Gonadal regulation of GABAA receptors in the different brain areas of the male Japanese quail.

Quantitative autoradiography was used to investigate the distribution and effects of gonadal hormones on [3H] muscimol (specific GABAA receptor ligand) binding in the male Japanese quail brain. In gonadally intact Japanese quail brains, [3H] muscimol revealed a heterogeneous distribution with high GABAA receptor levels in the cerebellum pars granularis (656 fmol/mg wet weight of tissue) and in the pars molecularis (405 fmol/mg wet weight of tissue). Low receptor levels were found in the nucleus preopticus anterior and the nucleus lateralis of the hypothalamic regions (less than 220 fmol/mg wet weight of tissue) as well as thalamic nuclei such as rotundus and pretectalis (220-261 fmol/mg wet weight of tissue). Castration resulted in [3H] muscimol binding changes in both brain areas that contain steroid receptors and brain areas devoid of steroid receptors. In fact, castration led to high binding levels in the preopticus anterior nucleus and in the anterior neostriatum area, brain areas that are known to contain gonadal steroid receptors. Castration also elevated [3H] muscimol binding in the hyperstriatum ventrale and reduced binding levels in the paleostriatum augmentatum and the stratum griscum centrale area; all of these areas are known to be devoid of gonadal steroid receptors. At this point it was also important to know whether the gonadal steroid effect is due to alterations in the number of binding sites (Bmax) and/or the affinity binding state (KD). The saturation binding study, dealing with some of the areas described above in brains of male quails castrated or castrated and treated with testosterone or estradiol, demonstrated that the steroid replacement therapy was responsible for the changes of the Bmax.(ABSTRACT TRUNCATED AT 250 WORDS)