Muscarinic and nicotinic influences on masculine sexual behavior in rats: effects of oxotremorine, scopolamine, and nicotine.

In this study, the role of cholinergic systems in the regulation of male sexual behavior was analyzed by different approaches. Both muscarinic agonists and antagonists, as well as a nicotine agonist, were administered to sexually experienced male rats. In Experiment 1, oxotremorine (OXO), a muscarinic agonist, decreased the intromission frequency and ejaculatory latency in a dose-dependent way. Moreover, an increase in ejaculatory frequency was observed. In Experiment 2, the muscarinic antagonist scopolamine (SCO) produced a dose-related impairment of sexual behavior, decreasing the percentage of sexually active males. The smaller doses of SCO delayed the initiation of sexual behavior and decreased ejaculatory frequency. In an attempt to analyze the effect of muscarinic supersensitivity on sexual behavior, in Experiment 3 a long-term blockade of muscarinic receptors (SCO for 17 days) was followed by OXO administration. Animals displayed a significant increase of mount frequency, which results in the decrease of both the hit rate and ejaculatory frequency. In Experiment 4, six doses of nicotine were acutely administered. Only the higher doses (0.4, 0.8, and 1.6 mg/kg) induced a decrease in intromission frequency, although no significant differences were found in any other parameter. These results strongly suggest that cholinergic participation in masculine sexual behavior regulation is mediated mainly through muscarinic system.