone (a weak, but specific inhibitor of the synaptosomal uptake of serotonin, that also binds to alpha-1 and alpha-2 adrenoreceptor sites) and mirtazapine (a postsynaptic drug which enhances noradrenergic and 5-HT1A-mediated serotonergic neurotransmission via antagonism of central alpha-2-auto- and hetero-adrenoreceptors). In our previous studies when ICR mice were tested with a hotplate analgesia meter, both trazodone and mirtazapine induced, a naloxone-reversible antinociceptive effect following i.p administration. Summing up the various interactions of trazodone and mirtazapine with opioid, noradrenergic and serotonergic agonists and antagonists, we found that the antinociceptive effect of trazodone is influenced by the opioid receptor subtypes mu and delta (and a clear 5-HT mechanism of antinociception), while the antinociceptive effect of mirtazapine is mainly influenced by kappa and mu opioid receptor subtype (combined with both serotonergic and noradrenergic receptors). This opioid profile of the two drugs may be one of the explanations to their efficacy in the treatment of insomnia, when sedatives (either benzodiazepines or the non-benzodiazepine "Z-compounds") cannot be prescribed.

Topics: Analgesics; Analgesics, Opioid; Animals; Antidepressive Agents; Depression; Disease Models, Animal; Male; Mice; Mice, Inbred ICR; Mirtazapine; Naloxone; Receptors, Opioid; Serotonin; Sleep; Sleep Wake Disorders; Trazodone; Zolpidem

Repeated injection of morphine during conditioned place preference (CPP) leads to spatial craving due to high-level nitric oxide (NO) in the central nucleus of amygdala (CeA). Silver nanoparticles (Ag-NPs) can produce oxygen-free radicals that lead to NO formation. We aimed to show the Ag-NPs protective effect on naloxone (NLX)-induced morphine withdrawal in the conditioned rats. Wistar rats (300-350 g) were implanted with cannulae in the CeA. After recovery, they were randomly divided into experimental and saline groups. CPP was conducted by three-phase unbiased program. Morphine (0.5-7.5 mg/kg) was injected subcutaneously (s.c.) once/per day during the conditioning phase. Naloxone (NLX) (0.05-0.4 μg/rat) was given, intra-CeA, 10 min before the CPP test. Ag-NPs (0.0001-0.01 μg/rat) were administered alone or prior to the NLX effective dose (0.4 μg/rat), intra-CeA. Conditioning score and withdrawal signs (wet dog shaking and scratching) were obtained and compared with saline group data. All rats' brains were collected in formalin 10% and after 48-72 h stained with NADPH-diaphorase, the NO marker. All data were analyzed by one-way or two-way ANOVA. Morphine (2.5-7.5 mg/kg, s.c.) induced a significant CPP vs. saline (1 mL/kg, s.c.). The single Ag-NPs had no significant effect, whereas the NLX caused meaningful WDS and scratching. However, the NLX pre-treatment in combination with Ag-NPs eliminated these signs. Furthermore, the NO level increased in the CeA. The Ag-NPs may protect the morphine-conditioned rats against the NLX-induced withdrawal symptoms due to high-level NO in the CeA.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Central Amygdaloid Nucleus; Conditioning, Psychological; Disease Models, Animal; Male; Metal Nanoparticles; Morphine; Naloxone; Narcotic Antagonists; Nitric Oxide; Rats, Wistar; Silver Compounds; Substance Withdrawal Syndrome

Patients with cholestatic liver diseases, such as primary biliary cirrhosis, usually suffer from pruritus. However, the pathogenesis of cholestatic pruritus is unclear, and there is no current effective treatment for it. In order to find a treatment for the condition, an appropriate mouse model should be developed. Therefore, here, we established a surgically-induced mouse model of cholestatic pruritus. The bile duct was ligated in order to block bile secretion from the anterior, right, and left lobes, with the exception of the caudate lobe. Serum levels of total bile acid increased after bile duct ligation (BDL). The spontaneous hind paw scratching was also increased in BDL mice. Spontaneous scratching was reduced in BDL mice by naloxone (µ-opioid receptor antagonist), U-50,488H (κ-opioid receptor agonist), and clonidine (α2-adrenoceptor agonist). Azelastine (H

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Adrenergic alpha-2 Receptor Agonists; Animals; Antipruritics; Bile Ducts; Cholestasis; Clonidine; Disease Models, Animal; Ligation; Liver; Male; Mice, Inbred ICR; Naloxone; Narcotic Antagonists; Pruritus; Receptors, Opioid, kappa

Opiate exposure during adolescence perturbs the brain's maturation process and potentially confers long-term adverse consequences, not only in exposed individuals but also in their posterity. Here, we investigate the outcomes of adolescent paternal morphine exposure on morphine withdrawal profile in male offspring.. Male Wistar rats were chronically subjected to 10 days of an escalating regimen of morphine during adolescence. After a 20-day washout period, adult males were allowed to copulate with naïve females. The adult male offspring were tested for somatic and affective components of naloxone-precipitated morphine withdrawal using conditioned place aversion. Moreover, electrical activity of the lateral paragigantocellularis (LPGi) nucleus, which is involved in development of opiate dependence, was recorded in response to a challenge dose of morphine via extracellular single-unit recordings.. Morphine-sired offspring exhibited augmented expression of naloxone-induced somatic and affective signs of opiate withdrawal compared to the control saline-sired counterparts. In vivo recording revealed that LPGi neurons displayed heterogeneous responses (inhibitory, excitatory, and no change) to acute morphine administration in both morphine- and saline-sired animals. The morphine-induced discharge inhibition was potentiated in morphine-sired offspring. However, the extent of discharge excitation in response to morphine did not reach significance in these subjects. Moreover, the lack of alteration in maternal behavior toward morphine-sired offspring indicates that this is due to germline-dependent transmission of epigenetic traits across generations.. Preconception paternal exposure to morphine during adolescence potentiates opiate withdrawal signs in male offspring which is mediated, at least in part, by epigenetic alteration of LPGi-related brain circuitry.

Topics: Age Factors; Animals; Disease Models, Animal; Electrophysiological Phenomena; Epigenesis, Genetic; Male; Medulla Oblongata; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Patch-Clamp Techniques; Paternal Exposure; Rats; Rats, Wistar; Substance Withdrawal Syndrome

Fish are useful animal models in research and have been employed in developing new pharmacological approaches. This study aimed to establish the use of silver catfish (Rhamdia quelen) as an animal model to evaluate antinociceptive activity. Initially, different concentrations of acetic acid (2.5-20%), formalin 1% (1-10 μL), menthol 0.5% (1-10 μL) or vehicle were injected in the lips to establish which concentration of each sample promotes nociceptive-like behavior in various parameters. The effect of morphine (0.5-10 mg/kg) on locomotion parameters was also evaluated for antinociceptive concentration determination. Morphine was administered intramuscularly immediately prior to algogen administration. The inhibition was evaluated with the antagonist naloxone (5 mg/kg), which was administered in the same way. Recording time varied according to the algogen used in each test and locomotor activity was evaluated by ANY-maze® software. Acid acetic at 15%, 10 μL of 1% formalin, and 1 μL of 0.5% menthol were chosen since they promoted nociceptive-like behavior in several parameters. Morphine (5 mg/kg) reversed the algogen-induced nociceptive-like behavior and naloxone inhibited this effect. Therefore, the proposed experimental model demonstrated specificity for nociception, since the reversion of the nociceptive-like behavior for a compound with well-described analgesic activity was observed. This new pharmacological model contributes to evaluating compounds with analgesic potential and developing new analgesic drugs, in addition to being a promising alternative to use with rodents.

Topics: Acetic Acid; Analgesia; Analgesics, Opioid; Animals; Catfishes; Disease Models, Animal; Injections; Lip; Menthol; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Nociception; Pain; Pain Measurement

Pain is susceptible to various cognitive factors. Suppression of pain by hunger is well known, but the effect of food intake after fasting (i.e. refeeding) on pain remains unknown. In the present study, we examined whether inflammatory pain behavior is affected by 24 h fasting and 2 h refeeding. In formalin-induced acute inflammatory pain model, fasting suppressed pain behavior only in the second phase and the analgesic effect was also observed after refeeding. Furthermore, in Complete Freund's adjuvant-induced chronic inflammatory pain model, both fasting and refeeding reduced spontaneous pain response. Refeeding with non-calorie agar produced an analgesic effect. Besides, intraperitoneal (i.p.) administration of glucose after fasting, which mimics calorie recovery following refeeding, induced analgesic effect. Administration of opioid receptor antagonist (naloxone, i.p.) and cannabinoid receptor antagonist (SR 141716, i.p.) reversed fasting-induced analgesia, but did not affect refeeding-induced analgesia in acute inflammatory pain model. Taken together, our results show that refeeding produce analgesia in inflammatory pain condition, which is associated with eating behavior and calorie recovery effect.

Topics: Acute Pain; Analgesics, Opioid; Animals; Chronic Pain; Disease Models, Animal; Eating; Food Deprivation; Formaldehyde; Freund's Adjuvant; Glucose; Hot Temperature; Hyperalgesia; Inflammation; Injections, Intraperitoneal; Male; Mice; Mice, Inbred C57BL; Naloxone; Narcotic Antagonists; Pain Management; Pain Measurement; Rimonabant

Lipopolysaccharide (LPS) or repeated water avoidance stress (WAS) induces visceral allodynia and gut hyperpermeability via corticotropin-releasing factor (CRF) and proinflammatory cytokines, which is a rat irritable bowel syndrome (IBS) model. As butyrate is known to suppress the release of proinflammatory cytokine, we hypothesized that butyrate alleviates these colonic changes in IBS models. The visceral pain was assessed by electrophysiologically measuring the threshold of abdominal muscle contractions in response to colonic distention. Colonic permeability was determined by measuring the absorbance of Evans blue in colonic tissue. Colonic instillation of sodium butyrate (SB; 0.37-2.9 mg/kg) for 3 days inhibited LPS (1 mg/kg)-induced visceral allodynia and colonic hyperpermeability dose-dependently. Additionally, the visceral changes induced by repeated WAS (1 h for 3 days) or CRF (50 µg/kg) were also blocked by SB. These effects of SB in the LPS model were eliminated by compound C, an AMPK inhibitor, or GW9662, a PPAR-γ antagonist, N

Topics: Animals; Butyrates; Colon; Disease Models, Animal; Electrodes; Hyperalgesia; Inflammation; Irritable Bowel Syndrome; Lipopolysaccharides; Male; Naloxone; Permeability; Rats; Rats, Sprague-Dawley; Sulpiride; Visceral Pain

Metformin has been shown to have anti-cytokine property. Lipopolysaccharide (LPS)-induced or repeated water avoidance stress (WAS)-induced visceral allodynia and increased gut permeability were pro-inflammatory cytokine-dependent responses, which were considered to be animal models of irritable bowel syndrome (IBS). We hypothesized that metformin improves symptoms in the patients with IBS by attenuating these visceral changes and tested the hypothesis in rats.. The threshold of the visceromotor response induced by colonic balloon distention was measured. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue for 15 min spectrophotometrically.. Subcutaneously injected LPS (1 mg/kg) reduced the threshold of visceromotor response, and metformin (5-50 mg/kg for 3 days) intraperitoneally attenuated this response in a dose-dependent manner. Repeated WAS (1 h daily for 3 days) induced visceral allodynia, which was also blocked by metformin. The antinociceptive effect of metformin on the LPS-induced allodynia was reversed by compound C, an adenosine monophosphate-activated protein kinase inhibitor or N. Metformin attenuated the visceral allodynia and increased gut permeability in animal IBS models. These actions may be evoked via activation of adenosine monophosphate-activated protein kinase, nitric oxide, and central dopamine D2 pathways. These results indicate the possibility that metformin can be useful for treating IBS.

Topics: AMP-Activated Protein Kinases; Animals; Colon; Disease Models, Animal; Domperidone; Dopamine Antagonists; Evans Blue; Hyperalgesia; Hypoglycemic Agents; Intestinal Mucosa; Irritable Bowel Syndrome; Lipopolysaccharides; Male; Metformin; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Nociception; Permeability; Protein Kinase Inhibitors; Pyrazoles; Pyrimidines; Rats; Rats, Sprague-Dawley; Stress, Physiological; Sulpiride

Chronic pain conditions, especially osteoarthritis (OA), are as common in individuals with Alzheimer's disease (AD) as in the general elderly population, which results in detrimental impact on patient's quality of life. However, alteration in perception of pain in AD coupled with deteriorating ability to communicate pain sensations often result in under-diagnosis and inappropriate management of pain. Therefore, a better understanding of mechanisms in chronic pain processing in AD is needed. Here, we explored the development and progression of OA pain and the effect of analgesics in a transgenic mouse model of AD.. Unilateral OA pain was induced chemically, via an intra-articular injection of monosodium iodoacetate (MIA) in the left knee joint of AD-mice (TASTPM) and age- and gender-matched C57BL/6J (WT). Pharmacological and biochemical assessments were conducted in plasma and spinal cord tissue.. MIA resulted in hind paw mechanical hypersensitivity (allodynia), initiating on day 3, in TASTPM and WT controls. However, from 14 to 28 days, TASTPM displayed partial attenuation of allodynia and diminished spinal microglial response compared to WT controls. Naloxone, an opioid antagonist, re-established allodynia levels as observed in the WT group. Morphine, an opioid agonist, induced heightened analgesia in AD-mice whilst gabapentin was devoid of efficacy. TASTPM exhibited elevated plasma level of β-endorphin post-MIA which correlated with impaired allodynia.. These results indicate an alteration of the opioidergic system in TASTPM as possible mechanisms underlying impaired persistent pain sensitivity in AD. This work provides basis for re-evaluation of opioid analgesic use for management of pain in AD.. This study shows attenuated pain-like behaviour in a transgenic mouse model of Alzheimer's disease due to alterations in the opioidergic system and central plasticity mechanisms of persistent pain.

Topics: Alzheimer Disease; Amyloid beta-Protein Precursor; Analgesics; Analgesics, Opioid; Animals; Arthralgia; Behavior, Animal; beta-Endorphin; Chronic Pain; Disease Models, Animal; Enzyme Inhibitors; Gabapentin; Humans; Hyperalgesia; Injections, Intra-Articular; Iodoacetic Acid; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Morphine; Naloxone; Narcotic Antagonists; Osteoarthritis; Pain Measurement; Pain Threshold; Quality of Life; Spinal Cord

Pain, a severely debilitating symptom of many human disorders, is a growing, unmet biomedical problem. Although the use of zebrafish (Danio rerio) to investigate both behavioral and physiological nociception-related responses is expanding rapidly, the characterization of behavioral phenotypes that reflect injury location is limited, making the results of such studies difficult to interpret. Here, we characterize putative nociception-related behavioral phenotypes in adult zebrafish following an intraperitoneal (i.p.) administration of acetic acid, a well-established protocol for visceral pain in rodents. Acetic acid (2.5 and 5.0%) induced an abdominal constriction-like response, which was assessed by measuring a body curvature index. Moreover, all doses tested (0.5-5.0%) reduced distance traveled and vertical activity in the novel tank test. Freezing duration increased following 5.0% acetic acid, whereas fish injected with 1.0, 2.5, and 5.0% spent more time in top area of the tank. Both morphine (an opioid analgesic) and diclofenac (a nonsteroidal anti-inflammatory drug, NSAID) prevented the 5.0% acetic acid-induced changes in body curvature index, whereas naloxone blocked these effects of morphine. Overall, zebrafish exposed to a single acetic acid i.p. injection display abnormal body curvature and specific changes in behavioral parameters sensitive to anti-nociceptive pharmacological modulation. We suggest that the abdominal constriction-like response represents a novel specific nociceptive-related phenotype in zebrafish. In general, our findings support the growing utility of zebrafish in translational pain research and antinociceptive drug discovery.

Topics: Acetic Acid; Analgesics, Opioid; Animals; Animals, Outbred Strains; Anti-Inflammatory Agents, Non-Steroidal; Behavior, Animal; Diclofenac; Disease Models, Animal; Drug Discovery; Drug Interactions; Female; Male; Morphine; Naloxone; Narcotic Antagonists; Nociception; Posture; Random Allocation; Visceral Pain; Zebrafish

The processing of pain in the central nervous system is now known to have an important immune component, including T cells of the adaptive immune system. T cells have been shown to release endogenous opioids, and although it is well known that opioids have effects on T-cell populations, very little attention has been given to the converse: how T cells may affect opioid regulation. We find here that, in addition to displaying significantly increased baseline pain sensitivity across various pain modalities, T-cell-deficient mice (CD-1 nude, Rag1 null mutant, and Cd4 null mutant) exhibit pronounced deficiencies in morphine inhibition of thermal or inflammatory pain. Nude mice are also deficient in endogenous opioid-mediated analgesia, exhibiting no stress-induced analgesia from restraint. The relevant T-cell subpopulation seems to be CD4 T cells because adoptive transfer of them but not CD8 cells into nude mice rescues both the pain and morphine analgesia phenotypes. As previously reported, we also observe a sex difference in CD-1 mice, with females requiring 2- to 3-fold more morphine than males to produce equal analgesia. Nude mice display no sex differences in morphine analgesia, and the sex difference is restored in nude mice of either sex receiving CD4 T cells from CD-1 donor male or female mice. These results suggest that CD4 T cells play an as yet unappreciated role in opioid analgesia and may be a driver of sex differences therein.

Topics: Adoptive Transfer; Analgesics, Opioid; Animals; Antigens, CD1; CD4 Antigens; CD4-Positive T-Lymphocytes; Disease Models, Animal; Female; Homeodomain Proteins; Hyperalgesia; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Sex Factors; Transforming Growth Factor beta1

Ocular pain is a core symptom of inflammatory or traumatic disorders affecting the anterior segment. To date, the management of chronic ocular pain remains a therapeutic challenge in ophthalmology. The main endogenous opioids (enkephalins) play a key role in pain control but exhibit only transient analgesic effects due to their rapid degradation. The aim of this study was to explore the antinociceptive and anti-inflammatory effects of topical administration of PL265 (a dual enkephalinase inhibitor) on murine models of corneal pain. On healthy corneas, chronic PL265 topical administration did not alter corneal integrity nor modify corneal mechanical and chemical sensitivity. Then, on murine models of corneal pain, we showed that repeated instillations of PL265 (10 mM) significantly reduced corneal mechanical and chemical hypersensitivity. PL265-induced corneal analgesia was completely antagonized by naloxone methiodide, demonstrating that PL265 antinociceptive effects were mediated by peripheral corneal opioid receptors. Moreover, flow cytometry (quantification of CD11b+ cells) and in vivo confocal microscopy analysis revealed that instillations of PL265 significantly decreased corneal inflammation in a corneal inflammatory pain model. Chronic PL265 topical administration also decreased Iba1 and neuronal injury marker (ATF3) staining in the nucleus of primary sensory neurons of ipsilateral trigeminal ganglion. These results open a new avenue for ocular pain treatment based on the enhancement of endogenous opioid peptides' analgesic effects in tissues of the anterior segment of the eye. Dual enkephalinase inhibitor PL265 seems to be a promising topical treatment for safe and effective alleviation of ocular pain and inflammation.

Topics: Administration, Topical; Animals; Anti-Infective Agents, Local; Benzalkonium Compounds; Capsaicin; Cornea; Corneal Injuries; Disease Models, Animal; Enzyme Inhibitors; Hyperalgesia; Inflammation; Lipopolysaccharides; Male; Mice; Mice, Inbred C57BL; Naloxone; Narcotic Antagonists; Pain; Pain Threshold; Propionates; Sensory System Agents; Trigeminal Ganglion

Bone cancer metastasis is extremely painful and decreases the quality of life of the affected patients. Available pharmacological treatments are not able to sufficiently ameliorate the pain, and as patients with cancer are living longer, new treatments for pain management are needed. Decitabine (5-aza-2'-deoxycytidine), a DNA methyltransferases inhibitor, has analgesic properties in preclinical models of postsurgical and soft-tissue oral cancer pain by inducing an upregulation of endogenous opioids. In this study, we report that daily treatment with decitabine (2 µg/g, intraperitoneally) attenuated nociceptive behavior in the 4T1-luc2 mouse model of bone cancer pain. We hypothesized that the analgesic mechanism of decitabine involved activation of the endogenous opioid system through demethylation and reexpression of the transcriptionally silenced endothelin B receptor gene, Ednrb. Indeed, Ednrb was hypermethylated and transcriptionally silenced in the mouse model of bone cancer pain. We demonstrated that expression of Ednrb in the cancer cells lead to release of β-endorphin in the cell supernatant, which reduced the number of responsive dorsal root ganglia neurons in an opioid-dependent manner. Our study supports a role of demethylating drugs, such as decitabine, as unique pharmacological agents targeting the pain in the cancer microenvironment.

Topics: Animals; Antimetabolites, Antineoplastic; beta-Endorphin; Bone Density; Bone Neoplasms; Cancer Pain; Cell Line, Tumor; Culture Media, Conditioned; Decitabine; Disease Models, Animal; Endothelin-1; Female; Ganglia, Spinal; Locomotion; Mice; Mice, Inbred BALB C; Naloxone; Neurons; Quaternary Ammonium Compounds; Receptor, Endothelin B; Weight-Bearing

Negative affective aspects of opiate abstinence contribute to the persistence of substance abuse. Importantly, interconnected brain areas involved in aversive motivational processes, such as the ventral tegmental area (VTA) and medial prefrontal cortex (mPFC), become activated when animals are confined to withdrawal-paired environments. In the present study, place aversion was elicited in sham and adrenalectomized (ADX) animals by conditioned naloxone-precipitated drug withdrawal following exposure to chronic morphine. qPCR was employed to detect the expression of brain derived neurotrophic factor (Bdnf) and the immediate early genes (IEG) early growth response 1 (Egr-1) and activity-regulated cytoskeletal-associated protein (Arc) mRNAs in the VTA and mPFC at different time points of the conditioned place aversion (CPA) paradigm: after the conditioning phase and after the test phase. Sham + morphine rats exhibited robust CPA, which was impaired in ADX + morphine animals. Egr-1 and Arc were induced in the VTA and mPFC after morphine-withdrawal conditioning phase. Furthermore, Bdnf expression was enhanced in the VTA during the test phase. Bdnf induction seemed to be glucocorticoid-dependent, given that was correlated with HPA axis function and was not observed in morphine-dependent ADX animals. In addition, BDNF regulation and function was opposite in the VTA and mPFC during aversive-withdrawal memory retrieval. Our results suggest that IEGs and BDNF in these brain regions may play key roles in mediating the negative motivational component of opiate withdrawal.

Topics: Adrenalectomy; AIDS-Related Complex; Animals; Avoidance Learning; Brain; Brain-Derived Neurotrophic Factor; Disease Models, Animal; Early Growth Response Protein 1; Gene Expression Regulation; Glucocorticoids; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Wistar; RNA, Messenger; Substance Withdrawal Syndrome

The endogenous opioid peptide system has been implicated in the neural modulation of fear and anxiety organised by the dorsal midbrain. Furthermore, previous results indicate a fundamental role played by inferior colliculus (IC) opioid mechanisms during the expression of defensive behaviours, but the involvement of the IC µ. The blockade of µ. Taken together, these results suggest that a decrease in µ

Topics: Animals; Anxiety; Behavior, Animal; Crotalus; Disease Models, Animal; Fear; Food Chain; Inferior Colliculi; Naloxone; Narcotic Antagonists; Panic Disorder; Rats; Rats, Wistar; Receptors, Opioid, mu; Signal Transduction

Pronounced analgesic activity of the innovative compound 4-(3,4-dibromthiophencarbonyl)-2,6,8,12-tetraacethyl-2,4,6,8,10,12hexaazatetracyclo[5,5,0,0

Topics: Analgesics; Animals; Disease Models, Animal; Gastric Mucosa; Male; Mice; Naloxone; Pain; Pain Measurement

Pain and inflammation are inherently linked responses to injury, infection, or chronic diseases. Given that acute inflammation in humans or mice enhances the analgesic properties of opioids, there is much interest in determining the inflammatory transducers that prime opioid receptor signaling in primary afferent nociceptors. Here, we found that activation of the transient receptor potential vanilloid type 1 (TRPV1) channel stimulated a mitogen-activated protein kinase (MAPK) signaling pathway that was accompanied by the shuttling of the scaffold protein β-arrestin2 to the nucleus. The nuclear translocation of β-arrestin2 in turn prevented its recruitment to the μ-opioid receptor (MOR), the subsequent internalization of agonist-bound MOR, and the suppression of MOR activity that occurs upon receptor desensitization. Using the complete Freund's adjuvant (CFA) inflammatory pain model to examine the role of TRPV1 in regulating endogenous opioid analgesia in mice, we found that naloxone methiodide (Nal-M), a peripherally restricted, nonselective, and competitive opioid receptor antagonist, slowed the recovery from CFA-induced hypersensitivity in wild-type, but not TRPV1-deficient, mice. Furthermore, we showed that inflammation prolonged morphine-induced antinociception in a mouse model of opioid receptor desensitization, a process that depended on TRPV1. Together, our data reveal a TRPV1-mediated signaling pathway that serves as an endogenous pain-resolution mechanism by promoting the nuclear translocation of β-arrestin2 to minimize MOR desensitization. This previously uncharacterized mechanism may underlie the peripheral opioid control of inflammatory pain. Dysregulation of the TRPV1-β-arrestin2 axis may thus contribute to the transition from acute to chronic pain.

Topics: Acute Pain; Analgesia; Analgesics, Opioid; Animals; beta-Arrestin 2; Chronic Pain; Disease Models, Animal; Freund's Adjuvant; Humans; Inflammation; Mice; Mice, Knockout; Naloxone; Narcotic Antagonists; Quaternary Ammonium Compounds; Signal Transduction; TRPV Cation Channels

The taste of sucrose is commonly used to provide pain relief in newborn humans and is innately analgesic to neonatal rodents. In adulthood, sucrose remains a strong motivator to feed, even in potentially hazardous circumstances (ie, threat of tissue damage). However, the neurobiological mechanisms of this endogenous reward-pain interaction are unclear. We have developed a simple model of sucrose drinking-induced analgesia in Sprague-Dawley rats (6-10 weeks old) and have undertaken a behavioral and pharmacological characterization using the Hargreaves' test of hind-paw thermal sensitivity. Our results reveal an acute, potent, and robust inhibitory effect of sucrose drinking on thermal nociceptive behaviour that unlike the phenomenon in neonates is independent of endogenous opioid signalling and does not seem to operate through classical descending inhibition of the spinal cord circuitry. Experience of sucrose drinking had a conditioning effect whereby the apparent expectancy of sucrose enabled water alone (in euvolemic animals) to elicit a short-lasting placebo-like analgesia. Sweet taste alone, however, was insufficient to elicit analgesia in adult rats intraorally perfused with sucrose. Instead, the sucrose analgesia phenomenon only appeared after conditioning by oral perfusion in chronically cannulated animals. This sucrose analgesia was completely prevented by systemic dosing of the endocannabinoid CB1 receptor antagonist rimonabant. These results indicate the presence of an endogenous supraspinal analgesic circuit that is recruited by the context of rewarding drinking and is dependent on endocannabinoid signalling. We propose that this hedonic sucrose-drinking model may be useful for further investigation of the supraspinal control of pain by appetite and reward.

Topics: Animals; Cannabinoid Receptor Antagonists; Disease Models, Animal; Dose-Response Relationship, Drug; Drinking Behavior; Freund's Adjuvant; Hot Temperature; Hyperalgesia; Injections, Spinal; Male; Naloxone; Narcotic Antagonists; Pain Threshold; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Reaction Time; Rimonabant; Spinal Cord; Sucrose; Sweetening Agents; Water Deprivation

The ability to detect noxious stimuli is essential to survival. However, pathological pain is maladaptive and severely debilitating. Endogenous and exogenous opioids modulate pain responses via opioid receptors, reducing pain sensibility. Due to the high genetic and physiological similarities to rodents and humans, the zebrafish is a valuable tool to assess pain responses and the underlying mechanisms involved in nociception. Although morphine attenuates pain-like responses of zebrafish, there are no data showing if the antagonism of opioid receptors prolongs pain duration in the absence of an exogenous opioid. Here, we investigated whether a common opioid antagonist naloxone affects the abdominal constriction writhing-like response, recently characterized as a zebrafish-based pain behavior. Animals were injected intraperitoneally with acetic acid (5.0%), naloxone (1.25 mg/kg; 2.5 mg/kg; 5.0 mg/kg) or acetic acid with naloxone to investigate the changes in their body curvature for 1 h. Acetic acid elicited a robust pain-like response in zebrafish, as assessed by aberrant abdominal body curvature, while no effects were observed following PBS injection. Although naloxone alone did not alter the frequency and duration of this behavior, it dose-dependently prolonged acetic acid-induced abdominal curvature response. Besides reinforcing the use of the abdominal writhing-like phenotype as a behavioral endpoint to measure acute pain responses in zebrafish models, our novel data suggest a putative role of endogenous opioids in modulating the recovery from pain stimulation in zebrafish.

Topics: Abdomen; Acetic Acid; Animals; Behavior, Animal; Constriction, Pathologic; Disease Models, Animal; Naloxone; Narcotic Antagonists; Pain; Visceral Pain; Zebrafish

Drug addiction is a chronic disorder resulted from complex interaction of genetic, environmental, and developmental factors. Epigenetic mechanisms play an important role in the development and maintenance of addiction and also memory formation in the brain. We have examined passive avoidance memory and morphine conditioned place preference (CPP) in the offspring of male and/or female rats with a history of adulthood morphine consumption. Adult male and female animals received chronic oral morphine for 21days and then were maintained drug free for 10days. After that, they were let to mate with either an abstinent or control rat. Male offspring's memory was evaluated by step through test. Besides, rewarding effects of morphine were checked with CCP paradigm. Offspring of abstinent animals showed significant memory impairment compared to the control group which was more prominent in the offspring of abstinent females. Conditioning results showed that administration of a high dose of morphine (10mg/kg) that could significantly induce CPP in control rats, was not able to induce similar results in the offspring of morphine abstinent parents; and CPP was much more prominent when it was induced in the offspring of morphine exposed females compared to the progeny of morphine exposed males. It is concluded that parental morphine consumption in adulthood even before mating has destructive effects on memory state of the male offspring and also leads to tolerance to the rewarding effects of morphine. These effects are greater when the morphine consumer parent is the female one.

Topics: Analysis of Variance; Animals; Avoidance Learning; Conditioning, Operant; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Male; Memory Disorders; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Wistar; Sex Factors; Substance Abuse, Oral

Neuropathic pain is relatively common and occurs in approximately 6-8% of the population. It is associated with allodynia and hyperalgesia. Thus, non-pharmacological treatments, such as transcranial direct current stimulation (tDCS) may be useful for relieving pain.. This study aimed to investigate the antiallodynic effect of tDCS in a mice model of neuropathic pain, and the underlying neurotransmission systems that could drive these effects.. Male, Swiss mice, weighing 25-35 g, were subjected to partial sciatic nerve ligation (PSNL). Allodynia was assessed using a Von Frey filament (0.6 g). First, the behavioral time-course of these mice was assessed after 5, 10, 15 and 20 min of tDCS (0.5 mA). Second, the mice that underwent PSNL were assigned to either the tDCS (0.5 mA, 15 min) or tDCS sham group, and further assigned to receive either saline or a drug (i.e., naloxone, yohimbine, a-methyl-p-tyrosine, q-chlorophenylalanine methyl ester, caffeine, 1,3-dipropyl-8-cyclopentylxanthine, AM281, AM630, flumazenil, MK-801, or lidocaine).. The antiallodynic effect of tDCS lasted 2 h and 4 h, after 10 min and 15 or 20 min of treatment, respectively (P < .001, P < .01, and P < .05, respectively). The antiallodynic effect of tDCS was associated with all the systems that were analyzed, i.e., the opioidergic (P < .01), adenosinergic (P < .001), serotonergic (P < .01), noradrenergic (P < .001), cannabinoid (P < .001), GABAergic, and glutamatergic (P < .001) systems. Lidocaine did not reverse the antiallodynic effect of tDCS (P > .05).. The antiallodynic effect of tDCS was associated with different neurotransmitters systems; the duration of these after-effects depended on the time exposure to tDCS.

Topics: Adenosine A1 Receptor Antagonists; Animals; Caffeine; Central Nervous System Stimulants; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Flumazenil; GABA Modulators; Hyperalgesia; Male; Mice; Morpholines; Naloxone; Narcotic Antagonists; Neuralgia; Pain Threshold; Physical Stimulation; Pyrazoles; Transcranial Direct Current Stimulation; Xanthines

In this study, we investigated the effects of recurrent hypoglycaemia on the adrenal catecholamine synthetic enzymes in a rat model of hypoglycaemia-associated autonomic failure (HAAF). We found that plasma adrenaline was significantly reduced by about 50% in response to recurrent hypoglycaemia versus single hypoglycaemia. However, tyrosine hydroxylase (TH) protein and phosphorylation at Ser31 and Ser40 were increased in HAAF; similarly, aromatic aminoacid decarboxylase protein was also increased indicating a likely increase in catecholamine synthesis in the adrenal gland. Opioid antagonists, naloxone and methylnaltrexone did not restore plasma adrenaline in HAAF; however, naloxone increased TH phosphorylation at Ser31 and Ser40.

Topics: Animals; Blood Glucose; Disease Models, Animal; Epinephrine; Hypoglycemia; Hypoglycemic Agents; Insulin; Male; Naloxone; Naltrexone; Narcotic Antagonists; Pure Autonomic Failure; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Serine; Tyrosine 3-Monooxygenase

To establish an animal model of bladder underactivity induced by prolonged and intense stimulation of somatic afferent axons in the tibial nerve.. In seven cats under α-chloralose anesthesia, tibial nerve stimulation (TNS) of 30-min duration was repeatedly (3-8 times) applied at 4-6 times threshold (T) intensity for inducing a toe twitch to produce bladder underactivity determined by cystometry. Naloxone (1 mg/kg, i.v.) was administered to examine the role of opioid receptors in TNS-induced bladder underactivity.. After prolonged (1.5-4 h) and intense (4-6T) TNS, a complete suppression of the micturition reflex occurred in six cats and an increase in bladder capacity to about 150% of control and a decrease in the micturition contraction amplitude to 50% of control occurred in one cat. The bladder underactivity was maintained for at least 1-1.5 h. Naloxone reversed the bladder underactivity, but an additional 30-min TNS removed the naloxone effect.. The results indicate that prolonged and intense activation of somatic afferent axons in the tibial nerve can suppress the central reflex mechanisms controlling micturition. This animal model may be useful for examining the pathophysiology of neurogenic bladder underactivity and for development of new treatments for underactive bladder symptoms.

Topics: Animals; Axons; Cats; Disease Models, Animal; Electric Stimulation; Female; Male; Naloxone; Narcotic Antagonists; Neurons, Afferent; Receptors, Opioid; Reflex; Tibial Nerve; Urinary Bladder, Underactive; Urination

Fentanyl is an opioid commonly prescribed for cancer pain. Using melanoma-bearing mice, we investigated whether peripheral action would contribute to fentanyl analgesia in cancer pain. Intravenous injection of fentanyl inhibited mechanical nociception in healthy mice, which was markedly inhibited by the opioid antagonist naloxone, but not naloxone methiodide, a peripherally acting opioid antagonist. Melanoma-bearing mice showed mechanical allodynia and spontaneous licking, a pain-related behavior, which were suppressed by intravenous and local injections of fentanyl. Both naloxone and naloxone methiodide inhibited the analgesic effect of intravenous fentanyl to the same degree. Electrophysiological analysis showed that melanoma growth increased the spontaneous and mechanical stimuli-evoked activity of the tibial nerve, which were inhibited by intravenous fentanyl. There was a greater expression of µ- opioid receptors in skin with a melanoma mass than in the contralateral normal skin. In addition, we found µ-opioid receptors in cultured melanoma cells. There was no difference between the number of µ-opioid receptors in the dorsal root ganglia and spinal cord of the melanoma-bearing and contralateral skin side. These results suggest that the analgesic effect of systemic fentanyl is produced via central and peripheral µ- opioid receptors in cancer pain, and cancer cells are a key site of peripheral action.

Topics: Action Potentials; Analgesics, Opioid; Animals; Cancer Pain; Cell Line, Tumor; Disease Models, Animal; Fentanyl; Humans; Hyperalgesia; Injections, Intramuscular; Injections, Intravenous; Male; Melanoma; Mice; Mice, Inbred C57BL; Naloxone; Narcotic Antagonists; Quaternary Ammonium Compounds; Receptors, Opioid; Receptors, Opioid, mu; Skin; Skin Neoplasms; Spinal Cord; Tibial Nerve; Xenograft Model Antitumor Assays

Topics: Analgesics; Animals; Behavior, Animal; Capsaicin; Coffee; Disease Models, Animal; Female; Formaldehyde; Glutamic Acid; Hot Temperature; Hyperalgesia; Male; Mice; Naloxone; Narcotic Antagonists; Ondansetron; Pain; Pain Measurement; Piperidines; Pyrazoles; Serotonin

Cognition and pain share common neural substrates and interact reciprocally: chronic pain compromises cognitive performance, whereas cognitive processes modulate pain perception. In the present study, we established a non-drug-dependent rat model of context-based analgesia, where two different contexts (dark and bright) were matched with a high (52°C) or low (48°C) temperature in the hot-plate test during training. Before and after training, we set the temperature to the high level in both contexts. Rats showed longer paw licking latencies in trials with the context originally matched to a low temperature than those to a high temperature, indicating successful establishment of a context-based analgesic effect in rats. This effect was blocked by intraperitoneal injection of naloxone (an opioid receptor antagonist) before the probe. The context-based analgesic effect also disappeared after optogenetic activation or inhibition of the bilateral infralimbic or prelimbic sub-region of the prefrontal cortex. In brief, we established a context-based, non-drug dependent, placebo-like analgesia model in the rat. This model provides a new and useful tool for investigating the cognitive modulation of pain.

Topics: Action Potentials; Analgesics; Animals; Disease Models, Animal; Electric Stimulation; Female; In Vitro Techniques; Naloxone; Narcotic Antagonists; Optogenetics; Pain; Pain Measurement; Pain Threshold; Patch-Clamp Techniques; Physical Stimulation; Prefrontal Cortex; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Time Factors

The aim of this study was to evaluate the antinociceptive effect of Kaempferol-3-O-rutinoside (KR), isolated from the plant Ouratea fieldingiana, on the orofacial nociception and possible mechanisms of action. Adult zebrafish (Danio rerio) were tested as a behavioral model to study formalin, glutamate, capsaicin, cinnamaldehyde and acidic saline-induced orofacial nociception, using as parameter the number of times the fish crossed the lines between the quadrants of a glass Petri dish during a specific time. Morphine was used as positive control. The effect of KR was tested for modulation by opioid (naloxone), nitrergic (L-NAME), TRPV1 (ruthenium red), TRPA1 (camphor) or ASIC (amiloride) antagonists. The effect of KR on zebrafish locomotor behavior was evaluated with the open field test. KR did not alter the fish's locomotor system and significantly reduced the orofacial nociceptive behavior induced by all noxious agents compared to the control group. The antinociceptive effect of KR was similar to morphine. All antagonists inhibited the antinociceptive effect of KR. KR has pharmacological potential for the treatment of acute orofacial pain and this effect is modulated by the opioid and nitrergic systems as well as TRPV1, TRPA1 and ASIC channels. These results can lead to the development of a new natural product for the treatment of orofacial pain and confirm the popular use of O. fieldingiana leaf for pain relief.

Topics: Analgesics; Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Facial Pain; Female; Kaempferols; Male; Morphine; Naloxone; Nociception; Ochnaceae; Plant Leaves; Zebrafish

The collective cognitive and motor deficits known as HIV-associated neurocognitive disorders (HAND) remain high even among HIV+ individuals whose antiretroviral therapy is optimized. HAND is worsened in the context of opiate abuse. The mechanism of exacerbation remains unclear but likely involves chronic immune activation of glial cells resulting from persistent, low-level exposure to the virus and viral proteins. We tested whether signaling through C-C chemokine receptor type 5 (CCR5) contributes to neurotoxic interactions between HIV-1 transactivator of transcription (Tat) and opiates and explored potential mechanisms.. Neuronal survival was tracked in neuronal and glial co-cultures over 72 h of treatment with HIV-1 Tat ± morphine using cells from CCR5-deficient and wild-type mice exposed to the CCR5 antagonist maraviroc or exogenously-added BDNF (analyzed by repeated measures ANOVA). Intracellular calcium changes in response to Tat ± morphine ± maraviroc were assessed by ratiometric Fura-2 imaging (analyzed by repeated measures ANOVA). Release of brain-derived neurotrophic factor (BDNF) and its precursor proBDNF from CCR5-deficient and wild-type glia was measured by ELISA (analyzed by two-way ANOVA). Levels of CCR5 and μ-opioid receptor (MOR) were measured by immunoblotting (analyzed by Student's t test).. Our results suggest a critical role for glial CCR5 in mediating neurotoxic effects of HIV-1 Tat and morphine interactions on neurons. A shift in the proBDNF/BDNF ratio that favors neurotrophic support may occur when glial CCR5 signaling is blocked. Some neuroprotection occurred only in the presence of morphine, suggesting that loss of CCR5 may fundamentally change signaling through the MOR in glia.

Topics: AIDS Dementia Complex; Analgesics, Opioid; Animals; CCR5 Receptor Antagonists; Corpus Striatum; Cytokines; Disease Models, Animal; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Maraviroc; Mice; Mice, Inbred C57BL; Mice, Transgenic; Naloxone; Narcotic Antagonists; Neuroglia; Neurons; Opiate Alkaloids; Receptors, CCR5; Receptors, Opioid, mu; tat Gene Products, Human Immunodeficiency Virus

Exercise is commonly recommended for patients with osteoarthritis (OA) pain. However, whether exercise is beneficial in ameliorating ongoing pain that is persistent, resistant to nonsteroidal antiinflammatory drugs (NSAIDs), and associated with advanced OA is unknown.. Rats treated with intraarticular (IA) monosodium iodoacetate (MIA) or saline underwent treadmill exercise or remained sedentary starting 10 days postinjection. Tactile sensory thresholds and weight bearing were assessed, followed by radiography at weekly intervals. After 4 weeks of exercise, ongoing pain was assessed using conditioned place preference (CPP) to IA or rostral ventromedial medulla (RVM)-administered lidocaine. The possible role of endogenous opioids in exercise-induced pain relief was examined by systemic administration of naloxone. Knee joints were collected for micro-computed tomography (micro-CT) analysis to examine pathologic changes to subchondral bone and metaphysis of the tibia.. Treadmill exercise for 4 weeks reversed MIA-induced tactile hypersensitivity and weight asymmetry. Both IA and RVM lidocaine D35, administered post-MIA, induced CPP in sedentary but not exercised MIA-treated rats, indicating that exercise blocks MIA-induced ongoing pain. Naloxone reestablished weight asymmetry in MIA-treated rats undergoing exercise and induced conditioned place aversion, indicating that exercise-induced pain relief is dependent on endogenous opioids. Exercise did not alter radiographic evidence of OA. However, micro-CT analysis indicated that exercise did not block lateral subchondral bone loss or trabecular bone loss in the metaphysis, but did block MIA-induced medial bone loss.. These findings support the conclusion that exercise induces pain relief in advanced, NSAID-resistant OA, likely through increased endogenous opioid signaling. In addition, treadmill exercise blocked MIA-induced bone loss in this model, indicating a potential bone-stabilizing effect of exercise on the OA joint.

Topics: Anesthetics, Local; Animals; Arthralgia; Arthritis, Experimental; Behavior, Animal; Disease Models, Animal; Enzyme Inhibitors; Hyperalgesia; Injections, Intra-Articular; Iodoacetic Acid; Knee Joint; Lidocaine; Male; Medulla Oblongata; Naloxone; Narcotic Antagonists; Osteoarthritis, Knee; Physical Conditioning, Animal; Rats; Rats, Sprague-Dawley; Tibia; Weight-Bearing; X-Ray Microtomography

The opioid system modulates the central reinforcing effects of ethanol and participates in the etiology of addiction. However, the pharmacotherapy of ethanol dependence targeted on the opioid system is little effective and varies due to individual patients' sensitivity. In the present study, we used two mouse lines with high (HA) and low (LA) activity of the endogenous opioid system to analyze the effect of opioid receptor blockade on ethanol drinking behavior. We found that LA and HA lines characterized by divergent magnitudes of swim stress-induced analgesia also differ in ethanol intake and preference. Downregulation of the opioid system in LA mice was associated with increased ethanol consumption. Treatment with a non-selective opioid receptor antagonist (naloxone) had no effect on ethanol intake in this line. Surprisingly, in HA mice, the blockage of opioid receptors led to excessive ethanol consumption. Moreover, naloxone selectively induced high levels of anxiety- and depressive-like behaviors in HA mice which was attenuated by ethanol. With the use of specific opioid receptor antagonists we showed that the naloxone-induced increase in ethanol drinking in HA mice is mediated mainly by δ and to a lower extent by μ opioid receptors. The effect of δ-opioid receptor antagonism was abolished in HA mice carrying a C320T transition in the δ-opioid receptor gene (EU446125.1), which impairs this receptor's function. Our results indicate that high activity of the opioid system plays a protective role against ethanol dependence. Therefore, its blockage with opioid receptor antagonists may lead to a profound increase in ethanol consumption.

Topics: Alcohol Drinking; Analgesia; Analysis of Variance; Animals; beta-Endorphin; Central Nervous System Depressants; Disease Models, Animal; Ethanol; Genotype; Maze Learning; Mice; Mood Disorders; Morphinans; Naloxone; Narcotic Antagonists; Receptors, Opioid, delta; Stress, Psychological; Swimming

Hydrogen therapy is a new medical approach for a wide range of diseases. The effects of hydrogen on central nervous system-related diseases have recently become increasingly appreciated, but little is known about whether hydrogen affects the morphine withdrawal process. This study aims to investigate the potential effects of hydrogen-rich saline (HRS) administration on naloxone-precipitated withdrawal symptoms and morphine withdrawal-induced anxiety-like behaviors. Mice received gradually increasing doses (25-100 mg/kg, i.p.) of morphine over 3 days. In the naloxone-precipitated withdrawal procedure, the mice were treated with three HRS (20 μg/kg, i.p.) injections, and naloxone (1 mg/kg, i.p.) was given 30 min after HRS administration. Body weight, jumping behavior and wet-dog shakes were immediately assessed. In the spontaneous withdrawal procedure, the mice were treated with HRS (20 μg/kg, i.p.) every 8-h. Mice underwent naloxone-precipitated or spontaneous withdrawal were tested for anxiety-like behaviors in the elevated plus-maze (EPM) and light/dark box (L/D box) paradigm, respectively. In addition, the levels of plasma corticosterone were measured. We found that HRS administration significantly reduced body weight loss, jumping behavior and wet-dog shakes in mice underwent naloxone-precipitated withdrawal, and attenuated anxiety-like behaviors in the EPM and L/D box tests after naloxone-precipitated withdrawal or a 2-day spontaneous withdrawal period. Hypo-activity or motor impairment after HRS administration was not observed in the locomotion tests. Furthermore, HRS administration significantly decreased the levels of corticosterone in morphine-withdrawn mice. These are the first findings to indicate that hydrogen might ameliorate withdrawal symptoms and exert an anxiolytic-like effect in morphine-withdrawal mice.

Topics: Adaptation, Ocular; Animals; Anti-Anxiety Agents; Anxiety; Corticosterone; Disease Models, Animal; Dose-Response Relationship, Drug; Head Movements; Hydrocortisone; Hydrogen; Locomotion; Male; Maze Learning; Mice; Mice, Inbred C57BL; Morphine; Naloxone; Sodium Chloride; Statistics, Nonparametric; Substance Withdrawal Syndrome

Due to its unclear pathophysiology, the pharmacological treatment of fibromyalgia is a challenge for researchers. Studies using medicinal plants, such as those from the genus Lippia, complexed with cyclodextrins (CDs) have shown innovative results.. The present research intended to evaluate the effect of an inclusion complex containing β-cyclodextrin (βCD) inclusion complex with Lippia grata (LG) essential oil in a chronic musculoskeletal pain model, its central activity and its possible interaction with neurotransmitters involved in pain.. After acid saline-induced chronic muscle pain, male mice were evaluated for primary and secondary hyperalgesia and muscle strength. Moreover, an antagonist assay was performed to assess the possible involvement of the opioidergic, serotonergic and noradrenergic pathways. In addition, Fos protein in the spinal cord was assessed, and a docking study and antioxidant assays were performed.. The treatment with LG-βCD, especially in the dose of 24mg/kg, was able to significantly decrease (p<0.05) the paw withdrawal and muscle threshold. Furthermore, LG-βCD was shown to affect the opioidergic and serotonergic pathways. There were no significant changes in muscle strength. Fos protein immunofluorescence showed a significant decrease in expression in the dorsal horn of the spinal cord. The main compounds of LG showed through the docking study interaction energies with the alpha-adrenergic and μOpioid receptors. In all antioxidant assays, LG exhibited stronger antioxidant activities than LG-βCD.. This study suggested that LG-βCD could be considered as a valuable source for designing new drugs in the treatment of chronic pain, especially musculoskeletal pain.

Topics: Analgesics; Animals; Antioxidants; beta-Cyclodextrins; Chronic Pain; Disease Models, Animal; Hyperalgesia; Lippia; Male; Methysergide; Mice; Molecular Docking Simulation; Musculoskeletal Pain; Naloxone; Oils, Volatile; Plant Leaves; Proto-Oncogene Proteins c-fos; Spinal Cord Dorsal Horn; Yohimbine

The present study explores the pain attenuating effect of perampanel, AMPA receptor antagonist, in chronic constriction injury-induced neuropathic pain. Chronic Constriction Injury was performed by putting four loose ligatures around the sciatic nerve. Pain was assessed by determining mechanical hyperalgesia, cold allodynia and heat hyperalgesia on 7th and 14th day post surgery. Perampanel (3mg and 6mg/kg, p.o.) was administered 30min before pain assessment test on 14th day post-surgery. CCI led to significant development of pain and peak symptoms were observed on 14th day. Perampanel significantly attenuated CCI-induced mechanical hyperalgesia, cold allodynia and heat hyperalgesia, at different time intervals 30, 60, 90, 120min, with more substantial effect observed at dose of 6mg/kgNaloxone was administered in CCI subjected rats before perampanel treatment to explore the potential role of opioids in anti-nociceptive effects of perampanel. Naloxone decreased the pain attenuating effects of perampanel significantly, indicating a critical role of opioid system in anti-nociceptive potential of perampanel. Perampanel has pain attenuating potential in CCI-induced neuropathic pain, which may be due to partly mediated through the opioid system.

Topics: Animals; Chronic Disease; Constriction; Disease Models, Animal; Female; Hyperalgesia; Male; Motor Activity; Naloxone; Neuralgia; Nitriles; Pyridones; Rats, Wistar

Topics: Adrenergic alpha-2 Receptor Antagonists; Animals; Disease Models, Animal; Dopamine; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Norepinephrine; Nucleus Accumbens; Rats; Rats, Sprague-Dawley; Septal Nuclei; Substance Withdrawal Syndrome

The GABAergic tail of the ventral tegmental area (tVTA), also named rostromedial tegmental nucleus (RMTg), exerts an inhibitory control on dopamine neurons of the VTA and substantia nigra. The tVTA has been implicated in avoidance behaviors, response to drugs of abuse, reward prediction error, and motor functions. Stimulation of the lateral habenula (LHb) inputs to the tVTA, or of the tVTA itself, induces avoidance behaviors, which suggests a role of the tVTA in processing aversive information. Our aim was to test the impact of aversive stimuli on the molecular recruitment of the tVTA, and the behavioral consequences of tVTA lesions. In rats, we assessed Fos response to lithium chloride (LiCl), β-carboline, naloxone, lipopolysaccharide (LPS), inflammatory pain, neuropathic pain, foot-shock, restraint stress, forced swimming, predator odor, and opiate withdrawal. We also determined the effect of tVTA bilateral ablation on physical signs of opiate withdrawal, and on LPS- and LiCl-induced conditioned taste aversion (CTA). Naloxone-precipitated opiate withdrawal induced Fos in μ-opioid receptor-positive (15%) and -negative (85%) tVTA cells, suggesting the presence of both direct and indirect mechanisms in tVTA recruitment during withdrawal. However, tVTA lesion did not impact physical signs of opiate withdrawal. Fos induction was also present with repeated, but not single, foot-shock delivery. However, such induction was mostly absent with other aversive stimuli. Moreover, tVTA ablation had no impact on CTA. Although stimulation of the tVTA favors avoidance behaviors, present findings suggest that this structure may be important to the response to some, but not all, aversive stimuli.

Topics: Animals; Antimanic Agents; Behavior, Animal; Carbolines; Conditioning, Classical; Disease Models, Animal; Lipopolysaccharides; Lithium Chloride; Male; Morphine Dependence; Naloxone; Narcotic Antagonists; Neuralgia; Neurotoxins; Olfactory Perception; Pain; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Substance Withdrawal Syndrome; Ventral Tegmental Area

To determine the role of opioid, β-adrenergic, and metabotropic glutamate 5 receptors in sacral neuromodulation of bladder overactivity.. In α-chloralose anesthetized cats, intravesical infusion of 0.5% acetic acid (AA) irritated the bladder and induced bladder overactivity. Electric stimulation (5 Hz, 0.2 ms, 0.16-0.7V) of S1 or S2 sacral dorsal roots inhibited the bladder overactivity. Naloxone, propranolol, or MTEP were given intravenously (i.v.) to determine different neurotransmitter mechanisms.. AA significantly (p < 0.05) reduced bladder capacity to 7.7 ± 3.3 mL from 12.0 ± 5.0 mL measured during saline infusion. S1 or S2 stimulation at motor threshold intensity significantly (p < 0.05) increased bladder capacity to 179.4 ± 20.0% or 219.1 ± 23.0% of AA control, respectively. Naloxone (1 mg/kg) significantly (p < 0.001) reduced the control capacity to 38.3 ± 7.3% and the bladder capacity measured during S1 stimulation to 106.2 ± 20.8% of AA control, but did not significantly change the bladder capacity measured during S2 stimulation. Propranolol (3 mg/kg) significantly (p < 0.01) reduced bladder capacity from 251.8 ± 32.2% to 210.9 ± 33.3% during S2 stimulation, but had no effect during S1 stimulation. A similar propranolol effect also was observed in naloxone-pretreated cats. In propranolol-pretreated cats during S1 or S2 stimulation, MTEP (3 mg/kg) significantly (p < 0.05) reduced bladder capacity and naloxone (1 mg/kg) following MTEP treatment further reduced bladder capacity. However, a significant inhibition could still be induced by S1 or S2 stimulation after all three drugs were administered.. Neurotransmitter mechanisms in addition to those activating opioid, β-adrenergic, and metabotropic glutamate 5 receptors also are involved in sacral neuromodulation.

Topics: Acetic Acid; Adrenergic beta-Antagonists; Analysis of Variance; Animals; Cats; Disease Models, Animal; Excitatory Amino Acid Antagonists; Female; Indicators and Reagents; Male; Naloxone; Narcotic Antagonists; Neurotransmitter Agents; Propranolol; Pyridines; Sacrum; Spinal Cord Stimulation; Spinal Nerve Roots; Thiazoles; Urinary Bladder, Overactive

This work aimed to determine the chemical fingerprint of hydroethanolic extract of leaves of Caryocar coriaceum (HELCC) and the gastroprotective activity. The chemical fingerprint of HELCC was analyzed by HPLC-DAD, to quantify total phenols and flavonoids were carried out by Folin-Ciocalteu reagent and aluminum chloride assay, while in vitro antioxidant activity was evaluated by the DPPH method. The methods used to determine pharmacological activity were: gastroprotective screening test in classical models of induced acute and chronic gastric lesions and physical barrier test. Further assays were performed to demonstrate the involvement of NO, prostaglandins, ATP-dependent potassium channels, TRPV, noradrenergic α2 receptors, histamines, and opioids. The DPPH method demonstrated the antioxidant activity of the extract, in vitro, explained by the presence of polyphenols and flavonoids. Oral administration of the extract, previously dissolved in deionized water, at a dose of 100 mg/kg decreased the lesions induced by indomethacin, acidified ethanol, ethanol and acetic acid by 75.0, 72.8, 69.4 and 86.2% respectively. It was demonstrated that opioid receptors, α

Topics: Animals; Antioxidants; Capsaicin; Chromatography, High Pressure Liquid; Chronic Disease; Disease Models, Animal; Ericales; Ethanol; Female; Flavonoids; Gastrointestinal Motility; Glyburide; Histamine; Indomethacin; Male; Mice; Mucus; Naloxone; NG-Nitroarginine Methyl Ester; Phenols; Phytotherapy; Plant Extracts; Plant Leaves; Protective Agents; Stomach Ulcer; Water; Yohimbine

The results of epidemiological, clinical, and in vivo and in vitro experimental studies on the effect of opioid analgesics on bone are inconsistent. The aim of the present study was to investigate the effect of morphine (an agonist of opioid receptors), buprenorphine (a partial μ opioid receptor agonist and κ opioid receptor antagonist), and naloxone (an antagonist of opioid receptors) on the skeletal system of female rats in vivo. The experiments were carried out on 3-month-old Wistar rats, divided into two groups: nonovariectomized (intact; NOVX) rats and ovariectomized (OVX) rats. The bilateral ovariectomy was performed 7 days before the start of drug administration. Morphine hydrochloride (20 mg/kg/day s.c.), buprenorphine (0.05 mg/kg/day s.c.), or naloxone hydrochloride dihydrate (2 mg/kg/day s.c.) were administered for 4 weeks to NOVX and OVX rats. In OVX rats, the use of morphine and buprenorphine counteracted the development of osteoporotic changes in the skeletal system induced by estrogen deficiency. Morphine and buprenorphine beneficially affected also the skeletal system of NOVX rats, but the effects were much weaker than those in OVX rats. Naloxone generally did not affect the rat skeletal system. The results confirmed the role of opioid receptors in the regulation of bone remodeling processes and demonstrated, in experimental conditions, that the use of opioid analgesics at moderate doses may exert beneficial effects on the skeletal system, especially in estrogen deficiency.

Topics: Analgesics, Opioid; Animals; Biomechanical Phenomena; Bone Remodeling; Buprenorphine; Compressive Strength; Disease Models, Animal; Drug Partial Agonism; Elastic Modulus; Female; Femur; Humans; Morphine; Naloxone; Narcotic Antagonists; Osteoporosis, Postmenopausal; Ovariectomy; Rats, Wistar; Receptors, Opioid, kappa; Receptors, Opioid, mu; Tibia

In the present study, we investigated the effects of microinjection of vitamin B

Topics: Analgesics; Animals; CA1 Region, Hippocampal; Catheters, Indwelling; Disease Models, Animal; Dose-Response Relationship, Drug; Exploratory Behavior; Facial Pain; Formaldehyde; Male; Maze Learning; Memory Disorders; Microinjections; Motor Activity; Naloxone; Narcotic Antagonists; Nootropic Agents; Rats, Wistar; Scopolamine; Vibrissae; Vitamin B 12

In this study, we evaluated the effects of atorvastatin, a lipid-lowering medication on morphine-induced tolerance and dependence in mice.. Tolerance was induced by subcutaneous administration of morphine (20mg/kg) to animals, twice a day for 9days. Atorvastatin was given at the doses of 5, 10 and 20mg/kg, 30min before each morphine administration, once daily for 9days. Hot plate test was employed to assess antinociceptive effect of morphine on days 1, 3, 5, 7 and 9. Dependence was evaluated by naloxone-precipitated withdrawal syndrome. We attempted to verify withdrawal regulation of induced nitric oxide synthase (iNOS), astroglia marker, glial fibrillary acidic protein (GFAP), ionized calcium-binding protein (Iba1), a microglia activation marker, a pro-inflammatory mediator, tumor necrosis alpha (TNF-α) and immune receptor, toll like receptor 4 (TLR-4) genes by real-time polymerase chain reaction (RT-PCR). Lipid peroxidation was estimated by assessing malondialdehyde (MDA) content in the spinal cord of animals.. Tolerance to antinociceptive effects of morphine was observed on days 7 and 9. Decrease in morphine-induced antinociception was reversed by concomitant intraperitoneal administration of atorvastatin (10 and 20mg/kg). Atorvastatin (10 and 20mg/kg) mitigated naloxone-induced withdrawal parameters. Brain expression levels of TNF-α, GFAP, Iba1 and iNOS increased in morphine withdrawn animals which were attenuated by nine days treatment with atorvastatin. Increased MDA was also normalized in withdrawn animals received atorvastatin.. Atorvastatin exhibits meaningful protective effects against both tolerance to antinociceptive effects of morphine and withdrawal-induced behavioral profile. Neuroprotective effects of atorvastatin is further supported via inhibition of glia activity and antioxidant effects.

Topics: Animals; Antioxidants; Astrocytes; Atorvastatin; Brain; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Drug Tolerance; Male; Mice; Microglia; Morphine; Morphine Dependence; Naloxone; Narcotics; Nociception; Random Allocation; Substance Withdrawal Syndrome

Treatments for chronic pain are inadequate, and new options are needed. Nonpharmaceutical approaches are especially attractive with many potential advantages including safety. Light therapy has been suggested to be beneficial in certain medical conditions such as depression, but this approach remains to be explored for modulation of pain. We investigated the effects of light-emitting diodes (LEDs), in the visible spectrum, on acute sensory thresholds in naive rats as well as in experimental neuropathic pain. Rats receiving green LED light (wavelength 525 nm, 8 h/d) showed significantly increased paw withdrawal latency to a noxious thermal stimulus; this antinociceptive effect persisted for 4 days after termination of last exposure without development of tolerance. No apparent side effects were noted and motor performance was not impaired. Despite LED exposure, opaque contact lenses prevented antinociception. Rats fitted with green contact lenses exposed to room light exhibited antinociception arguing for a role of the visual system. Antinociception was not due to stress/anxiety but likely due to increased enkephalins expression in the spinal cord. Naloxone reversed the antinociception, suggesting involvement of central opioid circuits. Rostral ventromedial medulla inactivation prevented expression of light-induced antinociception suggesting engagement of descending inhibition. Green LED exposure also reversed thermal and mechanical hyperalgesia in rats with spinal nerve ligation. Pharmacological and proteomic profiling of dorsal root ganglion neurons from green LED-exposed rats identified changes in calcium channel activity, including a decrease in the N-type (CaV2.2) channel, a primary analgesic target. Thus, green LED therapy may represent a novel, nonpharmacological approach for managing pain.

Topics: Analgesics; Animals; Calcium Channels, N-Type; Chronic Pain; Color; Disease Models, Animal; Dose-Response Relationship, Radiation; Female; Ganglia, Spinal; Male; Medulla Oblongata; Naloxone; Narcotic Antagonists; Pain Threshold; Phototherapy; Physical Stimulation; Posterior Horn Cells; Rats; Rats, Long-Evans; Rats, Sprague-Dawley; Reaction Time

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a functional disorder of the gastrointestinal (GI) tract. The major IBS-D symptoms include diarrhea, abdominal pain and discomfort. High density of opioid receptors (ORs) in the GI tract and their participation in the maintenance of GI homeostasis make ORs ligands an attractive option for developing new anti-IBS-D treatments. The aim of this study was to characterize the effect of methyl-orvinol on the GI motility and secretion and in mouse models mimicking symptoms of IBS-D.. In vitro, the effects of methyl-orvinol on electrical field stimulated smooth muscle contractility and epithelial ion transport were characterized in the mouse colon. In vivo, the following tests were used to determine methyl-orvinol effect on mouse GI motility: colonic bead expulsion, whole GI transit and fecal pellet output. An antinociceptive action of methyl-orvinol was assessed in the mouse model of visceral pain induced by mustard oil.. Methyl-orvinol (10. Methyl-orvinol could become a promising drug candidate in chronic therapy of functional GI diseases such as IBS-D.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Abdominal Pain; Analgesics; Analgesics, Opioid; Animals; Colon; Diarrhea; Disease Models, Animal; Gastrointestinal Motility; Gastrointestinal Transit; Irritable Bowel Syndrome; Male; Mice; Mice, Inbred BALB C; Muscle Contraction; Muscle, Smooth; Naloxone; Naltrexone; Receptors, Opioid; Thebaine

Visceral pain has a greater emotional component than somatic pain. To determine if the stress-induced analgesic response is differentially expressed in visceral versus somatic pain states, we studied the effects of a mild social stressor in either acute visceral or somatic pain states in mice. We show that the presence of an unfamiliar conspecific mouse (stranger) in an adjacent cubicle of a standard transparent observation box produced elevated plasma corticosterone levels compared with mice tested alone, suggesting that the mere presence of a stranger is stressful. We then observed noxious visceral or somatic stimulation-induced nociceptive behavior in mice tested alone or in mildly stressful conditions (ie, beside an unfamiliar stranger). Compared with mice tested alone, the presence of a stranger produced a dramatic opioid-dependent reduction in pain behavior associated with visceral but not somatic pain. This social stress-induced reduction of visceral pain behavior relied on visual but not auditory/olfactory cues. These findings suggest that visceral pain states may provoke heightened responsiveness to mild stressors, an effect that could interfere with testing outcomes during simultaneous behavioral testing of multiple rodents.. In mice, mild social stress due to the presence of an unfamiliar conspecific mouse reduces pain behavior associated with noxious visceral but not somatic stimulation, suggesting that stress responsiveness may be enhanced in visceral pain versus somatic pain states.

Topics: Acetic Acid; Animals; Capsaicin; Corticosterone; Cues; Disease Models, Animal; Formaldehyde; Male; Mice; Naloxone; Narcotic Antagonists; Nociception; Pain; Receptors, Opioid; Recognition, Psychology; Social Behavior; Stress, Psychological; Visual Perception

Topics: Analgesics, Opioid; Animals; Anxiety; Behavior, Animal; Disease Models, Animal; Male; Naloxone; Narcotic Antagonists; Panic; Periaqueductal Gray; Piperazines; Pyridines; Rats; Rats, Wistar; Receptors, Opioid, mu; Serotonin 5-HT1 Receptor Antagonists; Serotonin and Noradrenaline Reuptake Inhibitors; Tramadol

The neuroprotective role of the endogenous opioid system in the pathophysiological sequelae of brain injury remains largely ambiguous. Noteworthy, almost no data is available on how its genetically determined activity influences the outcome of mild traumatic brain injury. Thus, the aim of our study was to examine the effect of opioid receptor blockage on cognitive impairments produced by mild traumatic brain injury in mice selectively bred for high (HA) and low (LA) swim-stress induced analgesia that show innate divergence in opioid system activity. Mild traumatic brain injury was induced with a weight-drop device on anaesthetized mice. Naloxone (5mg/kg) was intraperitoneally delivered twice a day for 7days to non-selectively block opioid receptors. Spatial memory performance and manifestations of depressive-like behavior were assessed using the Morris Water Maze and tail suspension tests, respectively. Mild traumatic brain injury resulted in a significant deterioration of spatial memory performance and severity of depressive-like behavior in the LA mouse line as opposed to HA mice. Opioid receptor blockage with naloxone unmasked cognitive deficits in HA mice but was without effect in the LA line. The results suggest a protective role of genetically predetermined enhanced opioid system activity in suppression of mild brain trauma-induced cognitive impairments. Mice selected for high and low swim stress-induced analgesia might therefore be a useful model to study the involvement of the opioid system in the pathophysiology and neurological outcome of traumatic brain injury.

Topics: Analgesia; Animals; Behavior, Animal; Brain Concussion; Depression; Disease Models, Animal; Male; Memory Disorders; Mice; Mice, Inbred Strains; Naloxone; Narcotic Antagonists; Neuroprotection; Receptors, Opioid; Spatial Memory; Up-Regulation

Topics: Analgesics; Animals; Bone Marrow Cells; Bone Neoplasms; Cancer Pain; Cell Differentiation; Cells, Cultured; Disease Models, Animal; Enkephalins; Female; Genetic Therapy; Genetic Vectors; Humans; Hyperalgesia; Injections, Spinal; Naloxone; Pain Threshold; Protein Precursors; Rats; Rats, Sprague-Dawley; Stem Cell Transplantation

Chronic pain affects the lives of millions yearly, but few new treatments are available. Due to decreasing budgets and increasing costs of preclinical research, alternatives are sought with high translatability and low cost. Here we demonstrate the utility of a zebrafish-based model of nociception to serve as a novel screening tool for analgesic drugs. Zebrafish swimming behavior was measured following administration of various algogens including histamine, cinnamaldehyde, mustard oil, acetic acid and complete Freund's adjuvant. All compounds reduce distance traveled, thought to be an expression of nociception. Additionally, the suppression of swimming was attenuated by administration of the common analgesic, morphine. Together these data provide support for the use of zebrafish as a cost-effective and translatable model of nociception.

Topics: Acetic Acid; Acrolein; Analgesics, Opioid; Animals; Antineoplastic Agents, Phytogenic; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Freund's Adjuvant; Histamine; Histamine Agonists; Male; Morphine; Mustard Plant; Naloxone; Narcotic Antagonists; Nociception; Pain; Plant Oils; Swimming; Zebrafish

Adolescence is a gradual period of transition from childhood to adulthood. It is considered as a sensitive developmental time point that long lasting changes occur in the brain. The present study examined adolescent chronic escalating morphine administration on morphine tolerance and dependence in adulthood. Adolescent male Wistar rats (30days old) were administered increasing doses of morphine (2.5 to 25mg/kg, s.c.) every 12h, for 10days. Control rats received saline according to the same protocol. Thereafter, during adulthood (65-75days old), tolerance to antinociceptive effect of morphine was induced by subcutaneous injection of 3mg/kg morphine, once a day for 7days. Morphine analgesia was measured in the animals by tail flick test every two days, 10min before and 30min after morphine administration. Also, in another test, adult rats were administered morphine (10mg/kg, s.c.) twice a day for 9days to become morphine dependent. On day 10, naloxone (2mg/kg, i.p.) was injected 2h after morphine administration. Somatic signs of morphine withdrawal were then recorded in a clear Plexiglas test chamber for 25min. Results showed that adolescent morphine treatment significantly facilitates the development of tolerance to the analgesic effect of morphine and increases morphine withdrawal signs (grooming, head tremor, sniffing, scratching and teeth chattering) in adulthood compared to the saline group. Facilitation of morphine tolerance and potentiation of withdrawal signs suggests that chronic escalating morphine treatment during adolescence causes long-lasting effects on development of morphine tolerance and dependence in adulthood.

Topics: Age Factors; Analgesics, Opioid; Analysis of Variance; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar; Substance Withdrawal Syndrome; Time Factors

To investigate the effect of Yiguanjian\ (YGJ) cataplasm on the development of opioid dependence\ in a mouse model of naloxone-induced\ opioid withdrawal syndrome.. One hundred Swiss albino mice, of\ equal male to female ratio, were randomly and\ equally divided into 10 groups. A portion (3 cm2) of\ the backside hair of the mice was removed 1 day\ prior to the experiment. Morphine (5 mg/kg) was\ intraperitoneally administered twice daily for 5\ days. YGJ cataplasm was prepared and pasted on\ the bare region of the mice immediately before\ morphine administration on day 3 and subsequently\ removed at the end day 5. On day 6, naloxone (8\ mg/kg) was intraperitoneally injected to precipitate\ opioid withdrawal syndrome. Behavioral observation\ was performed in two 30-min phases immediately\ after naloxone injection.. The YGJ cataplasm significantly and\ dose-dependently attenuated morphine-naloxone-\ induced experimental opioid withdrawal, in\ terms of withdrawal severity score and the frequencies\ of jumping, rearing, forepaw licking, and circling\ behaviors. However, YGJ cataplasm treatment\ did not alter the acute analgesic effect of morphine.. YGJ cataplasm could attenuate opioid\ dependence and its associated withdrawal\ symptoms. Therefore, YGJ cataplasm could serve as\ a potential therapy for opioid addiction in the future.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Drugs, Chinese Herbal; Female; Humans; Male; Mice; Motor Activity; Naloxone; Opioid-Related Disorders; Substance Withdrawal Syndrome

The enhancement of GABAergic and monoaminergic neurotransmission has been the mainstay of pharmacotherapy and the focus of drug-discovery for anxiety and depressive disorders for several decades. However, the significant limitations of drugs used for these disorders underscores the need for novel therapeutic targets. Neuronal nicotinic acetylcholine receptors (nAChRs) may represent one such target. For example, mecamylamine, a non-competitive antagonist of nAChRs, displays positive effects in preclinical tests for anxiolytic and antidepressant activity in rodents. In addition, nicotine elicits similar effects in rodent models, possibly by receptor desensitization. Previous studies (Xiao et al., 2001) have identified two metabolites of methadone, EMDP (2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline) and EDDP (2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine), which are considered to be inactive at opiate receptors, as relatively potent noncompetitive channel blockers of rat α3β4 nAChRs. Here, we show that these compounds are likewise highly effective blockers of human α3β4 and α4β2 nAChRs. Moreover, we show that they display relatively low affinity for opiate binding sites labeled by [(3)H]-naloxone. We then evaluated these compounds in rats and mice in preclinical behavioral models predictive of potential anxiolytic and antidepressant efficacy. We found that EMDP, but not EDDP, displayed robust effects predictive of anxiolytic and antidepressant efficacy without significant effects on locomotor activity. Moreover, EMDP at behaviorally active doses, unlike mecamylamine, did not produce eyelid ptosis, suggesting it may produce fewer autonomic side effects than mecamylamine. Thus, the methadone metabolite EMDP may represent a novel therapeutic avenue for the treatment of some affective disorders.

Topics: Animals; Anti-Anxiety Agents; Antidepressive Agents; Blepharoptosis; Disease Models, Animal; Dose-Response Relationship, Drug; Humans; Male; Maze Learning; Mice; Mice, Inbred C57BL; Motor Activity; Naloxone; Protein Binding; Pyrrolidines; Rats; Rats, Sprague-Dawley; Swimming; Time Factors; Tritium

This study was designed to examine the effect of environmental enrichment during morphine dependency and withdrawal on the severity of naloxone-precipitated withdrawal signs, anxiety, and depressive-like behaviors and voluntary morphine consumption in morphine-dependent rats. The rats were injected with bi-daily doses (10 mg/kg, 12 h intervals) of morphine for 14 days following rearing in a standard environment (SE) or enriched environment (EE) during the development of morphine dependence and withdrawal. Then, rats were tested for withdrawal signs after naloxone injection, anxiety (the elevated plus maze) and depression-related behavior (sucrose preference test), and voluntary consumption of morphine using a two-bottle choice paradigm, in morphine-dependent and morphine-withdrawn rats. The results showed that EE decreased naloxone-precipitated withdrawal signs, but not anxiety or sucrose preference during dependence on morphine. The EE-withdrawn rats showed an increase in the elevated plus maze open arm time and entries and higher levels of sucrose preference than SE rats. Voluntary consumption of morphine was lower in the EE-withdrawn rats than in the SE groups in the second period of drug intake. Thus, exposure to EE reduced the severity of morphine dependence and voluntary consumption of morphine, alongside reductions in anxiety and depression-related behavior in morphine-withdrawn rats.

Topics: Analysis of Variance; Animals; Anxiety; Choice Behavior; Disease Models, Animal; Environment; Food Preferences; Male; Maze Learning; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Wistar; Substance Withdrawal Syndrome

Opioid abuse and dependence have evolved into an international epidemic as a significant clinical and societal problem with devastating consequences. Repeated exposure to the opioid, for example morphine, can induce profound, long-lasting behavioral sensitization and physical dependence, which are thought to reflect neuroplasticity in neural circuitry. Central serotonin (5-HT) neurotransmission participates in the development of dependence on and the expression of withdrawal from morphine. Serotonin 5-HT(2C) receptor (5-HT(2C)R) agonists suppress psychostimulant nicotine or cocaine-induced behavioral sensitization and drug-seeking behavior; however, the impact of 5-HT(2C)R agonists on behaviors relevant to opioid abuse and dependence has not been reported. In the present study, the effects of 5-HT(2C)R activation on the behavioral sensitization and naloxone-precipitated withdrawal symptoms were examined in mice underwent repeated exposure to morphine. Male mice received morphine (10 mg/kg, s.c.) to develop behavioral sensitization. Lorcaserin, a 5-HT(2C)R agonist, prevented the induction and expression, but not the development, of morphine-induced behavioral sensitization. Another cohort of mice received increasing doses of morphine over a 7-day period to induce morphine-dependence. Pretreatment of lorcaserin, or the positive control clonidine (an alpha 2-adrenoceptor agonist), ameliorated the naloxone-precipitated withdrawal symptoms. SB 242084, a selective 5-HT(2C)R antagonist, prevented the lorcaserin-mediated suppression of behavioral sensitization and withdrawal. Chronic morphine treatment was associated with an increase in the expression of 5-HT(2C)R protein in the ventral tegmental area, locus coeruleus and nucleus accumbens. These findings suggest that 5-HT(2C)R can modulate behavioral sensitization and withdrawal in morphine-dependent mice, and the activation of 5-HT(2C)R may represent a new avenue for the treatment of opioid addiction.

Topics: Aminopyridines; Analgesics, Opioid; Animals; Benzazepines; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Indoles; Locomotion; Male; Mice; Mice, Inbred Strains; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Reaction Time; Receptor, Serotonin, 5-HT2C; Serotonin Antagonists; Substance Withdrawal Syndrome; Time Factors

Both CB1 receptor antagonism and agonism, in particular by 2-arachidonyl glycerol (2-AG), have been shown to reduce somatic symptoms of morphine withdrawal (MWD). Here we evaluated the effects of both systemic pretreatment with the monoacylglycerol lipase (MAGL) inhibitor MJN110 (which selectively elevates 2-AG) and central administration of both MJN110 and the CB1 antagonist (AM251) on the affective properties of MWD. Acute MWD induced place aversion occurs when naloxone is administered 24 h following a single exposure to a high dose of morphine. Systemic pretreatment with the MAGL inhibitor, MJN110, prevented the aversive effects of acute MWD by a CB1 receptor-dependent mechanism. Furthermore, in a double dissociation, AM251 infusions into the central amygdala, but MJN110 infusions into the basolateral amygdala, interfered with the naloxone-precipitated MWD induced place aversion. As well, MJN110, but not AM251, infusions into the interoceptive insular cortex (a region known to be activated in acute MWD) also prevented the establishment of the place aversion by a CB1 mechanism of action. These findings reveal the respective sites of action of systemically administered MJN110 and AM251 in regulating the aversive effects of MWD.

Topics: Amygdala; Analysis of Variance; Animals; Arachidonic Acids; Cannabinoid Receptor Agonists; Carbamates; Cerebral Cortex; Conditioning, Operant; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Endocannabinoids; Glycerides; Male; Monoacylglycerol Lipases; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Succinimides

The goal of the present research was to assess the degree to which a pattern completion process operates in cue-induced relapse to cocaine-seeking behavior. Using a novel cue-preference version of the place preference task, rats were administered cocaine or saline, which resulted in a preference for the cocaine-paired cues. After 21 days of abstinence and prior to the preference test, for one group, PBS or naloxone was injected into the CA3 subregion of the hippocampus and for a second group, saline or naloxone was injected systemically. The results indicated that infusions of naloxone into CA3 or systemic injections produced a marked disruption for one and two cues, but had minimal disruptive effect for three or four cues, suggesting that naloxone injections disrupt CA3 function and trigger a deficit in a pattern completion process. Thus, it appears that cue-based activation of the dorsal CA3 might be a critical trigger via a pattern completion process. Based on additional analyses it appears that there is a disruption primarily for object touches for one cue naloxone injections into the CA3 or systemic injections, but no effect on time (spatial context). © 2016 Wiley Periodicals, Inc.

Topics: Animals; CA3 Region, Hippocampal; Central Nervous System Agents; Cocaine; Cocaine-Related Disorders; Conditioning, Operant; Cues; Disease Models, Animal; Dopamine Uptake Inhibitors; Drug-Seeking Behavior; Male; Naloxone; Rats, Long-Evans; Recurrence; Spatial Behavior

It is claimed that a correlation exists between disturbance of circadian rhythms by factors such as alteration of normal light-dark cycle and the development of addiction. However, the exact mechanisms involved in this relationship are not much understood. Here we have studied the effect of constant light on morphine voluntary consumption and withdrawal symptoms and also investigated the involvement of Per1, Per2 and dopamine D1 receptor in these processes. Male wistar rats were kept under standard (LD) or constant light (LL) conditions for one month. The plasma concentration of melatonin was evaluated by enzyme-linked immunosorbent assay (ELISA). Real-time PCR was used to determine the mRNA expression of Per1, Per2 and dopamine D1 receptor in the striatum and prefrontal cortex. Morphine preference (50mg/L) was evaluated in a two-bottle-choice paradigm for 10 weeks and withdrawal symptoms were recorded after administration of naloxone (3mg/kg). One month exposure to constant light resulted in a significant decrease of melatonin concentration in the LL group. In addition, mRNA levels of Per2 and dopamine D1 receptor were up-regulated in both the striatum and prefrontal cortex of the LL group. However, expression of Per1 gene was only up-regulated in the striatum of LL rats in comparison to LD animals. Furthermore, after one month exposure to constant light, morphine consumption and preference ratio and also severity of naloxone-induced withdrawal syndrome were significantly greater in LL animals. It is concluded that exposure to constant light by up-regulation of Per2 and dopamine D1 receptor in the striatum and prefrontal cortex and up-regulation of Per1 in the striatum and the possible involvement of melatonin makes animals vulnerable to morphine preference and addiction.

Topics: Animals; Circadian Rhythm; Corpus Striatum; Disease Models, Animal; Male; Melatonin; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Period Circadian Proteins; Photic Stimulation; Prefrontal Cortex; Rats, Wistar; Receptors, Dopamine D1; RNA, Messenger; Substance Withdrawal Syndrome

This study aimed to investigate the involvement of opioid receptors in the systemic and peripheral antinociceptive activities of montelukast in different animal models of pain. Rats and mice were injected with montelukast to produce analgesia. The formalin and acetic acid-induced writhing tests were used to assess the nociceptive activity. The results showed that i.p. administration of montelukast (0.3-10mg/kg) dose-dependently reduced flinching behavior in both the first and second phases of formalin test with mean ED50 of 0.55 and 5.31mg/kg, respectively. Also, intraplantar administration of montelukast (3-30μg/paw) produced antinociception against the two phases of formalin assay in a dose-dependent way with mean ED30 of 2.92 and 8.11μg/paw, respectively. Furthermore, pre-treatment with naloxone (a non-selective opioid receptor antagonist) significantly inhibited both the systemic and also peripheral antinociceptive actions of montelukast in formalin test. In writhing test, the results showed that intraperitoneal administration of montelukast (3-10mg/kg) significantly reduced the writhe number induced by acetic acid in mice. Moreover, co-administration of non-effective doses of montelukast (0.3 and 1mg/kg; i.p.) and morphine (0.25mg/kg; i.p.) significantly decreased the writhes number induced by acetic acid. Also, this effect was naloxone-reversible. These findings suggest that the systemic and peripheral antinociception produced by montelukast were mediated through the opioid receptors in central and peripheral nervous systems. Moreover, combination of montelukast and morphine could be noted as a new strategy for pain relief.

Topics: Acetates; Acetic Acid; Analgesics; Animals; Behavior, Animal; Cyclopropanes; Disease Models, Animal; Drug Synergism; Formaldehyde; Male; Mice; Naloxone; Pain; Quinolines; Rats; Receptors, Opioid; Sulfides; Visceral Pain

Emerging literature points to stress exposure as a potential contributor to the development of alcohol abuse, but animal models have yielded inconsistent results. Converging experimental data indicate that the endogenous opioid system modulates alcohol consumption and stress regulation. The aim of the present study is to examine the interplay between stress exposure, behavioral stress responses, ethanol (EtOH) consumption and the endogenous opioid system in an animal model of posttraumatic stress disorder. Rats were exposed to stress and then tested in a two-bottle free choice (TBC) assay or in a conditioned place preference paradigm. In some experiments, the endogenous opioid system was pharmacologically manipulated prior to stress exposure. The behavioral outcomes of stress exposure were assessed in an elevated plus-maze, with the acoustic startle response, and by monitoring the freezing response to trauma reminder. Immunoreactivity of phosphorylated opioid receptors in hippocampal subregions was also measured. Stress significantly increased the consumption of EtOH in the TBC assay. The severity of the behavioral response to stress was associated with EtOH consumption, cue-triggered freezing response to a trauma reminder, and endogenous levels of phosphorylated opioid receptors in the hippocampus. Pharmacologically manipulating the endogenous opioid system prior to stress exposure attenuated trauma cue-triggered freezing responses and blocked predator scent stress-induced potentiation of EtOH consumption. These data demonstrate a stress-induced potentiation of EtOH self-administration and reveal a clear association between individual patterns of the behavioral response to stress and alcohol preference, while indicating a role for the endogenous opioid system in the neurobiological response to stress.

Topics: Analgesics, Opioid; Animals; Brain; Choice Behavior; Conditioning, Operant; Disease Models, Animal; Ethanol; Freezing Reaction, Cataleptic; Male; Maze Learning; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Stress Disorders, Post-Traumatic; Stress, Psychological

A negative emotional state resulting from the withdrawal of drug addiction is thought to be an important factor that triggers and exacerbates relapse. Since the insular cortex is a key brain structure involved in the modulation of negative emotions, we investigated whether the integrity of the insular cortex was important for motivational aversion associated with morphine withdrawal as well as whether this kind of negative emotion induced neuroadaptation in the insular cortex. In this present study, a sensitive mouse conditioned place aversion (CPA) model measuring the motivational aversion of morphine withdrawal was first established. Our results showed that bilateral insular cortex lesions by kainic acid completely inhibited the expression of CPA. The expression of FosB/deltaFosB in the insular cortex was significantly increased 24 h after the CPA regime was performed, but the expression of c-Fos in the insular cortex did not changed. These findings indicate that the integrity of the insular cortex is essential to motivational aversion associated with morphine withdrawal, and that this kind of aversion induces neuroadaptation, observed as the increase of FosB/deltaFosB expression, in the insular cortex.

Topics: Animals; Cerebral Cortex; Disease Models, Animal; Kainic Acid; Male; Mental Disorders; Mice; Morphine; Naloxone; Narcotics; Proto-Oncogene Proteins c-fos; Random Allocation; Substance Withdrawal Syndrome

The aim of this study was to assess the effects of naloxone, an opioid receptor antagonist, on the renal injury as a remote organ after hepatic ischemia reperfusion (IR) in rats.. Forty male Wistar rats were randomly allocated into four groups as follows: sham, sham + naloxone, IR and IR + naloxone. In anesthetized rats, hepatic ischemia was applied for 30 min in IR and IR + naloxone groups. Sham + naloxone and IR + naloxone groups were given naloxone (3.0 mg/kg, iv) 30 min before ischemia. After 24 h, blood and tissue samples were obtained for histopathological, tissue malondialdehyde (MDA) and biochemical analyses.. Histopathological study of liver in IR group showed enlarged sinusoids, sinusoidal congestion, cellular degenerative changes and necrosis. The kidney of the rats with hepatic IR showed pathological changes in tubular cell swelling, tubular dilatation, moderate to severe necrosis, glomerular fibrosis and hemorrhage. Histological examination confirmed the extent of hepatic and renal changes in IR group was higher (P < 0.05) than in other groups. Rats that underwent hepatic IR exhibited significant increase in serum concentrations of urea and creatinine levels (P < 0.05). The serum alanine aminotransferase and aminotransferase values were significantly higher in IR group compared to the other groups (P < 0.05). Liver IR produced a significant increase in hepatic and renal tissue MDA levels, while pretreatment with naloxone was associated with a significantly lower MDA levels (P < 0.05).. The results of this study showed that naloxone pretreatment protected the renal injury from hepatic IR.

Topics: Acute Kidney Injury; Animals; Biopsy, Needle; Disease Models, Animal; Immunohistochemistry; Ischemic Preconditioning; Liver; Male; Naloxone; Random Allocation; Rats; Rats, Wistar; Reperfusion Injury; Sensitivity and Specificity

The search for new drugs for cancer pain management has been a long-standing goal in basic and clinical research. Classical opioid drugs exert their primary antinociceptive effect upon activating opioid receptors located in the central nervous system. A substantial body of evidence points to the relevance of peripheral opioid receptors as potential targets for cancer pain treatment. Peptides showing limited blood-brain-barrier permeability promote peripheral analgesia in many pain models. In the present study we examined the peripheral and central analgesic effect of intravenously administered biphalin - a dimeric opioid peptide in a mouse skin cancer pain model, developed by an intraplantar inoculation of B16F0 melanoma cells. The effect of biphalin was compared with morphine - a golden standard in cancer pain management. Biphalin produced profound, dose-dependent and naloxone sensitive spinal analgesia. Additionally, the effect in the tumor-bearing paw was largely mediated by peripheral opioid receptors, as it was readily attenuated by the blood-brain-barrier-restricted opioid receptor antagonist - naloxone methiodide. On the contrary, morphine facilitated its analgesic effect primarily by activating spinal opioid receptors. Both drugs induced tolerance in B16F0 - implanted paws after chronic treatment, however biphalin as opposed to morphine, showed little decrease in its activity at the spinal level. Our results indicate that biphalin may be considered a future alternative drug in cancer pain treatment due to an enhanced local analgesic activity as well as lower tolerance liability compared with morphine.

