Two types of lordosis-inhibiting systems in male rats: dorsal raphe nucleus lesions and septal cuts.

To examine the functional relationships between the dorsal raphe nucleus and the septum in the inhibitory regulation of feminine sexual behavior in male rats, castrated male rats received destruction of the dorsal raphe nucleus (DRL), interruption of the septal outputs (ARD), or both DRL and ARD (DRL+ARD). All animals were treated with estradiol by using Silastic tubes, and feminine sexual behavior was observed every other day for 10 days. Most castrated control male rats did not show lordosis throughout the tests. In contrast, all of the males with DRL alone or ARD alone displayed lordosis, but the lordosis quotients (LQ) in these groups were lower than those of the female control group. On the other hand, DRL+ARD males showed higher LQs than the DRL or the ARD males, being comparable to control females. Thus, two types of strong inhibitory influence exist in the dorsal raphe nucleus and the septum, and resist the facilitation of feminine sexual behavior by estrogen in male rats. Furthermore, these inhibitory systems operate independently, because an additive effect of DRL and ARD in facilitating lordosis was clearly observed in DRL+ARD males.