Immunocytochemical localization of the beta(3) subunit of the gamma-aminobutyric acid(A) receptor in the rat brain.

A novel anti-beta(3) subunit-specific GABA(A) receptor (GABA(A)R) antibody has been prepared by immunizing a rabbit with a bacterial fusion protein of the large intracellular loop of the beta(3) subunit. The antiserum immunoprecipitated the solubilized GABA(A) receptor. The anti-beta(3) antibody was affinity purified on immobilized beta(3) large intracellular loop peptide. In immunoblots, the purified antibody reacted with a 57 KDa peptide. Immunocytochemistry with the affinity-purified antibody has revealed the localization of the beta(3) subunit in the rat brain. A comparative study with the immunocytochemical distribution of the beta(2) subunit has also been performed. There are areas of the brain and cell types where the distribution of beta(2) and beta(3) overlap (i.e., cerebral cortex, cerebellum,and most layers of the olfactory bulb). There are also clear differences in the expression of beta(3) and beta(2) in other brain areas and cell types. Thus, high beta(3) but low or no beta(2) expression was observed in the corpus striatum and in granule cells of the olfactory bulb. In the hippocampus the expression of beta(3) was considerably higher than that of beta(2), but some hippocampal interneurons showed high expression of beta(2). High beta(2) but little or no expression of beta(3) was observed in thalamic nuclei, substantia nigra, globus pallidus, inferior colliculus and the short axon cells of the olfactory bulb.