The α9 nicotinic acetylcholine receptor (α9-nAChR) subunit is expressed in the vestibular and auditory periphery, and its loss of function could compromise peripheral input from the predominantly-cholinergic efferent vestibular system (EVS). A recent study has shown that α9-nAChRs play an important role in short-term vestibulo-ocular reflex (VOR) adaptation. We hypothesise that α9-nAChRs could also be important for other forms of vestibular plasticity, such as that needed for VOR recovery after vestibular organ injury. We measured the efficacy of VOR compensation in α9 knockout mice. These mice have deletion of most of the gene (chrna9) encoding the nAChR and thereby lack α9-nAChRs. We measured the VOR gain (eye-velocity/head-velocity) in 20 α9 knockout mice and 16 cba129 controls. We measured the sinusoidal (0.2-10Hz, 20-100°/s) and transient (1500-6000°/s2) VOR in complete darkness before (baseline) unilateral labyrinthectomy (UL), and then 1, 5 and 28 days after UL. On day 1 after UL, cba129 mice retained ~50% of their initial function for contralesional rotations, whereas α9 knockout mice only retained ~20%. After 28 days, α9 knockout mice had ~50% lower gain for both ipsilesional and contralesional rotations compared to cba129 mice. Cba129 mice regained ~75% of their baseline function for ipsilesional and ~90% for contralesional rotations. In contrast, α9 knockout mice only regained ~30% and ~50% function, respectively, leaving the VOR severely impaired for rotations in both directions. Our results show that loss of α9-nAChRs severely affects VOR compensation, suggesting that complimentary central and peripheral EVS-mediated adaptive mechanisms might be affected by this loss.
- mammalian efferent vestibular system
- vestibular compensation
- vestibular plasticity
- vestibulo-ocular reflex
- α9 knockout mice
- Copyright © 2015, Journal of Neurophysiology