Immunoelectron microscopic observation of cells in the rat retinal containing gamma-aminobutyric acid and catecholamine.

Interactions between gamma-aminobutyric acid (GABA)- and catecholamine (CA)-containing cells in the rat retina was revealed by a double-labeling immunocytochemical technique using the antisera to GABA- and CA-synthesizing enzymes, such as tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT). At the light microscopic level, GABA-, TH- and PMNT-immunoreactive (GABA-, TH- and PMNT-IR) amacrine cell bodies and their processes appeared in the inner nuclear layer and the inner plexiform layer, respectively. By electron microscopy observation, in the inner plexiform layer, GABA-, TH- or PMNT-IR amacrine cell processes were found making synaptic contacts with the axon terminals of immunonegative bipolar cells or with the processes of immunonegative amacrine cells. TH-IR amacrine cell processes formed synapse-like contacts with the GABA-IR amacrine cell perikarya and processes. In contrast, GABA-IR amacrine cell processes formed symmetric synaptic contacts onto the TH-IR as well as PNMT-IR amacrine cell processes. From these findings, it appears that the GABA- and CA-containing amacrine cells may interact with each other and play some important role in regulating the activities of bipolar cells and other unknown amacrine cells in the rat retina.