norbinaltorphimine and Disease-Models--Animal

It has been shown that kappa opioid receptor (KOR) antagonists, such as nor-binaltorphimine (nor-BNI), have antinociceptive effects in some pain models that affect the trigeminal system. Also, its anxiolytic-like effect has been extensively demonstrated in the literature. The present study aimed to investigate the systemic, local, and central effect of nor-BNI on trigeminal neuropathic pain using the infraorbital nerve constriction model (CCI-ION), as well as to evaluate its effect on anxiety-like behavior associated with this model. Animals received nor-BNI systemically; in the trigeminal ganglion (TG); in the subarachnoid space to target the spinal trigeminal nucleus caudalis (Sp5C) or in the central amygdala (CeA) 14 days after CCI-ION surgery. Systemic administration of nor-BNI caused a significant reduction of facial mechanical hyperalgesia and promoted an anxiolytic-like effect, which was detected in the elevated plus-maze and the light-dark transition tests. When administered in the TG or CeA, the KOR antagonist was able to reduce facial mechanical hyperalgesia induced by CCI-ION, but without changing the anxiety-like behavior. Moreover, no change was observed on nociception and anxiety-like behavior after nor-BNI injection into the Sp5C. The present study demonstrated antinociceptive and anxiolytic-like effects of nor-BNI in a model of trigeminal neuropathic pain. The antinociceptive effect seems to be dissociated from the anxiolytic-like effect, at both the sites involved and at the dose need to achieve the effect. In conclusion, the kappa opioid system may represent a promising target to be explored for the control of trigeminal pain and associated anxiety. However, further studies are necessary to better elucidate its functioning and modulatory role in chronic trigeminal pain states.

Topics: Animals; Anxiety; Central Amygdaloid Nucleus; Chronic Pain; Disease Models, Animal; Hyperalgesia; Male; Naltrexone; Nociception; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Trigeminal Neuralgia

Antipruritic effects of kappa opioid receptor (KOR) agonists have been shown in rodent models of acute and chronic scratching (itchlike behavior). Three KOR agonists, nalfurafine, difelikefalin, and nalbuphine, are in clinical studies for antipruritic effects in chronic itch of systemic and skin diseases. Nalfurafine (in Japan) and difelikefalin (in the USA) were approved to be used in the treatment of chronic itch in hemodialysis patients. The FDA-approved nalbuphine has been used in clinic for over 40 years, and it is the only narcotic agonist that is not scheduled. We aimed to study (a) antiscratch activity of nalbuphine against TAT-HIV-1 protein (controls HIV transcription)-, deoxycholic acid (DCA, bile acid)-, and chloroquine (CQ)-induced scratching in a mouse model of acute itch; and (b) whether the effect of nalbuphine is produced via KORs. First, dose-responses were developed for pruritogens. Mice were pretreated with nalbuphine (0.3-10 mg/kg) and then a submaximal dose of pruritogens were administered and the number of scratching bouts was counted. To study if the antiscratch effect of nalbuphine is produced via KOR, we used KOR knock out mice and pharmacologic inhibition of KORs using nor-binaltorphimine, a KOR antagonist. For this aim, we used CQ as a pruritogen. We found that: (a) TAT-HIV-1 protein elicits scratching in a dose-dependent manner; (b) nalbuphine inhibits scratching induced by TAT-HIV-1, DCA, and CQ dose-dependently; and (c) nalbuphine inhibits scratching induced by CQ through KORs. In conclusion, nalbuphine inhibits scratching elicited by multiple pruritogens.

Topics: Animals; Antipruritics; Behavior, Animal; Chloroquine; Deoxycholic Acid; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Mice; Nalbuphine; Naltrexone; Narcotic Antagonists; Pruritus; Receptors, Opioid, kappa; tat Gene Products, Human Immunodeficiency Virus

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

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

Patients with frontotemporal dementia (FTD) resulting from granulin (GRN) haploinsufficiency have reduced levels of progranulin and exhibit dysregulation in inflammatory and lysosomal networks. Microglia produce high levels of progranulin, and reduction of progranulin in microglia alone is sufficient to recapitulate inflammation, lysosomal dysfunction, and hyperproliferation in a cell-autonomous manner. Therefore, targeting microglial dysfunction caused by progranulin insufficiency represents a potential therapeutic strategy to manage neurodegeneration in FTD. Limitations of current progranulin-enhancing strategies necessitate the discovery of new targets. To identify compounds that can reverse microglial defects in Grn-deficient mouse microglia, we performed a compound screen coupled with high throughput sequencing to assess key transcriptional changes in inflammatory and lysosomal pathways. Positive hits from this initial screen were then further narrowed down based on their ability to rescue cathepsin activity, a critical biochemical readout of lysosomal capacity. The screen identified nor-binaltorphimine dihydrochloride (nor-BNI) and dibutyryl-cAMP, sodium salt (DB-cAMP) as two phenotypic modulators of progranulin deficiency. In addition, nor-BNI and DB-cAMP also rescued cell cycle abnormalities in progranulin-deficient cells. These data highlight the potential of a transcription-based platform for drug screening, and advance two novel lead compounds for FTD.

Topics: Animals; Bucladesine; Cell Cycle; Cells, Cultured; Cysteine Proteases; Disease Models, Animal; Frontotemporal Dementia; Gene Expression Profiling; Gene Expression Regulation; Gene Knockout Techniques; High-Throughput Nucleotide Sequencing; Humans; Lysosomes; Mice; Microglia; Models, Biological; Naltrexone; Progranulins; Sequence Analysis, RNA; Small Molecule Libraries

Bone resorption associated to chronic diseases, such as arthritis and periodontitis, results from exacerbated immuno-inflammatory host response that leads to tissue breakdown. The significance of opioid pathways as endogenous modulators of inflammatory events has already been described. Thus, the aim of this work is to determine whether some of the main three opioid receptors are endogenously activated to prevent bone loss during experimentally-induced alveolar bone resorption.. This study used an experimental model of alveolar bone resorption induced by ligature in rats. A silk thread was placed around the 2nd maxillary molar of male Wistar rats. In the 3rd, 4th and 5th day after ligation the rats received a local injection of different concentrations of opioid antagonists Cyprodime, Naltrindole, or Nor-binaltorphimine, which specifically block mü, delta and kappa opioid receptors, respectively. In the 7th experimental day, rats were euthanized and their maxillae collected for evaluation of alveolar bone and fiber attachment loss, morphometric counting of osteoclasts and osteoblasts, as well as the levels of cytokines IL-1β, IFN-γ, and IL-6 by ELISA.. Selective antagonism of kappa opioid receptors, but not mü and delta, exacerbated alveolar bone resorption induced by ligature in rats. The increased bone loss associated with higher number of osteoclasts surrounding alveolar bone, although osteoblasts' counting remained unchanged. The concentrations of IL-1β and IL-6 in periodontal tissues were also significantly higher in the rats treated with the kappa antagonist.. Inhibiting kappa opioid receptors exacerbates alveolar bone resorption.

Topics: Alveolar Bone Loss; Animals; Bone Resorption; Cytokines; Disease Models, Animal; Male; Morphinans; Naltrexone; Narcotic Antagonists; Osteoblasts; Osteoclasts; Periodontitis; Rats; Rats, Wistar; Receptors, Opioid

There is a major clinical need for new therapies for the treatment of chronic itch. Many of the molecular components involved in itch neurotransmission are known, including the neuropeptide NPPB, a transmitter required for normal itch responses to multiple pruritogens in mice. Here, we investigated the potential for a novel strategy for the treatment of itch that involves the inhibition of the NPPB receptor NPR1 (natriuretic peptide receptor 1). Because there are no available effective human NPR1 (hNPR1) antagonists, we performed a high-throughput cell-based screen and identified 15 small-molecule hNPR1 inhibitors. Using in vitro assays, we demonstrated that these compounds specifically inhibit hNPR1 and murine NPR1 (mNPR1). In vivo, NPR1 antagonism attenuated behavioral responses to both acute itch- and chronic itch-challenged mice. Together, our results suggest that inhibiting NPR1 might be an effective strategy for treating acute and chronic itch.

Topics: Animals; Behavior, Animal; Cell-Free System; Dermatitis, Contact; Disease Models, Animal; Ganglia, Spinal; Humans; Mice, Inbred C57BL; Mice, Knockout; Neurons; Pruritus; Receptors, Atrial Natriuretic Factor; Reproducibility of Results; Signal Transduction; Small Molecule Libraries

Although previous research has demonstrated a role for kappa opioid receptor-mediated signaling in escalated alcohol consumption associated with dependence and stress exposure, involvement of the dynorphin/kappa opioid receptor (DYN/KOR) system in binge-like drinking has not been fully explored. Here we used pharmacological and chemogenetic approaches to examine the influence of DYN/KOR signaling on alcohol consumption in the drinking-in-the-dark (DID) model of binge-like drinking. Systemic administration of the KOR agonist U50,488 increased binge-like drinking (Experiment 1) while, conversely, systemic administration of the KOR antagonist nor-BNI reduced drinking in the DID model (Experiment 2). These effects of systemic KOR manipulation were selective for alcohol as neither drug influenced consumption of sucrose in the DID paradigm (Experiment 3). In Experiment 4, administration of the long-acting KOR antagonist nor-BNI into the central nucleus of the amygdala (CeA) decreased alcohol intake. Next, targeted "silencing" of DYN+ neurons in the CeA was accomplished using a chemogenetic strategy. Cre-dependent viral expression in DYN+ neurons was confirmed in CeA of Pdyn-IRES-Cre mice and functionality of an inhibitory (hM4Di) DREADD was validated (Experiment 5). Activating the inhibitory DREADD by CNO injection reduced binge-like alcohol drinking, but CNO injection did not alter alcohol intake in mice that were treated with control virus (Experiment 6). Collectively, these results demonstrate that DYN/KOR signaling in the CeA contributes to excessive alcohol consumption in a binge-drinking model.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Behavior, Animal; Binge Drinking; Central Amygdaloid Nucleus; Disease Models, Animal; Dynorphins; Genetic Techniques; Male; Mice; Mice, Inbred C57BL; Naltrexone; Receptors, Opioid, kappa

