Social isolation-induced increase in ?4 and ? subunit gene expression is associated with a greater efficacy of ethanol on steroidogenesis and GABAA receptor function

Previously we have demonstrated that social isolation of rats reduces both the cerebrocortical and plasma concentrations of 3?-hydroxy-5?- pregnan-20-one (3?,5?-TH PROG), and potentiates the positive effects of acute ethanol administration on the concentrations of this neurosteroid. We now show that the ethanol-induced increase in 3?,5?-TH PROG is more pronounced in the brain than in the plasma of isolated rats. The ability of ethanol to inhibit isoniazid-induced convulsions is greater in isolated rats than in group-housed animals and this effect is prevented by treatment with finasteride. Social isolation modified the effects of ethanol on the amounts of steroidogenic regulatory protein mRNA and protein in the brain. Moreover, ethanol increased the amplitude of GABAA receptor-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurones with greater potency in hippocampal slices prepared from socially isolated rats than in those from group-housed rats, an effect inhibited by finasteride. The amounts of the ?4 and ? subunits of the GABAA receptor in the hippocampus were increased in isolated rats as were GABAA receptor-mediated tonic inhibitory currents in granule cells of the dentate gyrus. These results suggest that social isolation results in changes in GABAA receptor expression in the brain, and in an enhancement of the stimulatory effect of ethanol on brain steroidogenesis, GABAA receptor function and associated behaviour. © 2006 International Society for Neurochemistry.