naloxone and Inflammation

Evidence from postmortem analysis implicates the involvement of microglia in the neurodegenerative process of several degenerative neurological diseases, including Alzheimer's disease and Parkinson's disease. It remains to be determined, however, whether microglial activation plays a role in the initiation stage of disease progression or occurs merely as a response to neuronal death. Activated microglia secrete a variety of proinflammatory and neurotoxic factors that are believed to induce and/or exacerbate neurodegeneration. In this article, we summarize recent advances on the study of the role of microglia based on findings from animal and cell culture models in the pathogenesis of neurodegenerative diseases, with particular emphasis on Parkinson's disease. In addition, we also discuss novel approaches to potential therapeutic strategies.

Topics: Animals; Anti-Inflammatory Agents; Dopamine; Humans; Inflammation; Microglia; Naloxone; Nerve Degeneration; Neuroprotective Agents; Parkinson Disease

Topics: Animals; Dopamine; Humans; Inflammation; Naloxone; Narcotic Antagonists; Nerve Degeneration; Neurodegenerative Diseases; Neuroprotective Agents

Topics: Analgesics, Opioid; Animals; Corticotropin-Releasing Hormone; Cytokines; Forecasting; Gene Expression Regulation; Hormones; Humans; Inflammation; Leukocytes; Lymphocytes; Naloxone; Narcotic Antagonists; Neuroimmunomodulation; Neuropeptides; Neurosecretory Systems; Opioid Peptides; Pro-Opiomelanocortin; Rats; Receptors, Corticotropin-Releasing Hormone; Receptors, Opioid; Shock, Septic

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

This study aimed to investigate how opioids affect phagocytosis and microglial nitrite and nitric oxide synthase (iNOS) production during inflammation.. Opioids are a group of chemicals that are naturally found in the opium poppy plant and exert a variety of effects on the brain, including pain alleviation in some cases. They are commonly used in surgery and perioperative analgesia. However, research on the impact of opioids on microglial inflammatory factor production and phagocytosis is limited.. This study was designed to investigate the effects of opioids on inducible nitric oxide synthase (iNOS) activity and nitric oxide (NO) generation. Moreover, the influence of opioids on the engulfment of C8-B4 microglial cells after stimulation with LPS was also examined.. C8-B4 mouse microglial cells were exposed to various concentrations of opioids after stimulation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ). Nitrite production was assayed. The iNOS and Cox-2 were determined by Western blotting, and fluorescent immunostaining was performed to assess the percentage of microglia that engulfed fluorescent microspheres in total microglia cultivating with opioids after being activated by LPS.. After LPS and IFN-γ stimulation, microglia produced lower amounts of nitric oxide (NO) production with buprenorphine, salvinorin A, and naloxone (P<0.05). When combined with naloxone, no significant differences were found than buprenorphine. It was observed that buprenorphine and salvinorin A could suppress iNOS expression activated by LPS and IFN-γ. Phagocytosis was greatly increased after LPS stimulation, and a significant increase was observed after adding salvinorin A.. Buprenorphine and salvinorin A were found to reduce NO production and iNOS induction in microglial cells activated by LPS and IFN-γ. Salvinorin A promoted the phagocytosis of microglia cells treated by LPS.

Topics: Analgesics, Opioid; Animals; Buprenorphine; Inflammation; Interferon-gamma; Lipopolysaccharides; Mice; Microglia; Naloxone; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitrites; Phagocytosis

Oxidative stress and inflammation are major factors contributing to the progressive death of dopaminergic neurons in Parkinson's disease (PD). Recent studies have demonstrated that morphine's biosynthetic pathway, coupled with nitric oxide (NO) release, is evolutionarily conserved throughout animals and humans. Moreover, dopamine is a key precursor for morphine biosynthesis.. The present study evaluated a series of preclinical experiments to evaluate the effects of low-level morphine treatment upon neuro-immune tissues exposed to rotenone and 6-OHDA as models of PD, followed by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation assay and cell/tissue computer-assisted imaging analyses to assess cell/neuronal viability.. Morphine at normal physiological concentrations (i.e., 10-6 M and 10-7 M) provided neuroprotection, as it significantly inhibited rotenone and 6-OHDA dopaminergic insults; thereby, reducing and/or forestalling cell death in invertebrate ganglia and human nerve cells. To ensure that morphine caused this neuroprotective effect, naloxone, a potent opiate receptor antagonist, was employed and the results showed that it blocked morphine's neuroprotective effects. Additionally, co-incubation of NO synthase inhibitor L-NAME also blocked morphine's neuroprotective effects against rotenone and 6-OHDA insults.. Taken together, the present preclinical study showed that while morphine can attenuate lipopolysaccharide-induced inflammation and cell death, both naloxone and L-NAME can abolish this effect. Preincubation of morphine precursors (i.e., L-3,4-dihydroxyphenylalanine, reticuline, and trihexyphenidyl [THP] at physiological concentrations) mimics the observed morphine effect. However, high concentrations of THP, a precursor of the morphine biosynthetic pathway, induced cell death, indicating the physiological importance of morphine biosynthesis in neural tissues. Thus, understanding the morphine biosynthetic pathway coupled with a NO signaling mechanism as a molecular target for neuroprotection against oxidative stress and inflammation in other preclinical models of PD is warranted.

Topics: Animals; Dopaminergic Neurons; Humans; Inflammation; Morphine; Naloxone; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Oxidative Stress; Oxidopamine; Parkinson Disease; Rotenone; Signal Transduction

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

Eugenia pohliana DC.(Myrtaceae) is used in folk medicine by communities in Brazil. However, there are no reports on its biological activity. This is the first study to identify the components of E. pohliana essential oil (EpEO) and evaluate their antinociceptive and anti-inflammatory activities in an in vivo model at doses of 25, 50, and 100 mg/kg. The essential oil (EO) was obtained by hydrodistillation, and the analysis was performed by gas chromatography coupled with mass spectrometry. Antinociceptive activity was evaluated by writhing tests, tail movement, and formalin (neurogenic and inflammatory pain); naloxone was used to determine the nociception mechanism. Anti-inflammatory activity was assessed by oedema and peritonitis tests. We found that (E)-β-caryophyllene (BCP) (15.56%), δ-cadinene (11.24%) and α-cadinol (10.89%) were the major components. In the writhing test, there was a decrease in writing by 42.95-70.70%, in the tail movement, an increase in latency time by 69.12-86.63%, and in the formalin test, there was a reduction in pain neurogenic by 29.54-61.74%, and inflammatory pain by 37.42-64.87%. The antinociceptive effect of EpEO occurs through the activation of opioid receptors. In addition, a reduction in inflammation by 74.93‒81.41% was observed in the paw edema test and inhibition of the influx of leukocytes by 51.86‒70.38% and neutrophils by 37.74‒54.72% in the peritonitis test. It was concluded that EpEO has antinociceptive effect by the opioid pathway, as shown by the inhibitory effect of naloxone, and anti-inflammatory actions, and that its use does not cause hemolytic damage or behavioral change.

Topics: Analgesics; Animals; Anti-Inflammatory Agents; Edema; Eugenia; Inflammation; Mice; Myrtaceae; Naloxone; Nociception; Oils, Volatile; Pain; Peritonitis; Plant Extracts

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

Chronic morphine exerts deleterious effects on testicular function through either suppression of germ cells or somatic including Sertoli cells, probably through the activation of inflammatory, oxidative, and apoptosis biomarkers. Thus, the present study aimed to investigate whether the damaging effects of morphine dependence were reversed by the spontaneous morphine withdrawal or incubation with methadone and/or naloxone in Sertoli (TM4) cells using an in- vitro cell model of morphine dependence. Morphine dependence in TM4 cells was induced by increasing daily doses of morphine for 10 days and then maintained for two weeks in 5 μM. The cAMP levels were measured for an evaluation of morphine dependence. The cell viability and inflammatory, oxidative, apoptosis biomarkers, and glial cell-derived neurotrophic factor (GDNF) were measured after the end of treatment following the incubation of cells with methadone and naloxone and spontaneous withdrawal from morphine. We found that morphine dependence decreased cell viability, GDNF level and increased the levels of pro-oxidant, pro-inflammatory, and apoptotic biomarkers in TM4 cells, while spontaneous withdrawal from morphine and by naloxone decreased the levels of the biomarkers of pro-inflammatory and apoptotic in TM4 cells. Also, despite the low levels of pro-inflammatory factors following morphine withdrawal by methadone, it increased the cleaved/pro-caspase3 ratio in TM4 cells. This study showed that morphine dependence increased apoptosis probably via oxidative stress and inflammation pathways in TM4 cells. Also, it seems likely that spontaneous and naloxone withdrawal have beneficial consequences in the treatment of morphine dependence than methadone therapy, although they may require longer incubation periods.

Topics: Analgesics, Opioid; Animals; Apoptosis; Biomarkers; Cell Line; Cyclic AMP; Glial Cell Line-Derived Neurotrophic Factor; Inflammation; Male; Methadone; Mice; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Oxidative Stress; Oxidoreductases; Proto-Oncogene Proteins c-bcl-2; Sertoli Cells; Substance Withdrawal Syndrome

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; Depression; Inflammation; Male; Mice; Naloxone; Stress, Psychological; Toll-Like Receptor 4

Postpartum uterine infections are common reproductive diseases in postpartum cows. Evidence has shown that plasma β-endorphins increase during bovine uterine inflammation. However, the effect of β-endorphins on the inflammatory response in bovine endometrium has not been clarified. The aim of this study was to investigate the effect of β-endorphins on the inflammatory response of bovine endometrial epithelial and stromal cells, and to explore the possible mechanism. The cells were treated with E. coli lipopolysaccharide (LPS) to simulate inflammation, which was characterized by the significant activation of NF-κB signaling pathway and the increased gene expression of the downstream proinflammatory cytokines (approximately 1.2- to 15-fold increase, P < 0.05). By using Western blot and qPCR techniques, we found that β-endorphins inhibited the key protein expression of NF-κB pathway, and the gene expressions of TNF, IL1B, IL6, CXCL8, nitric oxide synthase 2, and prostaglandin-endoperoxide synthase 2 (P < 0.05). The co-treatment of β-endorphins and opioid antagonists showed that the anti-inflammatory effect of β-endorphins could be blocked (P < 0.05) by non-selective opioid antagonist naloxone or δ opioid receptor antagonist ICI 154129, but not the μ opioid receptor antagonist CTAP (P > 0.05). In conclusion, β-endorphins may inhibit the inflammatory response of bovine endometrial epithelial and stromal cells through δ opioid receptor.

Topics: Animal Husbandry; Animals; beta-Endorphin; Cattle; Cells, Cultured; Endometritis; Endometrium; Enkephalin, Leucine; Epithelial Cells; Escherichia coli; Female; Inflammation; Lipopolysaccharides; Naloxone; Narcotic Antagonists; NF-kappa B; Primary Cell Culture; Puerperal Infection; Receptors, Opioid, delta; Signal Transduction

Topics: Acute Pain; Analgesics; Animals; Behavior, Animal; CHO Cells; Cricetinae; Cricetulus; Cycloheptanes; Humans; Hyperalgesia; In Vitro Techniques; Inflammation; Male; Mice; Models, Molecular; Molecular Docking Simulation; Morphine; Movement; Naloxone; Naltrexone; Nociceptin; Oligopeptides; Opioid Peptides; Pain Management; Piperidines; Receptors, Opioid, mu

Mucosal CD4

Topics: Animals; Anti-Inflammatory Agents; Anti-Inflammatory Agents, Non-Steroidal; Apoptosis; CD4-Positive T-Lymphocytes; Colitis; Cytokines; Epithelial Cells; Inflammation; Interleukin-10; Intestinal Mucosa; Mice; Mice, Inbred C57BL; Mice, Knockout; Naloxone; Narcotic Antagonists; Permeability; Piroxicam; Quaternary Ammonium Compounds; Receptors, Opioid; Severity of Illness Index

Opioids such as morphine are the most effective treatment for pain, but termination of opioid use can produce severe withdrawal symptoms. The present study models this process by using home cage wheel running to assess well-being as a result of pain, morphine analgesia, and opioid withdrawal. Injection of CFA into the right hindpaw caused a dramatic decrease in wheel running and body weight. Implantation of two morphine pellets (75 mg each) resulted in an increase in body weight on Day 1 of administration and a more gradual restoration of wheel running that was only evident during the dark phase of the circadian cycle on Days 3 and 4 of morphine administration. Continuous morphine administration decreased wheel running during the relatively inactive light phase. These findings are consistent with the clinical goal of pain therapeutics to restore normal activity during the day and facilitate sleep at night. Administration of naloxone (1 mg/kg) on Day 5 of morphine administration depressed wheel running for approximately 4 h and caused an increase in wet dog shakes. Naloxone-precipitated changes were no longer evident 6 h after administration. These findings demonstrate that the use of morphine to treat pain does not protect against opioid withdrawal. Moreover, this study provides additional support for the use of home cage wheel running as a method to assess changes in well-being as a result of pain, analgesia, and opioid withdrawal.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Inflammation; Male; Morphine; Motor Activity; Naloxone; Narcotic Antagonists; Opioid-Related Disorders; Pain; Rats; Rats, Sprague-Dawley; 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

Preventing and treating opioid dependence and withdrawal is a major clinical challenge, and the underlying mechanisms of opioid dependence and withdrawal remain elusive. We hypothesized that prolonged morphine exposure or chronic inflammation-induced μ-opioid receptor activity serves as a severe stress that elicits neuronal alterations and recapitulates events during development. Here, we report that Wnt signaling, which is important in developmental processes of the nervous system, plays a critical role in withdrawal symptoms from opioid receptor activation in mice. Repeated exposures of morphine or peripheral inflammation produced by intraplantar injection of complete Freund's adjuvant significantly increase the expression of Wnt5b in the primary sensory neurons in dorsal root ganglion (DRG). Accumulated Wnt5b in DRG neurons quickly transmits to the spinal cord dorsal horn (DH) after naloxone treatment. In the DH, Wnt5b, acts through the atypical Wnt-Ryk receptor and alternative Wnt-YAP/TAZ signaling pathways, contributing to the naloxone-precipitated opioid withdrawal-like behavioral symptoms and hyperalgesia. Inhibition of Wnt synthesis and blockage of Wnt signaling pathways greatly suppress the behavioral and neurochemical alterations after naloxone-precipitated withdrawal. These findings reveal a critical mechanism underlying naloxone-precipitated opioid withdrawal, suggesting that targeting Wnt5b synthesis in DRG neurons and Wnt signaling in DH may be an effective approach for prevention and treatment of opioid withdrawal syndromes, as well as the transition from acute to chronic pain.

Topics: Analgesics, Opioid; Animals; Cells, Cultured; Chronic Disease; Inflammation; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Posterior Horn Cells; Receptors, Opioid; Substance Withdrawal Syndrome; Wnt Proteins; Wnt Signaling Pathway

Topics: Analgesics, Opioid; Animals; Binding, Competitive; Codeine; Freund's Adjuvant; Gastrointestinal Transit; Inflammation; Injections, Intraventricular; Male; Mice; Naloxone; Nociception; Pain; Rats, Wistar; Receptors, Opioid, mu

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

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

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

Morphine - the main pillar of nociceptive pain management - systemic use is associated with development of tolerance and dependence. Tolerance and dependence lay a heavy burden in clinical pain management settings. An added weight to this dilemma is that effective, safe, and tolerable solution to this problem is still beyond reach. Antidepressants were reported as possible alleviators of opioid tolerance and dependence. One of the increasingly used antidepressant in clinical practice is bupropion given its high safety and tolerability profile.. The study was performed on male Balb-c mice weighing 20-30g. Hot plate test was used for assessment of bupropion (5mg/kg, ip) possible analgesic activity and enhancement of morphine acute analgesia (1 and 5mg/kg, sc). Repeated morphine (5mg/kg, sc) administration for 9days developed tolerance and dependence, bupropion (5mg/kg, ip) was concurrently administered to evaluate its potential to modulate these processes. We also biochemically analyzed bupropion effect on these phenomena through modulation of neurotransmitters (glutamate and norepinephrine), inflammatory status (nitric oxide), and pro-antioxidant balance (malondialdehyde and reduced glutathione).. Bupropion was devoid of intrinsic analgesic activity and did not enhance morphine acute analgesia. However, bupropion significantly attenuated morphine tolerance and dependence development and abstinence syndrome with corresponding suppression of morphine induced changes in glutamate, norepinephrine, inflammatory status, and prooxidant-antioxidant balance.. Bupropion efficacy in attenuation of morphine tolerance and dependence with its high safety and tolerability profile provide an alternative option to conventional agents e.g., ketamine and clonidine to modulate these phenomena.

Topics: Animals; Brain; Bupropion; Dose-Response Relationship, Drug; Drug Tolerance; Glutamic Acid; Glutathione; Inflammation; Male; Malondialdehyde; Mice; Morphine; Morphine Dependence; Naloxone; Nitric Oxide; Norepinephrine; Organophosphorus Compounds; Oxidative Stress; Pain Measurement; Substance Withdrawal Syndrome

Topics: Analgesia; Analgesics, Opioid; Animals; Antigens, Ly; Carrageenan; Female; Inflammation; Macrophages; Mice; Morpholines; Naloxone; Narcotic Antagonists; Neutrophils; Oligopeptides; Pain; Piperazines; Pro-Opiomelanocortin; Pyrazoles; Quaternary Ammonium Compounds; Receptors, sigma; Sigma-1 Receptor

The mechanisms of axonal trafficking and membrane targeting are well established for sodium channels, which are the principle targets for perineurally applied local anaesthetics. However, they have not been thoroughly investigated for G protein coupled receptors such as mu-opioid receptors (MOR). Focusing on these axonal mechanisms, we found that axonal MOR functionality is quite distinct in two different pain states, i.e. hindpaw inflammation and nerve injury. We observed axonal membrane MOR binding and functional G protein coupling exclusively at sites of CCI nerve injury. Moreover at these axonal membrane sites, MOR exhibited extensive co-localization with the membrane proteins SNAP and Na/K-ATPase as well as NGF-dependent enhanced lipid rafts and L1CAM anchoring proteins. Silencing endogenous L1CAM with intrathecal L1CAM specific siRNA, disrupting lipid rafts with the perineurial cholesterol-sequestering agent MβCD, as well as suppressing NGF receptor activation with the perineurial NGF receptor inhibitor K252a abrogated MOR axonal membrane integration, functional coupling, and agonist-elicited antinociception at sites of nerve injury. These findings suggest that local conceptual changes resulting from nerve injury are required for the establishment of functional axonal membrane MOR. Axonal integration and subsequent accessibility of functionally coupled MOR are of great relevance particularly for patients suffering from severe pain due to nerve injury or tumour infiltration.

Topics: Analgesics, Opioid; Animals; Axons; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Fentanyl; Freund's Adjuvant; Inflammation; Male; Naloxone; Narcotic Antagonists; Neuralgia; Rats, Wistar; Receptors, Opioid, mu; Sciatic Nerve

Amylin (AMY) is a member of calcitonin family of peptides. In this study, the effects of intrathecal (i.t) injection of AMY on the inflammatory pain and on the cAMP accumulation in the rat spinal cells were investigated. By using AMY receptor antagonists, we also studied the pharmacology of AMY receptors in the spinal cells. Formalin model of inflammatory pain was induced by intraplantar injection of formalin. AMY (0.06250-2500pmol/rat) was administrated i.t 15min before the injection of formalin. Antagonists were injected i.t 10min before the injection of AMY and/or morphine. AMY reduced formalin-induced pain in a dose dependent mode. This effect was inhibited by the potent AMY antagonist, AC187 but not CGRP8-37. rAMY8-37, most commonly reported as a weak AMY antagonist, showed to be equally or more potent than AC187 in antagonizing the above effects. The opioid antagonist, naloxone, had no significant effects on AMY antinociceptive effects. Primary dissociated cell culture was used to investigate the effect of AMY on cAMP production and to characterize AMY receptors in the spinal cells. AMY moderately increases cAMP accumulation in the spinal cells with an EC50 value of 74.62nM. This effect was not affected by CGRP8-37 but was inhibited by AC187 and rAMY8-37 with pA2 values of 7.94 and 7.87 respectively. In conclusion, effects of AMY in reducing formalin induced pain and on the cAMP accumulation by spinal cells are mediated through undefined receptors.

Topics: Amylin Receptor Agonists; Analgesics; Analgesics, Opioid; Animals; Calcitonin Gene-Related Peptide; Cyclic AMP; Formaldehyde; Inflammation; Injections, Spinal; Islet Amyloid Polypeptide; Male; Morphine; Naloxone; Narcotic Antagonists; Nociception; Pain; Pain Threshold; Peptide Fragments; Primary Cell Culture; Rats; Rats, Sprague-Dawley; Receptors, Islet Amyloid Polypeptide; Spinal Cord

Major attention has been on dietary and medicinal phytochemicals that inhibit or reverse abnormal conditions caused by nociceptive and inflammatory stimuli. Garcinia kola (Guttiferae) seed, known as "bitter kola", plays an important role in African ethno-medicine and traditional hospitality like in the treatment of inflammation, colds, bronchitis, bacterial, and viral infections. A number of useful phytochemicals have been isolated from the seed, and the most prominent of them is kolaviron (Garcinia bioflavonoid), which has been suggested to have antinociceptive and anti-inflammatory potentials. The aim of this experiment is to explore the mechanisms of action of the antinociceptive and anti-inflammatory potentials of kolaviron.. The probable mechanisms of action of kolaviron were assessed by using naloxone, prazosin, and atropine to investigate the involvement of adrenergic, opioidergic, and cholinergic systems, respectively, using tail flick, the acetic acid-induced writhing, formalin-induced paw licking, and carrageenan-induced paw edema models. Also, hematoxylin and eosin (H&E) staining was used to analyze the level of inflammation.. In the acetic acid-induced writhing test in mice, pretreatment with naloxone, prazosin, and atropine significantly reversed the antinociception effects of kolaviron (200 mg/kg) when compared with control and kolaviron groups. In the formalin-induced paw licking test in mice, there was a significant decrease on the antinociceptive effects of kolaviron in the late phase when compared with the control, while the pretreatment with naloxone and prazosin significantly reversed the antinociception of kolaviron but atropine did not have any significant decrease when compared with the kolaviron group. In the tail flick latency assay in rats, pretreatment with naloxone and prazosin significantly reversed the antinociception of kolaviron but atropine; however, did not have any significant increase when compared with the control and kolaviron groups. The result of the study also shows a highly significant inhibition of paw edema in the carrageenan-induced receiving kolaviron when compared with the vehicle carrageenan-induced groups. Histological staining also showed that kolaviron significantly reduced the infiltration of inflammatory cells in the paw tissues.. Kolaviron possesses antinociceptive and anti-inflammatory activity, both centrally and peripherally, which justifies its folkloric use to relieve pain and inflammation. It may be exerting its effects through mechanisms that involve opioidergic and adrenergic systems, and may not involve the cholinergic system.