Chronic pain is associated with neuroplastic changes in the amygdala that may promote hyper-responsiveness to mechanical and thermal stimuli (allodynia and hyperalgesia) and/or enhance emotional and affective consequences of pain. Stress promotes dynorphin-mediated signaling at the kappa opioid receptor (KOR) in the amygdala and mechanical hypersensitivity in rodent models of functional pain. Here, we tested the hypothesis that KOR circuits in the central nucleus of the amygdala (CeA) undergo neuroplasticity in chronic neuropathic pain resulting in increased sensory and affective pain responses. After spinal nerve ligation (SNL) injury in rats, pretreatment with a long-acting KOR antagonist, nor-binaltorphimine (nor-BNI), subcutaneously or through microinjection into the right CeA, prevented conditioned place preference (CPP) to intravenous gabapentin, suggesting that nor-BNI eliminated the aversiveness of ongoing pain. By contrast, systemic or intra-CeA administration of nor-BNI had no effect on tactile allodynia in SNL animals. Using whole-cell patch-clamp electrophysiology, we found that nor-BNI decreased synaptically evoked spiking of CeA neurons in brain slices from SNL but not sham rats. This effect was mediated through increased inhibitory postsynaptic currents, suggesting tonic disinhibition of CeA output neurons due to increased KOR activity as a possible mechanism promoting ongoing aversive aspects of neuropathic pain. Interestingly, this mechanism is not involved in SNL-induced mechanical allodynia. Kappa opioid receptor antagonists may therefore represent novel therapies for neuropathic pain by targeting aversive aspects of ongoing pain while preserving protective functions of acute pain.

Topics: Animals; Central Amygdaloid Nucleus; Chronic Pain; Disease Models, Animal; Hyperalgesia; In Vitro Techniques; Male; Membrane Potentials; Naltrexone; Narcotic Antagonists; Neural Inhibition; Neuralgia; Neurons; Pain Threshold; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Signal Transduction; Synaptic Transmission

The dynorphin/κ-opioid receptor (KOR) system has been previously implicated in the regulation of cognition, but the neural circuitry and molecular mechanisms underlying KOR-mediated cognitive disruption are unknown. Here, we used an operational test of cognition involving timing and behavioral inhibition and found that systemic KOR activation impairs performance of male and female C57BL/6 mice in the differential reinforcement of low response rate (DRL) task. Systemic KOR antagonism also blocked stress-induced disruptions of DRL performance. KOR activation increased 'bursts' of incorrect responses in the DRL task and increased marble burying, suggesting that the observed disruptions in DRL performance may be attributed to KOR-induced increases in compulsive behavior. Local inactivation of KOR by injection of the long-acting antagonist nor-BNI in the ventral tegmental area (VTA), but not the infralimbic prefrontal cortex (PFC) or dorsal raphe nucleus (DRN), prevented disruption of DRL performance caused by systemic KOR activation. Cre-dependent genetic excision of KOR from dopaminergic, but not serotonergic neurons, also blocked KOR-mediated disruption of DRL performance. At the molecular level, we found that these disruptive effects did not require arrestin-dependent signaling, because neither global deletion of G-protein receptor kinase 3 (GRK3) nor cell-specific deletion of GRK3/arrestin-dependent p38α MAPK from dopamine neurons blocked KOR-mediated DRL disruptions. We then showed that nalfurafine, a clinically available G-biased KOR agonist, could also produce DRL disruptions. Together, these studies demonstrate that KOR activation in VTA dopamine neurons disrupts behavioral inhibition in a GRK3/arrestin-independent manner and suggests that KOR antagonists could be beneficial for decreasing stress-induced compulsive behaviors.

Topics: Animals; Behavior, Animal; Compulsive Behavior; Disease Models, Animal; Dopaminergic Neurons; Dorsal Raphe Nucleus; Female; Inhibition, Psychological; Male; Mice; Mice, Inbred C57BL; Morphinans; Naltrexone; Narcotic Antagonists; Prefrontal Cortex; Receptors, Opioid, kappa; Reinforcement, Psychology; Spiro Compounds; Stress, Psychological; Ventral Tegmental Area

Studies conducted since 1969 have shown that the release of serotonin (5-HT) in the dorsal horn of the spinal cord contributes to opioid analgesia. In the present study, the participation of the opioidergic system in antinociceptive effect serotonin at the peripheral level was examined.. The paw pressure test was used with mice (Swiss, males from 35 g) which had increased pain sensitivity by intraplantar injection of PGE. The selective antagonists for mu, delta and kappa opioid receptors, clocinnamox clocinnamox (40 μg), naltrindole (60 μg) and nor-binaltorfimina (200 μg), respectively, inhibited the antinociceptive effect induced by serotonin. Additionally, bestatin (400 μg), an inhibitor of enkephalinases that degrade peptides opioids, enhanced the antinociceptive effect induced by serotonin (low dose of 62.5 ng).. These results suggest that serotonin possibly induce peripheral antinociception through the release of endogenous opioid peptides, possible from immune cells or keratinocytes.

Topics: Analgesics; Animals; Cinnamates; Dinoprostone; Disease Models, Animal; Male; Mice; Morphine Derivatives; Naltrexone; Narcotic Antagonists; Opioid Peptides; Pain; Receptors, Opioid; Serotonin

This study aimed to investigate the protective effect of salvinorin A on the cerebral pial artery after forebrain ischemia and explore related mechanisms. Thirty Sprague-Dawley rats received forebrain ischemia for 10 min. The dilation responses of the cerebral pial artery to hypercapnia and hypotension were assessed in rats before and 1 h after ischemia. The ischemia reperfusion (IR) control group received DMSO (1 µL/kg) immediately after ischemia. Two different doses of salvinorin A (10 and 20 µg/kg) were administered following the onset of reperfusion. The 5th, 6th, and 7th groups received salvinorin A (20 µg/kg) and LY294002 (10 µM), L-NAME (10 μM), or norbinaltorphimine (norBIN, 1 μM) after ischemia. The levels of cGMP in the cerebrospinal fluid (CSF) were also measured. The phosphorylation of AKT (p-AKT) was measured in the cerebral cortex by western blot at 24 h post-ischemia. Cell necrosis and apoptosis were examined by hematoxylin-eosin staining (HE) and TUNEL staining, respectively. The motor function of the rats was evaluated at 1, 2, and 5 days post-ischemia. The dilation responses of the cerebral pial artery were significantly impaired after ischemia and were preserved by salvinorin A treatment. In addition, salvinorin A significantly increased the levels of cGMP and p-AKT, suppressed cell necrosis and apoptosis of the cerebral cortex and improved the motor function of the rats. These effects were abolished by LY294002, L-NAME, and norBIN. Salvinorin A preserved cerebral pial artery autoregulation in response to hypercapnia and hypotension via the PI3K/AKT/cGMP pathway.

Topics: Animals; Brain Ischemia; Cerebral Arteries; Chromones; Cyclic GMP; Disease Models, Animal; Diterpenes, Clerodane; Male; Morpholines; Naltrexone; NG-Nitroarginine Methyl Ester; Phosphatidylinositol 3-Kinases; Pia Mater; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Signal Transduction

Adolescents may be more sensitive to stress-induced alcohol drinking than adults, which would explain the higher prevalence of alcohol abuse and dependence in late adolescence than in adulthood. The present study analyzed the impact of restraint stress on the initiation of alcohol intake across 2 weeks of intermittent, two-bottle choice intake in male and female adolescent rats and adult female rats. Restraint stress significantly increased alcohol intake and preference in female adolescent rats but decreased alcohol intake and preference in male adolescent and female adult rats. The effects of restraint stress on alcohol intake were mitigated in adolescent females following administration of the κ opioid receptor antagonist norbinaltorphimine. Adolescent but not adult female rats that were subjected to restraint stress spent more time on the open arms of the elevated plus maze. Female adolescents exposed to stress also exhibited greater risk-taking behaviors in a concentric square field test compared with non-stressed controls. These results indicate age- and sex-related differences in the sensitivity to alcohol-stress interactions that may facilitate the initiation of alcohol use in female adolescents. The facilitatory effect of stress on alcohol intake was related to greater exploratory and risk-taking behaviors in young females after stress exposure.

Topics: Aging; Alcohol Drinking; Animals; Central Nervous System Depressants; Choice Behavior; Disease Models, Animal; Ethanol; Exploratory Behavior; Female; Male; Motor Activity; Naltrexone; Narcotic Antagonists; Rats, Wistar; Receptors, Opioid, kappa; Restraint, Physical; Risk-Taking; Sex Characteristics; Stress, Psychological

In a previous study, we showed that κ-opioid receptor stimulation with the selective agonist U50,488H ameliorated hypoxic pulmonary hypertension (HPH). However, the roles that pulmonary arterial smooth muscle cell (PASMC) proliferation, apoptosis, and autophagy play in κ-opioid receptor-mediated protection against HPH are still unknown. The goal of the present study was to investigate the role of autophagy in U50,488H-induced HPH protection and the underlying mechanisms.. Rats were exposed to 10% oxygen for three weeks to induce HPH. After hypoxia, the mean pulmonary arterial pressure (mPAP) and the right ventricular pressure (RVP) were measured. Cell viability was monitored using the Cell Counting Kit-8 (CCK-8) assay. Cell apoptosis was detected by flow cytometry and Western blot. Autophagy was assessed by means of the mRFP-GFP-LC3 adenovirus transfection assay and by Western blot.. Inhibition of autophagy by the administration of chloroquine prevented the development of HPH in the rat model, as evidenced by significantly reduced mPAP and RVP, as well as decreased autophagy. U50,488H mimicked the effects of chloroquine, and the effects of U50,488H were blocked by nor-BNI, a selective κ-opioid receptor antagonist. In vitro experiments showed that the inhibition of autophagy by chloroquine was associated with decreased proliferation and increased apoptosis of PASMCs. Under hypoxia, U50,488H also significantly inhibited autophagy, reduced proliferation and increased apoptosis of PASMCs. These effects of U50,488H were blocked by nor-BNI. Moreover, exposure to hypoxic conditions significantly increased AMPK phosphorylation and reduced mTOR phosphorylation, and these effects were abrogated by U50,488H. The effects of U50,488H on PASMC autophagy were inhibited by AICAR, a selective AMPK agonist, or by rapamycin, a selective mTOR inhibitor.. Our data provide evidence for the first time that κ-opioid receptor stimulation protects against HPH by inhibiting PASMCs autophagy via the AMPK-mTOR pathway.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; AMP-Activated Protein Kinases; Animals; Antihypertensive Agents; Apoptosis; Autophagy; Blood Pressure; Cell Proliferation; Cells, Cultured; Chloroquine; Disease Models, Animal; Hypertension, Pulmonary; Male; Myocytes, Smooth Muscle; Naltrexone; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Signal Transduction; TOR Serine-Threonine Kinases

