GABAergic influence on the development of the sexually dimorphic nucleus of male and female rats.

A large number of estrogen-sensitive neurons in rat hypothalamus use gamma-aminobutyric acid (GABA) as a neurotransmitter. As estrogens influence the size of the sexually dimorphic nucleus (SDN) of the preoptic area it was tested whether perinatal treatment of rats with the GABA-agonistic drug muscimol can induce similar changes as estrogens. Male and female rats were treated perinatally with muscimol or with the vehicle only and the vols. of the SDN of the preoptic area were determined morphometrically following maturation of the animals. The SDN vols. in treated males were significantly smaller (80.3%) compared to controls. There was no striking effect in females. Our data suggest an influence of the GABAergic system on the development of the sexually dimorphic nucleus of the preoptic area (SDN-POA). The muscimol treatment, however, did not mimic the effects of perinatal estrogen treatment. Since muscimol is a GABAA receptor stimulating drug it appears that this receptor subtype is not involved in the estrogen-induced changes in size of the SDN.