SEXUAL DIMORPHISM OF GABA(A) RECEPTOR LEVELS IN SUBCORTICAL BRAIN-REGIONS OF A WOODLAND RODENT (APODEMUS-SYLVATICUS)

This is the first report of quantitative autoradiography results showi ng sex differences of GABA(A) receptor levels in brain regions of a wi ld rodent (wood mouse, Apodemus sylvaticus) living in its natural habi tat. The labeling of this GABAergic site with its specific high affini ty radioligand [H-3] muscimol provided a heterogeneous and dimorphic b inding pattern in some of the neural centers. In the female, higher (g reater than or equal to 50 less than or equal to 65%) to moderately hi gher ( < 50%) binding levels than in the male, even after correction o f the specific binding values using the calculated quenching coefficie nts, were observed in the substantia nigra pars reticulata and ventral lateral thalamic nucleus, brain centers that are relays of motor circ uits. In the male, on the other hand, a higher level was only obtained in the caudate-putamen. Relays of the stria terminalis-hypothalamic-c entral gray pathway such as the bed nucleus of the stria terminalis, t he pontine central gray and the ventromedial hypothalamic nucleus, wer e among the other female brain areas with an extremely higher ( > 65%) to higher and moderately higher binding activity than in the male. Fr om the saturation analyses, it appeared that the binding differences w ere mainly due to B-max variations, although closer examinations revea led that changes in the K-D might have also accounted for [H-3] muscim ol binding differences, as shown by the high K-D and B-max values in t he bed nucleus of the stria terminalis, the substantia nigra pars reti culata and the pontine central gray of the female wood mouse. These fi ndings suggest that the dimorphic binding activity of GABA(A) receptor s in the above brain regions might be involved in neuronal circuitry m echanisms related to sex-specific social behaviors in rodents living i n their natural environmental conditions.