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

The effect of NO-nitro-L-arginine methyl ester (NAME), a potent inhibitor 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 the above behavioral responses dose dependently when injected into the paraventricular nucleus of the hypothalamus (PVN), but not in the caudate nucleus, medial septum, preoptic area, and the CA1 field of the hippocampus. When injected in the PVN, 5 mu g of NAME induced a 30% reduction of apomorphine and oxytocin responses, while 20 mu g induced an almost complete reduction. The effect of NAME seems to be related to the inhibition of guanylate cyclase secondary to the prevention of NO formation, because a dose-dependent reduction of apomorphine and oxytocin 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 neurotransmitter role of central NO in the control of penile and yawning.