Addiction is a chronic brain disorder that progressively invades all aspects of personal life. Accordingly, addiction to opiates severely impairs interpersonal relationships, and the resulting social isolation strongly contributes to the severity and chronicity of the disease. Uncovering new therapeutic strategies that address this aspect of addiction is therefore of great clinical relevance. We recently established a mouse model of heroin addiction in which, following chronic heroin exposure, 'abstinent' mice progressively develop a strong and long-lasting social avoidance phenotype. Here, we explored and compared the efficacy of two pharmacological interventions in this mouse model. Because clinical studies indicate some efficacy of antidepressants on emotional dysfunction associated with addiction, we first used a chronic 4-week treatment with the serotonergic antidepressant fluoxetine, as a reference. In addition, considering prodepressant effects recently associated with kappa opioid receptor signaling, we also investigated the kappa opioid receptor antagonist norbinaltorphimine (norBNI). Finally, we assessed whether fluoxetine and norBNI could reverse abstinence-induced social avoidance after it has established. Altogether, our results show that two interspaced norBNI administrations are sufficient both to prevent and to reverse social impairment in heroin abstinent animals. Therefore, kappa opioid receptor antagonism may represent a useful approach to alleviate social dysfunction in addicted individuals.

Topics: Animals; Antidepressive Agents, Second-Generation; Behavior, Animal; Disease Models, Animal; Fluoxetine; Grooming; Heroin; Heroin Dependence; Male; Mice; Mice, Inbred C57BL; Naltrexone; Narcotic Antagonists; Receptors, Opioid, kappa; Social Behavior; Time; Treatment Outcome

Opioids are frequently used for the treatment of pain following spinal cord injury (SCI). Unfortunately, we have shown that morphine administered in the acute phase of SCI results in significant, adverse secondary consequences including compromised locomotor and sensory recovery. Similarly, we showed that selective activation of the κ-opioid receptor (KOR), even at a dose 32-fold lower than morphine, is sufficient to attenuate recovery of locomotor function. In the current study, we tested whether activation of the KOR is necessary to produce morphine's adverse effects using nor-Binaltorphimine (norBNI), a selective KOR antagonist. Rats received a moderate spinal contusion (T12) and 24 h later, baseline locomotor function and nociceptive reactivity were assessed. Rats were then administered norBNI (0, 0.02, 0.08, or 0.32 μmol) followed by morphine (0 or 0.32 μmol). Nociception was reassessed 30 min after drug treatment, and recovery was evaluated for 21 days. The effects of norBNI on morphine-induced attenuation of recovery were dose dependent. At higher doses, norBNI blocked the adverse effects of morphine on locomotor recovery, but analgesia was also significantly decreased. Conversely, at low doses, analgesia was maintained, but the adverse effects on recovery persisted. A moderate dose of norBNI, however, adequately protected against morphine's adverse effects without eliminating its analgesic efficacy. This suggests that activation of the KOR system plays a significant role in the morphine-induced attenuation of recovery. Our research suggests that morphine, and other opioid analgesics, may be contraindicated for the SCI population. Blocking KOR activity may be a viable strategy for improving the safety of clinical opioid use.

Topics: Animals; Disease Models, Animal; Drug-Related Side Effects and Adverse Reactions; Male; Morphine; Motor Activity; Naltrexone; Narcotic Antagonists; Narcotics; Nociception; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Recovery of Function; Spinal Cord Injuries

Our previous studies indicated that highly selective κ opioid receptor agonists could protect the brain, indicating an important role of κ opioid receptor agonist in brain ischemia. In this study, we investigated the role and related mechanisms of κ opioid receptor agonists in brain ischemia in a middle cerebral artery occlusion mouse model.. Animal model.. Laboratory.. The middle cerebral artery occlusion model was established by 120 minutes of ischemia followed by 24-hour reperfusion in male adult mice.. Various doses of salvinorin A, a highly selective and potent κ opioid receptor agonist, were administered intranasally 10 minutes after initiation of reperfusion. Norbinaltorphimine (2.5 mg/kg, IP) as a κ opioid receptor antagonist was administered in one group before administration of salvinorin A (50μg/kg) to investigate the specific role of κ opioid receptor.. Infarct volume, κ opioid receptor expression, and Evans blue extravasation in the brain, and neurobehavioral outcome were determined. Immunohistochemistry and western blot were performed to detect the activated caspase-3, interleukin-10, and tumor necrosis factor-α levels to investigate the role of apoptosis and inflammation. κ opioid receptor expression was elevated significantly in the ischemic penumbral area compared with that in the nonischemic area. Salvinorin A reduced infarct volume and improved neurologic deficits dose-dependently. Salvinorin A at the dose of 50 μg/kg reduced Evans blue extravasation, suggesting reduced impairment of the blood-brain barrier and decreased the expression of cleaved caspase-3, interleukin-10, and tumor necrosis factor-α in the penumbral areas. All these changes were blocked or alleviated by norbinaltorphimine.. κ opioid receptors were up-regulated and played a critical role in brain ischemia and reperfusion. κ opioid receptor activation could potentially protect the brain and improve neurologic outcome via blood-brain barrier protection, apoptosis reduction, and inflammation inhibition.

Topics: Animals; Apoptosis; Blotting, Western; Brain Ischemia; Disease Models, Animal; Diterpenes, Clerodane; Male; Mice; Mice, Inbred C57BL; Naltrexone; Receptors, Opioid, kappa; Reperfusion Injury

To investigate the effects of high doses of pentazocine on antinociception induced by a high dose of morphine and the role of the kappa-opioid receptors (KORs) in these effects in mice.. Sixty-six C57BL/6J mice were pretreated with a KOR antagonist, nor-binaltorphimine (nor-BNI) (10mg·kg(-1)), or a normal saline placebo. All the mice received a subcutaneous injection of morphine (10mg·kg(-1)) 120min later and different doses of pentazocine (3, 10, 30, 56, 100mg·kg(-1)) or a normal saline placebo. A tail pressure test, hot plate test and tail flick test were performed before and at 30, 60, 90 and 120min after the injection of morphine.. The tail pressure test, hot plate test and tail flick test showed that pentazocine at doses of 10 to 100mg·kg(-1), but not at 3mg·kg(-1), had significant antagonizing effects on the antinociception induced by high-dose morphine to mechanical and thermal pain, and nor-BNI did not affect antinociception in combination with pentazocine at 10 to 100mg·kg(-1) and morphine at 10mg·kg(-1).. High-doses of pentazocine antagonize the antinociception induced by a high-dose of morphine in a dose-dependent manner, and this antagonistic effect is not associated with the activation of KORs.

Topics: Analgesics, Opioid; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Male; Mice; Mice, Inbred C57BL; Morphine; Naltrexone; Pain; Pentazocine; Receptors, Opioid, kappa

The association between morphine withdrawal and depressive-like symptoms is well documented, however, the role of dynorphin/κ opioid receptor system and the underlying neural substrates have not been fully understood. In the present study, we found that four weeks morphine abstinence after a chronic escalating morphine regimen significantly induced depressive-like behaviors in mice. Prodynorphin mRNA and protein levels were increased in the nucleus accumbens (NAc) after four weeks of morphine withdrawal. Local injection of κ opioid receptor antagonist nor-Binaltorphimine (norBNI) in the NAc significantly blocked the expression of depressive-like behaviors without influencing general locomotor activity. Thus, the present study extends previous findings by showing that prolonged morphine withdrawal-induced depressive-like behaviors are regulated by dynorphin/κ opioid receptor system, and shed light on the κ opioid receptor antagonists as potential therapeutic agents for the treatment of depressive-like behaviors induced by opiate withdrawal.

Topics: Animals; Antidepressive Agents; Depressive Disorder; Disease Models, Animal; Dose-Response Relationship, Drug; Enkephalins; Male; Mice, Inbred C57BL; Morphine; Motor Activity; Naltrexone; Narcotic Antagonists; Narcotics; Nucleus Accumbens; Protein Precursors; Receptors, Opioid, kappa; RNA, Messenger; Substance Withdrawal Syndrome

The kappa opioid receptor (KOR) is involved in mediating pruritus; agonists targeting this receptor have been used to treat chronic intractable itch. Conversely, antagonists induce an itch response at the site of injection. As a G protein-coupled receptor (GPCR), the KOR has potential for signaling via G proteins and βarrestins, however, it is not clear which of these pathways are involved in the KOR modulation of itch. In this study asked whether the actions of KOR in pruritus involve βarrestins by using βarrestin2 knockout (βarr2-KO) mice as well as a recently described biased KOR agonist that biases receptor signaling toward G protein pathways over βarrestin2 recruitment. We find that the KOR antagonists nor-binaltorphimine (NorBNI) and 5'-guanidinonaltrindole (5'GNTI) induce acute pruritus in C57BL/6J mice, with reduced effects in KOR-KO mice. βArr2-KO mice display less of a response to KOR antagonist-induced itch compared to wild types, however no genotype differences are observed from chloroquine phosphate (CP)-induced itch, suggesting that the antagonists may utilize a KOR-βarrestin2 dependent mechanism. The KOR agonist U50,488H was equally effective in both WT and βarr2-KO mice in suppressing CP-induced itch. Furthermore, the G protein biased agonist, Isoquinolinone 2.1 was as effective as U50,488H in suppressing the itch response induced by KOR antagonist NorBNI or CP in C57BL/6J mice. Together these data suggest that the antipruritic effects of KOR agonists may not require βarrestins.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Animals; Arrestins; beta-Arrestins; Chloroquine; Disease Models, Animal; Dose-Response Relationship, Drug; Guanidines; Isoquinolines; Male; Mice, Inbred C57BL; Mice, Knockout; Morphinans; Motor Activity; Naltrexone; Pruritus; Receptors, Opioid, kappa

