Bipolar cells of the chick retina containing alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors.

Abstract

Two cDNA clones for nicotinic acetylcholine receptor (nAChR) subunits sensitive to alpha-bungarotoxin (alpha-Bgt) have been isolated, the so-called alpha-Bgt binding proteins alpha 1 (or alpha 7 nAChR subunit) and alpha 2 (or alpha 8 nAChR subunit). Immunohistochemical experiments have shown that both alpha 7 and alpha 8 subunits, as well as subunits insensitive to alpha-Bgt (beta 2 and alpha 3), are present in amacrine and ganglion cells of the chick retina. However, only the alpha 8 subunit was observed in presumptive bipolar cells. The present study investigated in detail the pattern of distribution of the bipolar cells containing the alpha 8 nAChR subunit and its relation to the pattern of distribution of bipolar cells immunoreactive to protein kinase C (PKC). Presumptive alpha 8- and PKC-like immunoreactive (alpha 8-LI and PKC-LI) bipolar cells were observed sending their dendrites to the outer plexiform layers and their axons to the inner plexiform layer. Whereas alpha 8-LI bipolar cells corresponded to 40-53% of the whole population of bipolar cells, PKC-LI bipolar cells represented only 6-8% of the same population. The soma sizes of the alpha 8-LI bipolar cells were slightly smaller (mean +/- S.D.; 4.9 +/- 0.8 microns) than the soma sizes of the PKC-LI bipolar cells (5.4 +/- 0.9 microns). Double-labeling experiments indicated that probably all PKC-LI bipolar cells also contain alpha 8-LI. This indicates that two distinct groups of cholinoceptive bipolar cells exist in the chick retina, one that contains PKC-LI, and another one that does not.