The inhibitory effect of baclofen, a GABAβ receptor agonist, on lordosis was examined in female and male rats with dorsal raphe nucleus lesions (DRL) or cut of the septal fibers (ARD). Both female and male DRL and ARD rats showed higher lordosis quotients (LQ) than corresponding controls without brain surgery. This indicates that the dorsal raphe nucleus and the septum exert lordosis-inhibiting influences in female and male rats. After treatment with 10 mg/kg baclofen, the mean LQs in female control and female ARD groups were significantly lower than those of vehicle-treated control and ARD females. In DRL females, however, LQs did not decrease, even after the injection of baclofen. In males, baclofen also diminished lordosis in ARD rats, but not in DRL rats. These results suggest that the GABAB receptor system plays an inhibitory role in regulating lordosis behavior not only in female but also in male rats. Furthermore, the function of the GABA neurons depends on the inhibitory mechanism of the dorsal raphe nucleus in the regulation of female sexual behavior.
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