Articles: hyperalgesia.
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Pharmacol. Biochem. Behav. · Oct 2011
Synergistic anti-allodynic effects of nociceptin/orphanin FQ and cannabinoid systems in neuropathic mice.
Combinations of analgesics from different classes are commonly used in the management of chronic pain. The goal is to enhance pain relief together with the reduction of side effects. The present study was undertaken to examine the anti-allodynic synergy resulting from the combination of WIN 55,212-2, a cannabinoid CB1 receptor agonist, and JTC-801, a nociceptin/orphanin FQ receptor antagonist, on neuropathic pain. ⋯ Both WIN 55,212-2 and JTC-801 produced dose-dependent mechanical and cold anti-allodynic effects. As shown by isobolographic analysis, WIN 55,212-2/JTC-801 combinations interacted synergistically at all three ratios studied in the mechanical allodynia assay. In conclusion, co-administration of a cannabinoid with a nociceptin/orphanin FQ receptor antagonist resulted in a synergistic interaction, which may have utility in the pharmacological treatment of neuropathic pain.
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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. ⋯ 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.
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Activation of CNS cannabinoid subtype-1 (CB1) receptors has been shown to mediate the antinociceptive and other effects of systemically administered CB receptor agonists. The endogenous peptide CB receptor ligand hemopressin (HE) has previously demonstrated an antinociceptive effect in rats with a hind paw inflammation, without exhibiting characteristic CB1 receptor-mediated side-effects. The current study evaluated the effect of intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of HE in a rat model of neuropathic spinal cord injury (SCI) pain. ⋯ Pretreatment with rimonabant completely blocked the antinociceptive effect of centrally administered WIN 55,212-2, but pretreatment with HE did not. While the data confirm that activation of either supraspinal or spinal CB1 receptors leads to significant antinociception in SCI rats, the current data do not support an antinociceptive effect from an acute blockade of central CB1 receptors, HE's putative antinociceptive mechanism, in neuropathic SCI rats. Although such a mechanism could be useful in other models of pain with a significant inflammatory component, the current data indicate that activation of CB1 receptors is needed to ameliorate neuropathic SCI pain.
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Peripheral nerve injury often results in neuropathic pain that is manifested as hyperalgesia, and allodynia. Several studies suggest a functional role for neuronal nitric oxide synthase (nNOS) in the development or maintenance of neuropathic pain, but such a contribution remains unclear. In our current study, we found that intraplantar injection of the NOS substrate L-arginine or NO donor 3-morpholino-synonimine (SIN-1) produced mechanical hypersensitivity that lasted more than 24 h. ⋯ Intraplantar injection of the NOS inhibitor 7-nitroindazole (7-NI) or the non-specific NOS inhibitor L-N(G)-nitro-arginine methyl ester (L-NAME) effectively suppressed SNL-induced mechanical allodynia. Collectively, these data suggest that in the periphery nNOS upregulation induced by peripheral nerve injury contributes to mechanical hypersensitivity during the maintenance phase of neuropathic pain. Blocking nNOS signaling in the periphery may thus be a novel therapeutic strategy for the treatment of neuropathic pain.