The effects of alterations in nitric oxide levels in the paraventricular nucleus on copulatory behavior and reflexive erections in male rats

Purpose: To examine the effects of altered nitric oxide (NO) levels in the paraventricular nucleus (PVN) on copulatory behavior and reflexive erections in male rats. Materials and Methods: Extracellular nitrite (NO2-) and nitrate (NO3-) levels were measured in the PVN following administration of the NO precursor L-arginine (L-arg, 10 mM), the NO synthase inhibitor NG-monomethyl L-arginine (L-NMMA, 10 mM), or Ringer's solution via a dialysis probe to the PVN. The effects of alterations in extracellular NO on reflexive erections and copulatory behavior were assessed. Results: L-arg administration was associated with significant elevations of extracellular NO, and NO3- in the PVN, while L-NMMA significantly reduced NO2- and NO3- levels. A corresponding increase in reflexive erections was noted during infusion of L-arg in the PVN, with a corresponding decrease in reflexive erections observed during administration of L-NMMMA into the PVN (Student's t test for paired samples, p <0.05). Mount rate was unaffected by infusion of the either L-arg or L-NMMA. Conclusions: Altered NO levels in the PVN affected the frequency of reflexive erections, but not the mount rate. These studies contrast with previous observations of the effects of altered NO levels in the MPOA, and support the hypothesis that physiological specificity in the actions of NO on discrete brain nuclei may have important implications to erectile physiology and dysfunction.