Pain is often associated with depression of behavior and mood, and relief of pain-related depression is a common goal of treatment. This study tested the hypothesis that pain-related behavioral depression is mediated by activation of endogenous κ-opioid systems and subsequent depression of mesolimbic dopamine release. Adult male Sprague-Dawley rats were implanted with electrodes targeting the medial forebrain bundle (for behavior studies of intracranial self-stimulation (ICSS)) or with cannulae for microdialysis measures of nucleus accumbens dopamine (NAc DA). Changes in ICSS and NAc DA were examined after treatment with a visceral noxious stimulus (intraperitoneal injection of dilute lactic acid) or an exogenous κ-agonist (U69593). Additional studies examined the sensitivity of acid and U69593 effects to blockade by two analgesics (the nonsteroidal antiinflammatory drug ketoprofen and the μ-opioid agonist morphine) or by the κ-antagonist norbinaltorphimine (norBNI). The effects of acid were also examined on mRNA expression for prodynorphin (PDYN) and κ-opioid receptors (KORs) in mesocorticolimbic brain regions. Both acid and U69593 depressed ICSS and extracellular levels of NAc DA. Pain-related acid effects were blocked by ketoprofen and morphine but not by norBNI. The U69593 effects were blocked by norBNI but not by ketoprofen, and were only attenuated by morphine. Acid did not significantly alter PDYN or KOR in NAc, but it produced a delayed increase in PDYN in prefrontal cortex. These results support a key role for the mesolimbic DA system, but a more nuanced role for endogenous κ-opioid systems, in mediating acute pain-related behavioral depression in rats.

Topics: Analgesics, Opioid; Animals; Benzeneacetamides; Depression; Disease Models, Animal; Dopamine; Gene Expression Regulation; Ketoprofen; Lactic Acid; Male; Medial Forebrain Bundle; Morphine; Naltrexone; Narcotic Antagonists; Nucleus Accumbens; Pain; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Self Stimulation; Time Factors

The long term use of opioids for the treatment of pain leads to a group of maladaptations which includes opioid-induced hyperalgesia (OIH). OIH typically resolves within few days after cessation of morphine treatment in mice but is prolonged for weeks if histone deacetylase (HDAC) activity is inhibited during opioid treatment. The present work seeks to identify gene targets supporting the epigenetic effects responsible for OIH prolongation.. Mice were treated with morphine according to an ascending dose protocol. Some mice also received the selective HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) additionally. Chronic morphine treatment with simultaneous HDAC inhibition enhanced OIH, and several spinal cord genes were up-regulated. The expression of Bdnf (Brain-derived neurotrophic factor) and Pdyn (Prodynorphin) were most closely related to the observed behavioral changes. ChIP (Chromatin immuoprecipation) assays demonstrated that promoter regions of Pdyn and Bdnf were strongly associated with aceH3K9 (Acetylated histone H3 Lysine9) after morphine and SAHA treatment. Furthermore, morphine treatment caused an increase in spinal BDNF and dynorphin levels, and these levels were further increased in SAHA treated mice. The selective TrkB (tropomyosin-receptor-kinase) antagonist ANA-12 reduced OIH when given one or seven days after cessation of morphine. Treatment with the selective kappa opioid receptor antagonist nor-BNI also reduced established OIH. The co-administration of either receptor antagonist agent daily with morphine resulted in attenuation of hyperalgesia present one day after cessation of treatment. Additionally, repeated morphine exposure induced a rise in BDNF expression that was associated with an increased number of BDNF+ cells in the spinal cord dorsal horn, showing strong co-localization with aceH3K9 in neuronal cells. Lastly, spinal application of low dose BDNF or Dynorphin A after resolution of OIH produced mechanical hypersensitivity, with no effect in controls.. The present study identified two genes whose expression is regulated by epigenetic mechanisms during morphine exposure. Treatments aimed at preventing the acetylation of histones or blocking BDNF and dynorphin signaling may reduce OIH and improve long-term pain using opioids.

Topics: Analgesics, Opioid; Animals; Antineoplastic Agents; Azepines; Benzamides; Brain-Derived Neurotrophic Factor; Disease Models, Animal; Dynorphins; Epigenesis, Genetic; Gene Expression Regulation; Hydroxamic Acids; Hyperalgesia; Male; Mice; Mice, Inbred C57BL; Morphine; Naltrexone; Narcotic Antagonists; Pain Measurement; Spinal Cord; Vorinostat

Intraplantar administration of complete Freund's adjuvant (CFA) and formalin are two noxious stimuli commonly used to produce sustained pain-related behaviors in rodents for research on neurobiology and treatment of pain. One clinically relevant manifestation of pain is depression of behavior and mood. This study compared effects of intraplantar CFA and formalin on depression of positively reinforced operant behavior in an assay of intracranial self-stimulation (ICSS) in rats. Effects of CFA and formalin on other physiological and behavioral measures, and opioid effects on formalin-induced depression of ICSS, were also examined.. There were four main findings. First, consistent with previous studies, both CFA and formalin produced similar paw swelling and mechanical hypersensitivity. Second, CFA produced weak and transient depression of ICSS, whereas formalin produced a more robust and sustained depression of ICSS that lasted at least 14 days. Third, formalin-induced depression of ICSS was reversed by morphine doses that did not significantly alter ICSS in saline-treated rats, suggesting that formalin effects on ICSS can be interpreted as an example of pain-related and analgesic-reversible depression of behavior. Finally, formalin-induced depression of ICSS was not associated with changes in central biomarkers for activation of endogenous kappa opioid systems, which have been implicated in depressive-like states in rodents, nor was it blocked by the kappa antagonist norbinaltorphimine.. These results suggest differential efficacy of sustained pain stimuli to depress brain reward function in rats as assessed with ICSS. Formalin-induced depression of ICSS does not appear to engage brain kappa opioid systems.

Topics: Analgesics, Opioid; Animals; Body Weight; Conditioning, Operant; Disease Models, Animal; Formaldehyde; Freund's Adjuvant; Hyperalgesia; Inhibition, Psychological; Male; Morphine; Naltrexone; Narcotic Antagonists; Pain; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Self Stimulation

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

Several studies implicate stress as a risk factor for the development and maintenance of drug addictive behaviors and drug relapse. Kappa opioid receptor (KOR) antagonists have been shown to attenuate behavioral responses to stress and stress-induced reinstatement of cocaine and ethanol seeking and preference.. In the current study, we determined whether the selective KOR antagonist, norbinaltorphimine (nor-BNI), would block stress-induced reinstatement of nicotine preference.. Adult Institute of Cancer Research mice were conditioned with 0.5 mg/kg nicotine, injected subcutaneously (s.c.) for 3 days and tested in the nicotine-conditioned place preference (CPP) model. After 3 days extinction, nor-BNI (10 mg/kg, s.c.) was administered 16 h prior to a priming dose of nicotine (0.1 mg/kg, s.c.), and mice were tested in the CPP model for nicotine-induced reinstatement of CPP. A separate group of mice was subjected to a 2-day modified forced swim test (FST) paradigm to induce stress after 3 days extinction from CPP. Mice were given vehicle or nor-BNI (10 mg/kg, s.c.) 16 h prior to each FST session.. Nor-BNI pretreatment significantly attenuated stress-induced reinstatement of nicotine-CPP, but had no effect on nicotine-primed reinstatement.. Blockade of KORs by selective antagonists attenuates stress-induced reinstatement of nicotine-CPP. Overall, the kappa opioid system may serve as a therapeutic target for suppressing multiple signaling processes which contribute to maintenance of smoking, smoking relapse, and drug abuse in general.

Topics: Animals; Conditioning, Psychological; Disease Models, Animal; Extinction, Psychological; Male; Mice; Mice, Inbred ICR; Naltrexone; Narcotic Antagonists; Nicotine; Receptors, Opioid, kappa; Recurrence; Risk Factors; Self Administration; Smoking; Stress, Psychological

Drug dependence is characterized by dysregulation of brain reward systems and increased sensitivity to stress. Chronic exposure to drugs of abuse is associated with increased expression of the neuropeptide dynorphin, the endogenous ligand for kappa opioid receptors (KORs). Activation of KORs causes depressive- and aversive-like responses in rodents, raising the possibility that drug-induced upregulation of dynorphin plays a role independence-associated negative states. Here we used "binge" exposure to cocaine (3 daily intraperitoneal injections of 15 mg/kg for 14 days) to examine the development of dependence-like behavior in the intracranial self-stimulation (ICSS) test and the forced swim test (FST). When rats were tested 1 h before their first scheduled injection of each day-a period of drug withdrawal corresponding to 20 h after their last injection on the previous day-there were exposure-dependent increases in ICSS thresholds (a putative indicator of anhedonia) and decreases in latencies to immobility in the FST (a putative indicator of behavioral despair). Administration of the long-lasting KOR antagonist norBNI (20 μg, intracerebroventricular) before the beginning of the binge regimen attenuated the development of cocaine withdrawal-induced anhedonia in the ICSS test. In contrast, administration of norBNI in the midst of the binge regimen had no effect on expression of cocaine withdrawal-induced anhedonia in the ICSS test, although it did attenuate despair-like behavior in the FST. These data suggest that blockade of KORs before exposure to a stressor (in this case, cocaine withdrawal or forced swimming) can attenuate the development of stress-induced behavioral adaptations. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Topics: Analysis of Variance; Animals; Cocaine; Conditioning, Operant; Depression; Disease Models, Animal; Dopamine Uptake Inhibitors; Drug Administration Routes; Immobility Response, Tonic; Male; Naltrexone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Opioid, kappa; Reinforcement Schedule; Self Administration; Substance Withdrawal Syndrome; Swimming; Time Factors