Topics: Acetic Acid; Analgesics; Animals; Anti-Inflammatory Agents; Atropine; Carrageenan; Edema; Female; Flavonoids; Inflammation; Male; Mice; Naloxone; Pain; Phytotherapy; Plant Extracts; Prazosin; Rats; Rats, Wistar

This study was designed to investigate the contribution of prostaglandins to the maintenance of inflammatory pain. Inflammation was induced by intraplantar (i.pl.) injection of carrageenan in right hindpaw in rats. Indomethacin (non-selective COX inhibitor) was administered i.pl. 1 h after the carrageenan injection, and paw withdrawal latency (PWL) responding to noxious heat was measured. β-endorphin (β-END) and μ-opioid receptor (MOR) expressed in the inflamed site were examined by using immunocytochemistry, ELISA and RT-PCR techniques. The results showed that indomethacin dose-dependently increased PWL to the levels that were above the baseline on the day 2 and 3, referred to as hypoalgesia. The hypoalgesia was abolished by a local injection of the non-selective opioid receptor inhibitor naloxone methiodide. The number of β-END-positive cells, the content of β-END and the expression of MOR mRNA in the inflammatory site of inflammation model rats were all significantly increased by indomethacin. These results reveal a novel mechanism of prostaglandins for the inhibition of inflammation-induced endogenous opioid activity. This study provides further evidence that inhibition of prostaglandins in inflamed site could be a promising therapy for inflammatory pain.

Topics: Analgesics, Opioid; Animals; beta-Endorphin; Carrageenan; Indomethacin; Inflammation; Naloxone; Pain; Prostaglandins; Rats; Receptors, Opioid

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

Toll-like receptor 4 (TLR4) activation by bacterial infection, or by sterile inflammatory insult is a primary trigger of spontaneous preterm birth. Here we utilize mouse models to investigate the efficacy of a novel small molecule TLR4 antagonist, (+)-naloxone, the non-opioid isomer of the opioid receptor antagonist (-)-naloxone, in infection-associated preterm birth. Treatment with (+)-naloxone prevented preterm delivery and alleviated fetal demise in utero elicited by i.p. LPS administration in late gestation. A similar effect with protection from preterm birth and perinatal death, and partial correction of reduced birth weight and postnatal mortality, was conferred by (+)-naloxone administration after intrauterine administration of heat-killed E. coli. Local induction by E. coli of inflammatory cytokine genes Il1b, Il6, Tnf and Il10 in fetal membranes was suppressed by (+)-naloxone, and cytokine expression in the placenta, and uterine myometrium and decidua, was also attenuated. These data demonstrate that inhibition of TLR4 signaling with the novel TLR4 antagonist (+)-naloxone can suppress the inflammatory cascade of preterm parturition, to prevent preterm birth and perinatal death. Further studies are warranted to investigate the utility of small molecule inhibition of TLR-driven inflammation as a component of strategies for fetal protection and delaying preterm birth in the clinical setting.

Topics: Animals; Cytokines; Female; Inflammation; Lipopolysaccharides; Mice; Naloxone; Pregnancy; Premature Birth; Toll-Like Receptor 4

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

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

Trans-caryophyllene is a sesquiterpene present in many medicinal plants' essential oils, such as Ocimum gratissimum and Cannabis sativa. In this study, we evaluated the antinociceptive activity of trans-caryophyllene in murine models of acute and chronic pain and the involvement of trans-caryophyllene in the opioid and endocannabinoid systems. Acute pain was determined using the hot plate test (thermal nociception) and the formalin test (inflammatory pain). The chronic constriction injury (CCI) of the sciatic nerve induced hypernociception was measured by the hot plate and von Frey tests. To elucidate the mechanism of action, mice were pre-treated with naloxone or AM630 30 min before the trans-caryophyllene treatment. Afterwards, thermal nociception was evaluated. The levels of IL-1β were measured in CCI-mice by ELISA. Trans-caryophyllene administration significantly minimized the pain in both the acute and chronic pain models. The antinociceptive effect observed during the hot plate test was reversed by naloxone and AM630, indicating the participation of both the opioid and endocannabinoid system. Trans-caryophyllene treatment also decreased the IL-1β levels. These results demonstrate that trans-caryophyllene reduced both acute and chronic pain in mice, which may be mediated through the opioid and endocannabinoid systems.

Topics: Acute Pain; Administration, Oral; Analgesics; Animals; Cannabis; Chronic Pain; Formaldehyde; Hot Temperature; Hyperalgesia; Inflammation; Interleukin-1beta; Male; Mice; Mice, Inbred C57BL; Naloxone; Ocimum; Oils, Volatile; Phytotherapy; Plant Extracts; Polycyclic Sesquiterpenes; Sesquiterpenes

The present work reports the anti-inflammatory and antinociceptive activities of the ethanol extract obtained from the stem bark of Sterculia striata A. St.-Hil. & Naudin (Ss-EtOH) in the experimental models of edema induced by carrageenan, dextran, or histamin and nociception induced by chemical stimuli, such as acetic acid, formalin, capsaicin, or glutamate. The Ss-EtOH (50 mg/kg) promoted a marked inhibition on the hind paw edema induced by carrageenan or dextran (30% and 73%, respectively). Besides, Ss-EtOH (25 mg/kg) exhibited a slight activity (30%) on the hind paw edema induced by histamin. The Ss-EtOH (12.5 and 25 mg/kg) showed the antinociceptive activity on chemical stimuli induced by acetic acid (65.59% and 38.37%, respectively), formalin, in the initial (35.08% and 31.5%, respectively) and late phases (44.09% and 83.57%, respectively), capsaicin (43.77% and 51.31%, respectively), or glutamate (36.6% and 52.12%, respectively). Regarding the possible mechanism involved in the antinociceptive effect, Ss-EtOH (12.5 mg/kg) showed a decrease in the antinociceptive effect (65.8%) in the acetic acid model after pretreatment with naloxone. Thus, opioid mechanisms might be underlying this response.

Topics: Acetic Acid; Analgesics; Animals; Anti-Inflammatory Agents; Capsaicin; Carrageenan; Dextrans; Edema; Formaldehyde; Glutamic Acid; Histamine; Inflammation; Male; Mice; Naloxone; Pain; Phytotherapy; Plant Bark; Plant Extracts; Plant Stems; Rats, Wistar; Sterculia

We compared the gastrointestinal effects of milk-based diets in which the β-casein component was either the A1 or A2 type in male Wistar rats fed the experimental diets for 36 or 84 h. Gastrointestinal transit time was significantly greater in the A1 group, as measured by titanium dioxide recovery in the last 24 h of feeding. Co-administration of naloxone decreased gastrointestinal transit time in the A1 diet group but not in the A2 diet group. Colonic myeloperoxidase and jejunal dipeptidyl peptidase (DPP)-4 activities were greater in the A1 group than in the A2 group. Naloxone attenuated the increase in myeloperoxidase activity but not that in DPP-4 activity in the A1 group. Naloxone did not affect myeloperoxidase activity or DPP-4 activity in the A2 group. These results confirm that A1 β-casein consumption has direct effects on gastrointestinal function via opioid-dependent (gastrointestinal transit and myeloperoxidase activity) and opioid-independent (DPP-4 activity) pathways.

Topics: Animals; Caseins; Colon; Diet; Dipeptidyl Peptidase 4; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Gastrointestinal Transit; Inflammation; Jejunum; Male; Milk; Naloxone; Narcotic Antagonists; Peroxidase; Rats, Wistar

The analgesic activity of Porcellio laevis Latreille, Rhizoma Corydalis, and Radix Cynanchi Paniculati have been reported in recent years. A new formula named Jia-Yuan-Qing pill (JYQP) is therefore created by combining the three herbs at 9:7:7 ratio according to traditional Chinese theories. The present study aims to evaluate the effect of JYQP as a novel painkiller in various models. Acute toxicity test was applied to evaluate the safety of JYQP. Acetic-acid-induced writhing, hot plate test, formalin test, and naloxone-pretreated writhing test were employed to elaborate the analgesic activity of JYQP and its possible mechanism. A bone cancer pain mouse model was performed to further assess the effect of JYQP in relieving cancer pain. Test on naloxone-precipitated withdrawal symptoms was conduct to examine the physical dependence of mice on JYQP. Data revealed that JYQP reduced writhing and stretching induced by acetic acid; however, this effect could not be blocked by naloxone. JYQP specifically suppressed the phase II reaction time in formalin-treated mice; meanwhile, no analgesic effect of JYQP in hot plate test was observed, indicating that JYQP exerts analgesic activity against inflammatory pain rather than neurogenic pain. Furthermore, JYQP could successfully relieve bone cancer pain in mice. No physical dependence could be observed upon long-term administration in mice. Collectively, our present results provide experimental evidence in supporting clinical use of JYQP as an effective and safe agent for pain treatment.

Topics: Analgesics; Animals; Bone Neoplasms; Corydalis; Cynanchum; Female; Inflammation; Isopoda; Male; Medicine, Chinese Traditional; Mice; Mice, Inbred C57BL; Naloxone; Narcotic Antagonists; Pain; Phytotherapy; Plant Extracts

Phosphoinositide 3-kinase (PI3K) delta and gamma (the p110δ and p110γ isoforms of PI3K) actively participate in the process of inflammation. We sought to elucidate the possible roles of PI3Kδ and PI3Kγ in mediating the anti-inflammation effects of naloxone.. Murine macrophages were treated with endotoxin, endotoxin plus naloxone, or endotoxin plus naloxone plus the PI3K inhibitors (the PI3Kδ inhibitor IC87114, the PI3Kγ inhibitor AS252424, or IC87114 plus AS252424) and denoted as the LPS, LPS + N, LPS + N + IC, LPS + N + AS, and LPS + N + IC + AS group, respectively. Differences in inflammatory molecules and levels of nuclear factor-κB (NF-κB) activation and Akt activation (indicator of PI3K activity) among these groups were compared.. The concentrations of inflammatory molecules (macrophage inflammatory protein 2, tumor necrosis factor-α, interleukin-1β, and cyclooxygenase-2/prostaglandin E2) and the levels of NF-κB activation (p-NF-κB p65 and p-inhibitor-κB concentrations and NF-κB-DNA binding activity) of the LPS + N group were significantly lower than those of the LPS group (all P < 0.001). These data confirmed the anti-inflammation effects of naloxone. Moreover, the anti-inflammation effects of naloxone could be counteracted by the inhibitors of PI3Kδ and PI3Kγ, as the concentrations of inflammatory molecules and the levels of NF-κB activation of the LPS + N group were significantly lower than those of the LPS + N + IC, LPS + N + AS, and LPS + N + IC + AS groups (all P < 0.05). In contrast, the concentration of phosphorylated Akt of the LPS + N group was significantly higher than those of the LPS, LPS + N + IC, LPS + N + AS, and LPS + N + IC + AS groups (all P < 0.05).. PI3Kδ and PI3Kγ play crucial roles in mediating the anti-inflammation effects of naloxone.

Topics: Animals; Anti-Inflammatory Agents; Cell Line, Transformed; Class I Phosphatidylinositol 3-Kinases; Class Ib Phosphatidylinositol 3-Kinase; Endotoxemia; Enzyme Activation; Inflammation; Macrophages; Mice; Naloxone; Narcotic Antagonists; NF-kappa B; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt

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

The current study was designed to explore the antinociceptive, antiinflammatory and antipyretic activity of pistagremic acid (PA), isolated from Pistacia integerima bark in various animal paradigms. The results illustrated significant inhibition of noxious stimulation in acetic acid induced writhing test with maximum effect of 68% at 10mg/kg i.p. In tail immersion test, pretreatment with PA demonstrated marked activity during various assessment times in a dose dependent manner. The maximum pain inhibition was 59.46% at 10mg/kg i.p. after 90 min of PA treatment. However, the injection of naloxone did not antagonize this induced effect. PA significantly ameliorated post carrageenan induced edema dose dependently during various stages of inflammation. The effect was most dominant (60.02%) after 3(rd) h of drug administration when examined for 5h. Similarly, it provoked dose dependent antipyretic effect in febrile mice with maximum of 60.04% activity at 10mg/kg i.p. after 3rd hour of PA post treatment. Furthermore, molecular docking was carried out to understand the binding mode of PA. From the docking study it was observed that PA fits well in the active site of COX-2 enzyme due to hydrogen and hydrophobic moiety interactions to the important active site of molecule. In conclusion, PA possesses strong peripheral and central antinociceptive activity independent of opioidergic effect which was augmented by its anti-inflammatory and antipyretic activities.

Topics: Analgesics; Animals; Anti-Inflammatory Agents; Antipyretics; Female; Fever; Inflammation; Male; Mice; Mice, Inbred BALB C; Molecular Docking Simulation; Molecular Structure; Naloxone; Pain; Pistacia; Triterpenes

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

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

Long-lasting pain may partly be a consequence of ongoing neuroinflammation, in which astrocytes play a significant role. Following noxious stimuli, increased inflammatory receptor activity, influences in Na(+)/K(+)-ATPase activity and actin filament organization occur within the central nervous system. In astrocytes, the Ca(2+) signaling system, Na(+) transporters, cytoskeleton, and release of pro-inflammatory cytokines change during inflammation. The aim of this study was to restore these cell parameters in inflammation-reactive astrocytes. We found that the combination of (1) endomorphin-1, an opioid agonist that stimulates the Gi/o protein of the μ-opioid receptor; (2) naloxone, an opioid antagonist that inhibits the Gs protein of the μ-opioid receptor at ultralow concentrations; and (3) levetiracetam, an anti-epileptic agent that counteracts the release of IL-1β, managed to activate the Gi/o protein and Na(+)/K(+)-ATPase activity, inhibit the Gs protein, and decrease the release of IL-1β. The cell functions of astrocytes in an inflammatory state were virtually restored to their normal non-inflammatory state and it could be of clinical significance and may be useful for the treatment of long-term pain.

Topics: Actins; Analgesics, Opioid; Animals; Astrocytes; Calcium Signaling; Capillaries; Coculture Techniques; Cytokines; Cytoskeleton; Endothelial Cells; Glutamic Acid; Inflammation; Interleukin-1beta; Levetiracetam; Lipopolysaccharides; Male; Naloxone; Narcotic Antagonists; Nootropic Agents; Oligopeptides; Piracetam; Primary Cell Culture; Rats; Rats, Sprague-Dawley; Sodium-Potassium-Exchanging ATPase

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

Microglia-associated inflammation is closely related to the pathogenesis of retinal degenerative disorders. We have previously shown in vivo that naloxone protected photoreceptors from light-induced apoptosis possibly through inhibiting microglial activation. In this study, we attempted to explore the effect of lipopolysaccharide (LPS)-activated microglia on photoreceptor death and the influence of naloxone treatment using an in vitro retinal microglia and 661 W photoreceptor co-culture system. Immunofluorescent staining and ELISA measurements demonstrated that LPS activated microglia by changing the morphology and increasing the production of proinflammatory factors interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. Flow cytometry analysis of annexin V/propidium iodide staining showed that LPS-activated microglia promoted the apoptosis of co-cultured 661 W photoreceptor cells. Naloxone inhibited microglial activation and decreased the release of IL-1beta and TNF-alpha but could not prevent photoreceptors from undergoing apoptosis. Considering the dual role of microglia-associated inflammation in both neurotoxicity and neuroprotection, modulating the function, rather than simply inhibiting their activation, might be a new therapeutic method for preventing photoreceptor degeneration.

Topics: Animals; Apoptosis; Cell Line; Coculture Techniques; Inflammation; Interleukin-1beta; Lipopolysaccharides; Microglia; Naloxone; Neuroprotective Agents; Photoreceptor Cells, Vertebrate; Rats; Rats, Sprague-Dawley; Retina; Retinal Degeneration; Tumor Necrosis Factor-alpha

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

The aim of the present study was to investigate the mechanisms underlying the endogenous control of nociception at a peripheral level during inflammation. Using a pharmacological approach and the rat paw pressure test, we assessed the effect of an intraplantar injection of naloxone, an opioid receptor antagonist, and bestatin, an aminopeptidase inhibitor, on hyperalgesia induced by carrageenan, which mimics an inflammatory process, or prostaglandin E(2) (PGE(2)), which directly sensitizes nociceptors. Naloxone induced a significant and dose-dependent (25, 50 or 100 μg) increase in carrageenan-induced hyperalgesia, but not PGE(2)-induced hyperalgesia. Bestatin (400 μg/paw) significantly counteracted carrageenan-induced hyperalgesia, inducing an increase in the nociceptive threshold compared to control, but it did not modify hyperalgesia induced by PGE(2) injection into the rat paw. Positive β-endorphin immunoreactivity was increased in paw inflammation induced by carrageenan in comparison with the control group. However, PGE(2) did not significantly alter the immunostained area. These results provide evidence for activation of the endogenous opioidergic system during inflammation and indicate that this system regulates hyperalgesia through a negative feedback mechanism, modulating it at a peripheral level.

Topics: Animals; beta-Endorphin; Carrageenan; Dinoprostone; Dose-Response Relationship, Drug; Hyperalgesia; Inflammation; Leucine; Male; Naloxone; Narcotic Antagonists; Opioid Peptides; Pain Threshold; Protease Inhibitors; Rats; Rats, Wistar

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

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

Proopiomelanocortin (POMC)-derived beta-endorphin1-31 from immune cells can inhibit inflammatory pain. Here we investigated cytokine signaling pathways regulating POMC gene expression and beta-endorphin production in lymphocytes to augment such analgesic effects.. Interleukin-4 dose-dependently elevated POMC mRNA expression in naïve lymph node-derived cells in vitro, as determined by real-time PCR. This effect was neutralized by janus kinase (JAK) inhibitors. Transfection of Signal Transducer and Activator of Transcription (STAT) 1/3 but not of STAT6 decoy oligonucleotides abolished interleukin-4 induced POMC gene expression. STAT3 was phosphorylated in in vitro interleukin-4 stimulated lymphocytes and in lymph nodes draining inflamed paws in vivo. Cellular beta-endorphin increased after combined stimulation with interleukin-4 and concanavalin A. Consistently, in vivo reduction of inflammatory pain by passively transferred T cells improved significantly when donor cells were pretreated with interleukin-4 plus concanavalin A. This effect was blocked by naloxone-methiodide.. Interleukin-4 can amplify endogenous opioid peptide expression mediated by JAK-STAT1/3 activation in mitogen-activated lymphocytes. Transfer of these cells leads to inhibition of inflammatory pain via activation of peripheral opioid receptors.

Topics: Animals; Cells, Cultured; Concanavalin A; Inflammation; Interleukin-4; Janus Kinase 3; Lymphocytes; Male; Naloxone; Pain; Pro-Opiomelanocortin; Quaternary Ammonium Compounds; Rats; Rats, Wistar; RNA, Messenger; STAT1 Transcription Factor; STAT3 Transcription Factor

We sought to elucidate the effects of naloxone on regulating the up-regulation of inflammatory molecules and activation of the transcription factor nuclear factor-kappaB (NF-κB) induced by endotoxin. Possible roles of the μ-opioid receptors and L-type calcium channels in mediating the effects of naloxone in this regard were also investigated.. RAW264.7 cells were treated with phosphate buffered saline, naloxone, lipopolysaccharide (LPS), LPS plus naloxone, LPS plus naloxone plus morphine (i.e., the nonselective opioid receptors agonist), LPS plus naloxone plus fentanyl (i.e., the μ-opioid receptors agonist), or LPS plus naloxone plus BAY-K8644 (i.e., the L-type calcium channel activator). After harvesting, production of inflammatory molecules and expression NF-κB were evaluated.. The effects of LPS on inducing the up-regulation of macrophage inflammatory protein-2, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-6, nitric oxide/inducible nitric oxide synthase, and prostaglandin E(2)/cyclooxygenase 2 were inhibited by naloxone. Naloxone also inhibited the effects of LPS on inducing NF-κB activation, including inhibitor-κB (I-κB) degradation, NF-κB nuclear translocation, and NF-κB-DNA binding. The effects of naloxone on inhibiting IL-1β up-regulation and NF-κB activation were enhanced by morphine. In contrast, the effects of naloxone on inhibiting IL-1β up-regulation and I-κB degradation were counteracted by fentanyl. Moreover, except for TNF-α, the effects of naloxone on inhibiting inflammatory molecules up-regulation and NF-κB activation were significantly counteracted by BAY-K8644.. Naloxone significantly inhibited endotoxin-induced up-regulation of inflammatory molecules and NF-κB activation. The mechanisms may involve antagonizing the L-type calcium channels and, to a lesser extent, the μ-opioid receptors.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Anti-Inflammatory Agents; Calcium Channels, L-Type; Cell Line; Chemokine CXCL2; Fentanyl; Inflammation; Interleukin-1beta; Interleukin-6; Lipopolysaccharides; Macrophages; Mice; Models, Animal; Morphine; Naloxone; NF-kappa B; Receptors, Opioid, mu

Pluchea sagittalis, an herbaceous plant widely distributed in South America, is used in folk medicine for the treatment of digestive diseases and inflammation.. This study was designed to investigate the antinociceptive and gastroprotective effects of the ethanolic extract (EE) of aerial parts from Pluchea sagittalis in rodents.. The antinociceptive effects of EE was evaluated in mice after oral administration in chemical tests (acetic-acid, glutamate and formalin) or by biting behavior following intrathecal administration of cytokines such as interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) in mice. Furthermore, rats were treated with EE and subsequently exposed to acute gastric lesions induced by 80% ethanol. Afterwards the gastric lesion extension and the mucus levels of gastric mucosa were measured.. The oral administration of EE showed a dose-dependent inhibition of acetic acid-induced abdominal constrictions and glutamate-induced pain in mice, with ID(50) values of 624.0 (523.0-746.0) mg/kg and 368.0 (216.0-628.0) mg/kg, respectively. In the formalin test, the EE also produced significant inhibition of the inflammatory phase, with an ID(50) value of 411.0 (183.0-721.0) mg/kg; however, it was ineffective in the neurogenic phase caused by formalin. In addition, oral treatment with EE caused a significant inhibition of biting behavior induced by i.t. injection of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). The antinociception caused by the EE (300 mg/kg, p.o.) was not reversed by naloxone (1 mg/kg, i.p.) when assessed in the acetic acid writhing test. The EE (300-1000 mg/kg, p.o.) did not affect the motor coordination of animals in an open-field model. Oral treatment with the EE protected rats against gastric lesions induced by ethanol, with an ID(50) value of 55.0 (46.6-64.9) mg/kg, and increased the mucus levels of gastric mucosa to levels found in the non-lesioned group.. The mechanism by which the extract produced antinociception still remains unclear, but this effect seems to be primarily related to the modulation or inhibition of the action of pro-inflammatory mediators. Furthermore, these data support, at least in part, the ethnomedical use of Pluchea sagittalis.