Topics: Analgesia; Analgesics, Opioid; Animals; Blood-Brain Barrier; Cancer Pain; Cell Line, Tumor; Disease Models, Animal; Drug Tolerance; Enkephalins; Male; Melanoma, Experimental; Mice; Mice, Inbred C57BL; Morphine; Naloxone; Opioid Peptides; Permeability; Quaternary Ammonium Compounds; Receptors, Opioid; Skin Neoplasms

The anti-hyperalgesic effect of the complex containing α-terpineol (αTPN) and β-cyclodextrin (βCD) was analyzed in a non-inflammatory chronic muscle pain model, as well as its mechanism of action through docking study for a possible interaction with receptors. The αTPN-βCD complex was prepared and characterized through the thermogravimetry/derivate thermogravimetry (TG/DTG), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The model of chronic muscle pain was induced by two injections of pH 4.0 saline (20 μl) into the left gastrocnemius 5 days apart. After confirming hyperalgesia, male mice were treated with αTPN-βCD (25, 50 or 100 mg/kg; p.o.) or vehicle (saline 0.9%, p.o.) daily for 10 days. 1 h after the mechanical hyperalgesia, motor performance was evaluated. In addition, the systemic administration of naloxone and ondansetron tested the analgesic effect on the active opioid and serotonin receptors, respectively. The characterization tests indicated that αTPN was efficiently incorporated into βCD. The oral treatment with αTPN-βCD, at all doses tested, produced a significant (p < 0.001) decrease in the mechanical hyperalgesia, without causing any alteration in the force and in motor performance. This analgesic effect was reversed by the systemic administration of naloxone or ondansetron. These findings are corroborated by the docking study described in the present study, which verified a possible interaction of αTPN-βCD with opioid (MU, Kappa, Delta) and 5-HT receptors. Thus, it can be concluded that αTPN-βCD reduced the hyperalgesia followed by the chronic muscle pain model, probably evoked by the descending inhibitory pain system, specifically by opioid and serotoninergic receptors.

Topics: Analgesics; Animals; Behavior, Animal; beta-Cyclodextrins; Binding Sites; Cyclohexane Monoterpenes; Cyclohexenes; Disease Models, Animal; Fibromyalgia; Hyperalgesia; Male; Mice; Molecular Docking Simulation; Monoterpenes; Naloxone; Ondansetron; Protein Structure, Tertiary; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

Dehydrocorydaline (DHC) is an alkaloidal component isolated from Rhizoma corydalis. Previous studies have shown that DHC has anti-inflammatory and anti-tumor effects and that it can protect the cardiovascular system. However, there are few studies of the antinociceptive effects of DHC in vivo. This study explored the antinociceptive effects and possible mechanisms of DHC in mice using two inflammatory pain models: the acetic acid-induced writhing test and the formalin paw test. The intraperitoneal administration of DHC (3.6, 6 or 10 mg/kg) showed a dose-dependent antinociceptive effect in the acetic acid-induced writhing test and significantly attenuated the formalin-induced pain responses in mice. The antinociceptive effects of DHC were not associated with changes in the locomotor activity or motor responses of animals, and no obvious acute or chronic toxic effects were observed in the mice. Furthermore, the use of naloxone confirmed the involvement of the opioid receptor in the central antinociceptive effects of DHC. DHC reduced formalin-induced paw edema, which indicated that DHC may produce an anti-inflammatory effect in the periphery. In the formalin test, DHC decreased the expression of caspase 6 (CASP6), TNF-α, IL-1β and IL-6 proteins in the spinal cord. These findings confirm that DHC has antinociceptive effects in mice.

Topics: Acetates; Alkaloids; Analgesics; Animals; Anti-Inflammatory Agents; Cytokines; Disease Models, Animal; Dose-Response Relationship, Drug; Formaldehyde; Gene Expression Regulation; Humans; Injections, Intraperitoneal; Mice; Naloxone; Pain; Receptors, Opioid

To define likely targets (i.e. glia) and protocols (analgesic combinations) to improve postoperative pain outcomes and reduce chronic pain after surgery. Specifically, to assess the antihyperalgesic effects of the dexketoprofen : tramadol (DEX : TRM) combination, exploring the implication of glial activation.. In a mouse model of postincisional pain, we evaluated mechanical nociceptive thresholds (Von Frey) for 21 days postoperatively. We assessed DEX and TRM alone and combined (1 : 1 ratio) on postoperative hyperalgesia (POH, day 1) and delayed latent pain sensitisation (substantiated by a naloxone challenge; PS, day 21). The interactions were analysed using isobolograms, and concomitant changes in spinal glial cell activation were measured.. On day 1, DEX completely blocked POH, whereas TRM induced 32% inhibition. TRM, but not DEX, partially (47%) protected against PS, at 21 days. Co-administration of DEX : TRM (1 : 1 ratio) showed additivity for antihyperalgesia. Both drugs and their combination totally inhibited surgery-induced microglia activation on day 1, but had no effect on surgery-induced astrocyte activation (1 day) or re-activation after naloxone (21 days).. The DEX : TRM combination could have clinical advantages: a complete prevention of POH after surgery, together with a substantial (48%) inhibition of the development of PS by TRM. Microglia, but not astrocyte activation, could play a relevant role in the development of postoperative pain hypersensitivity.

Topics: Analgesics; Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Disease Models, Animal; Drug Combinations; Hyperalgesia; Ketoprofen; Male; Mice; Naloxone; Neuroglia; Pain Threshold; Pain, Postoperative; Tramadol

Individuals with Alzheimer's disease (AD) are in susceptible patient groups in which pain is an important clinical issue that is often underdiagnosed. However, it is unclear whether decreased pain complaints in patients with AD result from elevated pain tolerance or an impaired ability to communicate sensations. Here, we explored if AD-related pathology is present in key regions of the pain pathway and assessed whether nociceptive thresholds to acute noxious stimulation are altered in the double-mutant APPswe × PS1.M146V (TASTPM) transgenic mouse model of AD. TASTPM mice exhibited an age-dependant cognitive deficit at the age of 6 months, but not at 4 months, a deficit that was accompanied by amyloid plaques in the cortex, hippocampus, and thalamus. In the spinal cord, β-amyloid (APP/Aβ) immunoreactivity was observed in dorsal and ventral horn neurons, and the expression of vesicular glutamate transporter 2 (VGLUT2) was significantly reduced, while the expression of the inhibitory peptides enkephalins was increased in TASTPM dorsal horn, consistent with an increased inhibitory tone. TASTPM mice displayed reduced sensitivity to acute noxious heat, which was reversed by naloxone, an opioid antagonist. This study suggests that increased inhibition and decreased excitation in the spinal cord may be responsible for the reduced thermal sensitivity associated with AD-related pathology.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Analgesics, Opioid; Animals; Brain; Carrageenan; Cognition Disorders; Disease Models, Animal; Locomotion; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Pain; Pain Measurement; Presenilin-1; Recognition, Psychology; Sensory Thresholds

Bone marrow stromal cells (BMSCs) have shown potential to treat chronic pain, although much still needs to be learned about their efficacy and mechanisms of action under different pain conditions. Here, we provide further convergent evidence on the effects of BMSCs in rodent pain models.. In an orofacial pain model involving injury of a tendon of the masseter muscle, BMSCs attenuated behavioral pain conditions assessed by von Frey filaments and a conditioned place avoidance test in female Sprague-Dawley rats. The antihyperalgesia of BMSCs in females lasted for <8 weeks, which is shorter than that seen in males. To relate preclinical findings to human clinical conditions, we used human BMSCs. Human BMSCs (1.5 M cells, i.v.) attenuated mechanical and thermal hyperalgesia induced by spinal nerve ligation and suppressed spinal nerve ligation-induced aversive behavior, and the effect persisted through the 8-week observation period. In a trigeminal slice preparation, BMSC-treated and nerve-injured C57B/L mice showed reduced amplitude and frequency of spontaneous excitatory postsynaptic currents, as well as excitatory synaptic currents evoked by electrical stimulation of the trigeminal nerve root, suggesting inhibition of trigeminal neuronal hyperexcitability and primary afferent input by BMSCs. Finally, we observed that GluN2A (N-methyl-D-aspartate receptor subunit 2A) tyrosine phosphorylation and protein kinase Cgamma (PKCg) immunoreactivity in rostral ventromedial medulla was suppressed at 8 weeks after BMSC in tendon-injured rats.. Collectively, the present work adds convergent evidence supporting the use of BMSCs in pain control. As PKCg activity related to N-methyl-D-aspartate receptor activation is critical in opioid tolerance, these results help to understand the mechanisms of BMSC-produced long-term antihyperalgesia, which requires opioid receptors in rostral ventromedial medulla and apparently lacks the development of tolerance.

Topics: Animals; Behavior, Animal; Brain; Disease Models, Animal; Excitatory Postsynaptic Potentials; Female; Humans; Male; Mesenchymal Stem Cell Transplantation; Mesenchymal Stem Cells; Mice, Inbred C57BL; Naloxone; Neuralgia; Phosphorylation; Protein Kinase C; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Synapses; Tendons; Trigeminal Nerve

Liver disease has been known for a long time to affect brain function. We now report the function of opioidergic and dopaminergic antagonists on both spatial and object novelty detection deficits induced by hepatic encephalopathy (HE) following bile duct ligation (BDL), a model of chronic liver disease. Assessment of spatial and object novelty detection memories was carried out in the non-associative task. It consists of placing mice in an open field containing five objects and, after three sessions of habituation, examining their reactivity to object displacement (spatial novelty) and object substitution (object novelty). Both spatial and object novelty detection memories were impaired by BDL after 4 weeks. In the BDL mice, pre-test intraperitoneal administration of naloxone (μ-opioidergic receptor antagonist) at dose of 0.9mg/kg restored while sulpiride (D2-like dopamine receptor antagonist) at dose of 40mg/kg potentiated object novelty detection memory deficit. However, SCH23390 (D1-like dopamine receptor antagonist) at dose of 0.04mg/kg or sulpiride (20mg/kg) restored spatial novelty detection memory deficit. Moreover, SCH23390 or sulpiride impaired while naloxone did not alter both memories in sham-operated mice. Furthermore, subthreshold dose co-administration of dopaminergic antagonists together or each one plus naloxone did not alter both memory impairments in BDL mice, while all of three co-administration groups impaired object novelty detection and co-administration of naloxone plus sulpiride impaired spatial detection memory in sham-operated mice. In conclusion, we suggest that opioidergic and dopaminergic systems through separate pathways may contribute in memory impairments induced by BDL in the non-associative task.

Topics: Animals; Benzazepines; Disease Models, Animal; Dopamine Antagonists; Exploratory Behavior; Hepatic Encephalopathy; Locomotion; Male; Memory; Mice; Naloxone; Narcotic Antagonists; Receptors, Dopamine; Receptors, Opioid; Space Perception; Sulpiride

Vitex megapotamica (Spreng) Moldenke has been used in South American folk medicine to treat inflammatory diseases. However, the effects of V. megapotamica on animal models of nociception and depression have not been evaluated.. This study investigated whether the crude leaf extract of V. megapotamica exhibits antinociceptive and antidepressant-like effects in a Freund's adjuvant-induced chronic inflammation and depression model.. Chronic inflammation was induced in rats by the intraplantar administration of complete Freund's adjuvant (CFA; 100μl). The effect of oral crude extract of V. megapotamica (VmE; 3-30mg/kg, p.o.) on nociception (thermal hyperalgesia, mechanical allodynia and arthritis score), inflammation (edema, myeloperoxidase activity), immobility (forced swimming test), locomotor activity (open field), gastrointestinal transit, hyperalgesia and naloxone-precipitated morphine withdrawal syndrome was evaluated. Naloxone (0.4mg/kg, i.p.) was used to investigate the involvement of opioid system in the currently described effects of VmE.. Crude extract caused antinociceptive/antidepressant-like effects in the CFA-induced chronic inflammation model, which was prevented by naloxone. The VmE extract (10mg/kg, p.o.) did not alter the locomotor activity, gastrointestinal function and inflammatory parameters and did not cause hyperalgesia.. V. megapotamica induces opioid-dependent antinociception and antidepressant-like effect, without anti-inflammatory activity. The results support the use of VmE as analgesic and antidepressant.

Topics: Administration, Oral; Analgesics; Animals; Antidepressive Agents; Behavior, Animal; Depression; Disease Models, Animal; Freund's Adjuvant; Hyperalgesia; Inflammation; Male; Motor Activity; Naloxone; Narcotic Antagonists; Nociception; Pain Threshold; Phytotherapy; Plant Extracts; Plant Leaves; Plants, Medicinal; Rats, Wistar; Reaction Time; Swimming; Time Factors; Vitex

Topics: Analgesics; Animals; Bicuculline; Botulinum Toxins, Type A; Calcitonin Gene-Related Peptide; Capsaicin; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Functional Laterality; Hyperalgesia; Male; Naloxone; Pain; Pain Measurement; Rats; Rats, Wistar; Spinal Cord; Synaptosomal-Associated Protein 25

Dopamine (DA) is thought to represent a teaching signal and has been implicated in the induction of addictive behaviours. Previously, it has been proposed that the transcription factors Nurr1 and Pitx3, which are critical for transcription of a set of genes involved in DA metabolism in the mesolimbic pathway, are associated with addiction pathology. The aim of our study was to investigate abnormalities in the mesolimbic pathway associated with morphine dependence and withdrawal. Using quantitative real-time PCR, immunofluorescence, HPLC and Western blotting, here we studied the effects of single morphine administration, morphine dependence and morphine withdrawal on Nurr1 and Pitx3 expression as well as on the DA marker tyrosine hydroxylase (TH) and the turnover of DA in the ventral tegmental area (VTA) and/or nucleus accumbens. We showed that the three experimental conditions caused induction of Nurr1 and Pitx3 in the VTA, which correlated with changes in TH expression during chronic morphine administration. Present data also confirmed the colocalization of Nurr1 and Pitx3 with TH-positive neurons in the posterior VTA. Furthermore, during morphine dependence, Nurr1 was detected in the nucleus compartment of VTA TH-positive neurons, whereas Pitx3 was strongly detected in the nucleus of TH-positive neurons after single morphine administration and during morphine withdrawal. The number of TH neurons, number of Nurr1 or Pitx3-positive cells, and the number of TH neurons expressing Nurr1 or Pitx3 were not modified in the subpopulations of DA neurons. Present data provide novel insight into the potential correlation between Nurr1 and Pitx3 and DA neurons plasticity during opiate addiction in the mesolimbic pathway.

Topics: 3,4-Dihydroxyphenylacetic Acid; Analysis of Variance; Animals; Disease Models, Animal; Dopamine; Gene Expression Regulation; Homeodomain Proteins; Imaging, Three-Dimensional; Male; Microscopy, Confocal; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Nuclear Receptor Subfamily 4, Group A, Member 2; Rats; Rats, Wistar; RNA, Messenger; Transcription Factors; Tyrosine 3-Monooxygenase; Ventral Tegmental Area

Water immersion is widely used in physiotherapy and might relieve pain, probably by activating several distinct somatosensory modalities, including tactile, pressure, and thermal sensations. However, the endogenous mechanisms behind this effect remain poorly understood. This study examined whether warm water immersion therapy (WWIT) produces an antiallodynic effect in a model of localized inflammation and whether peripheral opioid, cannabinoid, and adenosine receptors are involved in this effect. Mice were injected with complete Freund's adjuvant (CFA; intraplantar; i.pl.). The withdrawal frequency to mechanical stimuli (von Frey test) was used to determine 1) the effect of WWIT against CFA-induced allodynia and 2) the effect of i.pl. preadministration of naloxone (a nonselective opioid receptor antagonist; 5 µg/paw), caffeine (a nonselective adenosine receptor antagonist; 150 nmol/paw), 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; a selective adenosine A1 receptor antagonist; 10 nmol/paw), and AM630 (a selective cannabinoid receptor type 2 antagonist; 4 µg/paw) on the antiallodynic effect of WWIT against CFA-induced allodynia. Moreover, the influence of WWIT on paw inflammatory edema was measured with a digital micrometer. WWIT produced a significant time-dependent reduction of paw inflammatory allodynia but did not influence paw edema induced by CFA. Naloxone, caffeine, DPCPX, and AM630 injected in the right, but not in the left, hind paw significantly reversed the antiallodynic effect of WWIT. This is the first study to demonstrate the involvement of peripheral receptors in the antiallodynic effect of WWIT in a murine model of persistent inflammatory pain.

Topics: Adenosine; Animals; Benzoxazines; Disease Models, Animal; Edema; Freund's Adjuvant; Hyperalgesia; Immersion; Indoles; Inflammation; Male; Mice; Morpholines; Naloxone; Naphthalenes; Narcotic Antagonists; Neurobiology; Pain Measurement; Receptor, Adenosine A1; Receptor, Cannabinoid, CB2; Receptors, Opioid; Water Purification

We examined antinociception and gene expression of mu-opioid receptor 1 (MOR1) in some brain areas of cholestatic rats, 21 days after common bile duct ligation (BDL). Cholestasis was induced in male Wistar rats during laparotomy and common BDL. Pain behavior was assessed on days 7, 14 or 21 of BDL using a hotplate test in control, sham and cholestatic groups. On day 21 of BDL, other groups of rats were sacrificed, whole brains were extracted, and the hypothalamus, prefrontal cortex (PFC), hippocampus and striatum in control, sham and cholestatic rats were dissected. We used a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method for evaluating MOR1 gene expression. The results revealed that cholestatic rats showed significant antinociception on days 14 and 21 of ligation with the most significant effect on day 21, which was prevented by naloxone (1 mg/kg). On the other hand, the expression of MOR1 gene compared to the sham group was decreased by 42% in the hypothalamus, 41% in the PFC, and 67% in the hippocampus after 21 days of BDL, while no significant change in its expression in the striatum was observed. It can be concluded that a change in endogenous opioid levels and its subsequent influence on the gene expression of MOR in some areas of the rat brain may underlie the altered nociception and other possible pathological changes such as pruritus after induction of cholestasis.

Topics: Analysis of Variance; Animals; Bile Duct Diseases; Brain; Disease Models, Animal; Gene Expression Regulation; Laparotomy; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Rats; Rats, Wistar; Receptors, Opioid, mu; RNA, Messenger; Time Factors

This study examined the role of β-adrenergic and opioid receptors in spinal reflex bladder activity and in the inhibition induced by pudendal nerve stimulation (PNS) or tibial nerve stimulation (TNS). Spinal reflex bladder contractions were induced by intravesical infusion of 0.25% acetic acid in α-chloralose-anesthetized cats after an acute spinal cord transection (SCT) at the thoracic T9/T10 level. PNS or TNS at 5 Hz was applied to inhibit these spinal reflex contractions at 2 and 4 times the threshold intensity (T) for inducing anal or toe twitch, respectively. During a cystrometrogram (CMG), PNS at 2T and 4T significantly (P < 0.05) increased bladder capacity from 58.0 ± 4.7% to 85.8 ± 10.3% and 96.5 ± 10.7%, respectively, of saline control capacity, while TNS failed to inhibit spinal reflex bladder contractions. After administering propranolol (3 mg/kg iv, a β₁/β₂-adrenergic receptor antagonist), the effects of 2T and 4T PNS on bladder capacity were significantly (P < 0.05) reduced to 64.5 ± 9.5% and 64.7 ± 7.3%, respectively, of the saline control capacity. However, the residual PNS inhibition (about 10% increase in capacity) was still statistically significant (P < 0.05). Propranolol treatment also significantly (P = 0.0019) increased the amplitude of bladder contractions but did not change the control bladder capacity. Naloxone (1 mg/kg iv, an opioid receptor antagonist) had no effect on either spinal reflex bladder contractions or PNS inhibition. At the end of experiments, hexamethonium (10 mg/kg iv, a ganglionic blocker) significantly (P < 0.05) reduced the amplitude of the reflex bladder contractions. This study indicates an important role of β₁/β₂-adrenergic receptors in pudendal inhibition and spinal reflex bladder activity.

Topics: Acetic Acid; Adrenergic beta-Antagonists; Animals; Cats; Disease Models, Animal; Electric Stimulation; Female; Male; Muscle Contraction; Naloxone; Narcotic Antagonists; Nerve Fibers, Unmyelinated; Neural Inhibition; Propranolol; Pudendal Nerve; Reflex; Spinal Cord Injuries; Spinal Nerves; Tibial Nerve; Urinary Bladder; Urodynamics

Chronic pain is a global burden that promotes disability and unnecessary suffering. To date, efficacious treatment of chronic pain has not been achieved. Thus, new therapeutic targets are needed. Here, we demonstrate that increasing endogenous adenosine levels through selective adenosine kinase inhibition produces powerful analgesic effects in rodent models of experimental neuropathic pain through the A3 adenosine receptor (A3AR, now known as ADORA3) signalling pathway. Similar results were obtained by the administration of a novel and highly selective A3AR agonist. These effects were prevented by blockade of spinal and supraspinal A3AR, lost in A3AR knock-out mice, and independent of opioid and endocannabinoid mechanisms. A3AR activation also relieved non-evoked spontaneous pain behaviours without promoting analgesic tolerance or inherent reward. Further examination revealed that A3AR activation reduced spinal cord pain processing by decreasing the excitability of spinal wide dynamic range neurons and producing supraspinal inhibition of spinal nociception through activation of serotonergic and noradrenergic bulbospinal circuits. Critically, engaging the A3AR mechanism did not alter nociceptive thresholds in non-neuropathy animals and therefore produced selective alleviation of persistent neuropathic pain states. These studies reveal A3AR activation by adenosine as an endogenous anti-nociceptive pathway and support the development of A3AR agonists as novel therapeutics to treat chronic pain.

Topics: Adenosine; Animals; Disease Models, Animal; Gene Expression Regulation; Hyperalgesia; Male; Medulla Oblongata; Mice; Mice, Inbred C57BL; Mice, Transgenic; Morpholines; Naloxone; Neuralgia; Neurons; Pain Measurement; Pain Threshold; Purinergic P1 Receptor Antagonists; Pyridines; Pyrimidines; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A3; Spinal Cord; Time Factors

The aim of the present study was to investigate the role of the amygdala in the potentiative effect of minocycline, a semisynthetic tetracycline antibiotic, on morphine analgesia in male Wistar rats. We also examined the involvement of the amygdala μ-opioid and N-methyl-D-aspartate (NMDA) receptors in the minocycline-induced potentiation of morphine analgesia. Intraperitoneal administration of morphine (3-9 mg/kg) induced analgesia in a tail-flick test. Bilateral intra-amygdala injection of minocycline (10-20 μg/rat) enhanced the analgesic response of an ineffective dose of morphine (3 mg/kg). Injection of a higher dose of minocycline into the amygdala also induced analgesia. Moreover, bilateral intra-amygdala injection of naloxone (0.5-1.5 µg/rat) reversed minocycline-induced potentiation of morphine analgesia. Pretreatment of animals with NMDA (0.01-0.1 μg/rat, intra-amygdala) also inhibited the potentiative effect of minocycline on morphine response. Bilateral intra-amygdala injection of the same doses of naloxone or NMDA plus morphine had no effect on the tail-flick latency in the absence of minocycline. It can be concluded that the amygdala has a key role in the potentiative effect of minocycline on morphine analgesia. In addition, amygdala opioidergic and glutamatergic mechanisms may be involved, probably through μ-opioid and NMDA receptors, in the modulation of the minocycline-induced potentiation of morphine analgesia in the tail-flick test.

Topics: Amygdala; Analgesics; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Excitatory Amino Acid Agonists; Hot Temperature; Injections, Intraperitoneal; Male; Minocycline; Morphine; N-Methylaspartate; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Random Allocation; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu

Chronic consumption of morphine induces physical dependency, anxiety, and neurodegeneration. In this study, morphine on its own has been used for the management of morphine-induced dependency, oxidative stress, and apoptosis. Forty-eight male rats were randomly divided into six groups. Rats in groups 1-5 were made morphine dependent by an increasing manner of morphine for 7 days (15-45 mg/kg). For the next 14 days, morphine was administered using the following regimen: (i) once daily 45 mg/kg (positive controls), (ii) the same dose at additional intervals (6 h longer than the previous intervals each time), (iii) 45 mg/kg of morphine at irregular intervals like of 12, 24, 36 h, (iv) decreasing dose once daily (every time 2.5 mg/kg less than the former dosage). Group 5 received 45 mg/kg of morphine and 10 mg/kg of SOD mimetic agent (M40401) injection per day. Group 6 (negative control) received saline solution only. On day 22, all animals received naloxone (3 mg/kg) and their Total Withdrawal Index (TWI) and blood cortisol levels were measured. After drug treatment, hippocampus cells were isolated, and oxidative, antioxidative, and apoptotic factors were evaluated. Various regimens of morphine reduced TWI, cortisol levels, Bax activity, caspase-3, caspase-9, TNF-α, and IL-1β and lipid peroxidation. In all treatment groups, GSH level, superoxide dismutase, glutathione peroxidase, and Bcl-2 activity were significantly increased. Furthermore, SOD mimetic agent c diminished morphine effect on SOD activity. Thus, varying the dosage regimen of morphine can reduce the severity of morphine-induced dependency and neurodegeneration.

Topics: Analgesics, Opioid; Animals; Anxiety; Apoptosis; Apoptosis Regulatory Proteins; Behavior, Animal; Biomarkers; Cells, Cultured; Disease Models, Animal; Drug Administration Schedule; Hippocampus; Hydrocortisone; Inflammation Mediators; Lipid Peroxidation; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Nerve Degeneration; Oxidative Stress; Rats, Wistar; Substance Withdrawal Syndrome; Time Factors

Clinical studies have tested the use of an engineered herpes virus to treat pain. We hypothesized that subcutaneous injections of an engineered herpes virus that expresses enkephalin would attenuate orofacial nociception and hypersensitivity in male and female rats by a central mechanism.. Herpes virus was injected subcutaneously around the mouth of male and female rats seventy-two hours before ligatures were placed on the masseter tendon, control treatment groups received either no virus or no ligature. Enkephalin expression was measured and von Frey filament testing and meal duration were utilized to measure mechanical hypersensitivity and the nociceptive response, respectively. Naloxone or naloxone methiodide was administered to rats injected with the enkephalin expressing virus to test if enkephalin was acting peripherally or centrally.. Ligature significantly lengthened meal duration and reduced the threshold to von Frey filaments for 18 days. Infection with the enkephalin transgene significantly decreased this response for at least 11 days but only in male rats. Virus injection significantly increased expression of enkephalin in the mental nerve that innervates the mouth region, the trigeminal ganglia and the trigeminal nucleus caudalis but no increase was observed in the masseter nerve after virus injection. Naloxone but not naloxone methiodide reversed the response to the enkephaline expressing virus.. The data suggests that sex should be a considered when using this virus and that viral transfection of the mental nerve with an enkephalin transgene can reduce nociception and hypersensitivity through a central mechanism.

Topics: Animals; Disease Models, Animal; Enkephalins; Female; Herpesviridae; Herpesviridae Infections; Hyperalgesia; Male; Masseter Muscle; Naloxone; Narcotic Antagonists; Nociception; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Trigeminal Ganglion; Trigeminal Nerve; Trigeminal Nuclei

Traumatic spinal cord injury (SCI) is one of the dreaded neurological conditions and finding a cure for it has been a hot area of research. Naloxone - a mu-opiate receptor (mor) antagonist was considered for SCI treatment based on its positive effects under shock conditions. In contrary to animal studies based reports about the potential benefits of naloxone in treating SCI, a large scale clinical trial [National Acute Spinal Cord Injury Study II (NASCIS II)] conducted in USA failed to witness any effectiveness. The inconsistency noticed was intriguing. Therefore, the objective of the present study was to re-examine the role of naloxone in treating SCI using a highly standardised Multicenter Animal Spinal Cord Injury Study (MASCIS) animal model of contusive SCI. Results indicated that naloxone produced negligible and insignificant neuroprotection. In an attempt to understand the cause for the failure, it was found that mu-opioid receptor (mor) gene expression was upregulated in the brain but was down regulated in the spinal cord after contusive SCI. Given that the beneficial effects of naloxone are through its action on the mor, the results indicate that unlike the brain, spinal cord might not be bracing to utilise the opiate system in the repair process. This could possibly explain the failure of naloxone treatment in NASCIS II. To conclude, opiate antagonists like naloxone may be neuroprotective for treating traumatic brain injuries, but not for traumatic/contusive spinal cord injuries.

Topics: Animals; Antigens, Nuclear; Brain; Bromodeoxyuridine; Disease Models, Animal; Down-Regulation; Female; Gene Expression; Motor Activity; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Neurons; Rats, Sprague-Dawley; Receptors, Opioid, mu; Spinal Cord; Spinal Cord Injuries; Up-Regulation

Histamine and opioid systems are involved in supraspinal modulation of pain. In this study, we investigated the effects of separate and combined microinjections of agonists and antagonists of histamine H1 and H2 and opioid receptors into the thalamic submedius (Sm) nucleus on the formalin-induced orofacial pain. Two guide cannulas were implanted into the right and left sides of the Sm in ketamine- and xylazine-anesthetized rats. Orofacial formalin pain was induced by subcutaneous injection of a diluted formalin solution (50 μl, 1.5%) into the vibrissa pad. Face rubbing durations were recorded at 3-min blocks for 45 min. Formalin produced a biphasic pain response (first phase: 0-3 min and second phase: 15-33 min). Separate and combined microinjections of histamine H1 and H2 receptor agonists, 2-pyridylethylamine (2-PEA) and dimaprit, respectively, and opioid receptor agonist, morphine, attenuated the second phase of pain. The analgesic effects induced by 2-PEA, dimaprit, and morphine were blocked by prior microinjections of fexofenadine (a histamine H1 receptor antagonist), famotidine (a histamine H2 receptor antagonist), and naloxone (an opioid receptor antagonist), respectively. Naloxone also prevented 2-PEA- and dimaprit-induced antinociception, and the analgesic effect induced by morphine was inhibited by fexofenadine and famotidine. These results showed the involvement of histamine H1 and H2 and opioid receptors in the Sm modulation of orofacial pain. Opioid receptor might be involved in analgesia induced by activation of histamine H1 and H2 receptors and vice versa.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Facial Pain; Formaldehyde; Histamine Agonists; Histamine Antagonists; Male; Morphine; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Opioid; Thalamic Nuclei

Endomorphins are endogenous opioid peptides in mammals and display a strong antinociceptive effect after central administration. However, the clinical usage of these peptides is limited because of their diminished analgesic effect following systemic injection and their inability to cross the blood-brain barrier. In this study, we characterized the in vivo effects of four novel endomorphin-1 analogues (termed MELs), which previously showed potential as highly potent analgesics with a good pharmacological profile in vitro. The analogues were administered intravenously to several rodent pain models to examine their antinociception and blood-brain barrier permeability. The tested peptides, especially MEL1214, showed good analgesic activity and blood-brain barrier permeability. Behavioral studies showed dose-dependent analgesic effect after systematic administration of MEL1214 in the tested pain models. Pre-treatment of subcutaneous administration of naloxone methiodide did not affect the antinociception of these peptides. As compared to morphine, MEL1214 was less prone to induce tolerance after consecutive intravenous administration for 5 days. Gastrointestinal transit was evaluated by the isolated colon response and bead expulsion to determine the potential constipation effect. In contrast to morphine, MEL1214 produced no significant constipation effect at an equivalent dose. MEL1214 shows promise as a suitable compound to treat pain with reduced side effects, and exhibits good potential to be further developed as a novel opioid analgesic in pain treatment.

Topics: Analgesics, Opioid; Animals; Blood-Brain Barrier; Capillary Permeability; Colon; Constipation; Disease Models, Animal; Drug Tolerance; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Nociceptive Pain; Oligopeptides; Quaternary Ammonium Compounds

Polyalthia longifolia var. pendula is a very popular herb in Bangladesh due to its traditional uses in treatment of rheumatism, bone fracture and gastric ulcer. The present study was conducted to investigate the antinociceptive activity of ethanol extract of P. longifolia (EEPL) bark.. Hot plate and tail immersion tests, acetic acid-induced writhing test, glutamate and formalin-induced paw licking tests in mice were employed in this study. In all the experiments EEPL was administered orally at the doses of 50, 100 and 200mg/kg body weight. To investigate the possible participation of opioid system in EEPL-mediated effects, naloxone was used to antagonize the action.. EEPL showed a significant antinociceptive activity against both heat and chemical-induced nociception. The effects were dose-dependent and significant at the doses of 100 and 200mg/kg of EEPL. Besides, pretreatment with naloxone caused significant inhibition of the antinociceptive activity induced by EEPL, revealing the possible involvement of the opioid receptors.. These results indicate the antinociceptive activity of the bark of P. longifolia and support the ethnomedical use of this plant in treatment of different painful conditions.

Topics: Analgesics; Animals; Bangladesh; Disease Models, Animal; Dose-Response Relationship, Drug; Ethanol; Medicine, Traditional; Mice; Naloxone; Pain; Plant Bark; Plant Extracts; Polyalthia; Receptors, Opioid

Selective activation of peripheral κ opioid receptors (KORs) may overcome the dose-limiting adverse effects of conventional opioid analgesics. We recently developed a vicinal disulfide-stabilized class of peptides with subnanomolar potency at the KOR. The aim of this study was to assess the analgesic effects of one of these peptides, named conorphin-1, in comparison with the prototypical KOR-selective small molecule agonist U-50488, in several rodent pain models. Surprisingly, neither conorphin-1 nor U-50488 were analgesic when delivered peripherally by intraplantar injection at local concentrations expected to fully activate the KOR at cutaneous nerve endings. While U-50488 was analgesic when delivered at high local concentrations, this effect could not be reversed by coadministration with the selective KOR antagonist ML190 or the nonselective opioid antagonist naloxone. Instead, U-50488 likely mediated its peripheral analgesic effect through nonselective inhibition of voltage-gated sodium channels, including peripheral sensory neuron isoforms NaV1.8 and NaV1.7. Our study suggests that targeting the KOR in peripheral sensory nerve endings innervating the skin is not an alternative analgesic approach.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Analgesics, Non-Narcotic; Animals; Carrageenan; Cisplatin; Disease Models, Animal; Freund's Adjuvant; Gene Expression Regulation; HEK293 Cells; Humans; Inflammation; Male; Mice; Mice, Inbred C57BL; Naloxone; Nerve Endings; Oligopeptides; Pain; Pain Measurement; Peptides; Peripheral Nervous System Diseases; Rats; Rats, Wistar; Receptors, Opioid, kappa; Skin

Cedrus atlantica essential oil (CaEO) presents analgesic and anti-inflammatory sedative properties. However, it remains unknown whether CaEO alleviates acute postoperative pain.. Here, we investigated the effect of CaEO on postoperative pain and its mechanisms related to the descending pain control in Swiss males mice induced by a plantar incision surgery (PIS) in the hindpaw.. Inhalation of CaEO (5', 30' or 60') markedly reduced mechanical hypersensitivity. This effect was prevented by pre-treatment with naloxone or p-chlorophenylalanine methyl ester (PCPA, 100mg/kg, i.p.)-induced depletion of serotonin. In addition, p-alpha-methyl-para-tyrosin (AMPT, 100mg/kg, i.p.)-induced depletion of norepinephrine, intraperitoneal injection of the α2-adrenergic receptor antagonist yohimbine (0.15 mg/kg, i.p.) or haloperidol (1mg/kg, i.p.) an antagonist of dopaminergic (D1 and D2) receptors prevented the effect of CaEO on hypersensitivity.. These findings suggest that CaEO alleviates postoperative pain by activating the descending pain modulation pathways on the opioidergic, serotonergic, noradrenergic (α2-adrenergic) and dopaminergic (dopamine D1 and D2 receptors) systems.

Topics: Administration, Inhalation; Adrenergic alpha-2 Receptor Antagonists; alpha-Methyltyrosine; Analgesics; Animals; Behavior, Animal; Cedrus; Disease Models, Animal; Dopamine Antagonists; Fenclonine; Foot; Haloperidol; Hyperalgesia; Male; Mice; Motor Activity; Naloxone; Narcotic Antagonists; Oils, Volatile; Pain, Postoperative; Phytotherapy; Serotonin Antagonists; Yohimbine

Light-emitting diode therapy (LEDT) has been clinically used as an alternative to low-level laser therapy; nevertheless, the molecular basis for LEDT effects remains unclear. The objective of this study was to evaluate the analgesic effect of LEDT in the mouse plantar incision (PI) model of postoperative pain, as well as to investigate some of the possible mechanisms involved in this effect, i.e., peripheral and central opioid receptors; migration of opioid-containing leukocytes to PI site and the L-arginine/nitric oxide (NO) pathway. To that end, mice were subjected to PI and treated with LEDT (950 nm, 80 mW/cm(2), 1 through 13 J/cm(2)). Mechanical hypersensitivity was assessed as withdrawal frequency percentage to 10 presentations of a 0.4-g von Frey filament. In addition, the animals were pretreated with systemic (i.p.), intra-plantar (i.pl.), or intrathecal injection (i.t) of naloxone (a nonselective opioid receptor antagonist; 1 mg/kg, i.p.; 5 μg/right paw or 5 μg/site, respectively) or a systemic injection of fucoidin (100 μg/mouse, i.p., an inhibitor of leukocyte rolling through binding to L- and P-selectins). Our results demonstrate, for the first time, that LEDT induced a dose-response analgesic effect in the model of PI in mice. At the dose of 9 J/cm(2) LEDT presented the most significant results through (1) activation of peripheral opioid receptors which involve, at least partially, the recruitment of opioid-containing leukocytes to the PI site and; (2) activation of the L-arginine/NO pathway. These results extend previous literature data and suggest that LEDT might be useful in the treatment of postoperative pain.

Topics: Animals; Arginine; Disease Models, Animal; Dose-Response Relationship, Radiation; Injections, Spinal; Leukocytes; Male; Mice; Naloxone; Narcotic Antagonists; Nitric Oxide; Pain, Postoperative; Phototherapy; Receptors, Opioid

Tarragon [Artemisia dracunculus L. (Asteraceae)] is used as a commercial flavoring and in perfumery. In traditional folk medicine, tarragon has been used for treatment of pain and gastrointestinal disturbances.. This study investigated the antinociceptive effect of the essential oil of A. dracunculus (EOAD) in various experimental models.. The median lethal dose (LD50) of EOAD was estimated using the method of Lorke. The antinociceptive effect was assessed using chemical (formalin and acetic acid) and thermal (hot-plate) nociceptive tests in rats and mice. In all experiments, EOAD was administered intraperitoneally at the doses of 10, 30, 100 and 300 mg/kg.. In the acute toxicity test, the value of estimated LD50 for EOAD was 1250 mg/kg. EOAD (100 and 300 mg/kg) significantly reduced (p < 0.001) the pain response in the first (59.5 and 91.4%) and second (52.5 and 86.3%) phases of the formalin test, respectively. Central involvement in analgesic profile was confirmed by the hot-plate test, in which the EOAD showed a significant analgesic activity by increasing latency time. EOAD (10, 30, 100 and 300 mg/kg) significantly (p < 0.001) inhibited (89, 95, 97 and 97%) the nociception produced by acetic acid. Naloxone failed to antagonize the antinociceptive effect of the essential oil in the acetic acid-induced writhing test. It seems that mechanism(s) other than opioid receptors is (are) involved in the analgesic effect of EOAD.. This study reported the peripheral and central antinociceptive activity of the EOAD and rationalized the traditional use of the plant in the treatment of different painful conditions.

Topics: Analgesics; Animals; Artemisia; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Injections, Intraperitoneal; Lethal Dose 50; Male; Medicine, Traditional; Mice; Naloxone; Oils, Volatile; Pain; Pain Measurement; Rats; Rats, Wistar; Toxicity Tests, Acute

The antinociceptive effect of cyanocobalamin (Vit B12) has been reported in animal models and human studies. Our previous study showed the effect of Vit B12 on morphine tolerance. The dependence and tolerance were induced in male mice using subcutaneous morphine injections, 3 times a day (50, 50 and 75 mg/kg/day) for 3 days. Mice also received Vit B12 (100, 250 and 500 µg/kg), clonidine, memantine and saline intraperitoneally before morphine administration. On fourth day mice received only 7 mg /kg morphine just before tail-flick test. To determine the expression of morphine dependence and tolerance, all compounds were injected once intraperitoneally on the day of experiment. The tolerance was evaluated by the tail-flick test. The effect of Vit B12 and other agents on dependence were evaluated by counting the number of jumps (induced by naloxone 5 mg/kg). Co-administration of Vit B12 (100-500 µg/kg) and morphine in 3 days reduced the development of tolerance to morphine analgesic effect (8.2±0.5 and 7.83±0.5 s. vs. normal saline, 3.57±0.3 s). Repeated administration of Vit B12, also, diminished the reduced naloxane withdrawal signs of naloxone withdrawal test (100-500 µg/kg: 5±1.9 and 1.2±0.8 jumps vs. normal saline 72.6±12.2). However, Vit B12 had no effect on the expression of morphine tolerance and physical dependence. It is concluded that co-administration of Vit B12 and morphine could reduce tolerance to analgesic effect of morphine chronic administration and also reduce its withdrawal symptoms.

Topics: Analgesics, Opioid; Animals; Clonidine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Male; Memantine; Mice; Morphine; Morphine Dependence; Naloxone; Pain; Vitamin B 12

This study investigated whether and how electroacupuncture (EA) attenuates cold hypersensitivity (allodynia) in a rat model of oxaliplatin-induced neuropathic pain. Cold allodynia [evaluated by immersing the tail into cold water (4 °C) and measuring the withdrawal latency] was induced 3 days after an oxaliplatin administration (6 mg/kg, i.p.). EA stimulation (2/100 Hz, 0.3-ms pulse duration, 0.2-0.3 mA) was delivered to ST36 acupoint or non-acupoint for 20 min. Low-frequency (2 Hz) EA at ST36 relieved cold allodynia more effectively than high-frequency EA at ST36 or low-frequency EA at non-acupoint. Naloxone (opioid antagonist, 2 mg/kg, i.p.) completely blocked such EA-induced anti-allodynia, whereas phentolamine (α-adrenergic antagonist, 2 mg/kg, i.p.) did not. Moreover, plasma β-endorphin levels significantly increased right after the end of EA and subsequently decreased. These results indicate that low-frequency EA at ST36 in rats has a marked relieving effect on oxaliplatin-induced cold allodynia that is mediated by the endogenous opioid, but not noradrenergic, system.

Topics: Adrenergic alpha-Antagonists; Animals; Behavior, Animal; beta-Endorphin; Cold Temperature; Disease Models, Animal; Electroacupuncture; Hyperalgesia; Male; Naloxone; Narcotic Antagonists; Organoplatinum Compounds; Oxaliplatin; Pain Threshold; Phentolamine; Rats; Rats, Sprague-Dawley; Reaction Time; Time Factors

Hypericum perforatum Linn. (Hypericaceae) (St. John's wort) attenuates opium withdrawal signs.. To explore the therapeutic potential of Hypericum perforatum in the management of opium-induced withdrawal syndrome.. The effect of the Hypericum perforatum hydro-ethanol extract was investigated for potential to reverse naloxone (0.25 mg/kg)-induced opium withdrawal physical signs. Rats received opium extract (80-650 mg/kg) twice daily for 8 days along with Hypericum perforatum (20 mg/kg, orally) twice daily in chronic treatment and the same single dose 1 h before induction of withdrawal syndrome in the acute treated group.. Hypericum perforatum reduced stereotype jumps and wet dog shake number in the chronic treatment compared to the saline control group (F(2, 24) = 3.968, p < 0. 05) and (F(2, 24) = 3.689, p < 0.05), respectively. The plant extract in the acutely treated group reduced diarrhea (F(2, 24) = 4.850, p < 0. 05 vs. saline). It decreased rectal temperature by chronic treatment at 30 min (F(2, 24) = 4.88, p < 0.05), 60 min (F(2, 240 = 5.364, p < 0.01) and 120 min (F(2, 24) = 4.907, p < 0.05).. This study reveals that the extract of Hypericum perforatum attenuates some physical signs of opium withdrawal syndrome possibly through direct or indirect interaction with opioid receptors. Further study is needed to clarify its mechanism.

Topics: Animals; Disease Models, Animal; Female; Hypericum; Male; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Opium; Phytotherapy; Plant Components, Aerial; Plant Extracts; Rats, Sprague-Dawley; Substance Withdrawal Syndrome

Opioid addiction is associated with cardiovascular disease. However, mechanisms linking opioid addiction and cardiovascular disease remain unclear. This study investigated the role of corticotropin-releasing factor (CRF) 1 receptor in mediating somatic signs and the behavioural states produced during withdrawal from morphine dependence. Furthermore, it studied the efficacy of CRF1 receptor antagonist, CP-154,526 to prevent the cardiac sympathetic activity induced by morphine withdrawal. In addition, tyrosine hydroxylase (TH) phosphorylation pathways were evaluated. Like stress, morphine withdrawal induced an increase in the hypothalamic-pituitary-adrenal (HPA) axis activity and an enhancement of noradrenaline (NA) turnover. Pre-treatment with CRF1 receptor antagonist significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropic hormone (ACTH) levels, NA turnover and TH phosphorylation at Ser31 in the right ventricle. In addition, CP-154,526 reduced the phosphorylation of extracellular signal-regulated kinase (ERK) after naloxone-precipitated morphine withdrawal. In addition, CP-154,526 attenuated the increases in body weight loss during morphine treatment and suppressed some of morphine withdrawal signs. Altogether, these results support the idea that cardiac sympathetic pathways are activated in response to naloxone-precipitated morphine withdrawal suggesting that treatment with a CRF1 receptor antagonist before morphine withdrawal would prevent the development of stress-induced behavioural and autonomic dysfunction in opioid addicts.

Topics: Animals; Cardiotonic Agents; Disease Models, Animal; Heart Ventricles; Hypothalamo-Hypophyseal System; Male; MAP Kinase Signaling System; Morphine Dependence; Naloxone; Narcotic Antagonists; Phosphorylation; Pituitary-Adrenal System; Protein Processing, Post-Translational; Rats; Rats, Sprague-Dawley; Receptors, Corticotropin-Releasing Hormone; Substance Withdrawal Syndrome; Tyrosine 3-Monooxygenase; Ventricular Dysfunction, Right; Weight Gain

μ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive. Here we devised a new conditional bacterial artificial chromosome rescue strategy to show, in mice, that targeted MOR expression in a subpopulation of striatal direct-pathway neurons enriched in the striosome and nucleus accumbens, in an otherwise MOR-null background, restores opiate reward and opiate-induced striatal dopamine release and partially restores motivation to self administer an opiate. However, these mice lack opiate analgesia or withdrawal. We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward. Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

Topics: Analysis of Variance; Animals; Conditioning, Operant; Corpus Striatum; Disease Models, Animal; Dopamine; Enkephalins; Exploratory Behavior; Flow Cytometry; Green Fluorescent Proteins; Mice; Mice, Transgenic; Microdialysis; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Neural Pathways; Neurons; Pain; Pain Measurement; Protein Precursors; Receptors, Opioid, mu; Reward; Substance Withdrawal Syndrome

The negative affective states of withdrawal involve the recruitment of brain and peripheral stress circuitry [noradrenergic activity, induction of the hypothalamic-pituitary-adrenocortical (HPA) axis and activation of heat shock proteins (Hsps)]. Corticotropin-releasing factor (CRF) pathways are important mediators in the negative symptoms of opioid withdrawal. We performed a series of experiments to characterize the role of the CRF₁ receptor in the response of stress systems to morphine withdrawal and its effect in the heart using genetically engineered mice lacking functional CRF₁ receptors.. Wild-type and CRF₁ receptor-knockout mice were treated with increasing doses of morphine. Precipitated withdrawal was induced by naloxone. Plasma adrenocorticotropic hormone (ACTH) and corticosterone levels, the expression of myocardial Hsp27, Hsp27 phosphorylated at Ser⁸², membrane (MB)- COMT, soluble (S)-COMT protein and NA turnover were evaluated by RIA, immunoblotting and HPLC.. During morphine withdrawal we observed an enhancement of NA turnover in parallel with an increase in mean arterial blood pressure (MAP) and heart rate (HR) in wild-type mice. In addition, naloxone-precipitated morphine withdrawal induced an activation of HPA axis and Hsp27. The principal finding of the present study was that plasma ACTH and corticosterone levels, MB-COMT, S-COMT, NA turnover, and Hsp27 expression and activation observed during morphine withdrawal were significantly inhibited in the CRF₁ receptor-knockout mice.. Our results demonstrate that CRF/CRF₁ receptor activation may contribute to stress-induced cardiovascular dysfunction after naloxone-precipitated morphine withdrawal and suggest that CRF/CRF₁ receptor pathways could contribute to cardiovascular disease associated with opioid addiction.

Topics: Adrenergic Neurons; Animals; Corticotropin-Releasing Hormone; Disease Models, Animal; Heart Ventricles; HSP27 Heat-Shock Proteins; Hypertension; Hypothalamo-Hypophyseal System; Male; Mice; Mice, 129 Strain; Mice, Knockout; Morphine Dependence; Naloxone; Nerve Tissue Proteins; Phosphorylation; Pituitary-Adrenal System; Protein Processing, Post-Translational; Receptors, Corticotropin-Releasing Hormone; Signal Transduction; Tachycardia

Interventions to reduce the cardiotoxicity of doxorubicin are clinically relevant. Pharmacological preconditioning mimicking ischemic preconditioning has been demonstrated with morphine and represents an acceptable clinical intervention. The purpose of this study was to examine if pretreatment in vivo with morphine could reduce doxorubicin-induced cardiotoxicity ex vivo in a rat model. Wistar rats were divided into six groups and pretreated with an intraperitoneal (i.p.) injection of 3 or 10 mg/kg morphine, 1 mg/kg naloxone and saline, 1 mg/kg naloxone and 3 mg/kg morphine or saline, 60 min before excision of the heart. Biochemical indices such as troponin T (TnT) and hydrogen peroxide (H2O2) in effluate were measured together with physiological parameters in Langendorff hearts before and after doxorubicin infusion (2 mg/mL 0.05 mL/min for 45 min). Myocardial content of doxorubicin was measured at the end of infusion. Pretreatment with morphine, irrespective of dosage, produced a significant loss in left ventricular-developed pressure and an increase of TnT and H2O2 in effluate before doxorubicin infusion (p < 0.05). Morphine also produced a significant increase in left ventricular end-diastolic pressure and an increase of TnT and H2O2 in effluate (p < 0.05) at the end of doxorubicin infusion. Naloxone, a non-selective opioid receptor antagonist, abolished the effects of morphine both before and after doxorubicin infusion. Morphine, irrespective of dosage, increased myocardial content of doxorubicin compared to pretreatment with saline (p < 0.05). Pretreatment with morphine is associated with a cardiodepressive effect and enhances cardiotoxicity of doxorubicin measured by increased myocardial accumulation of doxorubicin and physiological and biochemical indices. The negative effects observed in our rat model are abolished by naloxone.

Topics: Animals; Antibiotics, Antineoplastic; Cardiotoxicity; Disease Models, Animal; Doxorubicin; Drug Synergism; Heart Diseases; Hydrogen Peroxide; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Wistar; Troponin T

The aim of this study was to assess whether intraperitoneal administration of ginseng total saponins (GTS) has antihyperalgesic effects in a rat model of incisional pain. The proinflammatory responses and reversal of the antihyperalgesic effect of GTS by N-methyl-d-aspartate (NMDA) or naloxone were also evaluated.. Rats were injected intraperitoneally with 0.9% saline vehicle or various doses of GTS before or after a plantar incision. Paw withdrawal in response to application of the von Frey filament with the lowest bending force marked the mechanical withdrawal threshold (MWT). Blood samples were collected for the assessment of serum interleukin (IL)-1β and IL-6 levels. The IL levels were measured using an enzyme-linked immunosorbent assay kit. Rats were injected intraperitoneally with NMDA or naloxone before the GTS injection to assess the reversal of the antihyperalgesic effect of GTS.. The MWT measured 2 h after the plantar incision increased significantly after the postincision administration of 50, 100, or 200 mg/kg of GTS compared with the MWT at 2 h after plantar incision. The MWT also increased significantly after the preincision injection of 100 or 200 mg/kg of GTS compared with the MWT of the vehicle control. Administration of GTS suppressed the postincision rise in serum IL-1β levels and NMDA inhibited the increase in the MWT compared with GTS alone.. Intraperitoneal administration of GTS before or after surgery induces antihyperalgesic effects in a rat model of incisional pain. The effects on mechanical hyperalgesia may be associated with anti-inflammatory cytokines and NMDA signaling.

Topics: Acute Pain; Animals; Disease Models, Animal; Excitatory Amino Acid Agonists; Hyperalgesia; Injections, Intraperitoneal; Male; N-Methylaspartate; Naloxone; Narcotic Antagonists; Pain, Postoperative; Panax; Rats; Rats, Sprague-Dawley; Saponins

Opioids are standard therapy for the treatment of pain; however, adverse effects limit their use. Voltage-gated calcium channel blockers may be used to increase opioid analgesia, but their effect on opioid-induced side effects is little known. Thus, the goal of this study was to evaluate the action of the peptide Phα1β, a voltage-gated calcium channel blocker, on the antinociceptive and adverse effects produced by morphine in mice. A single administration of morphine (3-10 mg/kg) was able to reduce heat nociception as well as decrease gastrointestinal transit. The antinociception caused by a single injection of morphine was slightly increased by an intrathecal injection of Phα1β (30 pmol/site). Repeated treatment with morphine caused tolerance, hyperalgesia, withdrawal syndrome, and constipation, and the Phα1β (.1-30 pmol/site, intrathecal) was able to reverse these effects. Finally, the effects produced by the native form of Phα1β were fully mimicked by a recombinant version of this peptide. Taken together, these data show that Phα1β was effective in potentiating the analgesia caused by a single dose of morphine as well as in reducing tolerance and the adverse effects induced by repeated administration of morphine, indicating its potential use as an adjuvant drug in combination with opioids.. This article presents preclinical evidence for a useful adjuvant drug in opioid treatment. Phα1β, a peptide calcium channel blocker, could be used not only to potentiate morphine analgesia but also to reduce the adverse effects caused by repeated administration of morphine.

Topics: Analgesics, Opioid; Animals; Arthropod Proteins; Calcium Channel Blockers; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Gastrointestinal Transit; Hyperalgesia; Injections, Spinal; Male; Mice; Mice, Inbred C57BL; Morphine; Naloxone; Narcotic Antagonists; Nociceptive Pain; Pain Measurement; Peptides

An effective and safe treatment of insomnia in patients with neuropathic pain remains an unmet need. Melatonin and its analogs have been shown to have both analgesic and hypnotic effects; however, capacity of them on sleep disturbance with neuropathic pain as well as the precise mechanism is unclear.. The present study evaluated effects of piromelatine, a novel melatonin receptor agonist, on sleep disturbance in a neuropathic pain-like condition as well as the underlying mechanisms.. A mouse model of chronic neuropathic pain induced by partial sciatic nerve ligation (PSL) was employed. The antinociceptive and hypnotic effects of piromelatine were evaluated by measurement of thermal hyperalgesia, mechanical allodynia, and electroencephalogram (EEG) recordings in PSL mice. Pharmacological approaches were used to clarify the mechanisms of action of piromelatine.. PSL significantly lowered thermal and mechanical latencies and decreased non-rapid eye movement (NREM) sleep, and PSL mice exhibited sleep fragmentation. Treatment with 25, 50, or 100 mg/kg of piromelatine significantly prolonged thermal and mechanical latencies and increased NREM sleep. Moreover, the antinociceptive effect of piromelatine was prevented by melatonin antagonist luzindole, opioid receptor antagonist naloxone, or 5HT1A receptor antagonist WAY-100635. The hypnotic effect of piromelatine was blocked by luzindole but neither by naloxone nor WAY-100635.. These data indicate that piromelatine is an effective treatment for both neuropathic pain and sleep disturbance in PSL mice. The antinociceptive effect of piromelatine is likely mediated by melatonin, opioid, and 5HT1A receptors; however, the hypnotic effect of piromelatine appears to be mediated by melatonin receptors.

Topics: Analgesics; Animals; Disease Models, Animal; Hyperalgesia; Hypnotics and Sedatives; Indoles; Male; Melatonin; Mice; Naloxone; Narcotic Antagonists; Neuralgia; Pain Measurement; Peripheral Nerve Injuries; Piperazines; Pyrans; Pyridines; Receptor, Serotonin, 5-HT1A; Receptors, Melatonin; Receptors, Opioid; Sciatic Nerve; Serotonin Antagonists; Sleep Wake Disorders; Tryptamines

To investigate the effects of intrathecal morphine and fentanyl combined with low-dose naloxone on the expression of motilin and its receptor in a rat model of postoperative pain.. An intrathecal catheter was implanted, and saline, opioids (morphine and fentanyl) and naloxone were intrathecally administered 7 days later. An incisional pain model was established to induce pain behaviors in rats by unilateral plantar incision. Thermal hyperalgesia and mechanical allodynia were measured by using a radiant heat and electronic Von Frey filament, respectively. The expression of motilin in the hippocampus, stomach, duodenum, and plasma was determined by ELISA; and the expression of motilin receptor in the hippocampus was detected by Western blot assay.. Motilin and its receptor were detected in the hippocampus. Acute incisional pain increased the motilin expression in the hippocampus and duodenum, while decreasing its expression in the gastric body and plasma. Postoperative analgesia with morphine+fentanyl upregulated the expression of motilin in the hippocampus; however, motilin was downregulated in peripheral sites. Naloxone at 1 ng/kg restored motilin to baseline levels. Acute pain, morphine+fentanyl, and naloxone all induced the expression of motilin receptor in the hippocampus.. Acute pain, postoperative analgesia with opioids, and naloxone significantly impacted the expression of hippocampal and peripheral motilin. Variation trends in all sites were not identical. Intrathecal injection of low-dose naloxone upregulated paw withdrawal thermal latency and enhanced the analgesic effects of opioids. The findings presented here provide a new basis for central and peripheral regulations in GI motility, clinical postoperative analgesia, and management of analgesic complications.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Drug Therapy, Combination; Hippocampus; Injections, Spinal; Motilin; Naloxone; Pain Measurement; Pain, Postoperative; Rats; Rats, Sprague-Dawley; Receptors, Gastrointestinal Hormone; Receptors, Neuropeptide; Treatment Outcome; Up-Regulation

There is high comorbidity between depression and addiction. Features of addiction relevant to depression have been studied extensively, but less is known about features of depression relevant to addiction. Here, we have studied the effects of chronic mild stress (CMS), a valid animal model of depression, on measures of physical and psychological dependence resulting from subchronic treatment of rats with three drugs of abuse that act through disparate neurobiological mechanisms: morphine, nicotine and diazepam. In animals not treated subchronically with drugs of abuse, CMS increased the withdrawal-like effects of the opiate antagonist naloxone, but not those of the nicotinic antagonist mecamylamine or the benzodiazepine antagonist flumazenil. In animals treated subchronically with drugs of abuse, CMS exacerbated, precipitated and conditioned withdrawal effects associated with all three antagonists. CMS also potentiated withdrawal-induced and cue-induced place aversions associated with all three antagonists. All of the effects of CMS were reversed by chronic treatment with the specific serotonin reuptake inhibitor citalopram. These results suggest that treatment of comorbid depression, although not a primary treatment for addiction, may facilitate other treatments for addiction, by decreasing the severity of withdrawal symptoms and the likelihood of relapse.

Topics: Animals; Chronic Disease; Citalopram; Depressive Disorder; Diazepam; Disease Models, Animal; Flumazenil; GABA Modulators; Male; Mecamylamine; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Nicotine; Nicotinic Agonists; Nicotinic Antagonists; Rats, Wistar; Selective Serotonin Reuptake Inhibitors; Stress, Psychological; Substance Withdrawal Syndrome; Substance-Related Disorders

Increased activity of the endogenous opioid system in cholestasis results in analgesia. GABAA receptors have been ascribed both pronociceptive and antinociceptive roles in pain modulation. Considering the elevated endogenous opioid tone in cholestasis and the existence of close interaction between the GABAergic and opioidergic systems in pain control, the involvement of GABAA receptors in modulation of nociception in a model of elevated endogenous opioid tone, cholestasis, was investigated using muscimol and bicuculline as selective GABAA receptor agonist and antagonist respectively. Cholestasis was induced by ligation of the main bile duct using two ligatures and transsection of the duct between them. Cholestatic rats had increased tail-flick latencies (TFLs) compared to non-cholestatic rats. Administration of muscimol (0.2 and 0.4 mg/kg, s.c.) and bicuculline (0.5 and 1mg/kg, s.c.) to the cholestatic groups significantly increased and decreased respectively TFLs compared to the saline treated cholestatic group. Muscimol antinociception in cholestatic animals was attenuated by co-administration of naloxone or bicuculline. Furthermore, the combination of bicuculline and naloxone completely reversed the increased TFLs of cholestatic rats back to the level of unoperated animals. Muscimol and bicuculline injections into non-cholestatic animals did not alter TFLs. At the doses used here, none of the drugs impaired motor coordination, as revealed by the rotarod test. This study shows the involvement of GABAA receptors in pain modulation during cholestasis in rats.

Topics: Acute Pain; Animals; Bicuculline; Cholestasis; Disease Models, Animal; Muscimol; Naloxone; Rats; Receptors, GABA-A; Rotarod Performance Test

Pharmacological evidence has accumulated showing that glucocorticoids and glucocorticoid receptor (GR) facilitate several responses to different drugs of abuse. Recent findings have attributed a prominent role to the mineralocorticoid receptor (MR) in modulating behavior during the addictive process. The purpose of this study was to investigate the effects of MR blockade on: brain stress system responses to naloxone-induced morphine withdrawal, the somatic signs of abstinence; the effects of morphine withdrawal on noradrenaline (NA) turnover in the paraventricular nucleus (PVN), c-Fos expression and tyrosine hydroxylase (TH) phosphorylated at Ser31 levels in the nucleus tractus solitarius noradrenergic cell group (NTS-A2); and finally, hypothalamus-pituitary-adrenocortical (HPA) axis activity. The role of MR signaling was assessed with i.p. pretreatment with the MR antagonist, spironolactone. Rats were implanted with two morphine (or placebo) pellets. Six days later rats were pretreated with spironolactone or vehicle 30min before naloxone. The physical signs of abstinence, NA turnover, TH activation, c-Fos expression and the HPA axis activity were measured using HPLC, immunoblotting and RIA. Spironolactone attenuated the somatic signs of withdrawal that were seen after naloxone administration to chronic morphine treated animals. On the other hand, pretreatment with spironolactone resulted in no significant modification of the increased NA turnover, TH activation, c-Fos expression or HPA axis activity that occurred during morphine withdrawal. These results suggest that somatic signs of opiate withdrawal are modulated by MR signaling. However, blockade of MR did not significantly alter the brain stress system response to morphine withdrawal.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Enzyme Activation; Hypothalamo-Hypophyseal System; Hypothalamus; Male; Mineralocorticoid Receptor Antagonists; Morphine; Naloxone; Narcotic Antagonists; Norepinephrine; Opioid-Related Disorders; Paraventricular Hypothalamic Nucleus; Phosphorylation; Pituitary-Adrenal System; Proto-Oncogene Proteins c-fos; Rats, Sprague-Dawley; Receptors, Mineralocorticoid; Signal Transduction; Spironolactone; Substance Withdrawal Syndrome; Tyrosine 3-Monooxygenase

Antinociception induced by the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) is linked to opioid receptors. We studied the subtype of receptors to which CPA action is related, as well as a possible enhancement of antinociception when CPA is coadministered with opioid receptor agonists. Spinal cord neuronal nociceptive responses of male Wistar rats with inflammation were recorded using the single motor unit technique. CPA antinociception was challenged with naloxone or norbinaltorphimine. The antinociceptive activity of fentanyl and U-50488H was studied alone and combined with CPA. Reversal of CPA antinociception was observed with norbinaltorphimine (82.9±13% of control) but not with low doses of naloxone (27±8% of control), indicating an involvement of κ-opioid but not µ-opioid receptors. Low doses of CPA did not modify fentanyl antinociception. However, a significant enhancement of the duration of antinociception was seen when U-50488H was coadministered with CPA. We conclude that antinociception mediated by CPA in the spinal cord is associated with activation of κ-opioid but not µ-opioid receptors in inflammation. In addition, coadministration of CPA and κ-opioid receptor agonists is followed by significantly longer antinociception, opening new perspectives in the treatment of chronic inflammatory pain.

Topics: Adenosine; Animals; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Electric Stimulation; Fentanyl; Inflammation; Male; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Pain Measurement; Rats; Rats, Wistar; Receptors, Opioid, kappa; Reflex; Spinal Cord

Restraint stress modulates pain and inflammation. The present study was designed to evaluate the effect of acute restraint stress on inflammatory pain induced by subcutaneous injection of bee venom (BV). First, we investigated the effect of 1 h restraint on the spontaneous paw-flinching reflex (SPFR), decrease in paw withdrawal mechanical threshold (PWMT) and increase in paw volume (PV) of the injected paw induced by BV. SPFR was measured immediately after BV injection, and PWMT and PV were measured 2 h before BV and 2-8 h after BV. The results showed that acute restraint inhibited significantly the SPFR but failed to affect mechanical hyperalgesia. In contrast, stress enhanced significantly inflammatory swelling of the injected paw. In a second series of experiments, the effects of pretreatment with capsaicin locally applied to the sciatic nerve, systemic 6-hydroxydopamine (6-OHDA), and systemic naloxone were examined on the antinociception and proinflammation produced by acute restraint stress. Local capsaicin pretreatment inhibited BV-induced nociception and inflammatory edema, and had additive effects with stress on nociception but reduced stress enhancement of edema. Systemic 6-OHDA treatment attenuated the proinflammatory effect of stress, but did not affect the antinociceptive effect. Systemic naloxone pretreatment eliminated the antinociceptive effect of stress, but did not affect proinflammation. Taken together, our data indicate that acute restraint stress contributes to antinociception via activating an endogenous opioid system, while sympathetic postganglionic fibers may contribute to enhanced inflammation in the BV pain model.

Topics: Animals; Bee Venoms; Capsaicin; Disease Models, Animal; Edema; Hindlimb; Hyperalgesia; Inflammation; Male; Naloxone; Nociception; Oxidopamine; Pain; Rats; Rats, Sprague-Dawley; Restraint, Physical; Sciatic Nerve; Stress, Psychological; Sympathetic Nervous System

Stephanolepis hispidus is one of the most common filefish species in Brazil. Its skin is traditionally used as a complementary treatment for inflammatory disorders. However, there are very few studies on chemical and pharmacological properties using the skin of this fish. This study was undertaken in order to investigate the effect of aqueous crude extract of S. hispidus skin (SAE) in different nociception models. Here, we report that intraperitoneal administration of SAE inhibited the abdominal constrictions induced by acetic acid in mice. In addition to the effect seen in the abdominal constriction model, SAE was also able to inhibit the hyperalgesia induced by carrageenan and prostaglandin E2 (PGE2) in mice. This potent antinociceptive effect was observed in the hot plate model too, but not in tail-flick test. Naloxone, an opioid receptor antagonist, was able to block the antinociceptive effect of SAE in the abdominal constriction and hot plate models. In addition, SAE did not present cytotoxic or genotoxic effect in human peripheral blood cells. Our results suggest that aqueous crude extract from S. hispidus skin has antinociceptive activity in close relationship with the partial activation of opioid receptors in the nervous system. Moreover, aqueous crude extract from S. hispidus skin does not present toxicity and is therefore endowed with the potential for pharmacological control of pain.

Topics: Analgesics; Animals; Brazil; Disease Models, Animal; Fishes; Humans; Injections, Intraperitoneal; Male; Mice; Naloxone; Narcotic Antagonists; Pain; Rats; Rats, Wistar; Receptors, Opioid; Skin; Tissue Extracts

Bile duct ligation (BDL) is an animal model used in cholestatic disease research. Both opioidergic and nitrergic systems are known to be involved in cholestasis. The aim of this study was to investigate the possible interaction between these two systems in BDL-induced memory formation and exploratory behaviors in mice. Male mice weighing 25-30 g were divided into nonoperated controls, sham-operated, and BDL groups. One-trial step-down and hole-board paradigms were used to assess memory acquisition and exploratory behaviors, respectively. Cholestasis did not alter memory acquisition while increasing exploratory behaviors 7 days after BDL. A pretraining intraperitoneal injection of L-arginine (50, 100, and 200 mg/kg), L-NG-nitroarginine methyl ester (L-NAME) (5, 10, 20, and 40 mg/kg), or naloxone (0.125, 0.25, and 0.5 mg/kg) did not alter memory acquisition or exploratory behaviors, whereas morphine (5 and 7.5 mg/kg) decreased memory acquisition in sham-operated animals. Moreover, although injection of L-NAME and naloxone exerted no effect on memory acquisition in the 7 days post-BDL mice, L-arginine (100 and 200 mg/kg) and morphine (2.5, 5, and 7.5 mg/kg) injection reduced it. In contrast, L-NAME and naloxone, but not morphine or L-arginine, reduced the BDL-induced exploratory behaviors. Coadministration of subthreshold doses of morphine (1.25 mg/kg) and L-arginine (50 mg/kg) caused a memory deficit in 7 days post-BDL mice. However, the memory deficit induced by the effective doses of morphine (2.5 mg/kg) or L-arginine (200 mg/kg) in these mice was restored by the administration of either naloxone (0.5 mg/kg) or L-NAME (40 mg/kg). In addition, naloxone and L-NAME reduced the exploratory behaviors in L-arginine-pretreated mice but not in morphine-pretreated mice. We conclude that there appears to be a synergistic effect between opioidergic and nitrergic systems on memory acquisition and exploratory behaviors in cholestatic mice.

Topics: Analgesics, Opioid; Animals; Arginine; Avoidance Learning; Cholestasis; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Exploratory Behavior; Ligation; Male; Memory Disorders; Mice; Morphine; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Nitric Oxide

Electroacupuncture (EA) has been widely accepted and applied as an important acupuncture-related technique for acupuncture analgesia (AA) research. The involvement of opioid peptides and receptors in acute AA has been shown via pre-EA application of opioid receptor/peptide antagonists. In this study, we intended to reproducibly institute acupoint position and needling excluding influences from anaesthesia or restrainers on rats with complete Freund's adjuvant (CFA) hind paw inflammatory pain, as well as to explore opioid-dependency and anti-inflammatory effects in sustained acupuncture analgesia.. Accurate position and needling approach on acupoint GB30 was modelled by computer-based three-dimensional (3D) images and followed by an optimal EA treatment protocol (100 Hz, 2-3 mA, 20 min) at 0 and 24 h post-CFA in conscious free-moving rats. Opioid receptor antagonists, naloxone (NLX) and naltrindole (NTI) were applied intraplantarly post-EA at late phase (96 h) of CFA. Nociceptive thresholds were assessed by paw pressure threshold (Randall-Sellito) or paw withdrawal latency (Hargreaves), and anti-inflammatory effects were evaluated by measurement of plantar temperature and paw volume.. EA elicited significant sustained mechanical and thermal antinociception up to 144 h. Mechanical antinociception of EA was suppressed by peripheral intraplantar application of NLX and NTI. EA also reduced paw temperature and volume during the same time frame indicating anti-inflammatory effects.. By employing a reproducible EA treatment model on GB30 in free-moving rats, we demonstrated the involvement of peripheral opioid receptors mediated EA-induced long-term antinociception. Future studies should examine the specific neuroimmunological connection of EA-induced sustained antinociception in inflammation.

Topics: Acupuncture Analgesia; Acupuncture Points; Animals; Disease Models, Animal; Electroacupuncture; Freund's Adjuvant; Hyperalgesia; Inflammation; Male; Naloxone; Naltrexone; Pain Measurement; Rats; Rats, Wistar; Receptors, Opioid; Time

Urocortin 3 (Ucn 3) was tested for anxiolytic action in mice an elevated plus maze. For detection of the possible involvement of neurotransmitters, the mice were pretreated with receptor blockers: haloperidol, phenoxybenzamine, propranolol, atropine, methysergide, bicuculline or naloxone. The peptide was administered into the lateral brain ventricle; the receptor blockers were applied intra- peritoneally. Ucn 3 alone elicited dose-dependent bell-shaped anxiolytic action. The most effective dose was 0.5 μg. In the combined testing a 0.5 μg dose was used. Haloperidol, propranolol, atropine, methysergide, and naloxone, blocked the Ucn 3-induced anxiolytic action, while phenoxybenzamine and bicuculline were ineffective. The results suggest that dopaminergic, beta-adrenergic, cholinergic, serotonergic and opiate transmissions are involved in the anxiolytic action of Ucn 3.

Topics: Analysis of Variance; Animals; Anxiety; Atropine; Bicuculline; Disease Models, Animal; Dose-Response Relationship, Drug; Haloperidol; Male; Maze Learning; Methysergide; Mice; Naloxone; Neurotransmitter Agents; Propranolol; Time Factors; Urocortins

For the past few decades membrane zinc metallopeptidases have been identified as important therapeutic targets in the control of pain. In particular, neutral endopeptidase (NEP) has been shown to play critical roles in the metabolism of the endogenous peptides Met- and Leu-enkephalins. In this study, we have evaluated the activity of a new fluorinated peptidase inhibitor NESS002ie in both in vitro and in vivo assays. NESS002ie has been compared to the peptidomimetic compound thiorphan and the previously reported NEP selective thiol inhibitor C20. The metallopeptidases inhibitory activity of NESS002ie was tested in vitro using a highly, sensitive, continuous, fluorometric, enzyme assay. Also, the analgesic propriety of NESS002ie, thiorphan and C20 have been evaluated in vivo, by intraplantar, intravenous and intrathecal administration, through nociception assays based on formalin test in mice. Metallopeptidases assays have shown an inhibitory potency of NESS002ie in the nanomolar range for NEP and angiotensin-converting enzyme (ACE). The new fluorinated inhibitor showed higher analgesic activity and bioavailability compared to thiorphan and C20 when administered by both intravenous and intrathecal injections. More significantly, intrathecal injection of NESS002ie reduced both the first and the second phases of the formalin biphasic pain response. In addition, naltrindole and naloxone reversed the analgesic effect of NESS002ie with a diverse profile. This study shows an improvement in relief of inflammation and pain, in vivo, using NESS002ie compared to reference compounds thiorphan and C20. This significant effect could be due to the replacement of isobutyl chain of the thiol C20 with the trifluoromethyl group.

Topics: Analgesics; Animals; Disease Models, Animal; Formaldehyde; Male; Mice; Naloxone; Pain, Intractable; Protease Inhibitors; Sulfhydryl Compounds; Tyrosine

Among current theories of addiction, hedonic homeostasis dysregulation predicts that the brain reward systems, particularly the mesolimbic dopamine system, switch from a physiological state to a new "set point." In opiate addiction, evidence show that the dopamine system principal targets, prefrontal cortex (PFC), nucleus accumbens (NAC) and basolateral amygdala complex (BLA) also adapt to repeated drug stimulation. Here we investigated the impact of chronic morphine on the dynamics of the network of these three interconnected structures. For that purpose we performed simultaneous electrophysiological recordings in freely-moving rats subcutaneously implanted with continuous-release morphine pellets. Chronic morphine produced a shift in the network state underpinned by changes in Delta and Gamma oscillations in the LFP of PFC, NAC and BLA, in correlation to behavioral changes. However despite continuous stimulation by the drug, an apparent normalization of the network activity and state occurred after 2 days indicating large scale adaptations. Blockade of μ opioid receptors was nonetheless sufficient to disrupt this acquired new stability in morphine-dependent animals. In line with the homeostatic dysregulation theory of addiction, our study provides original direct evidence that the PFC-NAC-BLA network of the dependent brain is characterized by a de novo balance for which the drug of abuse becomes the main contributor.

Topics: Action Potentials; Amygdala; Animals; Brain Waves; Disease Models, Animal; Limbic System; Male; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Narcotics; Neural Pathways; Nucleus Accumbens; Opioid-Related Disorders; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Wakefulness

Approximately one third of the adult U.S. population suffers from some type of on-going, chronic pain annually, and many more will have some type of acute pain associated with trauma or surgery. First-line therapies for moderate to severe pain include prescriptions for common mu opioid receptor agonists such as morphine and its various derivatives. The epidemic use, misuse and diversion of prescription opioids have highlighted just one of the adverse effects of mu opioid analgesics. Alternative approaches include novel opioids that target delta or kappa opioid receptors, or compounds that interact with two or more of the opioid receptors.. Here we report the pharmacology of a newly synthesized bifunctional opioid agonist (RV-Jim-C3) derived from combined structures of fentanyl and enkephalin in rodents. RV-Jim-C3 has high affinity binding to both mu and delta opioid receptors.. Mice and rats were used to test RV-Jim-C3 in a tailflick test with and without opioid selective antagonist for antinociception. RV-Jim-C3 was tested for anti-inflammatory and antihypersensitivity effects in a model of formalin-induced flinching and spinal nerve ligation. To rule out motor impairment, rotarod was tested in rats.. RV-Jim-C3 demonstrates potent-efficacious activity in several in vivo pain models including inflammatory pain, antihyperalgesia and antiallodynic with no significant motor impairment.. This is the first report of a fentanyl-based structure with delta and mu opioid receptor activity that exhibits outstanding antinociceptive efficacy in neuropathic pain, reducing the propensity of unwanted side effects driven by current therapies that are unifunctional mu opioid agonists.

Topics: Acute Pain; Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Chronic Pain; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Enkephalins; Fentanyl; Male; Mice; Mice, Inbred ICR; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, mu

Glutamate homeostasis and microglia activation play an important role in the development and maintenance of neuropathic pain. We designed this investigation to examine whether ultra-low dose naloxone administered alone or in combination with morphine could alter the concentration of the excitatory amino acids (EAAs) glutamate and aspartate, as well as the expression of tumor necrosis factor-α (TNF-α) and its receptors (TNFR1 and TNFR2) in the spinal cord dorsal horn of rats with partial sciatic nerve transection (PST).. Male Wistar rats underwent intrathecal catheter implantation for drug delivery and were divided in 7 groups: sham-operated + saline (sham), PST + saline (S), PST + 15 ng naloxone (n), PST + 15 µg naloxone (N), PST + 10 µg morphine (M), PST + 15 ng naloxone + 10 µg morphine (Mn), PST + 15 µg naloxone + 10 µg morphine (MN). Thermal withdrawal latency and mechanical withdrawal threshold, TNF-α and TNFR expression in the spinal cord and dorsal root ganglia, and EAAs glutamate and aspartate concentration in cerebrospinal fluid dialysates were measured.. Ten days after PST, rats developed hyperalgesia (P < 0.0001) and allodynia (P < 0.0001), and increased TNF-α (P < 0.0001) and TNFR1 expression (P = 0.0009) were measured in the ipsilateral spinal cord dorsal horn. The antihyperalgesic and antiallodynic effects of morphine (10 μg) were abolished by high-dose naloxone (15 μg; P = 0.0031) but enhanced by ultra-low dose naloxone (15 ng; P = 0.0015), and this was associated with a reduction of TNF-α (P < 0.0001) and TNFR1 (P = 0.0009) expression in the spinal cord dorsal horn and EAAs concentration (glutamate: P = 0.0001; aspartate: P = 0.004) in cerebrospinal fluid dialysate. Analysis of variance (ANOVA) or Student t test with Bonferroni correction were used for statistical analysis.. Ultra-low dose naloxone enhances the antihyperalgesia and antiallodynia effects of morphine in PST rats, possibly by reducing TNF-α and TNFR1 expression, and EAAs concentrations in the spinal dorsal horn. Ultra-low dose naloxone may be a useful adjuvant for increasing the analgesic effect of morphine in neuropathic pain conditions.

Topics: Analgesics, Opioid; Animals; Aspartic Acid; Behavior, Animal; Disease Models, Animal; Down-Regulation; Drug Synergism; Glutamic Acid; Hyperalgesia; Injections, Spinal; Male; Morphine; Naloxone; Narcotic Antagonists; Pain Threshold; Posterior Horn Cells; Rats; Rats, Wistar; Reaction Time; Receptors, Tumor Necrosis Factor, Type I; Receptors, Tumor Necrosis Factor, Type II; Sciatic Nerve; Sciatica; Time Factors; Tumor Necrosis Factor-alpha

To observe the protein expression of growth associated protein-43 (GAP-43) in midbrain ventral tegmental area in morphine withdrawal rats at different time, and to evaluate the effect of GAP-43 on morphine withdrawal memory.. Rat models of morphine dependent 1 week, 2 weeks and 4 weeks were established by morphine hydrochloride intraperitoneal injection with increasing doses to establish natural withdrawal. The protein expression of GAP-43 in midbrain ventral tegmental area was observed by immunohistochemical staining and the results were analyzed by Image-Pro Plus 5.1 image analysis system.. With prolongation of dependent time, the expression of GAP-43 was decreased then increased in midbrain ventral tegmental area.. GAP-43 could play a role in morphine withdrawal memory in midbrain ventral tegmental area.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Female; GAP-43 Protein; Immunohistochemistry; Male; Mesencephalon; Morphine; Morphine Dependence; Naloxone; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Time Factors; Ventral Tegmental Area

Drug addiction is thought to result from an intractable and aberrant learning and memory in response to drug-related stimulation, and cholinergic neurotransmission plays an important role in this process. Phosphatidylethanolamine-binding protein (PEBP) is the precursor of the hippocampal cholinergic neurostimulating peptide (HCNP), an 11 amino acid peptide that enhances the production of choline acetyltransferase (ChAT) and assists in the development of cholinergic projections from the medial septal nuclei to the hippocampus. However, whether PEBP is involved in drug addiction remains unclear. In the present study, PEBP expression in the hippocampus, as detected by proteomics analysis, was found to be dramatically up-regulated after rats received chronic morphine treatment. Western blotting analysis revealed a specific up-regulation of PEBP expression in the hippocampus but not in any other brain regions assessed. A down-regulation of hippocampal PEBP levels induced by antisense oligodeoxynucleotides resulted in aggravated morphine dependence. Together, these findings indicate that PEBP is involved in morphine dependence. Moreover, the time course of PEBP expression changes and ChAT activity was investigated during chronic morphine treatment and withdrawal. The results showed that the hippocampal PEBP levels were up-regulated during chronic morphine treatment and returned to the baseline 3 days after withdrawal, after which PEBP levels were persistently up-regulated for 28 days after withdrawal. The changes in hippocampal ChAT activity followed a pattern that was similar to that of the PEBP levels. Taken together, these results suggest that hippocampal PEBP is involved in morphine dependence and withdrawal, perhaps through modulating cholinergic transmission in the hippocampus.

Topics: Analysis of Variance; Animals; Behavior, Addictive; Blotting, Western; Choline O-Acetyltransferase; Disease Models, Animal; Down-Regulation; Electrophoresis, Gel, Two-Dimensional; Hippocampus; Humans; Male; Morphine Dependence; Naloxone; Narcotic Antagonists; Neuropeptides; Oligonucleotides, Antisense; Phosphatidylethanolamine Binding Protein; Proteomics; Rats; Rats, Wistar; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Substance Withdrawal Syndrome; Thionucleotides; Up-Regulation

Recent studies have shown that topiramate, a structurally novel anticonvulsant, exerts antinociceptive activity in animal models of neuropathic, acute somatic, and visceral pain. This study was aimed to examine: (i) the effects of systemically and locally peripherally administered topiramate in the rat inflammatory pain model and (ii) the potential role and site(s) of gamma-aminobutyric acid (GABA), opioid, and adrenergic receptors in topiramate's antihyperalgesia. Rats received intraplantar (i.pl.) injections of the pro-inflammatory compound carrageenan. A paw pressure test was used to determine: (i) the effect of systemic and local peripheral topiramate on carrageenan-induced hyperalgesia and (ii) the effects of systemic and local peripheral bicuculline (selective GABAA receptor antagonist), naloxone (nonselective opioid receptor antagonist), and yohimbine (selective α2-adrenergic receptor antagonist) on topiramate-induced antihyperalgesia. Systemic topiramate (40-160 mg/kg; p.o.) produced a significant dose-dependent reduction in the paw inflammatory hyperalgesia induced by carrageenan. The antihyperalgesic effect of systemic topiramate was significantly decreased by systemic bicuculline (0.5-1 mg/kg; i.p.), naloxone (2-5 mg/kg; i.p.), and yohimbine (1-3 mg/kg; i.p.). Local peripheral topiramate (0.03-0.34 mg/paw; i.pl.) also produced significant dose-dependent antihyperalgesia, which was significantly depressed by local peripheral yohimbine (0.05-0.2 mg/paw; i.pl.) but not by local peripheral bicuculline (0.15 mg/paw; i.pl.) or naloxone (0.1 mg/paw; i.pl.). The results suggest that topiramate produces systemic and local peripheral antihyperalgesia in an inflammatory pain model, which is, at least partially, mediated by central GABAA and opioid receptors and by peripheral and most probably central α2-adrenergic receptors. These findings contribute to better understanding of topiramate's action in pain states involving inflammation.

Topics: Analgesics; Animals; Bicuculline; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Fructose; Hyperalgesia; Inflammation; Male; Naloxone; Rats; Rats, Wistar; Receptors, Adrenergic, alpha-2; Receptors, GABA-A; Receptors, Opioid; Topiramate; Yohimbine

A T-helper cell type 1-specific response leads to the elimination of intracellular infection with Brucella. Studies have shown that naloxone (NLX) can promote a cellular immune response in this respect. The current study was carried out to evaluate the induction of protective immunity in mice against brucellosis by vaccination with a combination of NLX, alum, and heat-killed Brucella melitensis 16 M (HKB).. Mice were categorized into five groups and received intraperitoneal vaccination on Days 0 and 7. Then serum levels of interferon (IFN)-γ and interleukin (IL)-4, the bacterial load, and the survival rate were measured 2 weeks after the last vaccination.. The serum levels of IFN-γ, IL-4, and immunoglobulin G in the NLX + alum + HKB group were shown to be significantly increased (p < 0.05). Furthermore, the lowest bacterial load was observed in this group. The survival rate in groups vaccinated with combinations containing adjuvants was 100%.. The combination of NLX and alum enhanced the immunogenicity of HKB, which can be used in the vaccination of animals and humans at risk of the disease.

Topics: Adjuvants, Immunologic; Alum Compounds; Animals; Antibodies, Bacterial; Bacterial Load; Brucella melitensis; Brucella Vaccine; Brucellosis; Disease Models, Animal; Immunoglobulin G; Interferon-gamma; Interleukin-4; Male; Mice; Mice, Inbred BALB C; Naloxone; Serum; Survival Analysis; Vaccination; Vaccines, Inactivated

Eugenol is utilized together with zinc oxide in odontological clinical for the cementation of temporary prostheses and the temporary restoration of teeth and cavities. This work explored the antinociceptive effects of the eugenol in different models of acute pain in mice and investigated its possible modulation of the inhibitory (opioid) and excitatory (glutamatergic and pro-inflammatory cytokines) pathways of nociceptive signaling. The administration of eugenol (3-300 mg/kg, p.o., 60 min or i.p., 30 min) inhibited 82 ± 10% and 90 ± 6% of the acetic acid-induced nociception, with ID₅₀ values of 51.3 and 50.2 mg/kg, respectively. In the glutamate test, eugenol (0.3-100 mg/kg, i.p.) reduced the response behavior by 62 ± 5% with an ID₅₀ of 5.6 mg/kg. In addition, the antinociceptive effect of eugenol (10 mg/kg, i.p.) in the glutamate test was prevented by the i.p. treatment for mice with naloxone. The pretreatment of mice with eugenol (10 mg/kg, i.p.) was able to inhibit the nociception induced by the intrathecal (i.t.) injection of glutamate (37 ± 9%), kainic (acid kainite) (41 ± 12%), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (55 ± 5%), and substance P (SP) (39 ± 8%). Furthermore, eugenol (10 mg/kg, i.p.) also inhibited biting induced by tumor necrosis factor alpha (TNF-α, 65 ± 8%). These results extend our current knowledge of eugenol and confirm that it promotes significant antinociception against different mouse models of acute pain. The mechanism of action appears to involve the modulation of the opioid system and glutamatergic receptors (i.e., kainate and AMPA), and the inhibition of TNF-α. Thus, eugenol could represent an important compound in the treatment for acute pain.

Topics: Acute Pain; Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Eugenol; Excitatory Amino Acid Antagonists; GABAergic Neurons; Hypnotics and Sedatives; Male; Mice; Motor Activity; Naloxone; Narcotic Antagonists; Receptors, Glutamate; Receptors, Kainic Acid; Signal Transduction; Tumor Necrosis Factor-alpha

Glutamate homeostasis plays a critical role in mediating the addiction-related behaviors. Therefore, preventing the disruption or reestablishing of it is a novel strategy for the treatment of addiction. Glutamate transporters are responsible for clearing extracellular glutamate and maintaining glutamate homeostasis. Our previous work demonstrated that aquaporin-4 (AQP4) deficiency attenuated morphine dependence, but the mechanisms are unclear. According to the recent evidence that AQP4 might form a functional complex with glutamate transporter-1 (GLT-1), this study focused on whether AQP4 participates in the modulation of GLT-1 and glutamate homeostasis in morphine-dependent mice.. We found that AQP4 knockout prevented the down-regulations of GLT-1 expression and glutamate clearance when mice were repeatedly treated with morphine. Further study revealed that inhibition of GLT-1 by dihydrokainic acid (DHK) initiated morphine dependence in AQP4 knockout mice. In addition, AQP4 knockout abolished both decreases and increases in the extracellular glutamate levels in the prefrontal cortex during repeated morphine treatment and naloxone-precipitated withdrawal.. AQP4 deficiency suppresses the down-regulation of GLT-1, and the disruption of glutamate homeostasis caused by repeated exposure to morphine, pointing to a strategy for maintaining glutamate homeostasis and thereby treating addiction through the modulation of AQP4 function and expression.

