GABA(A) RECEPTOR SUBUNITS IN THE RAT HIPPOCAMPUS .1. IMMUNOCYTOCHEMICAL DISTRIBUTION OF 13 SUBUNITS

The GABA(A) receptor is a ligand-operated chloride channel. It has a p entameric structure. In mammalian brain different subunits are recruit ed from four gene subfamilies. Using immunocytochemistry: we investiga ted the distribution of the 13 GABA(A) receptor subunits in the hippoc ampus of the rat. GABA(A) receptor subunits were heterogeneously distr ibuted within different hippocampal subfields. High concentrations of alpha(1)-, alpha(2)-, alpha(4)-, beta(3)-, gamma(2)- and delta-immunor eactivities were observed within the molecular layer of the dentate gy rus, representing the dendritic area of the granule cells. In the hipp ocampus proper, the predominant GABA(A) receptor subunits were alpha(1 ), alpha(2), alpha(5), beta(3) and gamma(2) that were located througho ut the strata radiatum and oriens of CA1 to CA3. Immunocytochemical st aining was there less prominent for alpha(4)-, beta(1)-, beta(2)-, gam ma(3)- and delta-subunits. In the hippocampus proper, the beta(1) subu nit was preferentially located in CA2. The alpha(4)- and delta-subunit s were somewhat more abundant in CA1 than in CA3. Numerous local circu it neurons in the hippocampus proper and the hilus of the dentate gyru s contained alpha(1)-, beta(2)- gamma(2)- and/or delta-subunits. alpha (3) and gamma(1) were present only in minute amounts and no alpha(6)-I R was detected in the hippocampal formation. The distribution of the G ABA(A) receptor subunits indicates the existence of heterogenously con stituted GABA(A) receptor complexes within Various hippocampal subfiel ds, which may exert different physiological or pharmacological propert ies upon stimulation by GABA or its agonists. (C) 1997 IBRO. Published by Elsevier Science Ltd.