Introduction: Neuropathic pain is a debilitating disease afflicting wider population now days. Peripheral nerve injury produces a persistent neuropathic pain. Recently, oxidative stress nitric oxide pathway has been proposed in the pathogenesis of such type of painful conditions. Melatonin, the secretory product of the pineal gland, has potent antioxidant properties. The objective of the present study was to explore possible nitric oxide mechanism in the protective effect of melatonin against sciatic nerve ligation induced behavioral and biochemical alterations in rats Materials and Methods: Sciatic nerve ligation was performed in Wistar male rats. Various behavioral parameters (thermal hyperalgesia, cold allodynia) as well as biochemical parameters (lipid peroxidation, reduced glutathione, catalse, and nitrite) were assessed in sciatic nerve. Drugs were administered for 21 consecutive days from the day of surgery. Results: Sciatic nerve ligation (CCI) significantly caused thermal hyeralgesia, cold allodynia and oxidative damage as compared to naïve and sham control. Chronic administration of melatonin (2.5 mg/kg and 5 mg/kg, ip) significantly reversed hyperalgesia, cold allodynia and attenuated oxidative damage (as indicated by reduced lipid peroxidation, nitric concentration, restoration of reduced glutathione and catalse activity) in sciatic nerve as compared to control (CCI). Further, L-NAME (5 mg/kg) (nitric oxide synthase inhibitor) pretreatment with effective doses of melatonin (2.5mg/kg and 5.0 mg/kg, ip) potentiated the protective effect of melatonin which was significant as compared to their effect per se in sciatic nerve. However, L-arginine (100 mg/kg) (nitric oxide precursor) pretreatment with melatonin (2.5mg/kg and 5.0 mg/kg, ip) significantly reversed the protective effects of melatonin in sciatic nerve. Conclusion- Result of present study suggests that nitric oxide mechanism might be involved in the protective effect of melatonin against CCI induced behavior alterations and oxidative damage in rats.
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