OXYTOCIN INCREASES NITRIC-OXIDE PRODUCTION IN THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS OF MALE-RATS - CORRELATION WITH PENILE ERECTION AND YAWNING

A dose of oxytocin (50 ng i.c.v.) that induces penile erection and yaw ning, increased the concentration of NO2- from 0.98 +/- 0.29 to 4.2 +/ - 0.79 mu M and of NO3- from 5.6 +/- 0.33 to 12.03 +/- 0.99 mu M in th e dialysate from the paraventricular nucleus of the hypothalamus of ma le rats, as measured by in vivo microdialysis. NO2- concentration was also increased by [Thr(4),Gly(7)]-oxytocin (100 ng i.c.v.) and oxytoci n(1-8) (1 mu g i.c.v.), which also induced penile erection and yawning , but not by oxytocin(1-6) (1 mu g i.c.v.) or oxytocin(7-9) (1 mu g i. c.v.), which were unable to induce these behavioral responses. The oxy tocin effect on NO2- concentration, penile erection and yawning was pr evented by the oxytocin receptor antagonist, d(CH2)(5)Tyr(Me)-Orn(8)-v asotocin (1 mu g i.c.v.), or by the nitric oxide synthase inhibitor, N -G-nitro-L-arginine methyl eater (200 mu g i.c.v.), but not by the dop amine receptor antagonist, haloperidol (0.5 mg/kg i.p.). The nitric ox ide scavenger, hemoglobin (200 mu g i.c.v.), prevented oxytocin-induce d NO2- concentration increase, but was unable to prevent penile erecti on and yawning. Methylene blue (300 mu g i.c.v.), an inhibitor of guan ylate cyclase, was ineffective on oxytocin-induced NO2- concentration increase, but, prevented the behavioral responses. The results suggest that oxytocin induces penile erection and yawning by increasing nitri c oxide synthase activity in the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas and mediating the behavio ral responses. (C) 1997 Elsevier Science B.V.