Topics: Abdominal Pain; Analgesics; Animals; Anti-Inflammatory Agents; Asteraceae; Behavior, Animal; Dose-Response Relationship, Drug; Gastric Mucosa; Gastrointestinal Agents; Inflammation; Male; Mice; Naloxone; Phytotherapy; Plant Components, Aerial; Plant Extracts; Rats; Rats, Wistar; Stomach Diseases

The development of opioid dependence involves classical neuronal opioid receptor activation and is due in part to engagement of glia causing a proinflammatory response. Such opioid-induced glial activation occurs, at least in part, through a non-classical opioid mechanism involving Toll-like-receptor 4 (TLR4). Among the immune factors released following the opioid-glia-TLR4 interaction, interleukin-1β (IL-1β) plays a prominent role. Previous animal behavioral studies have demonstrated significant heterogeneity of chronic morphine-induced tolerance and dependence between different mouse strains. The aim of this study was to investigate whether the heterogeneity of chronic opioid-induced IL-1β expression contributes to differences in opioid tolerance and withdrawal behaviors. Chronic morphine-induced tolerance and dependence were assessed in 3 inbred wild-type mouse strains (Balb/c, CBA, and C57BL/6) and 2 knockout strains (TLR4 and MyD88). Analysis of brain nuclei (medial prefrontal cortex, cortex, brain stem, hippocampus, and midbrain and diencephalon regions combined) revealed that, of inbred wild-type mice, there are significant main effects of morphine treatment on IL-1β expression in the brain regions analyzed (p<0.02 for all regions analyzed). A significant increase in hippocampal IL-1β expression was found in C57BL/6 mice after morphine treatment, whilst, a significant decrease was found in the mPFC region of wild-type Balb/c mice. Furthermore, the results of wild-type inbred strains demonstrated that the elevated hippocampal IL-1β expression is associated with withdrawal jumping behavior. Interestingly, knockout of TLR4, but not MyD88 protected against the development of analgesic tolerance. Gene sequence differences of IL - 1β and TLR4 genes alone did not explain the heterogeneity of dependence behavior between mouse strains. Together, these data further support the involvement of opioid-induced CNS immune signaling in dependence development. Moreover, this study demonstrated the advantages of utilizing multiple mouse strains and indicates that appropriate choice of mouse strains could enhance future research outcomes.

Topics: Animals; Brain; Cells, Cultured; Drug Tolerance; Hippocampus; Inflammation; Interleukin-1beta; Leukocytes; Lipopolysaccharides; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Knockout; Morphine Dependence; Motor Activity; Myeloid Differentiation Factor 88; Naloxone; Narcotic Antagonists; Neuroglia; Neuroimmunomodulation; Polymorphism, Single Nucleotide; Sequence Analysis, DNA; Substance Withdrawal Syndrome; Toll-Like Receptor 4

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

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

The analgesic effect induced by opiates is often potentiated during experimental inflammatory processes. We describe here that lower doses of systemic morphine are necessary to increase thermal withdrawal latencies measured in both hind paws of mice acutely inflamed with carrageenan than in healthy ones. This bilateral potentiation seems mediated through spinal opioid receptors since it is inhibited by the intrathecal (i.t.), but not intraplantar (i.pl.) administration of the opioid receptor antagonist naloxone-methiodide, and also appears when morphine is i.t. administered. Furthermore, the i.pl. administration of the nitric oxide (NO) synthase inhibitor, L-NMMA, or the K (ATP) (+) -channel blocker, glibenclamide, to carrageenan-inflamed mice inhibits the enhanced effect of systemic morphine in the paw that receives the injection of the drug, without affecting the potentiation observed in the contralateral one. The i.pl. administration of L-NMMA also partially antagonised the analgesic effect induced by i.t. morphine in inflamed mice. Finally, the increased analgesic effect evoked by the i.pl. administration of the NO donor SIN-1 either in the inflamed or in the contralateral paw of carrageenan-inflamed mice suggests that enhanced responsiveness to the peripheral analgesic effect of NO may be also underlying the bilateral potentiation of morphine-induced analgesia in acutely inflamed mice.

Topics: Acute Disease; Analgesia; Animals; Carrageenan; Glyburide; Inflammation; Injections, Spinal; Mice; Molsidomine; Morphine; Naloxone; Nociceptors; omega-N-Methylarginine; Pain; Quaternary Ammonium Compounds; Spinal Cord; Temperature

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

Co-infusion of ultra-low dose naloxone and morphine attenuates morphine tolerance through the prevention of mu opioid receptor-Gs protein coupling. We previously demonstrated that chronic intrathecal infusion of morphine leads to tolerance and spinal neuroinflammation. The aim of present study was to examine the possible mechanisms by which ultra-low dose naloxone modulates spinal neuroinflammation, particularly the role of anti-inflammatory cytokine interleukin 10 (IL-10). Morphine tolerance was induced in male Wistar rats by intrathecal infusion of morphine (15 microg/h) for 5 days, and co-infusion of naloxone (15 pg/h) was used to evaluate the impact on spinal cytokine expression. Recombinant rat IL-10 (rrIL-10) or anti-rat IL-10 antibody was injected to elucidate the effect of IL-10 on morphine tolerance. Our results showed that co-infusion of naloxone (15 pg/h) with morphine not only attenuated tolerance, shifting the AD(50) from 89.2 to 11.7 microg but also inhibited the increased expression of pro-inflammatory cytokine (TNF-alpha, IL-1beta, and IL-6) caused by chronic intrathecal morphine infusion. The increase of IL-10 protein and mRNA were 1.5- and 3-fold, respectively, compared to that in morphine-infused rat spinal cords. A combination of daily rrIL-10 (1 microg) injection with morphine infusion produced, in a less potent, preservative antinociception and inhibited pro-inflammatory cytokine production compared to ultra-low dose naloxone co-infusion, and the effect of ultra-low dose naloxone co-infusion was inhibited by daily intrathecal anti-rat IL-10 antibody injection. These results demonstrate that IL-10 contributes to the attenuation of pro-inflammatory cytokine expression caused by ultra-low dose naloxone/morphine co-infusion and thus the attenuation of morphine tolerance.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Antibodies, Neutralizing; Cytokines; Dose-Response Relationship, Drug; Drug Interactions; Drug Tolerance; Inflammation; Injections, Spinal; Interleukin-10; Male; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Wistar; Receptors, Opioid, mu; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Spinal Cord; Up-Regulation

Opioids provide effective analgesia in adult patients with painful inflammatory diseases. The proposed mechanism of action is the activation of peripheral opioid receptors, which may be up-regulated in such conditions. Here, by using a chronic inflammation model, namely subplantar injection of Complete Freund's adjuvant, we show a peripheral synergistic interaction between the histamine H(3) receptor agonist R-(alpha)-methylhistamine and fentanyl on the inhibition of thermal hyperalgesia and of peripheral substance P accumulation. Firstly, dose-related effects obtained for the subplantar antinociceptive effect of fentanyl (0.05-1 microg) in the presence of a fixed dose of R-(alpha)-methylhistamine (12.5 microg) showed a shift to the left when compared to that obtained with fentanyl alone. In a similar way, the subcutaneous administration of fentanyl (0.005-0.1mg/kg) plus a fixed dose of R-(alpha)-methylhistamine (0.5mg/kg) induced a supra additive effect on the inhibition of substance P accumulation in the hind-paw skin of inflamed mice. Interestingly, when a neurokinin-1 receptor antagonist was co-administered, the antinociceptive effects of the combined treatment were potentiated. The peripheral adjuvant effect of R-(alpha)-methylhistamine on fentanyl antinociception and inhibition of substance P accumulation was also demonstrated by means of opioid and histamine H(3) receptors selective antagonists: first, naloxone blockade of fentanyl-mediated effects were partially reversed by co-administration of R-(alpha)-methylhistamine, and second, thioperamide partially antagonised the combined R-(alpha)-methylhistamine/fentanyl effects. Overall, our results clearly show that R-(alpha)-methylhistamine enhances fentanyl effects at peripheral sites, and that the control of substance P levels might be one of the mechanisms responsible of such interaction.

Topics: Analgesics; Animals; Dose-Response Relationship, Drug; Drug Synergism; Drug Therapy, Combination; Fentanyl; Freund's Adjuvant; Histamine Agonists; Hyperalgesia; Inflammation; Male; Methylhistamines; Mice; Naloxone; Pain; Piperidines; Receptors, Histamine H3; Skin; Substance P

Painful bladder disorders vary in intensity with the menstrual cycle in women. We evaluated the influence of the correlate in rats (the estrous cycle) on the nociceptive visceromotor reflex to bladder distention in the presence/absence of inflammation and of spinal opioid blockade.. We recorded visceromotor reflexes as electromyogram responses of the abdominal musculature to graded (10 to 60 mm Hg) bladder distention in anesthetized female rats in the presence of intrathecal saline or naloxone (10 μg) 1 day after receiving intravesical zymosan or anesthesia alone.. In saline treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. When separated into phases, rats with bladder inflammation showed complex estrous cycle effects with significantly greater visceromotor reflexes to bladder distention during metestrus and proestrus than diestrus. In naloxone treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. Naloxone enhanced the overall magnitude of visceromotor reflexes to bladder distention in the inflamed and noninflamed conditions. The magnitude of visceromotor reflexes to bladder distention in noninflamed and inflamed conditions in the presence of naloxone was estrous phase dependent in the order, estrus >metestrus >diestrus >proestrus. Similar findings were apparent on analysis of data on responses at threshold intensity (30 mm Hg).. Data suggest that circulating hormones present during the estrous cycle alter bladder reactivity and opioid modulatory systems to maintain constancy of input from the bladder to the central nervous system.

Topics: Animals; Estrous Cycle; Female; Inflammation; Naloxone; Narcotic Antagonists; Opioid Peptides; Rats; Rats, Sprague-Dawley; Reflex, Abdominal; Urinary Bladder

There have been many reports indicating the analgesic and anti-inflammatory effects of 3,4-dihydroxychalcones. We have designed and synthesized a rigid 3,4-dihydroxychalcone (RDHC) as a possible drug effecting inflammation and nociception. The analgesic and anti-inflammatory effects were evaluated by formalin and hot-plate tests, respectively. The results showed that RDHC induced significant antinociceptive and anti-inflammatory effects (P < 0.01). Maximum analgesia (63.7%) was observed at 37.5 mg/kg in the first phase of the formalin test. The effect of RDHC was higher in the chronic phase (inflammation phase) of the formalin test (86.4%, P < 0.01). In addition, a significant analgesia (maximum possible effect; MPE = 30.1%) was observed in the hot plate test 45 min after injection of 37.5 mg/kg RDHC (P < 0.01). As a result of our findings, this new RDHC could be suggested for further pharmacological studies.

Topics: Analgesics; Analgesics, Opioid; Animals; Anti-Inflammatory Agents; Aspirin; Chalcone; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Formaldehyde; Hot Temperature; Inflammation; Male; Mice; Molecular Structure; Morphine; Naloxone; Narcotic Antagonists; Pain; Pain Measurement

The present studies examined the involvement of the rostral ventral medulla (RVM) in modulating the visceromotor response (VMR) evoked by urinary bladder distension (UBD) in adult female rats. The VMR was indexed by electromyographic (EMG) responses of the abdominal external oblique muscle to UBD. Experiment 1 showed that the predominant effect of electrical stimulation of the RVM in normal rats was to produce intensity-dependent inhibition of the VMR (54% of sites sampled). Facilitatory, biphasic, or no effects were obtained at the remaining sites. Experiment 2 showed that RVM-induced inhibition of the VMR was significantly attenuated by intraperitoneal (i.p.) administration of naloxone but not saline vehicle. In experiment 3, we examined the effect of lesions of the RVM in rats with inflamed bladders because previous research has shown that an endogenous opioid inhibitory system is engaged by bladder inflammation. Electrolytic lesions of the RVM but not sham lesions of the RVM significantly increased the VMR to graded UBD in rats with augmented VMRs induced by prior inflammation of the bladder. The present data suggest that the RVM can inhibit the VMR to UBD, acting in part via an opioid-inhibitory system, and that bladder inflammation can recruit the RVM to produce a net inhibitory effect on the VMR to UBD.. Stimulation of the RVM resulted in inhibitory, facilitatory, and biphasic modulation of the visceromotor reflex to urinary bladder distension. Inhibitory effects of stimulation were attenuated by naloxone, and lesions of the RVM enhanced the VMR in rats with inflamed bladders. These data indicate an important role of the RVM in modulating bladder pain.

Topics: Analysis of Variance; Animals; Dilatation, Pathologic; Efferent Pathways; Electric Stimulation; Electrodes; Electromyography; Female; Inflammation; Injections, Intraperitoneal; Medulla Oblongata; Naloxone; Narcotic Antagonists; Pain Measurement; Rats; Rats, Sprague-Dawley; Reflex; Urinary Bladder; Viscera; Visceral Afferents

Previous studies have provided evidence of the existence of a pain modulatory feedback pathway consisting of thalamic nucleus submedius (Sm)-ventrolateral orbital cortex-periaqueductal grey pathway, which is activated during acute pain and leads to depression of transmission of nociceptive information in the spinal dorsal horn. The aim of this study was to test the hypothesis that morphine microinjection into the Sm decreased spontaneous pain and bilateral thermal hyperalgesia, as well as ipsilateral mechanical allodynia, induced by subcutaneous injections of bee venom into the rat hind paw. Morphine (1.0, 2.5 or 5.0 microg in 0.5 microL) injected into the Sm, contralateral to the bee venom-injected paw, depressed spontaneous nociceptive behaviour in a dose-dependent manner. Furthermore, morphine significantly decreased bilateral thermal hyperalgesia and ipsilateral mechanical allodynia 2 h after bee venom injection. These morphine-induced effects were antagonized by 1.0 microg naloxone (an opioid antagonist) microinjected into the Sm 5 min before morphine administration. The results provided further support for the important role of the Sm and Sm-opioid receptors in inhibiting nociceptive behaviour and indicated for the first time that Sm opioid receptors were also effective in inhibiting the hypersensitivity provoked by bee venom-induced inflammation.

Topics: Analgesics, Opioid; Animals; Bee Venoms; Behavior, Animal; Brain Stem; Dose-Response Relationship, Drug; Hindlimb; Hyperalgesia; Inflammation; Injections, Subcutaneous; Male; Microinjections; Morphine; Naloxone; Narcotic Antagonists; Nociceptors; Pain; Pain Threshold; Rats; Rats, Sprague-Dawley; Reaction Time; Thalamic Nuclei; Time Factors

The aim of the present study was to evaluate the antinociceptive effect of the novel pyrazoline methyl ester: 4-methyl-5-trifluoromethyl-5-hydroxy-4,5-dihydro-1H-pyrazole methyl ester (MPF4).. The effect of MPF4 was assessed in two models of pain: arthritic pain caused by Complete Freund's Adjuvant (CFA) and postoperative pain caused by surgical incision in mice.. MPF4 given intraperitoneally (1.0 mmol/kg, i.p.) produced marked antinociception in inflammatory allodynia caused by CFA. The antinociceptive effect produced by MPF4 was reversed with the pre-treatment of animals with naloxone or naltrindole. Oral administration of MPF4 (1.0 mmol/kg, p.o), dipyrone (1.0 mmol/kg, p.o.) and morphine (0.026 mmol/kg, p.o.) also produced an anti-allodynic effect. However, none of the compounds evaluated reversed the paw edema produced by CFA. Moreover, MPF4, dipyrone and morphine also produced an anti-allodynic effect in the surgical incisional pain model. The maximal inhibitions obtained with preemptive drug treatment were 66+/-7%, 73+/-9% and 88+/-8% for MPF4 (1.0 mmol/kg, p.o.), dipyrone (1.0 mmol/kg, p.o.) and morphine (0.026 mmol/kg, p.o.), respectively. The maximal inhibitions obtained with curative drug treatment were 53+/-9%, 83+/-7% and 84+/-7%, for MPF4, dipyrone and morphine, respectively. Unlike indomethacin, MPF4 did not induce gastric lesions at the dose that caused the highest antinociception (1.0 mmol/kg, p.o). The anti-allodynic action of MPF4, dipyrone and morphine was not associated with impairment of motor activity.. The results of the present study suggest that MPF4 represents a potential target for the development of new drugs to treat persistent inflammatory pain.

Topics: Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Arthritis, Experimental; Dipyrone; Freund's Adjuvant; Indomethacin; Inflammation; Male; Mice; Morphine; Motor Activity; Naloxone; Naltrexone; Narcotic Antagonists; Pain; Pain, Postoperative; Postural Balance; Pyrazoles; Stomach Ulcer

The present study investigated the role of peripheral opioid receptors in mustard oil-induced nociceptive behavior and inflammation in the masseter muscles of lightly anesthetized rats. Experiments were carried out on male Sprague-Dawley rats weighing between 300 and 400 g. After initial anesthesia with sodium pentobarbital (40 mg/kg, i.p.), one femoral vein was cannulated and connected to an infusion pump for the intravenous infusion of sodium pentobarbital. The rate of infusion was adjusted to provide a constant level of anesthesia. Mustard oil (MO, 30 microl) was injected into the mid-region of the left masseter muscle via a 30-gauge needle. Intramuscularly-administered morphine significantly reduced shaking behavior but not MO-induced inflammation. Intramuscular pretreatment with naloxone, an opioid receptor antagonist, reversed antinociception produced by intramuscularly-administered morphine, while intracisternal administration of naloxone did not affect the antinociception of peripheral morphine. Pretreatment with d-Pen-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), a mu opioid receptor antagonist, but not naltrindole, a delta opioid receptor antagonist, nor norbinaltorphimine (nor-BNI), a kappa opioid receptor antagonist, reversed intramuscularly-administered morphine-induced antinociception. These results indicate that intramuscularly-administered morphine produces antinociception in craniofacial muscle nociception and that this intramuscularly-administered morphine-induced antinociception is mediated by a peripheral mu opioid receptor. Our observations further support the clinical approach of administering opioids in the periphery for the treatment of craniofacial muscle nociception.

Topics: Analgesics; Anesthesia, General; Animals; Inflammation; Injections; Injections, Intramuscular; Male; Masseter Muscle; Morphine; Mustard Plant; Naloxone; Naltrexone; Narcotic Antagonists; Nociceptors; Pain; Plant Oils; Psychomotor Performance; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Single-Blind Method; Somatostatin

The 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is an endogenous ligand of peroxisome proliferator-activated receptors gamma (PPAR-gamma) and is now recognized as a potent anti-inflammatory mediator. However, information regarding the influence of 15d-PGJ(2) on inflammatory pain is still unknown. In this study, we evaluated the effect of 15d-PGJ(2) upon inflammatory hypernociception and the mechanisms involved in this effect. We observed that intraplantar administration of 15d-PGJ(2) (30-300 ng/paw) inhibits the mechanical hypernociception induced by both carrageenan (100 mug/paw) and the directly acting hypernociceptive mediator, prostaglandin E(2) (PGE(2)). Moreover, 15d-PGJ(2) [100 ng/temporomandibular joint (TMJ)] inhibits formalin-induced TMJ hypernociception. On the other hand, the direct administration of 15d-PGJ(2) into the dorsal root ganglion was ineffective in blocking PGE(2)-induced hypernociception. In addition, the 15d-PGJ(2) antinociceptive effect was enhanced by the increase of macrophage population in paw tissue due to local injection of thioglycollate, suggesting the involvement of these cells on the 15d-PGJ(2)-antinociceptive effect. Moreover, the antinociceptive effect of 15d-PGJ(2) was also blocked by naloxone and by the PPAR-gamma antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662), suggesting the involvement of peripheral opioids and PPAR-gamma receptor in the process. Similar to opioids, the 15d-PGJ(2) antinociceptive action depends on the nitric oxide/cGMP/protein kinase G (PKG)/K(ATP)(+) channel pathway because it was prevented by the pretreatment with the inhibitors of nitric-oxide synthase (N(G)-monomethyl-l-arginine acetate), guanylate cyclase]1H-(1,2,4)-oxadiazolo(4,2-alpha)quinoxalin-1-one[, PKG [indolo[2,3-a]pyrrolo[3,4-c]carbazole aglycone (KT5823)], or with the ATP-sensitive potassium channel blocker glibenclamide. Taken together, these results demonstrate for the first time that 15d-PGJ(2) inhibits inflammatory hypernociception via PPAR-gamma activation. This effect seems to be dependent on endogenous opioids and local macrophages.

