Longer term progesterone treatment induces changes of GABAA receptor levels in forebrain sites in the female hamster: quantitative autoradiography study.

Quantitative receptor autoradiography was applied to evaluate the effects of one and three injections of 1 mg progesterone (P) on 3H muscimol binding levels in the different forebrain areas of the female hamster. The overall effect of P resulted in substantial increases in 3H muscimol binding in brain areas containing gonadal steroid receptors: medial preoptic area and ventromedial hypothalamic nucleus as well as in bed nucleus stria terminalis and subiculum. Similarly, the caudate putamen, a region where gonadal steroid receptors are not abundant, also showed substantial increases of 3H muscimol binding receptor levels. Moreover, female hamsters treated with P for 3 days presented altered 3H muscimol binding levels in the amygdala and thalamic nucleus that were, in some cases, not produced by one dose of P. P treatment also decreased GABAA binding in two areas of the thalamus. These results are consistent with the proposal that P may alter GABAergic inhibitory activity via changes in the levels of GABAA receptors in certain forebrain areas in the female hamster, changes which may be linked to the mediation of anxiolytic effects and to the inhibition of aggressive behavior. These data also suggest that P treatment increases the binding of high affinity GABA receptors in some forebrain sites and may be responsible for maintenance of the anxiolytic effects.