Differential development of α‐bungarotoxin‐sensitive and α‐bungarotoxin‐insensitive nicotinic acetylcholine receptors in the chick retina

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Abstract
The development of cells containing neuronal nicotinic receptors (nAChRs) in the chick retina was investigated by means of immunohistochemical techniques with antibodies directed against the α3 and α8 nAQhR subunits. The α3 subunit is one of the major α‐bungarotoxin‐insensitive nicotinic receptor subunits in the chick retina, whereas α8 appears to be the most common α‐bungarotoxin‐sensitive subunit in the same structure. α3‐like immunoreactivity (α3‐LI) was first detected in cells of the vitreal margin, on the embryonic day 4.5 (E4.5). α8‐LI was first detected in the same type of cell almost a day later. However, the processes of α8‐LI cells developed much faster than those of α3‐LI cells, generating visible stained laminae in the prospective inner plexiform, layer as early as E7. α3‐LI was only clearly seen in laminae of the inner plexiform layer by E12. By this date, both α3 and α8‐LI were seen in the same types of cells as in the adult retina, i. e., amacrines, displaced ganglion cells, and cells of the ganglion cell layer for α3‐LI; and amacrines, bipolar cells, and cells of the ganglion cell layer for α8‐LI, These results reveal different patterns of development of cells containing the α3 and α8 nAChR subunits in the chick retina and indicate that those nAChR subunits are expressed in the chick retina before choline acetyltransferase‐positive cells can be detected and well before synaptogenesis. These data also suggest that nAChRs may have a developmental function in the retina.