Topics: Analgesics; Animals; Carrageenan; Cytokines; Formaldehyde; Hyperalgesia; Inflammation; Macrophages; Male; Naloxone; Narcotic Antagonists; Pain; PPAR gamma; Prostaglandin D2; Rats; Rats, Wistar; Receptors, Opioid; Skin; Tumor Necrosis Factor-alpha

Transcutaneous electric nerve stimulation (TENS) is a noninvasive treatment used in physiotherapy practice to promote analgesia in acute and chronic inflammatory conditions. The aim of the present study was to investigate the action mechanism of TENS at high (HF: 130 Hz) and low (LF: 10 Hz) frequencies in an inflammation model produced by the injection of carrageenan in rat paws (Cg; 250 microg). After carrageenan administration (0 time), either HF or LF TENS was applied to the inflamed paw of rats for 20 minutes, and hyperalgesia was assessed hourly using the modified Randall-Selitto method (1957). HF and LF TENS inhibited the carrageenan-induced hyperalgesia by 100%. Pretreatment of animals with intraplantar naltrexone (Nx; 50 microg) reversed the analgesic effect of the LF TENS but did not alter the effect of HF TENS. The application of HF and LF TENS to the contralateral paw reversed the hyperalgesia of the inflamed paw similar to that observed when TENS was applied to the inflamed paw. However, LF TENS presented a longer-lasting analgesic effect than HF TENS. Our data demonstrate that HF and LF TENS induced antihyperalgesia. We also report that the antihyperalgesia provoked by LF TENS is partially due to the local release of endogenous opioids.. This study offers important information about physiotherapy practices aimed at pain relieving. TENS is a noninvasive treatment that promotes analgesia in acute and chronic inflammatory conditions. Scientists, patients, and the general population may benefit from this knowledge.

Topics: Analgesics; Animals; Carrageenan; Functional Laterality; Inflammation; Naloxone; Narcotic Antagonists; Opioid Peptides; Pain; Pain Management; Rats; Transcutaneous Electric Nerve Stimulation

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

We have previously shown that electroacupuncture (EA) produced antinociception through the release of endogenous opioid peptides to activate opioid receptors during acute nociception. EA produced tolerance after its prolonged application. It has reported that 100 Hz EA could reduce mechanical hyperalgesia in complete Freund's adjuvant (CFA)-induced inflammatory nociception rats. The present study aims to investigate the antinociceptive effect of EA and the development of EA tolerance in chronic inflammatory nociception rats with CFA injection into the hind paw plantar. The results showed that the antinociceptive effect of 100 Hz EA was significantly enhanced in CFA-induced inflammatory nociception rats. Naloxone at 20 mg/kg could significantly block this antinociceptive effect. Chronic tolerance to EA was developed faster in CFA-induced inflammatory nociception rats than in normal rats. Therefore, 100 Hz EA could enhance antinociceptive effects and accelerate tolerance development in CFA-induced inflammatory nociception rats. The enhancement of EA antinociceptive effect in CFA-induced inflammatory nociception rats might involve the endogenous opioid peptides such as dynorphin.

Topics: Animals; Drug Tolerance; Electroacupuncture; Female; Freund's Adjuvant; Inflammation; Naloxone; Nociceptors; Rats

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

Antinociception achieved after peripheral administration of opioids has opened a new approach to the treatment of severe and chronic pain. Additionally, opioid analgesics with restricted access to the central nervous system could improve safety of opioid drugs used in clinical practice. In the present study, peripheral components of antinociceptive actions of 6-amino acid-substituted derivatives of 14-O-methyloxymorphone were investigated after local intraplantar (i.pl.) administration in rat models of inflammatory and neuropathic pain. Their antinociceptive activities were compared with those of morphine, the classical mu-opioid receptor agonist. Intraplantar administration of morphine and the 6-amino acid derivatives produced dose-dependent reduction of formalin-induced flinching of the inflamed paw, without significant effect on the paw edema. Local i.pl. administration of the new derivatives in rats with neuropathic pain induced by sciatic nerve ligation produced antiallodynic and antihyperalgesic effects; however, the antinociceptive activity was lower than that observed in inflammatory pain. In both models, the 6-amino acid derivatives and morphine at doses that produced analgesia after i.pl. administration were systemically (s.c.) much less active indicating that the antinociceptive action is due to a local effect. Moreover, the local opioid antinociceptive effects were significantly attenuated by naloxone methiodide, a peripherally acting opioid receptor antagonist, demonstrating that the effect was mediated by peripheral opioid receptors. The present data indicate that the peripherally restricted 6-amino acid conjugates of 14-O-methyloxymorphone elicit antinociception after local administration, being more potent in inflammatory than in neuropathic pain. Opioid drugs with peripheral site of action can be an important target for the treatment of long lasting pain.

Topics: Analgesics, Opioid; Animals; Dose-Response Relationship, Drug; Hyperalgesia; Inflammation; Male; Morphine; Naloxone; Neuralgia; Oxymorphone; Pain; Rats; Rats, Wistar; Structure-Activity Relationship

In the present study, we measured the kinetics and distribution in vivo of the selective delta-opioid antagonist 11C-methylnaltrindole (11C-MeNTI) and the mu-opioid agonist 11C-carfentanil (11C-CFN) in patients with lung carcinoma using PET.. Paired measurements of 11C-MeNTI and 11C-CFN binding were performed in biopsy-proven small-cell (n = 2), squamous (n = 2), and adenocarcinoma (n = 3) lung cancer patients. Dynamic PET scans of increasing duration (0.5-8 min) were acquired over 90 min after an intravenous bolus injection of 370 MBq of tracer. Time-activity curves for tumor and normal lung parenchyma binding were generated using the region-of-interest (ROI) method. The mean activity at equilibrium was measured, and the specific-to-nonspecific binding ratio (tumor - lung)/lung was calculated. Four of 7 patients underwent an additional static 18F-FDG PET scan for clinical indications. Three of 7 patients underwent surgery, and stained sections of tumor were inspected for inflammation, necrosis, and scar tissue.. Increased binding of 11C-MeNTI and 11C-CFN was detected in all tumor types studied. 11C-MeNTI binding in tumor and healthy lung tissue was significantly more intense than that of 11C-CFN. The average specific-to-nonspecific binding ratio across cell types for 11C-MeNTI (4.32 +/- 1.31; mean +/- SEM) was greater than that of 11C-CFN (2.42 +/- 1.17) but lower than that of 18F-FDG (7.74 +/- 0.53). Intravenous naloxone produced 50% and 44% decreases in the specific-to-nonspecific binding ratios of 11C-MeNTI and 11C-CFN, respectively.. These data provide in vivo evidence for the presence of delta- and mu-opioid receptor types in the 3 major human lung carcinomas and suggest the suitability of 11C-MeNTI and 11C-CFN as investigational probes of lung carcinoma biology.

Topics: Adenocarcinoma; Aged; Carcinoma, Non-Small-Cell Lung; Carcinoma, Small Cell; Carcinoma, Squamous Cell; Coloring Agents; Female; Humans; Inflammation; Lung Neoplasms; Male; Middle Aged; Naloxone; Narcotic Antagonists; Necrosis; Radionuclide Imaging; Radiopharmaceuticals; Receptors, Opioid, delta; Receptors, Opioid, mu; Tissue Distribution

1 The milky white latex of the plant Calotropis procera induces inflammatory response upon accidental exposure and on local administration that could be effectively ameliorated by antihistaminic and standard anti-inflammatory drugs. 2 The aim of the present study was to evaluate the anti-oedematogenic and analgesic effect of the bradykinin antagonist, bradyzide (BDZ) and the opioidergic analgesic, morphine (Mor) against inflammatory hyperalgesia induced by the dried latex (DL) of C. procera in the rat paw oedema model. 3 An aqueous solution of DL (0.1 ml of 1% solution) was injected into the sub-plantar surface of the rat paw and the paw volume was measured at different time intervals. The inhibitory effect of bradyzide and morphine on oedema formation and hyperalgesic response was compared with that of cyproheptadine (CPH), a potent inhibitor of DL-induced oedema formation. 4 The hyperalgesic response was evaluated by the dorsal flexion pain test, compression test and by observing motility, stair-climbing ability, and the grooming behaviour of the rats. 5 The effect of these drugs was also evaluated against DL-induced writhings in the mouse model. 6 Both bradyzide and morphine inhibited DL-induced oedema formation by 30-40% and CPH was more effective in this regard (81% inhibition). The antihyperalgesic effect of both the drugs was more pronounced than that of CPH. Both bradyzide and morphine markedly inhibited the grooming behaviour and the effect of morphine could be reversed by pretreatment with naloxone. 7 Thus, our study shows that DL-induced oedema formation is effectively inhibited by antihistaminic/antiserotonergic drug and associated hyperalgesia by analgesic drugs.

Topics: Analgesics, Opioid; Animals; Behavior, Animal; Bradykinin Receptor Antagonists; Calotropis; Cyproheptadine; Edema; Grooming; Hindlimb; Hyperalgesia; Inflammation; Latex; Male; Mice; Morphine; Motor Activity; Naloxone; Pyrrolidines; Rats; Rats, Wistar; Shivering; Thiosemicarbazones

Defensins are one of the major groups of endogenous peptides that are considered to be important antibiotic-like effectors of host innate and adaptive antimicrobial immunity. The current study investigated the electrophysiological effects of externally applied human and rabbit defensins (HNP-1 and RNP-1, correspondingly) on afferent neurotransmission in the frog semicircular canals (SCC). Application of HNP-1 and RNP-1 induces a concentration-dependent decrease in resting activity. Threshold concentrations for both substances were of the order of 0.0001 nM. The firing evoked by L-glutamate (L-Glu) and its agonists alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), kainate and N-methyl-D-aspartate (NMDA) and (1S, 3R)-1-aminocyclopentane-trans-1,3-dicarboxilic acid (ACPD) could be inhibited by HNP-1, suggesting that defensins exert inhibitory control over both ionotropic and metabotropic glutamate receptors. HNP-1 considerably inhibited the L-glutamate/high Mg2+ -induced increase in frequency, thus, demonstrating its postsynaptic site of action. Acetylcholine (ACh) responses under HNP-1 did not differ from the frequency increase induced by ACh alone, and the ACh antagonist atropine left the response to HNP-1 intact. The specific opioid receptor antagonist naloxone (Nal) antagonized the inhibitory response evoked by HNP-1. The results obtained support the evidence for the recruitment of defensins in communication between the immune and nervous systems, and on the potential of sensory receptors to participate in the inflammatory response.

Topics: Acetylcholine; Action Potentials; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; alpha-Defensins; Animals; Atropine; Cholinergic Antagonists; Cycloleucine; Defensins; Dose-Response Relationship, Drug; Glutamic Acid; Humans; Immune System; In Vitro Techniques; Inflammation; Kainic Acid; N-Methylaspartate; Naloxone; Narcotic Antagonists; Neuroimmunomodulation; Neurons, Afferent; Rabbits; Rana temporaria; Receptors, Cholinergic; Receptors, Glutamate; Receptors, Opioid; Semicircular Canals; Synaptic Transmission; Vestibule, Labyrinth

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

The N-terminal metabolite of the undecapeptide substance P (SP), substance P1-7 (SP1-7), is known to modulate nociception in the central nervous system (CNS) and often has opposite effects from SP. This study investigated the ability of SP(1-7) to modulate the vasodilatation response to SP in anaesthetized rats under different injury conditions using a blister model of inflammation on the hind footpad. The results indicated that SP1-7 inhibited the vascular response to SP in a dose-dependent manner. The putative antagonists naloxone and D-Pro2-D-Phe7-SP1-7 (D-SP1-7) reversed the effect of SP1-7. D-SP1-7 improved the responsiveness to SP under chronic nerve injury, which suggests a role for endogenous SP1-7 in this model. SP1-7 did not inhibit the response to electrical stimulation of the sciatic nerve, which indicates that the heptapeptide interacts at a post-terminal binding site. The current results suggest that SP1-7 may have inhibitory properties in inflammation, analogous to its antinociceptive role in the central nervous system.

Topics: Animals; Central Nervous System; Dose-Response Relationship, Drug; Inflammation; Male; Naloxone; Neurons; Peptides; Protein Structure, Tertiary; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Substance P; Vasodilator Agents

Polyamines are thought to be involved in the regulation of numerous metabolic and electrophysiological processes in the nervous system. In this study we evaluated the effect of a synthetic polyamine-deficient diet on pain in a carrageenan (Car)-induced inflammatory rat model. Inflammation was induced with a unilateral subcutaneous injection of Car in a plantar hindpaw in rats fed without (control group) or with (deficiency group) a polyamine-deficient diet. Ipsilateral and contralateral hyperalgesia was evaluated using the Randall-Sellito pressure test. Heart rate changes were also recorded under general anesthesia. Then, the effects of a bupivacaine sciatic nerve block and subcutaneous injection of naloxone or ketamine were evaluated for Car-induced hyperalgesia. Data were analyzed using analysis of variance followed by unpaired Student's t-test (significance P < 0.05). Before Car injection, no significant difference was observed in response to mechanical stimuli between the control and the deficiency groups (n = 114 in pooled data). Car injection induced significant ipsilateral and contralateral hyperalgesia in the control groups, whereas a significant analgesic effect appeared in the deficient groups on both the ipsilateral and contralateral hindpaws. This analgesic effect was confirmed by the electrocardiogram recording that showed a significant increase in heart rate in the control group after Car injection compared with the deficiency group that showed a decrease in heart rate under general anesthesia. Bupivacaine sciatic nerve block had no significant effect on hypoalgesia phenomena induced by polyamine deficiency. Naloxone administration had no effect in the control group but reversed the analgesic effect in the deficiency group. Ketamine administration induced a significant analgesic effect in the control group and partly reversed the analgesic effect in the deficiency group. In conclusion, a synthetic polyamine-deficient diet had a significant general analgesic effect on Car-induced mechanical hyperalgesia. The mechanism of analgesic action remains to be elucidated.

Topics: Analgesia; Analgesics; Animals; Carrageenan; Diet; Hindlimb; Hyperalgesia; Inflammation; Ketamine; Male; Naloxone; Narcotic Antagonists; Nerve Block; Pain Threshold; Polyamines; Rats; Rats, Sprague-Dawley; Sciatic Nerve

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

Previous studies have shown that jaw reflexes and activity patterns of the jaw muscles were modulated in the presence of jaw muscle pain. However, there is no study comparing the modulatory effects on the jaw reflexes induced by noxious stimulation to the jaw muscle. To clarify this, effects of the application of mustard oil (MO), an inflammatory irritant, into the temporalis (jaw-closing) muscle on (1) jaw-opening reflex evoked by tooth pulp stimulation (TP-evoked JOR) as a nociceptive reflex, (2) jaw-opening reflex evoked by inferior alveolar nerve stimulation as a non-nociceptive reflex and (3) jaw-closing reflex evoked by trigeminal mesencephalic nucleus stimulation as a proprioceptive reflex were investigated in anesthetized rats. The MO application induced suppression of all reflexes, and the effect on the TP-evoked JOR was more prominent than on the other reflexes. To elucidate the involvement of endogenous opioid system for the suppressive effect, a systemic administration of naloxone following the MO application was conducted. The MO-induced suppressive effect on the TP-evoked JOR was reversed by the naloxone administration. The results suggest that noxious stimulation to the jaw muscle modulate jaw reflexes particularly for the nociceptive jaw-opening reflex, and the modulatory effect includes both facilitatory and inhibitory aspects. The results also suggest that pain modulatory systems such as the endogenous opioid system play a crucial role in the suppression of the nociceptive transmissions related to nociceptive reflexes, and in some pathological states, defense reflexes may not be evoked properly.

Topics: Analysis of Variance; Animals; Conditioning, Psychological; Dental Pulp; Electric Stimulation; Electromyography; Inflammation; Jaw; Male; Naloxone; Narcotic Antagonists; Neural Pathways; Nociceptors; Pain; Rats; Rats, Wistar; Reaction Time; Reflex; Temporal Muscle

The aim of this study was to evaluate the analgesic effect of the low level laser therapy (LLLT) with a He-Ne laser on acute inflammatory pain, verifying the contribution of the peripheral opioid receptors and the action of LLLT on the hyperalgesia produced by the release of hyperalgesic mediators of inflammation.. All analgesic drugs have undesired effects. Because of that, other therapies are being investigated for treatment of the inflammatory pain. Among those, LLLT seems to be very promising.. Male Wistar rats were used. Three complementary experiments were done. (1) The inflammatory reaction was induced by the injection of carrageenin into one of the hind paws. Pain threshold and volume increase of the edema were measured by a pressure gauge and plethysmography, respectively. (2) The involvement of peripheral opioid receptors on the analgesic effect of the laser was evaluated by simultaneous injection of carrageenin and naloxone into one hind paw. (3) Hyperalgesia was induced by injecting PGE2 for the study of the effect of the laser on the sensitization increase of nociceptors. A He-Ne laser (632.8 nm) of 2.5 J/cm2 was used for irradiation.. We found that He-Ne stimulation increased the pain threshold by a factor between 68% and 95% depending on the injected drug. We also observed a 54% reduction on the volume increase of the edema when it was irradiated.. He-Ne LLLT inhibits the sensitization increase of nociceptors on the inflammatory process. The analgesic effect seems to involve hyperalgesic mediators instead of peripheral opioid receptors.

Topics: Animals; Carrageenan; Dinoprostone; Edema; Hyperalgesia; Inflammation; Injections; Low-Level Light Therapy; Male; Naloxone; Narcotic Antagonists; Nociceptors; Pain; Pain Threshold; Rats; Rats, Wistar

P2X3/P2X2/3 receptors have emerged as important components of nociception. However, there is limited information regarding the neurochemical systems that are affected by antagonism of the P2X3/P2X2/3 receptor and that ultimately contribute to the ensuing antinociception. In order to determine if the endogenous opioid system is involved in this antinociception, naloxone was administered just prior to the injection of a selective P2X3/P2X2/3 receptor antagonist, A-317491, in rat models of neuropathic, chemogenic, and inflammatory pain. Naloxone (1-10 mg kg(-1), i.p.), dose-dependently reduced the antinociceptive effects of A-317491 (1-300 micromol kg(-1), s.c.) in the CFA model of thermal hyperalgesia and the formalin model of chemogenic pain (2nd phase), but not in the L5-L6 spinal nerve ligation model of neuropathic allodynia. In comparison experiments, the same doses of naloxone blocked or attenuated the actions of morphine (2 or 8 mg kg(-1), s.c.) in each of these behavioral models. Injection of a peripheral opioid antagonist, naloxone methiodide (10 mg kg(-1), i.p.), did not affect A-317491-induced antinociception in the CFA and formalin assays, suggesting that the opioid component of this antinociception occurred within the CNS. Furthermore, this utilization of the central opioid system could be initiated by antagonism of spinal P2X3/P2X2/3 receptors since the antinociceptive actions of intrathecally delivered A-317491 (30 nmol) in the formalin model were reduced by both intrathecally (10-50 nmol) and systemically (10 mg kg(-1), i.p.) administered naloxone. This utilization of the opioid system was not specific to A-317491 since suramin-, a nonselective P2X receptor antagonist, induced antinociception was also attenuated by naloxone. In in vitro studies, A-317491 (3-100 microM) did not produce any agonist response at delta opioid receptors expressed in NG108-15 cells. A-317491 had been previously shown to be inactive at the kappa and mu opioid receptors. Furthermore, naloxone, at concentrations up to 1 mM, did not compete for [3H] A-317491 binding in 1321N1 cells expressing human P2X3 receptors. Taken together, these results indicate that antagonism of spinal P2X3/P2X2/3 receptors results in an indirect activation of the opioid system to alleviate inflammatory hyperalgesia and chemogenic nociception.

Topics: Analgesia; Animals; Arthritis, Experimental; Dose-Response Relationship, Drug; Endorphins; Formaldehyde; Freund's Adjuvant; Inflammation; Injections, Spinal; Ligation; Male; Naloxone; Narcotic Antagonists; Pain; Peripheral Nervous System Diseases; Phenols; Polycyclic Compounds; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2; Receptors, Purinergic P2X2; Receptors, Purinergic P2X3; Suramin

The present study investigated the role of galanin in the transmission of nociceptive information in the spinal cord of rats with inflammation. Bilateral decreases in hindpaw withdrawal latencies (HWLs) to thermal and mechanical stimulation were observed after acute inflammation induced by injection of carrageenan into the plantar region of the rat left hindpaw. Intrathecal injection of galanin induced significant increases in the HWLs to thermal and mechanical stimulation in rats with inflammation. The galanin-induced antinociceptive effect was more pronounced in rats with inflammation than that in intact rats. The antinociceptive effect of galanin was partly inhibited by intrathecal injection of naloxone. Furthermore, intrathecal administration of galantide, an antagonist of galanin receptor, could attenuate the antinociceptive effect induced by intraperitoneal injection of morphine, suggesting an involvement of opioid systems in the galanin-induced antinociception. The results indicate that galanin plays an important role in the transmission of nociceptive information in the spinal cord of rats with inflammation, and opioid systems are involved in the galanin-induced antinociception.

Topics: Animals; Calcitonin; Carrageenan; Galanin; Inflammation; Injections, Spinal; Injections, Subcutaneous; Male; Naloxone; Narcotic Antagonists; Nociceptors; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Galanin; Receptors, Opioid; Spinal Cord

Codeine analgesia is dependent on metabolism to morphine. Metabolic capability is genetically determined in rats and humans, and individuals can be classified as extensive or poor metabolizers, as determined by the extent of production of morphine. Codeine is often given to infants and children. The aim of this study was to investigate the effects of developmental age on codeine analgesia in rats.. The effects of codeine were compared with those of morphine using withdrawal reflex responses to mechanical stimuli (with and without inflammation) and to noxious heat in two strains of rats (Sprague-Dawley and Dark Agouti) that have been used to model human metabolic phenotypes because of marked differences in enzyme activity. Effects of the opioids were compared at 3, 10, and 21 days of age and in adult rats.. Consistent age-related changes in the efficacy of codeine relative to morphine were noted for both strains of rats. For the extensive metabolizer (Sprague-Dawley) strain, codeine efficacy was substantially lower at 3 days of age (P < 0.001), but there was no difference between the effects of codeine and morphine for 10- and 21-day-old rats and adults (P > 0.05). Poor metabolizers (Dark Agouti strain) also had comparatively low efficacy for codeine compared with morphine in 3-day-old rats and in adults (P < 0.001). In 10- and 21-day-old Dark Agouti rats, there was no difference between either drug (P < 0.05).. Codeine analgesia is developmentally regulated, with low efficacy in the early postnatal period. Effects in the adult rat were not predictive of efficacy in development in either strain, which has important implications for further study and, possibly, for clinical use.

