DIFFERENTIAL SYNAPTIC LOCALIZATION OF 2 MAJOR GAMMA-AMINOBUTYRIC-ACIDTYPE-A RECEPTOR-ALPHA SUBUNITS ON HIPPOCAMPAL PYRAMIDAL CELLS

Hippocampal pyramidal cells, receiving domain specific GABAergic input s, express up to 10 different subunits of the gamma-aminobutyric acid type A (GABAA) receptor, but only 3 different subunits are needed to f orm a functional pentameric channel. We have tested the hypothesis tha t some subunits are selectively located at subsets of GABAergic synaps es. The alpha 1 subunit has been found in most GABAergic synapses on a ll postsynaptic domains of pyramidal cells. In contrast, the alpha 2 s ubunit was located only in a subset of synapses on the somata and dend rites, but in most synapses on axon initial segments innervated by axo -axonic cells. The results demonstrate that molecular specialization i n the composition of postsynaptic GABA(A) receptor subunits parallels GABAergic cell specialization in targeting synapses to a specific doma in of postsynaptic cortical neurons.