Differential expression of the α9 nicotinic acetylcholine receptor subunit in neonatal and adult cochlear hair cells

The expression of the α9 nicotinic acetylcholine receptor (nAChR) subunit was investigated in perinatal and adult rat cochleae using [³⁵S] labeled cRNA in situ hybridization techniques. In the adult, α9 expression showed both longitudinal and radial gradients. The highest expression occurs over outer hair cells (OHCs) in basal regions, and particularly, OHCs in row 1. In contrast, expression over IHCs is lowest in basal regions and highest in apical regions. During embryonic and postnatal ages, the pattern of α9 expression differs. Expression of α9 was nearly equivalent over IHCs and OHCs. Additionally, the greater epithelial ridge, which is adjacent to IHCs before birth, shows a high level of α9 expression. These data are consistent with current models of efferent synaptogenesis and suggest that the expression of the α9 nAChR may be influenced by the arrival of efferent axons.