Topics: Aging; Analgesics, Opioid; Animals; Body Weight; Carrageenan; Codeine; Dose-Response Relationship, Drug; Female; Hot Temperature; Inflammation; Morphine; Naloxone; Narcotic Antagonists; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Species Specificity

Low frequency electroacupuncture, which is commonly used in pain relief, is known to induce opioid-mediated analgesia. This study examined the contribution of the opioid system in mediating the anti-inflammatory effects of low frequency EA in a standard model of acute inflammation, the carrageenan-induced edema model. Carrageenan was injected in the hind paw of anesthetized rats and low frequency electroacupuncture was applied to acupoints equivalent to Zusanli (St 36) and Sanyinjiao (Sp 6) in humans just prior to the induction of inflammation in the ipsilateral leg. Induction of Fos protein, reflecting neuronal activation, was investigated in the spinal cord with immunohistochemistry. It was found that electroacupuncture strongly inhibited the carrageenan-induced edema by over 60%, and suppressed the associated Fos expression in the superficial laminae (I-II) of the ipsilateral dorsal horn by 50%. Neither the anti-edematous effect nor the suppression of Fos expression in the superficial spinal laminae was affected by intraperitoneal injection of the opioid antagonist naloxone. These results demonstrate that low frequency electroacupuncture is capable of inhibiting peripheral inflammation and the associated central neuronal activity via a non-opioid-dependent mechanism.

Topics: Animals; Electroacupuncture; Genes, fos; Inflammation; Naloxone; Narcotics; Rats; Rats, Sprague-Dawley; Spinal Cord

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

Vitamin B2 (riboflavin) has been proposed as a prophylactic therapy of migraine. However, so far there are no preclinical studies about the analgesic properties of this vitamin. The current study was designed to investigate the possible antinociceptive, antihyperalgesic and antiallodynic effect of riboflavin in formalin, carrageenan-induced thermal hyperalgesia, and spinal nerve ligation models, respectively. Oral riboflavin produced a dose-related antinociceptive (6.25-50 mg/kg), antihyperalgesic (25-150 mg/kg) and anti-inflammatory (50-150 mg/kg) effect. Gabapentin (100 mg/kg, positive control), but not riboflavin (150-600 mg/kg), reduced tactile allodynia in neuropathic rats. Riboflavin-induced antinociception in the formalin test was reversed by pretreatment with NG-L-nitro-arginine methyl ester and glibenclamide, but not by NG-D-nitro-arginine methyl ester or naloxone. Our results indicate that riboflavin is able to produce antinociception and anti-inflammatory, but not antiallodynic, effect in the rat. The effect of riboflavin could be due to the activation of K+ channels or nitric oxide release, but not activation of opioid mechanisms.

Topics: Analgesics; Animals; Carrageenan; Enzyme Inhibitors; Female; Glyburide; Hyperalgesia; Inflammation; Motor Activity; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Pain Measurement; Pain Threshold; Potassium Channel Blockers; Rats; Rats, Wistar; Riboflavin

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 mongrel male rats to study the effects of blockade of delta, mu, and kappa opiate receptors on antibody formation, delayed-type hypersensitivity (DTH), and changes in the numbers of antibody-forming cells (AFC) and nucleated cells in the lymph nodes and spleen in a local form of immune response in a model of rotation stress. These studies showed that rotation stress led to mild suppression of immune inflammation in DTH, significant increases in the numbers of AFC and nucleated cells in regional lymph nodes, but no change in the peripheral blood antibody titer. Blockade of delta, mu, and kappa opiate receptors with naloxone altered these stress-induced effects. It is suggested that abolition of the stimulating effect of rotation stress on the number of AFC and depression of DTH may be associated with blockade of the effects of beta-endorphin and met-enkephalin, which act predominantly via stimulation of delta receptors.

Topics: Animals; Antibody Formation; Cell Count; Immunity, Cellular; Inflammation; Lymph Nodes; Male; Naloxone; Narcotic Antagonists; Rats; Receptors, Opioid; Rotation; Spleen; Stress, Physiological; Weights and Measures

The effects of the S enantiomer of RB101, a complete inhibitor of enkephalin-catabolizing enzymes, alone or in combination with a functional NMDA receptor antagonist, (+)-HA966 were studied on the spinal c-Fos protein expression in the carrageenan model of inflammatory nociception. One hour 30min after intraplantar carrageenan in awake rats, c-Fos immunoreactive (c-Fos-IR) nuclei were preferentially located in the laminae I-II and V-VI of the spinal dorsal horn, i.e., spinal areas containing numerous neurons responding exclusively, or not, to peripheral nociceptive stimuli. RB101(S) (5, 10, 20 and 40mg/kg i.v.) dose-dependently reduced the total number of carrageenan-evoked c-Fos-IR nuclei (r=0.63, P<0.01), with 49+/-3% reduction (P<0.001) for the highest dose. Two highest doses of RB101(S) (20 and 40mg/kg) significantly reduced the number of carrageenan-evoked c-Fos-IR nuclei in both superficial I-II (32+/-7% and 36+/-5% reduction, respectively, P<0.05 for both) and deep V-VI (42+/-6% and 61+/-2% reduction, respectively, P<0.001 for both) laminae. The effects of RB101(S) were naloxone-reversible. Combination of low doses of RB101(S) (2.5 or 10mg/kg i.v.) and an inactive dose of (+)-HA966 (2.5mg/kg s.c.) produced supra-additive effects (39+/-4% and 51+/-5% reduction of the total number of c-Fos-IR nuclei, respectively, P<0.001 for both). These effects were partially reversed by naloxone. These results provide evidence for the potent effects of combination of RB101(S) and (+)-HA966. Considering the absence of major opioid side effects of RB101(S) and the marked increase of its antinociceptive effects by NMDA receptor antagonist, this type of drug combination could have beneficial therapeutical application.

Topics: Analgesics; Animals; Carrageenan; Disulfides; Drug Therapy, Combination; Enkephalins; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Immunohistochemistry; Inflammation; Male; Naloxone; Narcotic Antagonists; Pain; Phenylalanine; Proto-Oncogene Proteins c-fos; Pyrrolidinones; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Spinal Cord

The purpose of the present study was to investigate the role of the alpha(2A)-adrenoceptor subtype in inflammatory hyperalgesia, and in adrenergic-mu-opioid interactions in acute pain and inflammatory hyperalgesia. Behavioral responses to mechanical and thermal stimuli were studied in alpha(2A)-adrenoceptor knockout mice and their wild-type controls. Thermal nociception was evaluated as paw withdrawal latencies to radiant heat applied to the hindpaws. Mechanical nociception was measured using von Frey monofilament applications to the hindpaws. Mechanical and thermal hyperalgesia, induced with intraplantar carrageenan (1 mg/40 microl) were compared in alpha(2A)-adrenoceptor knockout and wild-type mice. The effects of the systemically administered mu-opioid receptor agonist morphine (1-10 mg/kg) were evaluated on mechanical withdrawal responses under normal and inflammatory conditions in knockout and wild-type mice. Withdrawal responses to radiant heat and von Frey monofilaments were similar in alpha(2A)-adrenoceptor knockout and wild-type mice before and after the carrageenan-induced hindpaw inflammation. Also, the antinociceptive effects of morphine in mechanical nociceptive tests were similar before and after carrageenan-induced hindpaw inflammation. Our observations indicate that alpha(2A)-adrenoceptors are not tonically involved in the modulation of inflammation-induced mechanical and thermal hyperalgesia. In addition, alpha(2A)-adrenoceptors do not appear to play an important role in mu-opioid receptor-mediated antinociception or antihyperalgesia.

Topics: Analgesia; Animals; Carrageenan; Dose-Response Relationship, Drug; Female; Hot Temperature; Hyperalgesia; Inflammation; Male; Mice; Mice, Knockout; Morphine; Naloxone; Nociceptors; Pain Measurement; Physical Stimulation; Receptors, Adrenergic, alpha-2; Receptors, Opioid, mu

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

The present study was conducted on rats with inflammation induced by subcutaneous injection of carrageenan into the left hindpaw. Intrathecal administration of oxytocin produced dose-dependent increases in the hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats with inflammation. The antinociceptive effect of oxytocin was blocked by intrathecal administration of atosiban, a selective oxytocin antagonist, indicating that oxytocin receptor mediates oxytocin-induced antinociception in the spinal cord. The oxytocin-induced antinociceptive effect was attenuated by intrathecal administration of the opioid antagonist naloxone, suggesting an involvement of the endogenous opioid system in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Furthermore, the antinociceptive effect of oxytocin was attenuated by intrathecal injections of the mu-receptor antagonist beta-funaltrexamine and the kappa-receptor antagonist nor-binaltorphimine, but not by the delta-receptor antagonist naltrindole, illustrating that mu- and kappa-receptors, but not delta-receptor, are involved in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Moreover, intrathecal administration of atosiban alone induced a hyperalgesia in rats with inflammation, indicating that endogenous oxytocin is involved in the transmission and regulation of nociceptive information in the spinal cord of rats with inflammation. The present study showed that both exogenous and endogenous oxytocin displayed antinociception in the spinal cord in rats with inflammation, and mu- and kappa-receptors were involved in oxytocin-induced antinociception.

Topics: Analgesics; Animals; Carrageenan; Hot Temperature; Inflammation; Injections, Spinal; Male; Naloxone; Naltrexone; Narcotic Antagonists; Oxytocin; Pain; Pain Measurement; Physical Stimulation; Rats; Rats, Wistar; Spinal Cord; Vasotocin

Noxious stimuli activate neuroendocrine axes, inhibiting inflammation, an effect that is powerfully attenuated by ongoing activity in subdiaphragmatic vagal afferents. To evaluate whether this inhibitory effect of vagal afferent activity is mediated by descending antinociceptive control, we tested whether antagonizing descending antinociceptive controls: (i) enhances the inhibition of inflammation produced by spinal nicotine (which stimulates central terminals of nociceptors) and (ii) occludes the enhancing effect of subdiaphragmatic vagotomy, in the rat. Spinal intrathecal co-administration of the alpha-adrenergic receptor antagonist phentolamine and the non-selective opioid receptor antagonist naloxone, and acute subdiaphragmatic vagotomy each produced enhancement, with similar magnitude, of nicotine-induced inhibition of plasma extravasation, produced by the potent inflammatory mediator, bradykinin. The combination of subdiaphragmatic vagotomy and intrathecal receptor antagonists, however, produced no further enhancement compared to each treatment alone. These findings support the suggestion that activity in descending antinociceptive controls modulates noxious stimulus-induced inhibition of inflammation and the vagal modulation of noxious stimulus-induced inhibition of inflammation is mediated by descending antinociceptive controls.

Topics: Adrenergic alpha-Antagonists; Animals; Bradykinin; Capillary Permeability; Dose-Response Relationship, Drug; Drug Combinations; Drug Synergism; Evans Blue; Extravasation of Diagnostic and Therapeutic Materials; Inflammation; Injections, Spinal; Knee Joint; Male; Naloxone; Narcotic Antagonists; Neural Inhibition; Nicotine; Phentolamine; Plasma; Rats; Rats, Sprague-Dawley; Spinal Cord; Spinal Cord Injuries; Stimulation, Chemical; Vagotomy; Vagus Nerve

Neuroimmune interactions control pain through activation of opioid receptors on sensory nerves by immune-derived opioid peptides. Here we evaluate mechanisms of intrinsic pain inhibition at different stages of Freund's adjuvant-induced inflammation of the rat paw. We use immunohistochemistry and paw pressure testing. Our data show that in early (6 h) inflammation leukocyte-derived beta-endorphin, met-enkephalin and dynorphin A activate peripheral mu-, delta- and kappa-receptors to inhibit nociception. In addition, central opioid mechanisms seem to contribute significantly to this effect. At later stages (4 days), antinociception is exclusively produced by leukocyte-derived beta-endorphin acting at peripheral mu and delta receptors. Corticotropin-releasing hormone (CRH) is an endogenous trigger of these effects at both stages. These findings indicate that peripheral opioid mechanisms of pain inhibition gain functional relevance with the chronicity of inflammation.

Topics: Animals; Corticotropin-Releasing Hormone; Dynorphins; Edema; Endorphins; Enkephalin, Methionine; Freund's Adjuvant; Hindlimb; Inflammation; Injections, Subcutaneous; Leukocytes; Male; Naloxone; Pain; Pain Threshold; Rats; Rats, Wistar; Stress, Physiological; Time Factors

It has been reported by Stein et al. that the immune system and peripheral opioid receptors are involved in the control of pain accompanying inflammation. Electroacupuncture (EA) is used to relieve various kinds of pain. However, little is known about the effect of electroacupuncture analgesia (EAA) during hyperalgesia elicited by inflammation. The aim of the present study was to compare (1) the individual variation of EAA, (2) the durability of EAA, and (3) the effect of naloxone on EAA between normal rats and rats subjected to acute inflammatory pain. Carrageenan was subcutaneously administered by intraplantar (i.pl.) injection of the left hind paw to induce a nociceptive response. Nociceptive thresholds were measured using the paw pressure threshold (PPT). Rats received EA at 3 Hz in the left anterior tibial muscles for 1 hour after carrageenan injection. Naloxone was administered by intraperitoneal (i.p.) or i.pl. injection just before EA. EAA was elicited in 15 of 29 normal rats. These rats were divided into responders and non-responders. EAA in the responder group was almost completely antagonized by i.p. injection of naloxone. In contrast, in all the rats with carrageenan-induced inflammation, EAA was elicited, lasted for at least 24 hours after carrageenan injection, and was dose-dependently antagonized by i.pl. injection, but not significantly by i.p. injection of naloxone. It seems likely that the EAA in the rats with carrageenan-induced inflammation differs from that in normal rats, and these findings suggest that peripheral opioid receptors are involved in EAA during inflammatory conditions.

Topics: Acupuncture Analgesia; Animals; Carrageenan; Electroacupuncture; Hyperalgesia; Inflammation; Male; Naloxone; Narcotic Antagonists; Pain Threshold; Pressure; Rats; Rats, Sprague-Dawley

The present study was to investigate the effect of intrathecal (i.t.) injection of interleukin-1 beta (IL-1 beta) on nociception in normal and inflammatory rats. Peripheral inflammation was induced by intraplantar injection (i.pl.) of carrageenan into unilateral hind paw. The nociceptive threshold to noxious thermal stimulation was measured by the paw withdrawal latency (PWL). Intrathecal injection of IL-1 beta (10 ng, 100 ng) significantly increased PWL in normal rats, the peak occurred at 5 min and the effect lasted for 30 min. Similarly, IL-1 beta (10 ng, 100 ng, i.t.) significantly increased the PWL and lasted for more than 60 min in inflammatory rats. Both in normal and inflammatory rats, the IL-1 beta-induced antinociceptive effect was completely abolished by IL-1ra (50 ng, i.t.), and apparently attenuated by naloxone (10 microg, i.t.) or mianserin (20 microg, i.t.). These results suggest that IL-1 beta produces antinociceptive effect by binding IL-1 receptor at the spinal level, and is related to the activation of opioid and 5-HT systems.

Topics: Animals; Carrageenan; Inflammation; Injections, Spinal; Interleukin-1; Male; Mianserin; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Serotonin Antagonists; Time Factors

The effect of intraplantarly (i.pl.)-injected methionine-enkephalin (ME) on Concanavalin A (Con A)-induced paw edema in Dark Agouti (DA) and Albino Oxford (AO) rats was investigated. ME suppressed edema in DA rats, which was antagonized with naloxone (non-selective opioid receptor antagonist) and naltrindole (delta opioid receptors antagonist). Potentiating effect of ME in AO rats was blocked by naloxone, nor-binaltorphimine (kappa opioid receptors antagonist) and beta-funaltrexamine (mu opioid receptors antagonist). Dexamethasone suppressed edema in both rat strains. These findings suggest that strain-dependent differences in the effects of ME on inflammation in DA and AO rats could be related to diversity in opioid receptors expression in these strains.

Topics: Animals; Dexamethasone; Dose-Response Relationship, Drug; Edema; Enkephalin, Methionine; Glucocorticoids; Inflammation; Kinetics; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Species Specificity; Time Factors

Topics: Analgesics; Animals; Behavior, Animal; Enzyme Inhibitors; Female; Formaldehyde; Glyburide; Inflammation; Methiothepin; Naloxone; Narcotic Antagonists; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Pain Measurement; Potassium Channel Blockers; Rats; Rats, Wistar; Serotonin Antagonists; Vitamin B Complex

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

Antinociceptive and anti-inflammatory effects and acute toxicity of aqueous infusion and ethanolic maceration extracts of the aerial parts of Zhumeria majdae were studied in mice and rats. Antinociceptive activity was determined using hot-plate and writhing tests. The effect of the extracts against acute inflammation was studied by acetic acid increased vascular permeability and xylene-induced ear edema in mice. The activity of the extracts against chronic inflammation was assessed using the cotton pellet test in rats. LD50 values of the infusion and maceration extracts were 3.09 g/kg body wt., and 3.94 g/kg body wt., respectively. Phytochemical screening of the extracts indicated the presence of flavonoids and tannins. In the hot-plate test, the intraperitoneal injection of both extracts showed significant and dose-dependent antinociceptive activity in mice. Naloxone, an opioid antagonist, on pretreatment inhibited the antinociceptive activity of the extracts. The extracts exhibited antinociceptive activity against acetic acid-induced writhing, which was partially blocked by naloxone. Both extracts showed significant effect against acute inflammation induced by acetic acid in mice. In the chronic inflammation test, efficacy of the extracts was similar to that of baclofen and dexamethasone in rats. It is concluded that the aqueous infusion and ethanolic maceration extract of the aerial parts of Zhumeria majdae have antinociceptive effects and this may be mediated by opioid receptors. The extracts also showed anti-inflammatory effects against acute and chronic inflammation.

Topics: Acetic Acid; Analgesics; Analgesics, Opioid; Animals; Anti-Inflammatory Agents; Anti-Inflammatory Agents, Non-Steroidal; Chromatography, High Pressure Liquid; Dexamethasone; Diclofenac; Edema; Female; Inflammation; Lamiaceae; Lethal Dose 50; Male; Mice; Morphine; Naloxone; Narcotic Antagonists; Pain; Phytotherapy; Plant Extracts; Rats; Rats, Wistar; Spectrum Analysis; Toxicity Tests, Acute; Xylenes

1. The anti-nociceptive effects of contralateral administration of kappa-opioid agonist U-50,488H were investigated in rats. 2. Inflammation was induced by unilateral injection of 1% carrageenan into the right hindpaw. Prior to carrageenan injection, U-50,488H or saline was administered into the left hindpaw. Withdrawal responses to mechanical and heat stimulation and oedema levels were evaluated at 3, 6 and 24 h post-carrageenan injection. 3. The results showed that the inflammatory effect of 1% carrageenan peaked after 6 h with bilateral decreases in withdrawal latencies and ipsilateral oedema formation. 4. Contralateral treatment with 0.01, 0.05, 0.3 and 2 mg of U-50,488H attenuated nociceptive reflexes to mechanical stimulation on the inflamed side at 6 h. The anti-nociceptive effect of contralateral treatment was dose-dependent at 3 and 24 h. The hindpaw withdrawal latencies to heat stimulation were prolonged at 3 and 24 h after contralateral treatment with 0.3 mg U-50,488H. No effect on inflammatory oedema formation was observed, except for a decrease at 3 h after treatment with 2 mg of U-50,488H. 5. Sciatic nerve denervation on the contralateral side abolished the anti-nociceptive effects of U-50,488H (0.3 and 2 mg). In contrast, contralateral injection of 1 mg morphine prolonged paw latencies in denervated rats. 6. Both co-administration of the peripherally selective opioid antagonist naloxone methiodide with 0.3 mg U-50,488H, and alternatively, systemic administration of 0.3 mg U-50,488H reversed the anti-nociceptive effects induced by contralateral injection of U-50,488H. 7. Taken together, our findings indicate that the contralateral administration of U-50,488H attenuates nociceptive behaviour resulting from acute inflammation. The effect is mediated via peripheral neuronal kappa-opioid receptors and, possibly, spinal cord mechanisms, suggesting a new treatment approach for acute inflammatory conditions.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Acute Disease; Analgesics, Opioid; Animals; Behavior, Animal; Denervation; Hindlimb; Hot Temperature; Inflammation; Male; Naloxone; Pain; Pain Measurement; Physical Stimulation; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Sciatic Nerve

The neuropeptide alpha CGRP (calcitonin gene-related peptide) is involved in the complex process of pain signaling, but the precise contribution of alpha CGRP remains unclear. Here we show that mice lacking alpha CGRP display an attenuated response to chemical pain and inflammation. Furthermore, alpha CGRP(-/-) mice do not show changes in heroin self-administration or morphine tolerance, but display a marked decrease in morphine withdrawal signs, suggesting an important contribution of alpha CGRP to opiate withdrawal.

Topics: Acetic Acid; Analgesics, Opioid; Animals; Calcitonin Gene-Related Peptide; Capsaicin; Carrageenan; Fixatives; Formaldehyde; Ganglionic Stimulants; Inflammation; Magnesium Sulfate; Mice; Mice, Transgenic; Morphine; Naloxone; Narcotic Antagonists; Nicotine; Opioid-Related Disorders; Pain; Substance Withdrawal Syndrome

1. Nicotine can activate primary afferent nociceptors, one result of which is to increase neurogenic plasma extravasation. In this study we have demonstrated a novel proinflammatory effect of sub-nanomolar nicotine, mediated by peripheral action at sensory neurons. This action is normally masked by adrenal medulla-derived delta-opioid receptor agonists. 2. While neurogenic plasma extravasation in the knee joint of the rat was not increased by intra-articular perfusion of nicotine (10(-8) M), perfusion of nicotine, at concentrations as low as 10(-10) M, combined with naloxone to block opioid receptors (or naltrindole to block delta-opioid receptors) was able to enhance bradykinin-induced plasma extravasation. This pro-inflammatory effect of intra-articular nicotine was mimicked by subcutaneous nicotine which was abolished by intra-articularly-administered hexamethonium, a nicotinic receptor antagonist. 3. Following denervation of the adrenal medulla, intra-articular nicotine, alone at 10(-8) M, enhanced plasma extravasation, which was no longer enhanced by naloxone. 4. Destruction of primary afferents by neonatal treatment with capsaicin or blockade of sensory neurotransmitter by neurokinin-1 receptor antagonist RP-87,580 abolished the pro-inflammatory effect of nicotine. 5. The effect of nicotine we describe in promoting inflammation is exerted at extremely low concentrations and therefore could have relevance to smokers, patients receiving medicinal nicotine as therapy and even second-hand smokers. Since receptor mechanisms on peripheral terminals of nociceptors may also be present on central terminals, actions of the endogenous nicotinic agonist acetylcholine, at central terminals of primary afferents or at other sites in the central nervous system, may be similarly modulated by opioids.

