PREVENTION BY N-G-NITRO-L-ARGININE METHYL-ESTER OF APOMORPHINE-INDUCED AND OXYTOCIN-INDUCED PENILE ERECTION AND YAWNING - SITE OF ACTION INTHE BRAIN

The effect of NO-nitro-L-arginine methyl ester (NAME), a potent inhibi tor of nitric oxide (NO) synthase, injected into different brain areas on penile erection and yawning induced by apomorphine or oxytocin was studied in male rats. The compound was found to be able to prevent th e above behavioral responses dose dependently when injected into the p araventricular nucleus of the hypothalamus (PVN), but not in the cauda te nucleus, medial septum, preoptic area, and the CA1 field of the hip pocampus. When injected in the PVN, 5 mu g of NAME induced a 30% reduc tion of apomorphine and oxytocin responses, while 20 mu g induced an a lmost complete reduction. The effect of NAME seems to be related to th e inhibition of guanylate cyclase secondary to the prevention of NO fo rmation, because a dose-dependent reduction of apomorphine and oxytoci n responses was obtained also with the inhibitor of guanylate cyclase methylene blue injected intracerebroventricularly (100-400 mu g ICV), but not into the PVN. The results provide further support for a neurot ransmitter role of central NO in the control of penile and yawning.