Topics: Animals; Aquaporin 4; Brain; Chromatography, High Pressure Liquid; Disease Models, Animal; Down-Regulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Transporter 2; Glutamic Acid; Homeostasis; Kainic Acid; Mice; Mice, Knockout; Microdialysis; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Tritium

Addiction is a chronic disease where periods of abstinence are riddled with instances of craving, withdrawal, and eventual relapse to escalated drug use. Cues previously associated with drug use can have a deleterious effect on this cycle by precipitating withdrawal symptoms. Here we focus specifically on the relationship between avoidance of a drug-paired taste cue and the ability of the drug-paired cue to elicit withdrawal and, ultimately, drug seeking and taking. We used a rat model of drug addiction and naloxone-induced loss of body weight to test whether a taste cue elicits withdrawal in anticipation of drug availability. Experiment 1 investigated the ability of a taste cue to elicit signs of withdrawal when it predicted experimenter-administered morphine (15 mg/kg, i.p.). In Experiment 2, a saccharin taste cue was paired with the opportunity to actively self-administer cocaine (0.167 mg/infusion, i.v.). The results show that presentation of a morphine- or cocaine-paired taste cue is sufficient to elicit naloxone-induced withdrawal symptoms, and greater withdrawal predicts greater cocaine self-administration in rats.

Topics: Animals; Cocaine; Cocaine-Related Disorders; Conditioning, Psychological; Cues; Disease Models, Animal; Dopamine Uptake Inhibitors; Drug-Seeking Behavior; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Recurrence; Reward; Saccharin; Substance Withdrawal Syndrome; Sweetening Agents; Taste

Geoffroea decorticans (chañar) fruits and their derivate product (arrope) have been traditionally used as food and a folk medicine for the treatment of a wide variety of diseases including bronchopulmonary disorders and to relieve dolorous process.. In order to evaluate the pharmacology action of this plant, studies were performed of antinociceptive and antioxidant activities.. The aqueous and ethanolic extracts and arrope of chañar were evaluated in various established pain models, including chemical nociception induced by subplantar formalin and intraperitoneal acetic acid and thermal nociception method, such as tail immersion test in rats. To examine the possible connection of the opioid receptor to the antinociceptive activity of extracts and arrope it was performed a combination test with naloxone, a non-selective opioid receptor antagonist.. The aqueous extract and arrope (1000 mg/kg) caused an inhibition of the pain in formalin test in the first phase, similar to morphine and decrease in the second phase. In a combination test using naloxone, diminished analgesic activity of aqueous extract and arrope were observed, indicating that antinociceptive activity is connected with the opioid receptor. The aqueous extract and arrope, caused an inhibition of the writhing response induced by acetic acid. Central involvement in analgesic profile was confirmed by the tail immersion test, in which the aqueous extract and arrope showed a significant analgesic activity by increasing latency time. The aqueous extract showed higher antioxidant activity than the arrope, it may be due to the cooking process.. This study has shown that the aqueous extract and arrope of Geoffroea decorticans (chañar) fruits, does possess significant antinociceptive effects. It is further concluded that aqueous extract with maximum inhibition of free radical is the most potent extract amount tested extracts. At the oral doses tested the aqueous extract and arrope were non-toxic. The present results justifies their popular use and constitutes the first validation study of the antinociceptive action.

Topics: Analgesics; Animals; Antioxidants; Disease Models, Animal; Fabaceae; Flavonoids; Fruit; Herb-Drug Interactions; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pharmaceutical Solutions; Phenols; Phytotherapy; Plant Extracts; Rats; Rats, Wistar

Physical injury, including surgery, can result in chronic pain; yet chronic pain following childbirth, including cesarean delivery in women, is rare. The mechanisms involved in this protection by pregnancy or delivery have not been explored.. We examined the effect of pregnancy and delivery on hypersensitivity to mechanical stimuli of the rat hindpaw induced by peripheral nerve injury (spinal nerve ligation) and after intrathecal oxytocin, atosiban, and naloxone. Additionally, oxytocin concentration in lumbar spinal cerebrospinal fluid was determined.. Spinal nerve ligation performed at mid-pregnancy resulted in similar hypersensitivity to nonpregnant controls, but hypersensitivity partially resolved beginning after delivery. Removal of pups after delivery prevented this partial resolution. Cerebrospinal fluid concentrations of oxytocin were greater in normal postpartum rats prior to weaning. To examine the effect of injury at the time of delivery rather than during pregnancy, spinal nerve ligation was performed within 24 h of delivery. This resulted in acute hypersensitivity that partially resolved over the next 2-3 weeks. Weaning of pups resulted only in a temporary return of hypersensitivity. Intrathecal oxytocin effectively reversed the hypersensitivity following separation of the pups. Postpartum resolution of hypersensitivity was transiently abolished by intrathecal injection of the oxytocin receptor antagonist, atosiban.. These results suggest that the postpartum period rather than pregnancy protects against chronic hypersensitivity from peripheral nerve injury and that this protection may reflect sustained oxytocin signaling in the central nervous system during this period.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Female; Hormone Antagonists; Hypersensitivity; Injections, Spinal; Naloxone; Narcotic Antagonists; Oxytocics; Oxytocin; Peripheral Nerve Injuries; Physical Stimulation; Postpartum Period; Rats; Rats, Sprague-Dawley; Spinal Nerves; Vasotocin; Weaning

Lecythis pisonis Camb., also known in Brazil as sapucaia, is used in folk medicine against pruritus, muscle pain and gastric ulcer.. To investigate the antinociceptive effect of ethanol extract from Lecythis pisonis leaves (LPEE), fractions (hexane-LPHF, ether-LPEF and ethyl acetate-LPEAF) and mixture of triterpenes [ursolic and oleanolic acids (MT)] in mice.. LPEE and LPEF were evaluated on the acetic acid induced writhings and formalin, capsaicin and glutamate tests. In addition, MT was investigated on the writhings induced by acetic acid, capsaicin and glutamate tests. In the study of some possible mechanisms involved on the antinociceptive effect of LPEF, it was investigated the participation of opioid system, K+ATP channels and L-arginine-nitric oxide pathway.. LPEE (12.5 and 25 mg/kg, p.o.), LPEF and MT (6.25, 12.5 and 25 mg/kg, p.o.) reduced the writhings in comparison to saline. LPEE (100 mg/kg, p.o.) and LPEF (50 mg/kg, p.o.) were effective in inhibiting both phases of formalin test. In capsaicin test, LPEE (100 and 200 mg/kg, p.o.), LPEF (12.5-50 mg/kg, p.o) and MT (6.25-25 mg/kg, p.o.) showed a significant antinociceptive effect compared to the control. LPEE (25 and 50 mg/kg, p.o.), LPEF (50 and 100 mg/kg, p.o.) and MT (12.5 and 25 mg/kg, p.o.) reduced the glutamate-evoked nociceptive response. Treatment with naloxone, L-arginine and glibenclamide reversed the effect of LPEF in glutamate test.. These results indicate the antinociceptive effect of Lecythis pisonis leaves and suggest that this effect may be related to opioid pathway, K+ATP channels, and L-arginine-nitric oxide modulation. Furthermore, these data support the ethnomedical use of this plant.

Topics: Acetic Acid; Acute Pain; Analgesics; Animals; Arginine; Behavior, Animal; Capsaicin; Disease Models, Animal; Formaldehyde; Glutamic Acid; Glyburide; Lecythidaceae; Male; Mice; Naloxone; Narcotic Antagonists; Phytotherapy; Plant Extracts; Plant Leaves

Peroxizome proliferator-activated receptor gamma (PPARγ) is highly expressed in the central nervous system where it modulates numerous gene transcriptions. Nitric oxide synthase (NOS) expression could be modified by simulation of PPARγ which in turn activates nitric oxide (NO)/soluble guanylyl-cyclase (sGC)/cyclic guanosine mono phosphate (cGMP) pathway. It is well known that NO/cGMP pathway possesses pivotal role in the development of opioid dependence and this study is aimed to investigate the effect of PPARγ stimulation on opioid dependence in mice as well as human glioblastoma cell line. Pioglitazone potentiated naloxone-induced withdrawal syndrome in morphine dependent mice in vivo. While selective inhibition of PPARγ, neuronal NOS or GC could reverse the pioglitazone-induced potentiation of morphine withdrawal signs; sildenafil, a phosphodiesterase-5 inhibitor amplified its effect. We also showed that nitrite levels in the hippocampus were significantly elevated in pioglitazone-treated morphine dependent mice. In the human glioblastoma (U87) cell line, rendered dependent to morphine, cAMP levels did not show any alteration after chronic pioglitazone administration while cGMP measurement revealed a significant rise. We were unable to show a significant alteration in neuronal NOS mRNA expressions by pioglitazone in mice hippocampus or U87 cells. Our results suggest that pioglitazone has the ability to enhance morphine-dependence and to augment morphine withdrawal signs. The possible pathway underlying this effect is through activation of NO/GC/cGMP pathway.

Topics: Animals; Cell Line, Tumor; Cyclic AMP; Cyclic GMP; Disease Models, Animal; Enzyme Inhibitors; Glioblastoma; Hippocampus; Humans; Hypoglycemic Agents; Male; Mice; Morphine Dependence; Naloxone; Narcotic Antagonists; Nitric Oxide; Nitric Oxide Synthase; Pioglitazone; PPAR gamma; RNA, Messenger; Signal Transduction; Substance Withdrawal Syndrome; Thiazolidinediones; Transfection

The present study aims to investigate the influence of electrical stimulation of periaqueductal gray (PAG) following peripheral nerve injury and its modulation by naloxone and N-methyl-D-aspartate (NMDA). Chronic neuropathic pain was induced by chronic constriction injury of the sciatic nerve, and subsequently a cannula was implanted in the PAG area for the purpose of electrical stimulation and intra-PAG drug administration. Intra-PAG administration of morphine, ketamine, and their combination were found to elicit antinociceptive response on hot-plate test. Electrical stimulation of PAG was also observed to demonstrate decreased pain response on hot-plate test, and this effect was reversed by the administration of naloxone, NMDA, and their combination, when injected into the PAG area. These findings suggest that apart from the opioid receptors, probably NMDA receptors also have a role to play in stimulation-produced analgesia.

Topics: Analgesia; Analgesics, Opioid; Animals; Disease Models, Animal; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Hot Temperature; Ketamine; Male; Morphine; N-Methylaspartate; Naloxone; Narcotic Antagonists; Neuralgia; Periaqueductal Gray; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Sciatic Nerve

Acute opiate exposure produces a state of dependence in humans and animals, which is revealed by signs and symptoms of withdrawal precipitated by opioid receptor antagonists. The physiological changes that underlie this state of acute dependence develop rapidly and can persist long after the end of chronic opiate exposure.. The purpose of this investigation was to determine the persistence of acute dependence after a single morphine exposure in rodents, focusing on changes in behavior thought to reflect the negative emotional consequences of withdrawal.. The acoustic startle reflex and conditioned place aversion were measured following naloxone administration at different time points after a single morphine exposure.. Naloxone administration produced significant potentiation of acoustic startle-a form of anxiety-like behavior-for at least 80 days after one exposure to morphine. In contrast, naloxone produced a conditioned place aversion 24 h but not 20 days after one morphine exposure.. Together with existing literature, these results suggest acute as well as chronic opiate exposure leave rodents persistently vulnerable to express anxiety-like behavior in response to opioid receptor antagonists or stressful experience. The adaptations in brain function that underlie this protracted state of dependence may provide a foundation for the escalation of withdrawal severity that develops over repeated opiate exposure, and increase the likelihood of progression from casual drug use to compulsive drug abuse.

Topics: Analgesics, Opioid; Animals; Anxiety; Avoidance Learning; Behavior, Animal; Disease Models, Animal; Male; Morphine; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Rats; Rats, Sprague-Dawley; Reflex, Startle; Substance Withdrawal Syndrome; Time Factors

Withdrawal from chronic opiates is associated with an increase in anxiogenic-like behaviours, but the anxiety profile in the morphine-dependent animals is not clear. Thus, one of the aims of the present study was to examine whether morphine-dependent rats would increase the expression of anxiogenic-like behaviours in novel and stressful conditions. Additionally, recent studies have shown that voluntary exercise can reduce anxiety levels in rodents. Therefore, another aim of this study was to examine the effect of voluntary exercise on the anxiety profile in both morphine-dependent animals and animals experiencing withdrawal. Rats were injected with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine over a period of 10 days in which they were also allowed voluntary exercise. Following these injections, anxiety-like behaviours were tested in the elevated plus-maze (EPM) model and the light/dark (L/D) box. We found reductions in time spent in, and entries into, the EPM open arms and reductions in time spent in the lit side of the L/D box for both sedentary morphine-dependent and withdrawn rats as compared to the sedentary control groups. The exercising morphine-dependent and withdrawn rats exhibited an increase in EPM open arm time and entries and L/D box lit side time as compared with the sedentary control groups. We conclude that voluntary exercise decreases the severity of the anxiogenic-like behaviours in both morphine-dependent and withdrawn rats. Thus, voluntary exercise could be a potential natural method to ameliorate some of the deleterious behavioural consequences of opiate abuse.

Topics: Analysis of Variance; Animals; Anxiety; Disease Models, Animal; Male; Maze Learning; Morphine; Morphine Dependence; Motor Activity; Naloxone; Narcotic Antagonists; Physical Conditioning, Animal; Rats; Rats, Wistar; Severity of Illness Index; Substance Withdrawal Syndrome; Time Factors

Recently, nuclear factor kappa B is indicated in the precipitation of opioid withdrawal syndrome. NF-κB activation is noted to control the transcription and biochemical activation of chemokines. Opioid receptor activation-linked chemokine stimulation is reported to mediate certain effects produced by prolonged opioid treatment. Ammonium pyrrolidine dithiocarbamate (APD) and RS 102895 are relatively selective inhibitors of NF-κB and C-C chemokine receptor 2, respectively.. The present study investigates the effect of APD and RS 102895 on morphine withdrawal signs in vitro and in vivo.. Morphine was administered twice daily for 5 days, following which a single day 6 injection of naloxone (8 mg/kg, i.p.) precipitated opioid withdrawal syndrome in mice. Withdrawal syndrome was quantitatively assessed in terms of withdrawal severity score and the frequency of jumping, rearing, fore paw licking and circling. Naloxone-induced contraction in morphine-withdrawn isolated rat ileum was employed as an in vitro model. An isobolographic study design was employed in the two models to assess potential synergistic activity between APD and RS 102895.. APD and RS 102895 dose-dependently attenuated naloxone-induced morphine withdrawal syndrome both in vivo and in vitro. APD was also observed to exert a synergistic interaction with RS 102895.. It is concluded that APD and RS 102895 attenuate morphine withdrawal signs possibly by a NF-κB and C-C chemokine receptor 2 activation pathway-linked mechanisms potentially in an interdependent manner.

Topics: Animals; Benzoxazines; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Female; Ileum; Male; Mice; Morphine; Naloxone; NF-kappa B; Piperidines; Pyrrolidines; Rats; Rats, Wistar; Receptors, CCR2; Substance Withdrawal Syndrome; Thiocarbamates

This study investigated the potential antinociceptive efficacy of a novel synthetic curcuminoid analogue, 2,6-bis-(4-hydroxy-3-methoxybenzylidene)cyclohexanone (BHMC), using chemical- and thermal-induced nociception test models in mice. BHMC (0.03, 0.1, 0.3 and 1.0 mg/kg) administered via intraperitoneal route (i.p.) produced significant dose-related inhibition in the acetic acid-induced abdominal constriction test in mice with an ID(50) of 0.15 (0.13-0.18) mg/kg. It was also demonstrated that BHMC produced significant inhibition in both neurogenic (first phase) and inflammatory phases (second phase) of the formalin-induced paw licking test with an ID(50) of 0.35 (0.27-0.46) mg/kg and 0.07 (0.06-0.08) mg/kg, respectively. Similarly, BHMC also exerted significant increase in the response latency period in the hot-plate test. Moreover, the antinociceptive effect of the BHMC in the formalin-induced paw licking test and the hot-plate test was antagonized by pre-treatment with the non-selective opioid receptor antagonist, naloxone. Together, these results indicate that the compound acts both centrally and peripherally. In addition, administration of BHMC exhibited significant inhibition of the neurogenic nociception induced by intraplantar injections of glutamate and capsaicin with ID(50) of 0.66 (0.41-1.07) mg/kg and 0.42 (0.38-0.51) mg/kg, respectively. Finally, it was also shown that BHMC-induced antinociception was devoid of toxic effects and its antinociceptive effect was associated with neither muscle relaxant nor sedative action. In conclusion, BHMC at all doses investigated did not cause any toxic and sedative effects and produced pronounced central and peripheral antinociceptive activities. The central antinociceptive activity of BHMC was possibly mediated through activation of the opioid system as well as inhibition of the glutamatergic system and TRPV1 receptors, while the peripheral antinociceptive activity was perhaps mediated through inhibition of various inflammatory mediators.

Topics: Analgesics; Animals; Curcumin; Cyclohexanones; Disease Models, Animal; Dose-Response Relationship, Drug; Inflammation; Inflammation Mediators; Inhibitory Concentration 50; Injections, Intraperitoneal; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Pain; Toxicity Tests, Acute

Drug addiction is an occurrence with physiological, psychological, and social outcomes. Repeated drug exposure causes neuronal adaptations and dependency. It has been shown that CaMKIIα enzyme contributes to morphine dependency. The locus coeruleus nucleus has been implied in the morphine withdrawal syndrome. This research focuses on the behavioral and molecular adaptations that occur in the locus coeruleus neurons in response to the chronic morphine exposure. Adult male Wistar rats were injected by morphine sulfate (10 mg/kg/s.c.) at an interval of 12 h for a period of nine subsequent days. On the tenth day, naloxone (1 mg/kg/i.p.) was injected 2 h after the morphine administration. Somatic withdrawal signs were investigated for 30 min. We concluded that the inhibition of CaMKIIα by administration of KN-93, the specific inhibitor of this enzyme, significantly attenuated some of the withdrawal signs. In molecular method, the expression of CaMKIIα protein has been enhanced in locus coeruleus of the morphine dependent rats. These findings indicate that CaMKIIα may be involved in the modulation of the naloxone-induced withdrawal syndrome, and treatment with KN-93 may have some effects on this system.

Topics: Animals; Benzylamines; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Disease Models, Animal; Gene Expression Regulation; Humans; Locus Coeruleus; Male; Microinjections; Morphine; Naloxone; Rats; Rats, Wistar; Substance Withdrawal Syndrome; Sulfonamides

Lithium is a major drug for bipolar disorder and mania. Recently, many studies have shown the neuroprotective effect of lithium in different models of neurodegenerative diseases. The present study was carried out to examine the effect of lithium in a rat model of neuropathic pain induced by partial sciatic nerve ligation and the possible role of opioid system in this effect. To do so, animals received acute injection of saline, lithium (5, 10 and 15 mg/kg,) and naloxone (1 mg/kg) or the combination of naloxone (1 mg/kg) with lithium (10 mg/kg) intraperitoneally on the testing days. Thermal hyperalgesia, mechanical and cold allodynia were measured on the days 3, 5, 7, 10 and 14 after surgery. Lithium decreased thermal hyperalgesia scores with dose of 5, 10 and 15 mg/kg and cold and mechanical allodynia scores with dose of 10 and 15 mg/kg, significantly. The opioid antagonist naloxone prevented the effect of lithium on thermal hyperalgesia and mechanical allodynia while it did not show any effect on the acetone-induced cold allodynia. Our results suggest that lithium can be considered as a therapeutic potential for the treatment of some aspects of neuropathic pain and that the opioid system may be involved in the lithium-induced attenuation of thermal hyperalgesia and mechanical allodynia.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Hyperalgesia; Lithium Chloride; Male; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Neuralgia; Neuroprotective Agents; Pain Measurement; Rats; Rats, Sprague-Dawley; Sciatic Nerve

This study describes the antinociceptive effects of μ-opioid agonists, d-Ala(2),N-Me-Phe(4),Gly(5)-ol-enkephalin (DAMGO) and morphine in a model of rat visceral pain in which nociceptive responses were triggered by 2% acetic acid intraperitoneal (i.p.) injections. DAMGO and morphine were administered i.p., to the same site where acetic acid was delivered or intracerebroventricularly (i.c.v.). The antinociceptive actions of i.p. versus i.c.v. administered DAMGO or morphine were evaluated in the late phase of permanent visceral nociceptive responses. Both compounds inhibited the nociceptive responses in a dose-dependent manner and exhibited more potent agonist activity after i.c.v. than i.p. administration. DAMGO and morphine showed comparable ED(50) values after i.p. injections. However, DAMGO was much stronger than morphine after central administration. Co-administration of the peripherally restricted opioid antagonist, naloxone methiodide (NAL-M), significantly attenuated the antinociceptive effects of i.p. DAMGO or morphine. On the other hand, i.c.v. injections of NAL-M partially antagonized the antinociceptive effect of i.p. morphine and failed to affect the antinociceptive action of i.p. DAMGO indicating the partial and pure peripheral antinociceptive effects of morphine and DAMGO, respectively. These results suggest the role of either central or peripheral μ-opioid receptors (MOR) in mediating antinociceptive effects of i.p. μ-opioid agonists in the rat late permanent visceral pain model which closely resembles the clinical situation.

Topics: Acetic Acid; Analgesics, Opioid; Analysis of Variance; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Interactions; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Morphine; Naloxone; Narcotic Antagonists; Quaternary Ammonium Compounds; Rats; Visceral Pain

Bile duct ligation (BDL) induces primary biliary cirrhosis characterized by cholestasis, impaired liver function and cognition including impairment of memory formation and anxiety-like behaviors. Endogenous opioid and acetylcholine levels are elevated in animal model of cholestasis. In addition, there is no data about the effects of interaction opioidergic and cholinergic systems of dorsal hippocampus (CA1) on amnesia-induced by cholestasis. Male mice weighing 25-35 g were used in this study. Cholestasis was induced by the ligation of the common bile duct. One-trial step-down and hole-board paradigms were used for the assessment of memory retrieval and anxiety-like behaviors respectively. All drugs injected intra-CA1. The data showed that cholestasis (24 days after BDL) decreased memory retrieval. Sole intra-CA1 injection of higher dose of mecamylamine (0.125, 0.25, 0.5 and 1 μg/mice) and scopolamine (0.125, 0.25, 0.5 1 and 2 μg/mice) but not all doses of naloxone (0.0125, 0.025 and 0.05 μg/mice) decreased memory retrieval in the sham operated BDL. The ineffective doses of naloxone (0.025 and 0.05 μg/mice), mecamylamine (0.5 μg/mice) and scopolamine (0.5 μg/mice) restored cholestasis-induced amnesia 24 days after BDL. Further, all cross co-administration ineffective doses of naloxone (0.0125 μg/mice), mecamylamine (0.125 μg/mice) and scopolamine (0.125 μg/mice) reversed cholestasis-induced amnesia. All doses of the drugs have no effect on exploratory behaviors. The data strongly revealed that synergistic effect between opioidergic and cholinergic systems of CA1 on the modulation of cholestasis-induced amnesia.

Topics: Amnesia; Animals; Animals, Outbred Strains; CA1 Region, Hippocampal; Cholestasis; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Exploratory Behavior; Male; Mecamylamine; Mental Recall; Mice; Microinjections; Muscarinic Antagonists; Naloxone; Narcotic Antagonists; Nicotinic Antagonists; Receptors, Opioid; Scopolamine

The leaves of Crassocephalum bauchiense have long been used in traditional Cameroonian medicine for the treatment of epilepsy, pain, inflammatory disorders, arthritis and intestinal pain.. In this study, we attempted to identify the possible antinociceptive action of the aqueous extract and the alkaloid fraction prepared from the leaves of Crassocephalum baucheiense.. Using acetic acid induced abdominal constrictions, formalin-, capsaisin- and glutamate-induced nociception, and hot plate assay procedures, the antinociceptive effects of the aqueous extract and the alkaloid fraction was assessed after oral administration in mice. Morphine sulfate was used as reference analgesic agent. Mice were submitted to the rota-rod task and open-field test in order to assess any non-specific muscle-relaxant or sedative effects of the extracts of Crassocephalum bauchiense. Male and female Swiss mice were used to assess acute toxicity of these extracts.. The aqueous extract and the alkaloid fraction of Crassocephalum bauchiense produced a significant antinociceptive effects in the acetic acid, formalin, glutamate, capsaicin and hot plate tests. These antinociceptive effects of Crassocephalum bauchiense were significantly attenuated by pretreatment with naloxone. The extracts of Crassocephalum bauchiense did not alter the locomotion of animals in the open-field or rotarod tests, which suggest a lack of a central depressant effect. The animals did not exhibit any acute toxicity to the aqueous extract and the alkaloid fraction, so it was not possible to calculate the LD(50).. The results confirm the popular use of Crassocephalum bauchiense as an antinociceptive, and contribute to the pharmacological knowledge of this species because it was shown that the aqueous extract and the alkaloid fraction of Crassocephalum bauchiense produced dose related antinociception in models of chemical and thermal nociception through mechanisms that involve an interaction with opioidergic pathway.

Topics: Acetic Acid; Administration, Oral; Alkaloids; Analgesics; Analgesics, Opioid; Animals; Asteraceae; Behavior, Animal; Capsaicin; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Formaldehyde; Glutamic Acid; Hot Temperature; Male; Mice; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Pain; Pain Threshold; Phytotherapy; Plant Extracts; Plant Leaves; Plants, Medicinal; Solvents; Time Factors; Water

Previous work demonstrated that both the opioid antagonist (-)-naloxone and the non-opioid (+)-naloxone inhibit toll-like receptor 4 (TLR4) signaling and reverse neuropathic pain expressed shortly after chronic constriction injury. The present studies reveal that the TLR4 contributes to neuropathic pain in another major model (spinal nerve ligation) and to long established (2-4 months) neuropathic pain, not just to pain shortly after nerve damage. Additionally, analyses of plasma levels of (+)-naloxone after subcutaneous administration indicate that (+)-naloxone has comparable pharmacokinetics to (-)-naloxone with a relatively short half-life. This finding accounts for the rapid onset and short duration of allodynia reversal produced by subcutaneous (+)-naloxone. Given that toll-like receptor 2 (TLR2) has also recently been implicated in neuropathic pain, cell lines transfected with either TLR4 or TLR2, necessary co-signaling molecules, and a reporter gene were used to define whether (+)-naloxone effects could be accounted for by actions at TLR2 in addition to TLR4. (+)-Naloxone inhibited signaling by TLR4 but not TLR2. These studies provide evidence for broad involvement of TLR4 in neuropathic pain, both early after nerve damage and months later. Additional, they provide further support for the TLR4 inhibitor (+)-naloxone as a novel candidate for the treatment of neuropathic pain.. These studies demonstrated that (+)-naloxone, a systemically available, blood-brain barrier permeable, small molecule TLR4 inhibitor can reverse neuropathic pain in rats, even months after nerve injury. These findings suggest that (+)-naloxone, or similar compounds, be considered as a candidate novel, first-in-class treatment for neuropathic pain.

Topics: Alkaline Phosphatase; Analysis of Variance; Animals; Cell Line, Transformed; Disease Models, Animal; Dose-Response Relationship, Drug; Humans; Injections, Subcutaneous; Lipopeptides; Lipopolysaccharides; Male; Naloxone; Narcotic Antagonists; Neuralgia; Pain Measurement; Rats; Rats, Sprague-Dawley; Signal Transduction; Spinal Cord Injuries; Time Factors; Toll-Like Receptor 4

Biphalin is an opioid linear octapeptide, which displays a broad affinity for all opioid receptors (μ, δ and κ), as well as exceptionally high antinociceptive activity. AM 94 is a biphalin analog and a selective agonist at μ and δ opioid receptors. This study investigated the antinociceptive profile of AM 94. All antinociception evaluations were made in adult male rats using the hot-plate test. AM 94 proved to induce greater and longer antinociception compared to biphalin following intracebroventricular (1 nmol/kg) and intravenous administration (1200 nmol/kg) as evaluated by % maximum possible effect (M.P.E.), when administered intracerebroventricularly and intravenously and sustained analgesia up to 210 min. The antinociceptive activities of biphalin and AM 94 were antagonized by naloxone (10mg/kg intraperitoneally). Our data suggest that AM 94 could be regarded as a novel pharmacologically active opioid compound for eliciting potent and sustained analgesia after central and peripheral administration.

Topics: Analgesics; Animals; Disease Models, Animal; Enkephalins; Injections, Intravenous; Injections, Intraventricular; Male; Naloxone; Narcotic Antagonists; Oligopeptides; Pain; Piperazines; Rats; Rats, Wistar; Time Factors

Pyrexia, algesia and inflammation are associated with several pathological conditions. Synthetic drugs available for the treatment of these conditions cause multiple unwanted effects. Several studies are ongoing worldwide to find natural healing agents with better safety profile. The current study was thus aimed at evaluating antipyretic, analgesic and anti-inflammatory activities of the methanolic extract of whole plant of V. betonicifolia (VBME).. VBME was employed to assess antipyretic activity in yeast induced hyperthermia. Analgesic profile was ascertained in acetic acid induced writhing, hot plat and tail immersion test. Nevertheless, the anti-inflammatory activity was tested in carrageenan induced paw edema and histamine induced inflammatory tests. BALB/c mice were used at test doses of 100, 200 and 300 mg/kg body weight intra peritoneally (i.p).. In yeast induced pyrexia, VBME demonstrated dose dependently (78.23%) protection at 300 mg/kg, similar to standard drug, paracetamol (90%) at 150 mg/kg i.p. VBME showed a dose dependent analgesia in various pain models i.e. acetic acid, hot plat and tail immersion having 78.90%, 69.96% and 68.58% protection respectively at 300 mg/kg. However, the analgesic action of VBME was completely antagonized by the injection of naloxone like opiate antagonists. Similarly carrageenan and histamine induces inflammation was significantly antagonized by VBME, 66.30% and 60.80% respectively at 300 mg/kg.. It is concluded that VBME has marked antipyretic, analgesic and anti-inflammatory activities in various animal models and this strongly supports the ethnopharmacological uses of Viola betonicifolia as antipyretic, analgesic and anti-inflammatory plant.

Topics: Acetaminophen; Acetic Acid; Analgesics; Animals; Anti-Inflammatory Agents; Antipyretics; Behavior, Animal; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Female; Fever; Histamine; Hot Temperature; Inflammation; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Pain; Phytotherapy; Plant Extracts; Tail; Viola; Yeasts

This study examines if injection of cobalt chloride (CoCl(2)) or antagonists of muscarinic cholinergic (atropine), μ(1)-opioid (naloxonazine) or 5-HT(1) serotonergic (methiothepin) receptors into the dorsal or ventral portions of the anterior pretectal nucleus (APtN) alters the antinociceptive effects of stimulating the retrosplenial cortex (RSC) in rats.. Changes in the nociceptive threshold were evaluated using the tail flick or incision pain tests in rats that were electrically stimulated at the RSC after the injection of saline, CoCl(2) (1 mM, 0.10 μL) or antagonists into the dorsal or ventral APtN.. The injection of CoCl(2), naloxonazine (5 μg/0.10 μL) or methiothepin (3 μg/0.10 μL) into the dorsal APtN reduced the stimulation-produced antinociception from the RSC in the rat tail flick test. Reduction of incision pain was observed following stimulation of the RSC after the injection of the same substances into the ventral APtN. The injection of atropine (10 ng/0.10 μL) or ketanserine (5 μg/0.10 μL) into the dorsal or ventral APtN was ineffective against the antinociception resulting from RSC stimulation.. μ(1)-opioid- and 5-HT(1)-expressing neurons and cell processes in dorsal and ventral APtN are both implicated in the mediation of stimulation-produced antinociception from the RSC in the rat tail flick and incision pain tests, respectively.

Topics: Animals; Atropine; Cerebral Cortex; Cobalt; Disease Models, Animal; Electric Stimulation Therapy; Male; Methiothepin; Naloxone; Pain Management; Pain Threshold; Rats; Rats, Wistar; Receptors, Opioid, mu; Receptors, Serotonin, 5-HT1

Artificial sweeteners are low-calorie substances used to sweeten a wide variety of foods. At present they are used increasingly not only by diabetics, but also by the general public as a mean of controlling the weight. This study was carried out to evaluate and compare antinociceptive activity of the artificial sweeteners, aspartame and sucrose and to study the mechanisms involved in this analgesic activity.. Forty eight white albino Wistar rats were divided into two groups of 24 rats each. Group 1 received sucrose and group 2 received aspartame solution ad libitum for 14 days as their only source of liquid. On 14(th) day, both groups of rats were divided into 3 subgroups having 8 rats each. Group Ia and IIa served as control. Group Ib and IIb were given naloxone and Ic and IIc received ketanserin, the opioid and serotonergic receptor antagonists, respectively.. Tail withdrawal latencies (tail flick analgesiometer) and paw licking/jumping latencies (Eddy's hot plate method) were increased significantly in both aspartame and sucrose group. The analgesia produced by aspartame was comparable with sucrose. The opioid receptor antagonist naloxone and the 5-HT(2A/2C) serotonergic receptor antagonist ketanserin partly reversed the antinociceptive effect of these sweeteners.. Thus, the artificial sweetening agent aspartame showed antinociceptive activity like sucrose in rats. Reduction in antinociceptive activity of aspartame and sucrose by opioid and serotoninergic antagonists demonstrate the involvement of both opioid and serotonergic system.

Topics: Analgesics, Non-Narcotic; Analysis of Variance; Animals; Aspartame; Disease Models, Animal; Ketanserin; Naloxone; Narcotic Antagonists; Pain; Rats; Rats, Wistar; Serotonin Antagonists; Sucrose

Babassu is the common Brazilian name of Orbignya speciosa Mart. (Arecaceae). The fruits are used for several disorders. In the present study, the antinociceptive effects of the ethanol extract (EE) and dichloromethane fraction (DF) obtained from leaves were investigated, as well as apigenin using nociception models (acetic acid-induced abdominal writhing, formalin, and hot plate).. Mice were treated with EE, DF (10, 30, and 100mg/kg, p.o.), apigenin (1mg/kg, p.o.), morphine (5mg/kg, s.c.), acetylsalicylic acid (100mg/kg, p.o.) or vehicle (0.1 ml, p.o.). The EE and DF reduced the contortions induced by acetic acid. Both also reduced the licking response in the formalin model. In the hot plate model, the antinociceptive effects were, at least, equal to that shown by morphine. To elucidate the antinociceptive mechanism of action of EE, DF, and apigenin the animals were pre-treated with atropine (nonselective muscarinic receptor antagonist, 1mg/kg, s.c.), naloxone (opioid receptor antagonist, 1mg/kg, s.c.), l-nitro arginine methyl ester (L-NAME, nitric oxide synthase inhibitor, 3mg/kg, s.c.) or mecamylamine (nicotinic receptor antagonist, 2mg/kg, s.c.) and evaluated in the hot plate model.. The antinociception produced by DF was abolished by atropine, naloxone or mecamylamine. The effect of apigenin was significantly blocked by atropine or naloxone.. The results obtained indicated that EE and DF have antinociceptive activity that is mediated, at least in part, by opioid and cholinergic systems. This effect can be attributed to the presence of apigenin, a flavonoid in the dichloromethane fraction.

Topics: Analgesics; Animals; Apigenin; Arecaceae; Aspirin; Atropine; Brazil; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Mecamylamine; Mice; Morphine; Naloxone; Pain; Plant Extracts; Plant Leaves

Ultra-low dose naloxone has been shown to restore the antinociceptive effect of morphine in pertussis toxin (PTX)-treated rats by suppressing spinal microglia activation and inhibiting inflammatory cytokine expression. This study was further investigated the mechanism by which ultra-low dose naloxone promotes analgesia in pertussis toxin-treated rats.. Male Wistar rats were implanted with an intrathecal (i.t.) catheter and injected either saline or PTX (1 μg). Four days later, rats randomly received either saline, or ultra-low dose naloxone, or recombinant rat interleukin-10 (rrIL-10) (1 μg) injection followed by saline or morphine (10 μg) 30 min later. In some experiments, mouse anti-rat IL-10 antibody (10 μg) was injected intrathecally into PTX injected rats daily on days 4, 5, 6, and 7. On day 7, ultra-low dose naloxone was given 1h after antibody injection with or without subsequent morphine injection.. PTX injection induced notable thermal hyperalgesia and mechanical allodynia. Injection of ultra-low dose naloxone preserved the antinociceptive effect of morphine in PTX-treated rats and associated an increasing of IL-10 protein expression. Intrathecal injection rrIL-10 alone or in combination with morphine, not only reversed mechanical allodynia but also partially restored the antinociceptive effect of morphine; injection of anti-rat IL-10 antibody attenuated the effect of morphine plus ultra-low dose naloxone on mechanical allodynia and completely inhibited the antinociceptive effect of morphine.. These results indicate that intrathecal ultra-low dose naloxone induces IL-10 expression in spinal neuron and microglia, which suppresses PTX-induced neuroinflammation and restores the antinociceptive effect of morphine.

Topics: Analgesics, Opioid; Animals; Antibodies; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Inflammation; Interleukin-10; Male; Mice; Microglia; Morphine; Naloxone; Narcotic Antagonists; Neurons; Pain; Pertussis Toxin; Random Allocation; Rats; Rats, Wistar; Recombinant Proteins; Spinal Cord; Up-Regulation

Opioid receptors are involved in reinstatement of alcohol seeking, yet there are no reports of their role in reacquisition of an extinguished alcohol seeking response. Here we investigated the effects of the opioid antagonist naloxone on reacquisition and compared these effects with those on acquisition. Rats were trained, extinguished, then retrained to respond for alcoholic beer. Upon retraining, a second group of rats with no prior experience with the contingency between response and reinforcer was trained under the same conditions. Reacquisition was faster than acquisition. Systemic injection of naloxone (1.25 or 5 mg/kg) reduced reacquisition but had no effect on acquisition. These results suggest that reacquisition and acquisition of alcohol seeking have dissociable neurochemical substrates.

Topics: Alcohol-Related Disorders; Analysis of Variance; Animals; Conditioning, Operant; Disease Models, Animal; Dose-Response Relationship, Drug; Extinction, Psychological; Male; Naloxone; Narcotic Antagonists; Rats; Rats, Long-Evans; Reaction Time; Self Administration

The efficacy of opioids in neuropathic pain is still controversial. Earlier studies have suggested that N-methyl-D-aspartate (NMDA) receptor binding can be affected by opioids and vice versa. The present study aims to explore the interactions between NMDA and opioid receptors using various combinations of drugs acting on these receptors.. We used an animal model of sciatic nerve ligation to induce neuropathic pain, and a hot-plate test was used to assess pain response.. It was observed that NMDA and naloxone increased the pain response. Ketamine reduced the pain response, which was further reduced when ketamine was administered in combination with naloxone, but not with NMDA, thus highlighting the activity of the NMDA receptor system. In addition, morphine was also found to increase latency to hind-paw lick, which was further reduced when given in combination with naloxone. Furthermore, triple drug combinations using ketamine+morphine+naloxone and ketamine+NMDA+naloxone demonstrated some significant interactions at these receptors.. Thus, our study establishes that neuropathic pain can probably be overcome using higher doses of opioids, and there exists some intimate relationships between NMDA and opioid systems that lead to pain modulation.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Excitatory Amino Acid Agonists; Ketamine; Male; Morphine; N-Methylaspartate; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid; Sciatic Neuropathy

Carvacrol (5-isopropyl-2-methylphenol) is a monoterpenic phenol which is present in the essential oil of oregano and thyme. We have investigated the behavioural effects of carvacrol in animal models of pain, such as acetic acid-induced abdominal constriction, formalin and hot-plate tests in mice. The spontaneous motor activity of animals treated with carvacrol was investigated using open-field and rotarod tests.. Carvacrol was administered orally, at single doses of 50 and 100 mg/kg while indometacin (5 mg/kg), morphine (7.5 mg/kg) and diazepam (2 mg/kg) were used as standard drugs. Naloxone (1 mg/kg) and l-arginine (150 mg/kg) were used to elucidate the possible antinociceptive mechanism of carvacrol on acetic acid-induced abdominal constriction and formalin tests.. The results showed that carvacrol produced significant inhibitions on nociception in the acetic acid-induced abdominal constriction, formalin and hot-plate tests. In the open-field and rotarod tests carvacrol did not significantly impair the motor performance. The effect of the highest dose of carvacrol in mice in the acetic acid-induced abdominal constriction and formalin tests were not reversed by naloxone or l-arginine.. Based on these results, it has been suggested that carvacrol presents antinociceptive activity that may not act through the opioid system nor through inhibition of the nitric oxide pathway.

Topics: Abdominal Pain; Acetic Acid; Analgesics; Animals; Arginine; Behavior, Animal; Cymenes; Disease Models, Animal; Formaldehyde; Hot Temperature; Male; Mice; Mice, Inbred Strains; Monoterpenes; Motor Activity; Naloxone; Narcotic Antagonists; Oils, Volatile; Origanum; Pain; Phytotherapy; Plant Extracts; Thymus Plant

H2S is a novel type of endogenous neural regulatory factor and gaseous mediator. Exogenous H2S can increase heroin-induced learning and memory damage in rat and alleviates heroin-induced rat hippocampus damage through antioxidant and anti-apoptosis effects.. Aim of this study was to identify whether hydrogen sulfide (H2S) protects heroin withdrawal rat is related with adenylate cyclase (AC)-cAMP-protein kinase A (PKA)-cAMP response element-binding protein (CREB) signaling pathway in heroin-dependent rat's nucleus accumbens or not.. Male Spragne-Dawley rats were randomly divided into Saline + Saline group, Saline + sodium hydrosulfide (NaHS) group, Saline + Heroin group, NaHS + Heroin group according to the principle of increasing heroin dosage day by day, with the establishment of heroin-naloxone-induced withdrawal symptoms determined at day 10. Then the levels of H2S and cAMP and AC and PKA activities were assayed, and the level of phosphorylated CREB (p-CREB), the levels of phosphorylated N-methyl-D-aspartate receptor 1 subunit (p-NR1), phosphorylated N-methyl-D-aspartate receptor 2a subunit (p-NR2A) and phosphorylated N-methyl-D-aspartate receptor 2b subunit (p-NR2B) were assayed in nucleus accumbens.. Exogenous H2S can alleviate heroin withdrawal symptoms by increasing the level of H2S level in nucleus accumbens. Exogenous H2S can decrease the high activities of AC, PKA and the high levels of cAMP, p-CREB caused by heroin. Furthermore, exogenous H2S can decrease the high level of p-NR1 and can increase the low levels of p-NR2A and p-NR2B caused by heroin. It is surprising that exogenous H2S treatment alone was able to raise the activities of AC and PKA as well as the levels of cAMP, p-CREB, p-NR1, p-NR2A and p-NR2B.. Exogenous H2S decreases naloxone-precipitated withdrawal signs, maybe through decreasing AC/cAMP/PKA/CREB/NMDR signaling pathway in heroin-dependent rats' nucleus accumbens.

Topics: Adenylyl Cyclases; Animals; Cyclic AMP; Cyclic AMP Response Element-Binding Protein; Cyclic AMP-Dependent Protein Kinases; Disease Models, Animal; Heroin Dependence; Male; Naloxone; Narcotic Antagonists; Nucleus Accumbens; Phosphorylation; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Second Messenger Systems; Substance Withdrawal Syndrome; Sulfides

Cholestasis is associated with analgesia. The histamine H(2) receptors control pain perception. The involvement of histamine H(2) receptors on modulation of nociception in a model of elevated endogenous opioid tone, cholestasis, was investigated in this study using zolantidine and cimetidine as two H(2) receptor antagonists and dimaprit as a selective H(2) receptor agonist. Cholestasis was induced by ligation of the main bile duct using two ligatures and transsection of the duct at the midpoint between them. A significant increase in tail-flick latencies was observed in cholestatic rats compared to non-cholestatic rats. Administration of zolantidine (10, 20 and 40 mg/kg) and cimetidine (25, 50 and 100 mg/kg) in the cholestatic group significantly increased tail-flick latencies while dimaprit (10 and 20 mg/kg) injection in the cholestatic group decreased tail-flick latencies compared to the saline treated cholestatic group. Antinociception produced by injection of zolantidine and cimetidine in cholestatic rats was attenuated by co-administration of naloxone. Drug injection in non-cholestatic rats did not alter tail-flick latencies compared to the saline treated rats at any of the doses. At the doses used here, none of the drugs impaired motor coordination as revealed by the rota rod test. These data show that the histamine H(2) receptor system may be involved in the regulation of nociception during cholestasis. According to the hypothesis that increasing the nociception threshold in cholestasis may lead to a decrease in the perception of pruritus, the provision of the drugs that increase the threshold to nociception may be a novel approach to the treatment of cholestatic pruritus.

Topics: Analgesia; Animals; Benzothiazoles; Cholestasis; Cimetidine; Dimaprit; Disease Models, Animal; Histamine H2 Antagonists; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Perception; Phenoxypropanolamines; Piperidines; Rats; Rats, Wistar; Receptors, Histamine H2; Rotarod Performance Test

We evaluated the effectiveness of intrathecal antagonists of α1- (WB4101) and α2- (idazoxan) adrenoceptors and serotonergic (methysergide), opioid (naloxone), muscarinic (atropine), GABA(A) (bicuculline) and GABA(B) (phaclofen) receptors in blocking 2- or 100-Hz electroacupuncture (EA)-induced analgesia (EAIA) in the rat tail-flick test. EA was applied bilaterally to the Zusanli and Sanyinjiao acupoints in lightly anesthetized rats. EA increased tail-flick latency, where the effect of 2-Hz EA lasted longer than that produced by 100-Hz EA. The 2-Hz EAIA was inhibited by naloxone or atropine, was less intense and shorter after WB4101 or idazoxan, and was shorter after methysergide, bicuculline, or phaclofen. The 100-Hz EAIA was less intense and shorter after naloxone and atropine, less intense and longer after phaclofen, shorter after methysergide or bicuculline, and remained unchanged after WB4101 or idazoxan. We postulate that the intensity of the effect of 2-Hz EA depends on noradrenergic descending mechanisms and involves spinal opioid and muscarinic mechanisms, whereas the duration of the effect depends on both noradrenergic and serotonergic descending mechanisms, and involves spinal GABAergic modulation. In contrast, the intensity of 100-Hz EAIA involves spinal muscarinic, opioid, and GABA(B) mechanisms, while the duration of the effects depends on spinal serotonergic, muscarinic, opioid, and GABA(A) mechanisms.. The results of this study indicate that 2- and 100-Hz EA induce analgesia in the rat tail-flick test activating different descending mechanisms at the spinal cord level that control the intensity and duration of the effect. The adequate pharmacological manipulation of such mechanisms may improve EA effectiveness for pain management.

Topics: Adjuvants, Anesthesia; Adrenergic alpha-Antagonists; Analgesia; Anesthetics, Intravenous; Animals; Atropine; Baclofen; Bicuculline; Biophysics; Dioxanes; Disease Models, Animal; Electroacupuncture; GABA Agents; Male; Methysergide; Models, Biological; Multivariate Analysis; Naloxone; Narcotic Antagonists; Pain; Pain Management; Pain Measurement; Rats; Rats, Wistar; Reaction Time; Serotonin Antagonists; Tail; Thiopental; Time Factors

Ischemia-reperfusion injury plays an important role in the development of primary allograft failure after heart transplantation. Inhibition of the Na+/H+ exchanger is one of the most promising therapeutic strategies for treating ischemia-reperfusion injury. Here we have characterized the cardioprotective efficacy of zoniporide and the underlying mechanisms in a model of myocardial preservation using rat isolated working hearts.. Rat isolated hearts subjected to 6 h hypothermic (1-4°C) storage followed by 45 min reperfusion at 37°C were treated with zoniporide at different concentrations and timing. Recovery of cardiac function, levels of total and phosphorylated protein kinase B, extracellular signal-regulated kinase 1/2, glycogen synthase kinase-3β and STAT3 as well as cleaved caspase 3 were measured at the end of reperfusion. Lactate dehydrogenase release into coronary effluent before and post-storage was also measured.. Zoniporide concentration-dependently improved recovery of cardiac function after reperfusion. The functional recovery induced by zoniporide was accompanied by up-regulation of p-extracellular signal-regulated kinase 1/2 and p-STAT3, and by reduction in lactate dehydrogenase release and cleaved caspase 3. There were no significant differences in any of the above indices when zoniporide was administered before, during or after ischemia. The STAT3 inhibitor, stattic, abolished zoniporide-induced improvements in functional recovery and up-regulation of p-STAT3 after reperfusion.. Zoniporide is a potent cardioprotective agent and activation of STAT3 plays a critical role in the cardioprotective action of zoniporide. This agent shows promise as a supplement to storage solutions to improve preservation of donor hearts.

Topics: Animals; Cardiotonic Agents; Cardiovascular Physiological Phenomena; Caspase 3; Cyclic S-Oxides; Disease Models, Animal; Dose-Response Relationship, Drug; Guanidines; Heart; Heart Transplantation; L-Lactate Dehydrogenase; Male; Mitogen-Activated Protein Kinase 3; Myocardium; Naloxone; Narcotic Antagonists; Pyrazoles; Rats; Rats, Wistar; Reperfusion Injury; STAT3 Transcription Factor

Previous studies have implicated the bed nucleus of the stria terminalis, central nucleus of the amygdala and the shell of the nucleus accumbens (collectively called the extended amygdala) as playing an important role in mediating the aversive emotion associated with opioid withdrawal. The paraventricular nucleus of the thalamus (PVT) provides a very dense input to the extended amygdala, and the PVT is densely innervated by orexin neurons, which appear to be involved in producing some of the physical and emotional effects associated with morphine withdrawal. In the present study, we confirm that the PVT is densely innervated by orexin fibers, whereas the regions of the extended amygdala associated with the effects of morphine withdrawal are poorly innervated. Microinjections of the orexin-1 receptor (OX1R) antagonist SB334867 or the orexin-2 receptor (OX2R) antagonist TCSOX229 at doses of 5.0 or 15.0 microg into the PVT region did not affect the acquisition of the conditioned place aversion (CPA) nor the physical effects produced by naloxone-precipitated morphine withdrawal. In contrast, microinjections of TCSOX229 (15.0 microg) in the PVT region significantly attenuated the expression of naloxone-induced CPA while microinjections of SB334867 at the same dose had no effect. The results from these experiments indicate a role for OX2R in the PVT on the expression of CPA associated with morphine withdrawal. Orexins may mediate the aversive effects of morphine withdrawal by engaging the extended amygdala indirectly through the action of orexins on the PVT.

Topics: Animals; Avoidance Learning; Benzoxazoles; Conditioning, Classical; Disease Models, Animal; Intracellular Signaling Peptides and Proteins; Male; Microinjections; Midline Thalamic Nuclei; Morphine; Naloxone; Naphthyridines; Neuropeptides; Orexin Receptors; Orexins; Rats; Rats, Sprague-Dawley; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; Substance Withdrawal Syndrome; Urea

Alum is the most commonly used adjuvant for human vaccination but is a poor inducer of cell mediated immunity and T helper 1 (Th1) responses. We have previously shown that naloxone (NLX), which is a general opioid antagonist, acts as an effective adjuvant in enhancing vaccine-induced cellular immunity and Th1 immune responses. Here, we tested the efficacy of an alum-NLX mixture, as a new adjuvant, in the induction of humoral and cellular immunity in response to endotoxin-removed lysate (ERL) of Salmonella typhimurium (S. typhimurium) as a model vaccine. BALB/c mice were divided into five vaccination groups. Mice in the experimental groups received either the ERL vaccine alone or in combination with the adjuvant alum, NLX or the alum-NLX mixture. Mice in the negative control group received phosphate-buffered saline. All mice were immunized on days 0 and 7. Two weeks after the last immunization, immune responses to S. typhimurium were assessed. Our results indicate that including the alum-NLX mixture as an adjuvant during vaccination increased the ability of the ERL vaccine to enhance lymphocyte proliferation, shifted the immune response toward a Th1 profile and increased S. typhimurium-specific IgG, IgG2a and the ratio of IgG2a to IgG1. This resulted in improved protective immunity against S. typhimurium. In conclusion, administering an alum-NLX mixture adjuvant in combination with the ERL vaccine enhances both humoral and cellular immunity, and shifts the immune response to a Th1 pattern.

Topics: Adjuvants, Immunologic; Alum Compounds; Animals; Antibodies, Bacterial; Cell Proliferation; Cytokines; Disease Models, Animal; Endotoxins; Immunoglobulin G; Lethal Dose 50; Liver; Lymphocyte Activation; Male; Mice; Mice, Inbred BALB C; Naloxone; Salmonella Infections; Salmonella typhimurium; Salmonella Vaccines; Spleen

Emilia sonchifolia (L.) DC. (Asteraceae) is a medicinal plant traditionally used in Brazilian folk medicine to treat asthma, fever, cuts, wounds and rheumatism. This study was conducted to establish the antinociceptive properties of hydroethanolic extract from aerial parts of Emilia sonchifolia in mice using chemical and thermal models of nociception.. To evaluate the antinociceptive effect of Emilia sonchifolia hydroethanolic extract (EsHE) administered by oral route, peripheral (acetic acid-induced abdominal writhing and formalin), spinal (tail flick) and supra-spinal (hot plate) behavioral models of acute pain were used. High-performance liquid chromatography (HPLC) was used to determine the fingerprint chromatogram of the EsHE.. The EsHE at test doses of 100 and 300 mg/kg, p.o. clearly demonstrated antinociceptive activity in all tests. The extract had a stronger antinociceptive effect than morphine. Administration of the opioid receptor antagonist, naloxone, completely inhibited the antinociceptive effect induced by EsHE (100mg/kg). The presence of phenolic compounds in the extract of Emilia sonchifolia was confirmed using HPLC.. The extract of Emilia sonchifolia markedly exhibits opioid-mediated anti-nociceptive activity action in mice. Thus, may be useful in the treatment of inflammatory hyperalgesic disorders, which supports previous claims of its traditional use.

Topics: Acetic Acid; Analgesics, Opioid; Animals; Asteraceae; Behavior, Animal; Brazil; Disease Models, Animal; Formaldehyde; Hot Temperature; Male; Medicine, Traditional; Mice; Morphine; Naloxone; Pain; Phenols; Phytotherapy; Plant Components, Aerial; Plant Extracts

This study aimed to investigate the effect of opium dependency on the healing of third-degree burns in rats.. Twenty-four rats were randomly divided to experimental and control groups. In the experimental group, opium was added to the drinking water for 21 days at increasing concentrations. The control group did not receive opium. To prove dependency on opium in the rats, naloxone was injected intraperitoneally. Full-thickness burn wounds were inflicted by applying an iron cuboid preheated to 94°C to the flank of all rats for 20 s. On day 14 after burn injury, full-thickness biopsies were taken. Blind histopathologic evaluation was performed to assess length and thickness of the re-epithelialization area, number of neutrophils, fibroblasts, mononuclear cells and new vessels, and percentage of tissue in repair (neutrophilic exudate, and granulation and fibrous tissue). Findings were analyzed using SPSS software.. The wound surface area was 95 ± 43.35 mm(2) in the control group and 120.4 ± 50.12 mm(2) in the experimental group (p = 0.224). The findings show that opium dependency has no significant effect on the healing of burn wounds in rats except for the number of monocytes on day 14 (p < 0.05).. Morphine dependency does not seem to be as effective on third-degree burn healing.

Topics: Animals; Burns; Disease Models, Animal; Female; Fibroblasts; Leukocytes, Mononuclear; Naloxone; Narcotic Antagonists; Neutrophils; Opioid-Related Disorders; Rats; Rats, Sprague-Dawley; Wound Healing

Opioids produce analgesic effects, and extended use can produce physical dependence in both humans and animals. Dependence to opiates can be demonstrated by either termination of drug administration or through precipitation of the withdrawal syndrome by opiate antagonists. Key features of the opiate withdrawal syndrome include hyperalgesia, anxiety, and autonomic signs such as diarrhea. The rostral ventromedial medulla (RVM) plays an important role in the modulation of pain and for this reason, may influence withdrawal-induced hyperalgesia. The mechanisms that drive opiate withdrawal-induced hyperalgesia have not been elucidated. Here, rats made dependent upon morphine received naloxone to precipitate withdrawal. RVM microinjection of lidocaine, kynurenic acid (excitatory amino acid antagonist) or YM022 (CCK2 receptor antagonist) blocked withdrawal-induced hyperalgesia. Additionally, these treatments reduced both somatic and autonomic signs of naloxone-induced withdrawal. Spinal application of ondansetron, a 5HT3 receptor antagonist thought to ultimately be engaged by descending pain facilitatory drive, also blocked hyperalgesia and somatic and autonomic features of the withdrawal syndrome. These results indicate that the RVM plays a critical role in mediating components of opioid withdrawal that may contribute to opioid dependence.. Manipulations targeting these descending pathways from the RVM may diminish the consequences of prolonged opioid administration-induced dependence and be useful adjunct strategies in reducing the risk of opioid addiction.

Topics: Animals; Disease Models, Animal; Efferent Pathways; Hyperalgesia; Male; Medulla Oblongata; Morphine Dependence; Naloxone; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome

Antidepressants are one of the recommended treatments for neuropathic pain. However, their analgesic action remains unpredictable, and there are no selection criteria for clinical use. Better knowledge of their mechanism of action could help highlight differences underlying their unequal efficacy.. We compared the activity of a tricyclic antidepressant (clomipramine) with selective 5-HT and noradrenaline reuptake inhibitors (milnacipran and duloxetine) in streptozocin-induced diabetic and chronic constriction nerve injury-induced neuropathic rats, after repeated injections. We looked for an opioidergic mechanism in their action.. Abolition of mechanical hyperalgesia was observed in mononeuropathic rats after five injections of clomipramine (5 mg·kg(-1) , s.c.) and milnacipran (10 or 20 mg·kg(-1) , i.p.) and in diabetic rats after clomipramine. An additional antinociceptive effect was obtained with five injections of duloxetine (3 mg·kg(-1) , i.p.) in both models and milnacipran (10 mg·kg(-1) , i.p.) in diabetic rats. These effects were observed with plasma antidepressant concentrations similar to those found in patients treated for neuropathic pain. Naloxone (1 mg·kg(-1) , i.v.) only suppressed the anti-hyperalgesic effects of clomipramine in both models of pain and of milnacipran in the traumatic model.. The opioid system appears to be involved in the mechanism of action of antidepressants that only have an anti-hyperalgesic effect but not in those that have a stronger (i.e. antinociceptive) effect. These differences between the antidepressants occurred whatever the aetiology of the neuropathy and, if confirmed in clinical trials, could be used to decide which antidepressant is administered to a patient with neuropathic pain.

Topics: Analgesics; Animals; Antidepressive Agents; Clomipramine; Cyclopropanes; Diabetes Mellitus, Experimental; Disease Models, Animal; Duloxetine Hydrochloride; Hyperalgesia; Male; Milnacipran; Naloxone; Neuralgia; Rats; Rats, Sprague-Dawley; Thiophenes

Opioid preconditioning against ischemia reperfusion injury has been well studied in myocardial and neuronal tissues. The objective of this study was to determine whether remifentanil could attenuate hepatic injury and to investigate the mechanisms.. A rat model of hepatic ischemia reperfusion injury and a hepatocyte hypoxia reoxygenation (HR) injury model were used, respectively, in two series of experiments. Remifentanil was administered before ischemia or hypoxia and the experiments were repeated with previous administration of naloxone, L-arginine and N-ω-nitro-L-arginine methyl ester, a nonselective opioid receptor antagonist, a nitric oxide donor, and nitric oxide synthase (NOS) inhibitor, respectively. Serum aminotransferase, cytokines, and hepatic lipid peroxidation were measured. Histopathology examination and apoptotic cell detection were assessed. For the in vitro study, cell viability, intracellular nitric oxide, apoptosis, and NOS expression were evaluated.. Remifentanil and L-arginine pretreatment reduced concentrations of serum aminotransferases and cytokines, decreased the concentrations of hepatic malondialdehyde and myeloperoxidase activity, and increased superoxide dismutase, nitric oxide, and inducible NOS expression in vivo. Decreased histologic damage and apoptosis were also seen in these two groups. These changes were prevented by previous administration of N-ω-nitro-L-arginine methyl ester but not naloxone. There was an increase in inducible NOS protein expression but not endogenous NOS in remifentanil and L-arginine pretreated groups compared with control, naloxone, and N-ω-nitro-L-arginine methyl ester groups.. Pretreatment with remifentanil can attenuate liver injury both in vivo and in vitro. Inducible NOS but not opioid receptors partly mediate this effect by exhausting reactive oxygen species and attenuating the inflammatory response.

Topics: Analgesics, Opioid; Animals; Arginine; Blotting, Western; Cell Survival; Cytokines; Disease Models, Animal; Ischemic Preconditioning; Lipid Peroxidation; Liver; Liver Diseases; Male; Naloxone; Narcotic Antagonists; Nitric Oxide Synthase; Piperidines; Rats; Rats, Sprague-Dawley; Remifentanil; Reperfusion Injury; Transaminases

The prevalence of opioid abuse and dependence has been on the rise in just the past few years. Animal studies indicate that extended access to heroin produces escalation of intake over time, whereas stable intake is observed under limited-access conditions. Escalation of drug intake has been suggested to model the transition from controlled drug use to compulsive drug seeking and taking. Here, we directly compared the pattern of heroin intake in animals with varying periods of heroin access. Food intake was also monitored over the course of escalation. Rats were allowed to lever press on a fixed-ratio 1 schedule of reinforcement to receive intravenous infusions of heroin for 1, 6, 12, or 23h per day for 14 sessions. The results showed that heroin intake in the 12 and 23h groups markedly increased over time, whereas heroin intake in the 1h group was stable. The 6h group showed a significant but modest escalation of intake. Total heroin intake was similar in the 12 and 23h groups, but the rate of heroin self-administration was two-fold higher in the 12h group compared with the 23h group. Food intake decreased over sessions only in the 12h group. The 12 and 23h groups showed marked physical signs of naloxone-precipitated withdrawal. These findings suggest that 12h heroin access per day may be the optimal access time for producing escalation of heroin intake. The advantages of this model and the potential relevance for studying drug addiction are discussed.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Drug-Seeking Behavior; Heroin; Heroin Dependence; Humans; Male; Naloxone; Rats; Rats, Wistar; Self Administration; Substance Withdrawal Syndrome; Time Factors

We defined the nature of the pharmacological interaction between ginsenosides and morphine in a nociceptive state and clarified the role of the different types of opioid receptor in the effects of ginsenosides. An intrathecal catheter was placed in male Sprague-Dawley rats. Pain was induced by formalin injection into the hindpaw. Isobolographic analysis was used to evaluate drug interactions. Furthermore, a nonselective opioid receptor antagonist (naloxone), a μ opioid receptor antagonist (CTOP), a δ opioid receptor antagonist (naltrindole), and a κ opioid receptor antagonist (GNTI) were given intrathecally to verify the involvement of the opioid receptors in the antinociceptive effects of ginsenosides. Both ginsenosides and morphine produced antinociceptive effects in the formalin test. Isobolographic analysis revealed a synergistic interaction after intrathecal delivery of the ginsenosides-morphine mix. Intrathecal CTOP, naltrindole, and GNTI reversed the antinociceptive effects of ginsenosides. RT-PCR indicated that opioid receptors' mRNA was detected in spinal cord of naïve rats and the injection of formalin had no effect on the expression of opioid receptors' mRNA. Taken together, our results indicate synergistic antinociception following intrathecal coadministration of a ginsenosides/morphine mix in the formalin test, and that μ, δ, and κ opioid receptors are involved in the antinociceptive mechanism of ginsenosides.. This article concerns the antinociceptive activity of ginsenosides, which increases antinociception by morphine. Thus, a spinal combination of ginsenosides and morphine may be useful in the management of acute pain as well as facilitated state pain.

Topics: Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Fixatives; Formaldehyde; Gene Expression Regulation; Ginsenosides; Injections, Spinal; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Reflex; Somatostatin

Pain is a major cause of distress, both physical and psychological. There is a continuous search for new pharmacologically active analgesic agents with minor adverse effects. Recently, the synthesis of (-)-(2S,6S)-(6-ethyl-tetrahydropyran-2-yl)-formic acid [tetrahydropyran derivative (TD)] was described. The objective of this study was to investigate antinociceptive effects of TD. Its activity was compared with the activity of morphine. The effects of TD and morphine were evaluated in models of inflammatory and noninflammatory pain. TD (6-1200 μmol/kg, intraperitoneally) significantly reduced the nociceptive effects induced by acetic acid or formalin in mice. TD also demonstrated an antinociceptive effect in the tail-flick and hot-plate model. The opioid receptor antagonist, naloxone (at 15 μmol/kg, intraperitoneally), reversed the antinociceptive activity of TD in all the models evaluated. Morphine and TD induced tolerance in mice. However, the onset of tolerance to TD was delayed compared with that induced by morphine. These results indicate that TD develops significant antinociceptive activity and, at least part of its effects seems to be mediated by the opioid system.

Topics: Acute Pain; Analgesics; Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Formates; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Pyrans

The present study explored the interaction between histaminergic and opioidergic systems at the level of the hippocampus in modulation of orofacial pain by intra-hippocampal microinjections of histamine, pyrilamine (an antagonist of histamine H(1) receptors), ranitidine (an antagonist of histamine H(2) receptors), morphine (an opioid receptor agonist) and naloxone (an opioid receptor antagonist) in separate and combined treatments. Orofacial pain was induced by subcutaneous (sc) injection of formalin (50 μl, 1%) in the upper lip region and the time spent face rubbing was recorded in 3 min blocks for 45 min. Formalin (sc) produced a marked biphasic (first phase: 0-3 min, second phase: 15-33 min) pain response. Histamine and morphine suppressed both phases of pain. Histamine increased morphine-induced antinociception. Pyrilamine and ranitidine had no effects when used alone, whereas pretreatments with pyrilamine and ranitidine prevented histamine- and morphine-induced antinociceptive effects. Naloxone alone non-significantly increased pain intensity and inhibited the antinociceptive effects of morphine and histamine. The results of the present study indicate that at the level of the hippocampus, histamine through its H(1) and H(2) receptors, mediates orofacial region pain. Moreover, morphine via a naloxone-reversible mechanism produces analgesia. In addition, both histamine H(1) and H(2) receptors, as well as opioid receptors may be involved in the interaction between histamine and morphine in producing analgesia.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Facial Pain; Formaldehyde; Hippocampus; Histamine; Male; Morphine; Naloxone; Pyrilamine; Rats; Rats, Wistar; Receptors, Histamine H1; Receptors, Histamine H2

Previous studies suggest that binge eating sugar leads to behavioral and neurochemical changes similar to those seen with drug addiction, including signs of opiate-like withdrawal. Studies are emerging that show multiple neurochemical and behavioral indices of addiction when animals overeat a fat-rich diet. The goal of the present study was to utilize liquid and solid diets high in sugar and fat content to determine whether opiate-like withdrawal is seen after binge consumption of these diets in Sprague-Dawley rats. Control groups were given ad libitum access to the sweet-fat food or standard chow. All rats were then given a battery of tests to measure signs of opiate-like withdrawal, which included somatic signs of distress, elevated plus-maze anxiety, and locomotor hypoactivity. Neither naloxone-precipitated (3 mg/kg) nor deprivation-induced withdrawal was observed in rats that were maintained on a nutritionally complete pelleted sweet-fat diet or a sweet, high-fat diet supplemented with standard rodent chow. Naloxone-precipitated withdrawal was also not seen in rats fed a liquid sweet-fat food. Further, body weight reduction to 85%, which is known to potentiate the reinforcing effects of substances of abuse, did not affect naloxone-precipitated signs of opiate-like withdrawal. Thus, unlike previous findings reported regarding rats with binge access to a sucrose solution, rats that binge eat sweet-fat combinations do not show signs of opiate-like withdrawal under the conditions tested. These data support the idea that excessive consumption of different nutrients can induce behaviors associated with addiction in different ways, and that the behaviors that could characterize "food addiction" may be subtyped based on the nutritional composition of the food consumed.

Topics: Analysis of Variance; Animals; Behavior, Addictive; Body Weight; Bulimia; Diet, High-Fat; Disease Models, Animal; Eating; Exploratory Behavior; Feeding Behavior; Food; Male; Maze Learning; Motor Activity; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Time Factors

The antioxidant and antinociceptive activities of Citrus limon essential oil (EO) were assessed in mice or in vitro tests. EO possesses a strong antioxidant potential according to the scavenging assays. Moreover, it presented scavenger activity against all in vitro tests. Orally, EO (50, 100, and 150  mg/kg) significantly reduced the number of writhes, and, at highest doses, it reduced the number of paw licks. Whereas naloxone antagonized the antinociceptive action of EO (highest doses), this suggested, at least, the participation of the opioid system. Further studies currently in progress will enable us to understand the action mechanisms of EO.

Topics: Administration, Oral; Analgesics; Animals; Antioxidants; Citrus; Disease Models, Animal; Free Radical Scavengers; Male; Mice; Naloxone; Oils, Volatile; Pain; Pain Measurement; Plant Extracts; Plant Leaves; Rutaceae

To investigate whether the tetracyclic antidepressant mirtazapine has a pain-suppressing effect in healthy animals.. In the first step, Swiss albino female mice weighing 25-35 g were used. Eight groups each containing 8 mice were established as follows:- Control (saline), mirtazapine 5 mg/kg, 10 mg/kg, and 20 mg/kg, mirtazapine 10mg/kg and its combinations L-Nitro-L-Arginine Methyl Ester (L-NAME) 100 mg/kg, L-Arginine 100 mg/kg, naloxone 1 mg/kg, and cyproheptadine 50 ug/kg. This study was performed in the Department of Pharmacology, Faculty of Medicine, Eskisehir Osmangazi University, Eskisehir, Turkey during March, April, and May 2009. One hour after the drugs were given intraperitoneally, hot plate, tail clip, tail flick, and writhing tests were used for evaluating antinociceptive effects. In the second step, the brain hippocampus of Sprague Dawley type male rats weighing 250±20 g were isolated and 0.6 um hippocampus slices were obtained. In vitro groups were established as control, mirtazapine 3x10(-3)M, 4x10(-3)M, 5x10(-3)M, mirtazapine 4x10(-3)M and its combinations L-NAME, L-Arginine, naloxone, and cyproheptadine 4x10(-3)M.. Mirtazapine did not show central spinal analgesic activity, but had significant peripheral and biphasic central analgesic effects at the supraspinal level. In addition, there were no significant differences between the different groups in nitric oxide synthase levels on the brain slices.. The nitrergic pathway does not have an effect on the central antinociceptive activity of mirtazapine, while opiatergic and serotonergic pathways have a significant role.

Topics: Analysis of Variance; Animals; Antidepressive Agents, Tricyclic; Arginine; Behavior, Animal; Cyproheptadine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Female; Gene Expression Regulation, Enzymologic; Hippocampus; In Vitro Techniques; Male; Mianserin; Mice; Mirtazapine; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase Type I; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Serotonin Antagonists

Neuropathic pain is a debilitating condition that is often difficult to treat using conventional pharmacological interventions and the exact mechanisms involved in the establishment and maintenance of this type of chronic pain have yet to be fully elucidated. The present studies examined the effect of chronic nerve injury on μ-opioid receptors and receptor-mediated G-protein activity within the supraspinal brain regions involved in pain processing of mice. Chronic constriction injury (CCI) reduced paw withdrawal latency, which was maximal at 10 days post-injury. [d-Ala2,(N-Me)Phe4,Gly5-OH] enkephalin (DAMGO)-stimulated [(35)S]GTPγS binding was then conducted at this time point in membranes prepared from the rostral ACC (rACC), thalamus and periaqueductal grey (PAG) of CCI and sham-operated mice. Results showed reduced DAMGO-stimulated [(35)S]GTPγS binding in the thalamus and PAG of CCI mice, with no change in the rACC. In thalamus, this reduction was due to decreased maximal stimulation by DAMGO, with no difference in EC(50) values. In PAG, however, DAMGO E(max) values did not significantly differ between groups, possibly due to the small magnitude of the main effect. [(3)H]Naloxone binding in membranes of the thalamus showed no significant differences in B(max) values between CCI and sham-operated mice, indicating that the difference in G-protein activation did not result from differences in μ-opioid receptor levels. These results suggest that CCI induced a region-specific adaptation of μ-opioid receptor-mediated G-protein activity, with apparent desensitization of the μ-opioid receptor in the thalamus and PAG and could have implications for treatment of neuropathic pain.

Topics: Analgesics, Opioid; Animals; Constriction; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Hyperalgesia; Male; Mice; Naloxone; Narcotic Antagonists; Pain Threshold; Protein Binding; Receptors, Opioid, mu; Sciatica; Sulfur Isotopes; Thalamus; Time Factors; Tritium

We investigated whether morphine plays a neuroprotective role in a neonatal rat pup model of bilateral carotid artery occlusion with hypoxia. At postnatal day 10, rats received either morphine (n = 7), naloxone (n = 7), or saline placebo (n = 15) after hypoxic-ischemic injury. Survival (days), weight gain and animal testing (negative geotaxis, surface righting, and rotarod) were compared between treatment groups. Lesion volume was delineated with magnetic resonance imaging at days 7 and 28-57 after injury. Survival in rats treated with morphine, naloxone, or saline was, respectively, 14, 29, and 73%. Median number of days of survival after bilateral carotid artery occlusion with hypoxia treated with morphine was 4 (95% confidence interval 4 to 22), with naloxone was 3 (95% confidence interval -1.4 to 21), and with placebo was 28 (95% confidence interval 18 to 28). There were no statistically significant differences in magnetic resonance imaging-derived ischemic lesion volumes, weight gain, or behavioral testing measures between the groups. Morphine was ineffective as a neuroprotectant in rat pups with severe hypoxic-ischemic injury and may have contributed to their decreased survival.

Topics: Animals; Animals, Newborn; Disease Models, Animal; Hypoxia-Ischemia, Brain; Infusions, Subcutaneous; Male; Morphine; Naloxone; Neuroprotective Agents; Rats; Rats, Sprague-Dawley; Survival Rate

The novel analgesic tapentadol HCl [(-)-(1R,2R)-3-(3-dimethylamino)-1-ethyl-2-methyl-propyl)-phenol hydrochloride] combines μ-opioid receptor (MOR) agonism and noradrenaline reuptake inhibition (NRI) in a single molecule and shows a broad efficacy profile in various preclinical pain models. This study analyzed the analgesic activity of tapentadol in experimental inflammatory pain. Analgesia was evaluated in the formalin test (pain behavior, rat and mouse), carrageenan-induced mechanical hyperalgesia (paw-pressure test, rat), complete Freund's adjuvant (CFA)-induced paw inflammation (tactile hyperalgesia, rat), and CFA knee-joint arthritis (weight bearing, rat). Tapentadol showed antinociceptive activity in the rat and mouse formalin test with an efficacy of 88 and 86% and ED(50) values of 9.7 and 11.3 mg/kg i.p., respectively. Tapentadol reduced mechanical hyperalgesia in carrageenan-induced acute inflammatory pain by 84% with an ED(50) of 1.9 mg/kg i.v. In CFA-induced tactile hyperalgesia, tapentadol showed 71% efficacy with an ED(50) of 9.8 mg/kg i.p. The decrease in weight bearing after CFA injection in one knee joint was reversed by tapentadol by 51% with an ED(25) of 0.9 mg/kg i.v. Antagonism studies were performed with the MOR antagonist naloxone and the α(2)-noradrenergic receptor antagonist yohimbine in the carrageenan- and CFA-induced hyperalgesia model. In the CFA model, the serotonergic receptor antagonist ritanserin was also tested. The effect of tapentadol was partially blocked by naloxone and yohimbine and completely blocked by the combination of both, but it was not affected by ritanserin. In summary, tapentadol showed antinococeptive/antihyperalgesic analgesic activity in each model of acute and chronic inflammatory pain, and the antagonism experiments suggest that both MOR activation and NRI contribute to its analgesic effects.

Topics: Adrenergic alpha-2 Receptor Antagonists; Analgesics; Analgesics, Opioid; Animals; Behavior, Animal; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Freund's Adjuvant; Hyperalgesia; Inflammation; Male; Mice; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Phenols; Random Allocation; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Serotonin 5-HT2 Receptor Antagonists; Tapentadol

Celastrus orbiculatus, a woody vine of the Celastraceae family, has been widely used as a traditional medicine for the treatment of many diseases, including rheumatoid arthritis and odontalgia. In this study, we assessed the sedative and antinociceptive activities of the methanolic extract of Celastrus orbiculatus (MCO).. The antinociceptive effect of MCO was evaluated using several experimental pain models, including thermal nociception methods, such as the tail immersion and the hotplate tests, as well as chemical nociception induced by intraperitoneal acetic acid and subplantar formalin administration in mice. To verify the possible connection of the opioid receptor to the antinociceptive activity of MCO, we performed a combination test with naloxone, a nonselective opioid receptor antagonist. The sedative effect of MCO was studied using the pentobarbital-induced sleeping model.. MCO demonstrated strong and dose-dependent antinociceptive activity compared to tramadol and indomethacin in various experimental pain models. The combination test using naloxone revealed that the antinociceptive activity of MCO is associated with activation of the opioid receptor. MCO also caused decreased sleep latency and increased sleeping time in the pentobarbital-induced sleeping model; however, MCO alone did not induce sleep.. In the present study, MCO showed potent antinociceptive and sedative activities. Based on these results, MCO may be considered a valuable anti-nociceptive and hypnotic agent for the treatment of various diseases.

Topics: Acetic Acid; Animals; Celastrus; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Formaldehyde; Hypnotics and Sedatives; Indomethacin; Male; Mice; Mice, Inbred ICR; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Phenobarbital; Plant Extracts; Plants, Medicinal; Reaction Time; Sleep; Time Factors; Tramadol

Manual acupuncture (MA) has presented analgesic activity against neuropathic pain in patients and animal models, yet a series of questions remain: Is MA effectiveness dependent of acupoint selection or combination? Is it equally efficient when treatment starts on the initial (acute) or sub-chronic phase of spinal nerve ligation (SNL)-induced neuropathy? Is MA effect related to the release of endogenous opioids? Does MA produce similar effects to gabapentin? To answer these questions rats submitted to the L5/L6 SNL injury were treated with unilateral MA (ST36 (Zusanli), SP6 (Sanyingjiao) or ST36+SP6 acupoint stimulation); or with gabapentin (30 mg/kg i.p., used as positive control). Both acupoints have been demonstrated to present analgesic activity and are used in clinical practice and basic science research. In addition, we investigated the influence of naloxone (1 mg/kg i.p., a nonselective opioid receptor antagonist) on MA treatment and also the effect of unilateral ST36+SP6 MA treatment beginning acutely (5 days) or sub-chronically (14 days) after SNL. Our results demonstrate that single or combined unilateral stimulation was able to reduce mechanical hypersensitivity with treatment beginning in both acute and sub-chronic phases of SNL-induced neuropathy; MA effect was blocked by naloxone, and finally; SP6+ST36 MA presented similar effect to gabapentin (30 mg/kg). In conclusion, our results demonstrate, for the first time, that unilateral MA (ST36, SP6 or ST36+SP6) reduces hypersensitivity induced by the SNL with effect dependent of the opioid system and comparable with the one obtained with gabapentin (used as positive control).

Topics: Acupuncture Points; Acupuncture Therapy; Amines; Analgesics; Analysis of Variance; Animals; Cyclohexanecarboxylic Acids; Disease Models, Animal; Gabapentin; gamma-Aminobutyric Acid; Hyperalgesia; Ligation; Male; Musculoskeletal Manipulations; Naloxone; Narcotic Antagonists; Neuralgia; Pain Measurement; Pain Threshold; Rats; Rats, Wistar; Spinal Nerves; Time Factors

We investigated whether capsaicin induces itching in skin with existing inflammation. We induced skin inflammation by intradermal injection of complete Freund's adjuvant (CFA) in the neck of mice. Four days later, we injected capsaicin in the same area and counted the number of scratching bouts for 30 min. We examined potential effects on pain in parallel experiments in which CFA and capsaicin were intradermally injected into hind paws. We used the time spent licking the hind paws during the 15 min after capsaicin injection as an estimate of pain. Capsaicin injection into the skin pretreated with CFA, but not into healthy skin, induced scratching. The scratching behavior was reduced by pretreatment with naloxone or capsazepine, selective antagonists for transient receptor potential vanilloid receptor-1 (TRPV1), but not morphine or mepyramine, selective antagonists for histamine 1 receptor. In animals injected with capsaicin into the hind paws, licking behavior was significantly inhibited via a μ-receptor-dependent mechanism. Our results show that TRPV1 activation, which normally induces pain, evokes an itch-related response in the presence of inflammation. This model may be interesting for future studies to explore the mechanism of a painful stimuli-induced itch observed under pathological conditions.

Topics: Adjuvants, Immunologic; Animals; Anti-Inflammatory Agents, Non-Steroidal; Behavior, Animal; Capsaicin; Dimethyl Sulfoxide; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Freund's Adjuvant; Inflammation; Injections, Intradermal; Male; Mice; Mice, Inbred C57BL; Morphine; Naloxone; Pain; Pruritus; Receptors, Opioid, mu; Reflex; Sensory System Agents; Skin; Time Factors; TRPV Cation Channels

Byrsonima intermedia A. Juss. is popularly known as "murici pequeno" and is native to the Brazilian Cerrado. This species has been used as an antimicrobial, anti-hemorrhagic, anti-diarrheal and anti-inflammatory. Nevertheless, scientific information regarding Byrsonima intermedia is limited; there are no reports related to its possible anti inflammatory and antinociceptive effects. This study employed in vivo inflammatory and nociceptive models to evaluate the scientific basis for the traditional use of Byrsonima intermedia.. Carrageenan-induced paw edema, peritonitis and fibrovascular tissue growth induced by s.c. cotton pellet implantation tests were used to investigate the anti-inflammatory activity of Byrsonima intermedia aqueous extract (BiAE) in rats. Mechanical nociceptive paw, formalin and hot plate tests were used to evaluate the antinociceptive activity in mice. High-performance liquid chromatography (HPLC), phytochemistry screening and determination of total phenolics and flavonoids were used to determine the chemical profile of the BiAE.. BiAE at test doses of 30-300 mg/kg p.o. clearly demonstrated anti-inflammatory effects by reduced carrageenan-induced paw edema, by inhibited leukocyte recruitment into the peritoneal cavity and, in the model of chronic inflammation, by using the cotton pellet-induced fibrovascular tissue growth in rats. The extracts at test doses of 30-300 mg/kg p.o. clearly demonstrated antinociceptive activity in all tests. Administration of the opioid receptor antagonist naloxone completely inhibited the antinociceptive effect induced by BiAE (100 mg/kg).. BiAE markedly exhibits anti-inflammatory action in rats and antinociceptive activity in mice. Thus, it may be useful in the treatment of inflammatory hyperalgesic disorders, which supports previous claims of its traditional use.

Topics: Analgesics; Animals; Anti-Inflammatory Agents; Behavior, Animal; Carrageenan; Chromatography, High Pressure Liquid; Cotton Fiber; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Flavonoids; Formaldehyde; Granuloma, Foreign-Body; Hot Temperature; Lipopolysaccharides; Male; Malpighiaceae; Mice; Motor Activity; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Peritonitis; Phenols; Plant Bark; Plant Extracts; Plant Stems; Plants, Medicinal; Rats; Rats, Wistar; Time Factors

Tolerance to the analgesic effect of opioids complicates the management of persistent pain states. We tested whether the intrathecal infusion of small interfering RNA (siRNA) against β-arrestin 2 would reduce tolerance to chronic morphine use and the severity of precipitated morphine withdrawal.. Intrathecal β-arrestin 2 (2 μg siRNA per 10 μl per rat) was injected once daily for 3 days. Rats then received a continuous intrathecal infusion of morphine (2 nmol h⁻¹) or saline for 7 days. Daily tail-flick (TF) and intrathecal morphine challenge tests were performed to assess the effect of intrathecal β-arrestin 2 siRNA on antinociception and tolerance to morphine. Naloxone withdrawal (2 mg kg⁻¹) was performed to assess morphine dependence.. In the daily TF test, the antinociception of intrathecal morphine was increased and maintained in rats receiving β-arrestin 2 siRNA compared with the control group (morphine alone). In the probe response test, rats receiving morphine infusion with β-arrestin 2 siRNA treatment showed a significant left shift in their dose-response curve, as measured by per cent maximal possible effect (MPE), such that the AD₅₀ was significantly decreased by a factor of 5.6 when compared with that of morphine-infused rats. In the naloxone-induced withdrawal tests, rats receiving β-arrestin 2 siRNA injection with morphine infusion showed a significant reduction in four of the six signs of withdrawal.. We show here that intrathecal β-arrestin 2 siRNA in rats enhances analgesia and attenuates naloxone-induced withdrawal symptoms. This may warrant further investigation in the context of long-term use of intrathecal opioids for controlling chronic pain.

Topics: Analgesics, Opioid; Animals; Arrestins; beta-Arrestin 2; beta-Arrestins; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Drug Tolerance; Injections, Spinal; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; RNA, Small Interfering; Sodium Chloride; Substance Withdrawal Syndrome

Neurotransmitter transporters can affect neuronal excitability indirectly via modulation of neurotransmitter concentrations or directly via transporter currents. A physiological or pathophysiological role for transporter currents has not been described. We found that GABA transporter 1 (GAT-1) cation currents directly increased GABAergic neuronal excitability and synaptic GABA release in the periaqueductal gray (PAG) during opioid withdrawal in rodents. In contrast, GAT-1 did not indirectly alter GABA receptor responses via modulation of extracellular GABA concentrations. Notably, we found that GAT-1-induced increases in GABAergic activity contributed to many PAG-mediated signs of opioid withdrawal. Together, these data support the hypothesis that GAT-1 activity directly produces opioid withdrawal signs through direct hyperexcitation of GABAergic PAG neurons and nerve terminals, which presumably enhances GABAergic inhibition of PAG output neurons. These data provide, to the best of our knowledge, the first evidence that dysregulation of a neurotransmitter transporter current is important for the maladaptive plasticity that underlies opiate withdrawal.

Topics: Analysis of Variance; Animals; Disease Models, Animal; GABA Antagonists; GABA Plasma Membrane Transport Proteins; gamma-Aminobutyric Acid; Gene Expression Regulation; Glutamate Decarboxylase; Green Fluorescent Proteins; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microdialysis; Morphine; Naloxone; Narcotic Antagonists; Nipecotic Acids; Oximes; Periaqueductal Gray; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Time Factors

In addition to analgesia, opioids may also produce paradoxical pain amplification [opioid-induced hyperalgesia (OIH)] either on abrupt withdrawal or during continuous long-term application. Here, we assessed antinociceptive and pronociceptive effects of three clinically used opioids at C-fiber synapses in the rat spinal dorsal horn in vivo. During 60 min of intravenous infusions of remifentanil (450 μg·kg⁻¹·h⁻¹), fentanyl (48 μg·kg⁻¹·h⁻¹), or morphine (14 mg·kg⁻¹·h⁻¹), C-fiber-evoked field potentials were depressed and paired-pulse ratios (PPR) were increased, indicating a presynaptic inhibition by all three opioids. After withdrawal, postsynaptic responses were enhanced substantially for the remaining of the recording periods of at least 3 h. Withdrawal from remifentanil led to long-term potentiation (LTP) of synaptic strength in C-fibers via activation of spinal μ-opioid receptors (MORs) and spinal NMDA receptors (NMDARs). Fentanyl and morphine caused an enhancement of synaptic transmission at C-fibers, which involved two distinct mechanisms: (1) an opioid withdrawal LTP that also required activation of spinal MORs and NMDARs and that was associated with a decrease in PPR suggestive of a presynaptic mechanism of its expression, and (2) an immediate-onset, descending facilitation of C-fiber-evoked field potentials during and after intravenous infusion of fentanyl and morphine. Immediate-onset, descending facilitation was mediated by the activation of extraspinal MORs, descending serotonergic pathways, and spinal 5-hydroxytryptamine-3 receptors (5-HT₃Rs). Our study identified fundamentally different pronociceptive effects of clinically used opioids and suggests that OIH can be prevented by the combined use of NMDAR and 5-HT₃R antagonists.

