Efferent control of hearing sensitivity and protection via inner ear supporting cells

Abstract

It is well-known that medial olivocochlear (MOC) efferent nerves innervate outer hair cells (OHCs) and inhibit OHC electromotility to control hearing sensitivity. Here, we report that the MOC nerve fibers associated with MOC neurotransmitter acetylcholine (ACh) receptors and presynaptic vesicular acetylcholine transporters (VAChT) also innervated the cochlear supporting cells (SCs). Application of ACh could evoke inward currents in SCs and reduced gap junctions (GJs) between them with long-lasting effect. We further found that uncoupling of GJs between SCs shifted OHC electromotility to the left hyperpolarization direction and enhanced the direct effect of ACh on OHC electromotility. Diminution of this control by deficiency of GJs between SCs compromised the regulation of active cochlear amplification and increased susceptibility to noise. These data suggest that the MOC efferent system has functional innervations with SCs. Such efferent innervation may have an important role in the protection of hearing from noise and slow efferent effect.