Topics: Adrenal Medulla; Analysis of Variance; Animals; Animals, Newborn; Bradykinin; Capsaicin; Dose-Response Relationship, Drug; Hexamethonium; Inflammation; Knee Joint; Male; Naloxone; Naltrexone; Narcotic Antagonists; Neurokinin-1 Receptor Antagonists; Neurons, Afferent; Nicotine; Nociceptors; Opioid Peptides; Rats; Rats, Sprague-Dawley; Receptors, Neurokinin-1; Receptors, Opioid; Sciatic Nerve; Time Factors

Due to low central nervous system (CNS) bioavailability of delta-opioid peptides, little is known about the effect of systemic administration of delta-opioid receptor ligands. The present study examined the effect of non-peptidergic delta-opioid receptor agonists, (+)-4-[(alphaR)-alpha-((2R,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) and (-)dibenzoyl-L-tartaric acid salt (SNC86), on the activity of alpha-motoneurons in decerebrate-spinal rats. The flexor reflex was facilitated by C-afferent conditioning inputs, shown by a decrease in mechanical threshold and increase in touch- and pinch-evoked responses. Systemic administration of SNC80 (10 micromol/kg) prevented and reversed the neuronal hyperactivity. We further examined the effect of this agonist on the hypersensitivity of the flexor reflex induced by intraplantar injection of Freund's adjuvant. SNC80 dose-dependently (1, 3, 5 and 10 micromol/kg) increased the mechanical threshold and decreased touch-, pinch- and Abeta-afferent inputs-evoked responses. Similar effects were seen with SNC86 (5 micromol/kg). Pretreatment with either naloxone (20 micromol/kg, i.p.) or (Cyclopropylmethyl)-6,7-dehydro-4,5alpha-epoxy-14beta-ethoxy-5beta-methylindolo [2',3':6',7']morphinan-3-ol hydrochloride (SH378; 5 micromol/kg, intraarterially (i.a.)), a novel selective delta-opioid receptor antagonist, completely abolished the anti-hypersensitivity effect of SNC80. The effect of SNC80 remained following intrathecal administration of mu-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP; 1.5 nmol). These results indicate that systemic injection of SNC80 exerted antihypersensitivity in models of both acute and tonic nociception and these effects are mediated mainly through a spinal delta-opioid mechanism.

Topics: Afferent Pathways; Animals; Benzamides; Central Nervous System; Conditioning, Psychological; Dose-Response Relationship, Drug; Drug Hypersensitivity; Electric Stimulation; Electrophysiology; Freund's Adjuvant; Hindlimb; Indoles; Inflammation; Male; Morphinans; Motor Neurons; Naloxone; Narcotic Antagonists; Pain Measurement; Piperazines; Rats; Rats, Wistar; Receptors, Opioid, delta; Receptors, Opioid, mu; Reflex; Somatostatin; Tartrates; Touch

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 tolerance to analgesia and dependence liability of dihydroetorphine following topical application were investigated in hairless rats with and without formalin-induced inflammation. The analgesic effect of dihydroetorphine (s.c.) was 4600- to 7200-fold more potent than that of morphine. In non-inflamed rats, the analgesic effect of 24-h topical application of dihydroetorphine tape (35 microg) and 4-day repeated tape applications (20 microg/5 h/day) decreased with time after the start of application, even though the plasma dihydroetorphine concentrations did not decrease. In formalin-inflamed rats, however, the tolerance to analgesia diminished. Naloxone-precipitated weight loss was observed after 24-h infusion of dihydroetorphine but not after the tape application in non-inflamed rats. A significant rewarding effect was found in the non-inflamed rats conditioned by s.c. injection and tape application but not in the formalin-inflamed rats. These results indicate that topical application of dihydroetorphine has a tolerance and dependence liability when there is no pain, and therefore, it should be used only for pain relief.

Topics: Administration, Cutaneous; Analgesics, Opioid; Animals; Conditioning, Psychological; Dose-Response Relationship, Drug; Drug Tolerance; Etorphine; Formaldehyde; Inflammation; Infusions, Intravenous; Injections, Subcutaneous; Male; Morphine; Naloxone; Narcotic Antagonists; Rats; Rats, Nude; Substance-Related Disorders; Time Factors; Weight Loss

This study investigates two new kappa-agonist tetrapeptides, FE 200665 and FE 200666, with high peripheral selectivity as a result of poor central nervous system penetration.. Four days after administration of Freund adjuvant into the hind paw of male Wistar rats, antinociceptive effects of intraplantar and subcutaneous injection of FE 200665 and FE 200666 were measured by paw pressure algesiometry and compared with the kappa-agonist U-69,593. Peripheral and kappa-receptor selectivity was assessed by the antagonists naloxone methiodide (NLXM) and nor-binaltorphimine, respectively. Antiinflammatory effects were evaluated by paw volume plethysmometry and histologic score.. Similar to intraplantar U-69,593, intraplantar FE 200665 (3-100 microg) and FE 200666 (1-30 microg) resulted in significant and dose-related increases of paw pressure thresholds. Higher doses of FE 200665 (0.2-20 mg) and FE 200666 (0.06-6 mg) were required by subcutaneous route to produce similar antinociceptive responses, supporting a peripheral site of action. nor-Binaltorphimine dose-dependently antagonized this effect, implying kappa-opioid selectivity. Analgesic effects of subcutaneous FE 200665 and FE 200666 were abolished by intraplantar nor-binaltorphimine, and both subcutaneous and intraplantar effects were dose-dependently antagonized by subcutaneous NLXM, further demonstrating a peripheral site of action. One to 6 days after Freund adjuvant inoculation, single and repeated intraplantar injections of FE 200665, FE 200666, and U-69,593 significantly reduced paw volume and histologic scores. Both changes were reversed by intraplantar nor-binaltorphimine and subcutaneous NLXM.. FE 200665 is a peripherally selective kappa-agonist with potent analgesic and antiinflammatory properties that may lead to improved analgesic-antiinflammatory therapy compared with centrally acting opioids or standard nonsteroidal antiinflammatory drugs.

Topics: Analgesics, Opioid; Animals; Anti-Inflammatory Agents, Non-Steroidal; Benzeneacetamides; Dose-Response Relationship, Drug; Inflammation; Injections, Spinal; Male; Naloxone; Naltrexone; Narcotic Antagonists; Opioid Peptides; Pain Threshold; Pyrrolidines; Rats; Rats, Wistar; Receptors, Opioid, kappa

To evaluate mu-opioid receptors in synovial membranes of horses and determine whether these receptors are up-regulated in nerve endings during inflammation.. Synovial tissue obtained from 39 client-owned horses during arthroscopy and 14 research horses during necropsy; brain and synovial tissues were obtained during necropsy from 1 horse, and control tissues were obtained from a mouse.. Horses were classified into 7 groups on the basis of histologically determined degree of inflammation. Binding of primary rabbit antibody developed against mu-opioid receptors in equine synovial tissue was studied, using western blot analysis. Synovial membranes were tested for mu-opioid receptors by immunohistochemical staining, using a diaminobenzidine-cobalt chloride chromogen. Homogenates of synovial membranes were evaluated by use of radioligand binding.. Examination of western blots of equine thalamus revealed that rabbit antibody developed against mu-opioid receptors yielded a band (molecular weight, 55 kd) that corresponded with that of other opioid receptors. Use of immunohistochemical staining of synovial tissue revealed considerable staining in the proliferative lining layer and in regions surrounding vascular structures. Specific radioligand binding of tissue homogenates was found in all groups. We did not detect significant differences in binding between horses with inflammation and horses without inflammation.. Results of immunohistochemical analysis and radioligand binding of tissue homogenates suggest that there are opioid receptors in synovial membranes of horses. Our results support the practice of intra-articular administration of opioids to relieve pain after arthroscopic surgery in horses.

Topics: Animals; Arthroscopy; Horse Diseases; Horses; Immunohistochemistry; Inflammation; Naloxone; Narcotic Antagonists; Receptors, Opioid, mu; Stifle; Synovial Membrane

1. We have studied the effect of palmitoylethanolamide (PEA, 2.5 - 30 mg kg(-1), i.p.) on upper gastrointestinal transit in control mice and in mice with chronic intestinal inflammation induced by croton oil. 2. PEA significantly and dose-dependently decreased intestinal transit. The inhibitory effect of PEA (10 mg kg(-1)) was not modified by the cannabinoid CB(1) receptor antagonist SR141716A (0.3 mg kg(-1), i.p.), the cannabinoid CB(2) receptor antagonist SR144528 (1 mg kg(-1), i.p.), N(G)-nitro-L-arginine methyl ester (L-NAME, 25 mg kg(-1), i.p.), yohimbine (1 mg kg(-1), i.p.), naloxone (2 mg kg(-1), i.p.) or hexamethonium (1 mg kg(-1), i.p.). 3. PEA levels were significantly decreased in the small intestine of croton oil-treated mice. In these animals, PEA also inhibited motility and this effect was not counteracted by SR141716A (0.3 mg kg(-1)), or SR144528 (1 mg kg(-1)). 4. Pre-treatment of mice with the amidase inhibitor phenylmethyl sulphonil fluoride (PMSF, 30 mg kg(-1), i.p.) did not modify the inhibitory effect of PEA, either in control or in mice with inflammation. 5. It is concluded that PEA inhibits intestinal motility with a peripheral mechanism independent from cannabinoid receptor activation. The decreased levels of PEA in croton oil-treated might contribute, at least in part, to the exaggerated transit observed during chronic intestinal inflammation.

Topics: Adrenergic alpha-Antagonists; Amides; Animals; Anti-Inflammatory Agents, Non-Steroidal; Camphanes; Croton Oil; Dose-Response Relationship, Drug; Endocannabinoids; Enzyme Inhibitors; Ethanolamines; Gastrointestinal Motility; Gastrointestinal Transit; Hexamethonium; Inflammation; Intestine, Small; Male; Mice; Mice, Inbred ICR; Naloxone; NG-Nitroarginine Methyl Ester; Nicotinic Antagonists; Nitric Oxide Synthase; Palmitic Acids; Phenylmethylsulfonyl Fluoride; Piperidines; Pyrazoles; Receptors, Cannabinoid; Receptors, Drug; Rimonabant; Yohimbine

Topics: Animals; Behavior, Animal; Female; Formaldehyde; Inflammation; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Rats; Rats, Wistar; Vitamin B Complex

Degeneration of dopaminergicrgic neurons in the substantia nigra of the brain is a hallmark of Parkinson's disease and inflammation and oxidative stress are closely associated with the pathogenesis of degenerative neurological disorders. Treatment of rat mesencephalic mixed neuron-glia cultures with lipopolysaccharide (LPS)-activated microglia, resident immune cells of the brain, to release proinflammatory and neurotoxic factors tumor necrosis factor-alpha, interleukin-1beta, nitric oxide, and superoxide and subsequently caused damage to midbrain neurons, including dopaminergic neurons. The LPS-induced degeneration of the midbrain neurons was significantly reduced by cotreatment with naloxone, an opioid receptor antagonist. This study focused on understanding the mechanism of action for the protective effect of naloxone on dopaminergic neurons because of relevance to Parkinson's disease. Both naloxone and its opioid receptor inactive stereoisomer (+)-naloxone protected the dopaminergic neurons with equal potency. Naloxone inhibited LPS-induced activation of microglia and release of proinflammatory factors, and inhibition of microglia generation of superoxide free radical best correlated with the neuroprotective effect of naloxone isomers. To further delineate the site of action, naloxone was found to partially inhibit the binding of [(3)H]LPS to cell membranes, whereas it failed to prevent damage to dopaminergic neurons by peroxynitrite, a product of nitric oxide and superoxide. These results suggest that naloxone at least in part interferes with the binding of LPS to cell membranes to inhibit microglia activation and protect dopaminergic neurons as well as other neurons in the midbrain cultures from inflammatory damage.

Topics: Animals; Cells, Cultured; Dopamine; Immunohistochemistry; Inflammation; Interleukin-1; Lipopolysaccharides; Mesencephalon; Microglia; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Naloxone; Narcotic Antagonists; Neurons; Nitrates; Nitrites; Oxidants; Rats; Rats, Inbred F344; Stereoisomerism; Substantia Nigra; Superoxides; Tumor Necrosis Factor-alpha; Tyrosine 3-Monooxygenase

Inflammation or injury often lead to chronic pain states such as hyperalgesia where the perception of a normally painful stimulus is significantly exaggerated. Interleukin-1beta (IL-1beta) is a cytokine that is an important mediator of the inflammatory response. In addition, IL-1beta has been implicated in the modulation of pain transmission in both the peripheral and central nervous systems. We evaluated the spinal effect of this cytokine in the presence and absence of a peripheral carrageenan inflammation in rats since the spinal cord is a major region of the central nervous system in which nociceptive input is processed and modulated. Our results indicate that intrathecal IL-1beta has no effect on the latency of paw withdrawal in response to a noxious thermal stimuluation in normal rats. In contrast, we have observed that IL-1beta produces significant antinociception when administered intrathecally in rats with peripheral inflammation (carrageenan model). The IL-1beta effect appears to be selective as it is reversed when IL-1beta is administered in the presence of an IL-1beta neutralizing antibody. We evaluated some putative mechanisms of this IL-1beta-mediated antinociception and found it to be non-opioid-dependent. Collectively, these data indicate that intrathecal IL-1beta has no effect on the processing of thermal nociceptive information in the absence of a peripheral inflammation. Therefore, the response to acute pain remains normal in these rats. In contrast, IL-1beta is antinociceptive when applied spinally during inflammation. These results indicate that IL-1beta reduces inflammatory hyperalgesia while sparing the protective functions of acute pain. This study offers new insights into the role of IL-1beta and nociceptive processing at the level of the spinal cord and suggests that development of IL-1beta agonists may be an alternative to opiate based therapies in the treatment of inflammatory pain.

Topics: Animals; Antibodies, Blocking; Carrageenan; Dose-Response Relationship, Drug; Inflammation; Injections, Spinal; Interleukin-1; Male; Naloxone; Narcotic Antagonists; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Time Factors

The pharmacological activity of phenylacetyl-Phe-Ser-Arg-N-(2, 4-dinitrophenyl)-ethylenediamine (TKI), a tissue kallikrein specific inhibitor, was assessed using models of nociception and inflammation in mice. Injection of TKI (13.6 - 136 micromol kg(-1), i.p. or 41 - 410 micromol kg(-1), s.c.) produced a dose-related inhibition of the acetic acid-induced writhes (by 37 to 85% or 34 to 80%, respectively). The antinociceptive activity of TKI (41 micromol kg(-1), i.p.) was maximal after 30 min injection and lasted for 120 min. The effect was unaltered by pretreatment with naloxone (8.2 micromol kg(-1), s.c.) or bilateral adrenalectomy. TKI (41 and 136 micromol kg(-1), i.p.) produced a dose-related decrease of the late phase of formalin-induced nociception by 79 and 98%, respectively. At 136 micromol kg(-1), i.p., TKI also shortened the duration of paw licking in the early phase by 69%. TKI (41 and 136 micromol kg(-1), i.p.) also reduced the capsaicin-induced nociceptive response (by 51 to 79%). TKI (41 micromol kg(-1), i.p. or 410 micromol kg(-1), s.c.) reduced the oedematogenic response, from the second to the fifth hour after carrageenin injection by 36 to 30% or by 47 to 39%, respectively. Pretreatment with TKI (41 micromol kg(-1), i.p.) reduced the capsaicin-induced neurogenic inflammation in the mouse ear by 54%. It is concluded that TKI presents antinociceptive and antiinflammatory activities mediated by inhibition of kinin formation by tissue kallikrein in mice. The results also indicate that the tissue kallikrein-dependent pathway contributes to kinin generation in nociceptive and inflammatory processes in mice.

Topics: Adrenalectomy; Analgesics, Non-Narcotic; Animals; Anti-Inflammatory Agents, Non-Steroidal; Edema; Enzyme Inhibitors; Female; Inflammation; Kinins; Male; Mice; Naloxone; Oligopeptides; Pain; Peritonitis; Tissue Kallikreins

The level of serotonin (5-HT) and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) in dorsal horn of spinal cord and periaqueductal gray (PAG) were measured using in vivo microdialysis coupled with high performance liquid chromatography and electrochemical detection. Intraplantar injection of carrageenan was used to evoke release. Extracellular concentrations of 5-HT and 5-HIAA in spinal dorsal horn and PAG significantly increased following carrageenan inflammation. The peak occurred at 3h and then gradually returned to baseline at 5-7h. The carrageenan-induced release of 5-HT and 5-HIAA in spinal cord rather than in PAG was decreased by intracerebroventricular (i.c.v.) injection of naloxone, and both in spinal dorsal horn and PAG, the release was increased by i.c.v. injection of bicuculine. These results suggest that activity of 5-HT in spinal cord and PAG increases with carrageenan inflammation; the carrageenan-induced release of 5-HT and 5-HIAA in spinal cord may be tonically modulated by supraspinal opioid and GABA systems, whereas the release in PAG may only be tonically modulated by endogenous GABA system in supraspinal level.

Topics: Animals; Bicuculline; Carrageenan; Cerebral Ventricles; Hydroxyindoleacetic Acid; Inflammation; Injections, Intraventricular; Kinetics; Male; Microdialysis; Naloxone; Periaqueductal Gray; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Serotonin; Spinal Cord; Time Factors

The synthesis of a new series of nonpeptide derivatives of interleukin-1 beta sequence is described. Compounds have been investigated for their relative activity regarding antinociception and suppression of inflammation. Several compounds with R1(R)Lys [CH2N]-Pro structure showed better efficacy in the inflamed paw pressure test than indometacin and morphine. In terms of the relative potencies the above mentioned products (i.e. compounds 2, 4, 5, 6; ED50 values of 0.002, 0.0035, 0.0032, 0.0074 mg/kg i.p. respectively) were 10-100 times more potent than indometacin and morphine (ED50 values of 0.22 and 0.75 mg/kg). Compounds 1-14 were not able to inhibit binding of labeled interleukin-1 beta to EL 4-6.1 murine cells, since they had no affinity for interleukin-1 beta receptors. The antinociceptive activity elicited by compound 4 in the rat inflamed paw pressure test was inhibited by naloxone, but the compound was inactive in the mouse hot plate and rat paw pressure tests. These results suggest that compound 4 exerts its antinociceptive activity through a mechanism which is based on the local release of endogenous opioids in injured tissue.

Topics: Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Carrageenan; Cells, Cultured; Drug Tolerance; Edema; Inflammation; Interleukin-1; Magnetic Resonance Spectroscopy; Male; Mice; Models, Molecular; Naloxone; Narcotic Antagonists; Pain Measurement; Peptide Fragments; Proline; Rats; Rats, Wistar; Reaction Time; Receptors, Interleukin

The aim of this study was to determine if the application of mustard oil (MO), a small-fiber excitant and inflammatory irritant, or other algesic chemicals (capsaicin, CAP, and bradykinin, BK) to the rat maxillary molar tooth pulp induces electromyographic (EMG) activity of the masseter and digastric muscles, and also to determine if endogenous opioid mechanisms may be involved in any documented EMG changes. Application of MO to the tooth pulp induced a significant increase in EMG activity of the ipsilateral masseter up to 30 min. The application of mineral oil to the pulp or MO application to the pulp-extirpated tooth did not induce any significant EMG increases. The application of CAP or BK to the pulp in contrast had much weaker effects on EMG activity of the jaw muscles. CAP produced a small but prolonged increase in masseter EMG activity, and BK induced a short-lasting increase in digastric EMG activity. The systemic administration of the opiate antagonist naloxone significantly reactivated (i.e. rekindled) the EMG response evoked by MO application to the pulp. Naloxone did not produce any such significant rekindling effect on EMG activity following CAP, BK or mineral oil application to the pulp or following MO application to the pulp-extirpated tooth. The MO, BK and especially CAP groups showed histological evidence of vasodilatation and polymorphonuclear leukocyte infiltration in the pulp tissue and a significant increase in plasma extravasation of Evans Blue dye, whereas mineral oil did not induce these changes. These findings suggest that pulp afferent inputs to the central nervous system evoked by BK. CAP and especially MO may induce enhanced jaw muscle activity. In addition, the naloxone data suggest that an opioid suppresive mechanism may be induced by the pulpal afferent inputs evoked by MO, and may serve to limit the jaw muscle activity elicited by these inputs.

Topics: Animals; Bradykinin; Capsaicin; Dental Pulp; Electromyography; Evans Blue; Inflammation; Jaw; Male; Masseter Muscle; Mustard Plant; Naloxone; Narcotic Antagonists; Neutrophils; Pain; Plant Extracts; Plant Oils; Rats; Rats, Sprague-Dawley

Systemic administration of opiates or direct injection of opioid peptides into the periaqueductal gray (PAG) produces a profound antinociception which is thought to be associated with inhibition of neuronal activity in the PAG. This inhibitory effect has been postulated to result from opiate inhibition of GABAergic neurons in the PAG. Whether this opioid-GABAergic system is affected in acute pain state has not been investigated. The present study was thus designed to determine the effects of unilateral peripheral inflammation on ventrocaudal PAG gamma-aminobutyric acid (GABA) release in the rat using in vivo microdialysis and subsequent high pressure liquid chromatography (HPLC) analysis. Microdialysis was chosen to perform direct and dynamic studies of amino acid concentrations in the PAG in control rats and in animals subjected to acute and prolonged inflammation caused by injection of 120 microl of Complete Freund's Adjuvant (CFA) into the hind paw. GABA release was significantly decreased in the CFA treated groups both 24 h as well as 7 days post-treatment. GABA release decreased to approximately one-fourth that of the 24 h mineral oil control group. Likewise, veratridine-induced release of GABA was decreased in rats treated with CFA 7 days prior to dialysis. Systemic injection of naloxone (5 mg/kg i.p.) caused selective and significant block in the decrease of veratridine-induced release of GABA in the 24 h CFA-treated rats. Taken together with data from our previous studies, these results suggest that the decrease in veratridine-induced GABA release in this study may be due to an increase opiate inhibition of GABA resulting from the induction of acute or prolonged elevation of nociceptive input.