Salvinorin A (SA) has a potent inhibitory action on mouse gastrointestinal (GI) motility and ion transport, mediated primarily by kappa-opioid receptors (KOR). The aim of the present study was to characterize possible antiinflammatory and antinociceptive effects of SA in the GI tract of mice.. Colonic damage scores and myeloperoxidase activity were determined after intraperitoneal (i.p.), intracolonic (i.c.), and oral (p.o.) administration of SA using the trinitrobenzene sulfonic acid (TNBS) and dextran sodium sulfate (DSS) models of colitis in mice. Additionally, KOR, cannabinoid (CB)1, and CB2 western blot analysis of colon samples was performed. The antinociceptive effect of SA was examined based on the number of behavioral responses to i.c. instillation of mustard oil (MO).. The i.p. (3 mg/kg, twice daily) and p.o. (10 mg/kg, twice daily) administration of SA significantly attenuated TNBS and DSS colitis in mice. The effect of SA was blocked by KOR antagonist nor-binaltorphimine (10 mg/kg, i.p.). Western blot analysis showed no influence of SA on KOR, CB1, or CB2 levels. SA (3 mg/kg, i.p. and 10 mg/kg, i.c.) significantly decreased the number of pain responses after i.c. instillation of MO in the vehicle- and TNBS-treated mice. The antinociceptive action of SA was blocked by KOR and CB1 antagonists. The analgesic effect of i.c. SA was more potent in TNBS-treated mice compared to controls.. Our results suggest that the drugs based on the structure of SA have the potential to become valuable antiinflammatory or analgesic therapeutics for the treatment of GI diseases.

Topics: Analgesics; Animals; Anti-Inflammatory Agents; Blotting, Western; Colitis; Colon; Dextran Sulfate; Disease Models, Animal; Diterpenes, Clerodane; Gastrointestinal Motility; Male; Mice; Naltrexone; Pain; Peroxidase; Receptor, Cannabinoid, CB1; Receptor, Cannabinoid, CB2; Receptors, Opioid, kappa; Salvia; Trinitrobenzenesulfonic Acid

By use of parallel chemistry coupled with physicochemical property design, a series of selective κ opioid antagonists have been discovered. The parallel chemistry strategy utilized key monomer building blocks to rapidly expand the desired SAR space. The potency and selectivity of the in vitro κ antagonism were confirmed in the tail-flick analgesia model. This model was used to build an exposure-response relationship between the κ K(i) and the free brain drug levels. This strategy identified 2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine, PF-4455242, which entered phase 1 clinical testing and has demonstrated target engagement in healthy volunteers.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Area Under Curve; Biphenyl Compounds; Brain; Disease Models, Animal; Dogs; Drug Design; Drug Discovery; Haplorhini; Humans; Metabolic Clearance Rate; Mice; Microsomes, Liver; Models, Chemical; Molecular Structure; Morphine; Narcotic Antagonists; Pain; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Receptors, Opioid, mu; Structure-Activity Relationship; Sulfonamides

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely used drugs for the management of acute and chronic pain. The role of the opioid system in the synergism between NSAIDs is not well characterized. Mice were injected with a 5% formalin solution (20 μl) into the upper right lip to perform an orofacial formalin test. The isobolographic method was used to determine the interaction between dexketoprofen, which is the (S)-(+) enantiomer of ketoprofen, and meloxicam co-administration. Additionally, the non-selective, opioid antagonist naltrexone, the selective δ opioid receptor (DOP) antagonist naltrindole and the selective κ opioid receptor (KOP) antagonist norbinaltorphimine were used to assess the opioid effects on this interaction. Intraperitoneal administration of dexketoprofen or meloxicam induced dose-dependent antinociception with different phase I and phase II potencies in the orofacial formalin test. Meloxicam displayed similar potencies (ED(50)) in phase I (7.20 mg/kg) and phase II (8.60 mg/kg). Dexketoprofen was more potent in phase I (19.96 mg/kg) than in phase II (50.90 mg/kg). The interactions between dexketoprofen and meloxicam were synergistic in both phases. This was determined based on the fixed ratios (1:1) of their ED(50) values, which were determined by isobolographic analysis. Furthermore, this antinociceptive activity does not seem to be modulated by opioid receptor blockers because they did not induce changes in the nature of this interaction. This finding may be relevant with regards to NSAID multi-modal analgesia where an opioid antagonist must be used.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Synergism; Facial Pain; Formaldehyde; Ketoprofen; Male; Meloxicam; Mice; Naltrexone; Narcotic Antagonists; Stereoisomerism; Thiazines; Thiazoles

Although studies demonstrate that electroacupuncture (EA) alleviates the sensory dimension of pain, they have not addressed EA's effect on the affective dimension. An inflammatory pain rat model, produced by a complete Freund adjuvant (CFA) injection into the hind paw, was combined with a conditioned place avoidance test to determine EA's effects and its underpinning mechanism on the affective dimension of pain. CFA-injected rats showed place aversion, i.e. the affective dimension of pain, by spending less time in a pain-paired compartment after conditioning than before, while saline-injected rats did not. CFA rats given EA treatment at GB30 before a post-conditioning test showed no aversion to the pain-paired compartment, indicating that EA inhibited the affective response. Intra-rostral anterior cingulate cortex (rACC) administration of a κ-, but not μ-opioid receptor antagonist, blocked EA action. These data demonstrate that EA activates opioid receptors in the rACC to inhibit the affective dimension of pain.

Topics: Affect; Animals; Avoidance Learning; Conditioning, Classical; Disease Models, Animal; Electroacupuncture; Freund's Adjuvant; Gyrus Cinguli; Hyperalgesia; Inflammation; Male; Naltrexone; Pain Management; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Receptors, Opioid, mu; Somatostatin

Research supports the effectiveness of acupuncture for conditions such as chronic low back and knee pain. In a five-patient pilot study the modality also improved the symptoms of chemotherapy-induced neuropathic pain. Using an established rat model of paclitaxel-induced peripheral neuropathy, we evaluated the effect of electroacupuncture (EA) on paclitaxel-induced hyperalgesia and allodynia that has not been studied in an animal model. We hypothesize that EA would relieve the paclitaxel-induced mechanical allodynia and hyperalgesia, which was assessed 30 min after EA using von Frey filaments. Beginning on day 13, the response frequency to von Frey filaments (4-15 g) was significantly increased in paclitaxel-injected rats compared to those injected with vehicle. EA at 10 Hz significantly (P<0.05) decreased response frequency at 4-15 g compared to sham EA; EA at 100 Hz only decreased response frequency at 15 g stimulation. Compared to sham EA plus vehicle, EA at 10 Hz plus either a μ, δ, or κ opioid receptor antagonist did not significantly decrease mechanical response frequency, indicating that all three antagonists blocked EA inhibition of allodynia and hyperalgesia. Since we previously demonstrated that μ and δ but not κ opioid receptors affect EA anti-hyperalgesia in an inflammatory pain model, these data show that EA inhibits pain through different opioid receptors under varying conditions. Our data indicate that EA at 10 Hz inhibits mechanical allodynia/hyperalgesia more potently than does EA at 100 Hz. Thus, EA significantly inhibits paclitaxel-induced allodynia/hyperalgesia through spinal opioid receptors, and EA may be a useful complementary treatment for neuropathic pain patients.

Topics: Analysis of Variance; Animals; Antineoplastic Agents, Phytogenic; Disease Models, Animal; Electroacupuncture; Hyperalgesia; Male; Naltrexone; Narcotic Antagonists; Paclitaxel; Pain Measurement; Pain Threshold; Peripheral Nervous System Diseases; Random Allocation; Rats; Rats, Sprague-Dawley; Somatostatin

This functional magnetic imaging study investigated the functional implications of genetic modification and pharmacological intervention on cerebral processing of heat-induced nociception in mice. Comparing dynorphin-overexpressing dream(-/-) with wild-type mice, smaller activated cortical and limbic brain structure sizes could be observed. Moreover, significantly reduced blood oxygenation level-dependent signal amplitudes were found in pain-related brain structures: sensory input, thalamic regions, sensory cortex, limbic system, basal ganglia, hypothalamus and periaqueductal grey. Administration of the specific kappa-opioid-receptor antagonist nor-binaltorphimine to dream(-/-) mice reversed this reduction to wild-type level in the same brain structures. These results show that blood oxygenation level-dependent functional magnetic imaging in the pain system of (transgenic) mice is feasible. Genetic modifications and pharmacological interventions modify brain responses in a structure-specific manner.

Topics: Animals; Biomedical Research; Brain Mapping; Disease Models, Animal; Genomics; Hot Temperature; Image Processing, Computer-Assisted; Kv Channel-Interacting Proteins; Magnetic Resonance Imaging; Male; Mice; Mice, Knockout; Naltrexone; Narcotic Antagonists; Oxygen; Pain; Physical Stimulation; Repressor Proteins

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

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

Narcotic bowel syndrome (NBS) is a subset of opioid bowel dysfunctions that results from prolonged treatment with narcotics and is characterized by chronic abdominal pain. NBS is under-recognized and its molecular mechanisms are unknown. We aimed to (1) develop a rat model of NBS and (2) to investigate its peripheral and central neurobiological mechanisms.. Male Wistar rats were given a slow-release emulsion that did or did not contain morphine (10 mg/kg) for 8 days. Visceral sensitivity to colorectal distension (CRD) was evaluated during and after multiple administrations of morphine or vehicle (controls). The effects of minocycline (a microglia inhibitor), nor-binaltorphimine (a kappa-opioid antagonist), and doxantrazole (a mast-cell inhibitor) were observed on morphine-induced visceral hyperalgesia. Levels of OX-42, P-p38 mitogen-activated protein kinase, rat mast cell protease II, and protein gene product 9.5 were assessed at different spinal segments (lumbar 6 to sacral 1) or colonic mucosa by immunohistochemistry.. On day 8 of morphine administration, rats developed visceral hyperalgesia to CRD (incipient response) that lasted for 8 more days (delayed response). Minocycline reduced the incipient morphine-induced hypersensitivity response to CRD whereas nor-binaltorphimine and doxantrazole antagonized the delayed hyperalgesia. Levels of OX-42 and P-p38 increased in the spinal sections, whereas rat mast cell protease II and protein gene product 9.5 increased in the colonic mucosa of rats that were given morphine compared with controls.. We developed a rat model of narcotic bowel-like syndrome and showed that spinal microglia activation mediates the development of morphine-induced visceral hyperalgesia; peripheral neuroimmune activation and spinal dynorphin release represent an important mechanism in the delayed and long-lasting morphine-induced colonic hypersensitivity response to CRD.

