NEUROCHEMICAL SIGNATURES REVEALED BY GLUTAMINE LABELING IN THE CHICKEN RETINA

Postembedding immunocytochemistry was used to determine the retinal di stribution of the amino acid glutamine, and characterize amino acid si gnatures in the avian retinal ganglion cell layer. Glutamine is a pote ntial precursor of glutamate and some glutamatergic neurons may use th is amino acid to sustain production of glutamate for neurotransmission . Ganglion cells, cells in the inner nuclear layer, and some photorece ptors exhibited glutamine immunoreactivity of varying intensity. Gangl ion cells demonstrated the highest level of immunoreactivity which ind icates either slow glutamine turnover or active maintenance of a large standing glutamine pool relative to other glutamatergic neurons. Mull er's cells in the avian retina are involved in glutamate uptake and ca rbon recycling by the rapid conversion of glutamate to glutamine, thus explaining the low glutamate and high glutamine immunoreactivity foun d throughout Muller's cells. Most chicken retinal ganglion cells are g lutamate (E) and glutamine (Q) immunoreactive but display diverse sign atures with presumed functional subsets of cells displaying admixtures of E and Q with GABA (gamma) and/or glycine (G). The four major gangl ion cell signatures are (1) EQ; (2) EQ gamma; (3) EQG; and (4) EQ gamm a G.