Topics: Animals; Chromatography, High Pressure Liquid; gamma-Aminobutyric Acid; Inflammation; Male; Microdialysis; Naloxone; Periaqueductal Gray; Rats; Rats, Sprague-Dawley; Reference Values; Veratridine

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

We evaluated the effects of systemic administration of a low dose of naloxone in rats with bilateral lesions in the area of the locus coeruleus (LC) under conditions of unilateral inflammation, compared with those in sham-operated rats. In each group, rats received a single s.c. injection of carrageenan (6 mg in 0.15 ml saline), and effects of a low dose of naloxone (5 microg/kg, i.p.) on thermal nociception were examined at 4 h and 7 days following the induction of unilateral hindpaw inflammation. The antinociceptive effect was assessed by prolongation of the paw withdrawal latency (PWL) to noxious thermal stimuli. Prior to induction of inflammation, the low dose of naloxone had no significant effect on PWLs in either the sham-operated or the LC-lesioned rats. Four hours after carrageenan injection, the low dose of naloxone produced prolongation of PWLs in the sham-operated rats but failed to induce antinociception in the LC-lesioned rats. Antinociceptive effects were observed in both groups of rats 7 days after carrageenan injection. These results suggest that the LC is involved in naloxone-induced anti-nociception during the early phase of inflammation.

Topics: Analgesics; Animals; Carrageenan; Dose-Response Relationship, Drug; Hindlimb; Inflammation; Injections; Locus Coeruleus; Male; Naloxone; Pain; Rats; Rats, Sprague-Dawley

Effects of the alpha2-adrenoceptor antagonist yohimbine on the antinociception produced by a low dose of naloxone were examined in a rat model of carrageenan-induced inflammation. In rats receiving saline prior to naloxone injection, the low dose of naloxone (5 microg/kg, i.p.) significantly prolonged paw withdrawal latency in response to noxious thermal stimuli for both the inflamed and the non-inflamed paws 4 h after carrageenan injection (6.0 mg in 0.15 ml saline). In rats receiving yohimbine, the low dose of naloxone failed to produce prolongation of paw withdrawal latencies 4 h after carrageenan, whereas naloxone produced antinociception 7 days after carrageenan. The results suggest that noradrenergic mechanisms are involved in naloxone-induced antinociception only in the early phase of carrageenan-induced inflammation.

Topics: Adrenergic alpha-2 Receptor Antagonists; Adrenergic alpha-Antagonists; Animals; Carrageenan; Hyperalgesia; Inflammation; Injections, Intraperitoneal; Male; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Yohimbine

The opioid antagonist, naloxone, produces equivocal effects on the magnitude of nociceptive responses in several animal models of persistent pain, including the formalin test. Hindpaw injection of dilute formalin produces not only inflammation but also phasic (Phase 1) and persistent (Phase 2) behavioral and cardiovascular nociceptive responses in the rat. To test the hypothesis that endogenous opioid systems contribute to the magnitude of responses to intraplantar formalin injection, we evaluated the effects of continuous naloxone administration (0.01-100 mg/kg per h, i.v.) on formalin-evoked hindpaw inflammation, on behavioral indices of pain, flinching and licking pain behavior, and on changes in mean arterial pressure and heart rate. We report that naloxone, at doses less than 100 mg/kg per h, did not change any formalin-evoked response. Although the 100 mg/kg per h dose significantly decreased these responses, it also produced muscle rigidity and profound bradycardia. We conclude that endogenous opioids do not significantly modulate the nociceptive processing induced by subcutaneous formalin.

Topics: Animals; Behavior, Animal; Blood Pressure; Formaldehyde; Heart Rate; Hemodynamics; Inflammation; Infusions, Intravenous; Injections, Subcutaneous; Male; Naloxone; Narcotic Antagonists; Pain; Rats; Rats, Sprague-Dawley

The present study was performed to explore the effects of intrathecal administration of calcitonin gene-related peptide8-37 (CGRP(8-37)) on the hindpaw withdrawal latency (HWL) to pressure in rats with one thermally injured hindpaw. Furthermore, the interaction of CGRP(8-37)and naloxone was studied. Thermal injury was performed by dipping the left paw into 60 degrees C for 20 s. This induced a significant increase in the volume of the left hindpaw (P<0.001) and significant bilateral decreases of the latency of hindpaw withdrawal response to mechanical stimulation (Left: P<0.001; right: P<0.05). Intrathecal administration of 10, 20 and 40 nmol of CGRP(8-37), but not of 1 or 5 nmol, induced a significant bilateral increase in HWLs (P<0.001). The effect of CGRP(8-37) was partly reversed by intrathecal injection of naloxone at a dose of 32 and 64 microg respectively. Using radioimmunoassay, we found a significant bilateral increase in the concentration of CGRP-like immunoreactivity in the perfusate of both hindpaws 24 h after unilateral thermal injury (left: P< 0.001; right: P< 0.05). There was also an increase in the amount of CGRP-like immunoreactivity in the cerebrospinal fluid (P< 0.001), but not in plasma. The results indicate that CGRP plays a role in the transmission of nociceptive information in the spinal cord of thermally injured rats. Furthermore, our findings suggest that opioids can modulate CGRP-related effects in the spinal cord.

Topics: Animals; Antibody Specificity; Burns; Calcitonin Gene-Related Peptide; Edema; Extracellular Space; Hot Temperature; Inflammation; Injections, Spinal; Male; Miotics; Naloxone; Narcotic Antagonists; Nociceptors; Pain; Peptide Fragments; Physical Stimulation; Pressure; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Reaction Time; Reflex; Spinal Cord

Immune cell-derived opioid peptides can activate opioid receptors on peripheral sensory nerves to inhibit inflammatory pain. The intrinsic mechanisms triggering this neuroimmune interaction are unknown. This study investigates the involvement of endogenous corticotropin-releasing factor (CRF) and interleukin-1beta (IL-1). A specific stress paradigm, cold water swim (CWS), produces potent opioid receptor-specific antinociception in inflamed paws of rats. This effect is dose-dependently attenuated by intraplantar but not by intravenous alpha-helical CRF. IL-1 receptor antagonist is ineffective. Similarly, local injection of antiserum against CRF, but not to IL-1, dose-dependently reverses this effect. Intravenous anti-CRF is only inhibitory at 10(4)-fold higher concentrations and intravenous CRF does not produce analgesia. Pretreatment of inflamed paws with an 18-mer 3'-3'-end inverted CRF-antisense oligodeoxynucleotide abolishes CWS-induced antinociception. The same treatment significantly reduces the amount of CRF extracted from inflamed paws and the number of CRF-immunostained cells without affecting gross inflammatory signs. A mismatch oligodeoxynucleotide alters neither the CWS effect nor CRF immunoreactivity. These findings identify locally expressed CRF as the predominant agent to trigger opioid release within inflamed tissue. Endogenous IL-1, circulating CRF or antiinflammatory effects, are not involved. Thus, an intact immune system plays an essential role in pain control, which is important for the understanding of pain in immunosuppressed patients with cancer or AIDS.

Topics: Analgesics, Opioid; Animals; Base Sequence; Corticotropin-Releasing Hormone; Immunohistochemistry; Inflammation; Interleukin-1; Male; Molecular Sequence Data; Naloxone; Oligonucleotides, Antisense; Pain; Radioimmunoassay; Rats; Rats, Wistar

1. Possible interactions between non-steroidal anti-inflammatory drugs (NSAIDs) and endogenous opioids were examined in electrophysiological experiments in alpha-chloralose anaesthetized spinalized rats without or with carrageenan-induced acute inflammation of one hindpaw. Spinal reflex responses, monitored as single motor unit discharges, were elicited by noxious pinch and electrical stimuli. 2. The mu-opioid agonist, fentanyl, was an effective depressant of reflexes under all conditions (ED50 6-14 micrograms kg-1, i.v.). In rats without peripheral inflammation the NSAID, flunixin, a niflumic acid derivative, had only a small effect that was not dose-dependent. However, in animals with unilateral inflammation, flunixin reduced spinal reflexes evoked both by noxious pinch stimuli (that activate peripheral nociceptors; ID50 4 mg kg-1, i.v.) and by electrical stimuli (that bypass nociceptor endings; ID50 6.5- 11 mg kg-1, i.v.), indicating that it has a central site of action at doses comparable to those used clinically. 3. The opioid antagonist, naloxone (1 mg kg-1, i.v.), reversed all actions of fentanyl. It did not reverse the small effects that flunixin had in rats without inflammation, showing that the NSAID is not a direct opioid agonist. In rats with carrageenan-induced inflammation of the hindpaw, however, naloxone fully reversed or prevented the antinociception by flunixin, but not that by the alpha 2-adrenoceptor agonist, medetomidine. 4. We conclude that under conditions of peripheral inflammation and the resultant central changes, the NSAID, flunixin, has antinociceptive actions that are mediated by endogenous opioids acting within the spinal cord.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Anti-Inflammatory Agents, Non-Steroidal; Carrageenan; Clonixin; Dose-Response Relationship, Drug; Electrophysiology; Excipients; Fentanyl; Inflammation; Male; Naloxone; Narcotic Antagonists; Rats; Rats, Wistar

1. Recent work in our laboratory has demonstrated that intrathecal administration of a selective antagonist of calcitonin gene-related peptide (CGRP), CGRP8-37, increased the hindpaw withdrawal latency (HWL) to thermal stimulation and hindpaw withdrawal threshold (HWT) to pressure in normal rats, and that these effects were more pronounced than in rats with mononeuropathy. 2. The present study was performed to investigate the effects of intrathecal administration of CGRP8-37 on the HWL and HWT in rats with unilateral hindpaw inflammation induced by subcutaneous injection of carrageenin. The effect of naloxone was also studied. 3. Subcutaneous injection of 0.1 ml of carrageenin into the plantar region of the left hindpaw induced a significant increase in the volume of the ipsilateral hindpaw (P < 0.001), and significant bilateral decreases of the HWL to thermal stimulation (ipsilateral: P < 0.001; contralateral: P < 0.01) and HWT to pressure (ipsilateral: P < 0.001; contralateral: P < 0.01). 4. Intrathecal administration of 10 nmol of CGRP8-37, but not of 1 or 5 nmol, induced a significant bilateral increase in the HWL and HWT in rats with experimentally induced inflammation (thermal test: P < 0.001; mechanical test: P < 0.001). 5. The effect of intrathecal administration of 10 nmol CGRP8-37 on HWL and HWT was significantly more pronounced in intact rats than in rats with experimentally induced inflammation (ipsilateral: P < 0.001; contralateral: P < 0.001). 6. The effect of CGRP8-37 on withdrawal responses in the inflamed paw was partly reversed by intrathecal injection of naloxone at a dose of 88 nmol in the thermal (ipsilateral: P < 0.01; contralateral: P = 0.14) and mechanical tests (ipsilateral: P < 0.05; contralateral: P = 0.60). 7. A significant bilateral increase in the concentration of CGRP-like immunoreactivity in the perfusate of both hindpaws was demonstrated 24 h after unilateral injection of carrageenin (ipsilateral: P < 0.001; contralateral: P < 0.05). There was also an increase in the amount of CGRP-like immunoreactivity in the cerebrospinal fluid (P < 0.001), but not in plasma (P = 0.75). 8. The present study demonstrates that acute experimentally-induced unilateral hindpaw inflammation, induces bilateral increases in the amount of CGRP-like immunoreactivity in hindpaw perfusates. Intrathecal administration of CGRP8-37 increased the HWL to thermal stimulation and HWT to pressure bilaterally. 9. The results indicate that CGRP plays a role i

Topics: Animals; Calcitonin; Calcitonin Gene-Related Peptide; Carrageenan; Drug Interactions; Hindlimb; Inflammation; Injections, Spinal; Male; Naloxone; Narcotic Antagonists; Pain Measurement; Peptide Fragments; Rats; Rats, Sprague-Dawley

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: Animals; Edema; Enkephalins; Evoked Potentials; Inflammation; Mustard Plant; Naloxone; Nerve Fibers; Neurons, Afferent; Neuropeptides; Neurotransmitter Agents; Paraffin; Plant Extracts; Plant Oils; Plants, Medicinal; Rats; Skin

Recent studies have shown peripheral antinociceptive effects of opiates in inflamed tissue. To test whether the afferent activity during an acute inflammation may also be suppressed by endogenous opioids, we studied whether the application of the opioid antagonist naloxone would alter the afferent discharges from the cat knee joint inflamed by kaolin and carrageenin. After i.a. bolus administration of naloxone (3 micrograms/kg and 1 mg/kg) close to the joint, neither the ongoing activity nor the responses to noxious and innocuous movements significantly changed in group III or group IV units. Since naloxone did not unmask opioidergic activity under these conditions, we conclude that the development of increased activity in joint afferents during an acute kaolin/carrageenin-induced inflammation is not tonically suppressed by endogenous opioids.

Topics: Afferent Pathways; Animals; Cats; Dose-Response Relationship, Drug; Inflammation; Joints; Knee; Naloxone; Narcotic Antagonists; Nociceptors

We have investigated the role of the endogenous opioid system (EOS) on the inflammatory response induced by subplantar (s.p.) injection of saline (SS) and carrageenan (CA) in the hindpaw of the rat. The administration of intraperitoneal (i.p.) naloxone was used in order to unmask the effects of endogenous opiates released during peripheral inflammation. Three groups of rats received one of the following s.p. treatments: SS, CA, or no injection (NI). Pain pressure threshold (PPT), paw volume (edema) and local temperature were evaluated in baseline conditions and 3 h after treatment. In each group, the effects of i.p. vehicle, naloxone and (+)-naloxone (0.1 mg/kg) were also investigated. Both SS and CA induced a significant inflammatory response with hyperalgesia, edema and local hyperthermia. The i.p. administration of naloxone but not that of (+)-naloxone 15 min prior to testing, significantly increased edema in all groups of treatment (P < 0.05), without altering PPT or local temperature. Two-way ANOVA revealed that treatment and drugs, as well as their interaction, had a significant impact on edema which was related to the effects of CA and naloxone. Our findings illustrate the involvement of the EOS in the physiological response to local injury, regulating microvascular leakage in the inflamed tissues.

Topics: Animals; Carrageenan; Hindlimb; Inflammation; Male; Naloxone; Narcotics; Rats; Rats, Sprague-Dawley; Temperature

1. Our recent studies in rats have demonstrated that the small-fiber excitant and inflammatory irritant mustard oil injected into the temporomandibular joint (TMJ) region can evoke a sustained and reversible increase of electromyographic (EMG) activity in jaw muscles and an acute inflammatory response. The aim of the present study was to test if opioid mechanisms are involved in modulating the EMG increase evoked by mustard oil. 2. Mustard oil injected into the rat TMJ region evoked significant increases of jaw muscle EMG activity; the vehicle mineral oil had no such effect. The increased EMG activity lasted up to 20 min, and by 30 min after the mustard oil injection had returned to control (preinjection) levels, at which time administration of the opiate antagonist naloxone (1.3 mg/kg i.v.) induced a significant recurrence of the increase in EMG activity. This "rekindling" of EMG activity appeared at 5 to 10 min after the naloxone administration and lasted for 10 to 20 min. In contrast, naloxone administration in the animals receiving mineral oil injection into the TMJ region did not "rekindle" the EMG activity, nor did the administration of the peripherally acting opiate antagonist methylnaloxone or the vehicle of naloxone. 3. These findings reveal that the application of the opiate antagonist naloxone produces a recurrence of increased jaw muscle activity reflexively evoked by mustard oil injection into the rat TMJ region. They suggest that central opioid depressive mechanisms activated by the mustard oil-induced afferent barrage limit the duration of the evoked EMG changes.

Topics: Afferent Pathways; Animals; Electromyography; Inflammation; Male; Masticatory Muscles; Mustard Plant; Naloxone; Narcotic Antagonists; Nociceptors; Oxymorphone; Plant Extracts; Plant Oils; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Recurrence; Temporomandibular Joint

To study the effects of the cytokine and neuroendocrine hormone beta-endorphin on the transendothelial migration of neutrophils, bovine pulmonary artery endothelial cells were grown to confluence on PVP-free polycarbonate filters coated with gelatin. Pretreatment of endothelial cell cultures with 1 to 10 mumol/liter of beta-endorphin for 60 min resulted in significantly stimulated migration of subsequently added neutrophils across the endothelial monolayer. The number of neutrophils that migrated across beta-endorphin-treated endothelial cells was similar to the number that traversed untreated monolayers in response to gradients of formylpeptide. Consistently, an additive effect was seen when migration was induced by both beta-endorphin pretreatment of the endothelial cells and a formylpeptide chemotactic gradient. When used at optimal concentration, beta-endorphin was equally effective in stimulating neutrophil migration as was tumor necrosis factor-alpha. In the absence of formylpeptide the effect of apical surface exposure of endothelial cells to beta-endorphin versus basal surface exposure was comparable. Stimulation of neutrophil transendothelial migration in this system appeared to be specific and mediated by opiate receptors, since excess concentration of naloxone completely abolished the effect of beta-endorphin but not of tumor necrosis factor-alpha. These results suggest that beta-endorphin, released during stress, may act upon the endothelium to promote emigration of neutrophils from the vasculature.

Topics: Animals; beta-Endorphin; Cattle; Cells, Cultured; Chemotaxis, Leukocyte; Endothelium, Vascular; Humans; Inflammation; N-Formylmethionine Leucyl-Phenylalanine; Naloxone; Neutrophils; Pulmonary Artery; Receptors, Opioid; Stimulation, Chemical; Tumor Necrosis Factor-alpha

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

Local analgesic effects of exogenous opioid agonists are particularly prominent in painful inflammatory conditions and are mediated by opioid receptors on peripheral sensory nerves. The endogenous ligands of these receptors, opioid peptides, have been demonstrated in resident immune cells within inflamed tissue of animals and humans. Here we examine in vivo and in vitro whether interleukin 1 beta (IL-1) or corticotropin-releasing factor (CRF) is capable of releasing these endogenous opioids and inhibiting pain. When injected into inflamed rat paws (but not intravenously), IL-1 and CRF produce antinociception, which is reversible by IL-1 receptor antagonist and alpha-helical CRF, respectively, and by the immunosuppressant cyclosporine A. In vivo administration of antibodies against opioid peptides indicates that the effects of IL-1 and CRF are mediated by beta-endorphin and, in addition, by dynorphin A and [Met]enkephalin, respectively. Correspondingly, IL-1 effects are inhibited by mu-, delta-, and kappa-opioid antagonists, whereas CRF effects are attenuated by all except a kappa-antagonist. Finally, IL-1 and CRF produce acute release of immunoreactive beta-endorphin in cell suspensions freshly prepared from inflamed lymph nodes. This effect is reversible by IL-1 receptor antagonist and alpha-helical CRF, respectively. These findings suggest that IL-1 and CRF activate their receptors on immune cells to release opioids that subsequently occupy multiple opioid receptors on sensory nerves and result in antinociception. beta-Endorphin, mu- and delta-opioid receptors play a major role, but IL-1 and CRF appear to differentially release additional opioid peptides.

Topics: Analysis of Variance; Animals; Antibodies; beta-Endorphin; Corticotropin-Releasing Hormone; Cyclosporine; Dose-Response Relationship, Drug; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Methionine; Humans; Inflammation; Injections; Interleukin-1; Male; Naloxone; Pain; Rats; Rats, Wistar; Recombinant Proteins; Regression Analysis; Somatostatin

RB101 (N-((R,S)-2-benzyl-3[(S)(2-amino-4-methylthio)butyl dithio]-1-ox-opropyl)-L-phenylalanine benzyl ester) is a recently developed full inhibitor of the enkephalin-catabolizing enzymes able to cross the blood-brain barrier, whereas RB38A ((R)-3-(N-hydroxycarboxamido-2-benzylpropanoyl)-L-phenylalanine) is as potent as RB101 but almost unable to enter the brain. In this study, we have investigated the effects of systemic administration of morphine, RB101 and RB38A on nociception induced by pressure on inflamed peripheral tissues. Antinociceptive test was performed between 4 and 5 days after injection into the rat left hindpaw of Freund's complete adjuvant to produce localized inflammation. Morphine (1, 2 and 4 mg/kg, i.v.) induced antinociception in inflamed paws at all the doses used, and only at the highest dose in non-inflamed paws. RB101 (10 and 20 mg/kg, i.v.) induced an antinociceptive response only in the inflamed paws. RB38A, also induced an antinociceptive effect in the inflamed paws, but only at the highest dose (20 mg/kg, i.v.). The responses induced by morphine and the inhibitors of enkephalin catabolism were antagonized by the systemic administration of naloxone (1 mg/kg) or methylnaloxonium (2 mg/kg) which acts essentially outside the brain. Central injection (i.c.v.) of methylnaloxonium (2 micrograms) blocked the effect of morphine only in non-inflamed paws, and slightly decreased the response induced by RB101 on inflamed paws. These results indicate that the endogenous opioid peptides, probably enkephalins, are important in the peripheral control of nociception from inflamed tissues.