Topics: Abdominal Pain; Animals; CD11b Antigen; Chymases; Colon; Delayed-Action Preparations; Disease Models, Animal; Gastrointestinal Transit; Hyperalgesia; Immunohistochemistry; Intestinal Mucosa; Male; Mast Cells; Microglia; Minocycline; Morphine; Naltrexone; Narcotic Antagonists; p38 Mitogen-Activated Protein Kinases; Pain Measurement; Pain Threshold; Pressure; Rats; Rats, Wistar; Spinal Cord; Syndrome; Thioxanthenes; Time Factors; Ubiquitin Thiolesterase; Xanthones

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

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

Topics: Animals; Antidepressive Agents; Anxiety Disorders; Brain; Depressive Disorder; Disease Models, Animal; Humans; Limbic System; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred WKY; Receptors, Opioid, kappa

Stress exposure increases the risk of addictive drug use in human and animal models of drug addiction by mechanisms that are not completely understood. Mice subjected to repeated forced swim stress (FSS) before cocaine develop significantly greater conditioned place preference (CPP) for the drug-paired chamber than unstressed mice. Analysis of the dose dependency showed that FSS increased both the maximal CPP response and sensitivity to cocaine. To determine whether FSS potentiated CPP by enhancing associative learning mechanisms, mice were conditioned with cocaine in the absence of stress, then challenged after association was complete with the kappa-opioid receptor (KOR) agonist U50,488 or repeated FSS, before preference testing. Mice challenged with U50,488 60 min before CPP preference testing expressed significantly greater cocaine-CPP than saline-challenged mice. Potentiation by U50,488 was dose and time dependent and blocked by the KOR antagonist norbinaltorphimine (norBNI). Similarly, mice subjected to repeated FSS before the final preference test expressed significantly greater cocaine-CPP than unstressed controls, and FSS-induced potentiation was blocked by norBNI. Novel object recognition (NOR) performance was not affected by U50,488 given 60 min before assay, but was impaired when given 15 min before NOR assay, suggesting that KOR activation did not potentiate CPP by facilitating memory retrieval or expression. The results from this study show that the potentiation of cocaine-CPP by KOR activation does not result from an enhancement of associative learning mechanisms and that stress may instead enhance the rewarding valence of cocaine-associated cues by a dynorphin-dependent mechanism.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Non-Narcotic; Analysis of Variance; Anesthetics, Local; Animals; Association Learning; Behavior, Animal; Cocaine; Conditioning, Operant; Cues; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Dynorphins; Exploratory Behavior; Male; Mental Recall; Mice; Mice, Inbred C57BL; Naltrexone; Narcotic Antagonists; Receptors, Opioid, kappa; Reward; Stress, Psychological; Swimming

Abnormalities in dopaminergic and serotonergic neurotransmission in the forebrain are believed to be involved in the underlying mechanism of schizophrenia; therefore, the direct blockade of the receptors associated with these systems is a central strategy for schizophrenia treatment, even though this strategy concurrently produces adverse effects like extrapyramidal effects. Kappa opioid receptors exist extensively in the brain and recent reports have suggested that these receptors are involved in modulating the release of several neurotransmitters including dopamine and serotonin. In the present study, we investigated the effect of TRK-820, (E)-N-[17-(cyclopropylmethyl)-4,5alpha-epoxy-3,14-dihydroxymorphinan-6beta-yl]-3-(furan-3-yl)-N-methylprop-2-enamide monohydrochloride, a selective kappa opioid receptor agonist, on phencyclidine-induced rat behavioral changes and on biochemical changes in the prefrontal cortex. First, TRK-820 dose-dependently inhibited phencyclidine-induced rat hyperlocomotion, which is one of the abnormal behaviors recognized as a rodent schizophrenia model. The inhibitory effect was completely antagonized with nor-BNI (nor-binaltorphimine hydrochloride), a selective kappa opioid receptor antagonist. Second, TRK-820 dose-dependently inhibited phencyclidine-induced stereotyped behaviors including head-weaving, which is considered a behavioral syndrome based on the impairment of the serotonergic system. Third, in an in vivo microdialysis study, TRK-820 dose-dependently attenuated the biochemical changes of both dopamine and serotonin in the prefrontal cortex of rats treated with phencyclidine without affecting their basal levels in normal rats. The initial findings that TRK-820 potentially modulates such monoamine changes and ameliorates abnormal behaviors related to their changes may suggest its therapeutic potential against the symptoms of schizophrenia.

Topics: Animals; Behavior, Animal; Disease Models, Animal; Dopamine; Extracellular Space; Hyperkinesis; Male; Morphinans; Naltrexone; Phencyclidine; Prefrontal Cortex; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Schizophrenia; Serotonin; Spiro Compounds

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

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

Periodontal disease is a chronic inflammatory condition of the tooth supporting tissues, the periodontium. Opioids have been shown to account for the relief of various chronic and acute inflammatory conditions. The aim of the present study was to investigate the participation of peripheral opioid receptors in development of periodontal disease.. Morphine and selective agonists and antagonists of opioid receptors were used in an experimental model of ligature-induced periodontal disease in rats. To evaluate the development of disease, the loss of fiber attachment, alveolar bone and number of cells in periodontal tissues were assessed. Measurements of these indicators were obtained by morphometric analysis of histological sections of periodontal-diseased tissues stained with hematoxylin and eosin.. Local administration of either morphine or a selective kappa-opioid agonist for three consecutive days from the onset of periodontal disease reduced the loss of periodontal tissues, without changing the number of leukocytes in inflamed periodontium. Nor-binaltorphimine, a selective kappa-antagonist, reversed the beneficial effects of both morphine and the compound U-50,488 in this model. The use of either an agonist or an antagonist of delta-opioid receptors, however, did not affect disease progression.. Our results showed that the beneficial effect of opioids in periodontal disease depended mainly on the activation of specific kappa-opioid receptors located in the periphery. Activation of such receptors could be considered in the management of periodontal disease, since it would not present the classical central side-effects associated with opioid use.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Opioid; Animals; Chronic Periodontitis; Disease Models, Animal; Male; Morphine; Naltrexone; Narcotic Antagonists; Peripheral Nervous System; Rats; Rats, Sprague-Dawley; Receptors, Opioid, delta; Receptors, Opioid, kappa

The broad applicability of receptor theory to diverse species, from invertebrates to mammals, provides evidence for the evolution in complexity of pharmacologic receptor diversification and of receptor-effector signal transduction mechanisms. However, pre-mammalian species have less receptor subtype differentiation, and thus, might share signal transduction pathways to a greater extent than do mammals, a phenomenon that we term 'pharmacologic congruence'. We have demonstrated previously that the lowest species considered to have a centralized nervous system, planarians, display both abstinence-induced and antagonist-precipitated withdrawal signs, indicative of the development of physical dependence. We report here: (1) amphetamine abstinence-induced withdrawal, and (2) the attenuation of cocaine and amphetamine, but not cannabinoid agonist (WIN 52212-2), abstinence-induced withdrawal by the opioid receptor antagonist naloxone and by the selective kappa-opioid receptor subtype antagonist nor-BNI (nor-Binaltorphimine), but not by the selective mu-opioid or the delta-opioid receptor subtype antagonists CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)) and naltrindole. These results provide evidence that the withdrawal from cocaine and amphetamine, but not cannabinoids, in planarians is mediated through a common nor-BNI-sensitive (kappa-opioid receptor-like) pathway.

Topics: Amphetamine; Analgesics; Analysis of Variance; Animals; Behavior, Animal; Benzoxazines; Cocaine; Disease Models, Animal; Dopamine Uptake Inhibitors; Drug Interactions; Morpholines; Naltrexone; Naphthalenes; Narcotic Antagonists; Planarians; Substance Withdrawal Syndrome; Time Factors

Our previous study showed that YGGFMKKKFMRFamide (YFa), a chimeric peptide of Met-enkephalin, and Phe-Met-Arg-Phe-NH2 induced naloxone-reversible antinociception and attenuated the development of tolerance to morphine analgesia. In continuation, the present study investigated which specific opioid receptors-mu, delta or kappa-mediate the observed YFa antinociception pharmacologically using specific antagonists and whether chronic administration of YFa at 26.01 micromol/kg per day induces tolerance and its effect on the expression of mu and kappa opioid receptors from day 4 to day 6, with endomorphine-1 (EM-1) and saline taken as positive and negative controls, respectively. Quantitative differential expression analysis was carried out by real-time reverse-transcriptase polymerase chain reaction, and the corresponding changes in protein levels were assessed by Western blot. A pharmacological investigation revealed that nor-binaltorphimine, a specific kappa opioid receptor-1 (KOR1) antagonist, completely antagonized the antinociception induced by 39.01 micromol/kg of YFa. Importantly, its chronic intraperitoneal administration did not result in significant tolerance over 6 days, whereas EM-1 induced significant tolerance after day 4. Differential expression analysis revealed that EM-1 caused up-regulation of mu opioid receptor-1 on day 4, followed by down-regulation on later days. Interestingly, YFa treatment caused a decrease on day 4, followed by an increase in the expression of KOR1 from day 5 onward. In conclusion, YFa induces kappa-specific antinociception, with no development of tolerance during 6 days of chronic treatment, which further articulates new directions for improved designing of peptide-based analgesics that may be devoid of adverse effects like tolerance.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enkephalin, Methionine; FMRFamide; Gene Expression Regulation; Male; Naltrexone; Narcotic Antagonists; Oligopeptides; Pain Measurement; Rats; Rats, Wistar; Reaction Time; Receptors, Opioid, kappa; Receptors, Opioid, mu; Time Factors

