NICOTINIC ACETYLCHOLINE-RECEPTORS IN THE GROUND-SQUIRREL RETINA - LOCALIZATION OF THE BETA-4 SUBUNIT BY IMMUNOHISTOCHEMISTRY AND IN-SITU HYBRIDIZATION

Immunohistochemical and in situ hybridization techniques were used to localize the beta 4 subunit of the neuronal nicotinic acetylcholine re ceptors (nAChRs) in the ground squirrel retina. The beta 4 nAChR subun it was detected in both transverse and horizontal sections of the reti na using a subunit-specific antiserum and the avidin-biotin complex te chnique. Two bands of labeled processes were seen in the inner plexifo rm layer, corresponding approximately to the laminae where the choline rgic cells arborize. Labeled cells were found in the ganglion cell lay er and the inner third of the inner nuclear layer. The cells in the ga nglion cell layer were medium- to large-sized and were frequently obse rved to give rise to axon-like processes. Most of the labeled neurons in the inner nuclear layer were small presumptive amacrine cells, but a few medium-to-large cells were also labeled. These could constitute a different class of amacrine cells or displaced ganglion cells. The l atter possibility is supported by the existence of nAChR-containing di splaced ganglion cells in the avian retina. in situ hybridization with a S-35-labeled cRNA probe revealed the expression of mRNA coding for the nAChR beta 4 subunit in the ganglion cell layer and the inner thir d of the inner nuclear layer. This finding confirmed the immunohistoch emical data of the cellular localization of beta 4 nAChR subunit. Thes e results indicate that the beta 4 nAChR subunit is expressed by speci fic subtypes of neurons on the ground squirrel retina. As the expressi on of that particular nAChR subunit appears to be very limited in the brain, the present data suggest that the retina might represent a usef ul model to study the function of nAChRs containing the beta 4 subunit .