Abstract

By acting through retinal nicotinic acetylcholine receptors (nAChRs), acetylcholine plays an important role in the development of both the retina and central visual pathways. Ligand binding and immunoprecipitation studies with subunit-specific antibodies showed that the expression of αBungarotoxin (αBgtx) and high-affinity epibatidine (Epi) receptors is regulated developmentally and increases until postnatal day 21 (P21). The increase in Epi receptors is caused by a selective increase in the subtypes containing the α2, α4, α6, β2, and β3 subunits. Immunopurification studies revealed three major populations of Epi receptors on P21: α6^* receptors (26%), which contain the α6β3β2, α6α4β3β2, and α6α3/α2β3β2 subtypes; α4(non-α6)^* receptors (60%), which contain the α2α4β2 and α4β2 subtypes; and (non-α4/non-α6)^* receptors (14%), which contain the α2β2/β4 and α3β2/β4 subtypes. These three populations can be pharmacologically discriminated using αconotoxin MII, which binds the α6^* population with high affinity. In situ hybridization showed that the transcripts for all of the subunits are heterogeneously distributed throughout retinal neurons at P21, with α3, α6, and β3 transcripts preferentially concentrated in the ganglion cell layer, α5 in the inner nuclear layer, and α4 and β2 distributed rather homogeneously. To investigate whether nAChR expression is affected by visual experience, we also studied dark-reared P21 rats. Visual deprivation had no effect on the expression of αBgtx receptors or the developmentally regulated Epi receptors containing the α2, α6, and/or β3 subunits but significantly increased the expression of the Epi receptors containing the α4 and β2 subunits. Overall, this study demonstrates that the retina is the rat neural region that expresses the widest array of nAChR subtypes. These receptors have a specific distribution, and their expression is finely regulated during development and by visual experience.