EFFECT OF SEX STEROIDS ON HYPOTHALAMIC GABA

Orchidectomy decreased gamma-aminobutyric acid (GABA) levels and the a ctivity of glutamic acid decarboxylase (GAD) in the acurate/median emi nence area (ARC/ME). The replacement treatment with estradiol benzoate (E2) or testosterone propionate (T) restored both paramenters back to the levels of the control intact rats. Dihydrotestosterone propionate (DHT) administration did not reverse the effect of castration. Hypoph ysectomy diminished GABA content and E2 and T treatments can not rever se this action. Administration of an antiserum to rat prolactin (PRL) blocked the stimulatory action of E2 on GABA concentration and GAD act ivity in the ARC/ME. Implants of anterior pituitaries or the combinati on of both grafting pituitaries and E2 administration increased GABA c ontent in the ARC/ME and anterior pituitary glands. These results indi cate that PRL may mediate the stimulatory effect of estrogen on ARC/ME GABA neurons.