extrasynaptic receptors (Mody 2001; Olsen and Sieghart 2009). GABAA receptor δ subunits are so far found to be exclusively present in extrasynaptic sites (Farrant and Nusser 2005). The α4 subunit has relatively low expression in the CNS (Wisden et al. 1992) and α4βδ GABAA receptors are exclusively extrasynaptic (Wei et al. 2003), whereas α4βγ2 may be localized at the synapse, as well as extrasynaptically (Hsu et al. 2003; Liang et al. 2006). Given this distinction, the study of synaptic vs. extrasynaptic GABAA receptors and the effect of ethanol on these receptors is essential to elucidate the mechanism involved in development of ethanol actions including tolerance and dependence. Additionally, the role of various subunits in GABAA receptor-mediated actions has been studied by recombinant expression studies in vitro and by genetically modified mouse models and pharmacologic modulators in vivo. In this review, we address the role of various subunits in ethanol actions by referring to various subunit-containing receptors. For example, the α1 subunit-containing receptors will be referred to as α1-GABAA receptors.