Topics: 2-Amino-5-phosphonovalerate; Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Antagonists; Granisetron; Hyperalgesia; Long-Term Potentiation; Male; Naloxone; Narcotic Antagonists; Nerve Fibers, Unmyelinated; Ondansetron; Pain Threshold; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Serotonin Antagonists; Somatostatin; Spinal Cord; Substance Withdrawal Syndrome; Synaptic Transmission

Early life status epilepticus (SE) could enhance the vulnerability of the immature brain to a second SE in adulthood (two-hit seizure model). Naloxone has been proved to possess inflammation inhibitory effects in nervous system. This study was designed to evaluate the dose-dependent protective effects of naloxone in kainic acid (KA)-induced two-hit seizure model.. After KA-induced SE at postnatal day 15 (P15), Sprague-Dawley rats were infused with either saline or different doses (1.92, 3.84, 5.76, and 7.68 mg/kg) of naloxone continuously for 12 h. De novo synthesis of cytokines (interleukin-1 beta [IL-1 beta], S100B) was assessed by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) at 12 h after P15 SE. Glial activation states were analyzed by western blotting of glial markers (glial fibrillary acidic protein [GFAP], S100B, Iba1) both at 12 h after P15 SE and at P45. After a second SE at P45, cognitive deteriorations were evaluated by Morris water tests and neuron injuries were evaluated by TdT-mediated dUTP nick end labeling (TUNEL) assays.. Naloxone reduced IL-1 beta synthesis and microglial activation most potently at a dose of 3.84 mg/kg. Attenuation of S100B synthesis and astrocyte activation were achieved most dramatically by naloxone at a dose of 5.76 mg/kg, which is equal to the most powerful dose in ameliorating cognitive injuries and neuron apoptosis after second SE.. Naloxone treatment immediately after early life SE could dose-dependently reduce cytokine production, glial activation, and further lower the vulnerability of immature brains to a second hit in adulthood.

Topics: Animals; Animals, Newborn; Apoptosis; Astrocytes; Behavior, Animal; Cytokines; Disease Models, Animal; Disease Susceptibility; Dose-Response Relationship, Drug; Enzyme-Linked Immunosorbent Assay; Glial Fibrillary Acidic Protein; Hippocampus; In Situ Nick-End Labeling; Interleukin-1beta; Kainic Acid; Maze Learning; Microglia; Naloxone; Neurons; Rats; Rats, Sprague-Dawley; Status Epilepticus

The implication of inducible nitric-oxide synthase (iNOS) on peripheral tolerance to morphine was evaluated in wild-type (WT) and iNOS knockout mice. Chronic inflammation was induced by subplantar (s.p.) injection of Complete Freund's Adjuvant (CFA), and morphine tolerance by subcutaneous implantation of a 75 mg morphine-pellet. Withdrawal was assessed after the intraperitoneal injection of 2 mg/kg naloxone. Antinociception was assessed (Randall-Selitto test) 5 min after a fixed dose of s.p. morphine (16 microg). In the absence of inflammation, s.p. morphine did not induce antinociception, while during CFA-inflammation produced 47.4 +/- 0.8 and 38.8 +/- 2.7% inhibitions respectively, in each genotype (P < 0.05). In morphine-tolerant mice with CFA-inflammation, no antinociception could be elicited in WT mice (2.4 +/- 0.3% inhibition); however, iNOS knockout mice showed significant antinociception (33.1 +/- 0.9%) (P < 0.001). Thus, iNOS gene deletion partially prevented tolerance to the peripheral effects of morphine, and significantly attenuated withdrawal-induced hyperactivity.

Topics: Animals; Arthritis, Experimental; Chronic Disease; Disease Models, Animal; Drug Tolerance; Gene Deletion; Inflammation; Inflammation Mediators; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphine; Naloxone; Nitric Oxide Synthase Type II; Pain Measurement; Substance Withdrawal Syndrome

Cues paired with drug administration trigger relapse to drug seeking by inducing conditioned drug craving and withdrawal. Because drug cues hinder abstinence in addicts, therapies that reduce responsiveness to drug cues might facilitate rehabilitation. Extinction is a means of reducing conditioned responses and involves exposure to the conditioned stimulus in the absence of the unconditioned stimulus with which it was paired previously. We examined conditioned withdrawal extinction using naloxone-induced conditioned place aversion (CPA) in morphine-dependent rats.. Morphine-dependent rats were trained to associate an environment with naloxone-precipitated withdrawal. Subsequently, they received extinction training in which they were confined in the previously naloxone-paired environment in the absence of acute withdrawal. In some rats, the N-methyl-D-aspartate (NMDA) receptor partial agonist D-cycloserine (DCS) was administered before extinction training.. Morphine withdrawal-induced CPA persists in the absence of extinction training. Administration of DCS before extinction training facilitates extinction.. D-cycloserine facilitates extinction of morphine withdrawal-associated place aversion. This effect is qualitatively similar to the effect of DCS on extinction of conditioned fear, raising the possibility of common neural mechanisms. This work extends our understanding of drug cue responsivity and provides a rationale for the development of extinction-based treatments for addiction.

Topics: Animals; Avoidance Learning; Conditioning, Operant; Cues; Cycloserine; Disease Models, Animal; Drug Interactions; Excitatory Amino Acid Agonists; Extinction, Psychological; Male; Morphine Dependence; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley

The antinociceptive profile of St. John's Wort (SJW) was investigated in mice in a condition of acute thermal and chemical pain, together with the mechanism that might underlie this effect. A dried extract of SJW induced a prolonged antinociception that persisted for 120 minutes after administration. The thermal antinociception was prevented by naloxone and by the protein kinase C (PKC) activator PMA, whereas the chemical antinociception was prevented by PMA, remaining naloxone insensitive. A chloroform (CHL) and a methanol (MET) fraction, obtained to investigate the involvement of the SJW main components, hyperforin and hypericin/flavonoid, respectively, increased pain threshold with a time course comparable to the dried extract. The CHL antinociception was prevented by naloxone, whereas the MET antinociception was antagonized by PMA. Purified hyperforin and hypericin showed an antinociceptive efficacy comparable to CHL and MET, respectively. Conversely, flavonoids were devoid of any effect. The administration of yohimbine and atropine did not modify SJW, CHL and MET antinociception. These results indicate that both CHL and MET fractions mediate the SJW-induced antinociception. In particular, the presence of hypericin was fundamental to induce both thermal and chemical antinociception through the inhibition of the PKC activity, whereas hyperforin selectively produced a thermal opioid antinociception.. This article presents evidence of a persistent thermal and chemical antinociception of SJW that is mainly mediated by PKC-inhibiting mechanisms. These findings identify important targets for a longer-acting activation of endogenous pain systems and should potentially help clinicians who seek safe, tolerable, and prolonged treatments for pain relief.

Topics: Acetic Acid; Analgesics; Analgesics, Opioid; Animals; Anthracenes; Chromatography, High Pressure Liquid; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Administration Schedule; Drug Compounding; Hypericum; Male; Mice; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Perylene; Phorbol Esters; Phytotherapy; Protein Kinase C; Quercetin; Somatostatin; Spectrometry, Mass, Electrospray Ionization; Statistics, Nonparametric; Time Factors

The relationship between pain severity and the extent of injury to a peripheral nerve remains elusive. In this study, we compared the pain behavior resulting from partial (1/3-1/2 thickness) and full L5 spinal nerve ligation (SNL) in rats. The decrease in paw withdrawal threshold (PWT) to mechanical stimuli in the hindpaw ipsilateral to the injury was comparable in the two groups on days 3-21 post-injury. However, the decreased PWT recovered earlier in the partial SNL group than in the full SNL group. These observations suggest that the duration of neuropathic pain behavior, but not the early development of mechanical allodynia, is dependent on the extent of nerve injury. On days 6 and 15 post-injury, when the mechanical allodynia was similar in the two groups, systemic morphine induced a greater reduction of mechanical allodynia in the partial SNL group than in the full SNL group. Furthermore, in partial SNL rats, at post-injury time points when they had largely recovered from the neuropathic pain state, systemic administration of naloxone hydrochloride (day 53) or naloxone methiodide (a non-selective peripherally acting opioid receptor antagonist; day 64) or intra-plantar injection of naloxone methiodide rekindled mechanical pain hypersensitivity in the ipsilateral hindpaw, suggesting a prolonged activation of endogenous opioidergic pain-inhibition. Therefore, partial SNL in rats may represent an efficient model for studying the mechanisms of neuropathic pain, testing effects of analgesic/antihyperalgesic drugs, and understanding endogenous pain-inhibitory mechanisms that lead to reversal of the pain behavior with time.

Topics: Analgesics, Opioid; Animals; Constriction, Pathologic; Disease Models, Animal; Ligation; Lumbosacral Region; Male; Morphine; Naloxone; Narcotic Antagonists; Pain; Peripheral Nervous System Diseases; Physical Stimulation; Rats; Rats, Sprague-Dawley; Spinal Nerves; Touch

Chronic morphine drives adaptations in synaptic transmission thought to underlie opiate dependence. Here we examine the role of micro-opioid receptor (MOR) trafficking in one of these adaptations, specifically, changes in GABA transmission in the ventral tegmental area (VTA). To address this question, we used a knock-in mouse, RMOR (for recycling MOR), in which genetic change in the MOR promotes morphine-induced receptor desensitization and endocytosis in GABA interneurons of the VTA. In wild-type mice (postnatal days 23-28) chronic morphine (10 mg/kg, s.c., twice daily for 5 d), induced a cAMP-dependent increase in the probability of GABA release onto VTA dopamine neurons. The increased GABA release frequency correlated with physical dependence on morphine measured by counting somatic signs of morphine withdrawal, such as, tremors, jumps, rears, wet-dog shakes, and grooming behavior precipitated by subcutaneous administration of naloxone (NLX) (2 mg/kg). This adaptation in GABA release was prevented in RMOR mice given the same morphine treatment, implicating MOR trafficking in this morphine-induced change in plasticity. Importantly, treatment with the cAMP activity inhibitor rp-cAMPS [(R)-adenosine, cyclic 3',5'-(hydrogenphosphorothioate) triethylammonium] (50 ng/0.5 microl), directly to the VTA, attenuated somatic withdrawal signs to systemic morphine produced by intra-VTA NLX (500 ng/0.5 microl), directly tying enhanced cAMP-driven GABA release to naloxone-precipitated morphine withdrawal in the VTA.

Topics: Adaptation, Physiological; Animals; Chimera; Cyclic AMP; Disease Models, Animal; Endocytosis; gamma-Aminobutyric Acid; Gene Knock-In Techniques; Interneurons; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Neural Inhibition; Receptors, Opioid, mu; Substance Withdrawal Syndrome; Synaptic Transmission; Thionucleotides; Ventral Tegmental Area

The activation of CB(2) receptors induces analgesia in experimental models of chronic pain. The present experiments were designed to study whether the activation of peripheral or spinal CB(2) receptors relieves thermal hyperalgesia and mechanical allodynia in two models of bone cancer pain.. NCTC 2472 osteosarcoma or B16-F10 melanoma cells were intratibially inoculated to C3H/He and C57BL/6 mice. Thermal hyperalgesia was assessed by the unilateral hot plate test and mechanical allodynia by the von Frey test. AM1241 (CB(2) receptor agonist), AM251 (CB(1) receptor antagonist), SR144528 (CB(2) receptor antagonist) and naloxone were used. CB(2) receptor expression was measured by Western blot.. AM1241 (0.3-10 mg.kg(-1)) abolished thermal hyperalgesia and mechanical allodynia in both tumour models. The antihyperalgesic effect was antagonized by subcutaneous, intrathecal or peri-tumour administration of SR144528. In contrast, the antiallodynic effect was inhibited by systemic or intrathecal, but not peri-tumour, injection of SR144528. The effects of AM1241 were unchanged by AM251 but were prevented by naloxone. No change in CB(2) receptor expression was found in spinal cord or dorsal root ganglia.. Spinal CB(2) receptors are involved in the antiallodynic effect induced by AM1241 in two neoplastic models while peripheral and spinal receptors participate in the antihyperalgesic effects. Both effects were mediated by endogenous opiates. The use of drugs that activate CB(2) receptors could be a useful strategy to counteract bone cancer-induced pain symptoms.

Topics: Analgesics; Animals; Bone Neoplasms; Camphanes; Cannabinoids; Cell Line, Tumor; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Ganglia, Spinal; Humans; Mice; Mice, Inbred C3H; Mice, Inbred C57BL; Naloxone; Osteosarcoma; Pain; Pain Measurement; Piperidines; Pyrazoles; Receptor, Cannabinoid, CB2; Spinal Cord

We previously demonstrated that several epoxyeicosatrienoic acids (EETs) produce reductions in myocardial infarct size in rats and dogs. Since a recent study demonstrated the release of opioids in mediating the antinociceptive effect of 14,15-EET, we hypothesized that endogenous opioids may also be involved in mediating the cardioprotective effect of the EETs. To test this hypothesis, we used an in vivo rat model of infarction and a rat Langendorff model. In the infarct model, hearts were subjected to 30 min occlusion of the left coronary artery and 2 h reperfusion. Animals were treated with 11,12-EET or 14,15-EET (2.5 mg/kg) alone 15 min before occlusion or with opioid antagonists [naloxone, naltrindole, nor-binaltorphimine (nor-BNI), and d-Phe-Cys-Tyr-d-Trp-Om-Thr-Pen-Thr-NH(2) (CTOP), a nonselective, a selective delta, a selective kappa, and a selective mu receptor antagonist, respectively] 10 min before EET administration. In four separate groups, antiserum to Met- and Leu-enkephalin and dynorphin-A-(1-17) was administered 50 min before the 11,12-EET administration. Infarct size expressed as a percent of the area at risk (IS/AAR) was 63.5 + or - 1.2, 45.3 + or - 1.0, and 40.9 + or - 1.2% for control, 11,12-EET, and 14,15-EET, respectively. The protective effects of 11,12-EET were abolished by pretreatment with either naloxone (60.5 + or - 1.8%), naltrindole (60.8 + or - 1.0%), nor-BNI (62.3 + or - 2.8%), or Met-enkephalin antiserum (63.2 + or - 1.7%) but not CTOP (42.0 + or - 3.0%). In isolated heart experiments, 11,12-EET was administered to the perfusate 15 min before 20 min global ischemia followed by 45 min reperfusion in control hearts or in those pretreated with pertussis toxin (48 h). 11,12-EET increased the recovery of left ventricular developed pressure from 33 + or - 1 to 45 + or - 6% (P < 0.05) and reduced IS/AAR from 37 + or - 4 to 20 + or - 3% (P < 0.05). Both pertussis toxin and naloxone abolished these beneficial effects of 11,12-EET. Taken together, these results suggest that the major cardioprotective effects of the EETs depend on activation of a G(i/o) protein-coupled delta- and/or kappa-opioid receptor.

Topics: 8,11,14-Eicosatrienoic Acid; Analgesics, Opioid; Animals; Disease Models, Animal; GTP-Binding Protein alpha Subunits, Gi-Go; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Somatostatin

The present study was carried out to determine the antiinflammatory and antinociceptive activities of a methanol extract of Zingiber zerumbet rhizomes (MEZZ) using various experimental model systems.. The MEZZ was prepared by macerating oven-dried (50 degrees C) powdered rhizomes (1.2 kg) of Z. zerumbet in 80% methanol in a ratio of 1:20 (w/v) for 48 h. The supernatant was collected, filtered and evaporated to dryness under reduced pressure (50 degrees C) yielding approximately 21.0 g of the crude dried extract. The crude dried extract was stored at -20 degrees C prior to use and was dissolved in normal saline (0.9% NaCl) immediately before administration at concentrations required to produce doses of 25, 50 and 100 mg/kg.. All dosages of MEZZ showed significant (p < 0.05) antiedema activity when assessed using the carrageenan-induced paw edema test and the cotton-pellet-induced granuloma test. The MEZZ exhibited significant (p < 0.05) antinociceptive activity when assessed by the writhing, hot plate and formalin tests. Pretreatment with naloxone (5 mg/kg) significantly decreased the latency of discomfort produced by the 100 mg/kg dose of MEZZ in the hot plate test.. MEZZ produced antiinflammatory and antinociceptive activities which may involve the inhibition of bradykinin-, prostaglandin-, histamine- and opioid-mediated processes.

Topics: Analgesics; Analysis of Variance; Animals; Anti-Inflammatory Agents; Bradykinin; Carrageenan; Disease Models, Animal; Histamine; Male; Methanol; Mice; Naloxone; Phytotherapy; Plant Extracts; Prostaglandins; Rats; Rats, Sprague-Dawley; Zingiber officinale

Preventing and reversing opioid dependence continues to be a clinical challenge and underlying mechanisms of opioid actions remain elusive. We report that matrix metalloproteinase-9 (MMP-9) in the spinal cord contributes to development of physical dependence on morphine. Chronic morphine exposure and naloxone-precipitated withdrawal increase activity of spinal MMP-9. Spinal inhibition or targeted mutation of MMP-9 suppresses behavioral signs of morphine withdrawal and the associated neurochemical alterations. The increased MMP-9 activity is mainly distributed in the superficial dorsal horn and colocalized primarily with neurons and small numbers of astrocytes and microglia. Morphine exposure and withdrawal increase phosphorylation of NR1 and NR2B receptors, ERK1/2, calmodulin-dependent kinase II, and cAMP response element binding proteins; and such phosphorylation is suppressed by either spinal inhibition or targeted mutation of MMP-9. Further, spinal administration of exogenous MMP-9 induces morphine withdrawal-like behavioral signs and mechanical allodynia, activates NR1 and NR2 receptors, and downregulates integrin-beta1, while a function-neutralizing antibody against integrin-beta1 suppresses MMP-9-induced phosphorylation of NR1 and NR2B. Morphine withdrawal-induced MMP-9 activity is also reduced by an nNOS inhibitor. Thus, we hypothesize that spinal MMP-9 may contribute to the development of morphine dependence primarily through neuronal activation and interaction with NR1 and NR2B receptors via integrin-beta1 and NO pathways. The other gelatinase, MMP-2, is not involved in morphine dependence. Inhibiting spinal MMP-9 or MMP-2 reduces chronic and/or acute morphine tolerance. This study suggests a novel therapeutic approach for preventing, minimizing, or reversing opioid dependence and tolerance.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Drug Tolerance; Enzyme Inhibitors; Female; Gene Expression Regulation; Hyperalgesia; Male; Matrix Metalloproteinase 9; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Nerve Tissue Proteins; Pain Threshold; Spinal Cord; Time Factors

Recently, opioid receptors have been shown to be expressed on group III and IV afferents, which comprise the sensory arm of the exercise pressor reflex. Although the stimulation of opioid receptors in the central nervous system has been shown to attenuate the exercise pressor reflex, the effect on the reflex of their stimulation in the periphery is unknown. We therefore tested the hypothesis that the activation of peripheral mu-opioid receptors attenuates the exercise pressor reflex. The pressor responses to static contraction were compared before and after the injection of the mu-opioid receptor agonist [d-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO; 1 microg) into the abdominal aorta of decerebrated rats in which one femoral artery had been occluded 72 h previously (n = 10) and in control rats whose femoral arteries were freely perfused (n = 8). DAMGO attenuated the peak pressor response to contraction in rats whose femoral arteries had been occluded (before: increase of 34 + or - 3 mmHg and after: increase of 22 + or - 2 mmHg, P = 0.008); the inhibitory effect of DAMGO was prevented by the injection of naloxone (100 microg) into the abdominal aorta (before: increase of 29 + or - 5 mmHg and after: increase of 29 + or - 5 mmHg, P = 0.646, n = 7). An intravenous injection of DAMGO (1 microg, n = 6) had no effect on the peak pressor response to contraction in both groups of rats. DAMGO had no effect on the peak pressor response to contraction in rats whose femoral arteries were freely perfused (before: Delta 23 + or - 4 mmHg, after: Delta 23 + or - 3 mmHg, n = 6) but appeared to have a small effect on topography of the response. DAMGO had no effect on the peak pressor response to tendon stretch in both groups of rats (both P > 0.05). We conclude that the stimulation of peripheral mu-opioid receptors attenuates the exercise pressor reflex in rats whose femoral arteries have been ligated for 72 h.

Topics: Animals; Arterial Occlusive Diseases; Baroreflex; Chronic Disease; Constriction, Pathologic; Disease Models, Animal; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Femoral Artery; Hindlimb; Injections, Intra-Arterial; Injections, Intravenous; Ligation; Male; Muscle Contraction; Muscle, Skeletal; Naloxone; Narcotic Antagonists; Neurons, Afferent; Physical Exertion; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Time Factors

Anti-nociceptive tolerance to opioids is a well-described phenomenon, which severely limits the clinical efficacy of opioids for the treatment of chronic pain syndromes. The mechanisms that drive anti-nociceptive tolerance, however, are less well understood. We have previously shown that glia have a central role in the development of morphine tolerance and that administration of a glial modulating agent attenuated tolerance formation. Recently, we have demonstrated that morphine enhances microglial Iba1 expression and P2X4 receptor-mediated microglial migration via direct mu opioid receptor signaling in in vitro microglial cultures. We hypothesize that P2X4 receptors drive morphine tolerance and modulate morphine-induced spinal glial reactivity. Additionally, we hypothesize that perivascular microglia play a role in morphine tolerance and that P2X4 receptor expression regulates perivascular microglia ED2 expression. To test these hypotheses, rats were implanted with osmotic minipumps releasing morphine or saline subcutaneously for seven days. Beginning three days prior to morphine treatment, P2X4 receptor antisense oligonucleotide (asODN) was injected intrathecally daily, to selectively inhibit P2X4 receptor expression. P2X4 receptor asODN treatment inhibited morphine-induced P2X4 receptor expression and blocked anti-nociceptive tolerance to systemically administered morphine. P2X4 receptor asODN treatment also attenuated the morphine-dependent increase of spinal ionized calcium binding protein (Iba1), glial fibrillary acidic protein (GFAP) and mu opioid receptor protein expression. Chronic morphine also decreased perivascular microglial ED2 expression, which was reversed by P2X4 receptor asODN. Together, these data suggest that the modulation of P2X4 receptor expression on microglia and perivascular microglia may prove an attractive target for adjuvant therapy to attenuate opioid-induced anti-nociceptive tolerance.

Topics: Analysis of Variance; Animals; Antigens, CD; Antigens, Differentiation, Myelomonocytic; Behavior, Animal; Calcium-Binding Proteins; CD11b Antigen; Disease Models, Animal; Drug Interactions; Drug Tolerance; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Microfilament Proteins; Microglia; Morphine; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Oligodeoxyribonucleotides, Antisense; Pain Measurement; Random Allocation; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Receptors, Opioid; Receptors, Purinergic P2X4; Signal Transduction; Spinal Cord; Time Factors

It has been demonstrated that calcitonin gene-related peptide (CGRP) plays important roles in the modulation of nociception in the nucleus accumbens (NAc) of rats. The present study is performed to explore the possible involvement of opioid receptors in the CGRP-induced antinociception in the NAc of rats. Intra-NAc administration of CGRP induces significant increases in the hindpaw withdrawal latency (HWL) to noxious thermal and mechanical stimulation in rats. Interestingly, the CGRP-induced antinociceptive effects are inhibited by following intra-NAc injection of the opioid receptor antagonist naloxone, suggesting that the opioid receptors are involved in the CGRP-induced antinociception in the NAc of rats. Furthermore, the CGRP-induced antinociception is attenuated by intra-NAc injection of mu-opioid receptor (MOR) antagonist beta-funaltrexamine (beta-FNA) and kappa-opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI), but not by delta-receptor (DOR) antagonist naltrindole. In the present study, we also demonstrated that there was no significant difference between the CGRP-induced antinociception and the morphine-induced antinociception in the NAc in rats. The results of the present study demonstrate that both mu- and kappa-opioid receptors are involved in the CGRP-induced antinociception in the NAc of rats.

Topics: Analgesics; Analysis of Variance; Animals; Calcitonin Gene-Related Peptide; Disease Models, Animal; Drug Interactions; Hyperalgesia; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Nucleus Accumbens; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Opioid

Chronic post-ischemic pain (CPIP) is an animal model of CRPS-I developed using a 3-h ischemia-reperfusion injury of the rodent hind paw. The contribution of local endothelin to nociception has been evaluated in CPIP mice by measuring sustained nociceptive behaviors (SNBs) following intraplantar injection of endothelin-1 or -2 (ET-1, ET-2). The effects of local BQ-123 (ETA-R antagonist), BQ-788 (ETB-R antagonist), IRL-1620 (ETB-R agonist) and naloxone (opioid antagonist) were assessed on ET-induced SNBs and/or mechanical and cold allodynia in CPIP mice. ETA-R and ETB-R expression was assessed using immunohistochemistry and Western blot analysis. Compared to shams, CPIP mice exhibited hypersensitivity to local ET-1 and ET-2. BQ-123 reduced ET-1- and ET-2-induced SNBs in both sham and CPIP animals, but not mechanical or cold allodynia. BQ-788 enhanced ET-1- and ET-2-induced SNBs in both sham and CPIP mice, and cold allodynia in CPIP mice. IRL-1620 displayed a non-opioid anti-nociceptive effect on ET-1- and ET-2-induced SNBs and mechanical allodynia in CPIP mice. The distribution of ETA-R and ETB-R was similar in plantar skin of sham and CPIP mice, but both receptors were over-expressed in plantar muscles of CPIP mice. This study shows that ETA-R and ETB-R have differing roles in nociception for sham and CPIP mice. CPIP mice exhibit more local endothelin-induced SNBs, develop a novel local ETB-R agonist-induced (non-opioid) analgesia, and exhibit over-expression of both receptors in plantar muscles, but not skin. The effectiveness of local ETB-R agonists as anti-allodynic treatments in CPIP mice holds promise for novel therapies in CRPS-I patients.

Topics: Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Endothelin Receptor Antagonists; Endothelin-1; Endothelin-2; Endothelins; Hyperalgesia; Keratinocytes; Male; Mice; Muscle, Skeletal; Naloxone; Narcotic Antagonists; Oligopeptides; Pain Measurement; Pain Threshold; Peptide Fragments; Peptides, Cyclic; Peripheral Nervous System; Physical Stimulation; Piperidines; Receptors, Endothelin; Reflex Sympathetic Dystrophy; Skin

Long-term use of morphine can cause neuronal dystrophic changes in specific areas of the brain. These changes may underlie the mechanism for developing morphine antinociceptive tolerance and physical dependence. We evaluated the effect of tianeptine, an antidepressant with prominent neuroprotective and neuroplastic properties, on the development of morphine antinociceptive tolerance and physical dependence. Male C57BL/6 mice were rendered tolerant to or dependent on morphine by subcutaneously injecting them with morphine (10 mg/kg) and intraperitoneally with saline or tianeptine (1, 3, or 5 mg/kg) twice daily for 6 days. The mice were given a daily tail-flick test 1 h after the first morphine injection to evaluate the development of their tolerance to morphine antinociception. To evaluate their physical dependence on morphine, 3 h after the final morphine injection on day 6, naloxone-HCl-precipitated (2 mg/kg, intraperitoneally) withdrawal symptoms were counted for 30 min, and body weight was checked 1 h after the naloxone injection. Tianeptine per se produced no antinociception, neither did it modify the antinociception produced by morphine, nor did it evoke the behavioral responses different from those in the saline controls. The combination of tianeptine with morphine significantly reduced the development of morphine antinociceptive tolerance and suppressed the incidence of naloxone-precipitated withdrawal symptoms. We conclude that tianeptine is an effective inhibitor of morphine-induced antinociceptive tolerance and physical dependence in mice. Our results would imply that comedication with tianeptine and morphine might benefit those who need long-term morphine treatment.

Topics: Analgesics, Opioid; Animals; Antidepressive Agents, Tricyclic; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Male; Mice; Mice, Inbred C57BL; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Pain; Substance Withdrawal Syndrome; Thiazepines

We tested the hypothesis that caveolin-3 (Cav-3) is essential for opioid-induced preconditioning in vivo. Cav-3 overexpressing mice, Cav-3 knockout mice, and controls were exposed to myocardial ischemia/reperfusion (I/R) in the presence of SNC-121 (SNC), a δ-selective opioid agonist, or naloxone, a nonselective opioid antagonist. Controls were protected from I/R injury by SNC. No protection was produced by SNC in Cav-3 knockout mice. Cav-3 overexpressing mice showed innate protection from I/R compared with controls that was abolished by naloxone. Our results show that opioid-induced preconditioning is dependent on Cav-3 expression and that endogenous protection in Cav-3 overexpressing mice is opioid dependent.

Topics: Analgesics, Opioid; Animals; Benzamides; Blood Pressure; Caveolin 3; Disease Models, Animal; Drug Administration Schedule; Heart Rate; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Naloxone; Narcotic Antagonists; Piperazines; Receptors, Opioid, delta; Time Factors

In the present study, the effects of tramadol on pentylenetetrazole (PTZ)-induced seizures and involvement of nitric oxide (NO) were assessed in mice. To determine the threshold for clonic seizures, PTZ was administered intravenously. Tramadol was administered intraperitoneally (0.5-50mg/kg) 30 minutes prior to induction of seizures. The effects of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 0.5, 1, 5, and 10mg/kg), the nitric oxide precursor L-arginine (10, 30, and 60 mg/kg), and the nonspecific opioid receptor antagonist naloxone (0.1, 0.5, 1, and 5mg/kg) on the anticonvulsant effect of tramadol were investigated. Administration of tramadol (1mg/kg) increased the threshold for seizures induced with PTZ in a monophasic, dose-independent, and time-dependent manner. Acute administration of L-NAME (5 and 10mg/kg) inhibited the anticonvulsant effect of tramadol (1mg/kg), whereas L-arginine, in the noneffective dose range (30 and 60 mg/kg), potentiated the seizure threshold when co-administered with a subeffective dose of tramadol (0.5mg/kg). Naloxone partially and dose-independently antagonized the anticonvulsant effect of tramadol (1mg/kg). These results indicate that the anticonvulsant effect of tramadol is mediated by the nitric oxide pathway and also by classic opioid receptors.

Topics: Analysis of Variance; Animals; Anticonvulsants; Arginine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Male; Mice; Mice, Inbred Strains; Naloxone; NG-Nitroarginine Methyl Ester; Nitric Oxide; Pentylenetetrazole; Seizures; Signal Transduction; Time Factors; Tramadol

In the present study, we investigated the possible influence of the opioidergic system of the dorsal hippocampus on anxiety-like behaviors.. Elevated plus-maze, which is one of the methods used for testing anxiety, was used in the present study. Rats were anesthetized with ketamine and xylazine and special cannulas were inserted stereotaxically into the CA1 region of the dorsal hippocampus. After 1 week of recovery, the effects of intra-CA1 administration of morphine (0.25, 0.5, 1 and 2 µg/rat; 1 µl/rat; 0.5 µl/in each side), naloxone (2, 4, 6 and 8 µg/rat), enkephalin (1, 2, 5 and 10 µg/rat) and naltrindole (0.25, 0.5, 1 and 2 µg/rat) on percentage open arm time (%OAT) and percentage open arm entries (%OAE) were determined.. Bilateral administration of morphine into CA1 decreases %OAT and %OAE, indicating an anxiogenic-like effect. Intra-CA1 injection of naloxone, an opioid receptor antagonist, increased both %OAT and %OAE, parameters of anxiolytic-like behavior. Bilateral administration of δ-opioid receptor agonist, [D-Pen(2,5) ]-enkephalin acetate hydrate into the CA1, induced an anxiolytic-like effect. Furthermore, intra-CA1 injection of δ-opioid receptor antagonist, naltrindole hydrochloride, increased anxiety-related behaviors.. The results of the present study demonstrate that activation of μ-opioid receptors in this area produce an anxiogenic response while activation of δ-opioid receptors produces an anxiolytic response.

Topics: Analgesics, Opioid; Animals; Anxiety; CA1 Region, Hippocampal; Disease Models, Animal; Enkephalin, D-Penicillamine (2,5)-; Male; Maze Learning; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Wistar; Receptors, Opioid, delta; Receptors, Opioid, mu

Chronic morphine exposure induces physical dependence and tolerance. Previous studies have shown that there is a decrease in met-enkephalin levels in states of morphine physical dependence, and that increasing enkephalin during opiate physical withdrawal ameliorates the severity of the morphine withdrawal syndrome. In order to investigate the role of spinal opioid peptide in the phenomenon of naloxone-precipitated withdrawal we examined the effect of herpes simplex virus vector-mediated overexpression of proenkephalin in lumbar dorsal root ganglia in rats with neuropathic pain treated with morphine. The morphine physical dependence was induced by chronic administration of intraperitoneal (IP) morphine for 2 weeks. Rats with neuropathic pain inoculated subcutaneously with the vector-mediated overexpression of proenkephalin showed a significant reduction in jumps, 'wet-dog' shakes, diarrhea and ptosis precipitated by naloxone after 2 weeks of morphine treatment. The global withdrawal score was also reduced significantly by vector-mediated overexpression of proenkephalin. These studies demonstrate a role for opioid peptide in the spinal cord in mediating some of the withdrawal response.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Enkephalins; Ganglia, Spinal; Gene Transfer Techniques; Genetic Vectors; Ligation; Lumbar Vertebrae; Male; Morphine; Morphine Dependence; Naloxone; Pain Threshold; Peripheral Nervous System Diseases; Protein Precursors; Rats; Rats, Sprague-Dawley; Simplexvirus; Spinal Nerve Roots; Substance Withdrawal Syndrome; Transgenes

To investigate the effects of morphine administered after reperfusion in a rabbit model of ischemic retinopathy.. The right eyes of 54 albino New Zealand rabbits were randomly allocated into nine treatment groups (n = 6 in each group). The eyes in saline-control group received 0.1 mL of phosphate-buffered saline solution intravitreally. In the ischemia-saline group, ischemia was induced by raising the intraocular pressure to 150 mmHg for 60 minutes. Then 0.1 mL of phosphate-buffered saline solution was administered intravitreally 5 minutes after reperfusion. The eyes in three ischemia-morphine groups (ischemia-morphine 0 hour, 1 hour, and 18 hours) received 0.1 mL of morphine (10 micromol/L) intravitreally 5 minutes, 1 hour, or 18 hours after termination of 60 minutes of ischemia, respectively. The eyes in ischemia-naloxone-morphine group received 0.05 mL of naloxone (10 micromol/L) intravitreally followed by injection of 0.05 mL morphine (10 micromol/L) 5 minutes after termination of ischemia. Toxicity controls were performed with morphine (10 micromol/L) and naloxone (10 micromol/L) without ischemia. Histologic evaluation was performed for all groups on the seventh postoperative day.. Sixty minutes of ischemia led to severe cell loss in ganglion cell layer and thinning of the inner nuclear layer in ischemia-saline group compared with that of the saline-control group (P < 0.001). Thickness of the inner plexiform layer to the inner limiting membrane (a measure of inner retinal thickness) was significantly increased due to edema (P < 0.001). Administration of morphine 5 minutes after reperfusion significantly improved all of the above mentioned indices compared with ischemia-saline group (P < 0.001). Administration of morphine 1 hour after reperfusion had also a significant effect on the improvement of above mentioned indices compared with saline-control group (P < 0.05). However, the number of ganglion cells was significantly higher in ischemia-morphine 0 hour group compared with ischemia-morphine 1 hour group (P < 0.001). Morphine treatment 18 hours after reperfusion did not change the amount of injury. Administration of naloxone 5 minutes before morphine abolished most of the morphine protective effects.. Intravitreal administration of morphine immediately after reperfusion maximally protects retina against ischemia-reperfusion injury. Pharmacologic evidence suggests that this protective phenomenon may be mediated in part by opioid receptors.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Injections; Male; Morphine; Naloxone; Narcotic Antagonists; Rabbits; Reperfusion Injury; Retina; Retinal Diseases; Retinal Ganglion Cells; Time Factors; Vitreous Body

H-Dmt-D-Arg-Phe-Lys-NH(2) ([Dmt(1)]DALDA), a highly selective micro-opioid peptide, is potently analgesic after systemic and intrathecal administration but is less potent given intracerebroventricularly. This study was performed to further characterize the analgesic effects of [Dmt(1)]DALDA.. We compared the effects of [Dmt(1)]DALDA and morphine after systemic administration in two different acute pain tests, the tail flick test and the paw withdrawal test, and examined how antagonizing the spinal opioid actions would affect their analgesic effects.. [Dmt(1)]DALDA was markedly more potent in the tail flick test than in the hot plate test, while the potencies of morphine were similar in the two tests. Intrathecal naloxone completely blocked the effect of systemic [Dmt(1)]DALDA in the tail flick test, while it only partially blocked the effect of morphine. At higher doses that produced analgesia in the hot plate test, the effect of [Dmt(1)]DALDA in this test was only partially blocked by naloxone.. Systemic [Dmt(1)]DALDA has a unique analgesic property clearly different from that of morphine and it has a propensity to produce spinal analgesia.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Injections, Spinal; Male; Morphine; Naloxone; Narcotic Antagonists; Oligopeptides; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu

To investigate the changes of pCREB protein expression in the distal cerebrospinal fluid contacting neurons induced by chronic morphine dependence and withdrawal.. Twenty-four Sprague-Dawley rats of both genders were randomly divided into three groups (n=8 each): control (Group I); chronic morphine dependence (Group II); chronic morphine abstinence (Group III). Chronic morphine dependence was induced by increasing doses of morphine, starting from 5 to 260 mg/kg/day in 12 days. The animals were killed 24 hours later. We evaluated morphine dependence by measuring the behavioral expression of morphine withdrawal and pCREB double labeled neuron recordings of dorsal raphe nucleus. The CB-HRP/pCREB double labeling method was used to observe the expression of pCREB in the distal cerebrospinal fluid contacting neurons.. The results showed the number of double labeled neuron of distal cerebrospinal fluid contacting neuron in dorsal raphe nucleus with up-regulated expression.. Morphine-dependent and withdrawal can activate the distal cerebrospinal fluid contacting neurons phosphorylation CREB in rat brain. The cerebrospinal fluid contacting neuron is related to morphine withdrawal and dependence rats.

Topics: Analysis of Variance; Animals; CREB-Binding Protein; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Neurons; Phosphorylation; Raphe Nuclei; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Time Factors

The opioid system has been implicated in major depression and in the mechanism of action of antidepressants. This study investigated the involvement of the opioid system in the antidepressant-like effect of the water-soluble B-vitamin folic acid in the forced swimming test (FST). The effect of folic acid (10 nmol/site, i.c.v.) was prevented by the pretreatment of mice with naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist), naltrindole (3 mg/kg, i.p., a selective delta-opioid receptor antagonist), naloxonazine (10 mg/kg, i.p., a selective mu(1)-opioid receptor antagonist, 24 h before), but not with naloxone methiodide (1 mg/kg, s.c., a peripherally acting opioid receptor antagonist). In addition, a sub-effective dose of folic acid (1 nmol/site, i.c.v.) produced a synergistic antidepressant-like effect in the FST with a sub-effective dose of morphine (1 mg/kg, s.c.). A further approach was designed to investigate the possible relationship between the opioid system and NMDA receptors in the mechanism of action of folic acid in the FST. Pretreatment of the animals with naloxone (1 mg/kg, i.p.) prevented the synergistic antidepressant-like effect of folic acid (1 nmol/site, i.c.v.) and MK-801 (0.001 mg/kg, i.p., a non-competitive NMDA receptor antagonist). Together the results firstly indicate that the anti-immobility effect of folic acid in the FST is mediated by an interaction with the opioid system (mu(1) and delta), likely dependent on the inhibition of NMDA receptors elicited by folic acid.

Topics: Analgesics, Opioid; Animals; Antidepressive Agents; Anxiety; Behavior, Animal; Disease Models, Animal; Dizocilpine Maleate; Drug Combinations; Excitatory Amino Acid Antagonists; Exploratory Behavior; Folic Acid; Mice; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Narcotics; Swimming

Previous investigation has shown that Thymus Vulgaris (TV) modulates pain. The aim of this work was to examine the role of TV on acute and chronic pain and compares its effect with dexamethasone (DEX) and stress (ST) by using hot plate, tail flick and formalin tests in mice. In this study male albino mice (25-30 g.) in 21 groups (n=147) were used. TV (100, 500 and 1000 mg/kg), DEX (0.5, 1 and 2 mg/kg) and vehicle (VEH) were injected 30 minutes before pain assessment tests. Stress was applied by 1 min swimming in cold water (18-22 degrees ). Acute and chronic pain was assessed by hot plate, tail flick and formalin tests. For assessment of the role of opioid receptors in antinoceception of TV extract, Naloxon (NAL, 2mg/kg, ip) as opioid receptor antagonist was injected before the injection of the more effective dose (500 mg/kg) of TV extract. Results indicated that TV, DEX and ST have analgesic effects in all tests (P<0.01 in comparison with control group). Above findings showed that TV extract, DEX and ST have modulatory effects on acute and chronic pain. Further research is required to determine the mechanisms by which TV extract has an inhibitory effect on pain sensation.

Topics: Analgesics; Animals; Dexamethasone; Disease Models, Animal; Dose-Response Relationship, Drug; Formaldehyde; Hot Temperature; Male; Mice; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Plant Extracts; Stress, Psychological; Thymus Plant

Herein we used electrophysiologic approaches in hippocampal area CA1 to estimate how morphine treatment alters the pentylenetetrazol (PTZ) effects.. Hippocampal slices taken from either control animals or animals made dependent via chronic morphine administration were examined. Changes in the population spike and epileptiform amplitudes were used as indices to quantify the effects of PTZ exposure in the control and morphine-dependent slices. Hippocampal slices taken either from control animals or from animals made dependent upon morphine were exposed to PTZ, either with or without morphine, naloxone, or morphine + naloxone.. Morphine dependence increased a PTZ-induced long-term potentiation (LTP) of the population spike in CA1 in vitro. This LTP was not found in rats that had spontaneously withdrawn morphine or withdrawn with naloxone in vivo after chronic morphine intake. Morphine or naloxone in vitro blocked the PTZ-induced LTP changes in control and morphine-dependent slices. However, PTZ-induced multiple population spikes (epileptiform activity) in CA1 was not blocked by naloxone.. It is concluded that dependence on morphine enhances PTZ-induced plastic and epileptic changes in CA1 excitability. We suggest that this model of neuronal activity in dependent slices could present an opportunity for studying the mechanisms underlying the increased likelihood of seizures in morphine users.

Topics: Animals; Convulsants; Disease Models, Animal; Drug Interactions; Electric Stimulation; Evoked Potentials; Hippocampus; In Vitro Techniques; Long-Term Potentiation; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Neural Pathways; Pentylenetetrazole; Rats; Rats, Inbred Strains; Statistics, Nonparametric; Substance Withdrawal Syndrome

Opioids are widely used for anesthesia but paradoxically induce postoperative pain hypersensitivity via N-methyl-D: -aspartate (NMDA) receptor modulation. Sevoflurane effects on opioid-induced hyperalgesia have not been yet evaluated in vivo. Nevertheless, some experimental in vitro studies reported anti-NMDA receptor properties for sevoflurane. The aim of this study was to evaluate sevoflurane effects on fentanyl-induced hyperalgesia in opioid-naive rats and in rats with inflammatory pain.. Sevoflurane effects on hyperalgesia were evaluated in Sprague-Dawley rats: opioid-naive rats, rats treated with fentanyl (4 x 60 microg kg(-1)) and rats with inflammatory pain (carrageenan) treated with fentanyl (4 x 60 microg kg(-1)). On day zero, subcutaneous fentanyl injections were administered and inflammatory pain was induced with one carrageenan injection in one hind paw. Rats were exposed to low concentrations of sevoflurane (1.0 or 1.5%) on day zero prior to fentanyl injections and inflammatory pain induction, and for the duration of the fentanyl analgesic effect. The nociceptive threshold (Randall-Selitto test) was evaluated daily for 7 days. On day seven, naloxone was injected and the nociceptive threshold was assessed 5 min later.. In rats without inflammatory pain but treated with fentanyl on day zero, sevoflurane 1.0% reversed the early (day zero) and long-lasting (day zero to day three) hyperalgesia classically described after high-doses of fentanyl (P < 0.05). This sevoflurane concentration antagonized the hyperalgesia induced by naloxone on day seven (P = 0.33). In a second experiment in rats with inflammatory pain, exposure to low concentrations of sevoflurane (1.0 and 1.5%) did not reduce fentanyl-induced hyperalgesia (P > 0.05), but nevertheless antagonized the naloxone induced hyperalgesia on day seven (P = 0.061).. Relatively low sevoflurane concentrations (1.0%) reverse fentanyl-induced hyperalgesia in rats without inflammatory pain. Nevertheless, the lack of effect of sevoflurane concentrations of 1.0% and 1.5% to oppose hyperalgesia following high-dose fentanyl and inflammatory pain suggests that sevoflurane anti-hyperalgesic properties are weak.

Topics: Analgesics, Opioid; Anesthetics, Inhalation; Animals; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Fentanyl; Hyperalgesia; Male; Methyl Ethers; Naloxone; Narcotic Antagonists; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Sevoflurane

We evaluated the effects of haloperidol and its metabolites on capsaicin-induced mechanical hypersensitivity (allodynia) and on nociceptive pain induced by punctate mechanical stimuli in mice.. Subcutaneous administration of haloperidol or its metabolites I or II (reduced haloperidol) dose-dependently reversed capsaicin-induced (1 microg, intraplantar) mechanical hypersensitivity of the hind paw (stimulated with a nonpainful, 0.5-g force, punctate stimulus). The order of potency of these drugs to induce antiallodynic effects was the order of their affinity for brain sigma-1 (sigma(1)) receptor ([(3)H](+)-pentazocine-labeled). Antiallodynic activity of haloperidol and its metabolites was dose-dependently prevented by the selective sigma(1) receptor agonist PRE-084, but not by naloxone. These results suggest the involvement of sigma(1) receptors, but discard any role of the endogenous opioid system, on the antiallodynic effects. Dopamine receptor antagonism also appears unlikely to be involved in these effects, since the D(2)/D(3) receptor antagonist (-)-sulpiride, which had no affinity for sigma(1) receptors, showed no antiallodynic effect. None of these drugs modified hind-paw withdrawal after a painful (4 g force) punctate mechanical stimulus in noncapsaicin-sensitized animals. As expected, the control drug gabapentin showed antiallodynic but not antinociceptive activity, whereas clonidine exhibited both activities and rofecoxib, used as negative control, showed neither.. These results show that haloperidol and its metabolites I and II produce antiallodynic but not antinociceptive effects against punctate mechanical stimuli and suggest that their antiallodynic effect may be due to blockade of sigma(1) receptors but not to dopamine receptor antagonism.

Topics: Analysis of Variance; Animals; Brain; Capsaicin; Disease Models, Animal; Dopamine Antagonists; Dose-Response Relationship, Drug; Female; Haloperidol; Hyperalgesia; Mice; Morpholines; Motor Activity; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Pentazocine; Physical Stimulation; Protein Binding; Radioligand Assay; Reaction Time; Receptors, sigma; Rotarod Performance Test; Sigma-1 Receptor; Tritium

The purpose of this work was to search for potential drugs with potent antitussive and expectorant activities as well as a low toxicity, but without addictive properties. Cholic acid-verticinone ester (CA-Ver) was synthesized based on the clearly elucidated antitussive and expectorant activities of verticinone in bulbs of Fritillaria and different bile acids in Snake Bile. In our previous study, CA-Ver showed a much more potent activity than codeine phosphate. This study was carried out to investigate the central antitussive mechanism and the addictive evaluation of CA-Ver.. Testing on a capsaicin-induced cough model of mice pretreated with naloxone, a non-selective opioid receptor antagonist, was performed for the observation of CA-Ver's central antitussive mechanism. We then took naloxone-induced withdrawal tests of mice for the judgment of CA-Ver's addiction. Lastly, we determined the opioid dependence of CA-Ver in the guinea pig ileum.. The test on the capsaicin-induced cough model showed that naloxone could block the antitussive effect of CA-Ver, suggesting the antitussive mechanism of CA-Ver was related to the central opioid receptors. The naloxone-urged withdrawal tests of the mice showed that CA-Ver was not addictive, and the test of the opioid dependence in the guinea pig ileum showed that CA-Ver had no withdrawal response.. These findings suggested that CA-Ver deserved attention for its potent antitussive effects related to the central opioid receptors, but without addiction, and had a good development perspective.

Topics: Animals; Antitussive Agents; Capsaicin; Cevanes; Cholic Acids; Cough; Disease Models, Animal; Drug Interactions; Female; Guinea Pigs; Ileum; In Vitro Techniques; Male; Mice; Naloxone; Opioid-Related Disorders; Receptors, Opioid; Substance Withdrawal Syndrome

Buprenorphine displays attributes of opioids, but also some features distinct from them. We examined spinal and supraspinal signal transduction of buprenorphine-induced anti-nociception in mice compared with morphine and fentanyl.. The opioid receptor antagonist naloxone, Pertussis toxin (PTX), G(z) protein antisense and nociceptin/orphanin-FQ receptor agonist nociceptin, and antagonist, JTC-801, were injected supraspinally (intracerebroventricular) and spinally (intrathecal). Also the cell-permeable Ser/Thr protein phosphatase inhibitor okadaic acid was given supraspinally.. Spinal naloxone (20 microg) or PTX (1 microg) attenuated morphine, fentanyl and buprenorphine (s.c.) anti-nociception. Supraspinal naloxone or PTX attenuated morphine and fentanyl, but not buprenorphine anti-nociception. Spinal G(z) protein antisense did not alter buprenorphine, morphine or fentanyl anti-nociception and supraspinal G(z)-antisense did not alter morphine or fentanyl anti-nociception. However, supraspinal G(z)-antisense (not random sense) reduced buprenorphine anti-nociception. Peripheral JTC-801 (1 mgxkg(-1), i.p.) enhanced the ascending (3 mgxkg(-1)) and descending (30 mgxkg(-1)) portions of buprenorphine's dose-response curve, but only spinal, not supraspinal, nociceptin (10 nmolxL(-1)) enhanced buprenorphine anti-nociception. Intracereboventricular okadaic acid (0.001-10 pg) produced a biphasic low-dose attenuation, high-dose enhancement of buprenorphine(3 or 30 mgxkg(-1), s.c.) anti-nociception, but did not affect morphine or fentanyl anti-nociception.. Buprenorphine has an opioid component to its supraspinal mechanism of analgesic action. Our present results reveal an additional supraspinal component insensitive to naloxone, PTX and nociceptin/orphanin-FQ, but involving G(z) protein and Ser/Thr protein phosphatase. These data might help explain the unique preclinical and clinical profiles of buprenorphine.

Topics: Acetylcholine; Adrenergic alpha-Antagonists; Aminoquinolines; Analgesics, Opioid; Anesthetics, Local; Animals; Benzamides; Brain; Buprenorphine; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Fentanyl; GTP-Binding Proteins; Injections, Intraventricular; Injections, Spinal; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Nociceptin; Nociceptin Receptor; Okadaic Acid; Oligonucleotides, Antisense; Opioid Peptides; Pain; Pain Measurement; Pain Threshold; Pertussis Toxin; Phosphoprotein Phosphatases; Piperazines; Pyridines; Receptor, Serotonin, 5-HT1A; Receptors, Opioid; Serotonin 5-HT1 Receptor Antagonists; Serotonin Antagonists; Signal Transduction; Yohimbine

Pfaffia glomerata (Spreng) Pedersen (Amaranthaceae) is a medicinal plant known in Brazil as "Paratudo" and "Brazilian ginseng" and is commonly used as tonic, antidiabetic and to treat gastric disorders.. This study evaluates the possible mechanism by which hydroalcoholic extract (HE) of Pfaffia glomerata exerts its antinociceptive effect.. The HE was evaluated in acetic acid and glutamate models of pain or by biting behavior following intrathecal (i.t.) administration of agonists of excitatory aminoacids (EAA) receptors glutamate and pro-inflammatory cytokines, IL-1beta and TNF-alpha in mice.. Oral administration of HE produced dose-dependent inhibition of acetic acid-induced visceral pain and glutamate-induced pain, with ID(50) of 64.6 (47.7-87.5)mg/kg and ID(50) of 370.8 (253.4-542.7)mg/kg, respectively. The HE (300 mg/kg, p.o.) antinociception, in the acetic acid test, was not affected by i.p. treatment of animals with naloxone. In addition, HE (300 mg/kg, p.o.) inhibited the pain-related behaviors induced by i.t. injection of trans-ACPD and TNF-alpha, but not by NMDA, AMPA, kainate or IL-1beta.. Our results suggest that inhibition of glutamatergic metabotropic receptors and TNF-alpha may account for the antinociceptive action reported for the HE in models of chemical pain used in this study.

Topics: Acetic Acid; Amaranthaceae; Analgesics; Animals; Behavior, Animal; Cycloleucine; Disease Models, Animal; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Injections, Spinal; Interleukin-1beta; Mice; Naloxone; Narcotic Antagonists; Pain; Phytotherapy; Plant Extracts; Plant Roots; Tumor Necrosis Factor-alpha

50% ethanol extract (ASE) of Amaranthus spinosus (whole plant) has been evaluated for antinociceptive and antiinflammatory activities.. Analgesic and antiinflammatory activities were studied by measuring nociception by formalin, acetic acid, hot plate, tail immersion method while inflammation was induced by carrageenan.. ASE had significant dose dependent percentage protection against acetic acid (0.6% of 10 ml) induced pain and the effects were also compared to aspirin, morphine and naloxone while formalin induced pain (0.05 ml of 2.5%) was significantly blocked only at higher dose (400mg/kg) in first phase. ASE significantly blocked pain emanating from inflammation at all the doses in second phase. The reaction time in hot plate was increased significantly and dose dependently where as pretreatment with naloxone rigorously reduced the analgesic potentials of ASE. Further in tail immersion test the same dose dependent and significant activity was observed. Aspirin had no effect on thermal induced pain i.e. hot plate and tail immersion tests but showed an effect on writhing test.. Our investigation show that Amaranthus spinosus possess significant and dose dependant antiinflammatory activity, it has also central and peripheral analgesic activity.

Topics: Acetic Acid; Amaranthus; Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Aspirin; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Formaldehyde; Hot Temperature; Male; Mice; Naloxone; Narcotic Antagonists; Pain; Phytotherapy; Plant Extracts

Withdrawal of opioid drugs leads to a cluster of unpleasant symptoms in dependent subjects. These symptoms are stimulatory in nature and oppose the acute, inhibitory effects of opiates. The conventional theory that explains the opioid withdrawal syndrome assumes that chronic usage of opioid drugs activates compensatory mechanisms whose stimulatory effects are revealed upon elimination of the inhibitory opioid drug from the body. Based on previous studies that show a dose-dependent dual activity of opiates, including pain perception, we present here an alternative explanation to the phenomenon of withdrawal-induced hyperalgesia. According to this explanation, the residual low concentration of the drug that remains after cessation of its administration elicits the stimulatory withdrawal hyperalgesia. The goal of the present study was to test this hypothesis. In the present study we rendered mice dependent on morphine by a daily administration of the drug. Cessation of morphine application elicited withdrawal hyperalgesia that was completely blocked by a high dose of the opiate antagonist naloxone (100 mg/kg). Similarly, naloxone (2 mg/kg)-induced withdrawal hyperalgesia was also blocked by 100 mg/kg of naloxone. The blockage of withdrawal hyperalgesia by naloxone suggested the involvement of opioid receptors in the phenomenon and indicated that withdrawal hyperalgesia is a direct effect of a residual, low concentration of morphine. Acute experiments that show morphine- and naloxone-induced hyperalgesia further verified our hypothesis. Our findings offer a novel, alternative approach to opiate detoxifications that may prevent withdrawal symptoms by a complete blockage of the opioid receptors using a high dose of the opioid antagonist.

Topics: Animals; Chronic Disease; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Hyperalgesia; Male; Mice; Mice, Inbred ICR; Morphine; Naloxone; Narcotic Antagonists; Nociceptors; Receptors, Opioid; Severity of Illness Index; Substance Withdrawal Syndrome; Substance-Related Disorders

To study the behavioral depression induced by a generalized limbic seizure and by an opioid. The hypothesis that an opioid fentanyl and an amygdala-evoked seizure induced behavioral depression through the nucleus accumbens was tested.. The behavioral depression induced by an amygdala-kindled seizure was studied in fully kindled rats, with or without prior injection of fentanyl (0.05 mg/kg, s.c.). Local infusion of a nonspecific opioid antagonist, naloxone, or saline, was made bilaterally in the nucleus accumbens. The durations of loss of righting reflex (LORR), loss of tail-pinch response, and catalepsy were assessed.. Fentanyl induced an LORR following a generalized kindled seizure. The combination of fentanyl and a generalized seizure, as compared to fentanyl alone or a generalized seizure alone, resulted in a prolonged duration of LORR, catalepsy, and loss of tail pinch response. Infusion of naloxone as compared to saline in the nucleus accumbens reduced the duration of catalepsy and LORR induced by fentanyl, with or without a generalized seizure.. Postictal depression that follows a generalized kindled seizure enhanced the behavioral effects of the opioid fentanyl. Network synaptic depression induced by the seizure acted synergistically with fentanyl to produce analgesia, catalepsy, and LORR, in part through the nucleus accumbens.

Topics: Amygdala; Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Electric Stimulation; Electroencephalography; Fentanyl; Functional Laterality; Kindling, Neurologic; Male; Naloxone; Narcotic Antagonists; Narcotics; Nucleus Accumbens; Rats; Rats, Long-Evans; Reflex; Seizures; Statistics, Nonparametric

The negative motivational aspects of withdrawal include symptoms of both anxiety and depression, and emerge after termination of chronic drug use as well as after acute drug exposure. States of acute withdrawal are an inherent part of intermittent drug use in humans, but the contribution of acute withdrawal to the development of addiction has received limited systematic investigation, because of a lack of preclinical models for withdrawal states that emerge spontaneously after acute drug exposure. Here, we have characterized a spontaneous increase in the magnitude of the acoustic startle reflex (ie, spontaneous withdrawal-potentiated startle) that emerges after acute morphine administration in rats, and compared the time course of startle potentiation and place conditioning. We find that startle potentiation seems to be related to a decrease in opiate receptor occupancy and reflects an anxiety-like state with a pharmacological profile similar to other signs of opiate withdrawal. Spontaneous startle potentiation emerges before the rewarding effects of morphine have subsided, even though naloxone administration after a single morphine exposure causes both startle potentiation and conditioned place aversion (CPA). These results show that negative emotional signs of withdrawal develop after just one exposure to morphine, and are likely a recurrent aspect of intermittent drug use that may contribute to the earliest adaptations underlying the development of addiction. Furthermore, the dissociation between spontaneous startle potentiation and CPA suggests anxiogenic and dysphoric manifestations of opiate withdrawal may be mediated by distinct neural mechanisms that are progressively engaged as withdrawal unfolds.

Topics: Acoustic Stimulation; Analysis of Variance; Animals; Anti-Anxiety Agents; Anxiety; Behavior, Animal; Chlordiazepoxide; Conditioning, Operant; Depression; Disease Models, Animal; Excitatory Amino Acid Antagonists; Isoquinolines; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Propranolol; Rats; Rats, Sprague-Dawley; Reflex, Startle; Substance Withdrawal Syndrome; Time Factors

The present study examined the antinociceptive effects of (O-methyl) N-benzoyl-tyramine (riparin I, ripI) isolated from the unripe fruit of Aniba riparia in chemical and thermal behavioral models of pain, such as acetic acid-induced abdominal writhing, formalin, and hot-plate tests in mice. Moreover, the involvement of the nitric oxide pathway as well as the opioid system in the antinociceptive action of ripI in the formalin test was investigated. RipI was administered both orally and intraperitoneally to male mice at single doses of 25 and 50 mg/kg. In the acetic acid-induced abdominal writhing, ripI decreased the number of writhings at both doses. In addition, in the formalin test, ripI reduced the paw licking time at both phases of the test. The effect of the highest dose of ripI in mice formalin test on the early phase was not reversed by naloxone (opioid receptor antagonist) but it was reversed by l-arginine (a nitric oxide precursor) in the late phase, suggesting that ripI may not act through opioid system and possibly acts through inhibition of nitric oxide pathway. In the hot-plate test, ripI increased the reaction time in the hot-plate test at the dose of 25 mg/kg, i.p., confirming the result found in the formalin test. Based on the obtained results, it is suggested that ripI presents antinociceptive activity that may be due to peripheral mechanisms (nitric oxide pathway) and central mechanisms, discarding the involvement of opioid system.

Topics: Acetic Acid; Administration, Oral; Analgesics; Analgesics, Opioid; Animals; Arginine; Behavior, Animal; Benzamides; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Formaldehyde; Hot Temperature; Injections, Intraperitoneal; Lauraceae; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Pain; Pain Measurement; Reaction Time; Time Factors; Tyramine

The antinociceptive effects of the selective noradrenaline reuptake inhibitor antidepressant reboxetine and its interaction with various opioid and noradrenaline receptor subtypes were evaluated. Reboxetine (i.p.) induced a weak dose-dependent antinociceptive effect in acute pain, using the hotplate model. The reboxetine-induced antinociception was significantly inhibited by the opioid receptor antagonists naloxone, nor-BNI, naltrindole and b-FNA, implying a non-selective role for the opioid receptors in the reboxetine's antinociceptive effect. The adrenergic antagonists yohimbine and phentolamine attenuated to some extent the reboxetine-induced antinociception, implying a minor adrenergic mechanism of antinociception. The addition of opioid or alpha2 agonists, did not potentiate the antinociception effect of reboxetine. Thus, it seems that reboxetine possesses a weak antinociceptive effect, mediated by non-selective opioid receptors and influenced somewhat by noradrenaline alpha2 receptors. These results suggest that reboxetine as monotherapy does not have sufficient efficacy in the management of acute pain. However, further research is needed in order to establish its possible use alone or in combination with other antidepressants or analgesics in the amelioration of chronic pain disorders.

Topics: Adrenergic Antagonists; Analgesics; Animals; Antidepressive Agents; Clonidine; Disease Models, Animal; Drug Interactions; Male; Mice; Mice, Inbred ICR; Morphine; Morpholines; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Reboxetine; Receptors, Opioid, mu

Cytotoxic Necrotizing Factor 1 (CNF1) is a protein toxin from Escherichia coli that constitutively activates the Rho, Rac and Cdc42 GTPases. These regulatory proteins oscillate between a cytosolic GDP-bound inactive form and a membrane-linked GTP-bound active form, orchestrating the actin cytoskeleton assembly and dynamics. We herein describe, for the first time, the ability of CNF1 to potently counteract the formalin-induced inflammatory pain in mice. The analgesic response due to CNF1 requires both the sustained activation of the Rac GTPase, with consequent cerebral actin cytoskeleton remodeling, and the up-regulation of the mu-opioid receptors (MORs), the most important receptors controlling pain perception. The crucial role of Rac is proved by the lack of analgesic activity in mice challenged with a recombinant CNF1, in which the enzymatic activity was abolished by substituting serine with cysteine at position 866. The importance of MORs is proved by the inability of CNF1 to induce any analgesic effect in MORs knockout mice and by the ability of naloxone to antagonize the analgesic effects. Furthermore, it is worth noting that the analgesic effect in mice occurs after both peripheral and central administration of CNF1. Hence, taken altogether, our findings provide new insights into the comprehension of intracellular mechanisms involved in pain modulation, and indicate this bacterial protein toxin as a novel tool in the field of pain control. Conceivably, this might pave the way for new therapeutic strategies.

Topics: Analgesics; Animals; Bacterial Toxins; Cell Line, Tumor; Cerebellum; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Escherichia coli Proteins; Formaldehyde; Humans; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Naloxone; Narcotic Antagonists; Neuroblastoma; NF-kappa B; p21-Activated Kinases; Pain; Pain Measurement; rac GTP-Binding Proteins; Receptors, Opioid, mu; rho GTP-Binding Proteins; Signal Transduction; Time Factors; Transfection; Up-Regulation

The mechanism of orthodontic pain and discomfort is poorly understood partly because of the limited number of animal behavioral models for pain assessment. This study aimed to develop a behavioral model for assessment of tooth-movement pain in rats using directed face-grooming activity. Male Sprague-Dawley rats weighing 200-300 g were used. They were videotaped on days 1, 3, 5, 7, and 14 after experimental tooth movement and their directed face-grooming behavior was evaluated. In addition, we also evaluated behavioral responses to the application of a progressively higher magnitude force and to multiple applications of an equal magnitude force. Finally, the effects of peripherally and systemically administered morphine and of the N-methyl-d-aspartate (NMDA) receptor antagonist, MK-801, on the behavioral responses were evaluated. The results indicated that time spent on directed face-grooming activity increased dramatically after initiating experimental tooth movement. The change concurred with the initial orthodontic pain response. This behavioral change was reproducible and was related to force magnitude. Application of both systemic and peripheral morphine and MK-801 could exert an analgesic effect on this pain model. These results suggest that directed face-grooming behavior can be a reliable measure for tooth-movement pain in rats, which could be widely used in investigating the orthodontic pain mechanism.

Topics: Animals; Dental Alloys; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Facial Pain; Grooming; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Nickel; Orthodontic Wires; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Stress, Mechanical; Time Factors; Titanium; Tooth Movement Techniques; Videotape Recording

Exercise improves cardiovascular health, strengthens muscles and bones, stimulates neuroplasticity, and promotes feelings of well-being. However, when taken to extremes, exercise can develop into an addictive-like behavior. To assess the addictive potential of exercise, withdrawal symptoms following injections of 1.0 mg/kg naloxone were compared in active and inactive male and female rats. Active and inactive rats were given food for 1 hr or 24 hr/day. Additionally, a group of inactive rats was pair-fed the amount of food consumed on the previous day by food-restricted active rats. Rats fed for 1 hr/day decreased food intake and lost weight. Additionally, food-restricted active rats increased wheel running. There was a direct relationship between the intensity of running and the severity of withdrawal symptoms. Active food-restricted rats displayed the most withdrawal symptoms, followed by active rats given 24-hr access to food. Only minimal withdrawal symptoms were observed in inactive rats. These findings support the hypothesis that exercise-induced increases in endogenous opioid peptides act in a manner similar to chronic administration of opiate drugs.

Topics: Analysis of Variance; Animals; Anorexia; Body Weight; Disease Models, Animal; Feeding Behavior; Female; Male; Motor Activity; Naloxone; Narcotic Antagonists; Physical Conditioning, Animal; Rats; Rats, Long-Evans; Sex Characteristics; Substance Withdrawal Syndrome

Several lines of evidence implicate dysfunction of glutamatergic neurotransmission in opiate dependence and withdrawal. Functional antagonists of glutamatergic system, including compounds acting on both ionotropic and metabotropic glutamate receptors (group I mGlu receptor antagonists and group II mGlu receptor agonists), have been shown to decrease behavioural signs of opiate withdrawal in rodents. In the present study we analyzed an influence of group III mGlu receptor agonist, ACPT-I, on opioid withdrawal syndrome, induced by repeated morphine administration and final naloxone injection. We show, that ACPT-I significantly attenuated typical symptoms of naloxone-induced morphine withdrawal, after peripheral administration in C57BL/6J mice. These data indicate an important role of group III mGlu receptors in morphine withdrawal states and suggest that activation of group III mGlu receptors may reduce opiate withdrawal symptoms.

Topics: Analysis of Variance; Animals; Body Weight; Cyclopentanes; Disease Models, Animal; Dose-Response Relationship, Drug; Head Movements; Male; Mice; Mice, Inbred C57BL; Morphine; Morphine Dependence; Motor Activity; Naloxone; Narcotic Antagonists; Receptors, Metabotropic Glutamate; Substance Withdrawal Syndrome; Time Factors; Tremor; Tricarboxylic Acids

Although it is known that both clonidine and loperamide cause delayed colonic transit in mice, these models of drug-induced experimental constipation have not yet been fully characterized. Therefore, the aims of this study were to validate the clonidine- and loperamide-induced delays of colonic transit in mice as models of atonic and spastic constipation, respectively, and to evaluate the effect of mustard oil, a TRPA1 agonist, in both models. Colonic transit was evaluated in mice by determining the time needed to evacuate a bead inserted into the distal colon. Both loperamide and clonidine dose-dependently prolonged the evacuation time. Clonidine (10 microg/kg) and loperamide (0.3 mg/kg) tripled the evacuation time compared to controls. These delays were antagonized by the administration of yohimbine and naloxone, respectively. Tegaserod, a gastrointestinal motor-stimulating drug, reversed the delay in both models, but the effects were diminished at high doses. Atropine, an antispastic drug, improved the loperamide-induced delay, but did not affect the clonidine-induced delay. Mustard oil accelerated the colonic transit dose-dependently in both models of drug-induced constipations. These results indicate that clonidine- and loperamide-induced delays in colonic transit are models of atonic and spastic constipation, respectively, and that mustard oil may be effective on both types of constipation.

Topics: Animals; Atropine; Clonidine; Constipation; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Gastrointestinal Transit; Indoles; Loperamide; Male; Mice; Mice, Inbred Strains; Mustard Plant; Naloxone; Plant Oils; Transient Receptor Potential Channels; TRPA1 Cation Channel; Yohimbine

Antidepressant drugs act as potent inhibitors of norepinephrine and/or serotonin reuptake and are widely used with opioids for the treatment of chronic pain. The mechanism of this increased analgesic action is unclear. We compared the antinociceptive effects of the intrathecal administration of morphine with that of a nonselective (amitriptyline) or selective (maprotiline or citalopram) antidepressant drug using the thermal withdrawal test in rats. We also investigated the possible mechanisms involved in the interactions of these drugs.. Male Wistar rats were anesthetized with sevoflurane and administered morphine and antidepressant drugs, or saline, through intrathecal injection. The antinociceptive effect was evaluated using the thermal withdrawal test before and after drug administration. The time for the withdrawal reaction was expressed as percentage of maximum possible effect (MPE). Animals were also pretreated with yohimbine (a nonselective alpha2-adrenergic antagonist) and naloxone (a nonselective opioid antagonist) for mechanism of action studies. Pharmacologic interaction was evaluated using isobolographic analysis of simultaneous administration of fixed proportions of maprotiline and morphine.. Single intrathecal administration of morphine (2 microg), amitriptiline (125 microg), citalopram (144 microg), and maprotiline (1.25 microg) produced 51.6% +/- 8.9%, 10.3% +/- 3.2%, 33.8% +/- 5.2%, and 48.5% +/- 9.2% MPE, respectively. The antinociceptive effect of morphine was increased when combined with amitriptyline (91.3% +/- 4.6% MPE) and maprotiline (86.9% +/- 9.2% MPE) but not with citalopram (40.6% +/- 4.6% MPE). Coadministration of maprotiline increased the antinociceptive duration of morphine by 4-fold (from 120 to 480 min), which was reversed by pretreatment with the alpha-2 adrenoceptor inhibitor, yohimbine, and the mu-type opioid receptor antagonist, naloxone. Isobolographic analysis demonstrated a synergistic interaction between morphine and maprotiline.. Selective norepinephrine reuptake inhibitors can significantly increase the intensity and duration of morphine antinociceptive activity via both alpha(2)-adrenergic and opioid receptors. This interaction was not observed with the selective serotonin inhibitor, citalopram.

Topics: Adrenergic alpha-Antagonists; Adrenergic Uptake Inhibitors; Amitriptyline; Analgesics, Opioid; Animals; Antidepressive Agents, Second-Generation; Behavior, Animal; Citalopram; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Drug Therapy, Combination; Injections, Spinal; Male; Maprotiline; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Wistar; Reaction Time; Selective Serotonin Reuptake Inhibitors; Time Factors; Yohimbine

To investigate the effects of ephedrine combined with various doses of naloxone on neural plasticity in rats after cerebral ischemia/reperfusion injury to explore the possibility of synergistic effect about ephedrine combined with naloxone, promoting the optimum ratio of neural remodeling and its molecular mechanism.. A total of 192 healthy adult Sprague-Dawley rats, 220-250 g, were used to establish models of left middle cerebral artery occlusion using the suture occlusion method. Were randomly divided into 8 groups: the rats were intraperitoneally injected with 1.5 mg x kg(-1) x d(-1) ephedrine (ephedrine group), with 0.1, 0.2, 0.3 mg x kg(-1) x d(-1) naloxone (low, moderate and high doses of naloxone groups) , with 1.5 mg x kg(-1) x d(-1) ephedrine + 0.1, 0.2, 0.3 mg x kg(-1) x d(-1) naloxone (ephedrine + low, moderate and high doses of naloxone groups), and with 0.5 mL saline (model group), respectively. At 1-4 weeks following cerebral ischemia, sensorimotor integration in rats was assessed using the beam walking test, brain-derived neurotrophic factor (BDNF) expression was detected in the hippocampal CA3 area using immunohistochemistry 1-4 weeks after surgery, immunofluorescence method of detecting ischemic hemisphere hippocampal expression, The number of nerve cells apoptosis was detected using TUNEL assay.. BWT, BDNF, TUNEL assay results showed three doses of naloxone group had no significant effect, the effects increased together with the quantitative ephedrine, and had the amount-effect relationship, in which ephedrine + high dose of naloxone group the recovery of movement was fastest, BDNF expression in the best and ischemic apoptosis in the hippocampus at least, ischemic injury to the minimum, speed up the process of neural remodeling.. The ephedrine and ephedrine + naloxone groups were accelerated motor function recovery rate in rat after cerebral ischemia, and the promotion of neural remodeling is closely related to the expression of BDNF, inhibit apoptosis in ischemic area, and with the increase of naloxone amount of additives, its role more clearly, the mechanism may be related to the dose of naloxone can significantly inhibit the ischemic area of apoptosis in early cerebral ischemia, so had the positive synergy effect with ephedrine to speed up the formation of neural remodeling.

Topics: Animals; Apoptosis; Brain Ischemia; Brain-Derived Neurotrophic Factor; Disease Models, Animal; Ephedrine; Female; Hippocampus; Humans; Male; Naloxone; Neuronal Plasticity; Random Allocation; Rats; Rats, Sprague-Dawley

Our previous studies have shown that morphine withdrawal induced hyperactivity of cardiac noradrenergic pathways. The purpose of the present study was to evaluate the effects of morphine withdrawal on site-specific phosphorylation of TH in the heart.. Dependence on morphine was induced by a 7-day s.c. implantation of morphine pellets in rats. Morphine withdrawal was precipitated on day 8 by an injection of naloxone (2 mg kg(-1)). TH phosphorylation was determined by quantitative blot immunolabelling using phosphorylation state-specific antibodies.. Naloxone-induced morphine withdrawal induced phosphorylation of TH at serine (Ser)40 and Ser31 in the right ventricle, associated with both an increase in total TH levels and an enhancement of TH activity. When HA-1004 (PK A inhibitor) was infused, concomitantly with morphine, it diminished the increase in noradrenaline turnover, total TH levels and TH phosphorylation at Ser40 in morphine-withdrawn rats. In contrast, the infusion of calphostin C (PKC inhibitor), did not modify the morphine withdrawal-induced increase in noradrenaline turnover and total TH levels. In addition, we show that the ability of morphine withdrawal to stimulate phosphorylation at Ser31 was reduced by SL327, an inhibitor of ERK 1/2 activation.. The present findings demonstrate that the enhancement of total TH levels and the increased phosphorylation state of TH during morphine withdrawal were dependent on PKA and ERK activities and suggest that these transduction pathways might contribute to the activation of the cardiac catecholaminergic neurons in response to morphine withdrawal.

Topics: Aminoacetonitrile; Animals; Cyclic AMP-Dependent Protein Kinases; Disease Models, Animal; Drug Implants; Isoquinolines; Male; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Morphine; Morphine Dependence; Myocardium; Naloxone; Naphthalenes; Narcotic Antagonists; Norepinephrine; Phosphorylation; Protein Kinase C-delta; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Serine; Substance Withdrawal Syndrome; Sulfonamides; Tyrosine 3-Monooxygenase

Previous reports suggest the antiestrogen ICI 182,780 (ICI) does not cross the blood-brain barrier (BBB). However, this hypothesis has never been directly tested. In the present study, we tested whether ICI crosses the BBB, penetrates into brain and hypothalamic tissues, and affects known neuroendocrine functions in ovariectomized rats. Using HPLC with mass spectrometry, ICI (1.0 mg/kg.d, 3 d) was detected in plasma and brain and hypothalamic tissues for up to 24 h with maximum concentrations of 43.1 ng/ml, and 31.6 and 38.8 ng/g, respectively. To evaluate antiestrogenic effects of ICI in the brain after systemic dosing, we tested its ability to block the effect of 17 alpha-ethinyl estradiol (EE) (0.3 mg/kg, 8 d) on tail-skin temperature abatement in the morphine-dependent model of hot flush and on body weight change. In the morphine-dependent model, EE abated 64% of the naloxone-induced tail-skin temperature increase. ICI pretreatment (1.0, 3.0 mg/kg.d) dose dependently inhibited this effect. ICI (3.0 mg/kg.d) alone showed estrogenic-like actions, abating 30% the naloxone-induced flush. In body weight studies, EE-treated rats weighed 58.5 g less than vehicle-treated rats after 8 d dosing. This effect was partially blocked by ICI (3.0 mg/kg.d) pretreatment. Similar to EE treatment, rats receiving 1.0 or 3.0 mg/kg.d ICI alone showed little weight gain compared with vehicle-treated controls. Thus, ICI crosses the BBB, penetrates into brain and hypothalamic tissues, and has both antiestrogenic and estrogenic-like actions on neuroendocrine-related functions.

Topics: Animals; Blood-Brain Barrier; Body Weight; Disease Models, Animal; Dose-Response Relationship, Drug; Estradiol; Estrogen Antagonists; Ethinyl Estradiol; Female; Fulvestrant; Hot Flashes; Hypothalamus; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Ovariectomy; Rats; Rats, Sprague-Dawley; Skin Temperature; Uterus

Naloxone is an opioid receptor antagonist with effects on the EEG and behavior in animals and humans and has been used clinically in drug-abuse treatment. The goal of this work in the rat is to determine whether treatment with naloxone during the suckling period would influence the propagation of cortical spreading depression (CSD), both in weaned young and adult animals. From the 7th to the 28th postnatal day, male rat pups were treated daily with a single subcutaneous injection of either 10mg/kg/d naloxone (n=21 rats) or equivalent volume (10ml/kg) of saline (n=16). In both treatment conditions, when the pups were 30-40 days- (young groups; 9 Naloxone- and 10 saline-treated rats), or 90-120-days old (adult groups; 12 Naloxone- and 6 saline-treated rats), a 4h CSD recording session was performed with electrodes at two points at a fixed distance apart on the parietal cortical surface. CSD propagation velocity was calculated based on the time spent for a CSD-wave to pass between the electrodes. In both young- and adult groups, naloxone-treated animals displayed lower CSD velocities (P<0.05) than the corresponding saline injected animals. Our results demonstrate, for the first time, that chronic neonatal exposure of rats to the opioid antagonist naloxone results in an impairing propagation of the CSD that is long lasting, suggesting the existence of one or more opioid-mediated processes influencing CSD.

Topics: Action Potentials; Aging; Animals; Animals, Newborn; Animals, Suckling; Brain; Chronic Disease; Cortical Spreading Depression; Disease Models, Animal; Drug Administration Schedule; Male; Naloxone; Narcotic Antagonists; Opioid Peptides; Opioid-Related Disorders; Rats; Rats, Wistar; Time

Preclinical behavioral pharmacological and neuropharmacological evidence indicates that the NMDA receptor plays an important role in opioid dependence, however, the neural substrates subserving these actions are poorly understood. The central nucleus of the amygdala (CeA) is a critical coordinator of autonomic, behavioral, and emotional systems impacted by opioids, however there is no evidence that the essential NMDA-NR1 (NR1) subunit gene in the amygdala plays a role in opioid dependence. To determine the role of the NR1 subunit gene in the amygdala with respect to physical and psychological opioid withdrawal, a spatial-temporal deletion of this gene was produced by microinjecting a recombinant adeno-associated virus (rAAV) expressing the GFP reporter and Cre recombinase (rAAV-GFP-Cre) into the CeA of adult "floxed" NR1 mice (fNR1). Amygdala microinjection of rAAV-GFP-Cre produced a decrease in NR1 gene expression and protein immunolabeling in postsynaptic sites of neurons without signs of compromised ultrastructural neuronal morphology. Amygdala NR1 gene deletion also did not affect locomotor, somatosensory, or sensory-motor behaviors. In addition, bilateral local NR1 gene deletion did not impact somatic or visceral withdrawal symptoms precipitated by naloxone in morphine-dependent mice. However, there was a significant deficit in the expression of an opioid withdrawal-induced conditioned place aversion in mice with amygdala NR1 deletion. These results indicate that functional amygdala NMDA receptors are involved in aversive psychological processes associated with opioid withdrawal. More generally, spatial-temporal deletion of the NR1 subunit by Cre-loxP technology is an effective means to elucidate the neurogenetic substrates of complex phenotypes associated with drug abuse.

Topics: Amygdala; Animals; Avoidance Learning; Cell Shape; Conditioning, Psychological; Disease Models, Animal; Gene Deletion; Genes, Reporter; Genetic Vectors; Glutamic Acid; Mice; Mice, Knockout; Morphine Dependence; Naloxone; Narcotic Antagonists; Neurons; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission

Stress and anxiety initiates a cascade of biochemical and endocrine event which results in behavioral and electrophysiological effects in both animals and humans. In this study, we investigated the effects of dexamethasone (DEX), as a synthetic glucocorticoid, and its interaction with opioidergic system on anxiety related behavior in mice. Young adult male mice were used in this study. A standard elevated plus-maze was used to determine anxiety levels in animal. Different doses of DEX (0.1, 0.5, 1, 2 and 10 mg/kg, SC) or vehicle was injected 30 min before of evaluation. Naloxone (1 and 2 mg/kg, IP) was injected 5 min before the DEX (0.5 and 1 mg/kg) administration. Results indicated that DEX at doses of 0.5 and 1 reduced and in dose of 10 mg/kg increased anxiety related behaviors significantly (P<0.05 in all cases). Also pretreatment of naloxone at doses of 1 and 2 mg/kg attenuated the effects of lower doses of DEX on anxiety related behaviors. Finding above indicated that peripheral administration of glucocorticoids induces biphasic effects on anxiety related behaviors: anxiolytic effects in lower doses and anxiogenic effects in a high dose. Data also revealed an involvement of opioidergic system in anxiolytic effects of glucocorticoids.

Topics: Animals; Anti-Anxiety Agents; Anxiety; Behavior, Animal; Dexamethasone; Disease Models, Animal; Dose-Response Relationship, Drug; Exploratory Behavior; Glucocorticoids; Injections, Subcutaneous; Male; Mice; Naloxone; Narcotic Antagonists; Neurons; Opioid Peptides; Receptors, Opioid

Rectal distension (RD) is known to induce upper gastrointestinal (GI) symptoms. The aim of this study was to investigate the effects and underlying mechanisms of RD on gastric slow waves (GSW) and motor activity and furthermore to investigate the effects and mechanisms of electroacupuncture (EA) on GSW and motor activity. Eight female hound dogs chronically implanted with gastric serosal electrodes and a gastric fistula were studied in six separate sessions. Antral motility, GSW, heart rate variability, and rectal pressure were evaluated for the above purposes. 1) RD at a volume of 120 ml suppressed antral motility significantly. Guanethidine blocked the inhibitory effect of RD. EA at ST36 was able to restore the suppressed antral contractions induced by RD (16.6+/-1.7 vs. 8.0+/-1.4, P<0.001). Naloxone partially blocked the effect of EA on antral contractions. 2) RD reduced the percentage of normal GSW from 98.8+/-0.8% at baseline to 76.1+/-8.6% (P<0.05) that was increased to 91.8+/-3.0% with EA. The effects of EA on the GSW were nullified by the presence of naloxone. 3) EA did not show any significant effect on rectal pressure, suggesting that the ameliorating effects of EA on RD-induced impaired gastric motility were not due to a decrease in rectal pressure. 4) EA increased the vagal activity suppressed by RD. In conclusion, RD inhibits postprandial gastric motility and impairs GSW in dogs, and the inhibitory effects are mediated via the adrenergic pathways. EA at ST36 is able to restore the RD-induced impaired GSW and motor activities, possibly by enhancing vagal activity, and is partially mediated via the opioid pathway. EA may have therapeutic potential for functional gastrointestinal disorders.

Topics: Adrenergic Agents; Animals; Catheterization; Disease Models, Animal; Dogs; Electroacupuncture; Female; Gastrointestinal Diseases; Gastrointestinal Motility; Guanethidine; Heart Rate; Naloxone; Narcotic Antagonists; Postprandial Period; Pressure; Rectum; Stomach; Sympathetic Nervous System; Vagus Nerve

We previously reported the synthesis of three new opioid agonists as well as their in vitro and in vivo activity [Girón, R., Abalo, R., Goicoechea, C., Martín, M.I., Callado, L.F., Cano, C., Goya, P., Jagerovic, N. 2002. Synthesis and opioid activity of new fentanyl analogs. Life Sci. 71, 1023-1034]. One of them, N-[1-phenylpyrazol-3-yl]-N-[1-(2-phenethyl)-4-piperidyl)] propenamide (IQMF-4), showed an interesting antinociceptive activity. Intraperitoneally (i.p.) administered, it was as effective as fentanyl or morphine, being less potent than fentanyl but more so than morphine. The aim of the present work was to evaluate its antinociceptive effect by different routes of administration, using the hot plate test, and to investigate possible side effects, such as tolerance and withdrawal, in vitro, using the myenteric plexus-longitudinal muscle strip preparation from guinea pig ileum, and in vivo, using the hot plate test. IQMF-4 was more potent than morphine when administered per os (p.o.), but less potent when administered intracerebroventricularly (i.c.v.). By both routes, fentanyl is more potent that IQMF-4. When IQMF-4 was administered i.p., naloxone methiodide, a peripherally acting antagonist, was able to completely block its antinociceptive effect, whereas, after i.c.v. administration, the blockade was only partial. An interesting feature of the new compound is that it induces tolerance in vitro but not in vivo. Moreover, though in vitro withdrawal was not different from fentanyl or morphine, in vivo withdrawal symptoms were significantly less frequent in mice treated with IQMF-4 than in those treated with morphine or fentanyl. Although more assays are required, these results show that IQMF-4 appears to be a potent analgesic compound with an interesting peripheral component, and reduced ability to induce dependence.

Topics: Administration, Oral; Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Fentanyl; Guinea Pigs; Hot Temperature; Ileum; Injections, Intraperitoneal; Injections, Intraventricular; Male; Mice; Morphine; Muscle Contraction; Muscle, Smooth; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Pain; Pain Measurement; Pain Threshold; Piperidines; Propane; Quaternary Ammonium Compounds; Reaction Time; Substance Withdrawal Syndrome; Time Factors

The use of nicotinic agonists for analgesia is limited by their unacceptable side effects. Sazetidine-A is a new partial agonist nicotinic ligand that has very high selectivity for beta2-containing nicotinic acetylcholine receptors. It potently and selectively desensitizes alpha4beta2 nicotinic acetylcholine receptors without measurable effects on alpha3beta4 receptors. The authors investigated the analgesic effects of Sazetidine-A using the formalin model of chronic inflammatory pain.. The formalin test was conducted after rats received intraperitoneal saline, Sazetidine-A (0.125, 0.25, 0.5, 1, 2 mg/kg), or subcutaneous epibatidine (2.5-5-10 mug/kg). In other experiments, Sazetidine-A was preceded by naloxone (0.5 mg/kg) or mecamylamine (10 mg). Effects of Sazetidine-A and epibatidine on locomotor were tested in an open field, and seizure activity was measured using the Racine scale. Locus coeruleus neuron extracellular single-unit spontaneous discharge was recorded in anesthetized animals after Sazetidine-A and epibatidine.. Higher doses of Sazetidine-A (0.5, 1, or 2 mg/kg) induced analgesia, with pain scores significantly lower than those seen after saline, lower doses of Sazetidine-A, and epibatidine (P < 0.001). Naloxone did not antagonize the effects of Sazetidine-A, and mecamylamine had partial, dose-dependent antagonistic effects. Epibatidine excited locus coeruleus neurons, whereas Sazetidine-A had no effect on these neurons. Epibatidine and Sazetidine-A affected animals' locomotor activity for the initial 20 min. While analgesic doses of epibatidine caused seizures, no seizure activity or other neurologic complications were seen in animals that received as much as four times the minimum analgesic dose of Sazetidine-A.. Sazetidine-A seems to be a potent analgesic without causing neurologic side effects.

Topics: Analgesics; Animals; Azetidines; Bridged Bicyclo Compounds, Heterocyclic; Cholinergic Agents; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Mecamylamine; Motor Activity; Naloxone; Narcotic Antagonists; Nicotinic Agonists; Nicotinic Antagonists; Pain; Pain Measurement; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Nicotinic; Sodium Chloride

The infusion or decoction of Mirabilis jalapa leaves is used in traditional medicine in Brazil to treat inflammatory and painful diseases.. The present study examined the antinociceptive effect of Mirabilis jalapa extracts from leaves and stems in models of pain in mice.. The crude hydroethanolic extract from leaves (CrdL) was more potent than the crude extract from stems (CrdS) to inhibit abdominal constrictions induced by acetic acid, with ID(50) values of 5.5 (2.3-13.1) and 18.0 (11.3-28.5) mg/kg, respectively. Among the fractions tested, the Eta fraction from leaves (Eta) was more effective (maximal inhibition of 83+/-8%) and potent (ID(50) of 1.1 (0.6-2.1) mg/kg) to induce antinociception. Eta and CrdL also possessed an antinociceptive effect in the tail-flick test. Pre-treatment with naloxone did not modify the antinociceptive effect of Eta, but co-administration with atropine completely prevented it. This suggests that the antinociceptive effect might depend on the cholinergic system. Instead, Eta was not able to alter the acetylcholinesterase activity in blood or spinal cord. Concerning side effects, Eta did not alter locomotor activity, body temperature, gastrointestinal transit and did not produce gastric lesions.. Our results demonstrate that Mirabilis jalapa presents antinociceptive activity in mice, which supports its folkloric use as an analgesic.

