IMMUNOCYTOCHEMICAL LOCALIZATION OF THE AMINO-ACID NEUROTRANSMITTERS IN THE CHICKEN RETINA

Postembedding immunocytochemistry was used to determine the cellular l ocalization of the amino acid neurotransmitters glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine in the avian retina. The t hrough retinal pathway was glutamatergic, with all photoreceptors, bip olar cells, and ganglion cells being immunoreactive for glutamate. Bip olar cells displayed the highest level of glutamate immunoreactivity, with the cell bodies terminating just below the middle of the inner nu clear layer. All lateral elements, horizontal cells, amacrine cells, a nd interplexiform cells were immunoreactive for glycine or GABA. The G ABAergic neurons consisted of two classes of horizontal cells and amac rine cells located in the lower part of the inner nuclear layer. GABA was also localized in displaced amacrine cells in the ganglion cell la yer, and a population of ganglion cells that co-localize glutamate and GABA. Both the horizontal cells and GABAergic amacrine cells had high levels of glutamate immunoreactivity, which probably reflects a metab olic pool. At least two types of horizontal cells in the avian retina could be discriminated on the basis of the presence of aspartate immun oreactivity in the H2 horizontal cells. (Glycine was contained in a su bclass of amacrine cells, with their cell bodies located between the b ipolar cells and GABAergic amacrine cells, two subclasses of bipolar c ells, displaced amacrine cells in the ganglion cell layer, and ganglio n cells that colocalize glutamate and glycine. Glycinergic amacrine ce lls had low levels of glutamate. We have also identified a new class o f glycinergic interplexiform cell, with its stellate cell body located in the middle of the inner nuclear layer among the cell bodies of bip olar cells. Neurochemical signatures obtained by analyzing data from s erial sections allowed the classification of subclasses of horizontal cells, bipolar cells, amacrine cells, and ganglion cells.