GABA A Receptor subunits have differential distributions in the rat retinae: In situ hybridization and immunohistochemistry

The distributions of nine different subunits of the gamma‐aminobutyric acid A (GABA A ) receptor (α 1 , α 2 , α 3 , 5 ; β 1 , β 2 , β 3 ; γ 2 ; δ) were investigated in the rat retina using immunocytochemistry and in situ hybridization. With the exception of the α 5 subunit, all subunits could be localized. Each subunit was expressed in characteristic strata within the inner plexiform layer (IPL). Some subunits (e.g., γ 2 ) showed a ubiquitous distribution, while others (e.g., δ) were restricted to narrow sublayers. Double labeling experiments using different combinations of the subunit‐specific antibodies revealed colocalizations of subunits within individual neurons. Additionally, GABA A receptor subunits were mapped to distinct populations of retinal neurons by coapplication of defined immunocytochemical markers and subunit‐specific antibodies. Cholinergic amacrine cells were found to express the α 2 , β1, β 2/3 and δ subunits, while dopaminergic amacrine cells express the α 2 , α 3 and γ 2 subunits. Dissociated rod bipolar cells express the γ 2 subunits. In summary, this study provides evidence for the existence of multiple GABA A receptor subtypes in the retina. The distinct stratification pattern of the subunits in the IPL suggests that different functional circuits involve specific subtypes of GABAA receptors. © 1995 Wiley‐Liss, Inc.