EVIDENCE FOR INVOLVEMENT OF NITRIC-OXIDE IN PRETECTAL ANALGESIA IN RAT

THE study was undertaken to evaluate the role of nitric oxide (NO) in pretectal (PTN)-induced analgesia in rats. Microinjection of varying concentrations of L-arginine (1 nM to 1 muM) produced a quick, long-lasting and concentration-dependent analgesic response, whereas similar concentrations Of D-arginine failed to produce analgesia. Moreover pretreatment with N-nitro-L-arginine methyl ester (L-NAME, 1 muM) significantly prevented L-arginine induced analgesia. Further, pretreatment of animals with methylene blue, a known guanylate cyclase inhibitor also prevented the development of analgesia. Our study suggests that L-arginine caused production of NO, which in turn activates pretectal analgesic system involving cyclic GMP.