Three subtypes of alpha-bungarotoxin-sensitive nicotinic acetylcholine receptors are expressed in chick retina

Abstract

A recent report described the isolation of cDNA clones encoding alpha 7 and alpha 8 subunits of alpha-bungarotoxin-sensitive nicotinic ACh receptors (alpha BgtAChRs) from chick brain and demonstrated that they were related to, but distinct from, the alpha subunits of nicotinic ACh receptors (nAChRs) from muscles and neurons. Monoclonal antibodies against the two alpha BgtAChR subunits were used to demonstrate that at least two subtypes are present in embryonic day 18 chicken brain. The predominant brain subtype contains alpha 7 subunits, while a minor subtype contains both alpha 7 and alpha 8 subunits. Both subtypes may also contain other subunits. Here we report the results of immune precipitation studies and immunohistochemical studies of alpha BgtAChRs in the chick retina. In addition to the two subtypes found in brain, a new alpha BgtAChR subtype that contains alpha 8 subunits, but not alpha 7 subunits, was identified and was found to be the major subtype in chick retina. This subtype has a lower affinity for alpha-bungarotoxin (alpha Bgt) than does the subtype containing only alpha 7 subunits. Small amounts of this alpha 8 subtype were also detected in brain by labeling with higher concentrations of 125I-alpha Bgt than had been used previously. The subtype containing only alpha 7 subunits comprised 14% of the alpha BgtAChRs in hatchling chick retina. The subtype containing alpha 8 subunits (but no alpha 7 subunits) accounted for 69%, and the alpha 7 alpha 8 subtype accounted for 17%. Amacrine, bipolar, and ganglion cells displayed alpha 8 subunit immunoreactivity, and a complex pattern of labeling was evident in both the inner and outer plexiform layers. In contrast, only amacrine and ganglion cells exhibited alpha 7 subunit immunoreactivity, and the pattern of alpha 7 subunit labeling in the inner plexiform layer differed from that of alpha 8 subunit labeling. These disparities suggest that the alpha BgtAChR subunits are differentially expressed by different populations of retinal neurons. In addition, the distribution of alpha BgtAChR subunit immunoreactivity was found to differ from that of alpha-Bgt-insensitive nAChR subunits.

Nicotinic Acetylcholine Receptor Subtypes Expression during Rat Retina Development and Their Regulation by Visual Experience

“…We and others (Britto et al, 1992;Keyser et al, 1993;Gerzanich et al, 1995;Gotti et al, 1997b;Barabino et al, 2001) Table 2 and Fig. 1, A and B.…”

“…Biochemical and pharmacological studies using nicotinic ligands and subunit-specific polyclonal antibodies (Abs) have identified the presence of three ␣Bgtx-binding subtypes in chick retina, the homomeric ␣7 and ␣8 and the heteromeric ␣7-␣8 subtype (Keyser et al, 1993;Gotti et al, 1994Gotti et al, , 1997b.…”

Pharmacological Properties of α9α10 Nicotinic Acetylcholine Receptors Revealed by Heterologous Expression of Subunit Chimeras

“…The subunit composition of native ␣7-containing nAChRs is uncertain, but data from rat brain are expected to correspond predominantly to homomeric ␣7 (Chen and Patrick, 1997;Drisdel and Green, 2000). Data from chick brain are expected to represent binding to a mixed population ␣7, ␣8, and ␣7␣8 nAChRs (Keyser et al, 1993).…”

The role of nAChR‐mediated spontaneous retinal activity in visual system development

“…Extensive work using immunohistochemistry and in situ hybridization in chick, mouse, rat, and rabbit have identified several subunits of nAChRs in the retina. There is expression of several subunits that comprise heteromeric nAChRs in the IPL, including the ␣3-6 (and ␣8 in chick) and ␤2-4 subunits (Swanson et al, 1987;Hoover and Goldman, 1992;Keyser et al, 1993;Hamassaki-Britto et al, 1994;Cimino et al, 1995;Zoli et al, 1995;Vailati et al, 1999;Champtiaux et al, 2002). Both mRNA and protein have been localized to several cell types in the inner retina, including RGCs, amacrine cells, displaced amacrine cells, and bipolar cells.…”