most common GABA-A subunit in the mammalian brain is the α1 subunit, which can be located both at synapses and outside of synapses, whereas the α4 or α5 subunits are thought to have a more restrictive expression and be mostly located extrasynaptically (Jin et al., 2011b; Brickley and Mody, 2012). It was, therefore, surprising that high expression levels were observed for the α4 and α5 mRNAs in both the caudate and putamen. Our results suggest a strong tonic contribution of the GABA-A receptor function in these regions in addition to the synaptic GABAergic transmission. In agreement, also in mice large tonic currents have been detected in electrophysiological experiments on dorsal striatal neurons (Ade et al., 2008). The δ subunit is known to be exclusively located extrasynaptically, to combine in the forebrain with α4β subunits to form GABA-A receptors that have high affinity for GABA and that are modulated by ethanol (Brickley and Mody, 2012). In our study, the δ subunit was significantly down-regulated in the caudate from alcoholics indicating decreased tonic inhibition in the caudate region, which would be expected to increase the basic excitability of the neurons. In animal models, the δ subunit-containing receptors have been shown to regulate