Endomorphin-1 and endomorphin-2 are endogenous peptides that are highly selective for mu-opioid receptors. However, studies of their functional efficacy and selectivity are controversial. In this study, we systematically compared the effects of intrathecal (i.t.) administration of endomorphin-1 and -2 on nociception assays and G protein activation with those of [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO), a highly effective peptidic mu-opioid receptor agonist.. Male Sprague-Dawley rats were used. Acute and inflammatory pain models were used to compare the duration and magnitude of antinociception. Agonist-stimulated [(35)S]GTP gamma S binding was used to observe the functional activity at the level of the receptor-G protein in both spinal cord and thalamic membranes. In addition, antagonists selective for each receptor type were used to verify the functional selectivity of endomorphins in the rat spinal cord.. After i.t. administration, endomorphin-1 and -2 produced less antinociceptive effects than DAMGO in the model of acute pain. Concentration-response curves for DAMGO-, endomorphin-1-, and endomorphin-2-stimulated [(35)S]GTP gamma S binding revealed that both endomorphin-1 and -2 produced less G protein activation (i.e., approximately 50%-60%) than DAMGO did in the membranes of spinal cord and thalamus. In addition, i.t. endomorphin-induced antinociception was blocked by mu-opioid receptor selective dose of naltrexone (P < 0.05), but not by delta- and kappa-opioid receptor antagonists, naltrindole and nor-binaltorphimine (P > 0.05).. Endomorphins are partial agonists for G protein activation at spinal and thalamic mu-opioid receptors. Both in vivo and in vitro measurements together suggest that DAMGO is more effective than endomorphins. Spinal endomorphins' antinociceptive efficacy may range between 53% and 84% depending on the intensity and modality of the nociceptive stimulus.

Topics: Analgesics; Analgesics, Opioid; Animals; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Partial Agonism; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Guanosine 5'-O-(3-Thiotriphosphate); Injections, Spinal; Male; Naltrexone; Narcotic Antagonists; Oligopeptides; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Spinal Cord; Sulfur Radioisotopes; Thalamus; Time Factors

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

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

Food intake and, subsequently, body weight are influenced by endogenous opioids acting in the central nervous system. Agonists for the opioid receptor increase food intake, whereas antagonists reduce food intake. Body weight, however, is the result of food consumed and energy expended. Although much has been reported about the effect of opioid antagonism on food intake, less has been reported about its effect on energy expended. This study investigated the effect of selective antagonism of the kappa opioid receptor on food intake, body weight, and indicators of energy expenditure in male obese Zucker rats (n=10). Energy expenditure was measured by indirect calorimetry, whereas general activity and body temperature were measured by implanted radio frequency telemetry. Central administration of 30 microg of the kappa opioid receptor (KOR) antagonist norbinaltorphamine resulted in a significant 34% reduction in food intake (p =.001), a small reduction in body weight, a reduction in resting energy expenditure (p = .06), a reduction in respiratory quotient (p =.06), a 14% reduction in general activity, and a reduction in core body temperature. Reduction in body weight as a result of KOR inhibition in this study was related to a decrease in food intake but not related to an increase in energy expended or activity.

Topics: Analysis of Variance; Animals; Body Temperature; Body Weight; Calorimetry, Indirect; Cardiac Catheterization; Disease Models, Animal; Drug Evaluation, Preclinical; Energy Intake; Energy Metabolism; Injections, Intravenous; Male; Motor Activity; Naltrexone; Narcotic Antagonists; Obesity; Rats; Rats, Zucker; Receptors, Opioid, kappa; Respiration; Telemetry

Neuropathic pain is often refractory to conventional pain therapies and thus requires exploration of effective drugs. We evaluated if processed Aconiti tuber (PAT), a traditional oriental herbal medicine that has been used as an analgesic, relieves neuropathic pain in the rat chronic constriction injury (CCI) model. Ten to 14 days after CCI in the right hind paw, six groups of rats received oral placebo, or PAT at 0.5, 1, 2, 3, or 5 g/kg. Additional groups received oral PAT, 2 g/kg, after pretreatment with intraperitoneal naloxone; intraperitoneal nor-binaltorphimine (norBNI); or intrathecal norBNI. As indicators of mechanical allodynia and thermal hyperalgesia, the pressure threshold of paw withdrawal (PWT) in response to linearly increasing pressure, and latency to paw withdrawal (PWL) in response to radiant heat, were measured before and after drug administration. Oral PAT dose-dependently increased PWT and PWL, which had been decreased due to CCI. The increases in PWT and PWL by oral PAT were inhibited by intraperitoneal and intrathecal norBNI: a selective kappa-opioid receptor antagonist, but not by intraperitoneal naloxone. These results indicate that oral PAT can alleviate mechanical allodynia and thermal hyperalgesia, dose-dependently, via spinal kappa-opioid receptor mechanisms in a rat CCI neuropathic pain model.

Topics: Aconitum; Analgesics; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Drugs, Chinese Herbal; Injections, Intraperitoneal; Injections, Spinal; Male; Naltrexone; Pain Measurement; Pain Threshold; Plant Tubers; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Sciatic Nerve; Sciatica

Although the neurochemical mechanisms contributing to alcohol withdrawal seizures are poorly understood, withdrawal seizures probably reflect neuronal hyperexcitability resulting from adaptation to chronic alcohol. Altered kappa-Opioid receptor (KOP-R) signaling has been observed in multiple seizure types; however, a role for this system in ethanol withdrawal seizures has not been systematically characterized. We hypothesized that pharmacological manipulations of the KOP-R would alter withdrawal in mice selectively bred for differences in ethanol withdrawal severity. Withdrawal Seizure-Prone (WSP) and Withdrawal Seizure-Resistant (WSR) mice were made physically dependent using chronic ethanol vapor inhalation, and the effects of the KOP-R antagonist nor-binaltorphimine or agonist U-50,488H on withdrawal severity were examined. Pretreatment with nor-binaltorphimine significantly increased handling-induced convulsion (HIC) severity in withdrawing WSR mice, with no observable effects in withdrawing WSP mice. In contrast, U-50,488H significantly decreased HIC severity in WSP mice, with no effects in WSR mice. During extended withdrawal (i.e. hours 12+), a rebound hyperexcitability was observed in WSP mice given agonist. Thus, administration of a KOP-R antagonist increased withdrawal severity in mice normally resistant to withdrawal seizures, while a KOP-R agonist reduced convulsion severity in animals susceptible to withdrawal seizures. These observations are consistent with differences in the KOP-R system observed in these lines at the molecular level, and suggest the KOP-R system may be a promising therapeutic target for management of ethanol withdrawal seizures. Finally, these findings underscore the importance of determining the potential for rebound increases in withdrawal severity during later withdrawal episodes.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Alcohol-Induced Disorders, Nervous System; Analgesics, Non-Narcotic; Analgesics, Opioid; Animals; Anticonvulsants; Brain; Central Nervous System Depressants; Disease Models, Animal; Drug Interactions; Drug Synergism; Ethanol; Male; Naltrexone; Receptors, Opioid, kappa; Seizures; Species Specificity; Substance Withdrawal Syndrome; Treatment Outcome

(+/-)-Pentazocine is widely used clinically to treat mild to moderate pain as a racemic compound. Although it is known that (-)-pentazocine acts as a kappa opioid receptor agonist to exhibit analgesic actions and (+)-pentazocine acts as a sigma receptor agonist without analgesic effects, their combined effect on memory has not been investigated in detail. In this study, the effect of (+)- and/or (-)-pentazocine on scopolamine-induced memory impairment in mice was investigated using spontaneous alternation performance in a Y-maze. (+)-Pentazocine (0.35 micromol/kg, s.c.) administered 30 min before behavioral testing significantly improved the impairment of spontaneous alternation induced by scopolamine. A higher dose of (-)-pentazocine (3.50 micromol/kg, s.c.) also reversed the scopolamine-induced impairment of alternation performance. Interestingly, the ameliorating effects of not only (+)-pentazocine, but also (-)-pentazocine were antagonized by a selective sigma receptor antagonist, N,N-dipropyl-2-[4-methoxy-3-(2-phenylenoxy)-phenyl]-ethylamine monohydrochloride (NE-100) (2.6 micromol/kg, i.p.). However, those effects were not antagonized by a selective kappa opioid receptor antagonist, nor-binaltorphimine (4.9 nmol/mouse, i.c.v.). Coadministration of (+)- and (-)-pentazocine (0.35 or 3.50 micromol/kg each) did not have any additive or antagonizing effects on the percent alternation. An antinociceptive effect was observed only with (-)-pentazocine (3.50 micromol/kg, s.c.), and was antagonized by nor-binaltorphimine (4.9 nmol/mouse, i.c.v.), but not by NE-100 (2.6 micromol/kg, i.p.). These results suggest that although the analgesic effect of pentazocine was mediated via kappa opioid receptors, the ameliorating effect on scopolamine-induced impairment of spontaneous alternation was mediated via sigma receptors, not via kappa opioid receptors.

Topics: Acetic Acid; Analgesics, Opioid; Analysis of Variance; Animals; Anisoles; Antipsychotic Agents; Behavior, Animal; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Interactions; Exploratory Behavior; Isomerism; Male; Maze Learning; Memory Disorders; Mice; Naltrexone; Narcotic Antagonists; Pain Measurement; Pentazocine; Propylamines; Receptors, Opioid, kappa; Receptors, sigma; Scopolamine

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

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

Rats exposed to learned helplessness (LH), an animal model of depression, showed a recovery following an intracerebroventricular injection of nor-binaltorphimine dihydrochloride (norBNI; a kappa-opioid antagonist). To investigate the potential role of dynorphin A and dynorphin B, we examined the effects of different stress/depression models on dynorphin A and dynorphin B immunoreactivity in hippocampus and nucleus accumbens (NAc). Immobilization stress (3 h) caused an increase in levels of dynorphin A and dynorphin B immunoreactivity in the hippocampus and the NAc. Forced swim stress also temporally increased dynorphin A levels in the hippocampus. Furthermore, exposure to LH produced a similar increase in dynorphin A and dynorphin B in the hippocampus and NAc. Infusions of norBNI into the dentate gyrus or CA3 regions of hippocampus and into the shell or core regions of NAc produced antidepressant-like effects in the LH paradigm. The degrees of norBNI's effects were stronger in the CA3 region and NAc shell and less effective in the dentate gyrus of hippocampus and NAc core. These results indicate that both dynorphin A and dynorphin B contribute to the effects of stress, and suggest that blockade of kappa-opioid receptors may have therapeutic potential for the treatment of depression.

