NITRIC-OXIDE PRODUCTION IS INCREASED IN THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS OF MALE RATS DURING NONCONTACT PENILE ERECTIONS ANDCOPULATION

Male rats put in the presence of a receptive female rat that they can see, hear and smell, but cannot touch, show penile erection episodes. These non-contact erections occur concomitantly with an increase in ni tric oxide production in the paraventricular nucleus of the hypothalam us, as detected by the increase in the NO2- and NO3- concentration in the paraventricular dialysate obtained from these males by in vivo mic rodialysis. NO2- concentration increased from 0.81 +/- 0.12 to 2.51 +/ - 0.43 mu M and that of NO3- from 4.50 +/- 0.73 to 8.31 +/- 2.3 mu M. The NO2- increase was prevented by the nitric oxide synthase inhibitor NG-nitro-L-arginine methylester (20 mu g) given unilaterally in the p araventricular nucleus, which also prevented non-contact erections. In contrast, the nitric oxide scavenger haemoglobin (20 mu g) prevented the NO2- increase, but not non-contact erections; while the guanylate cyclase inhibitor methylene blue (20 mu g) was ineffective on either r esponse. NO2- and NO3- concentration was also increased in the paraven tricular dialysate of male rats during in copula penile erections, tha t is, when sexual activity was allowed with the receptive females. As found with non-contact erections, N-G-nitro-L-arginine methylester pre vented NO2- increase and impaired copulatory behaviour; haemoglobin pr evented NO2- increase only; and methylene blue was ineffective on eith er response. The present results confirm that nitric oxide is a physio logical mediator of penile erection at the level of the paraventricula r nucleus of the hypothalamus.