Effects of local application of 5-HT into the median and dorsal raphe nuclei on male rat sexual and motor behavior.

The local application of 10 micrograms 5-hydroxytryptamine (5-HT) into the dorsal or median raphe nucleus was found to facilitate male rat sexual behavior, as evidenced by a decrease in time to ejaculation, and in number of intromissions preceding ejaculation. The application of a higher dose, 40 micrograms, at either site, inhibited the initiation of sexual behavior. There was a clear distinction between the motor effects observed after local application of 5-HT into the dorsal or the median raphe nuclei. Injections into the median raphe produced a dose-dependent increase, whereas injections into the dorsal raphe nucleus produced a dose-dependent decrease, in motor activity. Present results suggests an inhibitory and excitatory role of the median and the dorsal raphe serotonergic projections, respectively, as regards motor behavior, whereas projections from both nuclei appear to have an inhibitory role in the mediation of male rat sexual behavior.