Immunocytochemical and electrophysiological characterization of GABA receptors in the frog and turtle retina

The expression of GABA receptors (GABARs) was studied in frog and turtle re tinae. Using immunocytochemical methods, GABA(A)Rs and GABA(C)Rs were prefe rentially localized to the inner plexiform layer (IPL). Label in the IPL wa s punctate indicating a synaptic clustering of GABARs. Distinct, but weaker label was also present in the outer plexiform layer. GABA(A)R and GABA(C)R mediated effects were studied by recording electroretinograms (ERGs) and b y the application of specific antagonists. Bicuculline, the GABA(A)R antago nist, produced a significant increase of the ERG. Picrotoxin, when co-appli ed with saturating doses of bicuculline, caused a further increase of the E RG due to blocking of GABA(C)Rs. The putative GABA(C)R antagonist Imidazole -4-acidic acid (I4AA) failed to antagonize GABA(C)R mediated inhibition and , in contrast, appeared rather as an agonist of GABARs. (C) 2001 Elsevier S cience Ltd. All rights reserved.