GABAergic Regulation of Lordosis: Influence of Gonadal Hormones on Turnover of GABA and Interaction of GABA with 5-HT

The role of GABAergic neurons in activating female sexual behavior and possible mechanisms for GABAergic effects on behavior were examined in female rats. First, effects of the ovarian hormones estrogen and progesterone (P), at doses which promote lordosis, on levels and turnover/activity of GABA, were examined in brain areas which regulate lordosis. Utilizing AOAA, an inhibitor of GABA degradation, the accumulation rate of GABA (turnover/activity) was assessed in ovariectomized (Ovx), Ovx + estrogen and Ovx + estrogen + P-treated rats. Estradiol increased GABA accumulation rates in the arcuate-median eminence and in the area dorsal to and surrounding the VMN (VMN-S). P administration following estrogen priming enhanced GABA turnover in the medial preoptic area (mPOA) and further increased turnover in the VMN-S while GABA turnover decreased in the dorsomedial nucleus. No effects of hormones were noted in the VMN itself or in the dorsal midbrain central gray. Reverse dialysis of the GABA A antagonist bicuculline into the basomedial hypothalamus was associated with a time-dependent inhibition of lordosis and a 300% increase in 5-HT release in the basomedial hypothalamus as measured by in vivo dialysis. These results provide additional evidence that GABAergic neurons mediate the physiological regulation of female sexual behavior and suggest that such mediation may involve an interaction with 5-HT containing neurons.