Brain localization of cholinergic influence on male sex behavior in rats: agonists.

Cholinergic agonists were microinjected into either the lateral ventricle or the preoptic area of sexually experienced male rats. In Experiment 1 carbachol, injected into the lateral ventricles, delayed the initiation of sexual behavior. When injected into the preoptic area, carbachol again delayed the onset of copulation, but these delays were shorter than after ventricular injections. In addition, preoptic injections reduced the number of intromissions preceding ejaculation. In Experiment 2 ventricular injections of the muscarinic agonist oxotremorine again delayed initiation of sexual behavior and also slowed its rate. However, oxotremorine injections into the preoptic area, through cannulae angled to miss all ventricles, only decreased the number of intromissions preceding ejaculation. These data suggest that cholinergic synapses in proximity to the ventricles may decrease sexual arousal, while cholinergic mechanisms in or near the preoptic area may reduce ejaculatory threshold.