LOCALIZATION OF GABA-A RECEPTORS IN THE RAT RETINA

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitte r in the mammalian retina. The present paper describes the localizatio n of GABA(A) receptors in the rat retina as revealed by in situ hybrid ization and immunocytochemistry. In situ hybridization with probes aga inst various alpha subunits revealed a marked differential expression pattern. The alpha1 subunit gene is expressed mainly in the bipolar an d horizontal cell layer, the alpha2 gene in the amacrine and ganglion cell layer, and the alpha4 gene in a subpopulation of amacrine cells. Beta subunit mRNA is present diffusely throughout the entire inner nuc lear layer and in the ganglion cell layer. The monoclonal antibody bd 17 (against beta2/beta3 subunits) stained subpopulations of GABAergic and glycinergic amacrine cells as well as some ganglion cells and bipo lar cells. Immunoreactivity was not restricted to synaptic input sites . In the outer plexiform layer bipolar cell dendrites were immunoreact ive; in the inner plexiform layer mainly amacrine and ganglion cell pr ocesses were labeled, and bipolar cell axons appeared unstained. The r esults demonstrate a strong heterogeneity of GABA(A) receptors in the retina.