In situ hybridization (Wisden et al., 1992; Persohn et al., 1992) and immunohistochemical studies (Pirker et al., 2000; Fritschy et al., 1992) have indicated that α1, β1, β2, β3, and γ2 subunits are found throughout the brain, although differences in their distribution were observed. Subunits α2, α3, α4, α5, α6, γ1, and δ are more confined to certain brain areas and in some brain regions, a complementary distribution of α2, α4, β3, and δ versus α1, β2, and γ2 subunits was detected (Sieghart and Sperk, 2002). The δ subunit is frequently co-distributed with the α4 subunit, e.g. in the thalamus, striatum, outer layers of the cortex and in the dentate molecular layer. In the cerebellum, however, it is co-distributed with the α6 subunit (Pirker et al., 2000).