Topics: Acetylcholinesterase; Analgesics; Animals; Atropine; Body Temperature; Brazil; Disease Models, Animal; Gastrointestinal Transit; Inhibitory Concentration 50; Male; Medicine, Traditional; Mice; Mirabilis; Motor Activity; Naloxone; Pain; Pain Measurement; Plant Extracts; Plant Leaves; Plant Stems; Toxicity Tests

Naltrexone, a compound with high affinity for the mu opioid receptor (MOP-R) reduces alcohol consumption. SoRI-9409 is a derivative of naltrexone that has highest affinity at delta opioid receptors (DOP-Rs). We have investigated the effects of SoRI-9409 on ethanol consumption to determine the consequences of altering the naltrexone compound to a form with increased efficacy at DOP-Rs.. Effects of the opioid receptor antagonists, SoRI-9409 (0-30 mg/kg, IP), naltrexone (0-30 mg/kg, IP), or naltrindole (0-10 mg/kg, IP) on ethanol consumption was measured in high- and low-ethanol-consuming rats with two different drinking paradigms. SoRI-9409-, naltrexone-, and naltrindole-mediated inhibition of DOP-R-stimulated [(35)S]GTP gamma S binding was measured in brain membranes prepared from high-ethanol-consuming rats. The effects of SoRI-9409 on morphine-mediated analgesia, conditioned place preference, and anxiety were also examined.. In high- but not low-ethanol-consuming animals, SoRI-9409 is threefold more effective and selective at reducing ethanol consumption when compared with naltrexone or naltrindole for up to 24 hours. SoRI-9409 administered daily for 28 days continuously reduced ethanol consumption, and when the administration of SoRI-9409 was terminated, the amount of ethanol consumed remained lower compared with vehicle-treated animals. Furthermore, SoRI-9409 inhibits DOP-R-stimulated [(35)S]GTP gamma S binding in brain membranes of high-ethanol-consuming rats.. SoRI-9409 causes selective and long-lasting reductions of ethanol consumption. This suggests that compounds that have high affinity for DOP-Rs such as SoRI-9409 might be promising candidates for development as a novel therapeutic for the treatment of alcoholism.

Topics: Alcohol Drinking; Alcoholism; Animals; Behavior, Animal; Brain; Choice Behavior; Disease Models, Animal; Dose-Response Relationship, Drug; Ethanol; Food Preferences; Guanosine 5'-O-(3-Thiotriphosphate); Male; Morphine Derivatives; Naloxone; Narcotic Antagonists; Narcotics; Protein Binding; Rats; Rats, Long-Evans; Receptors, Opioid, delta; Sucrose

To investigate the anticonvulsant activity of root bark extract of Carissa edulis.. The median lethal dose (LD(50)) of Carissa edulis extract was determined using Lork's method (1983). The anticonvulsant activity of the extract was assessed in pentylenetetrazole (PTZ)-induced convulsion in mice and maximal electroshock test (MEST) in chicks, with benzodiazepine and phenytoin as standard drugs, respectively. While mechanistic studies were conducted using both flumazenil, a GABA(A)-benzodiazepine receptor complex site antagonist and naloxone a non-specific opioid receptor antagonist.. The median lethal dose (LD(50)) of Carissa edulis was 282.8mg/kg and over 5000mg/kg following intraperitoneal and oral administration, respectively. Carissa edulis produced 40% and 20% protection against convulsion at 5 and 20mg/kg, respectively, compared with 100% protection with benzodiazepine. The mean onset and percentage protection against convulsion in Carissa edulis extract-treated mice were reduced by flumazenil and naloxone. Carissa edulis exhibited dose-dependent inhibition of the convulsion induced by MEST with 20mg/kg providing 90% protection while phenytoin (20mg/kg) produced 100% protection.. These results suggest that Carissa edulis possesses biologically active constituent(s) that have anticonvulsant activity which supports the ethnomedicinal claims of the use of the plant in the management of epilepsy.

Topics: Administration, Oral; Animals; Anticonvulsants; Apocynaceae; Chickens; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Flumazenil; Injections, Intraperitoneal; Lethal Dose 50; Male; Mice; Naloxone; Phenytoin; Plant Bark; Plant Extracts; Plant Roots; Seizures; Toxicity Tests, Acute

Two-stage Fowler-Stephens orchiopexy has been accompanied by testicular atrophy in some cases but neither of the mechanisms responsible for testicular injury are clear, nor is there an effective agent that might prevent this injury. In this study we aimed to investigate the long-term effects of naloxone, a morphine antagonist, on testicular histopathology and oxidative stress after spermatic vessel ligation (SVL) in rats.. 32 prepubertal rats were randomly divided into four equal groups: group 1: control (only bilateral orchiectomies were performed); group 2: sham-operated group; group 3: SVL, and group 4: SVL+naloxone (1 mg/kg twice daily for 1 month). One month postoperatively, bilateral orchiectomies were performed to evaluate histopathologic findings and measurement of malondialdehyde (MDA) and nitric oxide (NO) levels.. Considering group 3, left SVL resulted in significant tissue damage in both testes, more severe in the ipsilateral testis. The SVL resulted in a significant increase in testicular MDA levels of both testes in this group (p < 0.05). While the ipsilateral testicular NO levels of groups 2 and 3 were significantly lower than of group 1 (p < 0.05), the contralateral testicular NO levels of all these groups were similar. After naloxone therapy, while there was no significant improvement in ipsilateral testicular histopathology (p > 0.05), the contralateral testicular histopathology improved significantly (p < 0.05). However, naloxone did not change either testicular MDA or NO levels.. The SVL led to bilateral testicular injury, and oxidative stress may be a reason for this injury. Naloxone significantly improved contralateral testicular injury without showing any antioxidative effect.

Topics: Animals; Disease Models, Animal; Ligation; Male; Malondialdehyde; Naloxone; Narcotic Antagonists; Nitric Oxide; Orchiectomy; Oxidative Stress; Rats; Rats, Wistar; Spermatic Cord; Testicular Diseases; Testis; Urologic Surgical Procedures, Male

Little is known about effects of naloxone, an opiate receptor antagonist, upon experimental autoimmune myocarditis (EAM) in mice. The aim of the present study was to test the effects of naloxone upon EAM in mice. Four-week-old C57BL/6 mice were injected with porcine cardiac myosin. Naloxone 1 mg/kg/day was given intraperitoneally daily on days 0 to 21 in experiment I (acute stage) and on days 21 to 42 in experiment II (chronic stage). For the analysis of endogenous opiate and neurohumoral system, plasma beta-endorphin and cytokines were measured. The cytotoxic activity of lymphocytes was determined by Cr-release assay. Naloxone reversed hypotension produced by massive myocardial injury in experiment I. In experiment I, the severity of cardiac pathology and inflammatory cytokines were decreased in the naloxone-treated group associated with higher beta-endorphin level compared with the untreated group. In addition, naloxone induced a shift from Th1 cytokine toward Th2 cytokine balance. Thus, cytotoxic activities of lymphocytes against EL-4 tumor cells were lower in the treated group than in the untreated group in experiment I, but not in experiment II. Naloxone is beneficial for heart failure caused by EAM in the acute stage, but not in the chronic stage, due to decreasing cytotoxic activities of lymphocytes and to its neurohumoral modulating effects.

Topics: Acute Disease; Animals; Autoimmune Diseases; beta-Endorphin; Cell Line, Tumor; Cytokines; Cytotoxicity Tests, Immunologic; Cytotoxicity, Immunologic; Disease Models, Animal; Erythrocytes; Mice; Mice, Inbred C57BL; Myocarditis; Myocardium; Naloxone; Narcotic Antagonists; Radioimmunoassay

In a previous study, we showed that electroacupuncture (EA) applied to the SI-6 point on the contralateral forelimb produces long-lasting and powerful analgesia in pain caused by ankle sprain in a rat model. To investigate the underlying mechanism of EA analgesia, the present study tested the effects of various antagonists on known endogenous analgesic systems in this model. Ankle sprain was induced in anesthetized rats by overextending their right ankle with repeated forceful plantar flexion and inversion of the foot. When rats developed pain behaviors (a reduction in weight-bearing of the affected hind limb), EA was applied to the SI-6 point on the contralateral forelimb for 30 min under halothane anesthesia. EA significantly improved the weight-bearing capacity of the affected hind limb for 2h, suggesting an analgesic effect. The alpha-adrenoceptor antagonist phentolamine (2mg/kg, i.p. or 30 microg, i.t.) completely blocked the EA-induced analgesia, whereas naloxone (1mg/kg, i.p.) failed to block the effect. These results suggest that EA-induced analgesia is mediated by alpha-adrenoceptor mechanisms. Further experiments showed that intrathecal administration of yohimbine, an alpha(2)-adrenergic antagonist, reduced the EA-induced analgesia in a dose-dependent manner, whereas terazosin, an alpha(1)-adrenergic antagonist, did not produce any effect. These data suggest that the analgesic effect of EA in ankle sprain pain is, at least in part, mediated by spinal alpha(2)-adrenoceptor mechanisms.

Topics: Acupuncture Analgesia; Acupuncture Points; Adrenergic alpha-Antagonists; Analysis of Variance; Animals; Ankle Injuries; Cross-Over Studies; Disease Models, Animal; Double-Blind Method; Male; Naloxone; Narcotic Antagonists; Pain; Pain Management; Pain Measurement; Randomized Controlled Trials as Topic; Rats; Rats, Sprague-Dawley; Sprains and Strains; Time Factors

Visceral pain is one of the most common forms of pain and for which new drugs would be welcome. The aim of this study was to investigate whether gabapentin inhibits induced abdominal contractions in mice and to examine the effect of its co-administration with morphine.. A total of 96 mice received acetic acid intraperitoneally after administration of saline or gabapentin (1, 5, 10, 50 and 100 mg kg(-1)) or morphine (0.25, 0.5, 1, 3 and 5 mg kg(-1)) or a combination of morphine and gabapentin. Other groups also received naloxone. The number of writhes were counted.. Both gabapentin and morphine reduced writhing in a dose-dependent manner. The number of writhes was decreased significantly by gabapentin (50 and 100 mg kg(-1)) and morphine (0.5, 1, 3 and 5 mg kg(-1)) (P < 0.001). Also, the lowest dose of morphine 0.25 mg kg(-1) when combined with low doses of gabapentin significantly decreased the number of writhes (P < 0.005). The combination of a low effective dose of gabapentin (50 mg kg(-1)) with a low dose of morphine decreased the writhing by 94% as compared to the controls. The antinociceptive effect of combined administration was not reversed by naloxone.. These data demonstrated the comparable efficacy of gabapentin with morphine in visceral pain. Also, the results showed that the combination of doses of gabapentin and morphine, which were ineffective alone, produced a significant analgesic effect in the writhing model of pain. This may be clinically important in the management of visceral pain.

Topics: Acetic Acid; Amines; Analgesics; Analgesics, Opioid; Analysis of Variance; Animals; Cyclohexanecarboxylic Acids; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Gabapentin; gamma-Aminobutyric Acid; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Sodium Chloride

A visceral pain model incorporating use of cyclophosphamide (CP) to induce bladder inflammation has been described. CP treatment in rats produces changes in behavior (abnormal postures and eye closure) and respiration rate indicative of visceral pain. We characterized the dose-dependency and progression of CP-induced cystitis pain after intraperitoneal (i.p.) CP. The behavioral and respiration rate changes were ameliorated by systemic morphine and ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine], a neuronal nicotinic acetylcholine receptor agonist, in a manner reversible by naloxone and mecamylamine, respectively. Sites of antinociceptive actions of morphine and ABT-594 were investigated using systemic, intrathecal (i.t.), or intracerebroventricular (i.c.v.) administration of blood-brain barrier impenetrant antagonists. Naloxone methiodide produced a complete antagonism of morphine antinociception after i.c.v. but not i.p. or i.t. administration. Chlorisondamine blocked ABT-594 antinociception after i.c.v. but not i.p. administration. Further pharmacological characterization of behavioral and respiration changes in CP-cystitis was performed using standard analgesics. The alpha(2)-adrenoceptor agonist clonidine produced a weak attenuation of CP-pain behavior. NSAIDs (ibuprofen, acetaminophen, and celecoxib) and anticonvulsants (gabapentin and lamotrigine) were without effect. These results demonstrate that morphine and ABT-594 produce antinociception in CP-cystitis by a predominantly supraspinal site of action, and that mechanisms producing robust centrally-mediated antinociception could be beneficial in cystitis pain.. In this article, potential antinociceptive effects of a variety of pharmacological agents were evaluated in a rat cystitis pain model. Morphine and a nicotinic acetylcholine receptor agonist ABT-594 were found to exert potent antinociception in this model. Findings presented here aid identification of agents to treat cystitis pain in the clinic.

Topics: Analgesics; Animals; Azetidines; Behavior, Animal; Brain; Chlorisondamine; Cyclophosphamide; Cystitis; Disease Models, Animal; Male; Mecamylamine; Morphine; Naloxone; Narcotic Antagonists; Nicotinic Antagonists; Pain; Pyridines; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Receptors, Nicotinic; Viscera

The effects of opiates in various infections are well known; however, very little is known about tuberculosis infection. Therefore, in the present study, we report for the first time, the effects of morphine during murine tuberculosis. Mice were infected intravenously with Mycobacterium tuberculosis H37Rv, administered morphine (0.1-100 mg/kg subcutaneously on day 0 and day +15) and sacrificed on day +30 for CFU enumeration in lungs and spleen. Morphine exerted maximum suppression of infection at 5 mg/kg, and sometimes completes elimination of infection; naloxone, silica and aminoguanidine blocked the protective effect of morphine. In vitro, morphine lacked direct antimycobacterial activity up to 1x10(-4) M concentration, as assessed by radiometric BACTEC method. In macrophage model of infection, morphine showed maximal killing at 1x10(-7) M concentration, the activity was blocked by naloxone and aminoguanidine. These observations suggest that morphine exerts a dose-dependent effect in murine tuberculosis, the protective effect being naloxone-reversible and may involve macrophage-mediated protective mechanisms. These results may be helpful in developing new opioid-like chemical entities against tuberculosis infection.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Guanidines; Injections, Subcutaneous; Lung; Macrophages, Peritoneal; Male; Mice; Morphine; Mycobacterium tuberculosis; Naloxone; Neuroimmunomodulation; Silicon Dioxide; Spleen; Tuberculosis, Pulmonary; Tuberculosis, Splenic

To investigate the effect of methylprednisolone (MP) and naloxone (Na) on pulmonary ischemia/reperfusion (I/R) injury in rats and to study its possible mechanism.. Seventy male Sprague-Dawley (SD) rats were used for reproduction of unilateral lung ischemia/reperfusion (I/R) injury, and they were randomly divided into five groups (14 rats in each group): sham operation group (sham group), I/R group, MP group,Na group, and MP+Na group. Each group was subdivided into two subgroups of 3-hour and 6-hour postinjury. I/R injury was produced by 45 minutes of cross-clamping of the pulmonary artery, followed by 3 hours or 6 hours of reperfusion. Apoptosis rate in lung tissue was assessed by the use of Annexin-V-PI with flow cytometry. Expression of I Kappa B-alpha and caspase-3 in lung tissue were observed by immunohistochemical stain and image analysis. The wet to dry weight (W/D) ratio, the pathological and ultrastructure changes in lung tissue were observed.. (1) The expression of I Kappa B-alpha in lung was obviously lower in I/R group than in 6-hour MP group (P<0.01), while expression of caspase-3 in lung tissue was significantly less intense in 3-hour and 6-hour Na group compared with I/R group (both P<0.05). Apoptosis rate in lung tissue was obviously lower in MP and 3-hour and 6-hour Na group than in I/R group (both P<0.01). The pathological and ultrastructure changes in lung tissue were less intensive. (2) Apoptosis rate, caspase-3 of lung tissue were significantly lower in MP+Na group than of 6-hour in MP, Na, I/R groups (P<0.05 or P<0.01) while the expression of I Kappa B-alpha was higher than of 6-hour Na group. The pathological and ultrastructure change in lung tissue were less more mark in MP+Na group than in other groups.. MP and Na inhibit apoptosis in lung I/R injury by either decreasing the activation of I Kappa B-alpha or caspase-3.MP and Na when used together in early period of lung I/R injury could exert more effective protection to lung tissue.

Topics: Animals; Apoptosis; Caspase 3; Disease Models, Animal; I-kappa B Proteins; Lung; Male; Methylprednisolone; Naloxone; NF-KappaB Inhibitor alpha; Random Allocation; Rats; Rats, Sprague-Dawley; Reperfusion Injury

Morphine can inhibit inflammatory edema in experimental animals. The mechanisms and sites by which opioids exert this effect are still under debate. Since the spinal level is a site for modulation of the neurogenic component of inflammation, we investigated the effect of intrathecal (i.t.) administration of morphine, and the involvement of spinal nitric oxide (NO)/cyclic-guanosine monophosphate-GMP pathway in carrageenan (CG)-induced paw edema.. Male Wistar rats received i.t. injections of drugs (20 microL) 30 min before paw stimulation with CG (150 microg). Edema was measured as paw volume increase (mL), and neutrophil migration was evaluated indirectly by myeloperoxidase (MPO) assay.. Morphine (37, 75, and 150 nmol) inhibited inflammatory edema, but had no effect on MPO activity. Coinjection with naloxone (64 nmol) reversed the effect of morphine. The corticosteroid synthesis inhibitor, aminoglutethimide (50 mg/kg, v.o.), administered 90 min before morphine injection did not modify its antiedematogenic effect. Low doses of the NO synthase inhibitor, N(omega)-nitro-L-arginine (L-NNA; 10 and 30 pmol) increased, while higher doses (3 and 30 nmol) inhibited edema. The guanylate cyclase inhibitor 1H-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 21 and 42 nmol) increased, while the phosphodiesterase type 5 inhibitor sildenafil (0.15 and 1.5 nmol) inhibited paw edema. Coadministration of a subeffective dose of L-NNA (3 pmol) or ODQ (10 nmol) with morphine prevented its antiedematogenic effect, but sildenafil (0.15 nmol) rendered a subeffective dose of morphine effective (18 nmol). ODQ also prevented the antiedematogenic effect of the NO donor S-nitroso-N-acetyl-penicilamine.. These results support the idea that morphine can act on opioid receptors at the spinal level to produce antiedematogenic, and that the NO/cGMP pathway seems to be an important mediator in this effect.

Topics: Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Carrageenan; Cyclic GMP; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Enzyme Inhibitors; Guanylate Cyclase; Inflammation; Injections, Spinal; Male; Morphine; Naloxone; Narcotic Antagonists; Neutrophil Infiltration; Neutrophils; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Oxadiazoles; Peroxidase; Phosphodiesterase Inhibitors; Piperazines; Purines; Quinoxalines; Rats; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Signal Transduction; Sildenafil Citrate; Spinal Cord; Sulfones; Time Factors

Analgesics such as morphine cause many side effects including addiction, but kappa-opioid receptor agonist can produce antinociception without morphine-like side effects. With the aim of developing new and potent analgesics with lower abuse potential, we studied the antinociceptive and physical dependent properties of a derivate of ICI-199441, an analogue of (-)U50,488H, named (2-(3,4-dichloro)-phenyl)-N-methyl-N-[(1S)-1-(2-isopropyl)-2-(1-(3-pyrrolinyl))ethyl] acetamides (LPK-26). LPK-26 showed a high affinity to kappa-opioid receptor with the Ki value of 0.64 nM and the low affinities to micro-opioid receptor and delta-opioid receptor with the Ki values of 1170 nM and >10,000 nM, respectively. It stimulated [(35)S]GTPgammaS binding to G-proteins with an EC50 value of 0.0094 nM. In vivo, LPK-26 was more potent than (-)U50,488H and morphine in analgesia, with the ED50 values of 0.049 mg/kg and 0.0084 mg/kg in hot plat and acetic acid writhing tests, respectively. Moreover, LPK-26 failed to induce physical dependence, but it could suppress naloxone-precipitated jumping in mice when given simultaneously with morphine. Taken together, our results show that LPK-26 is a novel selective kappa-opioid receptor agonist with highly potent antinociception effects and low physical dependence potential. It may be valuable for the development of analgesic and drug that can be used to reduce morphine-induced physical dependence.

Topics: Acetic Acid; Analgesics, Opioid; Animals; Behavior, Animal; CHO Cells; Cricetinae; Cricetulus; Disease Models, Animal; Dose-Response Relationship, Drug; Guanosine 5'-O-(3-Thiotriphosphate); Hot Temperature; Humans; Male; Mice; Motor Activity; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Pain; Pain Measurement; Pain Threshold; Protein Binding; Pyrroles; Rats; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Time Factors; Transfection

This study was performed to determine the antinociceptive and anti-inflammatory activities of aqueous extract of Kaempferia galanga leaves using various animal models. The extract, in the doses of 30, 100, and 300 mg/kg, was prepared by soaking (1:10; w/v) the air-dried powdered leaves (40 g) in distilled water (dH(2)O) for 72 h and administered subcutaneously in mice/rats 30 min prior to the tests. The extract exhibited significant (P < 0.05) antinociceptive activity when assessed using the abdominal constriction, hot-plate and formalin tests, with activity observed in all tests occurring in a dose-dependent manner. Furthermore, the antinociceptive activity of K. galanga extract was significantly (P < 0.05) reversed when prechallenged with 10 mg/kg naloxone. The extract also produced a significantly (P < 0.05) dose-dependent anti-inflammatory activity when assessed using the carrageenan-induced paw-edema test. In conclusion, this study demonstrated that K. galanga leaves possessed antinociceptive and anti-inflammatory activities and thus supports the Malay's traditional uses of the plant for treatments of mouth ulcer, headache, sore throat, etc.

Topics: Analgesics, Non-Narcotic; Analysis of Variance; Animals; Anti-Inflammatory Agents, Non-Steroidal; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Female; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Phytotherapy; Plant Extracts; Plant Leaves; Rats; Rats, Sprague-Dawley; Zingiberaceae

Rats with liver cirrhosis, evoked by chronic administration of thioacetamide (TAA), consumed voluntarily more alcohol than their healthy counterparts. Seeking the mechanisms underlying this phenomenon, the opioid system was screened for involvement and alterations. In vivo, the influence of chronically administered Naloxone and Naltrexone, non-specific opioid receptor antagonists, on alcohol intake was examined in free choice tests between 10% alcohol and tap water and ex vivo receptor binding studies were performed on cerebral membrane preparations.. TAA rats, selected for the study, had confirmed liver insufficiency: their plasma bilirubin concentrations were about 3 times higher, the prothrombin time was 50% longer and they consumed voluntarily 3 times more alcohol than the control animals. The drugs were given s.c. for five days, at the beginning of the dark phase of a 24h cycle, in a daily dose of 10 mg per kg body mass. Throughout the treatment, the rats were kept individually in metabolic cages with a free access to water, alcohol solution and food. Feed and fluid consumption, as well as the urine outputs, were recorded on the 2h, 4h, 6h and 24h after the drug administration. The mu opioid ligand - [(3)H]-(D-Ala(2), -N-MePhe(4), Glyol(5)) Enkephalin was used to obtain binding characteristics of the control and TAA rat brain membranes.. The drugs, if modified drinking behaviours, they did it transiently; alcohol, water and thus the total fluid intake by the cirrhotic and control rats was significantly less after 2h - 6h from either naloxone or naltrexone administration. Both drugs decreased general fluid consumption as such rather than the consumption of alcohol only, as observed from the recordings related to TAA rats. The binding data: K(d) of 2.62 +/- 0.98 nM and B(max) of 43.71 +/- 6.12 fmol/mg protein for cirrhotic rats, versus K(d) of 4.63 +/- 1.98 nM and B(max) 95.61 +/- 18.33 fmol/mg protein for the control ones, suggest that while the affinity of radioligand to cerebral mu receptors was similar for the two groups, there was a lower density of those receptors in the cirrhotic rats.. The results indicate some disturbances in the opioid system in cirrhotic rats. However, the low response to opioid therapy suggests that the opioid system may have only be partly involved in the development of the observed increased alcohol drinking in the rats with liver cirrhosis.

Topics: Alcohol Drinking; Animals; Behavior, Animal; Bilirubin; Brain; Disease Models, Animal; Drinking; Liver Cirrhosis; Male; Naloxone; Naltrexone; Narcotic Antagonists; Prothrombin Time; Radioligand Assay; Rats; Rats, Wistar; Receptors, Opioid, mu; Thioacetamide; Time Factors

The current study investigated the roles of various subtypes of opioid receptors expressed in the thalamic nucleus submedius (Sm) in inhibition of mirror-image allodynia induced by L5/L6 spinal nerve ligation in rats. Morphine was microinjected into the Sm, which produced a dose-dependent inhibition of mirror-image allodynia; this effect was antagonized by pretreatment with non-selective opioid receptor antagonist naloxone. Microinjections of endomorphin-1 (mu-receptor agonist), or [D-Ala(2), D-Leu(5)]-enkephalin (DADLE, delta-/mu-receptor agonist), also inhibited mirror-image allodynia, and these effects were blocked by the selective mu-receptor antagonist, beta-funaltrexamine hydrochloride. The DADLE-induced inhibition, however, was not influenced by the delta-receptor antagonist naltrindole. The kappa-receptor agonist, spiradoline mesylate salt, failed to alter the mirror-image allodynia. These results suggest that Sm opioid receptor signaling is involved in inhibition of mirror-image allodynia; this effect is mediated by mu- (but not delta- and kappa-) opioid receptors in the rat model of neuropathic pain.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Enkephalin, Leucine-2-Alanine; Hyperalgesia; Ligation; Male; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Neuralgia; Oligopeptides; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Spinal Nerves; Thalamic Nuclei

N-Allylation (-CH(2)-CHCH(2)) of [Dmt(1)]endomorphins yielded the following: (i) [N-allyl-Dmt(1)]endomorphin-2 (Dmt=2',6'-dimethyl-l-tyrosine) (12) and [N-allyl-Dmt(1)]endomorphin-1 (15) (K(i)mu=0.45 and 0.26nM, respectively) became mu-antagonists (pA(2)=8.59 and 8.18, respectively) with weak delta-antagonism (pA(2)=6.32 and 7.32, respectively); (ii) intracerebroventricularly administered 12 inhibited morphine-induced CNS-mediated antinociception in mice [AD(50) (0.148ng/mouse) was 16-fold more potent than naloxone], but not spinal antinociception, and (iii) 15 reversed the alcohol-elevated frequency in spontaneous inhibitory post-synaptic currents (IPSC) in hippocampal CA1 pyramidal cells in rat brain slices (P=0.0055). Similarly, N-allylation of the potent mu-opioidmimetic agonists, 1,6-bis-[H-Dmt-NH]-hexane and 3,6-bis-[Dmt-NH-propyl]-2(1H)-pyrazinone, converted them into mu-antagonists (pA(2)=7.23 and 7.17 for the N-allyl-derivatives 17 and 19, respectively), and exhibited weak delta-antagonism. Thus, N-allylation of Dmt containing opioid peptides or opioidmimetics continues to provide a facile means to convert selective mu-opioid agonists into potent mu-opioid antagonists.

Topics: Alkylation; Analgesics, Opioid; Animals; Brain; Disease Models, Animal; Guinea Pigs; Male; Mice; Morphine; Pain; Rats; Receptors, Opioid, mu; Structure-Activity Relationship; Synaptosomes; Vas Deferens

Sickle cell anemia is a common genetic disorder in African Americans. Opioid analgesics are traditionally the treatment for the severe pain associated with this disease. Here we reveal that the opioid antagonist naloxone possesses potent analgesic activity in two transgenic mouse models of sickle cell anemia (NY1DD and hBERK1) and not in their respective controls (ICR-CD1 and C57BL/6J) when administered by three parenteral routes [intracerebroventricular (i.c.v.), intrathecal, and subcutaneous]. In the NY1DD mice, naloxone (i.c.v.) possessed approximately 300-fold greater potency than morphine (i.c.v.). Other opioid antagonists (naltrexone, norbinaltorphimine, and naltrindole) were substantially less effective in producing analgesia. Naloxone and morphine were synergistic in NY1DD mice, suggesting different receptor systems. Microarray analysis suggested naloxone-induced down-regulation of the CC chemokine receptor (CCR)5 in NY1DD mice but not in control mice. Pretreatment of control mice with CC chemokine ligand 5 [CCL5 (RANTES)] enabled naloxone to produce analgesia similar to that observed in NY1DD mice. Mu opioid receptor knockout mice treated similarly also displayed analgesia. That the effect of CCL5 was specifically related to CCR5 and/or CCR1 activation was demonstrated by antagonism of analgesia with the chemokine antagonist methionylated RANTES. Similar antagonism of naloxone-induced analgesia also was observed when NY1DD mice were pretreated with methionylated RANTES. These results indicate that CCR5/CCR1 receptors are directly or indirectly involved in analgesia produced by naloxone. The present study suggests that naloxone may be clinically useful in the treatment of pain associated with sickle cell disease and other disorders involving inflammation.

Topics: Analgesics; Analgesics, Opioid; Anemia, Sickle Cell; Animals; Chemokine CCL5; Disease Models, Animal; Dose-Response Relationship, Drug; Down-Regulation; Drug Synergism; Injections, Intraventricular; Injections, Spinal; Injections, Subcutaneous; Male; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Mice, Knockout; Mice, Transgenic; Morphine; Naloxone; Pain; Pain Measurement; Receptors, CCR5

Chronic use of opioid is associated with pro-nociceptive phenomena such as hyperalgesia or tolerance. The interaction between opioid and non-steroidal anti-inflammatory drugs (NSAIDs) with respect to opioid-associated hyperalgesia and tolerance remains largely unknown. This study examines the effect of subcutaneous or intrathecal administration of ketorolac, an NSAID, on recurrent withdrawal induced hyperalgesia and tolerance to spinal morphine in rats. Animals were infused with morphine intrathecally, and daily subcutaneous naloxone was used for recurrent withdrawal purpose. We observed that escape latencies on hot box were decreased in animals subjected to withdrawal, and this decrease was reversed by subcutaneous ketorolac pretreatment. In addition, we observed that recurrent withdrawal did not significantly affect the magnitude of spinal morphine tolerance. Compared to controls, all morphine infused animals showed similar changes in their dose responses to spinal morphine, effective dose 50 values and tolerance ratios; and these changes were not affected by the ketorolac given subcutaneously. The effect of ketorolac on tolerance was further examined by directly delivering ketorolac to the spinal cord, and again we observed similar changes in the daily latency, percentage of area under the curve and percentage of maximal possible effects among groups infused with morphine, regardless of intrathecal ketorolac treatment. Together, our results demonstrate that recurrent withdrawal is associated with hyperalgesia but this has no effect on the tolerance development; ketorolac protects against recurrent withdrawal induced hyperalgesia without significantly altering spinal morphine tolerance.

Topics: Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Drug Tolerance; Hyperalgesia; Injections, Spinal; Ketorolac; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Pain Measurement; Pain, Intractable; Rats; Rats, Sprague-Dawley; Spinal Cord; Substance Withdrawal Syndrome

Current therapy for inflammatory pain includes the peripheral application of opioid receptor agonists. Activation of opioid receptors modulates voltage-gated ion channels, but it is unclear whether opioids can also influence ligand-gated ion channels [e.g., the transient receptor potential vanilloid type 1 (TRPV1)]. TRPV1 channels are involved in the development of thermal hypersensitivity associated with tissue inflammation. In this study, we investigated mu-opioid receptor and TRPV1 expression in primary afferent neurons in the dorsal root ganglion (DRG) in complete Freund's adjuvant (CFA)-induced paw inflammation. In addition, the present study examined whether the activity of TRPV1 in DRG neurons can be inhibited by mu-opioid receptor (mu-receptor) ligands and whether this inhibition is increased after CFA inflammation. Immunohistochemistry demonstrated colocalization of TRPV1 and mu-receptors in DRG neurons. CFA-induced inflammation increased significantly the number of TRPV1- and mu-receptor-positive DRG neurons, as well as TRPV1 binding sites. In whole-cell patch clamp studies, opioids significantly decreased capsaicin-induced TRPV1 currents in a naloxone- and pertussis toxinsensitive manner. The inhibitory effect of morphine on TRPV1 was abolished by forskolin and 8-bromo-cAMP. During inflammation, an increase in TRPV1 is apparently rivaled by an increase of mu-receptors. However, in single dissociated DRG neurons, the inhibitory effects of morphine are not different between animals with and without CFA inflammation. In in vivo experiments, we found that locally applied morphine reduced capsaicin-induced thermal allodynia. In summary, our results indicate that mu-receptor activation can inhibit the activity of TRPV1 via G(i/o) proteins and the cAMP pathway. These observations demonstrate an important new mechanism underlying the analgesic efficacy of peripherally acting mu-receptor ligands in inflammatory pain.

Topics: Animals; Cyclic AMP; Disease Models, Animal; Ganglia, Spinal; GTP-Binding Proteins; Inflammation; Male; Naloxone; Neurons, Afferent; Pain; Pertussis Toxin; Rats; Rats, Wistar; Receptors, Opioid, mu; RNA, Messenger; TRPV Cation Channels

The selective serotonin (5-HT) reuptake inhibitors (SSRIs) represent the first-line pharmacotherapy for obsessive-compulsive disorder (OCD), and atypical antipsychotic drugs, which block 5-HT2A receptors, are used in augmentation strategies. Opiate drugs are also effective in treatment-refractory OCD and Tourette syndrome. The 5-HT2A-related behavior (i.e., head twitch) has been related with tics, stereotypes, and compulsive symptoms observed in Tourette syndrome and OCD.. The aim of this study was to explore whether 5-HT2A-related behavior is affected by atypical opiate drugs.. Head-twitch response was induced in mice by administration of either 5-hydroxytryptophan (5-HTP) or the 5-HT2A/C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Dose-effect curves of atypical opiate drugs [(+/-)-tramadol, (-)-methadone and levorphanol], morphine, and other psychoactive drugs (fluvoxamine, desipramine, nefazodone, and clozapine) were performed. Opioid mechanisms were investigated by administration of naloxone.. All the opiates tested reduced both 5-HTP and DOI-induced behavior in a naloxone-reversible fashion, atypical opiates being more effective. The effects of the other drugs depended on the protocol, clozapine being the most effective.. Combined 5-HT and opioid properties result in a greater efficacy in antagonizing 5-HT2A-related behavior. These results provide behavioral evidence to support convergent effects of the 5-HT and opioid systems in discrete brain areas, offering the potential for therapeutic advances in the management of refractory stereotypes and compulsive behaviors.

Topics: 5-Hydroxytryptophan; Analgesics, Opioid; Animals; Clozapine; Desipramine; Disease Models, Animal; Dose-Response Relationship, Drug; Fluvoxamine; Indophenol; Levorphanol; Male; Methadone; Mice; Morphine; Naloxone; Narcotic Antagonists; Obsessive-Compulsive Disorder; Piperazines; Receptor, Serotonin, 5-HT2A; Receptor, Serotonin, 5-HT2C; Stereotyped Behavior; Tics; Tourette Syndrome; Tramadol; Triazoles

Fentanyl is a potent mu-opioid receptor agonist that is widely used for the treatment of severe chronic pain. Discontinuation of fentanyl administration has been shown to induce a negative emotional state.. The aim of the present studies was to investigate the effects of the partial mu-opioid receptor agonist buprenorphine on the negative emotional state associated with precipitated and spontaneous fentanyl withdrawal in rats.. Fentanyl and saline were chronically administered via osmotic minipumps. A discrete-trial intracranial self-stimulation procedure was used to provide a measure of brain reward function. Somatic signs were recorded from a checklist of opioid abstinence signs.. Naloxone induced a deficit in brain reward function in rats chronically treated with fentanyl. Buprenorphine dose-dependently prevented the naloxone-induced deficit in brain reward function. Discontinuation of fentanyl administration was also associated with a deficit in brain reward function. After explantation of the minipumps, the administration of buprenorphine induced a potentiation of brain reward function in the fentanyl-withdrawing rats, but did not affect brain reward function of saline-treated control rats. Buprenorphine prevented the somatic withdrawal signs associated with spontaneous fentanyl withdrawal and attenuated the somatic signs associated with precipitated fentanyl withdrawal.. Buprenorphine prevents affective and somatic fentanyl withdrawal signs. Moreover, buprenorphine is rewarding in rats previously exposed to fentanyl, but not in opioid-naïve rats. This pattern of results suggests that buprenorphine may be an effective treatment for the anhedonic-state associated with fentanyl withdrawal, but further study of buprenorphine's abuse potential is warranted.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Buprenorphine; Disease Models, Animal; Dose-Response Relationship, Drug; Emotions; Fentanyl; Male; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Wistar; Receptors, Opioid, mu; Reward; Substance Withdrawal Syndrome; Time Factors

Earlier, we reported that morphine-nimodipine combination produces significantly higher antinociception after intrathecal but not after systemic administration in mice. Different doses of morphine and nimodipine (5 microg of morphine, 5 microg of nimodipine, 5 microg each of morphine and nimodipine, 10 microg of morphine, 10 microg of nimodipine, 10 microg morphine with 5 microg nimodipine and 5 microg of morphine with 10 microg of nimodipine) were now injected intrathecally in Wistar rats to further characterise this antinociceptive effect. The acute antinociceptive effect was measured by the tail-flick test between 15 min to 7 h. The onset of maximum antinociception (100% MPE) was earlier (by 15 min) in nimodipine (5 microg) than in morphine (5 microg) treated group (by 30 min). Though earlier in onset, 5 microg nimodipine produced transient antinociception, which was significantly higher than saline treated controls for the initial 30 min only. Morphine (5 microg) produced significantly higher antinociception between 15 min to 3:30 h in comparison to control animals. However, co-administration of both morphine and nimodipine led to significantly higher antinociception than morphine alone at 4:00 h and also between 5:00 to 6:30 h. Interestingly, the combined antinociceptive action of morphine and nimodipine was not significantly different from 10 microg of morphine, which indicated synergistic interaction. Naloxone (5 mg/kg) could reverse this antinociceptive effect of morphine-nimodipine combination though it failed to reverse nimodipine (5 microg)-mediated antinociception at 15 min. Increasing the dose of either morphine or nimodipine to 10 mug did not increase antinociception except between 6:30-7:00 h. No obvious side effect was noted after administration of either morphine or nimodipine or both.

Topics: Analgesics, Opioid; Animals; Calcium Channel Blockers; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Synergism; Injections, Spinal; Male; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Nimodipine; Pain; Pain Measurement; Rats; Rats, Wistar; Receptors, Opioid, mu; Tail

Ethanol stimulates the dopaminergic mesoaccumbal pathway, which is thought to play a role in ethanol reinforcement. Mu (mu)-opioid (MOP) receptors modulate accumbal dopamine activity, but it is not clear whether MOP receptors are involved in the mechanism of ethanol-stimulated accumbal dopamine release.. We investigated the role that MOP receptors play in ethanol (2.0 g/kg)-stimulated accumbal dopamine release by using MOP receptor knockout mice (C57BL/6J-129SvEv and congenic C57BL/6J genotypes) along with blockade of MOP receptors with a mu1 selective antagonist (naloxonazine).. Both gene deletion and pharmacological antagonism of the MOP receptor decreased ethanol-stimulated accumbal dopamine release compared with controls with female mice showing a larger effect in the C57BL/6J-129SvEv genotype. However, both male and female mice showed reduced ethanol-stimulated dopamine release in the congenic MOP receptor knockout mice (C57BL/6J). No differences in the time course of dialysate ethanol concentration were found in any of the experiments.. The data demonstrate the existence of a novel interaction between genotype and sex in the regulation of ethanol-stimulated mesolimbic dopamine release by the MOP receptor. This implies that a more complete understanding of the epistatic influences on the MOP receptor and mesolimbic dopamine function may provide more effective pharmacotherapeutic interventions in the treatment of alcoholism.

Topics: Alcohol Drinking; Alcoholism; Animals; Basal Ganglia; Disease Models, Animal; Dopamine; Epistasis, Genetic; Ethanol; Genotype; Humans; Mice; Mice, Congenic; Mice, Inbred C57BL; Mice, Knockout; Microdialysis; Naloxone; Nucleus Accumbens; Receptors, Opioid, mu; Reinforcement, Psychology; Sex Characteristics

The antagonism by Tyr-D-Pro-Trp-Gly-NH2 (D-Pro2-Tyr-W-MIF-1), a Tyr-Pro-Trp-Gly-NH2 (Tyr-W-MIF-1) analog, of the antinociception induced by the mu-opioid receptor agonists Tyr-W-MIF-1, [D-Ala2,NMePhe4,Gly(ol)5]-enkephalin (DAMGO), Tyr-Pro-Trp-Phe-NH2 (endomorphin-1), and Tyr-Pro-Phe-Phe-NH2 (endomorphin-2) was studied with the mouse tail-flick test. D-Pro2-Tyr-W-MIF-1 (0.5-3 nmol) given intracerebroventricularly (i.c.v.) had no effect on the thermal nociceptive threshold. High doses of D-Pro2-Tyr-W-MIF-1 (4-16 nmol) administered i.c.v. produced antinociception with a low intrinsic activity of about 30% of the maximal possible effect. D-Pro2-Tyr-W-MIF-1 (0.25-2 nmol) co-administered i.c.v. showed a dose-dependent attenuation of the antinociception induced by Tyr-W-MIF-1 or DAMGO without affecting endomorphin-2-induced antinociception. A 0.5 nmol dose of D-Pro2-Tyr-W-MIF-1 significantly attenuated Tyr-W-MIF-1-induced antinociception but not DAMGO- or endomorphin-1-induced antinociception. The highest dose (2 nmol) of D-Pro2-Tyr-W-MIF-1 almost completely attenuated Tyr-W-MIF-1-induced antinociception. However, that dose of D-Pro2-Tyr-W-MIF-1 significantly but not completely attenuated endomorphin-1 or DAMGO-induced antinociception, whereas the antinociception induced by endomorphin-2 was still not affected by D-Pro2-Tyr-W-MIF-1. Pretreatment i.c.v. with various doses of naloxonazine, a mu1-opioid receptor antagonist, attenuated the antinociception induced by Tyr-W-MIF-1, endomorphin-1, endomorphin-2, or DAMGO. Judging from the ID50 values for naloxonazine against the antinociception induced by the mu-opioid receptor agonists, the antinociceptive effect of Tyr-W-MIF-1 is extremely less sensitive to naloxonazine than that of endomorphin-1 or DAMGO. In contrast, endomorphin-2-induced antinociception is extremely sensitive to naloxonazine. The present results clearly suggest that D-Pro2-Tyr-W-MIF-1 is a selective antagonist for the mu2-opioid receptor in the mouse brain. D-Pro2-Tyr-W-MIF-1 may also discriminate between Tyr-W-MIF-1-induced antinociception and the antinociception induced by endomorphin-1 or DAMGO, which both show a preference for the mu2-opioid receptor in the brain.

Topics: Analgesics, Opioid; Animals; Brain; Disease Models, Animal; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Hot Temperature; Injections, Intraventricular; Male; Mice; MSH Release-Inhibiting Hormone; Naloxone; Narcotic Antagonists; Oligopeptides; Pain; Pain Measurement; Pain Threshold; Reaction Time; Receptors, Opioid, mu; Somatostatin; Time Factors

While many preclinical models detect the analgesic activity of nonsteroidal antiinflammatory drugs (NSAIDs), the radiant heat tail-flick response has repeatedly been insensitive to this class of drugs. As the tail-flick test involves nociceptive processing at spinal circuits with supraspinal modulation, it seems reasonable to assume that the NSAIDs should not modify strong nociceptive stimuli, since the primary site of action of NSAIDs is likely to be in the periphery.. We injected 3-300 mug of diclofenac, dipyrone, ketorolac, lysine acetyl salicylate, and sodium salicylate intradermally into mice tails and evaluated the tail-flick response to radiant heat. These results were compared with intraperitoneally injected controls. We also evaluated the ability of naloxone to reverse the observed effects.. Intradermal injection of each NSAID produced a dose-dependent increase in tail-flick latency. Intraperitoneal NSAIDs injection produced no antinociceptive effects. Naloxone pretreatment had no effect on the antinociceptive effects of intradermal diclofenac, ketorolac, lysine acetyl salicylate, and sodium salicylate. Naloxone completely blocked the antinociceptive effects of intradermal dipyrone.. Local, but not systemic, administration of NSAIDs produced antinociception in the tail-flick thermal assay. The endogenous opioid system contributes to the peripheral antinociceptive effects of dipyrone, but not to that of diclofenac, ketorolac, lysine acetyl salicylate, or sodium salicylate, suggesting differences in the mechanisms of action among the NSAIDs.

Topics: Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Aspirin; Diclofenac; Dipyrone; Disease Models, Animal; Dose-Response Relationship, Drug; Hot Temperature; Injections, Intradermal; Injections, Intraperitoneal; Ketorolac; Lysine; Male; Mice; Mice, Inbred BALB C; Motor Activity; Naloxone; Narcotic Antagonists; Pain; Reaction Time; Sodium Salicylate; Tail; Time Factors

Tramadol (1RS, 2RS)-2-[(dimethylamino)-methyl]-1-(3-methoxyphenyl)-cyclohexanol) is an atypical centrally acting analgesic agent with weak opioid receptor affinity that, like some antidepressants, enhances the extraneuronal concentrations of the monoamine neurotransmitters, noradrenaline and serotonin, by interfering with their re-uptake and release mechanisms.. The present study was undertaken to evaluate the potential role of 5-HT(1A) receptors and opioids receptors in the analgesic effect of tramadol in neuropathic pain. With this aim, the effect of either a selective 5-HT(1A) receptor antagonist (WAY-100635, N-2-[4-(2-methoxyphenyl-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexane carboxamide) or a selective 5-HT(1A) receptor agonist (8-OH-DPAT, 8-hydroxy-2-(di-n-propylamine) tetralin hydrobromide) or an opioid receptor antagonist (naloxone; naloxone hydrochloride dihydrate) was investigated in combination with tramadol by means of the cold-plate test in the chronic constriction injury model in rats.. The results showed that WAY-100635 (0.8 mg/kg) significantly enhanced the antiallodynic effect of non-effective doses of tramadol (5-10 mg/kg). In contrast, 8-OH-DPAT (0.5 mg/kg) counteracted the antiallodynic effect of an effective dose of tramadol (22 mg/kg). Naloxone (0.5 mg/kg) partially counteracted the antiallodynic effect of tramadol (22 mg/kg).. These findings suggest the involvement of opioid and 5-HT(1A) receptors in the antinociceptive effect of tramadol and support the idea that the combination of tramadol with compounds having 5-HT(1A) antagonist properties could be a new strategy to improve tramadol-induced analgesia in neuropathic pain.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Analgesics, Opioid; Animals; Chronic Disease; Disease Models, Animal; Drug Interactions; Male; Naloxone; Narcotic Antagonists; Pain; Pain Threshold; Piperazines; Pyridines; Rats; Rats, Sprague-Dawley; Receptor, Serotonin, 5-HT1A; Receptors, Opioid; Sciatic Nerve; Sciatic Neuropathy; Serotonin 5-HT1 Receptor Agonists; Tramadol

The antinociceptive properties of Casearia sylvestris Sw. (Flacourtiaceae) were investigated in various models of pain-related behavior in mice. The hydroalcoholic crude extract of the plant (30-300mg/kg, per os) clearly inhibited nocifensive responses induced by ovalbumin (hindpaw licking) or acetic acid (writhes) in graded fashion. At 300mg/kg, the extract reduced nocifensive behaviors (from 71.1+/-13.3 to 14.8+/-9.3s; from 31.3+/-4.5 to 3.3+/-1.2 writhes, respectively) to similar extents as indomethacin (5mg/kg; 5.7+/-1.1s and 3.3+/-1.2 writhes, respectively). Significant antinociceptive effects in the hot plate test were only detected following administration of the highest extract dose, but this analgesic action appeared to be specific as the extract failed to change motor and exploratory activities. The antinociceptive effect of Casearia sylvestris extract in the acetic acid test was prevented by prior treatment with the non-selective opioid receptor antagonist naloxone (1mg/kg; 5.8+/-4.2 and 31.5+/-3.1 writhes in vehicle-treated and naloxone-treated groups, respectively), indicating that the endogenous opioid system is involved in its analgesic mechanism of action. Thus, our investigation suggests a potential therapeutic benefit of Casearia sylvestris Sw. in treating conditions associated with inflammatory pain.

Topics: Analgesics; Analgesics, Opioid; Animals; Casearia; Disease Models, Animal; Dose-Response Relationship, Drug; Lethal Dose 50; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Pain; Plant Extracts; Rats

The present study was performed to develop a new atopic dermatitis model characterized by not only itching but also inflammatory skin using BALB/c mice. From 18 days after the first systemic immunization, daily epicutaneous application of ovalbumin was performed for 2 weeks. Antigen challenge (ovalbumin) resulted in a significant increase of scratching behavior from day 23 to day 32. Moreover, skin symptoms such as erythema/hemorrhage, edema, excoriation/erosion and dryness/desquamation were also observed from day 19 to day 32. The frequency of scratching in the first stage (from day 24 to day 26 after the systemic first immunization) was decreased by chlorpheniramine and epinastine; however, in the last stage (from day 27 to day 30 after the systemic first immunization), both drugs showed no inhibition of scratching behavior. Therefore, an endogenous mediator other than histamine may be responsible for provoking the itching sensation in the last stage. Naloxone dose-dependently reduced the frequency of scratching in the last stage. Moreover, repeated local application of dexametasone significantly inhibited both scratching behavior and skin symptoms from day 24 to day 30. From these findings, it may be concluded that this model is essentially similar to atopic dermatitis in humans and could be used to elucidate the pathogenic mechanisms of atopic dermatitis and to develop appropriate new drugs for therapy.

Topics: Animals; Dermatitis, Atopic; Dexamethasone; Disease Models, Animal; Female; Histamine H1 Antagonists; Immunoglobulin E; Mice; Mice, Inbred BALB C; Naloxone; Ovalbumin; Pruritus; Skin

The opioid system is one in a number of peptidergic regulatory systems that support an appropriate anxiety level. The drugs that interact with the opioid system have been shown to influence anxiety, although there is a notable variability in their pharmacological effects. Biological mechanisms of this variability are considered to be the heterogeneity of opioid receptors, the ratio of the processes of their expression and desensitization, and the balance between the synthesis and degradation of endogenous opioid peptides. For instance, the anxiolythic effect of the synthetic derivate of enkephalin in rats was detected after stress-induced exhaustion of endogenous opioids, and its efficacy depended on the degree of delta- and mu-opioid receptor desensitization in some brain regions. The anxiolythic properties of the heptapeptide Selanc that has also been shown to affect the opioid system are most prominent in subjects with elevated activity of enzymes degrading endogenous opioid peptides. Thus, delicate correction of the opioid system with drugs of peptide nature is supposed to become a new approach to treatment of some forms of anxiety disorders accompanied with exhaustion of the endogenous opioid system and, in particular, of generalized anxiety disorder.

Topics: Animals; Anti-Anxiety Agents; Anxiety Disorders; Brain Chemistry; Disease Models, Animal; Enkephalins; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Oligopeptides; Opioid Peptides; Rats; Receptors, Opioid

Several diseases affect bone healing and physiology. Many drugs that are commonly used in orthopaedics as "analgesics" or anti-inflammatory agents impair bone healing. Stressful conditions are associated with decreased serum osteocalcin concentration. High endorphin levels alter calcium metabolism, blocking the membrane channels by which calcium normally enters cells. The consequent decrease of intracellular calcium impairs the activities of calcium-related enzymes. Naloxone is a pure opioid antagonist. Morphine-induced osteocalcin inhibition was abolished when osteoblasts were incubated with naloxone. Naloxone restored the altered cellular and tissue physiology by removing beta-endorphins from specific receptors. However, this is only possible if the circulating Ca concentration is adequate. The aim of the present study was to evaluate the efficacy of parenteral naloxone administration in inducing fast mineralization and callus remodelling in a group of sheep with a standardised bone lesion.. Twenty ewes were randomly assigned to 4 treatment groups. Group A acted as control, group B received a solution of calcium gluconate, group C a solution of naloxone, and group D a solution of calcium gluconate and naloxone. A transverse hole was drilled in the left metacarpus, including both cortices, then parenteral treatment was administered intramuscularly, daily for four weeks. Healing was evaluated by weekly radiographic examination for eight weeks. For quantitative evaluation, the ratio of the radiographic bone density between the drill area and the adjacent cortical bone was calculated. After eight weeks the sheep were slaughtered and a sample of bone was collected for histopathology. Group D showed a higher radiographic ratio than the other groups. Sheep not treated with naloxone showed a persistently lower ratio in the lateral than the medial cortex (P < 0.01). Histopathology of bone samples showed more caverns and fewer osteoblasts in group D than in the other groups (P

Topics: Animals; Bone and Bones; Calcium Gluconate; Disease Models, Animal; Drug Therapy, Combination; Female; Fracture Healing; Injections, Intramuscular; Metacarpus; Naloxone; Narcotic Antagonists; Osteogenesis; Radiography; Sheep

In pre-clinical models intended to evaluate nociceptive processing, acute stress suppresses reflex responses to thermal stimulation, an effect previously described as stress-induced "analgesia." Suggestions that endogenous opioids mediate this effect are based on demonstrations that stress-induced hyporeflexia is enhanced by high dose morphine (>5 mg/kg) and is reversed by naloxone. However, reflexes and pain sensations can be modulated differentially. Therefore, in the present study direct comparisons were made of opioid agonist and antagonist actions, independently and in combination with acute restraint stress in Long Evans rats, on reflex lick-guard (L/G) and operant escape responses to nociceptive thermal stimulation (44.5 degrees C). A high dose of morphine (>8 mg/kg) was required to reduce reflex responding, but a moderate dose of morphine (1 mg/kg) significantly reduced escape responding. The same moderate dose (and also 5 mg/kg) of morphine significantly enhanced reflex responding. Naloxone (3 mg/kg) significantly enhanced escape responding but did not affect L/G responding. Restraint stress significantly suppressed L/G reflexes (hyporeflexia) but enhanced escape responses (hyperalgesia). Stress-induced hyperalgesia was significantly reduced by morphine and enhanced by naloxone. In contrast, stress-induced hyporeflexia was blocked by both naloxone and 1 mg/kg of morphine. Thus, stress-induced hyperalgesia was opposed by endogenous opioid release and by administration of morphine. Stress-induced hyporeflexia was dependent upon endogenous opioid release but was counteracted by a moderate dose of morphine. These data demonstrate a differential modulation of reflex and operant outcome measures by stress and by separate or combined opioid antagonism or administration of morphine.

Topics: Acute Disease; Adaptation, Physiological; Analgesics, Opioid; Animals; Conditioning, Operant; Disease Models, Animal; Displacement, Psychological; Dose-Response Relationship, Drug; Escape Reaction; Female; Morphine; Naloxone; Narcotic Antagonists; Opioid Peptides; Rats; Rats, Long-Evans; Reaction Time; Reflex; Reflex, Abnormal; Restraint, Physical; Stress, Psychological

Psalmotoxin 1, a peptide extracted from the South American tarantula Psalmopoeus cambridgei, has very potent analgesic properties against thermal, mechanical, chemical, inflammatory and neuropathic pain in rodents. It exerts its action by blocking acid-sensing ion channel 1a, and this blockade results in an activation of the endogenous enkephalin pathway. The analgesic properties of the peptide are suppressed by antagonists of the mu and delta-opioid receptors and are lost in Penk1-/- mice.

Topics: Acid Sensing Ion Channels; Analgesics; Animals; Area Under Curve; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Enkephalins; Membrane Proteins; Mice; Mice, Knockout; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Nerve Tissue Proteins; Neurons; Pain; Pain Measurement; Peptides; Protein Precursors; Reaction Time; Sodium Channels; Spider Venoms; Spinal Cord; Time Factors

Passion flower (Passiflora incarnata) is used in traditional medicine of Europe and South America to treat anxiety, insomnia and seizure. Recently, it has shown antianxiety and sedative effects in human.. In this study, anticonvulsant effects of hydro- alcoholic extract of Passiflora, Pasipay, were examined by using pentylentetrazole model (PTZ) on mice. Pasipay, diazepam, and normal saline were injected intraperitoneally at the doses 0.4-0.05 mg/kg, 0.5-1 mg/kg and 10 ml/kg respectively 30 minutes before PTZ (90 mg/kg, i.p). The time taken before the onset of clonic convulsions, the duration of colonic convulsions, and the percentage of seizure and mortality protection were recorded. For investigating the mechanism of Pasipay, flumazenil (2 mg/kg, i.p) and naloxone (5 mg/kg, i.p) were also injected 5 minutes before Pasipay.. An ED50 value of Pasipay in the PTZ model was 0.23 mg/kg (%95 CL: 0.156, 0.342). Pasipay at the dose of 0.4 mg/kg prolonged the onset time of seizure and decreased the duration of seizures compared to saline group (p < 0.001). At the dose of 0.4 mg/kg, seizure and mortality protection percent were 100%. Flumazenil and naloxone could suppress anticonvulsant effects of Pasipay.. It seems that Pasipay could be useful for treatment absence seizure and these effects may be related to effect of it on GABAergic and opioid systems. More studies are needed in order to investigate its exact mechanism.

Topics: Animals; Anticonvulsants; Antidotes; Convulsants; Diazepam; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Epilepsy, Absence; Flumazenil; Injections, Intraperitoneal; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Passiflora; Pentylenetetrazole; Phytotherapy; Plant Components, Aerial; Plant Extracts; Receptors, GABA-A; Receptors, Opioid; Sodium Chloride; Treatment Outcome

Abdominal electromyographic (EMG) responses to noxious intensities of urinary bladder distention (UBD) are significantly enhanced 24 hours after zymosan-induced bladder inflammation in adult female rats. This inflammation-induced hypersensitivity is concomitantly inhibited by endogenous opioids because intraperitoneal (i.p.) naloxone administration before testing significantly increases EMG response magnitude to UBD. This inhibitory mechanism is not tonically active because naloxone does not alter EMG response magnitude to UBD in rats without inflammation. At the dose tested, naloxone does not affect bladder compliance in rats with or without inflammation. The effects of i.p. naloxone probably result from blockade of a spinal mechanism because intrathecal naloxone also significantly enhances EMG responses to UBD in rats with inflammation. Rats exposed to bladder inflammation from P90-P92 before reinflammation at P120 show similar hypersensitivity and concomitant opioid inhibition, with response magnitudes being no different from that produced by inflammation at P120 alone. In contrast, rats exposed to bladder inflammation from P14-P16 before reinflammation at P120 show markedly enhanced hypersensitivity and no evidence of concomitant opioid inhibition. These data indicate that bladder inflammation in adult rats induces bladder hypersensitivity that is inhibited by an endogenous opioidergic mechanism. This mechanism can be disrupted by neonatal bladder inflammation.. The present study observed that bladder hypersensitivity resulting from acute bladder inflammation is suppressed by an opioid-inhibitory mechanism. Experiencing bladder inflammation during the neonatal period can impair the expression of this opioid inhibitory mechanism in adulthood. This suggests that bladder insults during development may permanently alter visceral sensory systems and may represent 1 cause of painful bladder disorders.

Topics: Age Factors; Analgesics, Opioid; Analysis of Variance; Animals; Animals, Newborn; Dilatation, Pathologic; Disease Models, Animal; Electromyography; Female; Inflammation; Muscle Contraction; Naloxone; Narcotic Antagonists; Pain Measurement; Rats; Rats, Sprague-Dawley; Reflex; Urinary Bladder Diseases; Viscera; Zymosan

To investigate the analgesic effect of interleukin-2 (IL-2) in mice with spared nerve injury (SNI).. IL-2 was intraperitoneally injected in mice with induced SNI, and von Frey Filaments test and cold plate test were carried out to accesses the analgesic effects of IL-2 and the effect of naloxone in antagonizing the effects of IL-2.. IL-2 produced analgesic effects against hyperalgesia and allodynia in mouse models of SNI, and the effect of IL-2 lasted for more than 24 h, showing a double-peak pattern in its action with the two peaks occurring at 30 and 105 min, respectively. The effect of IL-2 could be significantly antagonized by naloxone.. IL-2 has long-lasting analgesic effects in mouse models of SNI model, showing a double-peak pattern of its action. The analgesic effect of IL-2 is probably mediated by opiate receptor.

Topics: Analgesics; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Humans; Hyperalgesia; Interleukin-2; Male; Mice; Mice, Inbred BALB C; Naloxone; Trauma, Nervous System

Paeoniflorin (PF), one of the active chemical compounds identified from the root of Paeonia lactiflora Pall, has been well-established to exhibit various neuroprotective actions in the central nervous system (CNS) after long-term daily administration. In the present study, by using the bee venom (BV) model of nociception and hypersensitivity, antinociceptive effects of PF were evaluated by intraperitoneal administration in conscious rats. When compared with saline control, systemic pre- and post-treatment with PF resulted in an apparent antinociception against both persistent spontaneous nociception and primary heat hypersensitivity, while for the primary mechanical hypersensitivity only pre-treatment was effective. Moreover, pre- and early post-treatment with PF (5 min after BV injection) could successfully suppress the occurrence and maintenance of the mirror-image heat hypersensitivity, whereas late post-treatment (3 h after BV) did not exert any significant impact. In the Rota-Rod treadmill test, PF administration did not affect the motor coordinating performance of rats. Furthermore, systemic PF application produced no significant influence upon BV-induced paw edema and swelling. Finally, the PF-produced antinociception was likely to be mediated by endogenous opioid receptors because of its naloxone-reversibility. Taken together, these results provide a new line of evidence showing that PF, besides its well-established neuroprotective actions in the CNS, is also able to produce analgesia against various 'phenotypes' of nociception and hypersensitivity via opioid receptor mediation.

Topics: Analgesics; Animals; Bee Venoms; Benzoates; Bridged-Ring Compounds; Disease Models, Animal; Glucosides; Hyperalgesia; Male; Monoterpenes; Motor Activity; Naloxone; Pain Threshold; Rats; Rats, Sprague-Dawley

Respiratory depression, the most serious side-effect of opioid treatment, is well documented for morphine, the most commonly used opioid in neonatal care. Less is known about methadone, a clinically relevant opioid analgesic, especially during neonatal development. This study was undertaken to determine the neonatal respiratory effects of methadone. We hypothesize that methadone is equipotent to morphine, compared to our previous morphine results in the same animal model, but has a much longer duration of action, due to its longer elimination half-life. Neonatal guinea pigs (3-14 days old) randomly received a single subcutaneous dose of methadone or saline. Using a non-invasive plethysmographic method, we measured ventilatory and metabolic parameters before injection and at intervals for 32 hr after injection while pups breathed "room air" or 5% CO(2) gas mixtures. Methadone-induced depression of ventilation was most evident during 5% CO(2) challenge. The onset of drug effects was within 15 min for all ages and doses, but the duration of action decreased with age. While the depth of methadone-induced respiratory depression did not depend on pup age, the control of breathing was different in 3-day-old pups, where inspiratory time increased fourfold; twice that of older pups. We conclude that methadone induces a naloxone reversible respiratory depression in guinea pig neonates and, in the very young, causes an abnormal breathing pattern due to changes in respiratory timing. Methadone is more potent than morphine with respect to neonatal respiratory depression, but surprisingly, the duration of methadone action was not longer than morphine.

Topics: Animals; Animals, Newborn; Blood Gas Analysis; Breath Tests; Carbon Dioxide; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Forced Expiratory Flow Rates; Guinea Pigs; Injections, Subcutaneous; Inspiratory Reserve Volume; Methadone; Naloxone; Narcotic Antagonists; Narcotics; Oxygen Consumption; Plethysmography; Prognosis; Respiratory Insufficiency

The rate and pattern of lever pressing were studied in 18 rats during 24-h sessions in which responding resulted in intravenous infusions of nicotine. There were four indications of the positive reinforcing effect of nicotine: (1) a greater number of lever presses when nicotine was response-contingent compared to when saline was available; (2) a greater number of responses on the lever resulting in an infusion of nicotine than on the control lever; (3) systematic decreases in the number of contingent nicotine infusions when nicotine was delivered noncontingently; and (4) systematic changes in the frequency of lever pressing as a function of dose. Under a fixed ratio 1 (FR 1) schedule, the number of infusions first increased and then decreased as the dose of nicotine was decreased (64, 32, 16, and 8 microg/kg infusion) and nicotine intake (mg/kg every 24 h) was directly related to the infusion dose. As the FR size was increased from 1 to 6, the number of lever presses increased and the number of infusions (32 microg/kg) remained stable. At FR values greater than 6, both the number of lever presses and infusions decreased. Presession injections of mecamylamine (0.75, 1.5, and 3.0 mg/kg, s.c.) decreased the number of infusions in a dose-related manner. Presession injections of hexamethonium (1.5 and 3.0 mg/kg, s.c.) or naloxone (0.75, 1.5, and 3.0 mg/kg, s.c.) did not alter the within- or between-session patterns of nicotine self-administration. Under the conditions of the present experiment, nicotine served as an effective reinforcer and the behavior was shown to be sensitive to both FR size and infusion dose. In addition, the results suggest that nicotine self-administration involves central nicotinic receptors and that opioid receptor antagonism has no effect on nicotine's reinforcing effects in rats.

Topics: Animals; Association Learning; Brain; Conditioning, Operant; Disease Models, Animal; Dose-Response Relationship, Drug; Hexamethonium; Humans; Infusions, Intravenous; Male; Mecamylamine; Naloxone; Nicotine; Nicotinic Antagonists; Rats; Rats, Long-Evans; Receptors, Nicotinic; Receptors, Opioid; Reinforcement Schedule

Opioid overdose, which is commonly associated with opioid induced respiratory depression, is a problem with both therapeutic and illicit opioid use. While the central mechanisms involved in the effects of opioids are well described, it has also been suggested that a peripheral component may contribute to the effects observed. This study aimed to further characterise the effects of the peripherally acting naloxone methiodide on the respiratory, analgesic and withdrawal effects produced by various opioid agonists. A comparison of the respiratory and analgesic effects of morphine, methadone and heroin in male Swiss-Albino mice was conducted and respiratory depressive ED(80) doses of each opioid determined. These doses (morphine 9 mg/kg i.p., methadone 7 mg/kg i.p., and heroin 17 mg/kg i.p.) were then used to show that both naloxone (3 mg/kg i.p.) and naloxone methiodide (30-100 mg/kg i.p.) could reverse the respiratory and analgesic effects of these opioid agonists, but only naloxone precipitated withdrawal. Further investigation in female C57BL/6J mice using barometric plethysmography found that both opioid antagonists could reverse methadone induced decreases in respiratory rate and increases in tidal volume. Its effects do not appear to be strain or sex dependent. It was concluded that naloxone methiodide can reverse the respiratory and analgesic actions of a variety of opioid agonists, without inducing opioid withdrawal.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Drug Interactions; Female; Heroin; Male; Methadone; Mice; Mice, Inbred C57BL; Morphine; Naloxone; Plethysmography, Whole Body; Quaternary Ammonium Compounds; Respiration; Respiratory Insufficiency; Substance Withdrawal Syndrome

Previous studies using c-Fos immunohistochemistry suggest that a sub-population of neurons in the midbrain periaqueductal gray region is activated during opioid withdrawal. The neurochemical identity of these cells is unknown but cellular physiological studies have implicated GABAergic neurons. The present study investigated whether GABAergic neurons are activated in the mouse periaqueductal gray during opioid withdrawal using dual-antibody immunohistochemistry for Fos and glutamic acid decarboxylase. Both chronic opioid treatment and naloxone-precipitated opioid withdrawal increased Fos expression in the periaqueductal gray, with the greatest increase being four-fold in the caudal ventrolateral subdivision following withdrawal. Neurons stained for both Fos and glutamic acid decarboxylase were greatly enhanced in all subdivisions of the periaqueductal gray following withdrawal, particularly in the lateral and ventrolateral divisions where the increase was up to 70-fold. These results suggest that activation of a subpopulation of GABAergic interneurons in the periaqueductal gray plays a role in opioid withdrawal.

Topics: Animals; Disease Models, Animal; Gene Expression Regulation; Genes, fos; Glutamate Decarboxylase; Mice; Naloxone; Narcotics; Neurons; Periaqueductal Gray; Substance Withdrawal Syndrome

Epilepsy remains a major medical problem of unknown aetiology. Potentially, viruses can be environmental triggers for development of seizures in genetically vulnerable individuals. An estimated half of encephalitis patients experience seizures and approximately 4% develop status epilepticus. Epilepsy vulnerability has been associated with a dynorphin promoter region polymorphism or low dynorphin expression genotype, in man. In animals, the dynorphin system in the hippocampus is known to regulate excitability. The present study was designed to test the hypothesis that reduced dynorphin expression in the dentate gyrus of hippocampus due to periadolescent virus exposure leads to epileptic responses. Encephalitis produced by the neurotropic Borna disease virus in the rat caused epileptic responses and dynorphin to disappear via dentate granule cell loss, failed neurogenesis and poor survival of new neurons. Kappa opioid (dynorphin) agonists prevented the behavioural and electroencephalographic seizures produced by convulsant compounds, and these effects were associated with an absence of dynorphin from the dentate gyrus granule cell layer and upregulation of enkephalin in CA1 interneurons, thus reproducing a neurochemical marker of epilepsy, namely low dynorphin tone. A key role for kappa opioids in anticonvulsant protection provides a framework for exploration of viral and other insults that increase seizure vulnerability and may provide insights into potential interventions for treatment of epilepsy.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Blotting, Northern; Borna Disease; Cell Survival; Disease Models, Animal; Dynorphins; Electroencephalography; Encephalitis, Viral; Enkephalins; Hippocampus; Male; Naloxone; Narcotic Antagonists; Neurons; Rats; Rats, Inbred Lew; Receptors, Opioid, kappa; Seizures

Several medications are approved for treatment of opiate abuse, but determinants of their clinical effectiveness are not completely understood. States of opiate dependence or withdrawal may constitute one important set of determinants. To test this hypothesis, the effects of naloxone, buprenorphine, and methadone were assessed on choice between heroin and food in nondependent rhesus monkeys and in heroin-dependent monkeys undergoing withdrawal. A choice procedure was used to permit dissociation of medication effects on the relative reinforcing properties of heroin from nonselective effects on response rates. In nondependent monkeys, increasing unit doses of heroin (0-0.1 mg/kg/injection) maintained dose-dependent increases in heroin choice. Chronic 5-day treatment with naloxone (0.01-0.32 mg/kg/h) or buprenorphine (0.01-0.1 mg/kg/day) produced dose-dependent rightward shifts in heroin choice dose-effect curves, whereas chronic methadone (0.1-0.56 mg/kg/h) had little effect on heroin choice up to doses that suppressed responding. In heroin-dependent monkeys, opiate withdrawal produced overt abstinence signs as well as increases in heroin choice, manifested as leftward shifts in heroin choice dose-effect curves. The withdrawal-associated increases in heroin choice suggest that opiate withdrawal increased the relative reinforcing efficacy of heroin in comparison with food, an effect that may be related to relapse in humans. Methadone prevented withdrawal-associated increases in heroin choice, whereas buprenorphine was less effective. These findings suggest that agonist medications such as methadone may derive their clinical utility from their ability to attenuate withdrawal-associated increases in opiate reinforcement. Moreover, this procedure may be useful for exploring mechanisms underlying withdrawal-associated increases in opiate reinforcement and for testing candidate medications.

Topics: Animals; Buprenorphine; Disease Models, Animal; Feeding Behavior; Heroin; Heroin Dependence; Macaca mulatta; Male; Methadone; Naloxone; Self Administration; Substance Withdrawal Syndrome

The antinociceptive effect and the mechanism of bee venom acupuncture (BVA) on inflammatory pain, especially in the rat model of collagen-induced arthritis (CIA), have not yet been fully studied. This study was designed to investigate the antinociceptive effect and its mu-opioid and alpha2-adrenergic mechanism of BVA in the CIA rat model. To induce CIA, male Sprague-Dawley rats were immunized with bovine type II collagen emulsified in Freund's incomplete adjuvant followed by a booster injection 14 days later. The antinociceptive effect was evaluated by tail flick latency (TFL). After induction of arthritis, the inflammatory pain threshold decreased as time passed, and there was no big change of the pain threshold after 3 weeks. Three weeks after the first immunization, BVA (0.25 mg/kg) injected into the Zusanli acupoint (ST36) showed the antinociceptive effect. Furthermore, the antinociceptive effect of BVA was blocked by yohimbine (alpha2-adrenergic receptor antagonist, 2 mg/kg, i.p) pretreatment, but not by naloxone (mu-opioid receptor antagonist, 2 mg/kg, i.p.) pretreatment. These results suggest that BVA can relieve inflammatory pain in CIA and the antinociceptive effect of BVA can be mediated by alpha2-adrenergic receptor.

Topics: Acupuncture Points; Adrenergic alpha-Antagonists; Animals; Arthritis, Experimental; Bee Venoms; Behavior, Animal; Collagen; Disease Models, Animal; Drug Administration Routes; Drug Interactions; Male; Naloxone; Narcotic Antagonists; Pain; Pain Management; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Adrenergic, alpha-2; Statistics, Nonparametric; Yohimbine

Previous studies have indicated that the ventrolateral orbital cortex (VLO) is involved in opioid-mediated antinociception in the tail flick test and formalin test. The aim of the current study was to examine the effect of opioids microinjected into the VLO on allodynia in the rat L5/L6 spinal nerve ligation (SNL) model of neuropathic pain and determine the roles of different subtypes of opioid receptors in this effect. The allodynia was assessed by both mechanical (von Frey filaments) and cold plate (4 degrees C) stimuli. Morphine (1.0, 2.5, and 5.0 microg) microinjected into the VLO contralateral to the nerve ligation dose-dependently depressed the mechanical and cold allodynia and these effects were reversed by nonselective opioid receptor antagonist naloxone (1.0 microg) administrated into the same site. Microinjection of endomorphin-1 (5.0 microg), a highly selective mu-opioid receptor agonist, and [D-Ala2, D-Leu5]-enkephalin (DADLE, 10 microg), a delta-/mu-opioid receptor agonist, also depressed the allodynia, and the effects of both drugs were blocked by selective mu-receptor antagonist beta-funaltrexamine (beta-FNA, 3.75 microg), but the effects of DADLE were not influenced by the selective delta-receptor antagonist naltrindole (5.0 microg). Microinjection of U-62066 (100 microg), a kappa-opioid receptor agonist, into the VLO had no effect on the allodynia. These results suggest that the VLO is involved in opioid-induced antiallodynia and mu- but not delta- and kappa-opioid receptor mediates these effects in the rat with neuropathic pain.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Male; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Physical Stimulation; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Spinal Cord Injuries; Time Factors

Opioids are commonly used in the treatment of moderate to severe pain. However, their chronic use is limited by analgesic tolerance and physical dependence. Few studies have examined how chronic pain affects the development of tolerance or dependence, and essentially no studies have looked at the role of both genetics and pain together. For these studies we used 12 strains of inbred mice. Groups of mice from each strain were tested at baseline for morphine analgesic sensitivity, mechanical nociceptive threshold, and thermal nociceptive threshold. Mice were then given morphine in a 4-day escalating morphine administration paradigm followed by reassessment of the morphine dose-response relationship. Finally, physical dependence was measured by administering naloxone. Parallel groups of mice underwent hind paw injection of complete Freund's adjuvant (CFA) to induce chronic hind paw inflammation 7 days prior to the beginning of testing. The data showed that CFA treatment tended to lower baseline ED(50) values for morphine and enhanced the degree of analgesic tolerance observed after 4 days of morphine treatment. In addition, the degree of jumping behavior indicative of physical dependence was often altered if mice had been treated with CFA. The influence of background strain was substantial for all traits measured. In silico haplotypic mapping of the tolerance and physical dependence data demonstrated that CFA pretreatment altered the pattern of the predicted associations and greatly reduced their statistical significance. We conclude that chronic inflammatory pain and genetics interact to modulate the analgesic potency of morphine, tolerance, and physical dependence.

Topics: Analgesics, Opioid; Animals; Chronic Disease; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Freund's Adjuvant; Genetic Predisposition to Disease; Genotype; Inflammation Mediators; Male; Mice; Mice, Inbred AKR; Mice, Inbred BALB C; Mice, Inbred C3H; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Inbred MRL lpr; Morphine; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Pain; Pain Threshold; Species Specificity

The present study investigated whether the loss of spinal mu-opioid receptors following peripheral nerve injury is related to mechanical allodynia. We compared the quantity of spinal mu-opioid receptor and the effect of its antagonists, such as naloxone and CTOP, on pain behaviors in two groups of rats that showed extremely different severity of mechanical allodynia 2 weeks following partial injury of tail-innervating nerves. One group (allodynic group) exhibited robust signs of mechanical allodynia after the nerve injury, whereas the other group (non-allodynic group) showed little allodynia despite having suffered the same nerve injury. In addition, we investigated the quantity of spinal mu-opioid receptor and the effect of its antagonists on pain behaviors after the rats had recovered from mechanical allodynia 16 weeks following nerve injury. Immunohistochemical and Western blot analyses at 2 weeks after nerve injury indicated that spinal mu-opioid receptor content was more reduced in the allodynic group compared to the non-allodynic group. Intraperitoneal naloxone (2 mg/kg, i.p.) and intrathecal CTOP (10 microg/rat, i.t.) administration dramatically induced mechanical allodynia in the non-allodynic group. However, as in naïve animals, neither the loss of spinal mu-opioid receptors nor antagonist-induced mechanical allodynia was observed in the rats that had recovered from mechanical allodynia. These results suggest that the loss of spinal mu-opioid receptors following peripheral nerve injury is related to mechanical allodynia.

Topics: Amino Acid Sequence; Animals; Axotomy; Disease Models, Animal; Hyperalgesia; Injections, Intraperitoneal; Injections, Spinal; Male; Molecular Sequence Data; Naloxone; Narcotic Antagonists; Neuralgia; Posterior Horn Cells; Pressure; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Somatostatin; Spinal Cord; Spinal Nerves; Stress, Mechanical; Tail

Although scopolamine is currently used to treat morphine addiction in humans, its extensive actions on behaviors have not been systematically analyzed yet, and the underlying mechanisms of its effects still remain ambiguous. The present study was carried out to clarify the possible mechanisms by evaluating the effects of scopolamine pretreatment and treatment on naloxone-precipitated withdrawal signs and some of other general behaviors in morphine dependent rats. Our results showed that scopolamine pretreatment and treatment attenuated naloxone-precipitated withdrawal signs including jumping, writhing posture, weight loss, genital grooming, teeth-chattering, ptosis, diarrhea and irritability, except for wet dog shakes, while general behaviors such as water intake, urine volume and morphine excretion in urine were increased. Our findings suggest that scopolamine has significant actions in the treatment of opiate addiction, which might result from increasing morphine excretion from urine.

Topics: Analysis of Variance; Animals; Behavior, Animal; Behavioral Symptoms; Disease Models, Animal; Drinking; Drug Interactions; Ethology; Male; Morphine; Morphine Dependence; Muscarinic Antagonists; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Scopolamine

To establish a visceral pain model via colorectal distension (CRD) and to evaluate the efficiency of behavioral responses of CRD by measuring the score of abdominal withdrawal reflex (AWR) in rats.. Thirty-eight male SD rats weighing 180-240 g were used to establish the visceral pain model. The rat was inserted intra-anally with a 7 cm long flexible latex balloon under ether anesthesia, and colorectal distensions by inflating the balloon with air were made 30 min after recovering from the anesthesia. Five AWR scores (AWR0 to AWR4) were used to assess the intensity of noxious visceral stimuli. It was regarded as the threshold of the minimal pressure (kPa). For abdominal flatting was induced by colorectal distension.. A vigorous AWR to distension of the descending colon and rectum was found in 100% of the awake rats tested. The higher the pressure of distension, the higher the score of AWR. The distension pressures of 0, 2.00, 3.33, 5.33 and 8.00 kPa produced different AWR scores (P<0.05). The pain threshold of AWR was constant for up to 80 min after the initial windup (first 1-3 distensions), the mean threshold was 3.69+/-0.35 kPa. Systemic administration of morphine sulfate elevated the threshold of visceral pain in a dose-dependent and naloxone reversible manner.. Scoring the AWR during colorectal distensions can assess the intensity of noxious visceral stimulus. Flatting of abdomen (AWR 3) to CRD as the visceral pain threshold is clear, constant and reliable. This pain model and its behavioral assessment are good for research on visceral pain and analgesics.

Topics: Abdominal Pain; Analgesics; Animals; Behavior, Animal; Catheterization; Colon; Dilatation, Pathologic; Disease Models, Animal; Male; Morphine; Naloxone; Narcotic Antagonists; Pain Threshold; Rats; Rats, Sprague-Dawley; Rectum; Reflex; Reproducibility of Results; Time Factors; Viscera

Aspects of drug withdrawal may become conditioned to previously neutral environmental stimuli via classical conditioning processes. Nevertheless, the significance of conditioned withdrawal effects in motivating drug intake remains largely unexplored. Here, we investigated the effects of conditioned withdrawal in modulating heroin consumption and brain reward sensitivity in rats. Rats intravenously self-administered heroin (20 microg/infusion) during 0 h (control), 1 h (nondependent), or 23 h (dependent) sessions and had daily intracranial self-stimulation (ICSS) thresholds assessed. ICSS thresholds remained stable and unaltered in control rats. In nondependent rats, heroin self-administration induced a transient activation of reward systems, reflected in lowering of ICSS thresholds. In dependent rats, heroin intake escalated across sessions and was associated with a gradual decrease in reward sensitivity, reflected in progressively elevated ICSS thresholds. Thus, as dependence develops, heroin may be consumed not only for its acute reward-facilitating effects, but also to counter persistent deficits in reward sensitivity. In nondependent rats, the opioid receptor antagonist naloxone (30 microg/kg) increased heroin consumption and reversed heroin-induced lowering of ICSS thresholds, effects resistant to classical conditioning. In contrast, in dependent rats naloxone (30 microg/kg) increased heroin consumption and also elevated ICSS thresholds above their already elevated baseline levels (i.e., precipitated withdrawal). Most importantly, stimuli repeatedly paired with naloxone-precipitated withdrawal provoked heroin consumption and elevated ICSS thresholds in dependent rats. Thus, conditioned stimuli predicting the onset of heroin withdrawal, and hence the reward deficits coupled with this state, may play a critical role in provoking craving and relapse in human opiate addicts.

Topics: Animals; Conditioning, Classical; Disease Models, Animal; Electric Stimulation; Heroin; Heroin Dependence; Male; Naloxone; Narcotic Antagonists; Rats; Reward; Self Stimulation; Substance Withdrawal Syndrome

The authors examined the role of the endogenous opioid system in infantile amnesia for contextual fear conditioning. Rats that were 18 days of age received an aversive footshock in a novel context. Rats displayed conditioned fear when tested 1 min after training but not 24 hr after training. Systemic injection of the opioid receptor antagonist naloxone prior to test, but not immediately after training, alleviated infantile amnesia. Naloxone also alleviated infantile amnesia when injected prior to test 7 days after training. These effects of naloxone were due to actions on central rather than peripheral opioid receptors and were not due to any tendency of the drug to produce fear or freezing. These results show that central opioid receptors regulate retrieval of fear memories in infant rats.

Topics: Amnesia; Animals; Animals, Newborn; Conditioning, Psychological; Disease Models, Animal; Dose-Response Relationship, Drug; Fear; Female; Freezing Reaction, Cataleptic; Male; Memory; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Retention, Psychology; Time Factors

Itching is the most important problem in many allergic and inflammatory skin diseases especially in atopic dermatitis. However, animal models for allergic dermatitis useful for the study of itching have rarely been established. We established a mouse allergic dermatitis model involving frequent scratching behavior by repeated painting with 2,4-dinitrofluorobenzene (DNFB) acetone solution onto the mouse skin, and comparatively examined the effects of tacrolimus and dexamethasone on the dermatitis and associated scratching behavior. Repeated DNFB painting caused typical dermatitis accompanied by elevated serum immunoglobulin E (IgE) and frequent scratching behavior. An apparent thickening of the epidermis and dermis, and the significant accumulation of inflammatory cells were observed. Increased interferon (IFN)-gamma mRNA expression and the induction of interleukin (IL)-4 and IL-5 mRNA expression were also observed in the skin lesion. The scratching behavior was inhibited by dibucaine and naloxone. Although tacrolimus reduced the increased expression of IFN-gamma and IL-4 mRNA, dexamethasone potently depressed that of IFN-gamma, IL-4 and IL-5 mRNA. Dexamethasone inhibited the accumulation of lymphocytes and eosinophils, although tacrolimus did not. Both drugs failed to inhibit the elevation of serum IgE levels. Tacrolimus significantly inhibited the scratching behavior that was associated with the inhibition of nerve fiber extension into the epidermis, whereas dexamethasone failed to have any effect. The mouse dermatitis model seems to be beneficial for the study of itching associated with allergic dermatitis, such as atopic dermatitis, and tacrolimus seems to exhibit an anti-itch effect through the inhibition of nerve fiber extension at least in part.

Topics: Allergens; Anesthetics, Local; Animals; Antipruritics; Behavior, Animal; Dermatitis, Allergic Contact; Dermatitis, Atopic; Dexamethasone; Dibucaine; Dinitrofluorobenzene; Disease Models, Animal; Glucocorticoids; Immunoglobulin E; Interferon-gamma; Interleukin-4; Interleukin-5; Male; Mice; Mice, Inbred BALB C; Naloxone; Narcotic Antagonists; Pruritus; RNA, Messenger; Skin; Tacrolimus

Cardiac arrest was induced with asphyxia to identify if naloxone alone increases resuscitation rate during cardiopulmonary resuscitation in a rat asphyxia model. The animals were randomized into either a saline group (Sal-gro, treated with normal saline 1 ml iv, n = 8), a low-dose naloxone group (treated with naloxone 0.5 mg/kg iv, n = 8), or a high-dose naloxone group (HN-gro, treated with naloxone 1 mg/kg iv, n = 8) in a blinded fashion during resuscitation. At the end of 10 minutes of asphyxia, cardiopulmonary resuscitation was started, and each drug was administered at the same time. The rate of restoration of spontaneous circulation was seen in 1 of 8, 3 of 8, and 7 of 8 animals in the Sal-gro, LN-gro, and HN-gro, respectively. The rate of restoration of spontaneous circulation in HN-gro was significantly higher than that in Sal-gro (P < .05). Naloxone (1 mg/kg) alone can increase resuscitation rate following asphyxial cardiac arrest in rats.

Topics: Animals; Asphyxia; Blood Pressure; Cardiopulmonary Resuscitation; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Heart Arrest; Heart Rate; Male; Naloxone; Narcotic Antagonists; Prospective Studies; Random Allocation; Rats; Rats, Sprague-Dawley; Reference Values; Respiration; Time Factors; Treatment Outcome

The endogenous opioid system is involved in modulating the experience of pain, the response to stress, and the action of analgesic therapies. Recent human imaging studies have shown a significant tonic modulation of visceral pain, raising the question of whether endogenous opioids tonically modulate the pain of visceral cancer.. Transgenic mice expressing the first 127 amino acids of simian virus 40 large T antigen, under the control of the rat elastase-1 promoter, that spontaneously develop pancreatic cancer were used to investigate the role of endogenous opioids in the modulation of pancreatic cancer pain. Visceral pain behaviors were assessed as degree of hunching and vocalization.. Although mice with late-stage pancreatic cancer displayed spontaneous, morphine-reversible, visceral pain-related behaviors such as hunching and vocalization, these behaviors were absent in mice with early-stage pancreatic cancer. After systemic administration of the central nervous system (CNS)-penetrant opioid receptor antagonists naloxone or naltrexone, mice with early-stage pancreatic cancer displayed significant visceral pain-related behaviors, whereas systemic administration of the CNS-nonpenetrant opioid antagonist naloxone-methiodide did not induce an increase in visceral pain behaviors.. Our findings suggest that a CNS opioid-dependent mechanism tonically modulates early and late-stage pancreatic cancer pain. Understanding the mechanisms that mask this pain in early stage disease and drive this pain in late-stage disease may allow improved diagnosis, treatment, and care of patients with pancreatic cancer.

