GABA (γ-aminobutyric acid) is the major inhibitory neurotransmitter in the human brain (Olsen and Sieghart, 2009). The fast inhibitory effect of GABA in the mature nervous system is mediated through GABA type-A (GABAA) receptors, which are heteropentameric ligand-gated ion channels permeable to chloride (Hevers and Luddens, 1998). GABAA receptors are distributed throughout the brain and composed of a diverse set of 19 subunits (α1–6, β1–3, γ1–3, δ, ε, θ, π, and ρ1–3) that vary in expression across brain regions (for a review, see (Olsen and Sieghart, 2009). The various GABAA receptor subtypes differ in subunit stoichiometry, a major determinant of their diverse pharmacological and electrophysiological properties (Barnard et al., 1998, Olsen and Sieghart, 2009). The majority of GABAA receptors contain two α, two β, and 1 γ subunit, with the α1β2γ2 and α2β3γ2 combinations comprising 75–85% of GABAA receptors in adult cortex (Rudolph et al., 2001).
