Effects of p-Chlorophenylalanine on male sexual behavior in female rats with mesencephalic raphe nuclei lesions

The role of serotonergic neurons in the mesencephalic raphe nuclei in regulating male sexual behavior in female rats was examined. The median or dorsal raphe nucleus lesions (MRL or DRL) were made in ovariectomized rats and behavioral tests were performed after implantation of Silastic tubes containing testosterone and treatment with serotonin synthesis inhibitor p- chlorophenylalanine (pCPA). Half of the animals in each group received 4 100 mg/kg pCPA injections before the behavioral test. As a result, the incidences and frequencies of mounts and intromissive patterns in the MRL and DRL groups were comparable to those in control females without brain surgery. Mount latency in the MRL females was shorter than that in the control females. When pCPA was given, most females with or without brain surgery showed mounts and intromissive patterns, and frequencies were higher than those in females without pCPA. These results suggest that the median raphe nucleus plays an inhibitory role in the onset mechanism for mounting. On the other hand, a stronger inhibitory influence in regulating male sexual behavior exists in other serotonergic neurons than those in the median and dorsal raphe nuclei in female rats.