Topics: Animals; Behavior, Animal; Cell Count; Disease Models, Animal; Dose-Response Relationship, Drug; Dynorphins; Endorphins; Escape Reaction; Helplessness, Learned; Immobilization; Immunohistochemistry; Limbic System; Male; Naltrexone; Rats; Rats, Sprague-Dawley; Stress, Physiological

Pruritus (itch sensation) is the most common side effect associated with spinal administration of morphine given to humans for analgesia. A variety of agents have been proposed as antipruritics with poorly understood mechanisms and they are effective with variable success. kappa-Opioid agonists possess several actions that are opposite to micro -opioid agonists. We proposed to investigate the role of kappa-opioid receptors (KORs) in morphine-induced scratching and antinociception in monkeys. Scratching responses were counted by observers blinded to treatment. Antinociception was measured by a warm water (50 degrees C) tail-withdrawal assay. Pretreatment with low doses of trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]-cyclohexyl)-benzeneacetamide (U-50488H) (0.032-0.18 mg/kg s.c.), a selective KOR agonist, dose dependently suppressed the s.c. morphine dose-effect curve for scratching and potentiated s.c. morphine-induced antinociception. In addition, s.c. U-50488H attenuated i.t. morphine (10 and 32 micro g)-induced scratching while maintaining or enhancing i.t. morphine-induced antinociception. The combination of s.c. or i.t. morphine with low doses of U-50488H did not cause sedation. More importantly, pretreatment with 3.2 mg/kg nor-binaltorphimine, a selective KOR antagonist, blocked the effects of s.c. U-50488H on both s.c. and i.t. morphine-induced scratching. These results indicate that activation of KOR attenuates morphine-induced scratching without interfering with antinociception in monkeys. This mechanism-based finding provides functional evidence in support of the clinical potential of KOR agonists as antipruritics in the presence of MOR agonist-induced pruritus.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Non-Narcotic; Animals; Disease Models, Animal; Drug Interactions; Female; Injections, Spinal; Injections, Subcutaneous; Macaca mulatta; Male; Morphine; Naltrexone; Narcotic Antagonists; Pruritus; Receptors, Opioid, kappa

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

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

The effects of the kappa-opioid receptor agonist, TRK-820, (-)-17-(cyclopropylmethyl)-3, 14beta-dihydroxy-4, 5alpha-epoxy-6beta-[N-methyl-trans-3-(3-furyl) acrylamido] morphinan hydrochloride, on the itch sensation were compared with those of histamine H1 receptor antagonists, using the mouse pruritogen-induced scratching model. Peroral administration of TRK-820 reduced the numbers of substance P- or histamine-induced scratches dose dependently. No obvious suppression of the spontaneous locomotor activity was observed at the doses used for the experiments, indicating that the inhibition of scratches was not due to the effect on general behavior. Furthermore, the scratching inhibitory activity of TRK-820 was dose dependently antagonized by the specific kappa-opioid receptor antagonist, nor-binaltorphimine, suggesting that the inhibitory activity was mediated via kappa-opioid receptors. Histamine H1 receptor antagonists, chlorpheniramine and ketotifen, did not inhibit substance P-induced scratches, or did so only partially. Both antihistamines inhibited the histamine-induced scratches completely. These results suggest that TRK-820 has antipruritic activity which is mediated by kappa-opioid receptors, and is effective in both antihistamine-sensitive and -resistant pruritus.

Topics: Animals; Antipruritics; Chlorpheniramine; Disease Models, Animal; Histamine; Histamine H1 Antagonists; Ketotifen; Male; Mice; Mice, Inbred ICR; Morphinans; Motor Activity; Naltrexone; Pruritus; Receptors, Opioid, kappa; Spiro Compounds; Substance P

The effects of intracerebroventricular (icv) administration of endomorphin-2 (E2) on arterial blood pressure and pain threshold in spontaneously hypertensive rats (SHR) and modification of these effects by K [OP2] and mu [OP3] opioid receptors antagonists were investigated. Endomorphin-2 administrated icv in doses of 8, 16 and 32 mcg produced dose-dependent analgesic and hypotensive effect. In SHR decrease in blood pressure amounted 2.667, 4.0 and 6.534 kPa, respectively. Pain threshold increased by 1.7, 3.6 and 8.9 (g x 10). In Wistar Kyoto (WKY) strain, being the normotensive controls, E2 in doses of 8 and 16 mcg decrease in blood pressure was less pronounced and amounted 1.200 and 1.467 kPa, respectively, whereas the pain threshold increased by 7.2 and 10.4 (g x 10), respectively. Both E2 effects were antagonized by equimolar icv doses of beta-funaltrexamine (beta-FNA). Equimolar doses of nor-binaltorphimine (nor-BNI) attenuated analgesic action of E2, but were without hypotensive action produced by E2. A strong correlation between drop in blood pressure and increase in pain threshold observed in the SHR and WKY strains after icv administration of E2, indicate close interaction between systems responsible for pain perception and blood pressure control.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Blood Pressure; Disease Models, Animal; Drug Interactions; Male; Naltrexone; Narcotic Antagonists; Oligopeptides; Pain; Pain Threshold; Rats; Rats, Inbred SHR; Rats, Inbred WKY

Long-term treatment of Parkinson's disease with levodopa is complicated by the emergence of involuntary movements, known as levodopa-induced dyskinesia. It has been hypothesized that increased opioid transmission in striatal output pathways may be responsible for the generation of dyskinesia. In this study, we have investigated the effect of blockade of opioid peptide transmission on levodopa-induced dyskinesia in a primate model of Parkinson's disease-the MPTP-lesioned marmoset. Coadministration of nonselective and mu- or delta-subtype-selective opioid receptor antagonists with levodopa resulted in a significant decrease in dyskinesia. There was no attenuation of the anti-parkinsonian actions of levodopa. These data suggest that specific mu- or delta-opioid receptor antagonists might be applicable clinically in the treatment of levodopa-induced dyskinesia in Parkinson's disease.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Callithrix; Disease Models, Animal; Drug Therapy, Combination; Dyskinesias; Female; Hypokinesia; Levodopa; Male; Morphinans; Motor Activity; Naltrexone; Narcotic Antagonists; Parkinsonian Disorders; Posture; Receptors, Opioid, delta; Receptors, Opioid, mu

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

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

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

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

1. The treatment of Parkinson's disease relies predominantly upon dopamine replacement therapy, usually with l-dihydroxyphenylalanine (L-DOPA). However, side-effects of long-term treatment, such as L-DOPA-induced dyskinesias can be more debilitating than the disease itself. Non-dopaminergic treatment strategies might therefore be advantageous. 2. The aim of this study was to investigate the potential anti-parkinsonian efficacy of the kappa-opioid receptor agonist, enadoline, and the alpha-adrenoreceptor agonist, clonidine, both alone or in combination, in the reserpine-treated rat model of Parkinson's disease. 3. Rats were treated with reserpine (3 mg kg-1), and experiments carried out 18 h later, at which time they exhibited profound akinesia (normal animals 1251+/-228 mobile counts h-1, reserpine-treated animals 9+/-2 mobile counts h-1). Both enadoline and clonidine increased locomotion in reserpine-treated rats in a dose-dependent manner. The maximum locomotor-stimulating effect of enadoline alone was seen at a dose of 0.2 mg kg-1 (208+/-63 mobile counts h-1). The maximum effect of clonidine was seen at a dose of 2 mg kg-1 (536+/-184 mobile counts h-1). 4. Co-administration of enadoline (0.1 mg kg-1) and clonidine (0.01 - 0.1 mg kg-1) at sub-threshold doses, synergistically increased locomotion. 5. The synergistic stimulation of locomotion in the reserpine-treated rat involved activation of kappa-opioid receptors and a combination of both alpha1 and alpha2-adrenoreceptors. 6. The results presented suggest a need for further studies on the potential of stimulating kappa-opioid and/or alpha-adrenoreceptors as a therapy for Parkinson's disease. Furthermore, the studies may offer potential mechanistic explanations of the ability of alpha2-adrenergic receptor antagonist to reduce L-DOPA-induced dyskinesia in Parkinson's disease.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Animals; Antiparkinson Agents; Benzofurans; Biogenic Monoamines; Clonidine; Disease Models, Animal; Drug Combinations; Drug Synergism; Locomotion; Male; Naltrexone; Narcotic Antagonists; Parkinson Disease, Secondary; Prazosin; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Reserpine; Yohimbine

The antinociceptive effect of intraplantar (i.pl.) ICI 204448 ((R,S)-N-[2-(N-methyl-3,4-dichloro-phenylacetamido)-2-(3-carbox yph enyl)- ethyl]pyrrolidine hydrochloride)) (20, 30, 40 and 50 micrograms), a kappa-opioid receptor agonist which has limited access to the central nervous system, was studied in a well-established rat model of peripheral mononeuropathy produced by moderate constriction of the sciatic nerve. Vocalization thresholds to paw pressure were used as a nociceptive test. On the injected nerve-injured paw, ICI 204448 at 20 and 30 micrograms had no significant effect, but higher doses (40 micrograms) produced a significant antinociceptive effect, which plateaued at 50 micrograms. By contrast, no antinociceptive effect was observed on the contralateral paw. The effect of ICI 204448 (40 micrograms) was significantly antagonised by the specific kappa-opioid receptor antagonist nor-binaltorphimine (20 and 30 micrograms), when co-injected in the nerve-injured paw.

Topics: Analgesia; Analysis of Variance; Animals; Behavior, Animal; Blood-Brain Barrier; Disease Models, Animal; Drug Interactions; Hindlimb; Male; Naltrexone; Narcotic Antagonists; Nerve Compression Syndromes; Pain Threshold; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Sciatic Nerve; Vocalization, Animal