Given that adolescent subjects differ from adults on many ethanol-related behaviors, it is possible that the spatial and temporal changes in GABAA receptor subunit expression throughout the developmental process may contribute to their phenotypic differences. Each subunit exhibits unique developmental expression patterns based on regions and age, suggesting that the expression and function of GABAA receptors during development may differ from those found in adults (Henschel et al. 2008). GABAA receptor subunit expression of α1, α2, α3, α5, and γ2 changes throughout development, reaching adult-like levels during the third month of life (Jenkins and Simmons 2006). Immunoreactivity of α1 subunit is low at birth and restricted to a few brain regions, with levels increasing during the first postnatal weeks (Fritschy et al. 1994). In contrast, α2 subunit distribution is widespread in the superficial layers (I–IV) of the neocortex (Yu et al. 2006) at birth. These levels decrease in some regions shortly after the appearance of the α1 subunit and co-expression occurs briefly, with α1 eventually replacing α2 subunit (Fritschy et al. 1994; Henschel et al. 2008). High levels of α3