Topics: Abdominal Pain; Animals; Disease Models, Animal; Female; Immunohistochemistry; Male; Mice; Naloxone; Narcotic Antagonists; Neurotransmitter Agents; Opioid Peptides; Pain Measurement; Pancreatic Neoplasms; Severity of Illness Index; Treatment Outcome

Topics: Animals; Conditioning, Classical; Disease Models, Animal; Electric Stimulation; Heroin; Heroin Dependence; Male; Naloxone; Narcotic Antagonists; Rats; Reward; Self Stimulation; Substance Withdrawal Syndrome

Naloxone is an opioid receptor antagonist. Even when used in modest doses, it has been associated with serious cardiopulmonary side-effects. In this experimental porcine study, we examined the cardiac effects of naloxone during an opioid overdose.. Cardiac parameters, changes in the left ventricular compliance and the magnitude of catecholamine release were evaluated in eight spontaneously breathing piglets under propofol sedation. Cardiac parameters were recorded every 30 s and transthoracic echocardiography was used for the continuous assessment of cardiac performance. Respiratory arrest was induced by morphine (8 mg/kg). Ten minutes after morphine administration, naloxone (80 microg/kg) was injected intravenously. Every 5 min, arterial blood gases were measured and, every 10 min, a sample for the analysis of plasma catecholamines was drawn.. There were no statistically significant changes in left ventricular ejection fraction and no signs of pulmonary hypertension. There was a statistically significant increase in the mean arterial pressure immediately after naloxone administration and in norepinephrine concentration before naloxone administration. After naloxone administration, the plasma catecholamine levels decreased in all but one animal. Two animals developed cardiac arrest (pulseless electrical activity and ventricular fibrillation) shortly after receiving naloxone. Although they were both administered naloxone prematurely due to hypoxic bradycardia, naloxone could have contributed to the development of ventricular fibrillation.. Naloxone did not cause changes in ejection fraction or mean pulmonary artery pressure in hypoxic and hypercarbic conditions. After naloxone administration, the plasma catecholamine levels returned to baseline in all but one animal, and two animals developed cardiac arrest.

Topics: Analgesics, Opioid; Animals; Carbon Dioxide; Cardiovascular Physiological Phenomena; Catecholamines; Disease Models, Animal; Drug Overdose; Electrocardiography; Hydrogen-Ion Concentration; Naloxone; Partial Pressure; Propofol; Swine

Thermoregulation is an integrated network of neuroendocrine, autonomic and somatosensory responses. Thermoregulatory dysfunction occurs during fluctuations or decline of gonadal hormone levels and results in vasomotor symptoms such as hot flushes and/or night-time sweating. The neurotransmitter serotonin (5-HT), has been reported to play a role in thermoregulation via changes in extracellular 5-HT levels and/or activation of various 5-HT receptors. The purpose of this study was to evaluate the role of the selective 5-HT reuptake inhibitor (SSRI), fluoxetine (FLX), on temperature regulation using ovariectomized (OVX) rodent models of thermoregulation. Single, subcutaneous (s.c.) administration of FLX (3, 10, 30 and 60 mg/kg) dose-dependently reduced core body temperature (CBT). FLX at 3 and 10 mg/kg s.c. showed no statistically significant decrease on tail-skin temperature (TST), whereas at higher doses (30 and 60 mg/kg) a significant decrease in TST was noted in the telemetry model. To mimic chronic SSRI treatment, a 5-HT(1A) antagonist (WAY-100635; 0.3 mg/kg) was administered 20 min prior to FLX (10 mg/kg). This combination showed no significant improvement on temperature dysfunction compared to FLX alone. Similarly, in a morphine-dependent model of temperature dysfunction FLX, was inactive at 10 mg/kg whereas the 30 and 60 mg/kg s.c. dose abated the naloxone-induced increase in TST by 55 and 81%, respectively. In summary, FLX affected CBT at all doses, but alleviated thermoregulatory dysfunction only at higher doses that are non-selective for the 5-HT system.

Topics: Animals; Body Temperature Regulation; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Combinations; Female; Fluoxetine; Hot Flashes; Morphine Dependence; Naloxone; Ovariectomy; Rats; Rats, Sprague-Dawley; Selective Serotonin Reuptake Inhibitors; Serotonin 5-HT1 Receptor Antagonists; Telemetry

Endogenous hemorphins, derived from degradation of the beta-chain of hemoglobin, lower arterial blood pressure and exert an antinociceptive action in experimental models of nociception. Hemopressin, derived from the alpha-chain of hemoglobin, also decreases blood pressure, but its effects on pain have not been studied. In this work, we examined the influence of hemopressin on inflammatory pain. Hemopressin reverted the hyperalgesia induced by either carrageenin or bradykinin when injected concomitantly or 2.5 h after the phlogistic agents. Hemopressin administered systemically also reverted the hyperalgesia induced by carrageenin. Naloxone did not prevent the antinociceptive action of this peptide. These data suggest that hemopressin inhibits peripheral hyperalgesic responses by mechanisms independent of opioid receptor activation.

Topics: Analgesics; Animals; Blood Pressure; Bradykinin; Carrageenan; Disease Models, Animal; Endorphins; Hemoglobins; Hyperalgesia; Inflammation; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Peptide Fragments; Peptides; Rats; Rats, Wistar; Receptors, Opioid; Time Factors

ABT-594 ((R)-5-(2-azetidinylmethoxy)-2-chloropyridine) represents a novel class of broad-spectrum analgesics whose primary mechanism of action is activation of the neuronal nicotinic acetylcholine receptors. The present study characterized the effects of ABT-594 in a rat chemotherapy-induced neuropathic pain model, where it attenuated mechanical allodynia with an ED50 = 40 nmol/kg (i.p.). This anti-allodynic effect was not blocked by systemic (i.p.) pretreatment with naloxone but was blocked completely with mecamylamine. Pretreatment with chlorisondamine (0.2-5 micromol/kg, i.p.) only partially blocked the effects of ABT-594 at the higher doses tested. In contrast, central (i.c.v.) pretreatment with chlorisondamine completely blocked ABT-594's anti-allodynic effect. Taken together, the data demonstrate that ABT-594 has a potent anti-allodynic effect in the rat vincristine model and that, in addition to its strong central site of action, ABT-594's effects are partially mediated by peripheral nicotinic acetylcholine receptors in this animal model of chemotherapy-induced neuropathic pain.

Topics: Acetylcholine; Analgesia; Animals; Azetidines; Chlorisondamine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Administration Schedule; Drug Evaluation, Preclinical; Drug Therapy, Combination; Humans; Mecamylamine; Naloxone; Nicotinic Agonists; Pain; Pyridines; Rats; Rats, Sprague-Dawley; Time Factors; Vincristine

Trigeminal neuropathic pain represents a real challenge to therapy because commonly used drugs are devoid of real beneficial effect or patients frequently become intolerant or refractory to some of these compounds. In a rat model of trigeminal neuropathic pain, which shares numerous similarities with human trigeminal neuralgia and trigeminal neuropathic pain, we used a genomic herpes simplex virus-derived vector (HSVLatEnk) to examine the possible effect of a local overproduction of proenkephalin A (PA) targeted to the trigeminal primary sensory neurons. Unilateral peripheral inoculation of recombinant vectors on the vibrissal pad territory resulted in an about ninefold increase in proenkephalin A mRNA levels in trigeminal ganglion ipsilateral to the infected side. Transgene-derived met-enkephalin accumulated in numerous nerve cell bodies of trigeminal ganglion and was transported through the sensory nerve fibers located in the infraorbital nerve. Bilateral mechanical hyperresponsiveness, which developed 2 weeks after chronic constrictive injury of the left infraorbital nerve, was significantly attenuated in animals overproducing PA in the trigeminal ganglion ipsilateral to the lesioned infraorbital nerve. This antiallodynic effect was reversed by both the opioid receptor antagonist naloxone and the peripherally acting antagonist naloxone methiodide. Our data demonstrate that the local overproduction of PA-derived peptides in trigeminal ganglion sensory neurons evoked a potent antiallodynic effect through the stimulation of mainly peripherally located opioid receptors and suggest that targeted delivery of endogenous opioids may be of interest for the treatment of some severe forms of neuropathic pain.

Topics: Animals; Disease Models, Animal; Enkephalins; Genetic Therapy; Male; Naloxone; Narcotic Antagonists; Neurons; Pain Threshold; Protein Precursors; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; RNA, Messenger; Simplexvirus; Transcriptional Activation; Trigeminal Ganglion; Trigeminal Neuralgia

To observe the multiple immunoregulating effects of beta-endorphin (beta-END) on synovium cells of collagen-induced arthritis (CIA) in rats and to determine whether the regulation involves the transcriptional factor-kappaB (NF-kappaB) signal pathway.. CIA was induced in female Wistar rats by immunization with native bovine type-II collagen emulsified with complete Freund's adjuvant. Synovial cells in the knees of the CIA rats were cultivated, and the effects of beta-END, beta-END receptor inhibitor (naloxone, Nal) in proliferation and apoptosis of the synovial cells were assayed by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, flow cytometry, and DNA integrity, respectively. The effects of beta-END and Nal on mRNA expression of several cytokines in the synovial cells, including tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, regulated upon activation normal T-cell expressed and secreted (RANTES), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2) and MMP-9 were estimated by quantitative reverse transcription-polymerase chain reaction. Effects of beta-END and Nal on NF-kappaB activity were analyzed using luciferase gene reporter assays. The effects of beta-END and Nal on p65NF-kappaB expression of the synovial cells were examined using Western blot.. 75% of the rats were demonstrated to have established the CIA model successfully. beta-END was shown to exert multiple effects on synovial cells of CIA rats including decreased proliferation, induced apoptosis, and downregulation of TNF-alpha, IL-1beta, IL-6, RANTES, iNOS, MMP-2 and MMP-9 mRNA expression. beta-END seemed to play an immunoregulating role by downregulating the activity and expression of NF-kappaB. It was found that the beta-END receptor blockage could counteract all the effects.. beta-END ameliorates synovial cell functions of CIA rats through binding with receptors and downregulating the NF-kappaB signal pathway. This suggests that beta-END, by blocking the activity and expression of NF-kappaB, is a potential anti-inflammatory and anti-rheumatic agent against CIA.

Topics: Analysis of Variance; Animals; Apoptosis; Arthritis; Arthritis, Experimental; beta-Endorphin; Cell Proliferation; Cells, Cultured; Chemokine CCL5; Collagen Type III; Cytokines; Disease Models, Animal; DNA Fragmentation; Dose-Response Relationship, Drug; Down-Regulation; Drug Interactions; Female; Flow Cytometry; Naloxone; NF-kappa B; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Synovial Membrane; Tomography, X-Ray Computed; Tumor Necrosis Factor-alpha

Acupuncture and acupressure points correlate well with sites on the body that have low transcutaneous electrical resistance (TER). Using lightly sedated, adult Sprague-Dawley rats, we identified an acupoint (i.e. site with low TER) located on the hind limb of the rat and compared the effects of acupressure at this site on the nociceptive threshold to an adjacent, non-acupoint site (i.e. site with high TER). Focal pressure (55.42 +/- 2.2 g) was applied to the site for 10 minutes and the tail flick response (TFR) was determined by draping the distal portion of the tail over a heated wire (75 +/- 5 degrees C). Three trials were performed during each of three randomized conditions (i.e. acupoint, placebo and control) and the trials were averaged. All rats tested (5/5) showed a statistically significant increase in TFR following 10 minutes of acupressure at the acupoint compared to placebo or control trials (p = 0.007). Acupressure at the placebo point resulted in a TFR that was not statistically different from the control. Systemic administration of naloxone completely abolished the tail-flick inhibition induced by acupressure at the acupoint. These data suggest that acupressure elicits an antinociceptive effect in rats that is mediated by the endogenous release of opioids.

Topics: Acupressure; Acupuncture Analgesia; Animals; Disease Models, Animal; Female; Male; Naloxone; Narcotic Antagonists; Nociceptors; Opioid Peptides; Pain; Pain Management; Rats; Rats, Sprague-Dawley

Oriental medicine uses acupuncture at the GV01 acupoint with great success to treat diarrhea. It significantly reduced the colonic motility and inflammation in colitic rats. Naloxone pretreatment blocked these effects. The therapeutic effects of acupuncture at GV01 in colitis may involve endogenous opioid pathways.

Topics: Acupuncture Points; Acupuncture Therapy; Animals; Colitis; Colon; Disease Models, Animal; Gastrointestinal Motility; Injections, Subcutaneous; Male; Naloxone; Narcotic Antagonists; Peroxidase; Rats; Rats, Sprague-Dawley; Trinitrobenzenesulfonic Acid

To investigate the effects of a combination of naloxone and methylprednisolone on nuclear factor-kappaB (NF-kappaB) p65 expression in the lung tissue in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rats.. ALI models were reproduced by intratracheal instillation of LPS (3 mg/kg). Four hours after LPS instillation, rats were randomly divided into five groups: normal saline group, LPS group, methylprednisolone group, naloxone group (LPS+naloxone) and combined drug group (LPS+naloxone+methylprednisolone). The level of interleukin-8 (IL-8) in serum was measured by immunoassay. Meanwhile, the expression of NF-kappaB p65 in the lung tissue was determined with immunohistochemical staining.. Naloxone and methylprednisolone significantly reduced the LPS-induced increase in IL-8 concentrations in serum in vivo, and suppressed the activation of NF-kappaB p65 in the lung tissue.. NF-kappaB activation is involved in the LPS-induced ALI in rats. Combination of naloxone and methylprednisolone could suppress the increase of IL-8 content and NF-kappaB activation in the lung tissue of rat in vivo in our experiment.

Topics: Acute Lung Injury; Animals; Disease Models, Animal; Interleukin-8; Lipopolysaccharides; Lung; Male; Methylprednisolone; Naloxone; NF-kappa B; Random Allocation; Rats; Rats, Wistar

To investigate the effect of naloxone on myocardial cell apoptosis and apoptosis-related gene Bcl-2 in rats with acute myocardial ischemia/reperfusion (AMIR) injury, and explore the mechanism of protective effect of naloxone on myocardium.. Thirty SD rats were randomly divided into three groups (n=10): ischemia/reperfusion group, naloxone preconditioning group (naloxone was injected intraperitoneally 10 minutes before ischemia and 2 hours after reperfusion), and normal control group. The left anterior descending branch (LAD) of rat coronary artery was tied and un-tied in ischemia/reperfusion group and naloxone preconditioning group to establish the AMIR model in rats. The animals were then sacrificed and hearts were harvested. The expression of Bcl-2 protein was observed by immunohistochemical technique. Radioimmunoassay (RIA) was used to determine tumor necrosis factor-alpha (TNF-alpha) in serum.. In the normal control group, there was no Bcl-2 expression and TNF-alpha level was (0.39+/-0.06) mug/L. Higher expression of Bcl-2 and increased TNF-alpha levels were found in ischemia/reperfusion group. The expression of Bcl-2 protein increased significantly [(+++) vs. (+)], and TNF-alpha was significantly lower in naloxone preconditioning group than those in the normal control group [(0.55+/-0.12) microg/L vs. (0.86+/-0.11) microg/L, P<0.01].. Naloxone can protect myocardium from AMIR injury by inhibiting the apoptosis of cardiomyocytes induced by TNF-alpha and up-regulating protein expression of bcl-2 gene.

Topics: Animals; Apoptosis; Disease Models, Animal; Myocardial Reperfusion Injury; Myocardium; Naloxone; Proto-Oncogene Proteins c-bcl-2; Random Allocation; Rats; Rats, Sprague-Dawley; Tumor Necrosis Factor-alpha

The present study was aimed at evaluating chronic stress models in mice with special attention to morphine treatment. We hypothesized that repeated periods of drug withdrawal induce chronic stress. To verify this hypothesis, mice were made dependent on morphine and then subjected to several types of repeated withdrawal. Body weight reduction, thymus involution, adrenal gland enlargement and activation of the hypothalamo-pituitary-adrenal axis were used as signs of chronic stress. The changes were compared to those induced by 'laboratory' models of chronic stress (2 weeks of repeated restraint or rat exposure) and to a disease model of streptozotocin-induced diabetes mellitus (STZ-DM). Mice were made dependent using increasing doses of morphine three times a day for 3 days (10-20-40 mg/kg s.c.). Thereafter, withdrawal was induced either spontaneously (morphine 40 mg/kg injected at 24- or 72-hour time intervals for 2 weeks) or repeatedly precipitated by naloxone (10 mg/kg s.c.) injected daily 3 h after morphine. The results show that repeated periods of spontaneous drug withdrawal (24 or 72 h) in morphine-dependent mice represent a mild stress load. Repeated withdrawal precipitated by naloxone induced clear chronic stress-like changes. Changes observed in the naloxone-precipitated withdrawal model were even more pronounced than those found in laboratory models, namely repeated restraint or exposure to the rat. The most severe chronic stress state developed in mice during untreated STZ-DM. Thus, naloxone-precipitated withdrawal in mice seems to be an appropriate model of chronic stress.

Topics: Animals; Chronic Disease; Diabetes Mellitus, Experimental; Disease Models, Animal; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Restraint, Physical; Social Environment; Stress, Physiological; Substance Withdrawal Syndrome

Dyskinesias and seizures are both medically refractory disorders for which cannabinoid-based treatments have shown early promise as primary or adjunctive therapy. Using the Borna disease (BD) virus rat, an animal model of viral encephalopathy with spontaneous hyperkinetic movements and seizure susceptibility, we identified a key role for endocannabinoids in the maintenance of a balanced tone of activity in extrapyramidal and limbic circuits. BD rats showed significant elevations of the endocannabinoid anandamide in subthalamic nucleus, a relay nucleus compromised in hyperkinetic disorders. While direct and indirect cannabinoid agonists had limited motor effects in BD rats, abrupt reductions of endocannabinoid tone by the CB1 antagonist SR141716A (0.3 mg/kg, i.p.) caused seizures characterized by myoclonic jerks time-locked to periodic spike/sharp wave discharges on hippocampal electroencephalography. The general opiate antagonist naloxone (NLX) (1 mg/kg, s.c.), another pharmacologic treatment with potential efficacy in dyskinesias or L-DOPA motor complications, produced similar seizures. No changes in anandamide levels in hippocampus and amygdala were found in convulsing NLX-treated BD rats. In contrast, NLX significantly increased anandamide levels in the same areas of normal uninfected animals, possibly protecting against seizures. Pretreatment with the anandamide transport blocker AM404 (20 mg/kg, i.p.) prevented NLX-induced seizures. These findings are consistent with an anticonvulsant role for endocannabinoids, counteracting aberrant firing produced by convulsive agents, and with a functional or reciprocal relation between opioid and cannabinoid tone with respect to limbic convulsive phenomena.

Topics: Animals; Anticonvulsants; Arachidonic Acids; Basal Ganglia; Borna Disease; Cannabinoid Receptor Modulators; Convulsants; Disease Models, Animal; Endocannabinoids; Limbic System; Male; Movement Disorders; Naloxone; Narcotic Antagonists; Piperidines; Polyunsaturated Alkamides; Pyrazoles; Rats; Rats, Inbred Lew; Receptor, Cannabinoid, CB1; Rimonabant; Seizures

To determine the effects of low-intensity exercise on chronic muscle pain and potential activation of the endogenous opioid system.. Randomized placebo-controlled trial.. Animal laboratory.. Sixty-three male Sprague-Dawley rats.. Rats performed a low-intensity exercise protocol for 5 consecutive days after the induction of chronic muscle pain. In a separate experiment, naloxone or saline was administered systemically before 5 low-intensity exercise sessions.. Mechanical hyperalgesia was measured using von Frey filaments to determine the mechanical withdrawal threshold.. Low-intensity exercise increased mechanical withdrawal threshold in the chronic muscle pain model. Naloxone attenuated the antihyperalgesic effects of low-intensity exercise.. Low-intensity exercise reversed mechanical hyperalgesia in the chronic muscle pain model through activation of the endogenous opioid system.

Topics: Analysis of Variance; Animals; Area Under Curve; Disease Models, Animal; Male; Muscular Diseases; Naloxone; Pain; Pain Measurement; Physical Conditioning, Animal; Probability; Random Allocation; Rats; Rats, Sprague-Dawley; Sensitivity and Specificity

Although oral administration of L-Dopa remains the best therapy for Parkinson disease, its long-term administration causes the appearance of abnormal involuntary movements such as dyskinesia. Although persistent striatal induction of some genes has already been associated with such pathologic profiles in hemiparkinsonian rats, molecular and cellular mechanisms underlying such long-term adaptations remain to be elucidated. In this study, using a rat model of L-Dopa-induced dyskinesia, we report that activity regulated cytoskeletal (Arc)-associated protein is strongly upregulated in the lesioned striatum and that the extent of its induction further varies according to the occurrence or absence of locomotor sensitization. Moreover, Arc is preferentially induced, along with FosB, nur77, and homer-1a, in striatonigral neurons, which express mRNA encoding the precursor of dynorphin. Given the likely importance of Arc in the regulation of cytoskeleton during synaptic plasticity, its upregulation supports the hypothesis that a relationship exists between cytoskeletal modifications and the longlasting action of chronically administrated L-Dopa.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Adrenergic Agents; AIDS-Related Complex; Amphetamine; Analgesics, Non-Narcotic; Animals; Antiparkinson Agents; Behavior, Animal; Carrier Proteins; Central Nervous System Stimulants; Corpus Striatum; Disease Models, Animal; Drug Interactions; Dynorphins; Dyskinesia, Drug-Induced; Functional Laterality; Homer Scaffolding Proteins; Immunohistochemistry; In Situ Hybridization; Levodopa; Male; Motor Activity; Naloxone; Naltrexone; Narcotic Antagonists; Neurons; Oxidopamine; Protein Precursors; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Stereotyped Behavior; Substantia Nigra; Time Factors; Tyrosine 3-Monooxygenase; Up-Regulation

The authors developed an animal model of binge eating where history of caloric restriction with footshock stress (R + S) causes rats to consume twice the normal amount of palatable food. The authors tested the hypothesis that binge eating is mediated by changes in opioid control of feeding by comparing rats' anorectic and orexigenic responses to naloxone and butorphanol, respectively, and by testing the ability of butorphanol to elicit binge eating of chow when palatable food was absent. Mu/kappa opioid-receptor blockade and activation had exaggerated responses in the R + S rats with naloxone suppressing binge eating to control levels, and although butorphanol did not trigger chow binge eating, it enhanced binge eating of palatable food. These responses in sated normal-weight rats strengthen evidence that reward, over metabolic need, drives binge eating.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Behavior, Animal; Body Weight; Bulimia; Butorphanol; Caloric Restriction; Disease Models, Animal; Electroshock; Energy Intake; Feeding Behavior; Female; Food Preferences; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Time Factors

The effect of clonidine on ethanol-induced gastric mucosal damage, gastric emptying and gastric motility was compared. The clonidine-induced gastroprotective effect (0.03-0.09 micromol/kg, s.c.) was antagonised by yohimbine (5 micromol/kg, s.c.), prazosin (0.23 micromol/kg; alpha2B-adrenoceptor antagonist) and naloxone (1.3 micromol/kg, s.c.). Clonidine also inhibited the gastric emptying of liquid meal (0.75-3.75 micromol/kg, s.c.) and gastric motor activity (0.75 micromol/kg, i.v.) stimulated by 2-deoxy-D-glucose (300 mg/kg, i.v.). Inhibition of gastric emptying and motility was reversed by yohimbine (5 and 10 micromol/kg, s.c., respectively), but not by prazosin (0.23 micromol/kg, s.c.) or naloxone (1.3 micromol/kg, s.c.). Oxymetazoline-an alpha2A-adrenoceptor agonist-inhibited both gastric emptying (0.67-6.8 micromol/kg, s.c.) and motility (0.185-3.4 micromol/kg, i.v.), whereas it failed to affect gastric mucosal lesions. The results indicate that in contrast to the gastroprotective effect, which is mediated by alpha2B-adrenoceptor subtype, alpha2A-adrenoceptor subtype may be responsible for inhibition of gastric emptying and motility. However, the site of action (central, peripheral, both) remains to be established.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Clonidine; Disease Models, Animal; Dose-Response Relationship, Drug; Ethanol; Gastric Emptying; Gastric Mucosa; Gastrointestinal Motility; Male; Muscle Contraction; Muscle, Smooth; Naloxone; Narcotic Antagonists; Oxymetazoline; Prazosin; Rats; Rats, Wistar; Receptors, Adrenergic, alpha-2; Stomach Ulcer; Yohimbine

An elevated startle response has been observed in humans and animals during withdrawal from multiple substances of abuse, a phenomenon thought to reflect the anxiogenic effects of withdrawal. Although anxiety is a common symptom of opiate withdrawal, few studies have examined the effects of morphine withdrawal on acoustic startle.. To develop a procedure for assessing opiate dependence through measurement of the startle reflex in rats.. The effects of opiate withdrawal on startle were evaluated using both spontaneous and naloxone-precipitated withdrawal from an acute dose of morphine. The ability of the treatment drugs clonidine and chlordiazepoxide to block withdrawal-induced increases in startle was also tested.. Spontaneous withdrawal from an injection of morphine sulfate produced a significant increase in acoustic startle 2 h (3.2 mg/kg) or 4 h (10 mg/kg) after drug administration. Morphine withdrawal (10 mg/kg morphine sulfate) precipitated by the opiate antagonist naloxone (2.5 mg/kg) also produced a significant increase in startle magnitude. This elevation of startle was blocked by both clonidine (35 microg/kg) and chlordiazepoxide (10 mg/kg).. These data demonstrate that both spontaneous and precipitated withdrawal from an acutely administered opiate produce anxiety-like effects on acoustic startle. This paradigm may be useful in the study of anxiety and the early mechanisms of drug dependence.

Topics: Acoustic Stimulation; Acute Disease; Animals; Chlordiazepoxide; Clonidine; Disease Models, Animal; Injections, Intravenous; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Sprague-Dawley; Reflex, Startle; Substance Withdrawal Syndrome; Time Factors

Previously, our laboratory showed that either abrupt (AW) or precipitated withdrawal (PW) from morphine led to profound suppression of murine splenic antibody responses to sheep red blood cells at 24 h post-withdrawal. In the present studies, we examined the immune mechanisms mediating suppression at that time point. A co-culture method was used to examine whether cells from withdrawn mice had (1) a deficit in function and/or (2) contained populations of suppressor cells. To examine the first hypothesis, cells from normal mice were co-cultured with cells from withdrawn mice in a 1:3 ratio (normal/withdrawn). To test the second hypothesis, the ratio was reversed. The results were paradoxical. Co-culture of cells in a 1:3 ratio showed that spleen cells from withdrawn mice had a deficit in macrophage function. Spleen cells from withdrawn mice also showed decreased mRNA levels of IL-1beta, IL-1-Ra, and TNF-alpha and a suppression of co-stimulatory molecule expression. To examine the second hypothesis, cells were co-cultured in a 3:1 ratio (normal/withdrawn). In this paradigm, spleen cells from abrupt withdrawn mice were shown to contain populations of both suppressor macrophages and B-cells. In vivo experiments carried out on mice 24 h post-withdrawal showed increased sensitivity to the lethal effects of LPS and increased production of TNF-alpha, implying a state of macrophage activation. Thus evidence for both suppressed and activated macrophages has been obtained in mice 24 h after abrupt withdrawal from morphine.

Topics: Animals; CD11b Antigen; Coculture Techniques; Disease Models, Animal; Drug Implants; Drug Interactions; Enzyme-Linked Immunosorbent Assay; Female; Hemolytic Plaque Technique; Immune Tolerance; Immunosuppression Therapy; Interleukins; Lipopolysaccharides; Lymphocytes; Macrophages; Mice; Mice, Inbred C3H; Morphine; Naloxone; Narcotic Antagonists; Narcotics; RNA, Messenger; Spleen; Substance Withdrawal Syndrome; Tumor Necrosis Factor-alpha

1. Gastro-oesophageal acid reflux may cause airway responses such as cough, bronchoconstriction and inflammation in asthmatic patients. Our previous results suggest that microvascular leakage induced, in the guinea-pig airways, by intra-oesophageal hydrochloric acid (HCl) infusion was mainly dependent on the release of tachykinins. Nociceptin, an endogenous ligand of the opioid receptor NOP, has been shown to inhibit bronchoconstriction and cough in guinea-pig or cat by inhibiting tachykinin release. 2. The purpose of this study was to investigate the effects of nociceptin on the intra-oesophageal HCl-induced airway microvascular leakage evaluated by Evans blue dye extravasation measurement in anaesthetised guinea-pigs pretreated with propranolol, atropine and phosphoramidon. 3. Infusion of intra-oesophageal HCl led to a significant increase in plasma extravasation in the main bronchi and trachea. This increase was abolished when animals underwent a bilateral vagotomy. 4. Airway microvascular leakage was inhibited by nociceptin (3-30 microg x kg(-1) i.v.) in a dose-dependent manner (maximal inhibition at the dose of 30 microg x kg(-1): 19.76+/-1.13 vs 90.92+/-14.00 ng x mg(-1) tissue for nociceptin and HCl infusion, respectively, in the main bronchi, P<0.01). The NOP receptor agonist [Arg(14),Lys(15)]N/OFQ mimicked the inhibitory effect of nociceptin, but at a 10-fold lower dose (3 microg x kg(-1) i.v). The NOP receptor antagonist J-113397 had no effect on plasma protein extravasation by itself, but was able to block the inhibitory effect of nociceptin. 5. Morphine (1 mg x kg(-1)) had a similar inhibitory effect as that of nociceptin. Naloxone pretreatment abolished the effect of morphine, but was enable to block the inhibitory effect of nociceptin. 6. Under similar conditions, nociceptin, in the previous range of concentration, was unable to counteract the airway microvascular leakage induced by substance P (SP). 7. These results suggest that airway plasma extravasation induced by intra-oesophageal HCl instillation might be inhibited by specific stimulation of the NOP receptor with nociceptin. Nociceptin is likely to act at a pre-junctional level, by inhibiting tachykinin release, since it was unable to prevent SP-induced airway plasma extravasation.

Topics: Animals; Benzimidazoles; Bronchi; Capillary Permeability; Disease Models, Animal; Gastroesophageal Reflux; Guinea Pigs; Hydrochloric Acid; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Nociceptin; Opioid Peptides; Piperidines; Receptors, Opioid; Substance P; Trachea; Vagotomy; Vasodilator Agents

Recent studies suggest that peripheral morphine may represent a valuable treatment in acute inflammatory painful diseases through peripheral or central mechanisms. In the present study, anti-inflammatory effects of systemic morphine on carrageenan-induced hind paw oedema were examined in a model of peripheral acute oedema in mice. Carrageenan induced a time-dependent inflammation that was maximal 3 h after administration. While intraperitoneal administration of morphine sulfate at a low dose (1 mg/kg) increased carrageenan-induced hind paw oedema, intraperitoneal injection of morphine sulfate at a high dose (7 mg/kg) resulted in significant anti-inflammatory effects on carrageenan-induced hind paw oedema. These anti-inflammatory effects were blocked by pretreatment with naloxone. Measuring the serum levels of interleukin-1beta revealed that increases in serum levels of this cytokine were involved in morphine anti-inflammatory effects. Pretreatment with naloxone decreased interleukin-1beta serum levels near to those of control group. In conclusion, these data demonstrate that morphine produced pro- or anti-inflammatory effects in a dose-dependent manner through peripheral or central mechanisms. The observed anti-inflammatory effects may be due to an increase in the cytokine production and/or release by host immune systems.

Topics: Analgesics, Opioid; Animals; Anti-Inflammatory Agents; Carrageenan; Disease Models, Animal; Edema; Hindlimb; Inflammation; Interleukin-1; Male; Mice; Morphine; Naloxone; Narcotic Antagonists

Lactoferrin (LF) is a ubiquitous protein which exists in milk, plasma, synovial fluids, cerebrospinal fluid and other biological fluids. LF is also well known as a natural immunomodulator. Recently, we found that bovine milk-derived LF (BLF) produced micro-opioid receptor-mediated analgesia. In this study, we examined whether oral administration of BLF causes anti-nociceptive and anti-inflammatory effects, and also whether it modulates LPS-induced TNF-alpha and IL-10 production in rat model of rheumatoid arthritis (RA), rat adjuvant arthritis. BLF was administrated once daily, starting 3 hr before (preventive experiment) or 19 days after (therapeutic experiment) adjuvant injection. In both experiments, BLF suppressed the development of arthritis and the hyperalgesia in the adjuvant-injected paw. The single-administered BLF produced a dose-dependent analgesia, which was reversed by naloxone, in the adjuvant arthritis rats. Both repeated and single administration of BLF suppressed TNF-alpha production and increased IL-10 production in the LPS-stimulated adjuvant arthritis rats. These results suggest that orally administered BLF has both preventive and therapeutic effects on the development of adjuvant-induced inflammation and pain. Moreover, the immunomodulatory properties of BLF, such as down-regulation of TNF-alpha and up-regulation of IL-10, could be beneficial in the treatment of RA. Thus, we concluded that LF can be safely used as a natural drug for RA patients suffering from joint pain.

Topics: Administration, Oral; Analysis of Variance; Animals; Arthritis, Experimental; Disease Models, Animal; Inflammation; Interleukin-10; Lactoferrin; Male; Naloxone; Pain; Rats; Rats, Wistar; Tumor Necrosis Factor-alpha

Peripheral electrical stimulation (PES) has been utilized to manage chronic pain associated with nerve injury. However, the data on clinical effectiveness are conflicting and the neurophysiological mechanism is not well known. This study was designed to assess whether PES relieved neuropathic pain and its possible mechanisms. The neuropathic pain model was made with lumbar 5th (L5) and 6th (L6) spinal nerve ligations in rats. Nociceptive responses of the rats were assessed by the cold plate test (the number and duration of paw lifts that occurred in 5 min on a 5 +/- 1 degrees C cold plate). PES with a frequency of 2 Hz and at increasing strengths was given for 30 min via stainless-steel needles inserted into standard acupoints on the leg and back, respectively. Immunochemistry was used to examine the immunoreactivity of the NMDA receptor 1 (NR1) subunit in the spinal cord dorsal horn. The results are as follows: (1) PES relieved neuropathic pain and the effect was blocked by 1.0 mg/kg naloxone. (2) The effect of one session of PES lasted up to 12 h. (3) Repetitive PES showed a cumulative effect and no tolerance was observed. (4) There was a significant increase of NR1 immunoreactivity in the superficial laminae of the spinal cord of neuropathic pain rats as compared with naive rats. This increase could be reversed by repetitive 2 Hz PES. These results suggest that PES can relieve neuropathic pain, and that mu-opioid receptors and NMDA receptors are involved in the effect of PES.

Topics: Animals; Disease Models, Animal; Electric Stimulation Therapy; Ligation; Male; Naloxone; Narcotic Antagonists; Neuralgia; Pain Measurement; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu

Mice lacking the mu-opioid receptor gene have been used to characterize the role of mu-opioid receptors in nociception and the analgesic actions of opioid agonists. In this study, the authors determined the role of mu-opioid receptors in neuropathic pain behaviors and the effectiveness of mu- and kappa-opioid receptor agonists on this behavior in mice.. The authors studied the behavioral responses of mu-opioid receptor knockout and wild-type mice to thermal and mechanical stimuli before and after neuropathic pain induced by unilateral ligation and section of the L5 spinal nerve. Response to mechanical stimuli was evaluated by determining the frequency of hind paw withdrawal to repetitive stimulation using a series of von Frey monofilaments. Thermal hyperalgesia was assessed by determining the paw withdrawal latencies to radiant heat and frequency of hind paw withdrawal to cooling stimuli. The effects of systemic morphine, the kappa-opioid agonist U50488H, and naloxone on responses to mechanical and thermal stimuli were also studied in spinal nerve-injured mice.. After spinal nerve injury, wild-type mice developed increased responsiveness to mechanical, heat, and cooling stimuli ipsilateral to nerve injury. mu-Opioid receptor knockout mice not only had more prominent mechanical allodynia in the nerve-injured paw, but also expressed contralateral allodynia to mechanical stimuli. Hyperalgesia to thermal stimuli was similar between mu-opioid knockout and wild-type animals. Morphine decreased mechanical allodynia dose dependently (3-30 mg/kg subcutaneous) in wild-type mice--an effect that was attenuated in the heterozygous mice and absent in the homozygous mu-opioid knockout mice. The kappa-opioid agonist U50488H (3-10 mg/kg subcutaneous) attenuated mechanical allodynia in wild-type, heterozygous, and homozygous mu-opioid mice. Naloxone in wild-type mice resulted in enhanced ipsilateral and contralateral allodynia to mechanical stimuli that resembled the pain behavior observed in mu-opioid receptor knockout mice.. The authors' observations indicate that (1) unilateral nerve injury induces a bilateral tonic activation of endogenous mu-opioid receptor-mediated inhibition that attenuates mechanical allodynia but not thermal hyperalgesia, (2) both mu- and kappa-opioid agonists attenuate neuropathic pain in mice, and (3) the antihyperalgesic actions of morphine are mediated primarily via mu-opioid receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Disease Models, Animal; Mice; Morphine; Naloxone; Pain; Reaction Time; Receptors, Opioid, mu; Spinal Nerves

Recent imaging reports demonstrate the activation of the orbitofrontal cortical (OFC) area during acute and chronic pain. The aim of this study was to compare the effects of chronic perfusion of this area with morphine on nociception in control rats and in rats subjected to mononeuropathy. Chronic perfusion of morphine, using miniosmotic pumps, produced significant and naloxone-reversible depression of tactile and cold allodynias and thermal hyperalgesia, observed in neuropathic rats, while it produced significant elevation and naloxone insensitive increase of acute nociceptive thresholds in control rats. The observed results support the idea that this area is a component of a flexible cerebral network involved in pain processing and perception.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Drug Administration Routes; Drug Administration Schedule; Frontal Lobe; Hyperalgesia; Mononeuropathies; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Reaction Time; Time Factors

Nociceptin/orphanin FQ (noci/OFQ), the endogenous ligand for the orphan ORL1 (opioid receptor-like1), has been shown to be anti- or pronociceptive and modify morphine analgesia in rats after central administration. We comparatively examined the effect of noci/OFQ on hyperalgesia and morphine analgesia in two experimental models of neuropathic pain: diabetic (D) and mononeuropathic (MN) rats. Noci/OFQ, when intrathecally (i.t.) injected (0.1, 0.3, or 1, to 10 microg/rat) was ineffective in normal rats, but reduced and suppressed mechanical hyperalgesia (paw-pressure test) in D and MN rats, respectively. This spinal inhibitory effect was suppressed by naloxone (10 microg/rat, i.t.) in both models. Combinations of systemic morphine with spinal noci/OFQ resulted in a strong potentiation of analgesia in D rats. In MN rats, an isobolographic analysis showed that the morphine+noci/OFQ association (i.t.) suppressed mechanical hyperalgesia in a superadditive manner. In summary, the present findings reveal that spinal noci/OFQ produces a differential antinociception in diabetic and traumatic neuropathic pain according to the etiology of neuropathy, an effect possibly mediated by opioid receptors. Moreover, noci/OFQ combined with morphine produces antinociceptive synergy in experimental neuropathy, opening new opportunities in the treatment of neuropathic pain.

Topics: Animals; Behavior, Animal; Body Weight; Diabetes Mellitus, Experimental; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Hyperalgesia; Male; Mononeuropathies; Morphine; Naloxone; Narcotic Antagonists; Nociceptin; Nociceptin Receptor; Opioid Peptides; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Sciatic Nerve; Streptozocin; Time Factors; Vocalization, Animal

Previous studies suggest that cholecystokinin (CCK) is implicated in the modulation of pain sensitivity and the development of neuropathic pain. We used CCK(2) receptor deficient (CCK(2) (-/-)) mice and assessed their mechanical sensitivity using Von Frey filaments, as well as the development and time course of mechanical hyperalgesia in a model of neuropathic pain. We found that CCK(2) (-/-) mice displayed mechanical hyposensitivity, which was reversed to the level of wild-type animals after administration of naloxone (0.1-10 mg/kg). On the other hand, injection of L-365260 (0.01-1 mg/kg), an antagonist of CCK(2) receptors, decreased dose-dependently, mechanical sensitivity in wild-type mice. The mechanism of reduced mechanical sensitivity in CCK(2) (-/-) mice may be explained by changes in interactions between CCK and opioid systems. Indeed, CCK(2) (-/-) mice natively expressed higher levels of lumbar CCK(1), opioid delta and kappa receptors. Next, we found that CCK(2) (-/-) mice did not develop mechanical hyperalgesia in the Bennett's neuropathic pain model. Induction of neuropathy resulted in decrease of lumbar pro-opiomelanocortin (POMC) gene expression in wild-type mice, but increase of POMC expression in CCK(2) (-/-) mice. In addition, induction of neuropathy resulted in further increase of opioid delta receptor in CCK(2) (-/-) mice. Gene expression results indicate up-regulation of opioid system in CCK(2) (-/-) mice, which apparently result in decreased neuropathy score. Our study suggests that not only pain sensitivity, but also mechanical sensitivity and the development of neuropathic pain are regulated by antagonistic interactions between CCK and opioid systems.

Topics: Animals; Benzodiazepinones; Disease Models, Animal; Dose-Response Relationship, Drug; Dynorphins; Enkephalins; Gene Expression; Hyperalgesia; Inflammation; Ligation; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Naloxone; Narcotic Antagonists; Pain Measurement; Pain Threshold; Phenylurea Compounds; Pro-Opiomelanocortin; Protein Precursors; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Receptors, Opioid; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sciatic Neuropathy; Time Factors

Experiments were performed on rats with opium abuse induced by chronic administration of morphine in increasing doses. We studied the effect of HLDF-6 peptide on symptoms of naloxone abstinence. Repeated administration of HLDF-6 peptide in a dose of 0.2 mg/kg 24 and 0.5 h before naloxone relieved the major symptoms of the abstinence syndrome. A possible neurochemical mechanism underlying the effect of HLDF-6 peptide is inhibition of enkephalinase A in structures of the endogenous antinociceptive system.

Topics: Animals; Behavior, Animal; Brain; Brain Chemistry; Disease Models, Animal; Male; Morphine Dependence; Naloxone; Neoplasm Proteins; Neprilysin; Protease Inhibitors; Rats; Rats, Wistar; Substance Withdrawal Syndrome

Menopause-associated thermoregulatory dysfunction, including hot flushes and night sweats, is effectively treated by hormonal therapies that include estrogens. Evidence suggests that estrogen regulates serotonin 2A (5-HT(2A)) receptor expression and that 5-HT(2A) receptors are involved in thermoregulation. Therefore, the role of 5-HT(2A) receptors in thermoregulation was assessed in two rat models of ovariectomy-induced thermoregulatory dysfunction. The first model is based on measurement of the tail-skin temperature (TST) increase following naloxone-induced withdrawal in morphine-dependent ovariectomized (OVX) rats (MD model), while the second model relies on telemetric assessment of diurnal TST changes in ovariectomized rats (telemetry model). Treatment with a 5-HT(2A/2C) receptor agonist, (-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI), prevented the naloxone-induced TST increase in the MD model and restored normal active-phase TST in the telemetry model. The selective 5-HT(2A) receptor antagonist, MDL-100907, had no effect on the naloxone-induced flush when administered alone in the MD model, but it decreased DOI's ability to abate the flush. In the telemetry model, MDL-100907 attenuated the DOI-induced decrease in active-phase TST. Interestingly, MDL-100907 increased TST in both models when given alone, with the TST increase occurring prior to the naloxone-induced flush in the MD model. To evaluate the role of central nervous system (CNS) 5-HT(2A) receptors in TST regulation, DOI was administered in combination with a known peripheral 5-HT(2A/2C) receptor antagonist, xylamidine, in the MD model. Xylamidine had no effect on DOI's ability to abate the naloxone-induced flush. These results indicate that activation of central 5-HT(2A) receptors restores temperature regulation in two rodent models of ovariectomy-induced thermoregulatory dysfunction.

Topics: Amidines; Amphetamines; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Endocrine System Diseases; Estradiol; Estrogens; Female; Fluorobenzenes; Naloxone; Ovariectomy; Piperidines; Rats; Reaction Time; Receptor, Serotonin, 5-HT2A; Serotonin Antagonists; Serotonin Receptor Agonists; Skin Temperature; Substance Withdrawal Syndrome; Telemetry; Time Factors

Several neurotransmitter mechanisms have been proposed as playing a role in the development of morphine tolerance. We provide evidence for the first time that endothelin antagonists can restore morphine analgesia in morphine-tolerant rats and prevent the development of tolerance to morphine. Studies were carried out in rats and mice treated with implanted placebo or implanted morphine pellet. The maximal tail-flick latency in morphine pellet + vehicle-treated rats (7.54 seconds) was significantly lower when compared with placebo pellet + vehicle-treated rats (10 seconds), indicating that tolerance developed to the analgesic effect of morphine. BQ123 potentiated tail-flick latency by 30.0% in placebo-tolerant rats and 94.5% in morphine-tolerant rats compared with respective controls. BMS182874 potentiated tail-flick latency by 30.2% in placebo-tolerant rats and 66.7% in morphine-tolerant rats. The enhanced analgesic effect of morphine after treatment with endothelin antagonists could be blocked by naloxone, indicating an opiate-mediated effect; but naloxone binding to brain membranes was not affected by BQ123. Guanosine triphosphate binding was stimulated by morphine and endothelin-1 in non-tolerant mice and not in morphine-tolerant mice; however, guanosine triphosphate binding was stimulated by BQ123 in morphine-tolerant mice and was unaffected in non-tolerant mice. These results suggest that uncoupling of G-protein occurs in morphine tolerance and endothelin antagonist restores the coupling of G-protein to its receptors. A combination use of endothelin antagonist and opiates could provide a novel approach in improving analgesia and eliminating tolerance.

Topics: Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Dansyl Compounds; Disease Models, Animal; Drug Therapy, Combination; Drug Tolerance; Endothelin A Receptor Antagonists; Guanosine 5'-O-(3-Thiotriphosphate); Injections, Intraventricular; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptors, Opioid, mu; Sulfur Radioisotopes; Time Factors

Previously, we have reported that in rat models of chronic pain, in particular, the very-high-efficacy 5-HT(1A) agonist F 13640 induces unprecedented pain relief by novel neuroadaptative mechanisms that involve inverse tolerance and cooperation with nociceptive stimulation in producing analgesia. The present studies detailed the actions of F 13640 and other compounds in the formalin model of tonic nociceptive pain. Intraperitoneal injection of F 13640 (0.01-2.5 mg/kg; t -15 min) caused a dose-dependent and complete inhibition of the paw elevation and paw licking that occurred both early (0-5 min) and late (22.5-27.5 min) after the intraplantar injection of diluted formaldehyde (2.5%) in the rat. The extent to which F 13640 and other 5-HT(1A) receptor ligands inhibited these pain behaviors correlated (p < 0.05) with the extent to which they activated 5-HT(1A) receptors. Under similar conditions, some inhibitory effects were also observed with various agents that are known to produce analgesia by different peripheral and/or central mechanisms (e.g., opioids, NA/5-HT reuptake inhibitors, COX-2 inhibitors and other nonsteroidal anti-inflammatory drugs, gabapentin, and ABT-594). However, with the possible exception of morphine, the effects of all of these agents at nontoxic doses were lower than those of F 13640, in particular in inhibition of early paw elevation. The 5-HT(1A) antagonist WAY 100635, but not naloxone, antagonized the actions of F 13640. These results help to establish large-magnitude 5-HT(1A) receptor activation as a new molecular mechanism of profound, central analgesia and suggest that F 13640 may be particularly effective against pain arising from severe tonic nociceptive stimulation.

Topics: Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Hindlimb; Male; Morphine; Naloxone; Narcotic Antagonists; Pain Measurement; Pain Threshold; Piperazines; Piperidines; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Serotonin Antagonists; Serotonin Receptor Agonists

We examined the pharmacologic characteristics of herpes simplex virus (HSV) vector-mediated expression of proenkephalin in the dorsal root ganglion in a rodent model of neuropathic pain. We found that: (i). vector-mediated enkephalin produced an antiallodynic effect that was reversed by naloxone; (ii). vector-mediated enkephalin production in animals with spinal nerve ligation prevented the induction of c-fos expression in second order sensory neurons in the dorsal horn of spinal cord; (iii). the effect of vector-mediated enkephalin enhanced the effect of morphine, reducing the ED(50) of morphine 10-fold; (iv). animals did not develop tolerance to the continued production of vector-mediated enkephalin over a period of several weeks; and, (v). vector transduction continued to provide an analgesic effect despite the induction of tolerance to morphine. This is the first demonstration of gene transfer to provide an analgesic effect in neuropathic pain. The pharmacologic analysis demonstrates that transgene-mediated expression and local release of opioid peptides produce some effects that are distinct from peptide analogues delivered pharmacologically.

Topics: Animals; Area Under Curve; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Enkephalins; Ganglia, Spinal; Genetic Vectors; Immunohistochemistry; Ligation; Male; Morphine; Naloxone; Narcotic Antagonists; Oncogene Proteins v-fos; Pain; Pain Measurement; Pain Threshold; Protein Precursors; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Simplexvirus; Spinal Cord Diseases; Time Factors; Transgenes

The effect of a hot water extract of black tea (Camellia sinensis (L.) O. Kuntze, Theaceae) on upper gastrointestinal transit and on diarrhoea was investigated employing conventional rodent models of diarrhoea. Black tea extract was found to possess antidiarrhoeal activity in all the models of diarrhoea used. Naloxone (0.5 mg/kg i.p.) significantly inhibited the antidiarrhoeal activity of the extract as well as loperamide, thus indicating a role of the opioid system in the antidiarrhoeal activity of the extract.

Topics: Animals; Antidiarrheals; Castor Oil; Diarrhea; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Gastrointestinal Motility; Loperamide; Male; Mice; Mice, Inbred BALB C; Naloxone; Phytotherapy; Plant Extracts; Rats; Rats, Sprague-Dawley; Tea

The physiologic role of the mu opioid receptor (MOR) in gut nociception, motility, and secretion is well established. To evaluate whether MOR may also be involved in controlling gut inflammation, we first showed that subcutaneous administration of selective peripheral MOR agonists, named DALDA and DAMGO, significantly reduces inflammation in two experimental models of colitis induced by administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) or peripheral expansion of CD4(+) T cells in mice. This therapeutic effect was almost completely abolished by concomitant administration of the opioid antagonist naloxone. Evidence of a genetic role for MOR in the control of gut inflammation was provided by showing that MOR-deficient mice were highly susceptible to colon inflammation, with a 50% mortality rate occurring 3 days after TNBS administration. The mechanistic basis of these observations suggests that the anti-inflammatory effects of MOR in the colon are mediated through the regulation of cytokine production and T cell proliferation, two important immunologic events required for the development of colon inflammation in mice and patients with inflammatory bowel disease (IBD). These data provide evidence that MOR plays a role in the control of gut inflammation and suggest that MOR agonists might be new therapeutic molecules in IBD.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; CD4-Positive T-Lymphocytes; Colitis; Colon; Cytokines; Disease Models, Animal; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, SCID; Naloxone; Narcotic Antagonists; Oligopeptides; Peroxidase; Receptors, Opioid, mu; Trinitrobenzenesulfonic Acid

Descending action from the locus coeruleus (LC) on the trigeminal sensorimotor function was evaluated in a rat model of oral-facial inflammation. For the induction of oral-facial inflammation, mustard oil (20% solution in 20microl mineral oil) was injected into the region of the temporomandibular joint (TMJ). One week before testing, rats received bilateral lesions of the LC using a cathodal current. The electromyogram (EMG) threshold, which is the threshold intensity for the onset of EMG activity of the masseter muscle evoked by pressure on the TMJ region, was used in the present study as an indicator of the trigeminal sensorimotor function. Following mustard oil injection, in the LC-lesioned rats, EMG thresholds significantly decreased at 30min, which lasted up to 240min. In contrast, EMG thresholds in the LC-intact rats returned to the level before injection after 180min. Systemic naloxone (1.3mg/kg, i.v.) produced a further decrease of EMG thresholds in both the LC-intact and LC-lesioned rats. Under the existence of naloxone, EMG thresholds in the LC-lesioned rats were significantly lower than those of the LC-intact rats. These results suggest that oral-facial inflammation activates the coeruleotrigeminal modulating system and that an action of this system is independent of the opioid depressive mechanism.

Topics: Animals; Disease Models, Animal; Electromyography; Inflammation; Injections, Intra-Articular; Locus Coeruleus; Male; Mustard Plant; Naloxone; Narcotic Antagonists; Pain Threshold; Physical Stimulation; Plant Extracts; Plant Oils; Rats; Rats, Sprague-Dawley; Temporomandibular Joint; Time Factors; Trigeminal Nuclei

Topics: alpha-Methyltyrosine; Analgesics; Animals; Antidepressive Agents; Cyclohexanols; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Fenclonine; Male; Mononeuropathies; Motor Activity; Naloxone; Narcotic Antagonists; Pain; Pain Threshold; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Venlafaxine Hydrochloride; Vocalization, Animal

The effects of the selective delta-1 (delta(1)) opioid receptor agonist, DPDPE, and the selective delta(2) opioid receptor agonist, DSLET, have been studied on the ventricular fibrillation threshold (VFT) in rats with an experimental post-infarction cardiosclerosis (CS). It has been found that CS induced a significant decrease in VFT. This CS-induced decrease in VFT was significantly reversed by intravenous administration of DPDPE (0.1 mg/kg) 10 min before VFT measurement. On the contrary, intravenous injection of DSLET (0.5 mg/kg) exacerbated the CS-induced cardiac electrical instability. Pretreatment with the selective delta opioid receptor antagonist, ICI 174,864 (0.5 mg/kg), completely abolished the changes in VFT produced by both DPDPE and DSLET. Previous administration of a nonselective peripherally acting opioid receptor antagonist, naloxone methiodide (5 mg/kg) also completely reversed the antifibrillatory action of DPDPE. Naloxone methiodide and ICI 174,864 alone had no effect on VFT. Pretreatment with the nonselective K(ATP) channel blocker, glibenclamide (0.3 mg/kg), or with the mitochondrial selective K(ATP) channel blocker, 5-hydroxydecanoic acid (5-HD, 5 mg/kg), completely abolished the DPDPE-induced increase in cardiac electrical stability. Glibenclamide and 5-HD alone had no effect on VFT. These results demonstrate that the delta opioid receptor plays an important role in the regulation of electrical stability in rats with post-infarction cardiosclerosis. We propose that peripheral delta(1) opioid receptor stimulation reverses CS-induced electrical instability via mitochondrial K(ATP) channels. On the contrary, delta(2) opioid receptor stimulation may exacerbate the CS-induced decrease in VFT. Further studies are necessary to determine the delta opioid receptor subtype which mediates the antifibrillatory effect of DPDPE and pro-fibrillatory effect of DSLET.

Topics: Adenosine Triphosphate; Analgesics, Opioid; Animals; Decanoic Acids; Disease Models, Animal; Drug Antagonism; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Glyburide; Hydroxy Acids; Male; Mitochondria, Heart; Myocardial Infarction; Myocardium; Naloxone; Potassium Channels; Quaternary Ammonium Compounds; Rats; Rats, Wistar; Receptors, Opioid, delta; Sclerosis; Ventricular Fibrillation

Tramadol (TRM) and metamizol (MTZ) are drugs with complex mechanisms of action, extensively used in combination in pain management. In the present investigation we have evaluated the interaction between MTZ:TRM in the ethacrinic acid writhing test in rats. Dose-response curves (s.c.) were obtained for each drug individually, combined in fixed potency ratios (1:0.3, 1:1, 1:3), and for MTZ in presence of a fixed-dose of TRM (3.5 mg/kg). Interactions were analysed using isobolograms, interaction indexes (INT-I) and ANOVA. We used naloxone (1 mg/kg s.c.) to determine the opioid-component of the effects (ED80). Isobolograms demonstrated antagonism at the ED20, for 1:0.3 and 1:3 mixtures (p<0.01), whereas 1:1 was additive. At the ED50 and ED80 all combinations showed synergy. Fixed-dose experiments demonstrated that treatment (p<0.0001), dose (p<0.0001), and their interaction (p<0.0001) were statistically significant. Naloxone partially antagonized TRM (67%), but not MTZ; the percentage reversal of the combinations was directly related to the dose of TRM in the combination. The results show that the MTZ:TRM interaction on antinociception is synergistic or antagonistic depending on the level of effect. Synergy is demonstrated at 50% or higher levels, thus supporting the results obtained in humans by our group. Below the ED50 antagonism or additivity is present depending on the ratio of the combination. The mechanisms of the interaction remain unknown.

Topics: Abdominal Pain; Acute Disease; Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Dipyrone; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Antagonism; Drug Interactions; Drug Synergism; Ethacrynic Acid; Male; Naloxone; Narcotic Antagonists; Pain Measurement; Rats; Rats, Sprague-Dawley; Tramadol; Visceral Afferents

Many drug-abusers engage in poly-drug abuse, but there has been relatively little quantification of withdrawal from poly-drug use. Planarians are an advantageous model for these studies due to mammalian-relevant neurotransmitter systems (e.g. dopamine, opioid, and 5-HT). We recently developed a metric that quantified an acute cocaine withdrawal phenomenon in planarians. However, despite much indirect evidence, we lacked direct evidence of a receptor- or carrier-mediated effect. We now report dose-related, naloxone- and nor-binaltorphine-sensitive acute abstinence-induced withdrawal and naloxone-precipitated withdrawal from the kappa-opioid agonist U-50,488H (trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]cyclohexyl)-benzeneacetamide). The less active enantiomer [1R,2R]U-50,488 produced significantly less withdrawal and U-50,488H withdrawal was not due to pH or osmolarity. These data provide pharmacologic evidence of a kappa-opioid receptor-mediated withdrawal phenomenon and neuroadaptation to a pharmacologic stimulus (adaptations in transduction mechanisms) in this model.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Adaptation, Physiological; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Hydrogen-Ion Concentration; Naloxone; Naltrexone; Narcotic Antagonists; Narcotics; Opioid-Related Disorders; Osmolar Concentration; Planarians; Reaction Time; Receptors, Opioid, kappa; Substance Withdrawal Syndrome

The effects of opiate dependence and antagonist-precipitated withdrawal on glucocorticoid (GR) and mineralocorticoid (MR) receptor mRNA levels in the rat brain were studied. Rats were allocated to one of four groups that differed in terms of type of drug pretreatment (morphine pellet versus placebo pellet) and type of injection on test (naloxone versus no injection). Injection of naloxone precipitated a somatic withdrawal syndrome among morphine pretreated rats. In situ hybridization histochemistry revealed a potent down-regulation of hippocampal GR mRNA 4 h after injection of naloxone. Levels of GR mRNA in the amygdala and hypothalamus were unchanged. Hippocampal MR mRNA levels from these same animals were unchanged. By contrast, neither chronic morphine exposure nor injection of naloxone in morphine naive animals affected GR or MR mRNA levels. These results show that during opiate dependence the levels of hippocampal GR mRNA are more sensitive to episodes of withdrawal than to chronic drug exposure and are consistent with an increased vulnerability to stress during opiate dependence.

Topics: Animals; Brain; Disease Models, Animal; Down-Regulation; Drug Administration Schedule; Glucocorticoids; Hippocampus; Male; Mineralocorticoids; Morphine; Naloxone; Narcotic Antagonists; Neurons; Opioid-Related Disorders; Rats; Rats, Sprague-Dawley; Receptors, Glucocorticoid; Receptors, Mineralocorticoid; RNA, Messenger; Stress, Physiological; Substance Withdrawal Syndrome

The antinociceptive effects of H2-agents cimetidine (CIM) and dimaprit (DMP) as well as their effects on the Tyr-MIF-1-evoked analgesia have been studied after intraperitoneal (i.p.) administration in rats. In the paw-pressure (PP) test Tyr-MIF-1 (1 mg/kg), CIM (50 and 100mg/kg) and DMP (5 and 10mg/kg) induced analgesia. Injected before DMP, naloxone (NAL) and CIM diminished or completely prevented the pain-relieving effect of H2-agonist DMP. The antinociceptive effect of Tyr-MIF-1 has been potentiated by DMP dose-dependently. CIM (50mg/kg) decreased the antinociceptive action of the combination Tyr-MIF-1 + DMP, while CIM (100mg/kg) expressed a weaker inhibitory effect on it. The data obtained clearly show that H2-receptor activation is involved in the mechanism of the Tyr-MIF-1 antinociceptive action.

Topics: Analgesics; Animals; Cimetidine; Dimaprit; Disease Models, Animal; Injections, Intraperitoneal; MSH Release-Inhibiting Hormone; Naloxone; Nociceptors; Pain Measurement; Pressure; Rats; Receptors, Histamine H2; Reflex

The motor signs of Parkinson's disease have been partly attributed to an overinhibition of the external globus pallidus (GP) that results from hyperactivity of striatopallidal GABA/enkephalinergic neurons. The goals of this study were to measure basal levels of extracellular fluid GABA in the GP of normal cats, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian cats and cats spontaneously recovered from MPTP-induced parkinsonism, and to examine the effects of opioid receptor activation on potassium (K+)-evoked GABA release in the GP in these animals. Basal GP GABA levels were increased 75% from normal in parkinsonian animals 1 week after MPTP administration and returned to control levels in recovered animals 6 weeks after MPTP administration. No significant differences were observed in K+-evoked GABA release across conditions. The opioid receptor agonist [D-Ala2]-Met-Enkephalinamide (DALA) significantly attenuated K+-evoked GABA release in the GP of MPTP-treated symptomatic and recovered cats, but had no significant effect on GABA release in normal animals. These data show that basal GP GABA levels are elevated coincident with expression of parkinsonian signs and return to normal in animals that have functionally compensated for a nigrostriatal lesion. DALA-induced inhibition of pallidal GABA release after a dopamine-depleting lesion, suggests that enkephalin may attenuate GABA release in the GP specifically after striatal dopamine loss.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Behavior, Animal; Cats; Disease Models, Animal; Enkephalin, Methionine; Extracellular Space; gamma-Aminobutyric Acid; Globus Pallidus; Male; Microdialysis; Naloxone; Narcotic Antagonists; Parkinsonian Disorders; Potassium; Recovery of Function

Itch is a major symptom of skin disease and is poorly understood, in part due to the lack of adequate small animal models. We show, using iontophoresis of histamine and capsaicin, that it is possible to induce scratching behaviour in both guinea pig and mouse. Use of iontophoresis may obviate the problems of induction of pain as well as itch when injection is used. The behavioural response to capsaicin, however, differs from that seen with histamine, raising the possibility that the use of scratch counts as a method of measuring itch severity needs to be set in the context of other responses. Naloxone partly inhibits scratching in mouse and guinea pig due to histamine. We also show that contact sensitization with 2-4 dinitrochlorobenzene (DNCB) can be used as a simple assay for chronic itch allowing study of scratching over at least a 15-h period. The characteristics of scratching (but not the time course) induced with DNCB are similar to those seen with histamine.

Topics: Acute Disease; Animals; Capsaicin; Chronic Disease; Dinitrochlorobenzene; Disease Models, Animal; Female; Guinea Pigs; Haptens; Histamine; Iontophoresis; Male; Mice; Mice, Inbred BALB C; Naloxone; Pruritus

Opiate withdrawal during pregnancy may occur because of voluntary or forced detoxification, or from rapid cycling associated with exposure to short-acting "street" opiates. Thus, animal modeling of prenatal withdrawal and development of potential therapeutic interventions is important. Direct developmental effects of opiates and/or withdrawal can be studied using a chick model. In ovo administration of the long-acting opiate N-desmethyl-l-alpha-noracetylmethadol (NLAAM) induces opiate dependence in the chick embryo. We examined activation of the hypothalamic-pituitary-adrenal (HPA) axis (assessed via serum corticosterone) and hemodynamic changes (assessed as changes in apparent diameter of vitelline (extraembryonic) blood vessels) after chronic NLAAM exposure and naloxone (Nx)-precipitated withdrawal during late stages of embryogenesis. Nx-precipitated withdrawal increased corticosterone 2- to 4.5-fold and diameters of vitelline blood vessels by 15 to 45%. NLAAM exposure itself did not effect these measures. In a second set of experiments, isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, was injected into eggs with embryos. IBMX similarly increased corticosterone and vitelline vessel diameter, with a similar time course and response magnitude. Previous studies found that serotonin(2) (5-HT(2)) receptors were involved in other withdrawal manifestations, so we determined whether they were likewise involved. Pretreatment with the 5-HT(2) antagonist ritanserin completely blocked HPA axis activation and vasodilation associated with both Nx-precipitated withdrawal and IBMX administration. This indicates that 5-HT(2) receptors, directly or indirectly, mediate these withdrawal manifestations in the chick embryo.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Chick Embryo; Corticosterone; Disease Models, Animal; Hypothalamo-Hypophyseal System; Methadyl Acetate; Morphogenesis; Naloxone; Narcotics; Pituitary-Adrenal System; Receptors, Serotonin; Ritanserin; Substance Withdrawal Syndrome

Arterially perfused, decerebrate preparations of the insectivore, Suncus murinus were made to determine whether the emetic reflex could be activated in such a preparation using a range of stimuli shown to be emetic in conscious or anaesthetised Suncus. Efferent phrenic and vagus nerve activities and electromyograms (EMGs) from the temporalis, abdominal oesophagus and trapezius muscles were recorded, as well as longitudinal shortening of the oesophagus and dorso-ventral movements of the thorax. The preparations swallowed spontaneously every 0.6 to 6.5 min. The duration of a swallow was 3.1 +/- 0.3 s (recorded as the time taken for the oesophagus to shorten and recover to its resting position) and the oesophagus shortened by 3.5 +/- 0.4 mm during a swallow. The emetic reflex was activated by electrical stimulation (30 Hz, 10-20 V, 0.2 ms pulse width, for 30 s) of abdominal vagal afferents (latency < 30 s) or by arterial perfusion with either 40 nM of the capsaicin analogue resiniferatoxin (latency 1.7 +/- 0.6 min), 6 microM nicotine (latency 1.6 +/- 0.1 min) or 1 microM of the phosphodiesterase IV inhibitor CP-80,633 (latency 8.9 +/- 3.9 min). These emetic stimuli produced somatic and visceral movements in Suncus preparations indicative of activation of the emetic reflex. There were pronounced contractions of the thorax that occurred simultaneously with oesophageal shortening and mouth opening, separated by thorax expansion and a burst of phrenic nerve activity. During emetic-like episodes, oesophageal shortenings were only 0.84 +/- 0.1 s in duration, faster than the duration of shortening observed during swallowing (cf. swallowing, 3.1 +/- 0.3 s; P < 0.0001). The shortening of the oesophagus during emetic-like episodes was 6.2 +/- 0.4 mm, which was greater than the shortening seen during swallowing (cf. swallowing, 3.5 +/- 0.4 mm; P < 0.0001). We conclude that the emetic reflex can be activated in our Suncus preparations and that this non-sentient small adult animal model can now be used to study the neurophysiology and pharmacology of swallowing and emesis.

Topics: Animals; Aorta, Thoracic; Decerebrate State; Deglutition; Disease Models, Animal; Diterpenes; Electric Stimulation; Esophagus; Female; Heart Rate; Male; Naloxone; Narcotic Antagonists; Nicotine; Nicotinic Agonists; Perfusion; Phrenic Nerve; Physical Stimulation; Pyrimidinones; Reflex; Respiratory Mechanics; Shrews; Vagus Nerve; Video Recording; Vomiting

Self-mutilation or self-injurious behaviour is a well known behavioural disorder in humans. The proposition that this behaviour in animals is a response to chronic pain of peripheral nerve injury has been met with controversy. In the present study a pharmacological model, which produces no sensory or motor loss was used to study how autotomy is related to pain. In a group of rats autotomy was induced by amphetamine in phenoxybenzamine and reserpine treated animals. The pain tests, both phasic and tonic were then performed. The results of this study showed that a total analgesia was produced in both phasic and tonic pain tests, in animals that exhibited autotomy. Injection of naloxone in these animals prevented autotomy. A correlation between autotomy and no pain is suggested in this pharmacological model of autotomy.

Topics: Adrenergic alpha-Antagonists; Adrenergic Uptake Inhibitors; Amphetamine; Analgesia; Animals; Behavior, Animal; Central Nervous System Stimulants; Chronic Disease; Denervation; Disease Models, Animal; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Phenoxybenzamine; Rats; Rats, Wistar; Reserpine; Self Mutilation

This study investigated the combined effect of neonatal maternal separation and acute psychological stress on pain responses in adult rats. Long-Evans dams and their male pups were reared under two conditions: 1) 180 min daily maternal separation (MS180) on postnatal days 2-14 or 2) no handling or separation (NH). At 2 mo of age, visceromotor responses to graded intensities of phasic colorectal distension (10-80 mmHg) at baseline as well as following acute 60 min water avoidance stress (WA) were significantly higher in MS180 rats. Both groups showed similar stress-induced visceral hyperalgesia in the presence of naloxone (20 mg/kg ip). MS180 rats had smaller stress-induced cutaneous analgesia in the tail-flick test compared with NH rats, with a residual naloxone-resistant component. MS180 rats showed an enhanced fecal pellet output following WA or exposure to a novel environment. These data suggest that early life events predispose adult Long-Evans rats to develop visceral hyperalgesia, reduced somatic analgesia, and increased colonic motility in response to an acute psychological stressor, mimicking the cardinal features of irritable bowel syndrome.

Topics: Animals; Animals, Newborn; Behavior, Animal; Colonic Diseases, Functional; Defecation; Disease Models, Animal; Eating; Female; Gastrointestinal Motility; Hyperalgesia; Male; Maternal Deprivation; Naloxone; Narcotic Antagonists; Nociceptors; Pain Threshold; Pregnancy; Rats; Rats, Long-Evans; Stress, Psychological; Weight Gain

Animal models simulating acute human pulpitis are still lacking. The rat incisors present a particular situation where most of their innervation is considered to be unmyelinated and concentrated mainly in the tooth pulp. This study reports on a new model for dental pain induced by inflammatory agents applied to the tooth pulps of incisors. In different groups of rats, artificial crowns were fixed on the lower incisors, after cutting 1-2mm of their distal extremities. A volume of 7-10 microl of solutions of saline, capsaicin (1-10mg/ml) or formalin (2.5% or 5%) was injected in the crown cavity, and the nociceptive behaviour was quantitated following a devised scoring method of four scales. Intradental application of capsaicin produced nociceptive scores in the form of one plateau for 1-2h depending on the concentration used. Similar results were obtained with intradental application of formalin 2.5%. The one plateau of nociceptive scores obtained with formalin contrasts with the biphasic aspect of nociceptive behaviour described with the intradermal formalin test. This discrepancy could be attributed to a difference in the types of afferent fibres involved in each situation. Pretreatment with morphine (2 mg/kg) attenuated, in a naloxone-reversible manner, the nociceptive behaviour observed following intradental application of capsaicin. Pretreatment with meloxicam (a cyclo-oxygenase-2 inhibitor) exerted a less pronounced attenuation of the nociceptive scores when compared with morphine. These results provide evidence for the validity of the described model for the simulation of tooth pulp inflammatory pain in awake animals.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Capsaicin; Crowns; Cyclooxygenase Inhibitors; Dental Pulp Cavity; Disease Models, Animal; Drug Interactions; Female; Formaldehyde; Gingiva; Inflammation; Male; Meloxicam; Morphine; Naloxone; Narcotic Antagonists; Nerve Fibers; Nociceptors; Pain Measurement; Rats; Rats, Sprague-Dawley; Thiazines; Thiazoles; Toothache

Previous research has revealed an antinociceptive (analgesic) effect of interleukin-2 (IL-2) in central and peripheral nervous systems. Unfortunately IL-2 is very short-lived in vivo, so it is impractical to apply IL-2 for analgesia in clinic. This study was performed to evaluate the effect of intrathecal delivery of human IL-2 gene on rat chronic neuropathic pain induced by chronic constriction injury of the sciatic nerve. Human IL-2 cDNA was cloned into pcDNA3 containing a cytomegalovirus promoter. The paw-withdrawal latency induced by radiant heat was used to measure the pain threshold. The results showed that recombinant human IL-2 had a dose-dependent antinociceptive effect, but that this only lasted for 10-25 min. The pcDNA3-IL-2 or pcDNA3-IL-2/lipofectamine complex in contrast also showed dose-dependent antinociceptive effects, but these reached a peak at day 2-3 and were maintained for up to 6 days. Liposome-mediated pcDNA3-IL-2 produced a more powerful antinociceptive effect than pcDNA3-IL-2 alone. The paw-withdrawal latencies were not affected by control treatments such as vehicle, lipofectamine, pcDNA3, or pcDNA3-lipofectamine. In the experimental groups, human IL-2 mRNA was detected by reverse transcription-polymerase chain reaction in the lumbar spinal pia mater, dorsal root ganglion, sciatic nerve, and spinal dorsal horn, but not in gastrocnemius muscle. The expressed IL-2 profile detected by western blot coincided with its mRNA profile except it was present in the spinal dorsal horn at a higher level. Furthermore, human IL-2 assayed by enzyme-linked immunosorbent assay in cerebrospinal fluid could still be detected at day 6, but lower than day 3. The antinociceptive effect of pcDNA3-IL-2 could be blocked by naloxone, showing some relationship of the antinociceptive effect produced by IL-2 gene to the opioid receptors. It is hoped that the new delivery approach of a single intrathecal injection of the IL-2 gene described here may be of some practical use as a part of a gene therapy for treating neuropathic pain.

Topics: Animals; Cation Exchange Resins; Chronic Disease; COS Cells; Disease Models, Animal; DNA, Complementary; Dose-Response Relationship, Drug; Genetic Therapy; Humans; Injections, Spinal; Interleukin-2; Ligation; Lipids; Liposomes; Male; Naloxone; Narcotic Antagonists; Organ Specificity; Pain; Pain Management; Pain Measurement; Rats; Rats, Sprague-Dawley; Recombinant Proteins; RNA, Messenger; Sciatic Neuropathy; Signal Transduction; Tissue Distribution; Transfection

The neural mechanisms involved in post-ictal analgesia remain to be elucidated. Pentylenetetrazol (PTZ) is used experimentally to induce seizure in animal subjects. This non-competitive antagonist blocks GABA-mediated Cl(-) flux. The aim of this work is to study the neurochemical basis of the antinociception induced by convulsions elicited by peripheral administration of PTZ (64 mg/kg). The analgesia was measured by the tail-flick test, in eight rats per group. Convulsions were followed by significant increase in the tail-flick latencies (TFL), at least for 30 min of the post-ictal period. Peripheral administration of naloxone (5 mg/kg and 10 mg/kg), atropine (1 mg/kg and 5 mg/kg), methysergide (1 mg/kg and 5 mg/kg) and ketanserine (1 mg/kg and 2 mg/kg) caused a significant decrease in the TFL in seizing animals, as compared to controls. However, while naloxone antagonized analgesia 15 and 25 min post convulsions, the other drugs caused a blockade of the post-ictal analgesia in a relatively greater period of time. These results indicate that endogenous opioids, serotonin and acetylcholine may be involved in post-ictal analgesia.

Topics: Analgesia; Animals; Atropine; Convulsants; Disease Models, Animal; Injections, Intraperitoneal; Ketanserin; Methysergide; Motor Activity; Muscarinic Antagonists; Naloxone; Narcotic Antagonists; Pain Measurement; Pentylenetetrazole; Rats; Rats, Wistar; Reaction Time; Reflex; Seizures; Serotonin Antagonists

Controversies surround the possible long-term physiological and psychological consequences of opioid use. Analgesic tolerance and addiction are commonly at the center of these controversies, but other concerns exist as well. A growing body of evidence suggests that hyperalgesia caused by the chronic administration of opioids can occur in laboratory animals and in humans. In these studies we describe a murine model of opioid-induced hyperalgesia (OIH). After the treatment of mice for 6 days with implanted morphine pellets followed by their removal, both thermal hyperalgesia and mechanical allodynia were documented. Additional experiments demonstrated that prior morphine treatment also increased formalin-induced licking behavior. These effects were intensified by intermittent abstinence accomplished through administration of naloxone during morphine treatment. Experiments designed to determine if the mu-opioid receptor mediated OLH in our model revealed that the relatively-selective mu-opioid receptor agonist fentanyl induced the thermal hyperalgesia and mechanical allodynia characteristic of OIH when administered in intermittent boluses over 6 days. In complimentary experiments we found that CXBK mice which have reduced mu-opioid receptor binding displayed no significant OIH after morphine treatment. Finally, we explored the pharmacological sensitivities of OIH. We found that the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801, the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and the heme oxygenase (HO) inhibitor tin protoporphyrin (Sn-P) dose-dependently reduced OIH in this model while the NSAID indomethacin had no effect. Thus we have characterized a murine model of OIH which will be useful in the pursuit of the molecular mechanisms underlying this phenomenon.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Fentanyl; Heme Oxygenase (Decyclizing); Hyperalgesia; Injections, Subcutaneous; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphine; Naloxone; Narcotic Antagonists; Nitric Oxide Synthase; Pain Measurement; Receptors, N-Methyl-D-Aspartate; Receptors, Opioid, mu

Opiate withdrawal behaviors in the infant differ from those of the adult. The neural circuitry underlying opioid withdrawal in the adult rat is well defined and includes the locus coeruleus (LC) and periaqueductal gray (PAG), with a minor role of the amygdala. Because the different behaviors that constitute the infant syndrome may be mediated by different neural circuits, we tested the hypothesis that these three sites are involved in opiate withdrawal. Pups were injected with morphine from day 1-6 after birth (b.i.d.) and on the morning of the seventh day. Withdrawal was then elicited by local injection of the opioid antagonist methylnaloxonium into the LC, PAG, or amygdala. Withdrawal signs were precipitated in a dose-dependent manner following injection into the LC or PAG, but not the amygdala. The withdrawal behaviors elicited from the LC and PAG included both the same and different behaviors. The results support the hypothesis that the neural circuitry mediating opiate withdrawal behaviors is similar in infant and adult animals, but the behaviors expressed are age-specific.

Topics: Age Factors; Amygdala; Animals; Animals, Newborn; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Locus Coeruleus; Male; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Neural Pathways; Opioid-Related Disorders; Periaqueductal Gray; Quaternary Ammonium Compounds; Rats; Rats, Long-Evans; Substance Withdrawal Syndrome

Endogenous opioids are involved in ischemic preconditioning (IP) in several species. Whether or not opioids are important for IP and short-term myocardial hibernation (STMH) in pigs is currently unknown. In 34 enflurane-anesthetized pigs, the left anterior descending coronary artery was flow constantly perfused. Subendocardial blood flow (Endo), infarct size (IS; percent area at risk), and the free energy change of ATP hydrolysis (DeltaG) were determined. After 90-min severe ischemia and 120-min reperfusion, IS averaged 28.3 +/- 5.4% (means +/- SE) (n = 8; Endo: 0.047 +/- 0.009 ml. min(-1) x g(-1)). IP by 10-min ischemia and 15-min reperfusion reduced IS to 9.9 +/- 3.8% (P < 0.05, n = 8; Endo: 0.044 +/- 0.009 ml. min(-1) x g(-1)). After naloxone (1 mg/kg iv followed by 2 microg x kg(-1) x min(-1)), IS averaged 25.8 +/- 7.0% (n = 6; Endo: 0.039 +/- 0.008 ml x min(-1) x g(-1)) without and 24.7 +/- 4.7% (n = 6; Endo: 0.044 +/- 0.006 ml x min(-1) x g(-1)) with IP. At 5-min moderate ischemia in the presence of naloxone, Endo decreased from 0.90 +/- 0.07 to 0.28 +/- 0.03 ml x min(-1) x g(-1)and DeltaG decreased from -58.6 +/- 1.0 to -52.6 +/- 0.4 kJ/mol. Prolongation of ischemia to 90 min did not alter Endo, but DeltaG recovered toward control values (57.7 +/- 1.1 kJ/mol), and the myocardium remained viable. These responses are identical to those of nonnaloxone-treated pigs. Endogenous opioids are involved in IP but not in STMH in pigs.

Topics: Adenosine Triphosphate; Animals; Coronary Circulation; Disease Models, Animal; Energy Metabolism; Female; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Myocardial Stunning; Myocardium; Naloxone; Narcotic Antagonists; Opioid Peptides; Swine, Miniature; Time Factors

To investigate the effects of naloxone and morphine during acute hypoxia.. Prospective, randomized animal study.. University laboratory.. Twenty-eight adult male Sprague Dawley rats, weighing 300-350 g.. The rats were implanted with a femoral catheter and subcutaneous electrodes for electrocardiogram recording and were randomly assigned to receive morphine (5 mg/kg), naloxone (5 mg and 10 mg/kg), or normal saline (control) (n = 7 in each). Fifteen minutes after intraperitoneal injection of the drug, each rat was exposed to hypoxic gas (5% oxygen, 95% N2) for 70 mins. Hypoxic survival time was measured. Mean arterial pressure (MAP), arterial pH, Paco2, Pao2, and base excess were measured before injection (baseline), 14 mins after injection (H0), and 6 mins (H1), 33 mins (H2), and 48 mins (H3) after exposure to hypoxia.. Hypoxic survival was similar between the naloxone 5 mg/kg and control groups (p = .183), significantly lower in the naloxone 10 mg/kg group (p < .01), and significantly higher in the morphine 5 mg/kg group (p < .05) compared with controls. MAP significantly decreased in all groups. However, at H2-H3, MAP was better preserved in both naloxone groups and was lower in the morphine group compared with controls. Paco2 was maintained higher at H0-H3 in the morphine group and lower at H2-H3 in both naloxone groups compared with controls.. During acute hypoxia, naloxone preserves arterial blood pressure and attenuates hypoxic ventilatory depression by antagonizing endogenous opiates, but it does not improve hypoxic survival. In contrast, morphine, which enhances the action of endogenous opiates, does improve hypoxic survival. The acute hypoxic tolerance of morphine may be partly attributable to a depression of oxygen consumption, increased cerebral blood flow secondary to high Paco2, and protective actions mediated by delta-opioid receptors.

Topics: Acute Disease; Animals; Blood Gas Analysis; Blood Pressure; Carbon Dioxide; Cerebrovascular Circulation; Disease Models, Animal; Drug Evaluation, Preclinical; Hypoxia; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Opioid Peptides; Oxygen; Oxygen Consumption; Prospective Studies; Random Allocation; Rats; Rats, Sprague-Dawley; Survival Analysis; Time Factors

It has been reported that opioid antinociceptive effects are enhanced in animal models of inflammation, but it remains unclear whether this sensitization to morphine is related to predominant central or peripheral increased effects.. The authors compared the behavioral effects of intraplantar and intravenous morphine and naloxone in a rat model of repeated acute carrageenan-induced inflammation in which enhanced responses to noxious stimuli result from sensitization in peripheral tissues or central sensitization. The antinociceptive effects of intraplantar morphine (50, 75, 100, 150, and 200 microg), intravenous morphine (0.3, 0.6, and 1 mg/kg), and the pronociceptive effects of intraplantar naloxone methiodide (150 microg) and intravenous naloxone (1 mg/kg) against noxious pressure (vocalization thresholds to paw pressure) in rats were assessed 3 h after one or two carrageenan plantar injections performed 7 days apart.. After the first carrageenan injection, intraplantar and intravenous morphine produced significant increase of vocalization thresholds to paw pressure in inflamed but not in noninflamed paws. After the second carrageenan injection, the antinociceptive effects of intraplantar morphine were significantly reduced compared with those obtained after the first carrageenan injection, whereas effects of intravenous morphine were significantly enhanced and present in both hind paws. Intravenous naloxone demonstrated similar pronociceptive patterns after the first and second carrageenan injection. Intraplantar naloxone methiodide produced pronociceptive effects in inflamed hind paw that were significantly enhanced after the second carrageenan injection.. When inflammation is enhanced by recurrent stimulations, the antinociceptive effects of systemic morphine are enhanced. This increase is more likely related to central than peripheral sites of action, beyond endogenous opioid system activation.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Inflammation; Male; Morphine; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Recurrence; Vocalization, Animal

The glutamatergic system is deeply involved in the development of opiate dependence and in the manifestation of opiate abstinence syndrome. In this study the effect of the increase in the endogenous glutamate (GLU) release due to 4-aminopyridine (4-AP), a potassium channel blocker, during the development of morphine (M) physical dependence and during the naloxone (NL)-precipitated abstinence syndrome was investigated. For the development of physical dependence M was intraperitoneally (i.p.) injected for 9 days 105 min following i.p. saline administration to a group of rats. In the first 3 days the dose of M was 10 mg x kg(-1). In the second 3 days the initial dose was doubled (20 mg x kg(-1)) and in the last 3 days the dose of M was raised to 40 mg x kg(-1). On day 10, the rats were divided into three groups at random and these three groups were i.p. given saline 105 min before 80 mg x kg(-1)M, 2 mg x kg(-1) 4-AP 105 min after 80 mg x kg(-1) M, and 80 mg x kg(-1) M 105 min before 2 mg x kg(-1) 4-AP, respectively. In a second group of rats, the rats were i.p. given 2 mg x kg(-1) 4-AP 105 min prior to M administration, which was increased every 3 days (10 mg x kg(-1), 20 mg x kg(-1), 40 mg x kg(-1)). On day 10, the rats were divided into two groups whose first injection was saline and 2 mg x kg(-1) 4-AP, respectively. The second injections of both groups after an interval of 105 min following the first one contained 80 mg x kg(-1) M. In contrast, one group of rats received only i.p. saline at every other injection time (the control group). Furthermore, another group of rats was i.p. administered 2 mg x kg(-1) 4-AP once a day, as the first injection. At the second injection time they were i.p. given saline. After a period of 15 min following the last administration on day 10, the rats belonging to all groups were i.p. injected with 2 mg x kg(-1) NL and immediately placed in a metal cage. Body weight loss (g), teeth chattering, rearing, wet-dog shaking, grooming, and jumping were determined or counted for 15 min. Penile erection, defecation, and diarrhoea were separately scored with one point for every individual occurrence, and the total score was named 'total number of others'. The administration of 4-AP before M appeared to intensify the development of dependence, and was most probably due to the Ca2+-induced inactivation of NMDA receptors as a result of excess release of GLU when the 4-AP took effect. The inactivation of NMDA receptors should have acted a

Topics: 4-Aminopyridine; Animals; Behavior, Animal; Calcium; Disease Models, Animal; Glutamic Acid; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

We determined the sites of the antinociceptive action of morphine in the experimental model of cyclophosphamide induced cystitis and investigated the afferent nerve fibers involved in nociception transmission originating from the bladder.. Cyclophosphamide (200 mg./kg.) given intraperitoneally was used to induce cystitis in male rats and their behavior was observed and scored. The effect of 2 mg./kg. systemic morphine given intravenously on cyclophosphamide induced behavioral modifications was tested when administered alone and after 100 microg. naloxone per rat given intrathecally at the L1 to L2 or L6 to S1 level. The spinal antinociceptive effect of morphine was also tested when administered intrathecally alone at 10, 100 and 200 microg. per rat at L1 to L2, alone at 100 microg. per rat at L1 to L2 or L6 to S1, alone at 100 microg. per rat at L1 to L2 and L6 to S1 simultaneously, alone at 200 microg. per rat at L1 to L2 and after 100 microg. naloxone per rat given intrathecally at L6 to S1 at 100 microg. per rat at L1 to L2.. Cyclophosphamide induced marked modifications in the behavior of the rats, including a decreased breathing rate, eye closing and specific postures. Morphine given intravenously reversed these behavioral disorders and this reversal was completely prevented by pretreatment with intrathecal naloxone. A dose of 100 microg. per rat given intrathecally also reversed these behavioral disorders by about 25% at the L1 to L2 and L6 to S1 levels. In addition, a dose of 100 microg. morphine per rat administered intrathecally and simultaneously at L1 to L2 and L6 to S1 produced an effect equal to the sum of those observed when administered separately, that is about 50%, whereas morphine at an intrathecal dose of 200 microg. at L1 to L2 produced the same effect as 100 microg. given intrathecally at the same level or at L6 to S1 (25%). Also, 100 microg. naloxone per rat administered intrathecally at L6 to S1 prevented the effect of 100 microg. morphine at L1 to L2.. These results confirm the previously reported antinociceptive effect of systemic morphine in this model of cyclophosphamide cystitis, suggest that this antinociceptive action is completely located at the spinal site and most importantly demonstrate by the pharmacological approach and behavioral analysis that nociceptive sensations originating from the bladder are conveyed by hypogastric and pelvic nerves in this cyclophosphamide cystitis model in the conscious rat.

Topics: Animals; Consciousness; Cyclophosphamide; Cystitis; Disease Models, Animal; Drug Interactions; Hypogastric Plexus; Injections, Intravenous; Injections, Spinal; Male; Morphine; Naloxone; Nerve Fibers; Nociceptors; Pain; Pain Measurement; Peripheral Nerves; Probability; Rats; Rats, Sprague-Dawley; Sensitivity and Specificity; Urinary Bladder

The present study was designed to explore the relationship between the cannabinoid and opioid receptors in animal models of opioid-induced reinforcement. The acute administration of SR141716A, a selective central cannabinoid CB1 receptor antagonist, blocked heroin self-administration in rats, as well as morphine-induced place preference and morphine self-administration in mice. Morphine-dependent animals injected with SR141716A exhibited a partial opiate-like withdrawal syndrome that had limited consequences on operant responses for food and induced place aversion. These effects were associated with morphine-induced changes in the expression of CB1 receptor mRNA in specific nuclei of the reward circuit, including dorsal caudate putamen, nucleus accumbens, and septum. Additionally, the opioid antagonist naloxone precipitated a mild cannabinoid-like withdrawal syndrome in cannabinoid-dependent rats and blocked cannabinoid self-administration in mice. Neither SR141716A nor naloxone produced any intrinsic effect on these behavioral models. The present results show the existence of a cross-interaction between opioid and cannabinoid systems in behavioral responses related to addiction and open new strategies for the treatment of opiate dependence.

