More recent work has been performed within a more narrow range of ethanol concentrations for studying physiologically relevant effects. Whole-cell recordings in the dentate gyrus of the mouse hippocampus indicated that the δ subunit-containing GABA-A receptors were potential targets of low ethanol concentrations (30mM), as revealed by the reduced excitability of dentate granule cells associated with enhanced tonic inhibition [29]. The majority of studies contend that 30mM is the most effective ethanol concentration in achieving optimal modulation of GABA-A receptors in hippocampal slice preparations. Some recent work suggests that ethanol modulation of GABA-gated current is dependent on the time course of exposure or by previous exposure to low ethanol concentrations. Using whole-cell patch clamp techniques to measure GABA-gated Cl- currents in pyramidal CA1 neurons from female rats, Smith et al. determined that 30mM ethanol optimally enhanced GABA-gated current; however, pretreatment with 1mM ethanol diminished this current following application of 30mM ethanol [30]. The efficacy of low ethanol concentrations in modulation of GABA-gated current in the CA1 hippocampal region may therefore be influenced by previous ethanol exposure. Other studies suggest that
