Vestibular hair cells of the chick express the nicotinic acetylcholine receptor subunit α9

The efferent cholinergic pathways to the vestibular periphery have yet to be fully characterized. While the nicotinic acetylcholine receptor subunit (nAChR) α9 is now regarded as the principle receptor for efferent cholinergic signaling to the organ of Corti, there is still uncertainty over how the more complex efferent effects of the labyrinth are produced. Recent experimental work has demonstrated that the nAChR α9 is present in the vestibular end-organs of the rat and mouse, suggesting that α9 may be one of the mediators of efferent cholinergic signaling in the vestibular periphery as well. In this experiment, we sought to determine whether α9 was also present in the vestibular end-organs of the chick. A homologue of α9 has been cloned recently from the chick cochlea. Using reverse transcription polymerase chain reaction (RT-PCR), individual vestibular end-organ preparations, including posterior ampulla, combined horizontal and superior ampulla, saccule, utricle, and the vestibular ganglion were screened for α9 messenger RNA expression. In each end-organ and the vestibular ganglion, a cDNA of the expected size was obtained by RT-PCR and was confirmed to be α9 by sequence analysis. Further, α9 mRNA was identified by RT-PCR from individually isolated type I and type II vestibular hair cells (single-cell RT-PCR). Lastly, insitu hybridization using digoxigenin-labeled α9 riboprobes confirmed the presence of α9 in type I and type II hair cells throughout the vestibular periphery. These results demonstrate the expression of α9 in the vestibular end-organs of the chick, and lend further support for the role of α9 as a mediator of efferent cholinergic signaling in vestibular hair cells.