Topics: Animals; Avoidance Learning; Cannabinoids; Caudate Nucleus; Conditioning, Operant; Disease Models, Animal; Heroin; Heroin Dependence; Male; Mice; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Nucleus Accumbens; Piperidines; Putamen; Pyrazoles; Rats; Rats, Wistar; Receptors, Cannabinoid; Receptors, Drug; Receptors, Opioid; Rimonabant; RNA, Messenger; Self Administration; Septum of Brain

The effect of some B vitamins in chemical and thermal models of nociception in mice was investigated. The association thiamine/pyridoxine/cyanocobalamin (TPC, 20-200 mg/kg, i.p. or per os), thiamine, pyridoxine (50-200 mg/kg, i.p.) or riboflavin (3-100 mg/kg, i.p) induced an antinociceptive effect, not changed by naloxone (10 mg/kg, i.p.), in the acetic acid writhing model. Treatment for 7 days with thiamine/pyridoxine/cyanocobalamin (100 or 200 mg/kg, i.p.), thiamine (50 or 100 mg/kg) or pyridoxine (50 or 100 mg/kg) or acute treatment with riboflavin (6 or 12 mg/kg, i.p) inhibited the nociceptive response induced by formaldehyde. The B vitamins did not inhibit the nociceptive response in the hot-plate model. Both 7-day thiamine/pyridoxine/cyanocobalamin (100 mg/kg, i.p.) or acute riboflavin (25 or 50 mg/kg, i.p.) treatment partially reduced formaldehyde-induced hindpaw oedema. The B vitamins antinociceptive effect may involve inhibition of the synthesis and/or action of inflammatory mediators since it was not observed in the hot-plate model, was not reversed by naloxone, only the second phase of the formaldehyde-induced nociceptive response was inhibited, and formaldehyde-induced hindpaw oedema was reduced.

Topics: Acetic Acid; Animals; Constriction; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Formaldehyde; Hindlimb; Injections, Intraperitoneal; Injections, Subcutaneous; Male; Mice; Motor Activity; Naloxone; Nociceptors; Pain; Pain Measurement; Pyridoxine; Riboflavin; Thiamine; Vitamin B 12; Vitamin B Complex

Cholestasis is associated with elevated plasma level of endogenous opioid peptides. Naloxone-precipitated withdrawal syndrome has been described in a mouse model of acute cholestasis. Thus we aimed at determining whether central noradrenergic hyperactivity is involved in manifestation of naloxone-precipitated withdrawal syndrome in mice with obstructive cholestasis. Acute cholestasis was induced by bile duct resection in mice and physical dependence was observed by precipitating a withdrawal syndrome with naloxone (2 mg/kg, intraperitoneally) 5 days after induction of cholestasis. Administration of clonidine (0.1 mg/kg, intraperitoneally), an alpha2-adrenoceptor agonist, 15 min. before naloxone injection significantly alleviates withdrawal severity in cholestatic mice. However, pretreatment of animals with yohimbine (3 mg/kg, intraperitoneally), an alpha2-adrenoceptor antagonist, 15 min. before clonidine blocked this ameliorative effect of clonidine. The results of this study support the evidence for involvement of the alpha2-adrenoceptors in the withdrawal syndrome of cholestasis in a mouse model.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Cholestasis; Clonidine; Disease Models, Animal; Male; Mice; Naloxone; Narcotic Antagonists; Opioid Peptides; Substance Withdrawal Syndrome; Yohimbine

In this study, the activity of the delta-opioid receptor subtype-selective agonist, SB 227122, was investigated in a guinea pig model of citric acid-induced cough. Parenteral administration of selective agonists of the delta-opioid receptor (SB 227122), mu-opioid receptor (codeine and hydrocodone), and kappa-opioid receptor (BRL 52974) produced dose-related inhibition of citric acid-induced cough with ED(50) values of 7.3, 5.2, 5.1, and 5.3 mg/kg, respectively. The nonselective opioid receptor antagonist, naloxone (3 mg/kg, i.m.), attenuated the antitussive effects of codeine or SB 227122, indicating that the antitussive activity of both compounds is opioid receptor-mediated. The delta-receptor antagonist, SB 244525 (10 mg/kg, i.p.), inhibited the antitussive effect of SB 227122 (20 mg/kg, i.p.). In contrast, combined pretreatment with beta-funaltrexamine (mu-receptor antagonist; 20 mg/kg, s.c.) and norbinaltorphimine (kappa-receptor antagonist; 20 mg/kg, s.c.), at doses that inhibited the antitussive activity of mu- and kappa-receptor agonists, respectively, was without effect on the antitussive response of SB 227122 (20 mg/kg, i.p.). The sigma-receptor antagonist rimcazole (3 mg/kg, i.p.) inhibited the antitussive effect of dextromethorphan (30 mg/kg, i.p.), a sigma-receptor agonist, but not that of SB 227122. These studies provide compelling evidence that the antitussive effects of SB 227122 in this guinea pig cough model are mediated by agonist activity at the delta-opioid receptor.

Topics: Animals; Carbazoles; Cell Line; CHO Cells; Cloning, Organism; Codeine; Cough; Cricetinae; Dextromethorphan; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Guinea Pigs; Humans; Hydrocodone; Levallorphan; Male; Naloxone; Narcotic Antagonists; Protein Binding; Pyridines; Pyrroles; Pyrrolidines; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

Amikacin sulphate (30 mg kg(-1)) administered either intraperitoneally (i.p.) or subcutaneously (s.c.) produced antinociceptive effect in BALB/c mice in the acetic acid writhing test which is employed as an inflammatory pain model. The lack of difference between two routes with regard to antinociceptive potency was taken as evidence for the absence of a local effect. Amikacin sulphate-induced antinociception seems unlikely to be due to non-specific behaviour alteration, since this drug, at a dose range of 15-100 mg kg(-1)did not affect motor coordination of mice in rot-a-rod test. Morphine (1 mg kg(-1)) also caused antinociception when administered i.p. or s.c. but the effect was greater with the latter route. At the i.p. site; the concurrent use of amikacin and morphine produced more remarkable antinociception compared to their individual usages. Besides, naloxone (2 mg kg(-1)) significantly decreased antinociceptive effect of amikacin but itself also exerted antinociception. At present, we have no plausible explanation for these findings at the i.p. site.

Topics: Acetates; Amikacin; Analgesics; Animals; Disease Models, Animal; Drug Interactions; Injections, Intraperitoneal; Injections, Subcutaneous; Mice; Mice, Inbred BALB C; Morphine; Naloxone; Pain; Pain Threshold

The effects of fmol doses of nociceptin/orphanin FQ on scopolamine-induced impairment of learning and/or memory were examined using spontaneous alternation of Y-maze and step-down type passive avoidance tasks. While fmol doses of nociceptin alone had no effect on spontaneous alternation or passive avoidance behavior in normal mice, administration of nociceptin (10 and/or 100 fmol/mouse) 30 min before spontaneous alternation performance or the training session of the passive avoidance task, significantly improved the scopolamine-induced impairment of spontaneous alternation and passive avoidance behavior. This ameliorating effect was not antagonized by nocistatin (0.5 and 5.0 nmol/mouse, i.c.v.), naloxone benzoylhydrazone (2.3, 11.2, and 56.1 micromol/kg, s.c.) or nor-binaltorphimine (4.9 nmol/mouse, i.c.v.). These results indicated that very low doses of nociceptin ameliorate impairments of spontaneous alternation and passive avoidance induced by scopolamine, and suggested that this peptide has bidirectional modulatory effects on learning and memory; impairment at high doses and amelioration at low doses.

Topics: Analgesics, Opioid; Animals; Avoidance Learning; Disease Models, Animal; Dizocilpine Maleate; Learning Disabilities; Male; Maze Learning; Memory Disorders; Mice; Naloxone; Naltrexone; Narcotic Antagonists; Neuroprotective Agents; Nociceptin; Opioid Peptides; Psychomotor Performance; Rats; Scopolamine

To develop a model of visceral pain in rats using a behavioral approach. Cyclophosphamide (CP), an antitumoral agent known to produce toxic effects on the bladder wall through its main toxic metabolite acrolein, was used to induce cystitis.. CP was administered at doses of 50, 100 and 200 mg./kg. i.p. to male rats, and their behavior observed and scored. The effects of morphine (0.5 to 4 mg./kg. i.v.) on CP-induced behavioral modifications were tested administered alone and after naloxone (1 mg./kg. s.c.). In addition, 90 minutes after CP injection, that is, at the time of administration of morphine, the bladder was removed in some rats for histological examination. Finally, to show that the bladder is essential for the CP-induced behavioral modifications, female rats also received CP at doses of 200 mg./kg. i.p. and of 20 mg. by the intravesical route, and acrolein at doses of 0.5 mg. by the intravesical route and of 5 mg./kg. i.v.. CP dose-relatedly induced marked behavioral modifications in male rats: breathing rate decrease, closing of the eyes and occurrence of specific postures. Morphine dose-dependently reversed these behavioral disorders. A dose of 0.5 mg./kg. produced a reduction of almost 50% of the behavioral score induced by CP 200 mg./kg. This effect was completely prevented by pretreatment with naloxone. At the time of administration of morphine, histological modifications of the bladder wall, such as chorionic and muscle layer edema, were observed. In female rats, CP 200 mg./kg. i.p. produced the same marked behavioral modifications as those observed in male rats. Administered at the dose of 20 mg. intravesically, CP did not produce any behavioral effects, whereas acrolein at 0.5 mg. intravesically induced behavioral modifications identical to those under CP 200 mg./kg. i.p., with the same maximal levels. Conversely, acrolein 5 mg./kg. i.v. did not produce any behavioral effects at all.. Overall, these results indicate that this experimental model of CP-induced cystitis may be an interesting new behavioral model of inflammatory visceral pain, allowing a better understanding of these painful syndromes and thus a better therapeutic approach to them.

Topics: Acrolein; Animals; Antineoplastic Agents, Alkylating; Behavior, Animal; Consciousness; Cyclophosphamide; Cystitis; Disease Models, Animal; Female; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Pelvic Pain; Rats; Rats, Sprague-Dawley; Urinary Bladder

Electroacupuncture has been proposed to be a low cost and practical method that allows effective pain management with minimal collateral effects. In this study we have examined the effect of electroacupuncture against the hyperalgesia developed in a model of post-incisional pain in rats. A 1-cm longitudinal incision was made through the skin and fascia of the plantar region of the animal hind paw. Mechanical hyperalgesia in the incision was evaluated 135 min after the surgery with von Frey filaments. The tension threshold was reduced from 75 g (upper limit of the test) to 1.36 +/- 0.36 g (mean +/- SEM) in control rats. It is shown that a 15-min period of electroacupuncture applied 120 min after surgery to the Zusanli (ST36) and Sanyinjiao (SP6) points, but not to non-acupoints, produces a significant and long-lasting reduction of the mechanical hyperalgesia induced by the surgical incision of the plantar surface of the ipsilateral hind paw. The tension threshold was reduced from 75 to 27.6 +/- 4.2 g in animals soon after the end of electroacupuncture. The mechanical threshold in this group was about 64% less than in control. Electroacupuncture was ineffective in rats treated 10 min earlier with naloxone (1 mg/kg, ip), thus confirming the involvement of opioid mechanisms in the antinociceptive effects of such procedure. The results indicate that post-incisional pain is a useful model for studying the anti-hyperalgesic properties of electroacupuncture in laboratory animals.

Topics: Animals; Case-Control Studies; Disease Models, Animal; Electroacupuncture; Hyperalgesia; Male; Naloxone; Narcotic Antagonists; Pain, Postoperative; Rats; Rats, Wistar; Time Factors

It has been well documented that there is opioid resistance in neuropathic pain. This indicates that the endogenous opioid system may not be involved effectively in modulating neuropathic pain. The present study sought to determine if activation of the descending pain inhibition system might produce analgesia in the animal neuropathic model we developed. Under ketamine anesthesia, male Sprague-Dawley rats were chronically implanted with stimulating electrodes in the ventral periaqueductal gray matter (PAG) and both the tibial and sural nerves of the sciatic nerve branches were severed. Pain sensitivity was measured with a von Frey filament and acetone applied to the sensitive area for 1 week postoperatively. Rats with neuropathic pain syndrome after transection of the tibial and sural nerves were tested as to the analgesic effects of ventral PAG stimulation for an additional two weeks. Electrical stimulation of the ventral PAG turned out to be highly effective in alleviating neuropathic pain. Mechanical allodynia and cold allodynia were reduced by PAG stimulation. Naloxone reversed the antiallodynic effects of ventral PAG stimulation. These results suggest that activation of the descending pain inhibition system including the ventral PAG reduces neuropathic pain syndrome and that opiates are involved in this system.

Topics: Analgesia; Animals; Axotomy; Cold Temperature; Disease Models, Animal; Electric Stimulation Therapy; Electrodes, Implanted; Hyperalgesia; Male; Naloxone; Narcotic Antagonists; Pain Measurement; Pain Threshold; Periaqueductal Gray; Physical Stimulation; Rats; Rats, Sprague-Dawley; Sciatic Neuropathy; Sural Nerve; Tibial Nerve

The tolerance and dependence after chronic medication with morphine are thought to be representative models for studying the plasticity, including the remodeling of neuronal networks. To test the hypothesis that changes in neuronal plasticity observed in opioid tolerance or dependence are derived from increased activity of the anti-opioid nociceptin system, the effects of chronic treatments with morphine were examined using nociceptin receptor knock-out (NOR(-/-)) mice and a novel nonpeptidic NOR antagonist, J-113397, which shows a specific and potent NOR antagonist activity in in vitro [(35)S]GTPgammaS binding assay and in vivo peripheral nociception test. The NOR(-/-) mice showed marked resistance to morphine analgesic tolerance without affecting morphine analgesic potency in tail-pinch and tail-flick tests. The NOR(-/-) mice also showed marked attenuation of morphine-induced physical dependence, manifested as naloxone-precipitated withdrawal symptoms after repeated morphine treatments. Similar marked attenuation of morphine tolerance was also observed by single subcutaneous (10 mg/kg) or intrathecal (1 nmol) injection of J-113397, which had been given 60 min before the test in morphine-treated ddY mice. However, the intracerebroventricular injection (up to 3 nmol) did not affect the tolerance. On the other hand, morphine dependence was markedly attenuated by J-113397 that had been subcutaneously given 60 min before naloxone challenge. There was also observed a parallel enhancement of NOR gene expression only in the spinal cord during chronic morphine treatments. Together, these findings suggest that the spinal NOR system develops anti-opioid plasticity observed on morphine tolerance and dependence.

Topics: Animals; Benzimidazoles; Binding, Competitive; Brain; Cell Membrane; Disease Models, Animal; Drug Administration Schedule; Drug Antagonism; Drug Tolerance; Guanosine 5'-O-(3-Thiotriphosphate); Male; Mice; Mice, Knockout; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Neuronal Plasticity; Nociceptin; Nociceptin Receptor; Opioid Peptides; Pain Measurement; Piperidines; Receptors, Opioid; Spinal Cord; Substance Withdrawal Syndrome

The effects of extracts, partially purified fractions and four flavonol glycosides 1-4 from Aristeguietia discolor were investigated on the naloxone-precipitated withdrawal contraction of the acute morphine dependent guinea-pig ileum in vitro. After a 4 min in vitro exposure to morphine a strong contraction of guinea-pig isolated ileum was observed after the addition of naloxone. Both MeOH extract (50, 100 and 200 mg/mL), the partially purified fractions I, L, M and N (50, 100 and 200 mg/mL) and flavonol glycosides 1-4 (1 x 10(-4) 5 x 10(-5) 1 x 10(-5) M), injected 10 min before morphine, were capable of blocking the naloxone-induced contraction after exposure to morphine in a concentration-dependent fashion. The results of the present paper suggest that flavonol glycosides from Aristeguietia discolor may play an important role in the control of morphine withdrawal.

Topics: Animals; Asteraceae; Disease Models, Animal; Flavonoids; Flavonols; Guinea Pigs; Ileum; Male; Medicine, Traditional; Morphine; Muscle Contraction; Muscle, Smooth; Naloxone; Narcotic Antagonists; Peru; Phytotherapy; Plant Extracts; Substance Withdrawal Syndrome

The d-enantiomer of the opioid methadone is a weak opioid with low micromolar affinity to the N-methyl-D-aspartate (NMDA) receptor. We have investigated the antinociception and in vivo NMDA antagonism after systemic administration of d-methadone in the rat spinal cord. d-Methadone caused antinociception in the Randall-Selitto model of inflammatory pain and inhibited the responses of hindlimb single motor units to noxious electrical and mechanical stimulation (ED(50) 6.6, 6.8 and 7.2 mg/kg intravenous (i.v.), respectively); the wind-up of these responses was only inhibited at the dose almost completely abolishing the baseline responses. d-Methadone inhibited the activity of spinal dorsal horn neurones evoked by both iontophoretic NMDA and (R, S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA, ED(50) 5.7 and 8.2 mg/kg i.v., respectively). After pre-treatment with naloxone, d-methadone was unable to inhibit nociception in the Randall-Selitto model, the NMDA- or AMPA-evoked neuronal activity or the motoneurone wind-up. Thus, in the antinociceptive dose range, the NMDA antagonism does not appear to contribute to the mechanism of d-methadone antinociception.

Topics: Action Potentials; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Analgesia; Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Methadone; N-Methylaspartate; Naloxone; Nociceptors; Pain; Pain Measurement; Pain Threshold; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

Several reports indicate that pregnancy and parturition are associated with elevated maternal pain thresholds to noxious stimuli. The objective of this study was to examine whether the human placental extract, a clinically used preparation, can inhibit experimental nociception. Nociception was assessed in mice using acetic acid-induced writhing and hot-plate tests. The human placental extract (200 and 400 mg/kg, i.p.) elicited dose-related antinociception in the acetic acid-induced writhing test. Furthermore, it (200 mg/kg, i.p.) potentiated the morphine-induced antinociception (1.25 mg/kg, s.c.). In the hot-plate test, the human placental extract (100, 200 and 400 mg/kg, i.p.) per se, displayed no significant antinociception but potentiated the duration of morphine (10 mg/kg, s.c.) analgesia. The potentiation by the extract of the morphine-induced antinociception in both acetic acid and hot-plate tests was, however, found to be naloxone sensitive. Mice treated with the extract (400 mg/kg, i.p.) neither manifested any overt behavioural change in the open-field test nor demonstrated significant influence on pentobarbital sleeping time, suggesting that it has no central depressant or sedative activity. The data provide evidence to show that the human placental extract has a peripheral analgesic property possibly mediated by an opioid mechanism.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Hot Temperature; Humans; Injections, Intraperitoneal; Injections, Subcutaneous; Male; Mice; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Narcotics; Pain; Pain Measurement; Pentobarbital; Placental Extracts; Sleep

In a model of self-sustaining status epilepticus induced in rats by 30 min intermittent stimulation of the perforant path through chronically implanted electrodes, a decrease in dynorphin-like immunoreactivity in the dentate gyrus and CA3 was observed 3 h and 24 h after the induction of status epilepticus. Enkephalin-like immunoreactivity decreased 3 h but not 24 h after perforant path stimulation. Injection into the hilus of the dentate gyrus 10 min prior to stimulation of the kappa-receptor agonist dynorphin-A(1-13), the delta-receptor antagonists ICI-174864 and naltrindole, as well as i.p. injection of naloxone prevented the development of status epilepticus. Perihilar administration of the delta-agonist [D-Ser2]Leu-enkephalin-Thr6 or the kappa-antagonist nor-Binaltorphimine, but not of the mu-agonist [D-Ala2,N-Me-Phe4,Gly-ol5]-Enkephalin, facilitated the establishment of self-sustaining status epilepticus. Injection into the hilus of dynorphin-A(1-13) after the end of perforant path stimulation, stopped established status epilepticus, while administration of naloxone, naltrindole and ICI-174864 were ineffective. We conclude that kappa-opioids in the hippocampus counteract initiation and maintenance of status epilepticus, while delta-opioids promote initiation, but not maintenance of seizure activity. These data are important for the understanding the mechanisms which underlie initiation and maintenance of status epilepticus and for the development of new approaches for its effective management.

Topics: Action Potentials; Analgesics; Analgesics, Opioid; Animals; Disease Models, Animal; Dynorphins; Electric Stimulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Immunohistochemistry; Male; Naloxone; Naltrexone; Narcotic Antagonists; Neurons; Opioid Peptides; Peptide Fragments; Perforant Pathway; Rats; Rats, Wistar; Receptors, Opioid, delta; Receptors, Opioid, kappa; Status Epilepticus

Endogenous inhibitory controls were studied in the spinal nerve ligation model of neuropathic pain. Atipamezole, a selective alpha2-adrenoceptor antagonist, produced both mechanical and cold allodynia in those rats which had not developed clear neuropathic symptoms. The same doses (50 microg i.t. or 1 mg/kg s.c.) did not increase the severity of symptoms in rats which had developed them. The opioid receptor antagonist naloxone (20 microg i.t. or 1 mg/kg s.c.) had no effect on the neuropathic symptoms. These results indicate that mechanical and cold allodynia are under endogenous noradrenergic rather than opioidergic control in this model of neuropathic pain.

Topics: Adrenergic alpha-Antagonists; Animals; Disease Models, Animal; Imidazoles; Ligation; Male; Naloxone; Narcotic Antagonists; Norepinephrine; Pain; Pain Measurement; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic; Sodium Chloride; Spinal Nerves

The effects of the extremely selective mu-opioid receptor agonist, [D-Arg2,Lys4]-dermorphin-(1-4)-amide (DALDA), the mu-opioid receptor agonist morphine, the mu/delta agonist D-Ala2, Leu5, Arg6-enkephalin (dalargin), the kappa-opioid receptor agonist spiradoline, and the sigma1-receptor antagonist DuP 734 on ventricular fibrillation threshold (VFT) was investigated in an experimental post-infarction cardiosclerosis model and an immobilization stress-induced model in rats. Both models produced a significant decrease in VFT. The postinfarction cardiosclerosis-induced decrease in VFT was significantly reversed by intravenous administration of dalargin (0.1 mg/kg), DALDA (0.1 mg/kg), or morphine HCl (1.5 mg/kg). Pretreatment with naloxone (0.2 mg/kg) completely eliminated the increase in cardiac electrical stability produced by DALDA. Both spiradoline (8 mg/kg, i.p.) and DuP 734 (1 mg/kg, i.p.) produced a significant increase in VFT in rats with post-infarction cardiosclerosis. This effect of spiradoline was blocked by nor-binaltorphimine. The immobilization stress-induced decrease in VFT was significantly reversed by administration of either DALDA, spiradoline or DuP 734. In conclusion, activation of either mu- or kappa1-opioid receptors or blockade of sigma1-receptors reversed the decrease in VFT in both cardiac compromised models. Since DALDA and dalargin essentially do not cross blood brain barriers, their effects on VFT may be mediated through peripheral mu-opioid receptors.

Topics: Animals; Anti-Arrhythmia Agents; beta-Endorphin; Disease Models, Animal; Dynorphins; Enkephalin, Leucine-2-Alanine; Heart; Immobilization; Ligands; Morphine; Myocardial Infarction; Myocardium; Naloxone; Naltrexone; Narcotic Antagonists; Oligopeptides; Piperidines; Pyrrolidines; Rats; Receptors, Opioid; Receptors, Opioid, delta; Stress, Physiological; Ventricular Fibrillation

The antinociceptive effects of intrathecal (IT) (1DMe)NPYF were studied in adult Sprague-Dawley rats. (1DMe)NPYF produced dose-dependent antinociception that was reduced by subcutaneous injection of naloxone. (1DMe)NPYF (0.5 nmol) also potentiated the antinociceptive effects of intrathecal morphine 7.8 nmol. This suggests that the antinociceptive effects of (1DMe)NPYF are partially mediated by opioid receptor activation. In carrageenan inflammation, 5-10 nmol of (1DMe)NPYF was effective against both thermal hyperalgesia and mechanical allodynia. In the neuropathic pain model, the lowest dose tested (0.5 nmol) showed antiallodynic effects against cold allodynia. The results suggest a potential role for (1DMe)NPYF in the treatment of pain including neuropathic pain.

Topics: Amino Acid Sequence; Analgesics, Non-Narcotic; Animals; Disease Models, Animal; Drug Antagonism; Injections, Spinal; Male; Motor Activity; Naloxone; Oligopeptides; Pain; Peripheral Nervous System Diseases; Rats; Rats, Sprague-Dawley

This study investigated a role of cholecystokinin (CCK) in the anxiolytic-like action of morphine, an agonist of mu-opioid receptors, in the rat plus-maze model of anxiety. The acute administration of morphine (1 mg/kg) induced a significant increase of exploratory activity in the plus-maze, but did not affect the locomotor activity in the motility test. The higher dose of morphine (2.5 mg/kg) tended to decrease the locomotor activity and, therefore, did not cause the anxiolytic-like action in the plus-maze. The other drugs (naloxone, BOC-CCK-4, L-365,260) and their combinations with morphine (0.5-1 mg/kg) did not affect the locomotor activity of rats. The opioid antagonist naloxone itself (0.5 mg/kg) did not change the exploratory activity in the plus-maze, but potently antagonized the anxiolytic-like action of morphine (1 mg/kg). An agonist of CCK(B)receptors BOC-CCK-4 (1-50 microgram/kg) induced a dose-dependent anxiogenic-like action in the plus-maze. Nevertheless, only one dose of BOC-CCK-4 (10 microgram/kg) completely reversed the action of morphine. Also, one dose of CCK(B)receptor antagonist L-365,260 (10 microgram/kg) was effective to modify the behaviour of rats in the elevated plus-maze. Namely, this dose of L-365,260 increased the ratio between open and total arm entries, a behavioural measure believed to reflect the anxiolytic-like action in the elevated plus-maze. The combination of L-365,260 (100 microgram/kg) with the sub-effective dose of morphine (0.5 mg/kg) caused the anxiolytic-like action in the plus-maze not seen if the drugs were given alone. In conclusion, morphine induces a potent anxiolytic-like action in the elevated plus-maze and CCK is acting as an endogenous antagonist of this effect of morphine.

Topics: Analgesics, Opioid; Animals; Anti-Anxiety Agents; Anxiety; Benzodiazepinones; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Fear; Injections, Subcutaneous; Locomotion; Male; Maze Learning; Morphine; Naloxone; Narcotic Antagonists; Phenylurea Compounds; Rats; Rats, Wistar; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Tetragastrin

To assess the role of beta-EP in the physiological and pathophysiological process of respiratory regulation in chronic hypoxic rats.. The chronic hypoxic rat model was established by intravenous injections of papain 6 times, once a week. The concentration of beta-endorphin in medulla, pons, hypothalamus, central gray and plasma of chronic hypoxic rats were measured by radioimmunoassay. All animals were pretreated with sodium pentobartital (35 mg/kg) before experiment. 102 rats were randomly divided into three groups. Group 1 (n = 36). The respiratory rate (RR) and tidal volume (VT) were measured after intravenous injection of naloxone (NLX, 2 mg/kg), beta-EP (40 micrograms/kg, 160 micrograms/kg) or normal saline, Group 2 (n = 48). By the intracerebroventricular administration of NLX and beta-EP to the models, RR, VT and PaCO2 were observed after microinjection 5, 15, 30, 45, 60 min. Group 3 (n = 18). The respiratory effects of beta-EP after directly into the nucleus tractus solitari of the anaesthetised rats were investigated.. The beta-EP contents in medulla, pons, hypothalamus, central gray and plasma of chronic hypoxic rats were significantly increased compared with control subjects (P < 0.01). It suggested that the pathophysiology of chronic hypoxic process infleuced the contents of beta-EP in the CNS and plasma in rats. Intracerebroventricular microinjection of beta-EP in normal rats, resulted in a significant decrease in RR (P < 0.05). No significant difference in RR and VT was observved after intravenous injection of naloxone (2 mg/kg) and beta-EP (40 micrograms/kg, 160 micrograms/kg) in treatment group compared with the control group (P > 0.05), Intracerebroventricular microinjection of NLX in chronic hypoxic rats, resulted in a marked increase in RR (P < 0.05) and central hypercapnic-sensitivity (t = 2.76, P < 0.05), Intracerebroventriculalr microinjection of beta-EP in chronic hypoxic models, resulted in severe respiratory depression after injection 15, 30, 45, 60 min (RR t = 3.41, 6.54, 6.97, 7.87, P < 0.01; VT t = 3.07, 7.27, 6.14, 6.08).. These results indicate the beta-endorphin may be involved in central respiratory control of chronic hypoxic rats.

Topics: Animals; beta-Endorphin; Chronic Disease; Disease Models, Animal; Hypoxia; Male; Naloxone; Narcotic Antagonists; Oxygen; Rats; Rats, Sprague-Dawley; Respiration

The effect of herbal preparation Qingjunyin (QJY) on the animal model of drug dependence was studied. After the morphinistic models of white rats and mice were made by ever increasing doses of morphine each time, the animals were divided into large dosage QJY group, small dosage QJY group, sustained morphine group and control group. The withdrawal symptoms were observed after naloxone was given to the animals intraperitoneally. The results showed that QJY groups withdrawal symptoms of the addicted white rats were alleviated, the number of jumps of the addicted mice was reduced, the scores of the principal symptoms of the animals were decreased, while the body weights of the animals were gained, comparing with the control group, the difference was significant (P < 0.01). The effects of QJY enhanced in the large dosage group, which suggests QJY has abstinence effects.

Topics: Animals; Body Weight; Disease Models, Animal; Dose-Response Relationship, Drug; Drugs, Chinese Herbal; Female; Male; Mice; Morphine Dependence; Naloxone; Phytotherapy; Rats; Rats, Wistar; Substance Withdrawal Syndrome

Adrenal chromaffin cells produce analgesic substances, such as catecholamines and enkephalins, and intrathecal (i.t.) implantation of either allografted adrenal tissue or xenogenic chromaffin cells produce antinociception in animals. We evaluated the analgesic effect of bovine chromaffin cells in a model of central pain in which rats exhibit chronic allodynia-like behavior after photochemically induced ischemic spinal cord injury. Bovine chromaffin cells or endothelial cells were injected i.t. onto the lumbar spinal cord and their effects on mechanical and cold allodynia-like behaviors were studied for up to 8 weeks. The chronic allodynia-like behavior was stable for months without signs of remission and i.t. implantation of human endothelial cells did not alleviate the chronic allodynia-like behavior for the entire observation period. In contrast, 2 weeks after i.t. implantation of bovine chromaffin cells, the mechanical allodynia was abolished in the spinally injured rats, and the enhanced response to cold stimuli was significantly reduced. The overall effects were significant up to 8 weeks after i.t. implantation, although the anti-allodynic effect decreased towards the end of the observation period. No signs of side-effects were noted after i.t. implantation. The allodynia-like state was temporarily restored by naloxone (0.5 mg/kg) or phentolamine (0.3 mg/kg) injected intraperitoneally. Immunohistochemical examination revealed that tyrosine hydroxylase (TH)-positive chromaffin cells could be identified adjacent to the spinal cord up to 4 weeks after i.t. implantation, whereas at 8 weeks the TH-positive cells were sparse. It is concluded that bovine chromaffin cells stay viable in rat spinal cord for a considerable period of time after i.t. administration and alleviate chronic allodynia-like behavior in spinally injured rats, possibly through activation of opioid and alpha-adrenoceptors. The present results further document a new therapeutic approach for the treatment of chronic neuropathic pain.

Topics: Animals; Behavior, Animal; Cattle; Cell Transplantation; Chromaffin Cells; Cold Temperature; Disease Models, Animal; Endothelium; Female; Hyperalgesia; Injections, Spinal; Naloxone; Narcotic Antagonists; Neurons, Afferent; Phentolamine; Pressure; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha; Receptors, Opioid; Spinal Cord Injuries; Sympatholytics; Tail; Tyrosine 3-Monooxygenase; Vocalization, Animal

Sensory nerves mediate peripheral inflammation via the release of sensory peptides at the site of tissue injury. Using a blister model of inflammation, we have previously documented that endogenous opioids modulate chronic but not acute inflammation. Hemorphins are nonclassical opioid peptides found in the region of the beta-chain of hemoglobin (Hb). The heptapeptide hemorphin-7 is identical with residues 35-41 of the beta-chain of the human Hb. The aim of this study was to examine the effect of hemorphin-7 on the inflammatory response in acute and chronic injury models.. We have used a vacuum-induced blister model in the footpad of anaesthetized rats to induce an inflammatory response in naive skin by (a) electrical stimulation (ES) of the distal end of the cut sciatic nerve at 20 V, 5 Hz, 2 ms for 1 min or (b) superfusion of sensory peptides; substance P (SP) or calcitonin gene related peptide (CGRP) over the blister base. In addition, we examined the effect of hemorphin-7 on the inflammatory response to SP induced in a previously injured but healed skin site (recurrent injury model) and in denervated skin site due to chronic nerve lesion (chronic injury model).. The results showed that prior and concomitant perfusion of hemorphin-7 over the blister base inhibited the acute inflammatory response to ES of the sciatic nerve at C-fibre strength in a dose-dependent manner. Significant inhibition was achieved at 20 and 200 microM concentration of hemorphin-7. When hemorphin-7 (20 microM) was perfused prior to and together with SP or CGRP (both at 1 microM), over the base of acutely induced blister in naive skin, it significantly reduced the inflammatory response to SP (both plasma extravasation and vasodilatation), but was without effect on the vasodilatation response to CGRP. Naloxone, the general opioid antagonist at (1 mg/kg i.v.) reversed the inhibitory effect of hemorphin-7 on the inflammatory response to SP. On the other hand, hemorphin-7 had no effect on the inflammatory response to SP in the recurrent injury or the chronic injury models.. The results of this study suggest that hemorphins might play a role in inhibiting the inflammatory response in acute, but not in recurrent or chronic injury conditions. Evidence is also provided that the modulatory inhibitory effect of hemorphin-7 is mediated via activation of opioid receptor(s). The significance of this study in conjunction with our previous work, is that it raises the possibility that different endogenous inhibitory mechanisms may operate under different injury conditions - endogenous hemorphins and opioids may modulate acute and chronic inflammation, respectively.

Topics: Animals; Blister; Calcitonin Gene-Related Peptide; Disease Models, Animal; Dose-Response Relationship, Drug; Electric Stimulation; Hemoglobins; Hindlimb; Inflammation; Male; Naloxone; Narcotic Antagonists; Nerve Fibers; Opioid Peptides; Peptide Fragments; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Substance P; Vacuum; Wound Healing

An opioid withdrawal syndrome was precipitated by naloxone administration in rats treated with morphine. The withdrawal caused alteration of several physiological signs. The aim of the study was to investigate whether the altered physiological profiles were modified by utilising tizanidine, an alpha 2 adrenergic receptor agonist which is capable of affecting faecal and urinary excretion, rectal temperature, pain threshold levels and salivation. To induce an opioid withdrawal syndrome, morphine was administered in three daily intraperitoneal injections for four days at doses of 9, 16 and 25 mg/kg (1st day), 25, 25 and 50 mg/kg (2nd day), 50, 50 and 50 mg/kg (3rd day) and 50, 50 and 100 mg/kg (4th day): naloxone was injected (30 mg/kg) i.p. 180 min after the last morphine injection. Tizanidine was administered orally at 0.17, 0.35 and 0.7 mg/kg, 60 min after the last morphine injection. Signs such as faecal and urine excretion, rectal temperature and latency times to thermal stimulus, salivation, jumping and wet dog shakes were affected in different ways by morphine, naloxone, tizanidine and by the combination of these agents. Notably, the administration of tizanidine in rats receiving morphine and naloxone decreased the intensity of certain withdrawal symptoms, including altered excretion of faeces and urine, salivation and wet dog shake behavior. Body temperature levels and nociceptive threshold values were also modified. The effects caused by tizanidine administration may be due to its alpha 2 receptor agonist activity interfering with a mechanism involved in the regulation of these previously mentioned withdrawal symptoms. Thus, the use of this drug may be indicated as a possible control of the acute phase of opioid withdrawal in heroin addicts.

Topics: Adrenergic alpha-Agonists; Analgesics; Analysis of Variance; Animals; Behavioral Symptoms; Body Temperature; Clonidine; Disease Models, Animal; Drug Interactions; Male; Morphine; Muscle Relaxants, Central; Naloxone; Narcotic Antagonists; Narcotics; Opioid-Related Disorders; Pain Threshold; Parasympatholytics; Peristalsis; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Urination

Treatment of opiate addiction is generally directed at the suppression of withdrawal symptoms through maintenance of the 'addicted' state with methadone. Yet relatively little is known regarding the neural substrates that contribute to, and maintain the prolonged state of withdrawal experienced by addicts. Opiates can profoundly alter the dynamics of brain and peripheral cholinergic systems, and central administration of anticholinergic drugs in dependent rats has been shown to decrease the expression of precipitated withdrawal symptoms. The purpose of this study was to determine whether the adaptive changes to M2 muscarinic receptors in autonomic centers are linked to the expression of withdrawal phenomena. During the peak period of withdrawal, there was a significant increase in both the expression of M2 muscarinic receptors and its corresponding mRNA within the rostral ventrolateral medulla, a primary vasomotor region. That most of these changes in receptor expression were adaptive in nature was suggested by the fact that when the acetylcholinesterase inhibitor DFP was co-administered with morphine, both the increased mRNA expression and the appearance of withdrawal symptoms were inhibited. Thus, interference with morphine-induced M2 muscarinic receptor adaptation in critical brain regions was correlated with a reduction in the development of physical dependence.

Topics: Animals; Behavior, Animal; Blood Pressure; Body Weight; Disease Models, Animal; Infusions, Intravenous; Injections, Subcutaneous; Isoflurophate; Male; Morphine; Morphine Dependence; Naloxone; Pirenzepine; Rats; Rats, Wistar; Receptor, Muscarinic M2; Receptors, Muscarinic; Substance Withdrawal Syndrome; Vasomotor System

Intraperitoneal (i.p.) administration of (+/-) pentazocine (10, 30 & 50 mg/kg), a Sigma opioid agonist, resulted in a dose dependent anticonvulsant action against maximal electroshock seizures in mice. This anticonvulsant effect of pentazocine was not antagonized by both the doses of naloxone (1 and 10 mg/kg) suggesting thereby that its anticonvulsant action is probably mediated by Sigma opiate binding sites. Its anticonvulsant effect was potentiated by both the anticonvulsant drugs viz. diazepam and diphenylhydantoin. Morphine, mu opioid agonist, on the other hand, failed to protect the animals against maximal electroshock seizures when it was given in doses of 10-40 mg/kg body wt.

Topics: Analgesics, Opioid; Animals; Anticonvulsants; Diazepam; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Female; Male; Mice; Mice, Inbred Strains; Naloxone; Narcotic Antagonists; Pentazocine; Seizures; Treatment Outcome

Acute morphine dependence was compared in mice selectively-bred for high (HA) and low (LA) swim stress-induced analgesia and high (HAR) and low (LAR) levorphanol analgesia by counting the number of naloxone-precipitated jumps. Whereas LAR mice displayed greater acute morphine dependence than HAR mice, HA and LA mice did not differ. No genotypic differences were observed in non-dependent mice, discounting possible differences in basal naloxone sensitivity and/or opioid peptide levels. Thus, the two selection projects, while both producing lines exhibiting highly divergent sensitivity to morphine analgesia, have not had analogous effects on all opioid measures, supporting the notion of independent genetic mediation of opioid analgesia and dependence. Further, these data suggest that analgesic sensitivity may not predict sensitivity to morphine dependence.

Topics: Analgesia; Animals; Behavior, Animal; Disease Models, Animal; Exercise Test; Levorphanol; Male; Mice; Mice, Inbred Strains; Morphine; Morphine Dependence; Naloxone; Selection, Genetic

Naloxone enhances bladder activity in patients with chronic spinal cord injury. However, there are few reports on naloxone for bladder morbidity in acute spinal cord injury.. We performed a prospective, controlled study of the effects of naloxone on bladder function in rabbits with and without surgical transection of the spinal cord at the 10th thoracic vertebra. Acute and chronic stages of injury were defined according to bladder function. Naloxone was given intravenously at both stages, and intrathecally at the acute stage. Bladder activity was monitored by cystometry. Blood concentrations of methionine-enkephalin were measured by radioimmunoassay.. Spinal cord injuries were acute 1 or 2 days after surgery, and chronic after 1 or 2 weeks. Bladder capacity significantly decreased after 0.01 mg of intravenous naloxone in uninjured control rabbits, and after 0.03 mg of intravenous naloxone in rabbits with chronic-phase injuries. During the acute-injury phase, 0.3 mg of intravenous naloxone, or 0.02 mg of intrathecal naloxone, was necessary to evoke the micturition reflex. No significant changes in blood enkephalin levels were seen before or after spinal cord injury.. In rabbits with acute spinal cord injury, intrathecal naloxone evoked the micturition reflex at a much lower dose than did intravenous naloxone. Intrathecal naloxone promises to become a new therapy for the acute stage of spinal cord injury for active recovery of bladder function, and could replace current therapy.

Topics: Animals; Disease Models, Animal; Electromyography; Enkephalins; Injections, Intravenous; Injections, Spinal; Male; Naloxone; Prospective Studies; Rabbits; Spinal Cord Injuries; Time Factors; Urinary Bladder; Urodynamics

1. We evaluated the ability of the functional antagonist at the glycine site of the N-methyl-D-aspartate (NMDA) receptor complex, (+)-(1-Hydroxy-3-aminopyrrolodine-2-one) ((+)-HA966), to modulate the antinociceptive action of systemic morphine in a rat model of neuropathic pain produced by chronic constriction injury to the sciatic nerve. Mechanical (vocalization threshold to hindpaw pressure) and thermal (struggle latency to hindpaw immersion into a water bath) stimuli were used. 2. In the mechanical test, morphine (0.05, 0.1 and 0.3 mg kg(-1), i.v.) alone produced dose-dependent effects in both neuropathic and uninjured rats. Likewise, morphine (0.1, 0.3 and 1 mg kg(-1), i.v.) dose-dependently increased struggle latencies of the nerve-injured hindpaw in the hot noxious (46 degrees C) test but was ineffective in the non-noxious warm (44 degrees C) and cold (10 degrees C) test. 3. Pretreatment with (+)-HA966 (2.5 mg kg(-1), s.c.) dose-dependently enhanced the effect of morphine in the mechanical test with the relative potency being nerve-injured hindpaw > contralateral hindpaw > uninjured rat. 4. Likewise, (+)-HA966 dose-dependently enhanced the effect of morphine against a hot (46 degrees C) stimulus and produced, in combination with morphine, a dose-dependent effect against a warm (44 degrees C) stimulus. In the cold (10 degrees C) test, (+)-HA966 reversed the ineffectiveness of the highest dose of morphine. 5. Naloxone blocked the effect of the combination of (+)-HA966 with morphine in all tests. The drug combination produced no motor deficits in animals using the rotarod test. 6. These findings suggest that combined administration of antagonists, acting at the glycine site of the NMDA receptor complex and morphine may be a promising approach in the treatment of neuropathic and acute pain.

Topics: Analgesics, Opioid; Animals; Binding Sites; Cold Temperature; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Therapy, Combination; Excitatory Amino Acid Antagonists; Glycine; Hot Temperature; Male; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Nociceptors; Pain; Peripheral Nervous System Diseases; Pyrrolidinones; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Stress, Mechanical

This study investigated the interplay of cholecystokinin (CCK) and endogenous opioid peptides in the regulation of anxiety. The acute administration of non-selective CCK agonist caerulein (1 and 5 microg/kg) and a selective CCK(B) receptor agonist BOC-CCK-4 (1, 10 and 50 microg/kg) induced a dose-dependent anxiogenic-like action in the plus-maze model of anxiety. BOC-CCK-4 displayed a similar efficacy with caerulein, indicating that the described effect was mediated via CCK(B) receptor subtype. The opioid antagonist naloxone itself (0.5 mg/kg) did not change the exploratory activity of rats in the plus-maze. However, the combination of naloxone with the sub-effective doses of caerulein (1 microg/kg) and BOC-CCK-4 (1 microg/kg) induced a significant inhibition of exploratory behaviour in rats. Accordingly, CCK and endogenous opioid peptides have an antagonistic role in the exploratory model of anxiety in rats.

Topics: Animals; Anxiety; Ceruletide; Cholecystokinin; Disease Models, Animal; Drug Synergism; Exploratory Behavior; Male; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Tetragastrin

The N-methyl-D-aspartate (NMDA) receptor-nitric oxide (NO) pathway has been linked to opiate withdrawal. Pretreatments with four inhibitors of NO synthase, 7-nitro indazole, 3-bromo-7-nitro indazole, S-methyl-L-thiocitrulline and aminoguanidine, which exhibit different isoform selectivity in vitro, were evaluated for their ability to attenuate signs of naloxone-precipitated morphine withdrawal. In separate experiments, effects of NO synthase inhibitors on blood pressure were measured in naive and morphine-dependent rats. 7-Nitro indazole, 3-bromo-7-nitro indazole and S-methyl-L-thiocitrulline, which are specific inhibitors of the constitutive isoforms, produced dose-dependent reductions of several signs of withdrawal. Blood pressure was unaffected by the indazoles, whereas S-methyl-L-thiocitrulline produced a strong vasoconstrictor response. Aminoguanidine, which selectively inhibits inducible NO synthase, reduced fewer signs of opioid withdrawal, had a lower relative potency and exhibited no vasopressor activity. These data suggest that constitutive isoforms, but not the inducible isoform of NO synthase, have a primary role in NO-mediated processes that modulate the opioid withdrawal syndrome in the rat.

Topics: Analysis of Variance; Animals; Blood Pressure; Citrulline; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Induction; Enzyme Inhibitors; Guanidines; Heart Rate; Indazoles; Isoenzymes; Male; Morphine; Naloxone; Narcotic Antagonists; Nitric Oxide Synthase; Rats; Rats, Inbred F344; Substance Withdrawal Syndrome; Thiourea

The ability of the selective cholecystokinin(B) (CCK(B)) receptor antagonist L-365,260 (0.2 mg/kg s.c.) to modulate the antinociceptive action of relatively low doses of systemic morphine (0.1, 0.3 and 1.0 mg/kg i.v.) was evaluated using a well established rat model of peripheral unilateral mononeuropathy. Behavioural tests based on both mechanical (vocalization threshold to paw pressure) and thermal (struggle latency after immersion of the paw into a cold (10 degrees C), warm (44 degrees C) or hot (46 degrees C) water bath) stimuli were used. Experiments were performed 2 weeks after the surgery when the pain-related behaviour has fully developed. We demonstrated a differential effect of L-365,260 depending both on the dose of morphine and the test used. Pretreatment with the CCK(B) receptor antagonist (0.2 mg/kg) inverted the ineffectiveness of the lowest dose (0.1 mg/kg i.v.) of morphine against the noxious (46 degrees C) thermal stimulus, and the effect of the combination was equal to that seen after the dose 0.3 mg/kg of morphine alone. Likewise, in the mechanical test, the already enhanced effect of this dose (0.1 mg/kg) of morphine on the nerve-injured paw was further increased (by 4-fold) after L-365,260 pretreatment. These effects were abolished by naloxone (0.01 mg/kg i.v.). However, the effects of the higher doses (0.3 and 1.0 mg/kg i.v.) of morphine against the mechanical or noxious thermal stimuli were not significantly enhanced by pretreatment with the CCK(B) receptor antagonist. Further, L-365,260 was found to be completely ineffective in modulating the responses to morphine at 10 degrees C and at 44 degrees C.

Topics: Analgesics; Animals; Benzodiazepinones; Cold Temperature; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Hot Temperature; Male; Morphine; Naloxone; Narcotic Antagonists; Pain; Phenylurea Compounds; Rats; Rats, Sprague-Dawley; Receptor, Cholecystokinin B; Receptors, Cholecystokinin; Sciatic Nerve; Stress, Mechanical; Vocalization, Animal

The blockade of veratrine-stimulated phosphoinositide breakdown in rat cerebral cortical miniprisms has been used as a model of drug action on voltage-dependent sodium channels. The kappa-opioid agonists bremazocine, (+/-)- and (+)-trans-U-50488, U-62066 (spiradoline) and U-69593 inhibited the response to veratrine with IC50 values of 35, 13, 15, 9, and > 100 microM, respectively. Bremazocine, at concentrations inhibiting the response to veratrine, did not inhibit the phosphoinositide breakdown response to the sodium ionophore monensin, indicating the specificity of the assay for sodium channels. The inhibitory actions of bremazocine upon veratrine-stimulated phosphoinositide breakdown were not antagonised by naloxone. This study thus confirms previous data suggesting that the kappa-opioid receptor agonists can affect Na(+)-channel function in a manner unrelated to their actions at kappa-opioid receptors. However, for the compounds tested, such effects are only found at rather high concentrations of the compounds.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Benzeneacetamides; Benzomorphans; Brain; Disease Models, Animal; Inositol Phosphates; Naloxone; Pyrrolidines; Rats; Receptors, Opioid, kappa; Sodium Channels

The effect of indole alkaloids from Sickingia williamsii Standl. (Rubiaceae) on the effects of morphine withdrawal have been examined in-vitro. All the indole alkaloids isolated from S. williamsii (10(-4), 5 x 10(-5) and 10(-5) M) significantly and in a concentration-dependent manner reduced the effects of morphine withdrawal on the guinea-pig ileum. The results suggest that these alkaloids might be potential anti-addictive agents.

Topics: Acetylcholine; Alkaloids; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Electric Stimulation; Guinea Pigs; Ileum; Indoles; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Rubiaceae; Substance Withdrawal Syndrome

Chronic treatment with Withania somnifera (Ws) (family: Solanaceae, 100 mg/kg) commercial root extract followed by saline on days 1-9 failed to produce any significant change in tailflick latency from the saline pretreated group in mice. However, repeated administration of Ws (100 mg/kg) for 9 days attenuated the development of tolerance to the analgesic effect of morphine (10 mg/kg). Ws (100 mg/kg) also suppressed morphine-withdrawal jumps, a sign of the development of dependence to opiate as assessed by naloxone (2 mg/kg) precipitation withdrawal on day 10 of testing.

Topics: Administration, Oral; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Female; Injections, Subcutaneous; Male; Mice; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Plant Extracts; Plant Roots; Saline Solution, Hypertonic; Substance Withdrawal Syndrome

An opioid withdrawal syndrome was induced in rats by repeated morphine administration and final naloxone injection. The withdrawal causes alteration of several physiological signs. The aim of the study was to describe a quantitative opioid abstinence syndrome to validate the methodology by utilizing clonidine, a well-known antiwithdrawal agent, and propose the procedure for the screening of antiabstinence drugs. In particular, rats were treated with saline, morphine, naloxone, morphine and naloxone and four doses of clonidine (0, 0.04, 0.1, and 0.25 mg/kg orally). In rats repeatedly exposed to morphine and then injected with naloxone, signs like excretion of feces and urine, salivation, behavioral jumping and wet dog shakes, rectal temperature, and pain threshold have been observed. Consequently, the objective symptoms observed in morphine plus naloxone-treated animals have been taken as markers of opioid withdrawal. These factors have been quantitatively measured and grouped to form a standardized procedure of opioid abstinence syndrome. In addition, it is possible to observe that the antiabstinence drug clonidine exerted effects on modified physiological signs appearing in morphine-dependent rats treated with naloxone, like fecal excretion, levels of rectal temperature, latency times, salivation as well as jumping behavior. The effects exerted by clonidine in this procedure and in other methods are compared and appear to be similar. In addition, comparative observations referring to both the previous methods and the present procedure related to the type of signs studied, the modality of evaluation, and suppressive activity exerted by the antiwithdrawal agent, clonidine, are performed: the greater accuracy of the proposed method becomes apparent. Thus, this experimental model, validated by the antiabstinence agent clonidine, is proposed as a useful screen for drugs affecting opioid withdrawal syndrome.

Topics: Administration, Oral; Adrenergic alpha-Agonists; Animals; Behavior, Animal; Body Temperature; Clonidine; Defecation; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Pain Threshold; Rats; Rats, Sprague-Dawley; Salivation; Substance Withdrawal Syndrome; Urination

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.

Topics: Animals; Arginine; Cerebellum; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Injections, Subcutaneous; Male; Mice; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Stereoisomerism; Substance Withdrawal Syndrome

The aim of this study was to investigate the possible involvement of the mu-opioid system on the learned-helplessness paradigm, an experimental model of depression, in rats. In this test, rats were first exposed to inescapable foot-shocks (IS); 48 h later, they were submitted to a daily shuttle-box session (30 trials) for 3 consecutive days. Avoidance responses, escape failures and animal activity during each intertrial interval were recorded. Twice daily injections of morphine (0.25-8 mg/kg per day, SC), a mu-opioid agonist, reduced the increased escape failures induced by IS, as did tricyclic antidepressants. Significantly higher intertrial activity was observed in rats treated with morphine (2-8 mg/kg per day) compared with their associated control groups. Naloxone (1 and 2 mg/kg, IP), a mu-opioid antagonist, injected 10 min before each shuttle-box session impaired escape behavior in non-stressed rats and worsened the escape deficit induced by IS. Morphine-induced improvement of escape behavior and increase in intertrial activity were clearly reversed by a low inactive dose of naloxone (0.5 mg/kg). These results suggest that mu-opioid receptor mediation is involved in the deleterious effects of uncontrollable stress.

Topics: Animals; Avoidance Learning; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Helplessness, Learned; Male; Morphine; Naloxone; Rats; Rats, Wistar

We have examined the effect of the micro-opioid analgesic buprenorphine on osteoclastic bone resorption in vitro and in the rat adjuvant arthritis model. In the bone slice assay buprenorphine inhibited osteoclastic bone resorption with an IC50 of 1 microM. This effect was not mimicked by the micro-opioid agonist ([D-Ala, N-Me-Phe, Gly-ol]-enkephalin and was not prevented by the micro-opioid antagonist naloxone. Since other agents that inhibit osteoclastic bone resorption, such as bisphosphonates and calcitonin prevent bone erosion in the rat adjuvant arthritis model, we also examined the effect of buprenorphine in this model. Surprisingly, buprenorphine exacerbated inflammation measured by paw volume and increased joint destruction assessed by X-ray scores, in the injected paws and particularly in the non-injected paws. These studies also show that attempts to ameliorate animal suffering in this chronic model by using centrally acting analgesics such as buprenorphine may lead to complications in interpreting screening results obtained with novel, potential anti-arthritic compounds.

Topics: Analgesics; Analgesics, Opioid; Animals; Arthritis, Experimental; Arthrography; Bone Resorption; Buprenorphine; Cells, Cultured; Disease Models, Animal; Edema; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Femur; Lethal Dose 50; Naloxone; Narcotic Antagonists; Osteoclasts; Rats

Topics: Amino Acid Sequence; Animals; Blood Pressure; Death; Disease Models, Animal; Female; FMRFamide; Heart Rate; Molecular Sequence Data; Naloxone; Neuropeptides; Rats; Resuscitation; Shock, Hemorrhagic

We investigated the effects of the opiate antagonist naloxone on the release of beta-endorphin and cortisol in rats subjected to sepsis. Sepsis was induced in weanling male Wistar albino rats (3-4 weeks old, 75-90 g) by cecal ligation and double perforation (CLP). Forty animals were randomly allocated to four groups. Group 1 was given naloxone hydrochloride 0.5 mg/kg subcutaneously after CLP and this treatment was repeated at 2-h intervals until the rats were killed. Group 2 rats underwent a sham operation. Group 3 (control group) rats had CLP. Group 4 consisted of nonoperated animals used to establish normal reference values. Eighteen hours after CLP or sham operation, the rats were killed by cervical dislocation and a blood sample was drawn via cardiac puncture to determine the beta-endorphin and cortisol levels. The beta-endorphin levels were significantly higher in the control group than in the sham-operated, naloxone-treated (NT), and nonoperated rats (P < 0.05). However, there were no significant differences in plasma beta-endorphin levels between sham-operated, NT and nonoperated rats (P > 0.05). Plasma cortisol levels were significantly higher in the control group compared with the other three groups and this difference was more significant in sham-operated and nonoperated rats (P < 0.01). However, no difference existed between sham-operated, NT, and nonoperated rats (P > 0.05). This study demonstrates that the endogenous opioid system may play a role in the activation of the pituitary-adrenal axis following sepsis, and shows that the increase in beta-endorphin and cortisol could be blocked by naloxone.

Topics: Animals; beta-Endorphin; Disease Models, Animal; Hydrocortisone; Male; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar; Sepsis

The aim of the present study was to evaluate the action of the descending modulation system from the locus coeruleus (LC) in a rat model of unilateral hyperalgesic inflammation. Unilateral hindlimb inflammation was produced by a subcutaneous injection of carrageenan (6 mg in 0.15 ml saline). One week before testing, rats received bilateral lesions of the LC using anodal current. Nociception was assessed by measuring withdrawal of the paw from a noxious thermal stimulus. Four hours after carrageenan injection, paw withdrawal latencies (PWLs) in the inflamed paw of the LC-lesioned rats were significantly shorter than those of the sham-operated rats. This difference in PWL between the two groups was not observed at 7 days, whereas edema and hyperalgesia still remained in the inflamed paw. At 4 h, systemic naloxone produced a further decrease of the PWL in the LC-lesioned rats but not in the sham-operated rats. These results suggest that inflammation-induced activation of the descending modulation system from the LC occurs in only the acute phase of inflammation and that a decrease in the extent of the development of hyperalgesia in the acute phase of inflammation might depend on the interaction between the descending modulation system from the LC and the opioid inhibitory system.

Topics: Analysis of Variance; Animals; Carrageenan; Disease Models, Animal; Efferent Pathways; Endorphins; Hindlimb; Hyperalgesia; Inflammation; Locus Coeruleus; Male; Naloxone; Pain; Rats; Rats, Sprague-Dawley

Topics: Acupuncture Analgesia; Adrenocorticotropic Hormone; Animals; Brain; Disease Models, Animal; Ear, External; Electroacupuncture; Endorphins; Female; Mice; Morphine Dependence; Naloxone; Narcotic Antagonists; Rats; Substance Withdrawal Syndrome

Pentylenetetrazol (PTZ) and sodium valproate (VPA) produce acutely in the naive rat various behavioural effects resembling signs of opiate withdrawal in the morphine-treated subject. Suggestions in the literature that these substances may activate directly some of the neural consequences of opiate and drug withdrawal prompted us to look for and examine possible aversive effects of these substances at non-toxic doses. With a sensitive two-flavour, three-trial taste aversion procedure, relatively low doses of PTZ and VPA (5 and 160 mg/kg, respectively) do indeed have aversive effects. The maximum aversions were produced by 10 and 20 mg/kg PTZ and 320 mg/kg VPA and were equivalent to those of morphine withdrawal precipitated by 0.01-0.03 mg/kg naloxone in a morphine pellet-implanted animal. Moreover, the maximum aversions with PTZ and VPA were significantly higher than the maximum aversions seen with naloxone in the drug-naive animal under the same training conditions. Thus, the data from the present study confirmed the notion that low doses of PTZ and VPA in the naive animal may activate processes activated by drug withdrawal, including those important for the motivational effect of withdrawal. However, it was also pointed out that the lowest dose VPA producing aversion was higher than that found here to produce writhes and ataxia (80 mg/kg) but the same as that required for shaking (160 mg/kg), while the PTZ aversion was at a dose lower than that known to produce a PTZ cue. Implications were discussed for using withdrawal-like phenomena as a model in the non-treated organism of clinically-relevant withdrawal effects.

Topics: Animals; Avoidance Learning; Conditioning, Classical; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Morphine Dependence; Motivation; Naloxone; Neurologic Examination; Opioid-Related Disorders; Pentylenetetrazole; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome; Taste; Valproic Acid

Acute resistive loading of the airway has been shown to activate the endogenous opioid system, with subsequent depression of ventilation. The present investigation was designed to assess the effect of chronic airway loading on ventilation and CO2 sensitivity, and to determine whether the endogenous opioid system contributes to long-term modulation of ventilatory control in this setting. A flow-resistive ventilatory load was imposed in 2-mo-old rats by surgical implantation of a circumferential tracheal band that approximately tripled tracheal resistance. Respiration and CO2 sensitivity were serially and noninvasively assessed by barometric plethysmography over a period of 21 wk. Ventilatory output was assessed as minute inspiratory effort, which was defined as the product of plethysmograph signal amplitude, inspiratory time, and respiratory rate (RR). CO2 sensitivity was calculated as the percent change in minute inspiratory effort from room air to CO2 exposure. The effect of naloxone administration on these parameters was also determine. Arterial blood gases demonstrated hypercapnia with maintenance of normoxia in loaded rats; these findings persisted for the duration of the study. Two days after surgery, rats with tracheal obstruction demonstrated a lower RR than controls during room air breathing and during CO2 stimulation. CO2 sensitivity was significantly depressed in obstructed animals at this time. Escape from suppression of RR and CO2 sensitivity was evident by 14 to 21 d after obstruction; however, suppression of these parameters reappeared and was maintained from 56 to 147 d after obstruction. Naloxone augmented minute inspiratory effort during CO2 stimulation at 2 d after obstruction but not thereafter; naloxone had no effect in control rats. These data indicate that chronic airway loading suppresses RR and CO2 sensitivity in a triphasic manner. The early suppression is partially reversible by naloxone; late-appearing suppression is unaffected by naloxone and is presumably mediated by mechanisms that do not involve endogenous opioids.

Topics: Airway Obstruction; Airway Resistance; Animals; Carbon Dioxide; Chronic Disease; Disease Models, Animal; Eating; Hypercapnia; Inhalation; Male; Naloxone; Opioid Peptides; Oxygen; Oxygen Consumption; Plethysmography; Pulmonary Ventilation; Rats; Rats, Sprague-Dawley; Respiration; Tracheal Diseases

In a rat model of peripheral mononeuropathy produced by moderate constriction of the sciatic nerve, we have shown that various i.v. doses of morphine and selective opioid agonists produce potent and long-lasting antinociceptive effects on the vocalization threshold to paw pressure. For all the opioids, the antinociceptive effects were more marked for the paw on the nerve-injured side (nerve-injured paw) than for the sham-operated paw. One contributory mechanism could be a peripheral action of the opioid agonists in the nerve-injured paw. This hypothesis was tested in the present study, using systemic morphine and low doses of local naloxone or its quaternary salt naloxone methiodide, exhibiting peripherally acting antagonist properties. The effects of escalating doses of naloxone (0.5-2 microgram injected i.v. or intraplantar into the nerve-injured paw) or naloxone methiodide (5-30 micrograms into the nerve-injured paw) on the antinociceptive effect of morphine (1 mg/kg i.v.) were evaluated using the vocalization threshold to paw pressure in neuropathic rats at two weeks after placing ligatures, a time when the behavioural pain-related disorders have reached a maximum.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Analgesics; Animals; Constriction; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Morphine; Naloxone; Peripheral Nervous System Diseases; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Vocalization, Animal

1. The opioid activity of the amphibian peptide, [Lys7]dermorphin, was studied in rats and mice. When administered intracerebroventricularly (i.c.v.), intravenously (i.v.) or subcutaneously (s.c.) it produced a long lasting analgesia. Its antinociceptive potency exceeded that of morphine 290 times by i.c.v. injection, and 25-30 times by peripheral administration. 2. The dose-response curves of [Lys7]dermorphin antinociception were shifted to the right by the pretreatment with naloxone (0.1 mg kg-1, s.c.) or with the mu 1-selective antagonist, naloxonazine (10 mg kg-1, i.v. 24 h before peptide injection). 3. The peptide also displayed potent antinociceptive effects in a chronic inflammatory pain model (rat Freund's adjuvant arthritis). In this pain model, systemic administration of the peptide raised the nociceptive threshold more in inflamed than in healthy paw. 4. High central and peripheral doses of [Lys7]dermorphin in rats produced catalepsy. The cataleptic response was antagonized by naloxone but left unchanged by naloxonazine pretreatment. 5. In rats and mice, central or peripheral administration of [Lys7]dermorphin induced a significantly slower development of tolerance to the antinociceptive effect than did morphine. 6. Upon naloxone precipitation of the withdrawal syndrome, [Lys7]dermorphin-dependent mice made fewer jumps and lost less weight than the morphine-dependent animals. Withdrawal hyperalgesia did not develop in [Lys7]dermorphin-dependent mice. 7. In conclusion, [Lys7]dermorphin seems to be a unique opioid peptide having a high penetration into the blood-brain barrier despite its low lipid solubility. This peptide causes fewer side-effects than other opioids and appears less likely than morphine to cause physical dependence in rats and mice.

Topics: Analgesics, Opioid; Animals; Body Weight; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Tolerance; Male; Mice; Morphine; Naloxone; Nociceptors; Oligopeptides; Opioid Peptides; Rats; Rats, Wistar; Receptors, Opioid, mu; Substance-Related Disorders

Intracerebroventricular injection of dopamine (0.5-4.0 mg) produced dose-dependent and short-lasting emesis (1-8 min) in cats, which was abolished after ablation of the area postrema. Relatively selective alpha 2-adrenoceptor antagonists (yohimbine and idazoxan) and a mixed alpha 1- and alpha 2-adrenoceptor antagonist (tolazoline), but not a non-selective alpha 1-adrenoceptor antagonist (prazosin), injected intracerebroventricularly inhibited the emesis induced by intracerebroventricular dopamine. However, dopamine receptor antagonists (chlorpromazine, droperidol, spiperone, domperidone, triflupromazine, sulpiride and metoclopramide), an antimuscarinic drug (atropine), a ganglionic blocking agent (mecamylamine), an opioid receptor antagonist (naloxone) and a 5-HT receptor antagonist (methysergide), all injected intracerebroventricularly, had no significant effect on emesis evoked by intracerebroventricular dopamine. The emetic response to intracerebroventricular dopamine was attenuated in cats pretreated with intracerebroventricular reserpine, 6-hydroxydopamine, alpha-methyl-p-tyrosine and hemicholinium-3. It is postulated that dopamine-induced emesis is mediated through the release of noradrenaline acting at alpha 2-adrenoceptors and that it depends on the integrity of monoaminergic and possibly cholinergic structures within the area postrema. It appears, therefore, that the emetic effect of intracerebroventricular dopamine is mediated by adrenergic rather than dopaminergic mechanisms in the area postrema, at least in the cat.

Topics: Adrenergic alpha-Antagonists; alpha-Methyltyrosine; Animals; Atropine; Cats; Cerebral Ventricles; Dioxanes; Disease Models, Animal; Dopamine; Dopamine Antagonists; Dose-Response Relationship, Drug; Female; Hemicholinium 3; Idazoxan; Injections, Intraventricular; Male; Mecamylamine; Methyltyrosines; Methysergide; Naloxone; Oxidopamine; Prazosin; Reserpine; Tolazoline; Tyrosine 3-Monooxygenase; Vomiting; Yohimbine

This study evaluated the modulatory role of endogenous opioids on ventilation in young and mature, lean and obese male Zucker rats. Naloxone, an opioid receptor antagonist, and saline (control) were administered subcutaneously to awake rats, and ventilation in air and in response to an hypoxic and an hypercapnic gas challenge measured. In response to naloxone young, obese but not lean rats exhibited a marked increase of ventilation in all three conditions. Older obese Zucker rats that were morbidly obese breathed at a frequency of over 200 breaths per minute and showed only a modest increase of ventilation in response to naloxone. Older lean rats increased ventilation with naloxone only when exposed to hypercapnia. Unlike the stimulatory effects hypoxia and hypercapnia had on ventilation in older, lean rats, the ventilatory responses of the obese, older rats to hypoxia and to hypercapnia were blunted. We conclude that the obese Zucker rat may be a good animal model to assess how chest wall loading and endogenous opioids interact in the development of ventilatory control abnormalities.

Topics: Animals; Disease Models, Animal; Hypercapnia; Hypoxia; Male; Naloxone; Obesity; Opioid Peptides; Pulmonary Ventilation; Rats; Rats, Zucker; Respiration

The acute and chronic effects of paroxetine and fluvoxamine on naloxone withdrawal-induced place aversion in morphine dependent rats were investigated. Acutely administered fluvoxamine (25 mg/kg s.c. given 30 min prior to naloxone withdrawal pairing) and chronic daily paroxetine (10 mg/kg s.c.) coadministration with a morphine induction protocol, both attenuated morphine withdrawal place aversion. Conversely, acutely administered paroxetine (up to 25 mg/kg s.c.) or chronic daily fluvoxamine (10 mg/kg s.c.) coadministration with morphine did not modify subsequent withdrawal place aversion. Previous radioligand binding studies indicate that fluvoxamine has opioid-displacing properties. It is suggested therefore that acute fluvoxamine may have decreased withdrawal aversion, probably through serotonin and also, in part, via an opioid-like mechanism whereas chronic paroxetine decreased withdrawal aversion by a serotonergic mechanism, but it is not clear whether opioid systems play any role in the action of paroxetine.

Topics: Analysis of Variance; Animals; Conditioning, Psychological; Disease Models, Animal; Drug Administration Schedule; Fluvoxamine; Injections, Subcutaneous; Male; Morphine; Naloxone; Paroxetine; Rats; Rats, Sprague-Dawley; Selective Serotonin Reuptake Inhibitors; Serotonin; Substance Withdrawal Syndrome; Substance-Related Disorders

It has been proposed that opioids act at the level of the medulla to produce facial pruritus. Supporting this hypothesis, microinjection of mu-opioid receptor agonists into the medullary dorsal horn (MDH; trigeminal subnucleus caudalis) of monkeys produces facial scratching behavior. The present study sought to establish a rodent model of opioid-induced facial pruritus. To this end, morphine (0.1, 0.3 or 1.0 micrograms/0.2 microliter) or saline (0.2 microliter) was unilaterally microinjected into the MDH of male Sprague-Dawley rats. Behavior for the 20 min preceding and the 80 min after this microinjection was videotaped. Morphine produced dose-dependent increases in facial scratching behavior ipsilateral to the microinjections with the peak effect at 30-40 min after microinjection. Facial scratching continued for the entire 80 min post-microinjection test period. Morphine also produced a lesser degree of facial scratching contralateral to the microinjections. Increases in facial scratching ipsilateral to the microinjection of 0.3 microgram morphine into the MDH were attenuated by 0.4 mg/kg s.c. naloxone. These findings support the hypothesis that the MDH is a critical site of action of opioid agonists in producing facial pruritus.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Face; Functional Laterality; Male; Medulla Oblongata; Microinjections; Morphine; Naloxone; Narcotic Antagonists; Pruritus; Rats; Rats, Sprague-Dawley

We have characterised pressor responses to stimulation of the ureter in anaesthetised rats (n = 20) as a model of acute visceral pain. The left ureter was cannulated close to the bladder and graded stimuli applied (5-90 mmHg, 30 s). The threshold was approximately 25 mmHg. Suprathreshold pressures evoked responses proportional to the stimulus intensity, which were little altered when stimulation of the kidney was prevented by ligation of the ureteric-pelvic junction. The stimulus response curve was dose-dependently attenuated by morphine (1-3 mg kg-1 i.v.), in a naloxone reversible manner. The characteristics of the responses observed correlate well with pain sensation in man and with the properties of ureteric primary afferent neurones in animals.

Topics: Analgesics, Opioid; Anesthesia; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Kidney Pelvis; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Pressure; Rats; Rats, Wistar; Ureter

Substance P, a putative neurotransmitter or neuromodulator of nociception or pain in the spinal cord, exhibits both antinociceptive and hyperalgesic properties. Investigators have shown that the N-terminal metabolite of substance P, substance P(1-7), produces naloxone-reversible antinociception when given supraspinally and systemically in mice and hyperalgesia when injected intrathecally in rats. The goal of our investigation was to identify the receptors mediating these actions of substance P(1-7) at the initial site of release of substance P, i.e. in the spinal cord. Thirty minutes after intrathecal injection, substance P(1-7) produced naloxone-reversible antinociception in a dose-dependent manner in the abdominal stretch assay. When administered with naloxone, substance P(1-7) produced hyperalgesia 5 and 10 min after injection, which was inhibited by dizocilpine (MK-801), a phencyclidine ligand and non-competitive antagonist of N-methyl-D-aspartate. Antinociception was inhibited by the mu-selective opioid antagonist beta-funaltrexamine, but not by the mu 1-selective opioid antagonist naloxonazine or the delta-selective antagonist naltrindole, indicating a mu 2-opioid receptor-mediated effect. These findings suggest that the N-terminal portion of substance P may modulate nociception or pain, as demonstrated in the acetic acid abdominal stretch (writhing) assay, via activation of two different receptor systems. Substance P(1-7)-induced hyperalgesia is mediated by a phencyclidine-sensitive mechanism and antinociception involves activity at mu-opioid, most likely mu 2, receptors.

Topics: Animals; Biological Assay; Disease Models, Animal; Dizocilpine Maleate; Hyperalgesia; Injections, Spinal; Injections, Subcutaneous; Male; Mice; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Peptide Fragments; Phencyclidine; Receptors, Opioid, mu; Spinal Cord; Substance P

We administered capsaicin or vehicle in 2-day-old rat pups, and for over 6 months examined the rats for damaged skin and for the behaviors of scratching, gnawing and biting their skin. By 35 days of age, all rats in the capsaicin group (n = 10) had damaged skin (i.e., lesions, hair loss and red skin) on the rostral half of their bodies. Skin damage remained prevalent over 6 months, whereas vehicle-treated rats (n = 8) had virtually no skin damage. Gnawing and biting behaviors were rarely observed, however, rats in the capsaicin group frequently scratched themselves. There was a significant positive correlation between the frequency at which rats scratched themselves and the total area of skin damage. Morphine (3.0 mg/kg, i.p.) greatly increased scratching behavior in only the capsaicin-treated rats and naloxone (0.5 mg/kg, i.p.) significantly reduced scratching in these rats. Thus, neonatal capsaicin, in its destruction of the majority of primary afferent C-fibers, is capable of inducing opioid-sensitive scratching behavior.

Topics: Animals; Animals, Newborn; Behavior, Animal; Capsaicin; Disease Models, Animal; Injections, Spinal; Injections, Subcutaneous; Male; Morphine; Naloxone; Nerve Fibers; Rats; Rats, Sprague-Dawley; Self Mutilation; Skin; Substance P

Acute inflammation of the sigmoid wall was induced by perendoscopic injection of formalin (50 microliters, 5%) under brief anesthesia in rats. The procedure was followed by behavioral patterns that significantly differed from those in animals injected with isotonic saline instead of formalin. Analysis of the formalin-induced behaviors allowed for the calculation of a pain score that evolved in a biphasic manner along the 3 h of test. The score was dose-dependently reduced by morphine (0.5-4 mg/kg), and the analgesic effect of the largest morphine dose was abolished by naloxone (2.4 mg/kg). These results suggest that formalin into the sigmoid colon is a new model of visceral pain, presumably through direct irritation at injection site and/or localized acute inflammation of the intestinal wall.

Topics: Acute Disease; Animals; Colitis; Disease Models, Animal; Female; Formaldehyde; Morphine; Naloxone; Pain; Pain Measurement; Palliative Care; Rats; Rats, Sprague-Dawley; Sodium Chloride; Viscera

The possibility that opioid peptides participate in alteration of spinal cord conduction following trauma to the cord was investigated in a rat model using a pharmacological approach. Spinal cord injury was produced in urethane anesthetized animals by a longitudinal incision into the right dorsal horn of T10-11 segments (2 mm deep and 5 mm long). Spinal cord evoked potentials (SCEP) were recorded epidurally from the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral tibial and sural nerves at the ankle. SCEP from both rostral and caudal segments consisted of a small positive peak followed by a high negative peak. Infliction of trauma in untreated rats resulted in an immediate depression of the rostral maximal negative peak (MNP) amplitude. This depression was long-lasting. Later, a significant increase in the latency of the rostral MNP amplitude occurred. Naloxone was administered in a high dosage (10 mg/kg, i.p.) to block mu-, delta- and kappa-opioid receptors 30 min before injury. This drug treatment inhibited the immediate post-injury decrease of the rostral MNP amplitude without any significant effect on latency changes. Measurement of water content in the traumatized spinal cord segment showed a significant reduction in the drug treated animals 5 h after trauma (71.46 +/- 0.54) as compared with untreated controls (74.65 +/- 0.76). However, 1 mg or 5 mg/kg dosages of the drug were not effective in reducing the SCEP changes or edema after injury. These results strongly suggest that blockade of kappa-opioid receptors with high doses of naloxone is important in reduction of trauma induced alteration of SCEP and edema formation in spinal cord injury.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Edema; Evoked Potentials; Male; Naloxone; Neural Conduction; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Spinal Cord Injuries

In this study, the effect of naloxone and mannitol was investigated on focal cerebral ischemia induced by middle cerebral artery occlusion with the transorbital approach in the rabbit model. Rabbits were randomly and blindly assigned to one of three groups (six animals in each): (1) a control group that received equal volumes of physiological saline solution; (2) a naloxone group that received a 5 mg/kg bolus of naloxone i.v. 1 h after occlusion, followed by 2 mg/kg per hour i.v. infusion for 5 h; (3) a mannitol group that received 0.2 g/kg twice with an interval of 10 min at 5 h. The neurological outcome was better in rabbits treated with naloxone than in the others. The ratio of ischemic to total neurons in the cortex was smaller in the naloxone group than in the control and mannitol groups (P < 0.05). In addition, there was a statistically significance reduction in infarct size in the naloxone group compared with the other groups (P < 0.05). Edema was severe in the control and mannitol groups, but moderate in the naloxone group. There was no statistically significant difference in Na+, K+, and water content between groups. Our data provide evidence for the beneficial effects of naloxone on promoting neurological recovery and preserving the ischemic area.

Topics: Animals; Body Water; Brain Ischemia; Cerebral Cortex; Disease Models, Animal; Infusions, Intravenous; Mannitol; Motor Activity; Naloxone; Potassium; Rabbits; Random Allocation; Sodium; Water-Electrolyte Balance

Elevation of plasma corticosterone (PCS) has been used as an indicator of morphine withdrawal, but it is not clear whether the magnitude of elevation is related to the intensity of the dependence. The dose-dependent effects of naloxone on PCS and body weight were studied in male Sprague-Dawley rats rendered physically dependent on morphine by injecting increasing doses of 40-120 mg/kg/day, s.c. twice daily for 1-6 days. Naloxone (0.01-2.0 mg/kg, s.c.) was administered 3 hr after the last morphine administration. Naloxone elevated PCS levels in a dose-dependent manner in all groups treated with morphine, and the elevation was correlated with the number of days of morphine treatment. Naloxone also reduced dose-dependently the body weight in all groups treated with morphine; in this case, a reverse correlation was obtained between the body weight changes and the PCS levels. It was confirmed that PCS elevation is a quantitative sign of naloxone-precipitated morphine withdrawal and that the elevation is indicative of the degree of morphine physical dependence.

Topics: Analysis of Variance; Animals; Body Weight; Corticosterone; Disease Models, Animal; Dose-Response Relationship, Drug; Injections, Subcutaneous; Male; Morphine; Morphine Dependence; Naloxone; Rats; Rats, Sprague-Dawley; Substance Withdrawal Syndrome

Pain associated-anxiety induced by formalin, which resulted in a significant delay in the development of tolerance to morphine antinociception, failed to prevent the development of physical dependence as evidenced by naloxone challenge. Dependence also developed in mice rendered tolerant to morphine. Thus, the development of morphine dependence was observed in the absence and presence of tolerance to morphine antinociception; Our results further confirm the dissociation of opioid tolerance and dependence in the animal model of experimental pain/anxiety.

Topics: Analgesia; Animals; Anxiety; Disease Models, Animal; Drug Tolerance; Formaldehyde; Injections, Intraperitoneal; Injections, Subcutaneous; Male; Mice; Morphine; Morphine Dependence; Naloxone; Pain; Pain Threshold

Topics: Animals; Disease Models, Animal; Evoked Potentials; Indomethacin; Naloxone; Neural Conduction; Nimodipine; Rats; Serotonin Antagonists; Shock, Traumatic; Spinal Cord Injuries

It is well known that opioids regulate luteinizing hormone (LH) secretion through not fully understood mechanisms. This study describes the effects of naloxone on the episodic release of LH in adult sham-operated and pituitary-grafted female rats. Animals were rendered hyperprolactinemic by transplanting 2 pituitary glands beneath the kidney capsule. Naloxone (2 mg/kg/h) or saline (0.5 ml/h) were administered iv through jugular cannulae and subjects were bled at 7 min intervals for a period of 3 h. As expected, pituitary-grafting was followed by an increase in mean values of prolactin during the bleeding period. Naloxone administration decreased mean serum prolactin levels in sham-operated rats and did not further change them in pituitary-grafted animals. Hyperprolactinemia was associated with increases in mean serum LH levels during the bleeding period and in the absolute amplitude of LH peaks. Naloxone administration increased mean values of LH and the absolute amplitude of LH peaks, and decreased their frequency in sham-operated rats. Neither pituitary grafting nor naloxone administration modified the frequency, duration or relative amplitude of LH peaks. However, naloxone administration reduced the mean half-life of LH in sham-operated rats to a similar extent than did pituitary grafting. Naloxone failed to further change the mean half-life of LH in pituitary-grafted rats. These results suggest that opioids modulate the pulsatile pattern of LH and that these effects are blunted in pituitary-grafted animals.

Topics: Analysis of Variance; Animals; Disease Models, Animal; Female; Half-Life; Hyperprolactinemia; Luteinizing Hormone; Naloxone; Pituitary Gland; Prolactin; Pulsatile Flow; Radioimmunoassay; Rats; Rats, Sprague-Dawley

The antinociceptive effect of the octapeptide vapreotide, an analog of somatostatin, was studied after systemic injection in normal mice using the hot plate and abdominal stretching assays, and in normal rats using the paw pressure analgesiometric assay. Vapreotide was ineffective at 1 microgram/kg s.c. in the hot plate test in mice, but 30 min after injection it induced an antinociceptive effect at s.c. injected doses of 8, 64, 512 and 4096 micrograms/kg, with an ED50 of 213 +/- 5 micrograms/kg. For the three highest doses this effect persisted 24 hr after the injection (maximal increase: +80 +/- 23% for 512 micrograms/kg) and disappeared at 48 hr. In the phenylbenzoquinone stretching test, in mice, the ED50 was 186 +/- 6 micrograms/kg (maximal decrease: -63 +/- 5%); the effect persisted 24 hr only for the same two highest doses. Using the paw pressure test, in rats, a dose-dependent increase in paw withdrawal and vocalization thresholds was observed for 21 and 24 hr, respectively, after s.c. injections of 16, 64 and 512 micrograms/kg. Global scores obtained for vocalization thresholds were significantly increased (vs. paw withdrawal thresholds) for 64 and 512 micrograms/kg. Carrageenan-induced nociception in rats was reduced for 21 hr by 64 and 512 micrograms/kg s.c.; scores of the contralateral noninflamed paw were also increased. Vapreotide administered locally in the inflamed paw was inactive. No change in edema volume was obtained after systemic injection of vapreotide.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amino Acid Sequence; Analgesics; Animals; Brain; Disease Models, Animal; Edema; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; In Vitro Techniques; Inflammation; Male; Membranes; Mice; Molecular Sequence Data; Morphine; Motor Activity; Naloxone; Necrosis; Nociceptors; Octreotide; Pain Measurement; Rats; Rats, Sprague-Dawley; Somatostatin; Spinal Cord; Time Factors; Tritium

Morphine, fentanyl and pethidine exhibited a biphasic dose response relationship with respect to their effects on seizure thresholds to bicuculline, pentylenetetrazole, N-methyl-DL-aspartate (NMDLA) and kainic acid in mice. The usual pattern was for low doses to be anticonvulsant and higher doses to be proconvulsant. However this pattern was reversed for fentanyl and pethidine when NMDLA was used to induce seizures. The low dose effects of all three opioid drugs was sensitive to 1 mg kg-1 naloxone in all seizure models. The responses to high doses of pethidine were unaffected or enhanced by this dose of naloxone. Naloxone reversed the effects of the higher doses of morphine and fentanyl in all models except bicuculline induced seizures.

Topics: Analgesics, Opioid; Animals; Anticonvulsants; Bicuculline; Convulsants; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Kainic Acid; Male; Mice; N-Methylaspartate; Naloxone; Pentylenetetrazole; Seizures

Naloxone is an opioid antagonist used frequently in studies of appetite regulation in lean and obese animals and humans. Body condition may affect plasma and tissue distribution of injected naloxone and thus confound interpretation of responses to naloxone in lean compared with obese subjects. The objective of this experiment was to determine the effect of dietary obesity per se on the pharmacokinetic behavior of iv-injected naloxone (3 mg/kg) in lean (46 kg body weight) and dietary obese (77 kg body weight) sheep that were maintained at equilibrium weight. To this end, an HPLC procedure combined with electrochemical detection was developed for measuring naloxone in sheep plasma. Naloxone disappearance from plasma followed an apparent first-order process, the kinetics of which were described best using a two-compartment open model. Components of the biexponential equations describing the plasma concentration (C)-time (t) curves for naloxone disappearance in lean (Ct = 1814e(-0.190t) + 413e(-0.017t)) and obese (Ct = 2282e(-0.282t) + 573e(-0.018t)) sheep were similar (p > 0.05). Mean (+/- SE) elimination half-lives for naloxone in lean (42.7 +/- 4.6 min) and obese (44.3 +/- 10.2 min) sheep were similar (p > 0.05). Volume of distribution of naloxone (Vd) was extensive but also similar (p > 0.05) in lean (5.6 +/- 0.9 L/kg) and obese (4.1 +/- 0.6 L/kg) sheep. Naloxone was distributed extensively throughout the body fluids and trapped or stored in significant amount in extravascular tissues because the naloxone Vd greatly exceeded 100% of body weight in both lean (557 +/- 86 mL/100 g) and obese (413 +/- 58 mL/100 g) sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Body Fluid Compartments; Chromatography, High Pressure Liquid; Diet; Disease Models, Animal; Female; Naloxone; Obesity; Sensitivity and Specificity; Sheep

Opiate withdrawal is a common occurrence in human opiate addicts that is no life threatening but is hypothesized to be a significant factor which may contribute to drug taking behavior in these opiate dependent individuals. The purpose of this study was to compare the time course for the development of tolerance, dependence and abstinence using a rat model. Rats were made dependent by implantation of 2 morphine pellets s.c. (75 mg morphine base). Morphine implanted rats exhibited analgesia as measured in a tail-dip assay, for up to 12 h post-implant after which the development of tolerance resulted in tail-flick latencies returning to the level of control rats. Withdrawal was evaluated by injection of the opiate antagonist, naloxone (1 mg/kg s.c.). Rating of the abstinence syndrome revealed significant withdrawal signs by 3 h post-implant which became increasingly intense up to 24 h post-implant. Withdrawal could be precipitated for at least 13 days post-implant, while by 18 days post-implant almost no abstinence signs were observed. Plasma morphine levels following implantation of 2 pellets remained relatively stable from 3-12 days post-implantation. These results further extend the characterization of opiate abstinence following subcutaneous pellet implantation. These results also suggest that opiate abstinence develops within the first 24 h and follows the time course of the development of tolerance. The characterization of the evolution of opiate tolerance, physical dependence and abstinence under similar experimental conditions is critical to the design of future studies to examine the neural bases for these phenomena.

Topics: Analgesia; Animals; Delayed-Action Preparations; Disease Models, Animal; Drug Implants; Drug Tolerance; Injections, Subcutaneous; Male; Morphine; Naloxone; Pain Measurement; Rats; Rats, Sprague-Dawley; Rats, Wistar; Substance Withdrawal Syndrome; Substance-Related Disorders

The house musk shrew Suncus murinus recently has been introduced for the study of emesis. We investigated the emetic effects of the opioids morphine (0.1-21.5 mg/kg i.p.) and loperamide (0.01-10 mg/kg i.p.) and found a complete lack of emetogenic potential. Nicotine, however, dose dependently induced vomiting in the Suncus with an ED50 of 8.8 mg/kg s.c. and a 100% incidence at 20 mg/kg. This drug-induced vomiting was reduced by morphine or loperamide: ED50 values obtained were 1.2 mg/kg i.p. for morphine and 0.7 mg/kg i.p. for loperamide. Naloxone (2 mg/kg s.c.) antagonised the inhibitory effect of morphine (2 mg/kg i.p.) or loperamide (10 mg/kg i.p.). Serotonin (20 mg/kg s.c.) had less reliable emetogenic potency than nicotine in the Suncus with incidences between 50 and 100%. However, the serotonin-induced vomiting was abolished by morphine and loperamide and this inhibition was antagonised by naloxone. These results suggest that systemically administered opioids are pure antiemetics in Suncus murinus in contrast to other animal models and man. Naloxone antagonism indicates that this antiemetic effect is mediated by opioid receptors.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Injections, Intraperitoneal; Injections, Subcutaneous; Loperamide; Male; Morphine; Naloxone; Nicotine; Serotonin; Serotonin Antagonists; Shrews; Vomiting

To clarify the relationship between changes in haemodynamics, liberation of tumour necrosis factor and generation of plasma kallikrein, and to see if treatment with a combination of drugs was successful in preventing activation of tumour necrosis factor and plasma kallikrein in experimental endotoxic shock.. Controlled study.. 22 juvenile pigs.. 15 animals received 0.01 mg/kg endotoxin infusion, the rest being given the same volume of saline. 10 received no treatment, and 5 were given a combination of methylprednisolone, naloxone, ketanserin, promethazine, C1 esterase inhibitor, antithrombin III and aprotinin.. Assessment of the liberation of tumour necrosis factor, generation of plasma kallikrein, and haemodynamic and cellular effects of endotoxaemia.. There was a linear statistical relationship between decreases in cardiac output and increases in packed cell volume, and between increases in packed cell volume and plasma kallikrein activity. The combination treatment totally blocked all the effects of the infusion of endotoxin.. Endotoxin affects several mediators, but combination treatment can prevent some of these effects.

