Immunocytochemical localization of glutamate, GABA and glycine in the human retina

Abstract

The amino acids glutamate, GABA and glycine, putative neurotransmitters in the mammalian retina, were localized immunocytochemically in the human eye. The posterior two thirds of an eye were immersion-fixed in a mixture of glutaraldehyde and paraformaldehyde in sodium phosphate buffer. Semithin sections of the retina were obtained after osmication, dehydration and embedding in an epoxy resin. Strong glutamate-like immunoreactivity (PAP method) was observed in ganglion cells and processes including axons in the nerve fiber layer, in the perikaryal cytoplasm and processes of many bipolar cells, and in round structures probably representing rod spherules in the inner plexiform layer. Numerous structures in the inner and outer plexiform layers were moderately labeled, as were photoreceptor inner segments and perikaryal cytoplasm (rods stronger than cones), and some bipolar and amacrine cells. Glutamate immuno-reactivity could not be detected in Muller cells. Strong GABA-like immunoreactivity appeared in many amacrine cells, varicosities in the inner plexiform layer and small cells in the ganglion cell layer, and a few cells resembling ganglion cells. Strong glycine-like immunoreactivity was seen in varicosities in the inner plexiform layer, and moderate to strong immunoreactivity in populations of both amacrine and bipolar cells. Glycine immunostaining was occasionally seen in small cells of the ganglion cell layer.