Anorexigenic action of nitric oxide synthase inhibition in the raphe nuclei

The present report examined the effects of midbrain raphe nuclei injections of nitric oxide synthase inhibitors NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI) on eating behavior. L-NAME (5-500 pmol) and 7-NI (2-200 pmol) were administered into either the dorsal or median raphe nucleus. Both nitric oxide synthase inhibitors decreased food intake in adult male Sprague-Dawley rats when injected into either raphe site. Further, eating elicited by dorsal and median raphe injections of the 5-HT1A agonist 8-OH-DPAT (0.8 nmol) was attenuated by L-NAME or 7-NI pretreatment. Our findings indicate that nitric oxide acts within the raphe to alter food intake. The inhibitory effects of L-NAME and 7-NI on eating elicited by 8-OH-DPAT further suggest that nitric oxide and 5-HT systems interact in the control of food intake.