Developmental mRNA expression of the α10 nicotinic acetylcholine receptor subunit in the rat cochlea

A recently discovered α10 subunit of the nicotinic acetylcholine receptor (nAChR) family is believed to form a heteromeric receptor with the α9 nAChR subunit in auditory hair cells. In the present study, the α10 nAChR subunit expression in the developing and adult rat inner ear was analyzed by PCR and localized using isotopic in situ hybridization. Unlike the α9 subunit, the α10 subunit was not detected at embryonic day 18 (E18). From E21 through postnatal day 15 (P15), the α10 subunit was localized over both inner hair cell (IHC) and outer hair cell (OHC) regions, but in the mature cochlea detectable levels of α10 mRNA were found only over the OHC region. From E21 through adult ages, there was also a small but consistent basal to apical gradient of α10 expression; that is, higher levels in basal regions and lower levels in apical regions. Previously, we detected the α9 nAChR subunit over IHCs as early as E18 and throughout adult ages with a clear basal-apical gradient of expression. Our studies raise the question of whether the α9 and α10 subunits are differentially regulated during embryonic and postnatal development.