GABAAReceptor subunits have differential distributions in the rat retinae: In situ hybridization and immunohistochemistry

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Abstract
The distributions of nine different subunits of the gamma‐aminobutyric acidA (GABAA) receptor (α1, α2, α3, 5; β1, β2, β3; γ2; δ) were investigated in the rat retina using immunocytochemistry and in situ hybridization. With the exception of the α5 subunit, all subunits could be localized. Each subunit was expressed in characteristic strata within the inner plexiform layer (IPL). Some subunits (e.g., γ2) 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, GABAA 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 α2, β1, β2/3 and δ subunits, while dopaminergic amacrine cells express the α2, α3 and γ2 subunits. Dissociated rod bipolar cells express the γ2 subunits. In summary, this study provides evidence for the existence of multiple GABAA 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.