Low ethanol concentrations selectively augment the tonic inhibition mediated by δ subunit-containing GABAA receptors in hippocampal neurons

In central neurons, a tonic conductance is activated by ambient levels of the inhibitory transmitter GABA. Here, we show that in dentate gyrus granule cells, where tonic inhibition is mediated by delta subunit-containing GABA(A) receptors, this conductance is augmented by low concentrations (30 mM) of ethanol. In contrast, the tonic inhibition mediated by alpha5 subunit-containing receptors of CA1 pyramidal cells is not affected. The effect of ethanol on tonic inhibition specifically reduces the excitability of the dentate gyrus and identifies the delta subunit-dependent tonic inhibition as a likely site of ethanol action in the brain.