Topics: Animals; Disease Models, Animal; Drug Therapy, Combination; Escherichia coli Infections; Hemodynamics; Kallikreins; Ketanserin; Methylprednisolone; Naloxone; Promethazine; Protease Inhibitors; Shock, Septic; Swine; Tumor Necrosis Factor-alpha

The purpose of this study was to determine the effects of naloxone on systemic hemodynamics and reflex function in dogs with congestive heart failure induced by rapid pacing.. We have shown previously that naloxone, an opiate receptor antagonist, improves cardiac output, aortic blood pressure, systolic performance and the baroreflex function in conscious dogs with chronic right-sided congestive heart failure. However, whether endogenous opioids also play a role n mediating the reduction of myocardial and baroreflex function in animals with left heart failure remains controversial.. We administered naloxone (1 mg/kg body weight) and normal saline solution to 15 dogs with pacing-induced congestive heart failure (225 beats/min for 8 weeks) and 11 control dogs. In addition to systemic hemodynamic measurements, the slope of pressure-area relation obtained from echocardiography with intravenous bolus injection of phenylephrine was taken as a load-independent index of myocardial contractility. Baroreflex function was estimated by the slope of the regression line relating systolic aortic pressure and RR interval.. Plasma beta-endorphin levels were elevated in dogs with congestive heart failure. Naloxone administration increased heart rate, mean aortic pressure, first derivative of left ventricular pressure, cardiac output and myocardial contractility in pacing-induced congestive heart failure. These changes correlated significantly with basal plasma beta-endorphin levels and were accompanied by increases in plasma beta-endorphin and catecholamines after naloxone administration. However, unlike the hemodynamic and cardiac effects of naloxone, baroreflex function did not change after naloxone in dogs with congestive heart failure.. The increase in basal plasma beta-endorphin suggests that the endogenous opiate system is activated in left-sided congestive heart failure. Because naloxone improves the systemic hemodynamics and myocardial contractile function under this condition, the endogenous opioids appear to play an important role in mediating the myocardial depression that occurs in heart failure. However, the endogenous opiate system has no apparent effect on the regulation of baroreflex control in heart failure induced by rapid pacing.

Topics: Animals; Baroreflex; beta-Endorphin; Disease Models, Animal; Dogs; Epinephrine; Heart Failure; Hemodynamics; Myocardial Contraction; Naloxone; Narcotic Antagonists; Norepinephrine; Ventricular Function, Left

A course injection of Rhodiola rosea extract for eight days was reported to increase the resistance of experimental animals to adrenalin- or CaCl2-induced arrhythmias. Preliminary injection of naloxone in a dose of 0.5 mg/kg eliminated the antiarrhythmic effect of Rhodiola. Indomethacin had no effect the antiarrhythmic action of Rhodiola. The antiarrhythmic effect of Rhodiola course injections was assumed to be associated with the induction of opioid peptides biosynthesis.

Topics: Animals; Anti-Arrhythmia Agents; Calcium Chloride; Cardiac Complexes, Premature; Disease Models, Animal; Drug Evaluation, Preclinical; Epinephrine; Indomethacin; Male; Naloxone; Plant Extracts; Rats; Rats, Wistar; Ventricular Fibrillation

A rat model of infravesical outflow obstruction was modified to allow cystometric investigation in conscious, free-moving animals after intrathecal drug administration. The catheter position and extent of drug distribution were controlled by injection of dye and dissection of the spinal canal. Continuous cystometries were performed in awake normal rats as well as rats with bladder hypertrophy and hyperactivity following infravesical outflow obstruction. In some animals of each group, cystometry was performed with simultaneous recording of intra-abdominal pressure. The possible effects of the presence of the intrathecal catheter were studied, as well as the effects of saline, local anesthetics, morphine and naloxone administered through the catheter. Neither the presence of the intrathecal catheter nor injection of saline affected the cystometric pattern. Bupivacaine (50 micrograms) produced paralysis of both lower extremities and a complete, though reversible, suppression of micturition in normal rats. In rats with hypertrophy, intrathecal bupivacaine in doses of 50 micrograms and 100 micrograms produced decreases in micturition pressure, increases in bladder capacity and dribbling incontinence. However, the amplitude of spontaneous contractile activity increased after the administration. The inhibitory effects of morphine (0.5-10 micrograms) on micturition in normal rats, which were rapidly reversed by naloxone, were in accordance with results obtained in previous studies in anesthetized animals. Rats with bladder hypertrophy showed a similar response to morphine and naloxone. However, the bladder hyperactivity was not inhibited by morphine. We conclude that the present model seems reliable for the study of spinal mechanisms in the development of detrusor instability associated with infravesical outflow obstruction.

Topics: Animals; Bupivacaine; Disease Models, Animal; Female; Hypertrophy; Injections, Spinal; Morphine; Muscle Contraction; Muscle, Smooth; Naloxone; Rats; Rats, Sprague-Dawley; Spinal Cord; Urinary Bladder; Urinary Bladder Neck Obstruction

This study evaluated the antinociceptive effects of systemically administered selective opioid agonists of mu (DAMGO), delta (BUBU) and kappa (U 69593) receptors on the vocalization threshold to paw pressure in a rat model of peripheral unilateral mononeuropathy produced by loose ligatures around the common sciatic nerve. DAMGO (0.5-2 mg/kg), BUBU (1.5-6 mg/kg) and U 69593 (0.75-3 mg/kg) injected intravenously (i.v.) produced a potent long-lasting antinociceptive effect on both hind paws. The effects on the lesioned paw were clearly and statistically more potent than for the non-lesioned paw. The selective antinociceptive effect of 2 mg/kg DAMGO, 3 mg/kg BUBU and 1.5 mg/kg U 69593 were completely prevented by prior administration of the appropriate antagonists: 0.1 mg/kg naloxone, 1 mg/kg naltrindole and 0.4 mg/kg MR 2266. The present data clearly show that an acute i.v. injection of these selective opioid agonists induces potent antinociceptive effects in a rat model of peripheral neuropathy. These data are discussed with regard to the classical view that there is opioid resistance in neuropathic pain.

Topics: Analgesics; Animals; Benzeneacetamides; Benzomorphans; Disease Models, Animal; Drug Interactions; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Male; Naloxone; Naltrexone; Narcotic Antagonists; Oligopeptides; Pain; Pain Measurement; Pain Threshold; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Vocalization, Animal

The effects of opiate and non-steroidal anti-inflammatory agents on the in vitro canine ureter were compared using a new model for the assessment of ureteric pharmacology. A pressure measuring catheter attached to a pressure transducer and pre-calibrated pen recorder was ligated into the lumen of 2.5 cm segments of normal canine ureter. The segments were immersed in an organ bath at physiological pH and temperature and spontaneous contractility was observed in 90% of them. Morphine had a spasmogenic effect on ureteric activity which was unaffected by naloxone. This effect was similar to that of histamine and prostaglandin F2 alpha and was abolished by chlorpheniramine but not by cimetidine. Pethidine produced a transient stimulation followed by inhibition of ureteric activity which was unaffected by naloxone. Both indomethacin and diclofenac produced an abrupt inhibition which was reversible with prostaglandin F2 alpha. These data suggest that pethidine or a non-steroidal anti-inflammatory agent may by virtue of their spasmolytic effects be a superior choice of therapy for the acutely obstructed ureter.

Topics: Acute Disease; Animals; Anti-Inflammatory Agents, Non-Steroidal; Colic; Disease Models, Animal; Dogs; Dose-Response Relationship, Drug; Histamine; In Vitro Techniques; Morphine; Muscle Contraction; Muscle, Smooth; Naloxone; Ureter; Ureteral Diseases

The antiarrhythmic properties of the opiate antagonist naloxone have been reported in a variety of models of arrhythmia. To determine the generality and the possible central involvement of its antiarrhythmic activity, the effects of naloxone were assessed against cardiac arrhythmias induced by intravenous bolus injections of picrotoxin. Naloxone at doses of 0.33 and 1 mg/kg significantly reduced the incidence and severity of picrotoxin-induced arrhythmias in a dose-related manner, without alteration of blood pressure and heart rate. The results demonstrate the antiarrhythmic efficacy of naloxone in an additional animal model. They further suggest that the antiarrhythmic actions of naloxone may be mediated by the central nervous system via both the autonomic and GABAergic pathways.

Topics: Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Chi-Square Distribution; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Electrocardiography; Female; Incidence; Male; Naloxone; Picrotoxin; Rats; Rats, Inbred Strains

The potential effect of intracerebroventricular (icv) alpha N-acetyl human beta-endorphin-(1-31) on morphine dependence was examined in mice and rats. Animals were rendered tolerant-dependent by subcutaneous (sc) implantation of an oily suspension (10 ml/Kg mouse and 3 ml/Kg rat) containing 0.1 g/ml of morphine. After 72 h of chronic morphine, 1 mg/Kg sc naloxone precipitated in both species a withdrawal syndrome that was moderate in animals pretreated with the acetylated derivative of beta-endorphin. Doses of 28 fmols/rat or 80 fmols/mouse alpha N-acetyl human beta-endorphin-(1-31) reduced the number of animals presenting the jumping behaviour, as well as the number of jumps recorded. Moreover, less than half of the rats presented the other withdrawal signs evaluated: squeak on touch, diarrhoea, chattering, chewing, ptosis and body shakes. This activity could be observed when alpha N-acetyl human beta-endorphin was injected 1 h to 24 h before naloxone; longer intervals resulted in a significant loss of this activity. The alpha 2 agonist clonidine given icv at pmol-nmol doses decreased the incidence of morphine withdrawal syndrome. Combinations of these two substances generally did not produce any further enhancement of the effects of clonidine and alpha N-acetyl beta-endorphin when used alone. Icv injections of the antagonist of alpha 2-adrenoceptors yohimbine prevented both clonidine and alpha N-acetyl beta-endorphin-(1-31) from reducing the jumping behaviour displayed by morphine-abstinent mice. It is suggested that alpha N-acetyl beta-endorphin produces this alleviation of the morphine withdrawal syndrome by improving the efficiency of alpha 2-mediated agonist effects after acting on a neural substrate that is distinct from the mu opioid receptor binding site.

Topics: Animals; beta-Endorphin; Clonidine; Disease Models, Animal; Male; Mice; Morphine; Naloxone; Rats; Rats, Inbred Strains; Substance Withdrawal Syndrome; Yohimbine

The results of treatment with thyrotropin-releasing hormone (TRH), naloxone and dexamethasone treatments albino rats with experimental spinal cord injury were compared. All the animals were made paraplegic by the application clip method of Rivlin and Tator. Treatment was administered i.p. as bolus injections in two doses, at 45 and 120 min after the injury. Animals were allocated randomly to four experimental groups: (1) TRH (0.6 mg per dose), (2) naloxone (0.8 mg per dose), (3) dexamethasone (0.6 mg per dose), and (4) control (saline). TRH-treated rats showed significantly better histopathological scores than either naloxone or dexamethasone-treated ones (Kruskal Wallis: 24.058 P less than 0.001).

Topics: Animals; Dexamethasone; Disease Models, Animal; Injections, Intraperitoneal; Male; Naloxone; Random Allocation; Rats; Rats, Inbred Strains; Spinal Cord; Spinal Cord Injuries; Thyrotropin-Releasing Hormone

The aim was to evaluate the effects of an opiate agonist (U50,488H) and an opiate antagonist (naloxone) in myocardial ischaemia.. A left thoracotomy was performed and the left coronary artery was ligated in adult Sprague-Dawley rats of either sex (350-400 g). Blood pressure, heart rate and electrocardiogram were measured before and after injections of U50,488H or naloxone and throughout the 30 min postligation period.. Following coronary artery occlusion, all rats in the control group developed arrhythmias, bradycardia, and hypotension. U50,488H potentiated and naloxone attenuated the ischaemia induced arrhythmias, bradycardia, and hypotension.. The potentiating and blocking effects of U50,488H and naloxone, respectively, suggest that endogenous opioid peptides are involved in the pathophysiology of myocardial ischaemia and play an important role in ischaemic heart disease.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Arrhythmias, Cardiac; Blood Pressure; Coronary Disease; Disease Models, Animal; Female; Heart Rate; Male; Naloxone; Pyrrolidines; Rats; Rats, Inbred Strains

Stress is an important risk factor in cardiovascular diseases, including hypertension. Endogenous opioids are known to be elevated in stress and in various models of hypertension with differing etiologies. Blockade of endogenous opioids with naloxone has been demonstrated to attenuate or reverse the elevation in blood pressure in both renovascular and spontaneous hypertension. In the current study, increased blood pressure was induced using a model of psychosocial stress. During the first week of stress, systolic blood pressure rose rapidly to reach a level that was sustained throughout the remaining period of stress. Chronic infusion of the opiate antagonist, naloxone, both prevented and completely reversed the elevated blood pressure due to psychosocial stress. These data demonstrate that elevated endogenous opioids are important factors in cardiovascular regulation and are likely to influence both the development and maintenance of stress-induced hypertension.

Topics: Animals; Blood Pressure; Disease Models, Animal; Endorphins; Hypertension; Male; Naloxone; Rats; Rats, Inbred Strains; Stress, Psychological

Chronic L-DOPA treatment of Parkinson's disease frequently leads to the development of motoric overstimulation and hyperkinetic movements. To investigate this problem in the laboratory, rats surgically altered by unilateral 6-hydroxydopamine lesions (6-OHDA) were chronically treated with one L-DOPA (10 mg/kg i.p.) injection per day for 20 days. In this 6-OHDA rotation model, the unilateral dopamine denervation results in a profound contralateral sensory-motor neglect and the animals spontaneously rotate in a direction ipsilateral to the dopamine depleted hemisphere. Initially, the L-DOPA treatment did not alter the response bias but after several weeks, the response bias was reversed and the animals rotated in the formerly akinetic direction, contralaterally, at a significantly higher level. Using this overstimulation effect as an analogue of the clinically observed L-DOPA overstimulation, animals were given naloxone in conjunction with the L-DOPA treatment. Naloxone (0.10, 0.25 and 0.50 mg/kg i.p.) produced a dose related decrease in the L-DOPA induced contralateral rotation. Consistent with an expected selective effect on the L-DOPA induced rotation, a dose related increase in ipsilateral rotation was observed. These results suggest that naloxone can attenuate the overstimulation effect of L-DOPA and that this effect is not attributable to non-specific response suppression effects.

Topics: Animals; Carbidopa; Chromatography, High Pressure Liquid; Disease Models, Animal; Dopamine; Dose-Response Relationship, Drug; Drug Administration Schedule; Dyskinesia, Drug-Induced; Hydroxydopamines; Levodopa; Male; Mesencephalon; Naloxone; Oxidopamine; Parkinson Disease; Rats; Rats, Inbred Strains; Time Factors

The current study investigates the action of anxiolytics, antidepressants, neuroleptics, antipyretics, muscle relaxants, antihypertensives and naloxone in a novel animal model of anxiety, based on the evidence that mice removed last from their cage develop hyperthermia (stress-induced hyperthermia, SIH) when compared to those removed first. Alprazolam (0.15-0.6 mg/kg), chlordiazepoxide (25 mg/kg), estazolam (1 mg/kg), phenobarbital (20 mg/kg), ethanol (2 and 4 g/kg), buspirone (5 and 10 mg/kg) and prazosin (1 and 2 mg/kg), as well as repeatedly administered diazepam (5 mg/kg), inhibited SIH. In contrast, tofisopam (12.5-200 mg/kg), desipramine (15 and 30 mg/kg), amitriptyline (10 mg/kg), fluoxetine (10 and 20 mg/kg), tranylcypromine (5 and 10 mg/kg), chlorpromazine (1 and 2 mg/kg), clozapine (2 and 4 mg/kg), pimozide (0.5 and 1 mg/kg), l-sulpiride (15 and 30 mg/kg), l-propranolol (5 and 10 mg/kg), acetyl salicylic acid (200 and 400 mg/kg), indomethacin (2.5 and 5 mg/kg), verapamil (2.5 and 5 mg/kg), captopril (25 and 50 mg/kg), dantrolene (10 and 20 mg/kg), mephenesin (300 and 600 mg/kg), d-amphetamine (1 and 4 mg/kg) and naloxone (2.5 and 15 mg/kg) were inactive, as were 10 mg/kg imipramine, amitriptyline and fluoxetine injected every day for 21 days. Reserpine at high doses (1.25 and 2.5 mg/kg) but not at a lower dose (0.62 mg/kg) prevented SIH, but in this case animals showed a behavioural syndrome which could have interfered with the occurrence of the hyperthermia.

Topics: Animals; Anti-Anxiety Agents; Anti-Inflammatory Agents, Non-Steroidal; Antidepressive Agents; Antipsychotic Agents; Anxiety; Benzodiazepines; Body Temperature; Disease Models, Animal; Male; Mice; Naloxone

A study of the dose-response effects of naloxone and methylprednisolone after rat ventral spinal cord injury is presented. The spinal cord injury model used herein is unique in that it results in a ventral compression of the spinal cord without the need for a prior laminectomy. This allows for a close approximation of the human clinicopathological situation. There was a statistically significant positive effect on neurological outcome with a naloxone dose of 2.5 mg/kg, whereas higher and lower doses yielded little or no influence on outcome. Methylprednisolone was observed to offer similar results. These results, however, did not achieve statistical significance. The early administration of moderately high doses (45-60 mg/kg), however, offered the best results. The responses to the treatment regimens presented here offer hope for spinal cord injury victims. The observed dose-response relationships indicate that erroneous conclusions may arise from studies using inappropriate doses of narcotic antagonists, as well as other drugs.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Methylprednisolone; Naloxone; Paraplegia; Rats; Rats, Inbred Strains; Spinal Cord Injuries; Spinal Fractures

Inoculation of the right hind paw with Mycobacterium butyricum led to an inflammation reflected in a reduction in the threshold to respond to noxious pressure. Chronic perfusion of naloxone at a 'high' dose of 3.0 mg/kg/hr blocked the antinociceptive action of the mu-agonist, morphine, and the kappa-agonist, U69 593. In contrast, a 'low' dose of 0.16 mg/kg/hr antagonized the action only of morphine. Two days postimplantation, the hyperalgesia to pressure was potentiated in rats receiving the high, but not the low dose of naloxone. At 6 days, this difference was no longer seen. At 7 days, pumps were removed; one day later, in rats which had been receiving the high, (but not low) dose of naloxone, thresholds on the inflamed paw no longer differed from those on the uninflamed paw. This may reflect supersensitivity to an endogenous opioid. The data suggest that kappa-receptors may contribute to control of nociception in inflammatory pain. However, this role does not appear to be essential.

Topics: Animals; Benzeneacetamides; Disease Models, Animal; Inflammation; Male; Morphine; Mycobacterium Infections; Naloxone; Nociceptors; Pain; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid

In an experimental model of mononeuropathy in the rat, created by 4 ligatures around the sciatic nerve, i.v. naloxone 1 week after surgery induces bidirectional effects (antinociceptive effects at very low doses, hyperalgesic effects with high doses). Using the same nociceptive test (vocalization thresholds to paw pressure), the activity of the same doses of naloxone (3 micrograms/kg, and 1 mg/kg) was investigated 2 weeks after sciatic ligation, when the behavioural pain-related disorders are at a maximum. Three micrograms/kg naloxone produced a significant antinociceptive effect on the lesioned and non-lesioned paw, which was clearly related to the degree as well as to the duration of pain-related signs in the rat. By contrast, the high dose of naloxone did not induce a mean significant effect when tested on either paw; however, it elicited a potent hyperalgesic effect in those rats which had recovered from hyperalgesia at this 2 week time point after the sciatic injury.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Naloxone; Pain; Peripheral Nervous System Diseases; Rats; Rats, Inbred Strains; Vocalization, Animal

The effect of the dosage and timing of administration of naloxone after spinal cord injury in rats via the ventral compression technique is presented. The rat ventral compression technique allows for a ventral compression of the spinal cord without the requirement of a previous laminectomy. It therefore facilitates the creation of an experimental lesion that is similar to that observed in the human clinicopathological situation. The first part of the two-part study presented herein involved the determination of the optimal dose of naloxone, administered intraperitoneally 45 minutes after the creation of the lesion. Of the groups studied (control group through 10.0 mg/kg group), 2.0 mg/kg of naloxone proved to be superior to both lesser and greater dosages. The second part of the study involved the administration of a 2.0 mg/kg dose of naloxone at varying intervals ranging from 10 minutes before lesioning to 24 hours after lesioning. A multiphasic response was again demonstrated, with an optimal time of administration occurring 45 minutes after the creation of the lesion. A significant effect was offered by a midrange dose of naloxone (2.0 mg/kg), administered at 45 minutes after injury (P less than 0.02 by analysis of variance and Duncan's multiple range test). These findings are discussed with respect to recent evidence regarding the effects of narcotic antagonists on both mu and kappa narcotic receptors. Past and future experiments must account for these responses to multiphasic dosage and timing of administration. Failure to do so may lead to erroneous conclusions.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Naloxone; Nervous System; Rats; Rats, Inbred Strains; Spinal Cord Compression; Spinal Cord Injuries

In this study we determined if endogenous opioid peptides may contribute to the depression of ventilation seen in dystrophic hamsters. Ventilation of control and dystrophic awake hamsters was determined prior to either naloxone (1 mg/kg) or saline administration and then 5, 15 and 30 minutes postinjection. Subsequently, animals were exposed to a hypercapnic challenge (7% CO2 in O2). Control hamsters increased ventilation significantly (p less than 0.01) after naloxone compared to saline treatment. In contrast, dystrophic hamsters showed no difference in ventilation when they received either naloxone or saline. Both groups increased ventilation significantly (p less than 0.05) after hypercapnic challenge, whether they had received naloxone or saline. Although dystrophic hamsters can respond to a ventilatory stimulant (CO2), naloxone did not increase ventilation, possibly indicating that endogenous opioids are not responsible for their depressed ventilation.

Topics: Animals; Carbon Dioxide; Cricetinae; Disease Models, Animal; Endorphins; Male; Mesocricetus; Muscular Dystrophy, Animal; Naloxone; Respiratory Mechanics

There are numerous reports of a temporal relationship between LH secretion and a subsequent flushing response in menopausal women. We have developed a morphine-dependent animal model to study the mechanisms of the hot flush. Administration of naloxone to these animals results in a surge in LH secretion which precedes the elevation in tail skin temperature (TST). In the present study, we utilized central administration of an LH-RH agonist and antagonist to evaluate the skin temperature response in our animal model. Ovariectomized female rats were fitted with unilateral cannula in the lateral ventricle (LV). One week later these animals were midly restrained to allow for continuous measurement of tail skin temperatures (TST). Central administration of naloxone was without effect in controls but produced a 5-6 degree C rise of TST in the morphine-dependent rat while central administration of 10 microliters of the saline vehicle produced no changes in TST in either group. A similar increased sensitivity to LH-RH was observed in morphine-dependent rats. Administration of 5 or 10 micrograms of the LH-RH agonist (Des-Gly10, [im-Bzl-D-His6]LH-RH ethylamide) into the LV produced a significantly greater elevation in TST (4 degrees C) in the morphine-dependent rats compared to a negligible rise in TST in the control rats; however, administration of a larger dose of 20 micrograms of the LH-RH agonist produced similar TST responses of about 4 degrees C in both groups. Intravenous administration of the LH-RH agonist (10 micrograms) was ineffective in producing any temperature effect in morphine-dependent rats. Thus, it appears that the morphine-dependent rat is more sensitive to the LH-RH agonist and the temperature response is mediated by a central mechanism which is similar to that observed following administration of a dose of naloxone. In a subsequent study central administration of the LH-RH agonist (5 micrograms/10 microliters) resulted in a similar rise in serum LH in both control and morphine-dependent rats, suggesting that the elevation in TST is not closely associated with LH secretion. Further support for a role of LH-RH in our animal model was obtained following central administration of an LH-RH antagonist [( D-Phe2.6, Pro3]LH-RH) which blocked the rise in TST associated with systemic administration of naloxone (1 mg/kg, s.c.) in morphine-dependent rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Animals; Body Temperature Regulation; Climacteric; Disease Models, Animal; Female; Gonadotropin-Releasing Hormone; Morphine; Naloxone; Rats; Substance Withdrawal Syndrome

Guinea pigs given naloxone hydrochloride, 15 mg/kg subcutaneously (s.c.) 2 h after a single dose of morphine sulphate, 15 mg/kg s.c. exhibit a withdrawal response which is characterized by a marked increase in locomotor activity. In this study the effects of haloperidol on the morphine locomotor withdrawal response of guinea-pigs were investigated. Locomotor activity was measured in a cage fitted with a single infra-red photocell and detector. Haloperidol, at a dose of 1 mg/kg, s.c., given 0.5 h prior to administration of naloxone slightly enhanced the morphine locomotor withdrawal response, and at a dose of 10 mg/kg, markedly enhanced the response. Chronic pretreatment of guinea pigs with haloperidol, 1 mg/kg, daily for 21 days did not alter the locomotor withdrawal response. It remains to be established whether the enhancement by haloperidol of the opiate withdrawal response is a functional reflection of its interaction with dopamine, sigma or other receptors.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Guinea Pigs; Haloperidol; Male; Morphine; Motor Activity; Naloxone; Substance Withdrawal Syndrome; Time Factors

1. The effects of morphine withdrawal were evaluated in vitro by monitoring the actions of naloxone on the depolarization-induced release of [3H]-noradrenaline (NA) in cortical slices taken from naïve or dependent rats. The effects of dihydropyridine molecules acting on Ca2+-channels (nimodipine and Bay K 8644) were also studied in this model. 2. Naloxone (10(-8)-10(-5) M) dose-dependently enhanced the K+ induced release of [3H]-NA in slices taken from dependent rats, but failed to modify the [3H]-NA release from 'naïve' slices. 3. The naloxone-induced potentiation of release was significantly reversed by nimodipine (10(-8)-10(-6) M). These doses of nimodipine did not change [3H]-NA release (both basal and K+ induced) in preparations obtained from naïve rats. 4. Bay K 8644 potentiated the K+-induced [3H]-NA release from cortical slices taken from naïve rats to a similar extent as that of naloxone in dependent rats. 5. These results suggest that the naloxone potentiation of the depolarization-induced [3H]-NA release in slices taken from dependent rats may be considered a model of morphine withdrawal in vitro. In this model dihydropyridine Ca2+-channel antagonists suppress morphine-withdrawal effects in a similar manner to observations made in vivo.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Calcium; Cerebral Cortex; Dihydropyridines; Disease Models, Animal; In Vitro Techniques; Ion Channels; Morphine; Naloxone; Nimodipine; Norepinephrine; Rats; Substance Withdrawal Syndrome; Tritium

Inoculation of the right hind paw with Mycobacterium butyricum rapidly led to swelling and inflammation. The afflicted limb showed an enhanced sensitivity to noxious pressure (hyperalgesia) and a reduced sensitivity to noxious heat 24 h following treatment. Both naloxone and MR 2266 (which has greater activity at kappa-opioid receptors) further increased the sensitivity to pressure (that is, potentiated the hyperalgesia) but did not affect the response to heat. They did not affect the response of the uninflamed paw. At 1 week, only MR 2266 was effective. At both 24 h and 1 week, the inflamed paw showed pronounced supersensitivity to the antinociceptive action of morphine against noxious pressure. At both 24 h and (to a greater extent) 1 week, a rise in levels of immunoreactive (ir)-dynorphin (DYN) was seen in the ipsilateral dorsal horn of the lumbar spinal cord. There was no alteration in the contralateral dorsal horn or in either ventral horn. Furthermore, levels of ir-met-enkephalin (ME) and ir-leu-enkephalin (LE) were unaffected. There was no difference in the density of mu-, delta- or kappa-binding sites in any part of the lumbar cord, at either 24 h or 1 week, between ipsilateral and contralateral tissue. By 3 and 5 weeks postinoculation, the symptoms had spread to the contralateral hind limb and ir-DYN was elevated in the contralateral dorsal horn and the ipsilateral ventral horn. At 5 weeks, levels of ir-ME and ir-LE also were increased in the ipsilateral and contralateral dorsal horns, but not in the contralateral ventral horn. Furthermore, levels of ir-DYN were increased in the cervico-thoracic spinal cord, and rats displayed adrenal hypertrophy and a rise in plasma levels of ir-beta-endorphin (beta-EP). These data indicate: (1) Peripheral inflammation localized to a single limb selectively modifies levels of ir-DYN in ipsilateral dorsal horn. The effect is specific to DYN as compared to ME and LE. The density of mu-, delta-, or kappa-receptors in the lumbar spinal cord is unmodified. (2) The altered response to opioid agonists and antagonists shown by rats with an inflamed limb may be selective to the injured tissue. (3) Alterations in opioid systems associated with unilateral hind limb inflammation may not be exclusively chronic in nature: they appear very rapidly (within 24 h) of the induction of pain. With time, the contralateral limb becomes affected and, eventually, the effects resemble those seen with generalized polyarthritis.

Topics: Animals; Benzomorphans; Disease Models, Animal; Dynorphins; Endorphins; Hindlimb; Inflammation; Male; Naloxone; Pain; Rats; Rats, Inbred Strains; Receptors, Opioid; Spinal Cord

This study evaluated the effects of naloxone hydrochloride in the treatment of Escherichia coli-induced shock in baboons. The baboons were studied for 12 hours and monitored for survival times. All baboons were intravenously infused for two hours with E coli and treated as follows: group 1, E coli (control); group 2, E coli plus naloxone hydrochloride, 0.5 mg/kg bolus plus 0.5 mg/kg/h for 9.5 hours; and group 3, E coli plus naloxone hydrochloride, 2.0 mg/kg bolus plus 2.0 mg/kg/h for 3.8 hours. Naloxone was administered after arterial pressure had reached the nadir (more than two hours following initiation of E coli infusion). Mean arterial pressure was supported by the lower dose of naloxone; however, sustained leukopenia and neutropenia were not reversed by its infusion. Naloxone prevented the increase in plasma beta-endorphin level and blunted the increase in plasma cortisol level. Despite these effects, naloxone did not prevent multiple-organ disease and did not decrease mortality.

Topics: Animals; beta-Endorphin; Blood Pressure; Blood Urea Nitrogen; Creatinine; Disease Models, Animal; Drug Evaluation, Preclinical; Escherichia coli Infections; Female; Heart Rate; Hydrocortisone; Injections, Intravenous; Male; Monitoring, Physiologic; Naloxone; Papio; Sepsis; Shock, Septic; Time Factors

The cardiovascular and metabolic responses to treatment with naloxone or buprenorphine (a partial opiate agonist) were investigated in a porcine model of septicaemia. Animals anaesthetised with alpha-chloralose were infused with live E. coli over two hours. They were then divided into three groups and received either naloxone (2 mg kg-1 + 1.5 mg kg-1 hr-1) or buprenorphine (0.3 mg kg-1) or an equivalent volume of normal saline. Treatment was started one hour after commencing the infusion, by which time a significant fall in cardiac index (CI), stroke index (SI), mean arterial pressure (MAP), and pH had occurred in all groups, together with a significant rise in mixed venous blood lactate and packed cell volume. Treatment with both naloxone and buprenorphine resulted in significant improvements in CI, pH, and base excess and in a fall in mixed venous lactate and packed cell volume. Although no significant effect on survival was seen at three hours after the start of treatment, buprenorphine may prove to be a suitable alternative to naloxone in the management of septic shock.

Topics: Animals; Blood Pressure; Buprenorphine; Cardiac Output; Disease Models, Animal; Erythrocyte Indices; Escherichia coli Infections; Female; Lactates; Naloxone; Shock, Septic; Swine

We have previously described the paradoxical antinociceptive effect of low doses of an opiate antagonist, naloxone, in rats suffering from chronic arthritis induced by Freund's adjuvant. In the present work, the appearance of this naloxone sensitivity was studied, using a model of inflammatory hyperalgesia with a more rapid onset, namely carrageenin-induced rat paw edema. In these animals, an extremely low dose of naloxone (3 micrograms/kg i.v.), induced a clear antinociceptive effect (as gauged by the vocalisation threshold to paw pressure), which was observed for both the edematous and the contralateral hind-paw. Small and transient 1 h after carrageenin injection, this effect increased progressively 4 h and 24 h later, reaching a level comparable to that observed with morphine 1 mg/kg i.v. in normal rats, at 24 h. Electrophysiological studies performed in parallel, confirmed the behavioural data so that 24 h after the injection of carrageenin, naloxone (3 micrograms/kg i.v.) reduced the VB thalamic neuronal responses elicited by stimulation of the inflamed paw by 50%. Hypothesis concerning the mechanisms of the paradoxical action of naloxone in models of inflammatory hyperalgesia are discussed.

Topics: Action Potentials; Animals; Carrageenan; Disease Models, Animal; Dose-Response Relationship, Drug; Inflammation; Male; Naloxone; Nociceptors; Pain; Rats; Rats, Inbred Strains; Thalamus; Time Factors

The alterations in plasma levels of immunoreactive metenkephalin (ir-metenkephalin) and catecholamines in adrenal vein and arterial blood in response to endotoxin, as well as the effects of subsequent naloxone administration, have been investigated in a canine model. Animals were anaesthetised with alpha chloralose and allowed to breathe spontaneously. The left lumbar adrenal vein was cannulated and an intermittent choke allowed retrograde sampling of the adrenal effluent. Severe shock was produced by the administration of a large bolus of E. coli endotoxin (5 mg/kg) followed by a continuous infusion (2 mg/kg per hour). One hour after induction of shock the circulating volume was expanded using a colloidal gelatin solution. Thirty minutes later one group of five animals received a bolus of naloxone (2 mg/kg) followed by a continuous infusion of (1.5 mg/kg per hour), while a control group of five animals was given an equivalent volume of isotonic saline. The production of endotoxin shock was associated with marked increases in adrenal vein and systemic levels of adrenaline and noradrenaline. Naloxone administration transiently limited the fall in adrenal vein levels of adrenaline and noradrenaline (P less than 0.05) following volume replacement and was associated with a sustained increase in systemic adrenaline levels (P less than 0.05). Changes in mean arterial pressure confirmed a significant haemodynamic response to naloxone (P less than 0.05). Alterations in ir-metenkephalin levels in the adrenal vein closely followed the changes in catecholamines, whereas arterial levels rose progressively and were unaffected by naloxone. We conclude that in canine endotoxin shock the opiate antagonist naloxone can transiently increase catecholamine levels in the adrenal effluent and produce a more sustained rise in systemic adrenaline levels. Moreover, the adrenal medulla is not the only source of circulating ir-metenkephalin.

Topics: Adrenal Glands; Animals; Arteries; Disease Models, Animal; Dogs; Endotoxins; Enkephalin, Methionine; Epinephrine; Naloxone; Norepinephrine; Radioimmunoassay; Reference Values; Shock, Septic; Veins

We evaluated the hypothesis that increased endogenous opioid activity mediates part or all of the left ventricular contractile and pump dysfunction previously demonstrated in HCl-induced metabolic acidemia. Eighteen Western newborn lambs were catheterized and instrumented; pacing wires were sutured to the right atrial appendage; a catheter mounted micromanometer pressure transducer was inserted into the left ventricle; and a 2.5 F thermistor was inserted into the distal abdominal aorta. The lambs were studied 3 days after surgery. Metabolic acidemia was produced with an infusion of 0.5 N HCl into the inferior vena cava. Inhibition of endogenous opioids was achieved with a bolus of 2 mg/kg of intravenous naloxone, which was demonstrated to inhibit morphine sulfate-induced myocardial dysfunction. The effects of opioid inhibition were contrasted with our previously published results after restoration of a normal arterial pH with intravenous sodium bicarbonate. In agreement with our previous study, we found that reducing the arterial pH from 7.41 +/- 0.01 to 6.97 +/- 0.04 was associated with a 45% reduction in cardiac output which resulted from a 50% reduction in stroke volume. These changes in turn were mediated by a 35% reduction in the maximal first derivative of left ventricular pressure and/or a 63% increase in systemic vascular resistance which we used to estimate contractility and afterload, respectively. Left ventricular end diastolic pressure increased during acidemia. Although opioid inhibition produced a consistent increase in the maximal first derivative of left ventricular pressure, this increase was relatively small and was not associated with a significant change in cardiac output, stroke volume, or systemic vascular resistance.

Topics: Acidosis; Animals; Animals, Newborn; Asphyxia Neonatorum; Bradycardia; Cardiac Output, Low; Disease Models, Animal; Endorphins; Heart Ventricles; Humans; Hydrochloric Acid; Infant, Newborn; Naloxone; Sheep; Stroke Volume

Thirty-six male Sprague-Dawley rats were divided into three groups (n = 12): simple hemorrhagic shock group, saline-treated group, and naloxone-treated group. Synchronous videotape recording with two cameras was used to observe the relationship between the change of blood pressure and that of microcirculation of cremaster muscle. It has been suggested that the temporary plugging of capillaries by WBC may be the explanation for no reflow in microvessels after transfusion and infusion during the irreversible stage of shock. Administration of naloxone (2 mg/kg iv) followed by reinfusion of the shed blood is associated with an increase in blood pressure and pulse pressure. Coincidentally, a pulsatile movement of the blood, impacted on the stationary blood cells in capillaries, eventually dislodges them and leads to reperfusion of capillaries. Thereafter systemic blood pressure and carotid artery red blood cell velocity were increased and remained stable. The 24-hr survival rate was significantly increased in the naloxone-treated group (10/12), as compared with that in the saline-treated group (1/12). The mechanism of naloxone treatment is discussed. The suggestion is advanced that the effects on cardiac and microcirculatory performance may influence each other, and that both contribute to the pathogenesis of irreversible hemorrhagic shock.

Topics: Administration, Topical; Animals; Arterioles; Blood Flow Velocity; Blood Pressure; Disease Models, Animal; Infusions, Intravenous; Male; Microcirculation; Naloxone; Rats; Rats, Inbred Strains; Shock, Hemorrhagic

Topics: Animals; Cats; Disease Models, Animal; Naloxone; Rats; Spinal Cord Injuries

In order to test the hypothesis that endogenous opioids may mediate some of the circulatory derangements in cirrhosis, we studied the haemodynamic effects of naloxone, an opioid antagonist, in patients and in a rat model of biliary cirrhosis. In 9 patients with alcoholic cirrhosis and 5 control patients without significant liver disease, cardiac output, systemic vascular resistance, mean arterial pressure, heart rate, hepatic venous pressures and O2 content, hepatic and azygos blood flows and serum catecholamines were measured before and 30 min after naloxone 3.2 mg i.v. bolus. No significant changes were observed in either group of patients. Similarly in 16 conscious rats, 8 sham-operated and 8 with cirrhosis due to bile duct ligation, cardiac output, systemic vascular resistance, mean arterial pressure, heart rate, and splanchnic organ blood flows were measured by radioactive microspheres, before and 20 min after naloxone 1 mg/kg i.v. bolus. No significant changes were observed in either group. We failed to detect any evidence that endorphins are involved in tonic haemodynamic control in cirrhosis.

Topics: Adult; Aged; Animals; Disease Models, Animal; Endorphins; Female; Hemodynamics; Humans; Liver Cirrhosis, Alcoholic; Male; Middle Aged; Naloxone; Rats; Rats, Inbred Strains

The endogenous opiate beta-endorphin is released concomitantly with adrenocorticotropin from the pituitary during stress. In the present study we investigated the possible involvement of opiate receptors in the cardiovascular depression associated with hypovolemic shock in the nonhuman primate. Changes in circulating levels in beta-endorphin were monitored during hemorrhagic shock in 18 female baboons. Plasma levels of beta-endorphin increased significantly during hemorrhagic shock and were significantly correlated with a decrease in cardiac output (P less than 0.05). Single bolus administration of the opiate receptor antagonist naloxone (2 or 5 mg/kg) produced a transient but significant improvement in cardiac output (P less than 0.05) and mean arterial pressure (P less than 0.05). Hemodynamic improvement was maintained with a constant infusion of naloxone. Opiate receptor blockade with the longer acting antagonist naltrexone (2 or 5 mg/kg) significantly increased mean arterial pressure (MAP; P less than 0.05), and CO (P less than 0.05), and decreased heart rate. Our results suggest that the baboon is an excellent model for the study of hemorrhagic shock and provide further evidence for endogenous opiate involvement in the cardiovascular pathophysiology of hemorrhagic shock.

Topics: Animals; beta-Endorphin; Disease Models, Animal; Dose-Response Relationship, Drug; Endorphins; Female; Hemodynamics; Naloxone; Naltrexone; Narcotic Antagonists; Papio; Shock, Hemorrhagic; Time Factors

The present studies examined whether dependence could be induced by continuous infusion of delta-9-tetrahydrocannabinol (THC), as evidenced by behavioral disruptions during withdrawal of THC administration. Four rhesus monkeys lever pressed under fixed-ratio schedules for their daily food rations during four, daily, 0.5 -hr sessions. Initially, the monkeys were tested before, during and after continuous i.v. infusions of THC. A dosage regimen of 0.05 mg/kg/hr for 10 days for three of the monkeys and a somewhat greater regimen in the fourth had little direct effect on rates of respondings for food during THC infusion, but marked decreases in response rates occurred in each monkey during withdrawal. These effects generally did not occur until the second day of withdrawal, and often lasted for over a week. These initial demonstrations were replicated subsequently with lower solvent concentrations. In the final study, THC was administered for a greater number of days and at higher dosages than during any of the previous studies. Response rate reductions again occurred within 2 to 3 days of withdrawal. When THC was readministered, reversal of the withdrawal effects occurred in that withdrawal-induced rate decreases were halted and rates increased subsequently. Administration of THC was discontinued after 2 to 3 days of its readministration. Response rates again decreased within the first 3 days after this withdrawal and then recovered slowly with time. Withdrawal of THC administration can disrupt operant behavior, and these disruptions can be reversed by resumption of THC administration, indicating that dependence upon this drug can be produced in rhesus monkeys.

Topics: Animals; Conditioning, Operant; Disease Models, Animal; Dronabinol; Drug Administration Schedule; Drug Tolerance; Macaca; Macaca mulatta; Male; Naloxone; Solvents; Substance Withdrawal Syndrome; Substance-Related Disorders; Time Factors

Topics: 5-Hydroxytryptophan; Animals; Apomorphine; Bromocriptine; Clonazepam; Disease Models, Animal; Guinea Pigs; Haloperidol; Lisuride; Morphine; Myoclonus; Naloxone; Scopolamine; Tremorine

A rabbit model of hemorrhagic shock is used in assessing the use of naloxone as an adjunct in the treatment of hemorrhagic shock. In vitro oxidation rates of labelled glucose are used as parameters of early tissue damage. Naloxone, given as an adjunct to volume replacement, significantly improves the in vitro capabilities of lung and liver tissues, but has no effect on kidney cortex. Changes in MABP are not affected by naloxone in this rabbit model, and serum lysosomal enzyme activity is not significantly improved. It is proposed that naloxone exerts some of its beneficial effect at the cellular level.

Topics: Animals; Blood Pressure; Disease Models, Animal; Glucose; Glucuronidase; In Vitro Techniques; Kidney Cortex; Liver; Lung; Naloxone; Rabbits; Shock, Hemorrhagic

Changes of the evoked spinal cord potential (ESP) were measured in Wistar rats by giving acute compression to the spinal cord injury. The effects of Naloxone, methylprednisolone and prostaglandin E1 on ESP of the damaged spinal cord were also closely examined. Normal ESP of rats showed two negative peaks, an initial wave (the 1st potential) and a subsequent gentle and small wave (the 2nd potential). After placing a 10 g weight on the spinal cord, the potential decreased in amplitude and prolonged in latency, disappearing one by one within five minutes. After removal of the weight, the potentials reappeared in the reverse order of their disappearance. Recovery of the potentials was more remarkable in rats treated with Naloxone, methylprednisolone, and prostaglandin E1. This animal model proved useful in studying of acute compression injury of the spinal cord.

Topics: Animals; Disease Models, Animal; Evoked Potentials; Male; Methylprednisolone; Naloxone; Prostaglandins E; Rats; Rats, Inbred Strains; Spinal Cord; Spinal Cord Compression

The proximal left M1 and the common trunk of A2 were clipped in 12 adult dogs. Naloxone was injected after placing the clips onto 6 dogs. Neither the systemic blood pressure nor the local cerebral blood flow were influenced by naloxone. In another group of 6 dogs with chronic right hemiplegia, naloxone proved passably effective in improving the hemiplegia. Eight patients with neurological deficits of various etiologies were administered levallorphan. The improvement in motor performance and/or elevation of mental activity was observed more or less in all but 2 of the patients. It was considered that the effect of opiate antagonists is based partially on the facilitation of synaptic transmission exaggerated by the arousal response.

Topics: Adult; Aged; Animals; Blood Flow Velocity; Brain Ischemia; Cats; Cerebrovascular Circulation; Chick Embryo; Disease Models, Animal; Dogs; Female; Humans; Injections, Intravenous; Levallorphan; Male; Middle Aged; Naloxone; Narcotic Antagonists; Nervous System Diseases; Tomography, X-Ray Computed

We determined how the following drugs affected survival of 350-gm Sprague-Dawley rats subjected to intra-abdominal sepsis according to the method of Wichterman et al (J Surg Res 29:189-201, 1980): gentamicin (4.5 mg/kg/day), clindamycin (30 mg/kg/day), naloxone (2 mg/kg/hr), or methylprednisolone given either as a continuous infusion (2 mg/kg/hr) or as a bolus (30 mg/kg). A control group received only saline in a volume equal to the drug vehicle volume. Treatment was started immediately after cecal ligation and puncture. Drugs not given by bolus were infused by Alzet mini-pump (Model 2001) for 7 days. Percent of original population surviving at 10 days was (size of original population): saline--48% (92), antibiotics--86% (43), naloxone--30% (43), continuous methylprednisolone--14% (43), bolus methylprednisolone--93% (45). Survival of animals receiving either antibiotics or bolus methylprednisolone was significantly increased over the control population.

Topics: Animals; Anti-Bacterial Agents; Bacterial Infections; Cecum; Disease Models, Animal; Drug Administration Schedule; Ligation; Male; Methylprednisolone; Naloxone; Punctures; Rats; Rats, Inbred Strains

There is increasing evidence suggesting that endogenous opioid peptides play a role both in temperature regulation and in the etiopathology of seizures. We have studied the effects of the opioid antagonist naloxone on hyperthermia-induced seizures in unrestrained 15 day old rat pups. Saline injected control animals exposed to an ambient temperature of 40 degrees C for one hr showed a gradual increase in body temperature reaching a maximum of 42 degrees C at 50 min of exposure; at this time, all animals had convulsions and 86% died. Animals pre-treated with 10 mg/kg naloxone reached a maximum core temperature of 41 degrees C after 60 min at 40 degrees C and no convulsions or deaths were observed. When animals were exposed for 60 min to a 27 degrees C environment, saline controls maintained their normal body temperature throughout the experiment, while 5 mg/kg naloxone produced a marked hyperthermic effect. These experiments suggest that endogenous opioids may play a role in both temperature adaptation and hyperthermia-induced seizures in the rat pup.

Topics: Adaptation, Physiological; Animals; Disease Models, Animal; Hot Temperature; Naloxone; Rats; Rats, Inbred Strains; Seizures, Febrile

The effects are reported of acute and long-term continuous administration of three opiate antagonists--naloxone, naltrexone, and diprenorphine--on neurological function, survival, and infarct size in a feline model of acute focal cerebral ischemia. All three drugs produced statistically significant improvement in motor function following acute administration without concomitant changes in level of consciousness; saline had no effect. Naloxone and naltrexone significantly prolonged survival (p less than 0.01); diprenorphine did not. Infarct size was not altered by any treatment administered. These findings confirm previous work suggesting that, with the appropriate methodology, treatment with opiate antagonists partially reverses neurological deficits. They also show that opiate antagonists prolong survival in certain conditions of acute and subacute focal cerebral ischemia without altering the area of infarcted tissue.

Topics: Animals; Brain Ischemia; Cats; Cerebrovascular Disorders; Consciousness; Diprenorphine; Disease Models, Animal; Male; Morphinans; Movement; Naloxone; Naltrexone; Pupil; Sensation

Twenty-eight hours of endorphin receptor blockade by subcutaneous naloxone infusion produced behavioral and respiratory symptoms resembling opiate abstinence syndrome. Rats were implanted subcutaneously with two Alzet osmotic minipumps delivering 0.7 mg/kg per hour naloxone or with two control minipumps containing distilled water only. They were observed for 10 minutes under blind conditions at 16 and 28 hours post-implantation. The naloxone-infused rats showed significantly more wet dog shakes, abdominal writhes and overall abstinence-like symptoms than did the control rats. These symptoms decreased after 28 hours despite continued naloxone infusion. Acute administration of naloxone failed to produce abstinence-like symptoms, even when combined with the trauma of carrying two implanted water-filled minipumps for 28 hours. In another experiment, naloxone-infused rats showed a highly significant 53.4% elevation of O2 consumption over water-infused control rats in a pure O2 atmosphere at 28 hours after implantation. This difference disappeared at 48 hours post-implantation. In contrast to the effect of naloxone infusion, acute administration of three different doses of naloxone failed to significantly increase O2 consumption.

Topics: Animals; Behavior, Animal; Body Weight; Disease Models, Animal; Humans; Male; Naloxone; Narcotics; Oxygen Consumption; Rats; Rats, Inbred Strains; Receptors, Opioid; Substance Withdrawal Syndrome

Young and mature, genetically obese and non-obese, spontaneously hypertensive rats (SHR) were injected with saline (controls) or naloxone for 12 weeks. Naloxone stilled the hyperphagia to a normal intake in the obese SHR (Obese/SHR) so that young Obese/SHR did not develop their usual massive obesity and mature Obese/SHR that had become massively obese were reduced to leanness. The naloxone-treated young, obese and non-obese SHR (controls) exhibited marked reduction of the weight of their pituitary and adrenal glands, whereas the pituitary and adrenal glands of naloxone-treated mature, obese and non-obese/SHR were greatly increased in weight. The elevated systolic blood pressure of the obese and non-obese rats was reduced after chronic treatment with naloxone. Naloxone treatment caused reduction of blood ACTH, corticosterone, and beta endorphin levels but elevated growth hormone levels. The characteristic hyperinsulinemia, hyperlipidemia, hyperglycemia, elevated BUN levels, and the Cushingoid spectrum of degenerative changes found in Obese/SHR did not appear in naloxone-treated rats.

Topics: Adrenal Glands; Adrenocorticotropic Hormone; Animals; beta-Endorphin; Blood Pressure; Body Weight; Corticosterone; Cushing Syndrome; Disease Models, Animal; Endorphins; Female; Growth Hormone; Male; Naloxone; Obesity; Organ Size; Pituitary Gland; Rats; Rats, Inbred SHR; Rats, Inbred Strains

The development of permanent paraplegia in spinal injured cats is accompanied by a large progressive decline in total ascorbic acid (AA) and a transient increase in oxidized (AAox) ascorbate. Since AA is involved in a variety of processes required for normal central nervous system (CNS) performance we suggested that such large ascorbate loss may contribute to derangements in spinal cord function following injury. We now demonstrate that methylprednisolone (15 mg/kg) and naloxone (10 mg/kg), two treatments that preserve neurologic function in this model, rapidly block deteriorating ascorbate status. Naloxone at 1 mg/kg, a treatment providing no therapeutic benefit, has no protective effect on ascorbate. The results strongly support the hypothesis that loss of ascorbate homeostasis reflects irreversible loss of neurologic function following spinal cord injury.

Topics: Animals; Ascorbic Acid; Cats; Disease Models, Animal; Homeostasis; Locomotion; Methylprednisolone; Naloxone; Paraplegia; Spinal Cord Injuries; Time Factors

A model of endotoxin-induced shock was developed in anesthetized spontaneously hypertensive rats. E. coli lipopolysaccharide (13 mg/kg i.v.) reduced systolic and diastolic blood pressure by at least 51 mm Hg in 80-90% of rats. Naloxone (1.25-10.0 mg/kg i.v.) partially restored blood pressure of hypotensive rats for 6-15 minutes after injection. Win 44441-3 (0.25-2.0 mg/kg i.v.) raised blood pressure for 3-12 minutes after injection. Ten minute pretreatment with naloxone (10 mg/kg i.v.) or Win 44441-3 (0.5 mg/kg i.v.) did not appreciably reduce the hypotensive effect of E. coli lipopolysaccharide. This model is a rapid and convenient bioassay for evaluating the effects of opioid antagonists in endotoxin shock. In this model naloxone and Win 44441-3 exhibited beneficial effects but a prolonged duration of action of the Win compound over naloxone was not observed.

Topics: Animals; Azocines; Disease Models, Animal; Escherichia coli; Lipopolysaccharides; Male; Naloxone; Rats; Rats, Inbred SHR; Shock, Septic

By isolating young rats (90-100 g) a state of hypertension and tachycardia was induced after 7 days or a longer period of social deprivation. Clonidine, a drug used to treat hypertension in man, readily reversed the high blood pressure and heart rate in this experimental model of hypertension. In two different tests, an elevated nociceptive threshold was shown to be present in isolated animals as compared to group-housed rats. Naloxone was found to reverse this hypoalgesic state. The opiate antagonist also diminished the high blood pressure in the socially-deprived animals. Moreover, after 7 days of isolation, 24 hr of housing the rats in groups of five made the level of blood pressure and the sensitivity to pain return to control values. In this experimental model, in which hypertension was linked to stressful housing conditions, the data suggest that high blood pressure and hypoalgesia are closely associated.

Topics: Animals; Clonidine; Disease Models, Animal; Heart Rate; Hypertension; Male; Naloxone; Pain; Rats; Rats, Inbred Strains; Sensory Thresholds; Social Isolation

Evidence has been accumulating to indicate that the spinal cord plays an important role in the expression of several narcotic abstinence signs in the intact animal. One characteristic and reproducible withdrawal sign which can be elicited in both intact and spinal-transected dependent rats is the naloxone-induced increase in arterial blood pressure. Employing this model, this autonomic component of narcotic withdrawal was quantitated in dependent spinal (C1)-transected rats with intact dorsal roots and in those with surgical lesions of the dorsal roots from T3 to L4. The withdrawal-associated hypertension observed in animals with intact dorsal roots was abolished in the rats having the lesioned roots. The central spinal location of the opiate receptors mediating the naloxone response was confirmed by experiments demonstrating the failure of a selective peripherally acting narcotic antagonist to elicit a comparable withdrawal response. It was concluded that continuous afferent input and spinal opiate receptors are requirements for the expression of spinal narcotic withdrawal.

Topics: Animals; Blood Pressure; Disease Models, Animal; Ganglia, Spinal; Male; Morphine; Naloxone; Neural Inhibition; Neural Pathways; Rats; Rats, Inbred Strains; Substance Withdrawal Syndrome; Time Factors

Recent evidence has suggested a relationship between the endogenous opioid peptides and the pathophysiology of various shock states. In the present study, we investigated the relationship between the effectiveness of naloxone (an opiate antagonist) and nalbuphine (an opiate agonist/antagonist), and the changes in circulating levels of catecholamines in the nonhuman primate subjected to hemorrhagic shock. Plasma levels of catecholamines were measured using high-performance liquid chromatography (HPLC) during hemorrhagic shock in 15 female baboons. Plasma levels of both epinephrine and norepinephrine increased significantly during hemorrhagic shock (p less than 0.05), which correlated with an increase in heart rate. Bolus administration of naloxone (5 mg/kg) significantly increased both plasma epinephrine (p less than 0.01) and norepinephrine (p less than 0.05) over shock levels along with a transient but significant increase in cardiac output (p less than 0.05) and mean arterial pressure (p less than 0.05), and a significant decrease in heart rate (p less than 0.05). Improvements in hemodynamics were maintained with a constant infusion of naloxone (5 mg/kg/hr), which also caused a further significant increase in plasma epinephrine (p less than 0.01). Administration of a single bolus of the opiate agonist/antagonist nalbuphine (5 mg/kg) dramatically decreased cardiac output and mean arterial pressure and had no effect on circulating catecholamines. Our results suggest that (1) the beneficial action of high-dose naloxone in primate hemorrhagic shock may be attributable in part to a drug-induced increase in circulating endogenous catecholamines; and (2) the failure of high-dose nalbuphine to improve cardiovascular function may be related to its partial agonist (cardiodepressant) properties at higher doses.

Topics: Animals; Catecholamines; Disease Models, Animal; Female; Hemodynamics; Morphinans; Nalbuphine; Naloxone; Papio; Shock, Hemorrhagic

Topics: Animals; Disease Models, Animal; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

This study was designed to investigate the concept that endogenous opioids are involved in the pathogenesis of septic shock. Infusion of live Escherichia coli (1.0-1.6 X 10(10) organisms/kg) in splenectomized dogs induced profound hypotension (p less than 0.001), peripheral vasodilatation (p less than 0.001), and metabolic acidosis (p less than 0.05) with maintenance of cardiac index as compared to control splenectomized dogs. Treatment with naloxone (3 mg/kg bolus and 2 mg/kg/hr infusion for 2.5 hours), a specific opiate antagonist, during septic shock attenuated the hypotension (p less than 0.002) and systemic acidosis (p less than 0.02) without altering cardiac index or total peripheral resistance. These experimental results indicate that naloxone may be of therapeutic value in the management of the early vasodilatory stage of septicemia.

Topics: Animals; Blood Pressure; Cardiac Output; Disease Models, Animal; Dogs; Escherichia coli Infections; Female; Heart Rate; Hemodynamics; Male; Naloxone; Sepsis; Shock, Septic; Splenectomy; Vascular Resistance

Topics: Animals; Disease Models, Animal; Estradiol; Female; Follicle Stimulating Hormone; Gonadotropin-Releasing Hormone; Humans; Luteinizing Hormone; Male; Naloxone; Pregnancy; Prolactin; Sex Differentiation; Testosterone; Thyrotropin-Releasing Hormone; Transsexualism; Twins

Temporary aortic occlusion produces a consistent degree of spinal cord injury in the unanesthetized rabbit. This 'spinal stroke' model was utilized to examine the potential therapeutic effects of the opiate antagonist naloxone in central nervous system ischemia. Naloxone treatment resulted in dose-related enhancement of motor recovery; greatest functional recovery was observed in rabbits treated with a dose of 2 mg/kg per h. This dose compares well with the high doses of naloxone shown to have a beneficial effect in other experimental models of stroke and spinal injury. In contrast, clinical stroke studies, which have been largely unsuccessful, have utilized naloxone doses which are several orders of magnitude lower than those successfully employed in experimental models.

Topics: Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Ischemia; Naloxone; Rabbits; Spinal Cord; Spinal Cord Injuries

The specific opiate receptor antagonist, naloxone, can produce haemodynamic improvement and increased survival in experimental shock. The efficacy of naloxone therapy in a canine model of endotoxin shock has been evaluated both with and without intravascular volume replacement. Animals were anaesthetized with alpha-chloralose and allowed to breathe spontaneously. A large bolus dose of endotoxin was followed by a continuous infusion and treatment was instituted one hour after the endotoxin bolus. In the absence of volume replacement, naloxone caused only limited and transient increases in mean arterial pressure (MAP) and left ventricular (LV) dp/dt max, with little effect on cardiac index (CI). Total peripheral resistance index (TPRI) tended to rise in both control and naloxone-treated dogs. In volume-replaced animals, naloxone produced substantial and sustained increases in the MAP and LV dp/dt max with an associated rise in the CI. TPRI rose initially in this series and then fell progressively. Further analysis of the improvements in the CI showed an increase in stroke index with a tendency for heart rate to fall. These findings suggest a myocardial action of naloxone in endotoxin shock, which is augmented by volume replacement. An initial, transient vasoconstrictor effect cannot, however, be excluded. Further work is required to determine the mechanism of the effects described.

Topics: Animals; Blood Cell Count; Blood Pressure; Capillaries; Cardiac Output; Disease Models, Animal; Dogs; Hemodynamics; Naloxone; Plasma Substitutes; Pulmonary Circulation; Shock, Septic; Time Factors; Vascular Resistance

Physical dependence on morphine-type drugs (morphine, codeine and pethidine) in mice were examined by the drug-admixed food method. Mice were treated with drug-admixed food of increasing concentration (1, 2 and 3 mg/g food) every third day for 9 days. Morphine- and codeine-treated mice showed withdrawal signs when they were given naloxone (5 mg/kg, s.c.), while pethidine-treated mice did not show the withdrawal signs. However, mice treated with pethidine-admixed food (1-6 mg/g food) for 28 days showed naloxone precipitated withdrawal signs. Thus, the data obtained with mice indicate that pethidine produces a weak physical dependence. On the other hand, codeine (40 mg/kg, s.c.) and pethidine (100 mg/kg, s.c.) administration suppressed the abrupt withdrawal signs of morphine-dependent mice that were treated with morphine-admixed food, while the withdrawal signs were completely suppressed in mice administered only 5 mg/kg morphine. These results suggest that the physical dependence liability of morphine type drugs can be predicted by the drug-admixed food method.

Topics: Administration, Oral; Animals; Codeine; Disease Models, Animal; Humans; Male; Meperidine; Mice; Mice, Inbred ICR; Morphine Dependence; Naloxone; Opioid-Related Disorders; Substance Withdrawal Syndrome; Toxicology

A comparison of several methods for developing physical dependence to morphine was made. Male Sprague-Dawley rats were treated with morphine-admixed food (drug-admixed food, DAF; 0.5 and 1 mg/g food), morphine slow release emulsion (SRE; 75, 100 and 150 mg/kg) and morphine (75 mg) pellets. In the SRE and pellet methods, the typical signs of morphine toxicity, such as catatonia, exophthalmos and shallow respiratory movements, were observed 15-20 min after the treatment and these signs were maintained for 14-18 hr. In rats treated with SRE and pellets, plasma morphine levels reached a maximum 1 day after the morphine treatment, and subsequently decreased, while plasma morphine levels in rats treated with DAF increased treatment period-dependently. Withdrawal signs precipitated by naloxone (3 mg/kg, sc) in rats treated with DAF, SRE and pellets were characterized by loss of body weight, shaking, vocalization, diarrhea, ptosis, tooth-chattering, nose bleed, salivation and lacrimation. Naloxone-precipitated withdrawal signs reached a maximum 1-2 days after treatment with SRE and pellets, and were correlated with the duration of DAF treatment. Rats treated with DAF, SRE (150 and 225 mg/kg) and pellets for 3 days, manifested loss of body weight, diarrhea etc. after the morphine withdrawal. Maximum body weight loss in each group was 7-10% at 1-2 days after the morphine withdrawal. It was thus, concluded that physical dependence on morphine can be induced rapidly by these three methods. However, the SRE and pellet methods induced morphine toxicity and it was difficult to maintain physical dependence on morphine in these rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Disease Models, Animal; Dosage Forms; Humans; Male; Morphine; Morphine Dependence; Naloxone; Rats; Rats, Inbred Strains; Substance Withdrawal Syndrome; Time Factors

Rats were implanted with an intrathecal catheter aimed at the lumbar enlargement (LE). Morphine hydrochloride (240 micrograms/day) was infused continuously on the spinal cord for 14 days with an osmotic minipump delivering 0.5 microliter/h solution or a bolus dose of naltrexone (37.5, 75 or 150 micrograms) was injected intrathecally. Intrathecally infused morphine delivered on the dorsum of the LE induced analgesia, as tested on the hot plate, whereas normal saline was without effect. Naltrexone caused hyperalgesia revealed as decreased threshold for vocalization to electrical stimulation of the tail. Rats with unilaterally sectioned sciatic nerves that were continuously infused with morphine on the dorsum of the LE autotomized significantly less than saline controls. Nerve sectioned rats injected with naltrexone had an overall level of autotomy similar to saline controls. However, autotomy had a somewhat earlier onset and was more severe with naltrexone than with saline. It is therefore concluded that intrathecal infusion of opiates specifically reduces autotomy, a behavior that may occur as a result of chronic discomfort or pain following nerve injury. Furthermore, the endogenous opiate system at the spinal level may be involved in the control of autotomy.

Topics: Animals; Behavior, Animal; Differential Threshold; Disease Models, Animal; Injections, Spinal; Male; Morphine; Naloxone; Naltrexone; Nociceptors; Pain; Rats; Rats, Inbred Strains; Sciatic Nerve; Time Factors

The effects of 3 different non-noxious stressors on body temperature (Tb) were investigated in the rat: (1) loose restraint in cylinders, (2) removal of the rats from cylinders, exposure to a novel environment and replacement in cylinders, a stressor called here 'novelty', and (3) gentle holding of the rats by the nape of the neck. Loose restraint and 'novelty' produced hyperthermia. On the contrary, holding induced hypothermia. Hypophysectomy (HX) reduced basal Tb, abolished restraint hyperthermia and reduced both 'novelty' hyperthermia and holding hypothermia. Dexamethasone ( DEXA ) had no effect upon either restraint or novelty hyperthermia but reduced the hypothermia. Naloxone (Nx) produced a slight fall in basal Tb accounting for its reduction of restraint and 'novelty' hyperthermias ; it did not affect holding hypothermia. The inhibitory effects of HX suggest a participation of the pituitary in the hyperthermias ; the neurointermediate lobe would be involved as the hyperthermias were not affected by DEXA , which is known to block the stress-induced release of pituitary secretions from the anterior lobe but not from the neurointermediate lobe. In contrast, substances from the anterior lobe might participate in hypothermia due to holding since it is reduced by HX and DEXA . As to the effects of Nx, endogenous opioids would not be significantly involved in the thermic effects of the stressors used in this study; they might play, if any, only a minor role in the regulation of basal Tb. These results are compared with those previously obtained on nociception using the same non-noxious stressors. It emerges that, depending on the stressor, different types of association between thermoregulation and nociception may occur, i.e. hyperthermia with analgesia, hyperthermia with hyperalgesia and hypothermia with hyperalgesia.

Topics: Animals; Body Temperature Regulation; Dexamethasone; Disease Models, Animal; Endorphins; Hypophysectomy; Male; Naloxone; Pain; Pituitary Gland; Rats; Rats, Inbred Strains; Stress, Physiological

Many vasoactive mediators have been implicated in causing or maintaining the hypotension of endotoxic shock. What has yet to be firmly established is the relative importance of each of these mediators in a given shock model. In a canine endotoxic shock model (LD100), we studied the effects of opiate and prostaglandin inhibition 60 min after endotoxin administration. After thiopental anesthesia, the animals were instrumented to measure various cardiovascular parameters. Endotoxic shock was induced by injecting E. coli endotoxin (0111:B4) (1 mg/kg i.v.). Drug intervention occurred 60 min after endotoxin administration. Naloxone (2 mg/kg i.v.) improved mean arterial pressure (MAP) transiently. A more significant increase of MAP (85% of preshock levels) was attained after ibuprofen (12.5 mg/kg i.v.) administration secondary to an increase in total peripheral resistance (TPR). All groups had 0% 24-hour survival. These data suggest that the endogenous opioids, presumably inhibited by naloxone, seem to contribute little to this lethal canine endotoxic shock model. By contrast, the prostanoids which are inhibited by ibuprofen appear to be more hemodynamically significant in this model.

Topics: Animals; Blood Pressure; Disease Models, Animal; Dogs; Endorphins; Hemodynamics; Ibuprofen; Male; Naloxone; Prostaglandins; Shock, Septic; Vascular Resistance

The effects of naloxone on the cardiovascular, hematologic and metabolic derangements associated with endotoxic and hemorrhagic shock were studied in unanesthetized horses. In the first of 3 experiments blood glucose and lactate levels, hematocrit, white, red and differential white cell counts, rectal temperature and clinical signs were obtained before and after endotoxin (10 micrograms/Kg) administration in 5 horses. In the second experiment, two groups of 3 horses received either intravenous naloxone (0.04 mg/Kg) or saline, 7 minutes prior to endotoxin. In a third experiment two groups of 4 horses received either saline or naloxone (0.20 mg/Kg) immediately following acute hemorrhage. In the second and third experiments, pulse, mean arterial and right ventricular pressures, and heart rate were also observed. Endotoxin and acute hemorrhage produced hypothermia, leukopenia, lymphopenia, neutropenia, elevations in hematocrit, blood glucose and blood lactate, and clinical signs of shock. Naloxone (0.040 mg/Kg IV) significantly lowered endotoxin-induced increases in right ventricular pressure and heart rate, and at a higher dose (0.20 mg/Kg) antagonized the decrease in pulse and heart rate, and tachycardia observed after acute hemorrhage. These results suggest endogenous opioids are involved in the pathogenesis of shock. Naloxone appeared to attenuate some of the cardiovascular responses associated with shock and thus may be of therapeutic value in shock management.

Topics: Animals; Blood Pressure; Disease Models, Animal; Endotoxins; Female; Heart Rate; Hemodynamics; Horses; Male; Naloxone; Pulse; Shock, Hemorrhagic; Shock, Septic

Interferon injection in morphine dependent rats prior to naloxone treatment eliminates 7 behavioral sings of the abstinence (withdrawal) phenomenon. When a single injection of interferon was given prior to chronic morphine treatment it reduces opiate addiction liability.

Topics: Animals; Disease Models, Animal; Humans; Interferons; Male; Morphine; Morphine Dependence; Naloxone; Rats; Substance Withdrawal Syndrome

On the basis of our investigations it seems that: The opiate antagonist naloxone in a dose of 5.0 mg/kg has a significant protective effect in stress-ulcer model in the rat; No such effect was seen in drug (indomethacin) or cysteamine induced (duodenal) ulcer models; The interaction of naloxone with indomethacin seems to show a sex-difference.

Topics: Animals; Cysteamine; Disease Models, Animal; Female; Gastric Mucosa; Indomethacin; Male; Naloxone; Peptic Ulcer; Rats; Rats, Inbred Strains; Receptors, Opioid; Sex Factors; Stress, Physiological

A highly predictive spinal "stroke" model in the unanesthetized rabbit was utilized to compare the effects of naloxone and the delta-selective opiate antagonist M154,129 on neurological recovery following ischemic injury to the central nervous system. Naloxone treatment protected against both moderate (20 min aortic occlusion) and severe (25 min aortic occlusion) degrees of ischemic spinal injury, whereas treatment with M154,129 failed to improve recovery in either model. These findings confirm that naloxone therapy can alter the pathophysiological sequelae caused by a critical reduction in blood flow to the central nervous system and suggests that its beneficial effects do not relate to actions at the delta-opiate receptor.

Topics: Animals; Cerebrovascular Disorders; Disease Models, Animal; Enkephalin, Leucine; Male; Motor Activity; Naloxone; Rabbits; Spinal Cord

The effect of naloxone on learned performance reinforced by food was examined in 2 experiments. Male rats were trained to run down a short runway for 5 (45 mg) food pellets per trial and were then shifted either to 1 or 0 pellets. Following such an abrupt reinforcement shift, animals typically show an emotional disruption of performance (Crespi, 1942) referred to as "depression". We examined the postshift depression-effect in groups treated either with saline (SAL) or naloxone (NAL). In experiment 1 NAL groups received a single 10 mg/kg (s.c.) injection prior to each postshift session. When compared with SAL controls, NAL animals showed an exaggerated postshift depression-effect. Furthermore, a single (0.3 mg/kg, s.c.) injection of the enkephalin analog FK 33-824 (D-Ala2, MePhe4, Met-(0)5-o1) produced a dramatic recovery of performance. In the second experiment, these effects were replicated at a low NAL dose (1 mg/kg), which had no direct effect on motor performance. These findings suggest that opiate systems may modulate the incentive motivation that maintains learned performance.

Topics: Animals; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; Depression; Disease Models, Animal; Enkephalin, Methionine; Hormones; Humans; Learning; Male; Motor Activity; Naloxone; Rats; Rats, Inbred Strains; Reinforcement, Psychology

Topics: Animals; Cats; Cerebrovascular Circulation; Disease Models, Animal; Myocardial Contraction; Naloxone; Rats; Respiration; Shock; Spinal Cord Injuries

Topics: Animals; Brain Ischemia; Disease Models, Animal; Gerbillinae; Humans; Naloxone

Beta-Endorphin (0.3 or 0.6 nanomoles) was infused into the A10-ventral tegmental area (VTA) of male Wistar rats previously treated for 6 days with either morphine sulfate or lactose via subcutaneously implanted silastic pellets. Beta-Endorphin microinfusions occurred at 24 and 96 hours after pellets were removed. Profound changes in locomotor response to beta-endorphin were found, with morphine-pretreated rats showing a spontaneous switch from hyporesponsiveness to hyperresponsiveness over 72 hours, compared to lactose-pretreated controls. These findings may reflect on current biochemical theories regarding the "switch" process in bipolar affective disease. The data can be viewed within a heuristic model of receptor changes which may underlie the transition from depression to mania.

Topics: Affective Disorders, Psychotic; Animals; beta-Endorphin; Bipolar Disorder; Dextroamphetamine; Disease Models, Animal; Endorphins; Humans; Limbic System; Male; Morphine; Motor Activity; Naloxone; Neural Pathways; Rats; Rats, Inbred Strains; Receptors, Dopamine; Substance Withdrawal Syndrome; Tegmentum Mesencephali

The effects of naloxone and thyrotropin releasing hormone (TRH) were compared in an incremental air embolization model of experimental stroke in dogs. Naloxone treatment significantly improved the cortical somatosensory evoked response and had a beneficial effect on local cerebral blood flow, whereas TRH treatment had no effect on these variables. These findings may implicate endorphins in the pathophysiology of stroke and indicate that naloxone may have a therapeutic role in this condition. Moreover, the lack of effect of TRH in this model, in contrast to its therapeutic effect in experimental spinal injury, indicates that the pathophysiologic responses to ischemic cerebral injury and traumatic spinal injury may differ.

Topics: Animals; Brain Ischemia; Cerebrovascular Circulation; Cerebrovascular Disorders; Disease Models, Animal; Dogs; Evoked Potentials, Somatosensory; Male; Naloxone; Spinal Cord Injuries; Thyrotropin-Releasing Hormone

The effects of naloxone or thyrotropin releasing hormone (TRH) upon neurologic outcome were evaluated in gerbil models of cerebral ischemia. Following temporary bilateral carotid occlusion, hypotension was transiently reversed by these endorphin antagonists. However, neither drug altered time to awaken, time to death, or the severity of neurologic signs (ptosis, movement, retracted paws, circling, righting reflexes, seizures, or opisthotonus) when evaluated by a blinded rater. Hot plate escape and roto-rod performance were also unaltered by naloxone or TRH; TRH, but not naloxone, increased respiratory rates. Thus, the transient improvement of cardiorespiratory function produced by these drugs is unrelated to the morbidity and mortality associated with temporary cerebral ischemia in the gerbil. Additional studies evaluating the effects of naloxone or TRH upon neurologic outcome following permanent unilateral carotid occlusion also failed to show any therapeutic effects of these drugs. Both morphine and TRH exacerbated the effects of ischemia. Of gerbils which developed neurologic impairment, the deficit was usually ipsilateral to the occluded carotid. Collectively, these results indicate that neither naloxone nor TRH prevents ischemic deficits in the gerbil. Further studies with different cerebral ischemia models in other species are required to clarify the possible therapeutic effects of these drugs in experimental stroke.

Topics: Animals; Arterial Occlusive Diseases; Brain Ischemia; Carotid Artery Diseases; Disease Models, Animal; Gerbillinae; Male; Motor Activity; Naloxone; Thyrotropin-Releasing Hormone

In pentobarbital-anaesthetized rats (60 mg/kg, i.p.) renal pelvis distension with a pressure of 80 cm H2O caused a decline in mean arterial blood pressure. This pressure response, which disappeared rapidly after cessation of the distension, was used to study the effects of analgesic drugs known to be effective in renal colic pain in man. Morphine (0.75 and 1 mg/kg, s.c.) and the decapeptide caerulein (1.6, 4 and 8 microgram/kg, s.c.) abolished the pressure response. The effects of the largest doses lasted for at least 30 min. Ineffective in this respect were (a) desulphated caerulein (40 microgram/kg, s.c.) and (b) additional doses of pentobarbital (20 and 40 mg/kg, s.c.). This shows (a) the importance of the sulphated tyrosine (known from previous studies on central effects) and (b) the missing influence of the depth of anaesthesia. Naloxone (0.5 mg/kg, s.c.) abolished the effect of morphine (1 mg/kg, s.c.) but failed to influence that of caerulein (8 microgram/kg, s.c.). Even a fourfold dose of naloxone (2 mg/kg, s.c.) did not weaken the effect of caerulein. Naloxone, per se, was ineffective. These results suggest different mechanisms of the present effects of morphine and caerulein. It appears that renal pelvis distension in the anaesthetized rat can serve as a model of renal colic.

Topics: Animals; Blood Pressure; Ceruletide; Disease Models, Animal; Kidney Pelvis; Male; Morphine; Naloxone; Pain; Pentobarbital; Rats; Rats, Inbred Strains

Topics: Animals; Brain Ischemia; Disease Models, Animal; Gerbillinae; Naloxone; Research Design

Pregnant near-term rabbits were given an intravenous dose of saline or the opiate antagonist naloxone and then asphyxiated. The fetuses were delivered by cesarean section and evaluated for respiration, color, muscle tone, response to stimulation, and general activity at 1, 3, 5, 10, 15, and 30 minutes of age. The naloxone-treated pups had significantly better scores during the first 15 minutes after birth than the saline-treated pups. Naloxone did not adversely affect the scores of nonasphyxiated pups. These data suggest that endogenous opiates worsen the neonatal depression caused by intrauterine asphyxia and that this effect can be reversed by naloxone.

Topics: Animals; Animals, Newborn; Asphyxia Neonatorum; Depression; Disease Models, Animal; Humans; Infant, Newborn; Naloxone; Rabbits

Topics: Alcoholism; Animals; Disease Models, Animal; Ethanol; Humans; Isoquinolines; Macaca mulatta; Male; Naloxone; Naltrexone; Narcotics; Rats; Rats, Inbred Strains; Self Administration; Tetrahydroisoquinolines

Topics: Alcohol Drinking; Alcoholism; Animals; Disease Models, Animal; Ethanol; Humans; Isoquinolines; Male; Morphine; Motor Activity; Naloxone; Rats; Rats, Inbred Strains; Tetrahydroisoquinolines

Clonidine and L-alpha-methylnoradrenaline (but not D-alpha-methylnoradrenaline) increase the release of a substance with beta-endorphin immunoreactivity from slices of brainstem of spontaneously hypertensive rats, but not that of normotensive rats. It was reported earlier that opiate antagonists inhibit the hypotensive action of clonidine and alpha-methyldopa in spontaneously hypertensive but not in normotensive rats and that beta-endorphin has hypotensive effects of its own. Together, these findings indicate that release of beta-endorphin by central alpha-receptor agonists may contribute to the antihypertensive action of these drugs.

Topics: Adrenergic alpha-Agonists; Animals; Brain Stem; Clonidine; Disease Models, Animal; Endorphins; Hypertension; Immunoassay; Male; Naloxone; Nordefrin; Rats

Phencyclidine (PCP) given to male Wistar rats produced hyperactivity and various stereotypic motor behaviors. Methadone, apomorphine, and naloxone were tested for their effects on PCP-induced stereotypy. Methadone (0.5 mg/kg) had no effect on the hyperactivity produced by PCP, but significantly attenuated PCP-induced stereotypy when given both before and after PCP. Low doses of apomorphine were equally effective as methadone in attenuating PCP-induced stereotypy. However, when naloxone was given after methadone or apomorphine to PCP-treated rats, the full PCP-induced stereotypy was again observed. Naloxone pretreatment on doses up to 20 mg/kg was not effective in antagonizing PCP-induced behavioral effects. Methadone and apomorphine antagonism of PCP-induced stereotypy may be mediated by opiate receptors. The results of this study and observations from human studies collectively suggest the possible effectiveness of opiates in treating PCP-induced and functional psychoses.

Topics: Animals; Apomorphine; Brain Chemistry; Disease Models, Animal; Humans; Male; Methadone; Motor Activity; Naloxone; Phencyclidine; Psychoses, Substance-Induced; Rats; Rats, Inbred Strains; Stereotyped Behavior; Time Factors

Topics: Alcoholism; Animals; Corticosterone; Disease Models, Animal; Ethanol; Humans; Male; Naloxone; Rats; Starvation; Time Factors

The narcotic antagonist naloxone has been shown to reverse hypotension in hemorrhagic and septic shock in rats and dogs. This study was undertaken to investigate the hemodynamic effects of naloxone on hemorrhagic shock in the pig. Thirteen pigs were anesthetized with pentobarbital and were bled to a mean arterial pressure of 54 per cent of the initial mean arterial pressure. Seven pigs received naloxone in increasing doses of 1.0, 2.5 and 5.0 milligram per kilogram intravenously, while the six pigs in the control group were given identical volumes of normal saline solution. Results indicate an increase in mean arterial pressure in the pigs of the naloxone group compared with that for the pigs in the saline solution treated group. There was no increase in cardiac output after the administration of naloxone or after the injections of saline solution. Peripheral vascular resistance increased in pigs in the naloxone group compared with that in pigs in the saline solution group. These results are in accordance with the concept that naloxone may reverse hypotension in hemorrhagic shock by antagonizing endogenous opiate-like substances and that the latter may be involved in the physiopathology of shock. The rapid increase in peripheral vascular resistance after the administration of naloxone suggests a change in sympathetic reflex as a possible mechanism of naloxone action.

Topics: Animals; Blood Pressure; Cardiac Output; Disease Models, Animal; Hemodynamics; Naloxone; Shock, Hemorrhagic; Swine; Vascular Resistance

Adjuvant-induced arthritic rats were observed clinically and behaviorally. The clinical disease has a duration of greater than 1 month and can be divided into a pre-clinical (1-10 days), an acute (15-30 days), postacute (30-50 days) and a late phase (greater than 50 days). Adjuvant arthritis induces significantly quantitatively changes in the rats' behaviour. Two types of behavioural change merit special attention: freezing (arresting) and scratching. Freezing is significantly increased in the acute and postacute phases; it is increased by morphine, this effect being blocked by naloxone. Scratching is significantly increased in the acute, postacute and late phases; it is decreased by morphine, this effect being blocked by naloxone. The chronic presence of scratching, and the effects of morphine and naloxone on it, allow us to consider it as a possible pain-rated behaviour and therefore as a possible parameter for the study of chronic pain in animals.

Topics: Animals; Arthritis; Arthritis, Experimental; Behavior, Animal; Chronic Disease; Disease Models, Animal; Drug Interactions; Humans; Morphine; Naloxone; Pain; Rats

Topics: Aging; Animals; Atropine; Blood Pressure; Disease Models, Animal; Hypertension; Naloxone; Pain; Rats; Rats, Inbred Strains

The opiate antagonist naloxone has been used to treat cats subjected to cervical spinal trauma. In contrast to saline-treated controls, naloxone treatment significantly improved the hypotension observed after cervical spinal injury. More critically, naloxone therapy significantly improved neurologic recovery. These findings implicate endorphins in the pathophysiology of spinal cord injury and indicate that narcotic antagonists may have a therapeutic role in this condition.

Topics: Animals; Blood Pressure; Cats; Disease Models, Animal; Endorphins; Naloxone; Spinal Cord; Spinal Cord Injuries

Topics: Alcoholic Intoxication; Animals; Caffeine; Cats; Dextroamphetamine; Disease Models, Animal; Dogs; Ethanol; gamma-Aminobutyric Acid; Humans; Maleates; Naloxone; Pentylenetetrazole; Rabbits; Strychnine

Topics: Animals; Avoidance Learning; Behavior Therapy; Disease Models, Animal; Humans; Male; Morphine; Morphine Dependence; Naloxone; Rats

Small doses of the opiate antagonist naloxone selectively abolished overeating in genetically obese mice (ob/ob) and rats (fa/fa). Elevated concentrations of the naturally occurring opiate beta-endorphin were found in the pituitaries of both obese species and in the blood plasma of the obese rats. Brain levels of beta-endorphin and Leu-enkephalin were unchanged. These data suggest that excess pituitary beta-endorphin may play a role in the development of the overeating and obesity syndrome.

Topics: Animals; Disease Models, Animal; Eating; Endorphins; Feeding Behavior; Female; Male; Mice; Mice, Obese; Naloxone; Obesity; Pituitary Gland; Rats

Topics: Age Factors; Animals; Animals, Newborn; Behavior, Animal; Corticosterone; Disease Models, Animal; Eye; Female; Growth; Humans; Morphine; Morphine Dependence; Naloxone; Pituitary-Adrenal System; Rats; Vagina

Topics: Animals; Conditioning, Operant; Disease Models, Animal; Female; Humans; Injections, Intravenous; Morphine Dependence; Naloxone; Rats

Topics: Acupuncture Therapy; Animals; Disease Models, Animal; Humans; Male; Naloxone; Rats; Substance Withdrawal Syndrome; Substance-Related Disorders

Topics: Animals; Disease Models, Animal; Humans; Morphine; Morphine Dependence; Naloxone; Rats; Substance Withdrawal Syndrome; Time Factors

Topics: Animals; Brain; Brain Chemistry; Bucladesine; Cyclic AMP; Cyclic GMP; Depression, Chemical; Disease Models, Animal; Drug Implants; Humans; Male; Morphine; Morphine Dependence; Motor Activity; Naloxone; Phosphoric Diester Hydrolases; Rats; Stimulation, Chemical; Substance Withdrawal Syndrome

A new type of morphine implantation pellet for the rapid induction of physical dependence in mice can be prepared by absorbing 7 mg morphine sulphate onto molecular sieves Type 4A (BDH). The small cylindrical pellets can be implanted subcutaneously without trauma and the need for anaesthesia, and are easily removed at any time from the animals. The peak of physical dependence is reached 24 h after implantation, and mortality is negligible. Withdrawal symptoms can be precipitated by intraperitoneal injection of naloxone, without removal of the pellet, and up to 70% of a group of mice show the characteristic urge to jump off a raised platform. This type of pellet has definite advantages over some other sustained-release preparations used in studies on morphine addiction in small animals.

Topics: Animals; Disease Models, Animal; Drug Implants; Female; Humans; Male; Mice; Morphine; Morphine Dependence; Naloxone; Substance Withdrawal Syndrome

Topics: Animals; Behavior, Animal; Conditioning, Classical; Conflict, Psychological; Disease Models, Animal; Extinction, Psychological; Humans; Male; Morphine; Morphine Dependence; Naloxone; Punishment; Reinforcement Schedule; Reward; Substance Withdrawal Syndrome

Topics: Acetylcholine; Adaptation, Physiological; Animals; Brain; Disease Models, Animal; Dopamine; Drug Interactions; Humans; Mice; Morphine Dependence; Naloxone; Parasympathetic Nervous System; Rats; Substance Withdrawal Syndrome

The experimental paradigm reported here provides a useful animal model with which to further study the effects of regional electrostimulation and its possible relationship with electrical acupuncture. What similarities there may be between electrical acupuncture and the technique of regional electrocerebral stimulation used for production of electrosleep and electronarcosis in animals and man (Wageneder et al., 1966) remain to be elucidated. Further research studies, both clinical and basic, are clearly needed to answer some of the questions relating to the safety, efficacy, and possible mechanisms by which a technique such as electrical acupuncture may exert its effects.

Topics: Acupuncture Therapy; Animals; Behavior, Animal; Disease Models, Animal; Ear; Electric Stimulation; Humans; Male; Morphine Dependence; Motor Activity; Naloxone; Rats; Substance Withdrawal Syndrome

Weight loss and shock-elicited aggression have been compared as quantitative indices of morphine abstinence in rats. A range of doses of morphine was administered to rats by i.p. injection twice daily for 12-15 days. After injections were stopped, morphine-abstinent rats lost weight precipitously, and showed an increased frequency of fighting in response to aversive stimulation (foot-shock). Recovery of weight appeared complete after 15-20 days but a significant increase in aggression was found at 18 days post-withdrawal; this virtually disappeared after 52 days. Both the amount of weight lost and the frequency of fighting increased as a function of the previous maintenance dose of morphine; the effective dose range appeared similar for these two indices. Weight loss was much less variable than fighting, had the advantage of rapid, objective measurement, and appeared to be the more reliable index of abstinence.

Topics: Aggression; Animals; Body Weight; Disease Models, Animal; Dose-Response Relationship, Drug; Electroshock; Humans; Male; Morphine; Morphine Dependence; Naloxone; Rats; Substance Withdrawal Syndrome

Topics: Animals; Behavior, Animal; Cyclazocine; Disease Models, Animal; Dose-Response Relationship, Drug; Humans; Levallorphan; Morphine Dependence; Motor Activity; Naloxone; Rats; Substance Withdrawal Syndrome

Topics: Acute Disease; Animals; Disease Models, Animal; Dogs; Female; Humans; Male; Morphine Dependence; Naloxone; Substance Withdrawal Syndrome; Time Factors

Topics: 5-Hydroxytryptophan; Animals; Behavior, Animal; Delayed-Action Preparations; Disease Models, Animal; Drug Synergism; Heroin; Humans; Male; Morphine; Morphine Dependence; Motor Activity; Naloxone; Rats; Substance Withdrawal Syndrome; Theophylline