The effects of lesions in the mesencephalic raphe systems on male rat sexual behavior and locomotor activity.

Lesions were produced in the median and the dorsal raphe nuclei of the rat, and the effects of these injuries on various behaviors were studied. The median raphe lesions had facilitatory effects on the male rat sexual behavior, as evidenced by a decrease in the number of intromissions prior to ejaculation, as well as shortening of the ejaculation latency and the postejaculatory interval. No effects were seen on the masculine sexual behavior after lesions in the dorsal raphe nucleus. The median raphe lesions drastically increased the locomotory activity whereas the dorsal raphe lesions did not. Treatment with FG5893, a 5-HT1A agonist/5-HT2A receptor antagonist, increased the locomotor activity of the dorsal-raphe-lesioned rats but did not affect the median-raphe-lesioned animals. These results suggest that the dorsal and the median raphe nuclei play different roles in the neural regulation of the sexual behavior and locomotor activity of the male rat. The median raphe nucleus appears to exert a modulatory influence upon these behaviors, which probably is mediated by serotonergic neural pathways.