Scholze_2011_Dev.Neurobiol_71_390

Heteropentameric nicotinic acetylcholine receptors (nAChR) mediate fast synaptic transmission in ganglia of the autonomic nervous system. It is undisputed that alpha3 and beta4 are the predominant subunits in the superior cervical ganglion (SCG); however, reports on the presence of receptors that contain alpha4 have been controversial. Here, we have searched for the presence of alpha4-containing nAChRs in the postnatal rat and mouse SCG. We now show by immunoprecipitation combined with radioligand binding that alpha4-containing receptors constitute about 20% of hetero-oligomeric nAChRs in postnatal Day 3 (P3) mice. However, already by P9, the level of alpha4 approaches zero. In contrast, the number of alpha4-containing receptors is close to zero in the rat SCG at all times investigated. Deletion of the beta2 subunit by using alpha5beta2-double knockout (KO) mice removes all alpha4-containing receptors, suggesting that in the postnatal mouse SCG, alpha4 co-assembles only with beta2 but not with beta4. alpha4beta2 receptors are, on the other hand, up-regulated in the SCG of P3 alpha5beta4-double KO mice, where they make up about 50% of receptors that bind [(3) H]-epibatidine. Nonetheless, receptors on the surface of SCG neurons from alpha5beta4-double KO mice maintained for one to two days in culture comprise <10% of alpha4beta2 and >90% of alpha3beta2, as determined by patch clamp recordings with alpha4beta2- and alpha3beta2-specific ligands. We propose that in the P3 SCG of wild type mice, alpha3beta4 (+/-alpha5) represent about 62% of receptors, whereas 17% are alpha3beta2beta4, and 21% are alpha4beta2 (+/-alpha5) receptors.