Nicotinic acetylcholine receptor subunit mRNA expression in adult and developing rat medullary catecholamine neurons

Nicotinic acetylcholine receptors (nAChRs) mediate numerous visceral functions via medullary catecholamine (CA) neurons found in the nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (DMV), and ventrolateral medulla (VLM). However, the nAChR subtypes involved are not known. We have therefore characterized expression of nine nAChR subunit mRNAs in adult and developing rat medullary CA nuclei using combined isotopic/nonisotopic in situ hybridization. Tyrosine hydroxylase (TH) mRNA, the CA-synthesizing enzyme, was used as a marker for CA neurons, because these nuclei consist of heterogeneous populations of cells. Subunit mRNA expression varied within and between nuclei, along the rostrocaudal axis, between cell types, and across development. All CA neurons expressed beta 2 mRNA, whereas alpha 2 mRNA was completely absent. alpha 6 And beta 3 mRNA expression were restricted mainly to the VLM. alpha 4, alpha 5, And alpha 7 mRNA expression was significantly greater in the rostral than in the caudal VLM. alpha 3 And beta 4 mRNAs were highly expressed in the dorsal region of the NTS, whereas dense alpha 7 mRNA expression was restricted to the DMV and ventral NTS. The remaining subunit mRNAs were detected to some degree in both DMV and NTS. Except for alpha 4 mRNA, which peaked prenatally, expression levels of subunit transcripts in the NTS and DMV were lower during development compared with adults. In the VLM, alpha 3, alpha 4, and alpha 5 mRNAs expression peaked perinatally, whereas alpha 6 and beta 3 levels increased with age. These variations in nAChR subunit mRNA expression suggest that different receptor subtypes may produce function-specific regulation of medullary CA systems.