Localization of GABAA receptors in the rat retina

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian retina. The present paper describes the localization of GABAA receptors in the rat retina as revealed by in situ hybridization and immunocytochemistry. In situ hybridization with probes against various alpha subunits revealed a marked differential expression pattern. The alpha 1 subunit gene is expressed mainly in the bipolar and horizontal cell layer, the alpha 2 gene in the amacrine and ganglion cell layer, and the alpha 4 gene in a subpopulation of amacrine cells. beta subunit mRNA is present diffusely throughout the entire inner nuclear layer and in the ganglion cell layer. The monoclonal antibody bd 17 (against beta 2/beta 3 subunits) stained subpopulations of GABAergic and glycinergic amacrine cells as well as some ganglion cells and bipolar cells. Immunoreactivity was not restricted to synaptic input sites. In the outer plexiform layer bipolar cell dendrites were immunoreactive; in the inner plexiform layer mainly amacrine and ganglion cell processes were labeled, and bipolar cell axons appeared unstained. The results demonstrate a strong heterogeneity of GABAA receptors in the retina.