GABAERGIC CONTROL OF RECEPTIVITY IN THE FEMALE RAT

GABAergic neurotransmission has been implicated in the control of the steroid-dependent behavior, lordosis. GABA has dual effects on lordosis: it facilitates lordosis through actions in the medial hypothalamus (mHYP) and it inhibits lordosis through actions in the preoptic area (POA). In the present study, gonadally intact and ovariectomized female rats were behaviorally tested with a sexually active male. Brains were removed from sexually receptive female either 1 or 24 h after behavioral testing. There was a significant difference in endogenous GABA concentration in HYP and POA between receptive, postreceptive and ovariectomized nonreceptive females. Specifically, GABA levels in postreceptive females were higher in the HYP (20%) and lower in the POA (21%) in comparison to receptive females (p < 0.05). There was also a significant change in binding parameters of H-3-muscimol in the HYP and POA of receptive females as compared to 24 h postreceptive and ovariectomized rats. Attempts to modulate H-3-GABA release from hypothalamic tissue slices by estrogen or progesterone in ovariectomized rats yielded no effect on this parameter.