IMMUNOCYTOCHEMICAL LOCALIZATION OF GAMMA-(2) SHORT AND GAMMA-(2) LONGSUBUNITS OF THE GABA(A) RECEPTOR IN THE RAT-BRAIN

The distribution of the short (gamma(2S)) and long (gamma(2L)) subunit s of the GABA(A) receptors in the rat brain has been revealed by light microscopy immunocytochemistry with novel subunit-specific antibodies (anti-gamma(2S) and anti-gamma(2L)). We have also used other subunit- specific antibodies including anti-gamma(2)IL2 (which recognizes both gamma(2S) and gamma(2L)), anti-alpha(1)COOH, and the monoclonal antibo dy 62-3G1 to beta(2/3) for comparing the regional and cellular distrib ution of the most abundant GABA(A) receptor subunits in the rat brain. The distributions of gamma(2S) and gamma(2L) immunoreactivities are s imilar throughout the brain although the relative intensity of both si gnals varies depending on the brain area and neuronal type. In the hip pocampus, cerebral cortex, and olfactory bulb (particularly mitral, pe riglomerular, and tufted neurons), gamma(2S) was more abundant than ga mma(2L). In contrast, the inferior colliculus, medulla, and the cerebe llar Purkinje cells displayed more gamma(2L) than gamma(2S) immunolabe ling. An important difference in the distribution of the various subun its was found in cerebellum: gamma(2S) and gamma(2L) were predominantl y localized in the molecular layer, whereas alpha(1), and beta(2/3) we re more abundant in the granular layer. In the thalamus, gamma(2L) and gamma(2S) were less abundant than either alpha(1) or beta(2/3) subuni ts. The results showed that there is colocalization of gamma(2S) and g amma(2L) subunits in some brain areas and neuronal types, as well as a reas of mismatch. Colocalization and mismatches were also found among alpha(1), beta(2/3), and gamma(2), probably resulting from the heterog eneity in the subunit composition of the GABA(A) receptors through the brain.