Aim:Cobratoxin (CTX),the long-chain α-neurotoxin from Thailand cobra venom,has been demonstrated to have analgesic action in rodent pain models.The present study evaluated the anti-inflammatory and anti-nociceptive effects of CTX on adju-vant arthritis (AA) in rats.Methods: Arthritis was induced by injection of complete Freund's adjuvant (CFA) in rats.Paw swelling and hyperalgesia of AA rats were measured at various times after CFA administration.Tumor necrosis factor-a (TNF-α),interleukin-1 (IL-1),interleukin-2 (IL-2) and interleukin-10 (IL-10) levels in serum were determined with ELISA.Histopathological changes in synoviocytes were examined under a microscope.Involvement of the cholinergic system in the effects of CTX was examinedby pretreatment of animals with the α7 nicotinic receptor (α7-nAChR) antagonist methyllycaconitine (MLA).Results: CFA induced marked paw swelling and reduced thresholds of mechanical and cold-induced paw withdrawal.The lev-els of TNF-α,IL-1 and IL-2 in the serum of AA rats were increased,whereas the level of IL-10 was decreased.Histopathologi-cal examination of synoviocytes showed pronounced inflammation and accumulation of collagen.The administration of CTX (17.0 μg/kg,ip) significantly reduced paw swelling and mechanical and thermal hyperalgesia.CTX also reduced the produc-tion ofTNF-α,IL-1,and IL-2 but increased the production of IL-10 and altered pathohistological changes.The analgesic and anti-inflammatory efficacy of CTX was significantly reduced by MLA (3 mg/kg,sc).Conclusion: These results indicate that CTX has a beneficial effect on CFA-induced arthritis by modulating the production of inflammatory cytokines,α7-nAChR appears to mediate the anti-nociceptive and anti-inflammatory actions of CTX.
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