Sexual maturation modifies the GABAergic control of gonadotrophin secretion in female rats

Administration of aminooxyacetic acid, (an inhibitor of gamma-aminobutyric acid (GABA)-transaminase which enhances the hypothalamic GABA content) increased luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels in prepubertal rats (16 days of age), and decreased the levels of these pituitary hormones in peripubertal rats (30 days of age). Prepubertal and peripubertal female rats were administered with muscimol, a GABAA-antagonist, with baclofen, a GABAB agonist, and with bicuculline, a GABA-antagonist, and the serum concentrations of LH and FSH were determined. In prepubertal rats, muscimol increased both LH and FSH levels, while in peripubertals the GABAA agonist showed the opposite effect, i.e. both gonadotrophins were decreased after its administration. Baclofen lowered serum concentrations of LH and FSH at the different ages studied. Administration of bicuculline produced a decrease in LH and FSH concentrations in prepubertal rats, and an increase of these values in peripubertal rats. These results indicate that GABA exerts a stimulatory tone on gonadotrophin secretion in prepubertal rats and an inhibitory one in peripubertal animals. This effect is most probably mediated by GABAA receptors. It is suggested that the change in the effect on gonadotrophin secretion of the activation of GABAA receptors which takes place during sexual maturation in the female rats is related to the central mechanisms involved in the onset of puberty.