GABA A receptor subunits in the rat hippocampus I: Immunocytochemical distribution of 13 subunits

Abstract

The GABA A receptor is a ligand-operated chloride channel. It has a pentameric structure. In mammalian brain different subunits are recruited from four gene subfamilies. Using immunocytochemistry, we investigated the distribution of the 13 GABA A receptor subunits in the hippocampus of the rat. GABA A receptor subunits were heterogeneously distributed within different hippocampal subfields. High concentrations of α 1-, α 2-, α 4-, β 3-, γ 2- and δ-immunoreactivities were observed within the molecular layer of the dentate gyrus, representing the dendritic area of the granule cells. In the hippocampus proper, the predominant GABA A receptor subunits were α 1, α 2, α 5, β 3 and γ 2 that were located throughout the strata radiatum and oriens of CA1 to CA3. Immunocytochemical staining was there less prominent for α 4-, β 1-, β 2-, γ 3- and δ- subunits. In the hippocampus proper, the β 1 subunit was preferentially located in CA2. The α 4- and δ-subunits were somewhat more abundant in CA1 than in CA3. Numerous local circuit neurons in the hippocampus proper and the hilus of the dentate gyrus contained α 1-, β 2-, γ 2- and/or δ-subunits. α 3 and γ 1 were present only in minute amounts and no α 6-IR was detected in the hippocampal formation. The distribution of the GABA A receptor subunits indicates the existence of heterogenously constituted GABA A receptor complexes within various hippocampal subfields, which may exert different physiological or pharmacological properties upon stimulation by GABA or its agonists.