We investigated the contribution of NO-cyclic GMP (cGMP) pathway to the antinociceptive effects of ketamine in mice by using the nitric oxide synthase inhibitor nitro(g)-L-arginine methyl ester (L-NAME). Intraperitoneal (i.p.) (1 5 or 10 mg/kg) or intrathecal (i.th.) (10 30 or 60 mug/mouse) administration of ketamine produced dose-dependent antinociceptive effects in the acetic acid-induced writhing and formalin tests but not in the tail-flick nor in hot-plate tests. pretreatment of mice with ...