NITRIC-OXIDE SYNTHASE INHIBITORS PREVENT N-METHYL-D-ASPARTIC ACID-INDUCED PENILE ERECTION AND YAWNING IN MALE-RATS

The effect of N-G-nitro-L-arginine methylester (NAME) and N-mono-methy l-L-arginine (NMMA), inhibitors of nitric oxide (NO) synthase on penil e erection and yawning induced by N-methyl-D-aspartic acid (NMDA) inje cted in the paraventricular nucleus of the hypothalamus (PVN) was stud ied in male rats. NAME (75-150 mu g) and NMMA (250-500 mu g), but not N-monomethyl-D-arginine (D-NMMA)(250-500 mu g) prevented both response s in a dose-dependent manner when given intracerebroventricularly (i.c .v.) 15 min before NMDA (50 ng). NMDA-induced penile erection and yawn ing was also prevented by the guanylate cyclase inhibitor methylene bl ue (200-400 mu g i.c.v.), but not by the NO scavenger methemoglobin (5 0-100 mu g i.c.v.). NAME (10-20 mu g), but not Methylene blue or methe moglobin (10-20 mu g), prevented NMDA-induced responses also when inje cted in the PVN 15 min before NMDA. The present results suggest that N MDA-induced penile erection and yawning is mediated by an increased NO synthesis in the PVN.