IMMUNOHISTOCHEMICAL LOCALIZATION OF GABA(A) RECEPTORS IN THE SCOTOPIC PATHWAY OF THE CAT RETINA

The distribution of GABA(A) receptors in the inner plexiform layer of cat retina was studied using monoclonal antibodies against the beta2/beta3 subunits. A dense band of receptor labeling was found in the inner region of the inner plexiform layer where the rod bipolar axons terminate. Three forms of evidence indicate that the GABA(A) receptor labeling is on the indoleamine-accumulating, GABAergic amacrine cell that is synaptically interconnected with the rod bipolar cell terminal. (1) Electron microscopy showed that the anti-GABA(A) receptor antibody (62-3G1) labeled profiles that were postsynaptic to rod bipolar axons and made reciprocal synapses. (2) Indoleamine uptake (and the subsequent autofluorescence) combined with GABA(A) receptor immunohistochemistry showed co-localization of the two markers in half of the receptor-positive amacrine cells. (3) Double labeling demonstrated that half of the receptor-positive somata also contained GABA. These results indicate that a GABAergic amacrine cell interconnected with the rod bipolar cell, most likely the so-called A17 amacrine cell, itself bears GABA(A) receptors.