GABA-like Immunoreactivity in the Cat Retina: Electron Microscopy

The synaptic organization of the cat retina was studied with antibodies against the GABA-GA (glutaraldehyde)-BSA (bovine serum albumin) complex. The postembedding technique combined with immunogold labelling ensured ultrastructural preservation and made identification of synapses possible. The most common putative GABA-ergic synapses in the inner plexiform layer were amacrine-to-bipolar-cell synapses followed by amacrine-to-ganglion-cell and amacrine-to-amacrine-cell synapses. GABA-immunoreactive amacrine cells received most of their synaptic input from bipolar cells followed by other amacrine cells. Synapses between two labelled amacrine cells were common. Rod bipolar cells were the predominant input source and also the preferred output target of GABA-labelled amacrine cells. OFF- and ON-ganglion cells received putative GABA-ergic synapses at their dendrites in laminas a and b, respectively, and also at their somata. In the outer plexiform layer, synapses of interplexiform cells onto bipolar cell dendrites expressed GABA-like immunoreactivity. In both the cone pedicles and the rod spherules, GABA-like immunoreactivity was observed in horizontal cell processes.