In vivo GABA release from the medial preoptic area of diestrous and ovariectomized rats.

The push-pull cannula technique was used to examine the endogenous release of GABA from the medial preoptic area (MPO) of unanesthetized rats. In diestrous females the mean resting release of GABA was 27.1 +/- 2.0 pmol/min. GABA release was significantly elevated by increasing the potassium concentration in the perfusion solution to 50 mM, whereas it was dramatically inhibited by mercaptoproprionic acid (1.0 mM), a glutamic acid decarboxylase inhibitor. A comparison between diestrous females and chronically castrated animals indicated that endogenous GABA release in OVX animals was only 60-70% of that in diestrous animals. A model for the presynaptic inhibition of NE by estrogen receptive GABAergic neurons in the MPO is proposed.