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 subunit are found within the frontal and perirhinal cortex, with up-regulation occurring from PD 10 to 30; the α5 subunit has high expression throughout the brain, especially in the deep cortical layers (Yu et al. 2006). The initial increases in α1, α2, α3, and γ2 found during the early postnatal period change during development, and decrease until PD 60, while α5 levels decrease from the high levels found in early development throughout the aging process (Yu et al. 2006). Prominent throughout development, β2 and β3 immunoreactivity shows consistent levels in both the neonatal and adult brain (Fritschy et al. 1994). In humans, a similar increase in α1 and γ2 expression occurs with age in the temporal lobe, hippocampus, and basal ganglia (Kanaumi et al. 2006).