Topics: Analgesics; Animals; Disulfides; Enkephalins; Hydroxamic Acids; Inflammation; Injections, Intraventricular; Male; Morphine; Naloxone; Narcotic Antagonists; Neprilysin; Pain; Pain Measurement; Phenylalanine; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley

The effect of inflammation, induced by unilateral intraplantar injection of Freund's adjuvant, on opioid receptors transported in the sciatic nerve and on opioid receptors present in the paw of the rat was studied by means of in vitro receptor autoradiography using [125I]beta-endorphin (human) as ligand. In the absence of inflammation, human beta-endorphin binding sites accumulated proximally and distally to a ligature placed on the sciatic nerve in a time-dependent manner, indicating bidirectional axonal transport. Some human beta-endorphin binding was also visible in non-inflamed paw tissue. Inflammation of the paw tissue massively increased human beta-endorphin binding on both sides of the sciatic nerve ligature and in the ipsilateral paw tissue. In inflamed paw tissue, beta-endorphin binding accumulated in the cutaneous nerve fibers as well as in the immune cells infiltrating the surrounding tissue. In the sciatic nerve and paw tissue, beta-endorphin binding was displaced by (D-Ala2, N-methyl-Phe4, Gly-ol5)enkephalin and (D-Pen2, D-Pen5)enkephalin, selective mu- and delta-opioid receptor agonists, respectively, and by the universal opioid antagonist naloxone, but not by U-50,488H, a k-selective receptor agonist. Taken together, these data provide neuroanatomical evidence for local inflammation-induced enhanced axonal transport of opioid receptors in rat sciatic nerve and accumulation in paw tissue.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Axonal Transport; beta-Endorphin; Biological Transport; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Foot; Freund's Adjuvant; Inflammation; Ligation; Male; Naloxone; Nerve Tissue Proteins; Pyrrolidines; Rats; Rats, Wistar; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Sciatic Nerve

This study concerned the effect of Ga-Al-As diode laser irradiation (780 nm, continuous wave, 31.8 J/s/cm2, spot size od 0.2 mm, 3 minutes/dose) on hyperalgesia induced in the hind paw of rats by injecting carrageenin. The pressure-pain thresholds of hind paws were measured by the Randall-Selitto test for evaluation of hyperalgesia. Two doses of laser irradiation, given to the inflamed region immediately before and after the injection of carrageenin, partially (approximately 50%) inhibited the occurrence of hyperalgesia accompanied with a progression of inflammation. This analgesic effect was equal to that of indomethacin (4 mg/kg, i.o.). In another group, the hyperalgesia was removed almost completely for at least 24 hours by one dose of laser irradiation, which was given 3 hours after the carrageenin injection, whereas the edema was not inhibited. This analgesic effect, however, was partially (approximately 50%) antagonized with a dose of 10 mg/kg (i.p.) of naloxone and totally inhibited with 30 mg/kg. These results suggest that low-power laser irradiation on inflamed regions of carrageenin-treated rats has a marked analgesic effect and that certain mechanisms that are not related to endogenous opioids are involved in a part of the mechanisms of the analgesic effects.

Topics: Analgesia; Animals; Carrageenan; Hyperalgesia; Indomethacin; Inflammation; Laser Therapy; Male; Naloxone; Pain Measurement; Rats; Rats, Wistar

We used an experimental model of neurogenic inflammation, plasma extravasation induced by bradykinin or capsaicin, to study the effect of receptor-selective opioid agonists on plasma extravasation. Plasma extravasation was induced in the knee joint of the rat by continuous perfusion of either bradykinin (160 ng/ml), an inflammatory mediator produced at sites of tissue injury, that produces plasma extravasation significantly dependent on the sympathetic postganglionic neuron, or capsaicin (5 mg/ml), a C-fiber excitotoxin, that induces plasma extravasation that is dependent on both primary afferents and sympathetic post-ganglionic neurons. When selective delta-((d-Pen2,5)-enkephalin) or kappa-(trans-3,4-dichloro-N-methyl-N[2-(- pyrolidinyl)cyclohexyl]benzeneacetamide; U50,488H) opioid agonists were perfused with bradykinin, plasma extravasation was significantly attenuated. Co-perfusion of the non-selective opioid antagonist naloxone (1 microM), reversed this opioid-induced inhibition of bradykinin-induced plasma extravasation. In contrast, co-perfusion of a selective mu-opioid agonist (Tyr-d-Ala-Gly-NMe-Phe-Gly-ol) did not reduce bradykinin-induced plasma extravasation. Tyr-d-Ala-Gly-NMe-Phe-Gly-ol was, however, able to completely inhibit the plasma extravasation produced by capsaicin. These results suggest that delta- and kappa-, but not mu-selective opioids inhibit bradykinin-stimulated plasma extravasation, while a mu-selective opioid inhibits primary afferent-dependent plasma extravasation. Therefore, inhibition of neurogenic plasma extravasation by receptor-selective opioids may depend on the relative contribution to plasma extravasation of unmyelinated afferent and sympathetic postganglionic neuron terminals. Our findings can also explain, in part, the variation in anti-inflammatory effects of receptor-selective opioids reported in different inflammatory conditions.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Bradykinin; Capsaicin; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Inflammation; Joints; Male; Naloxone; Pyrrolidines; Rats; Rats, Wistar; Receptors, Opioid, delta; Receptors, Opioid, kappa

One day after intraplantar inoculation of Mycobacterium butyricum into the right hind-paw, unilaterally inflamed and control rats were implanted subcutaneously with osmotic mini-pumps delivering naloxone at 0.16 or 3.0 mg/kg/h or vehicle. As determined three days after implantation, 0.16 mg/kg/h of naloxone completely antagonized the antinociceptive action of the mu-agonist, morphine, but did not affect antinociception evoked by the kappa-agonist, U69,593. In contrast, at 3.0 mg/kg/h, naloxone blocked both morphine- and U69,593-induced antinociception. Thus, 0.16 mg/kg ("low dose") and 3.0 mg/kg ("high dose") of naloxone block mu, or mu- plus kappa-opioid receptors, respectively. Pumps were removed one week following their implantation. Inoculation was associated with a sustained hyperalgesia of the inflamed paw to noxious pressure, and elevation in resting core temperature, a loss of body weight, hypophagia, hypodipsia and a reduction in mobility. These parameters were differentially modified by the high as compared to the low dose of naloxone. Two days following implantation of pumps delivering the high dose of naloxone, the hyperalgesia of the inflamed paw was potentiated: by six days, this effect was lost. Further, one day after removal of pumps yielding the high dose, the inflamed paw showed a normalization of thresholds, that is a "rebound antinociception". One day later, this effect had subsided. In distinction, at no time did the low dose of naloxone modify nociceptive thresholds. The high dose of naloxone enhanced the reduction in body weight and food intake shown by unilaterally inflamed rats whereas the low dose was ineffective. Neither dose affected the reduction in water intake or hypothermia of unilaterally inflamed animals. The high dose of naloxone reduced the mobility of unilaterally inflamed rats whereas the low dose was ineffective. Finally, by 10 days following pump removal, pathology had transferred to the contralateral paw. In rats which had received the high but not the low dose, this transfer was blocked. It is concluded that blockade of kappa-opioid receptors with a high dose of naloxone experts pronounced functional effects in unilaterally inflamed rats. In distinction, selective blockade of mu-receptors with a low dose is ineffective. The changes seen include not only an enhancement of the hyperalgesia of the inflamed tissue, but also an exacerbation of variables (body weight, food intake and motility) which reflect pain states.

Topics: Analgesics; Animals; Behavior, Animal; Benzeneacetamides; Body Temperature; Body Weight; Inflammation; Male; Morphine; Naloxone; Nociceptors; Pain; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu

This study examined the possible peripheral activity of eel calcitonin in the modulation of the response to noxious pressure on inflamed paws in rats (Randall and Selitto test). The intraplantar injection of eel calcitonin (20-200 ng/rat) but not the subcutaneous administration (200 ng and 2 micrograms/rat, s.c.), was able to significantly inhibit hyperalgesia induced by intraplantar injection of carrageenin. The development of oedema on the other hand was not inhibited. The intraplantar administration of eel calcitonin (200 ng/rat) in a non-inflamed paw did not modify paw pressure thresholds. Eel calcitonin (200 ng/rat, intraplantar, i.pl.) was also able to elicit an antinociceptive effect on formalin-induced hyperalgesia, both when the peptide was injected before or after (60 min) formalin. This effect, at difference with morphine (80 micrograms/rat, i.pl.), was not blocked by naloxone (10 micrograms/rat, i.pl.). These results demonstrate the local antinociceptive effect of eel calcitonin in inflammatory pain and might indicate a new way of using calcitonin in the control of pain.

Topics: Analgesics; Animals; Calcitonin; Carrageenan; Edema; Foot; Inflammation; Injections; Male; Naloxone; Rats; Rats, Inbred Strains

In a rat model of localized hyperalgesic inflammation induced by intraplantar injection of carrageenin, the effect of a relatively high dose of naloxone (1 mg/kg i.v.) was investigated using the measure of the vocalization threshold as a nociceptive test, on both the inflamed and non-inflamed paws. The effects of the drug were determined at two different periods after the intraplantar injection of carrageenin, in the same group of rats. We showed that 4 h after carrageenin (a few hours after the onset of the inflammatory process), naloxone induced a significant further decrease in the vocalization threshold induced by pressure on either paw, suggesting that naloxone had reduced a tonically active inhibitory system involving endogenous opioid peptides. Twenty-four hours after carrageenin, a consistent hyperalgesic effect of naloxone was observable only in rats which had recovered from their carrageenin-induced hyperalgesia. A significant negative correlation between the behavioral effect of naloxone and the degree of hyperalgesia determined for each animal was observed. This suggests that the tonic inhibition exerted by the endogenous opioids was particularly effective in rats which recovered from their initial hyperalgesia. By contrast, these opioid controls could have been weaker in those rats which remained hyperalgesic.

Topics: Animals; Carrageenan; Endorphins; Inflammation; Male; Naloxone; Nociceptors; Pain; Rats; Rats, Inbred Strains; Sensory Thresholds; Time Factors; Vocalization, Animal

The objective of the present study was to characterize stimulation-produced antinociception from the periaqueductal gray matter (PAG) in rats with unilateral hindlimb inflammation induced by an intraplantar injection of Freund's complete adjuvant. Rats were chronically implanted with a bipolar stimulating electrode in the PAG. Nociception was assessed using a paw pressure test. Prior to inflammation, PAG stimulation significantly increased paw pressure threshold in both paws compared to non-stimulated controls. Following inflammation, PAG stimulation inhibited nociception in the inflamed, but not the non-inflamed paw. Systemic administration of naloxone blocked antinociception from ventral, but not dorsal PAG stimulation sites. Intrathecal, but not subcutaneous, administration of quaternary naltrexone completely blocked stimulation-produced antinociception from the PAG. The known increased levels of endogenous opioids occurring in the spinal cord ipsilateral to the site of inflammation suggest a mechanism for the selective antinociceptive effect of ventral PAG stimulation seen for the inflamed paw.

Topics: Analysis of Variance; Animals; Electric Stimulation; Freund's Adjuvant; Hindlimb; Inflammation; Male; Mycobacterium; Naloxone; Naltrexone; Pain; Periaqueductal Gray; Rats; Rats, Inbred Strains; Spinal Cord

Using a blister model of inflammation in the rat hind footpad, the present study was undertaken to examine possible peripheral effects of specific mu (DAGO) and delta (DSLET) opioid receptor agonists on an inflammatory response induced by substance P, the putative mediator of neurogenic inflammation. When perfused over the blister base, SP induced both plasma extravasation and vasodilatation responses. These responses were significantly inhibited in the presence of either opioid receptor agonist in a naloxone reversible manner. DSLET inhibited SP responses in a dose dependent manner and was 100 times more potent than DAGO. The role of primary afferent sensory nerve terminals in these modulatory effects was investigated in rats pretreated as neonates with capsaicin. The ability of DAGO and DSLET to inhibit the inflammatory response in these rats was significantly less than that in controls. The data raises the possibility that the inhibitory effect of the opioid receptor agonists on the inflammatory response might reflect a role for opioids in modulating tachyphylaxis to SP.

Topics: Administration, Topical; Amino Acid Sequence; Animals; Blister; Capillary Permeability; Capsaicin; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Inflammation; Male; Molecular Sequence Data; Naloxone; Oligopeptides; Perfusion; Peripheral Nerves; Rats; Skin; Substance P; Vasodilation

Topics: Animals; Endorphins; Enkephalin, Leucine; Inflammation; Naloxone; Nociceptors; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Somatostatin

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

This study investigated the involvement of endogenous opioid peptides in mediating cold water swim (CWS) stress-induced antinociception (SIA) in rats with unilateral hind paw inflammation induced by Freund's complete adjuvant (FCA). Following 0.5, 1 and 2 min of CWS, there was a duration-dependent elevation of paw pressure threshold (PPT) in both inflamed and non-inflamed paws which was maximal immediately after CWS and returned to control values within 15 min. The antinociception elicited in the inflamed paw was significantly greater than that elicited in the non-inflamed paw. The antinociception induced by a 1 min CWS was dose dependently antagonized by tertiary naloxone (0.125-1 mg/kg s.c.) and completely reversed by tertiary naltrexone (0.5 mg/kg). Quaternary naltrexone (5-40 mg/kg s.c.) was similarly effective in reversing the elevation of inflamed PPT induced by a 1 min CWS stress. In contrast, similar doses of quaternary naltrexone had no effect against centrally mediated morphine antinociception in non-inoculated rats. Adrenalectomy was without effect on the pattern of SIA seen in FCA-treated rats. Surgical hypophysectomy completely abolished the differential antinociception induced by 0.5 and 1 min durations of CWS but had little effect on that following 2 min of CWS stress. Inhibition of hypophysial corticotrophic cell secretion with dexamethasone (300 micrograms/kg) injected s.c. 120 min prior to CWS completely abolished the differential SIA at all durations of CWS tested. beta-Endorphin 12.5 micrograms/kg administered i.v. in non-stressed rats also caused a greater elevation of PPT in inflamed than in non-inflamed paws. This effect was not reversed by concomitant i.v. administration of (-) tertiary naloxone 5 mg/kg or quaternary naltrexone 20 mg/kg.

Topics: Adrenalectomy; Analysis of Variance; Animals; Cold Temperature; Dose-Response Relationship, Drug; Endorphins; Foot; Hypophysectomy; Inflammation; Male; Naloxone; Naltrexone; Nociceptors; Pituitary-Adrenal System; Rats; Rats, Inbred Strains; Receptors, Opioid; Stress, Physiological; Swimming

Rats were subcutaneously implanted with minipumps delivering naloxone (3.0 mg/kg/h) or distilled water. One day later, they were inoculated in the plantar surface of the right hind paw with Mycobacterium butyricum. Naloxone blocked the antinociceptive action of the mu-agonist, morphine, and the kappa-agonist, U69,593, and led to a sustained reduction in food and water intake. Thus, opioid receptors were effectively occupied. Rats receiving naloxone showed significantly less hindlimb swelling on days 2 and 3 post-implantation. On day 2 but not 5 post-implantation, the hyperalgesic response of the inoculated paw to noxious pressure was potentiated in rats receiving naloxone. At six days post-implantation, pumps were removed. Ten days after removal, the inflammation and hyperalgesia had spread to the contralateral hindlimb and to the forelimbs. The degree of this transfer was less pronounced in rats which had been receiving naloxone. These data suggest that opioids, via kappa-receptors, play a role in the control of nociception under inflammatory pain: however, this role may not be indispensable. Further, the processes governing the development and spread of inflammatory disease may be modulated by opioid mechanisms.

Topics: Analgesics; Animals; Benzeneacetamides; Drinking Behavior; Feeding Behavior; Inflammation; Male; Morphine; Naloxone; Pain; Pain Measurement; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu

This study utilized inhibitors of the enzymatic degradation of enkephalins to investigate the possibility that this class of opioid peptides contributes to the stress-induced antinociception seen in inflamed peripheral tissues of rats with Freund's complete adjuvant-initiated unilateral hind paw inflammation. Following a 1-min cold water swim stress, rats previously injected in both hind paws with vehicle showed a transient elevation of paw pressure threshold, which was much greater in inflamed than in noninflamed paws and returned to control levels within 15 min. This preferential antinociception was significantly pronounced and prolonged in rats previously injected bilaterally with a cocktail of the enkephalinase inhibitors thiorphan (0.2 mg intraplantar) and bestatin (0.2 mg intraplantar). The enhancement of stress-induced antinociception by thiorphan/bestatin was dose-dependently antagonized by tertiary naloxone (0.125-2 mg kg-1 s.c.). Evidence for a peripheral site of action of enkephalin-like peptides in this model was provided by the antagonism of the actions of thiorphan/bestatin by quaternary naltrexone (10-20 mg kg-1 s.c.). Systemic administration of the orally active enkephalinase inhibitor SCH 34826 (5-40 mg kg-1 i.p.) was also able to dose-dependently potentiate the preferential stress-induced antinociception in a naloxone (1 mg kg-1 s.c.) reversible manner.

Topics: Analgesia; Animals; Dioxolanes; Dipeptides; Enkephalins; Inflammation; Leucine; Male; Naloxone; Naltrexone; Neprilysin; Rats; Rats, Inbred Strains; Receptors, Opioid; Stress, Physiological; Swimming; Thiorphan

This study examined a possible peripheral site of action of opioids in the modulation of the response to noxious pressure on inflamed tissue. Rats developed a unilateral localized inflammation upon injection of Freund's complete adjuvant into one hindpaw. 4-6 days after inoculation, intraplantar administration of mu, delta and kappa selective agonists [D-Ala2,N-methyl-Phe4,Gly-ol5]-en-kephalin (1 micrograms), [D-Pen2,5]-enkephalin (40 micrograms) and U-50, 488H (50 micrograms) produced marked antinociceptive effects in inflamed but not noninflamed paws. Equivalent doses applied systemically (s.c. and i.v.) were without effect. Dose dependency and stereospecificity of these effects were demonstrated using (-)- and (+)-morphine and (-)- and (+)-tifluadom. Furthermore, by use of (-)- and (+)-naloxone, dose-dependent and stereospecific antagonism was shown. Lastly, reversal of effects of [D-Ala2,N-methyl-Phe4,Gly-Ol5]-enkephalin, [D-Pen2,5]-enkephalin and U-50,488H by mu, delta and kappa selective antagonists D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, ICI 174,864 and nor-BNI, respectively, indicated that these agents interact with discriminable populations of receptors. These observations suggest that several selective opioid agonists can modulate responses to noxious pressure through a peripheral opioid receptor-specific site of action in inflammation and that these receptors possess distinguishable pharmacological characteristics resembling those of mu, delta and kappa receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesia; Animals; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Inflammation; Male; Naloxone; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Sensory Thresholds

Rats received an injection of Freund's complete adjuvant into the right hindpaw and developed localized inflammation. Four to six days after inoculation, the antinociceptive effect of both the mu-agonist, morphine, and the kappa-agonist U-50,488H, administered subcutaneously, was markedly enhanced in the inflamed paws. This effect was dose dependently antagonized by low dose of intraplantar, but not subcutaneous or intravenous, (-)-naloxone. (+)-Naloxone was inactive. These data indicate that the enhanced antinociceptive effects of both agonists in inflammation are mediated by a peripheral, opioid receptor-specific mechanism.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Freund's Adjuvant; Inflammation; Male; Morphine; Naloxone; Pyrrolidines; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu; Stereoisomerism

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

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

Topics: Analgesia; Animals; Arthritis; Arthritis, Experimental; Carrageenan; Edema; Inflammation; Naloxone; Rats

The plasma extravasation response to dynorphin-(1-13) was investigated using the Evans blue dye leakage technique. Dynorphin induced plasma extravasation in rat and guinea-pig abdominal skin with a similar potency to substance P. In rat skin dynorphin, unlike substance P, produced its action entirely by release of histamine and 5-hydroxytryptamine since the response was abolished by pretreatment of rats with mepyramine and methysergide. Pretreatment of rats with capsaicin or the tachykinin antagonist, spantide, reduced but did not abolish the response to dynorphin, indicating that its action was not mediated primarily by a neurogenic mechanism. Since the response was not significantly reduced by naloxone it was concluded that the plasma extravasation response to dynorphin was mediated by receptors other than mu opiate receptors. Thus dynorphin, if released from sensory nerves, might play a role in neurogenic inflammation.

Topics: Analgesics; Animals; Dynorphins; Female; Inflammation; Male; Mast Cells; Naloxone; Peptide Fragments; Plasma; Rats; Rats, Inbred Strains; Skin; Substance P

The present paper shows that a mixture of gangliosides (GA = GM1 + GD1a + GD1b + GT1b) is provided with a specific and powerful antinociceptive activity. The GA is active in reducing acetic acid and phenylquinone writhings, the acetic acid capillary-induced permeability and some acute inflammatory reactions. These actions seem to be mostly due to an anti-exudative property of the compounds which shows up right after the administration. The mixture of four gangliosides given in the proportion naturally occurring in the nervous system is more active than each single component in increasing the pain threshold, presenting therefore a synergistic effect. It is suggested that gangliosides can reduce the exudative phenomena interfering with the membrane permeability of the nerve-endings breaking interfering with the membrane permeability of the nerve-endings breaking the vicious circle of the neurogenic mechanisms of plasma extravasation.

Topics: Acetates; Acetic Acid; Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Benzoquinones; Carrageenan; Gangliosides; Inflammation; Male; Mice; Naloxone; Quinones; Rats; Rats, Inbred Strains; Reaction Time; Receptors, Opioid; Reserpine; Time Factors

Rats exposed to combined cold and restraint exhibited reduced paw oedema following an injection of carrageenin. Under the same experimental conditions, the local inflammation became fully evident when animals were pretreated with naloxone, 5 mg/kg, s.c. The same dose of the narcotic antagonist also increased the intensity of gastric damage in restrained, cold-exposed rats. On the contrary, gastric ulcerations were practically inexistent in stressed rats treated with 10 mg/kg s.c. of morphine. It is suggested that the opioid peptidergic system is involved in the body's reactivity to stressful stimuli.

Topics: Animals; Endorphins; Inflammation; Male; Morphine; Naloxone; Rats; Stomach Ulcer; Stress, Physiological

In a study of nonsteroidal antiinflammatory and analgesic agents, a series of 1,3-dihydro-3-(substituted phenyl)imidazo[4,5-b]pyridin-2-ones-and 3-(substituted phenyl)triazolo[4,5-b]pyridines was prepared. Many of the imidazolones were alkylated on the free nitrogen. In a modified Randall-Selitto analgesic assay, the pain thresholds of both the inflamed and normal foot were elevated. This is not commonly observed with nonsteroidal antiinflammatory agents. The most active compounds were 1,3-dihydro-3[3,4-(methylenedioxy)phenyl]imidazo[4,5-b]pyridin-2-one (I-15) and its N-allyl (I-21) and N-isopropyl (I-121) derivatives. In the triazole series the 3-(2-fluoro- and 2,4-difluorophenyl)triazolo[4,5-b]pyridines (T-1 and T-8) were the best. The imidazole compounds were somewhat superior in analgesic activity to codeine and d-propoxyphene without showing any narcotic characteristics. Some of the compounds also possessed activity against carrageenan-induced foot edema in the rat, so these compounds represent a new class of nonnarcotic analgesic antiinflammatories, capable of producing a greater degree of analgesia than that obtainable with other nonsteroidal antiinflammatory agents.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Female; Humans; Inflammation; Mice; Naloxone; Pyridines; Pyridones; Rats; Reaction Time; Structure-Activity Relationship; Substance Withdrawal Syndrome