Influence of gender and brain region on neurosteroid modulation of GABA responses in rats.

Neuroactive steroid derivatives of progesterone, testosterone and glucocorticoids can alter physiological responses to gamma-aminobutyric acid (GABA), apparently through direct, non-steroid receptor mechanisms. The present study examined gender-related differences and regional variations in the ability of tetrahydrodeoxycorticosterone (THDOC), 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha-5alpha-THP, tetrahydroprogesterone), androsterone, and dihydroandrosterone (DHA) to alter physiological GABA responses. Steroid modulation of GABA-activated 36chloride influx into microsac preparations from cortex, hippocampus, amygdala, cerebellum and hypothalamus-preoptic area in adrenalectomized-gonadectomized rats of both sexes were tested. The effects of THDOC and 3alpha-5alpha-THP were also examined in groups of intact male and female rats. All four steroids increased GABA-activated chloride influx, although the maximal enhancement in GABA responses differed significantly among brain regions. The rank order of maximal THDOC and 3alpha-5alpha-THP effects was hippocampus > cortex approximately amygdala > hypothalamus-preoptic area approximately cerebellum. Regional differences in potentiation of GABA responses were seen with androsterone, but not dihydroandrosterone. The rank order of androgenic potentiation of GABA responses was amygdala approximately hippocampus > cortex approximately HPA > cerebellum. Slight gender-related differences in responses to steroids were seen with THDOC, with males showing greater maximal enhancement of GABA responses with THDOC than females in the amygdala and hypothalamus-preoptic area. Since sex differences were observed with the glucocorticoid derivative THDOC, but not the progesterone derivative 3alpha-5alpha-THP or androgenic steroids, it appears neuroactive steroid modulation of GABA responses can be differentially affected by the hormonal milieu in a regionally-specific manner.