The Medial Olivocochlear System Attenuates the Developmental Impact of Early Noise Exposure

Abstract

The early onset of peripheral deafness profoundly alters the functional maturation of the central auditory system. A prolonged exposure to an artificial acoustic environment has a similar disruptive influence. These observations establish the importance of normal patterns of sound-driven activity during the initial stages of auditory development. The present study was designed to address the role of cochlear gain control during these activity-dependent developmental processes. It was hypothesized that the regulation of auditory nerve activity by the medial olivocochlear system (MOCS) would preserve normal development when the immature auditory system was challenged by continuous background noise. To test this hypothesis, knock-out mice lacking MOCS feedback were reared in noisy or quiet environments and then evaluated with behavioral paradigms for auditory processing deficits. Relative to wild-type controls, noise-reared knock-out mice showed a decreased ability to process rapid acoustic events. Additional anatomical and physiological assessments linked these perceptual deficits to synaptic defects in the auditory brainstem that shared important features with human auditory neuropathy. Our findings offer a new perspective on the potentially damaging effects of environmental noise and how these risks are ameliorated by the protective role of MOCS feedback.

Deterioration of the Medial Olivocochlear Efferent System Accelerates Age-Related Hearing Loss in Pax2-Isl1 Transgenic Mice

“…The MOC efferent innervation is important for the maintenance and function of OHCs. The activation of the MOC system enhances auditory processing of distracting noise [56][57][58], and it may thus protect the inner ear from acoustic trauma [59][60][61]. MOC terminals are the endings of the efferent fibers, which make OHCs hyperpolarized when activated.…”

Sound-Evoked Olivocochlear Activation in Unanesthetized Mice

“…Collectively, these descending pathways are believed to mediate a number of adaptive phenomena such as signal-innoise detection (de Boer and Thornton 2008), tuning specificity (Bauerle et al 2011;Yan et al 2005), experience-dependent perceptual reweighting (Bajo et al 2010), and protection of the inner ear from acoustic trauma (Lauer and May 2011;Maison and Liberman 2000). Of the three systems, the olivocochlear projections are the best understood, thanks in part to recent studies that have taken advantage of the genetic tools uniquely available in the mouse.…”

Functional Development of the Vestibular System

“…Nicotinic α9 ACh receptor subunits are almost exclusively present in the inner ear and have been found in both auditory hair cells and vestibular hair cells (Lustig et al, 1999;Gomez-Casati et al, 2005;Kong et al, 2006), colocalized with potassium channels of the SK or BK type (Glowatzki and Fuchs, 2000;Kong et al, 2007). Although there is evidence that auditory efferents play a role in protecting against noise damage in the inner ear (Maison et al, 2002;Lauer and May, 2011), and despite similarities between the two systems, the role of vestibular efferents has remained elusive to date (Sadeghi et al, 2007;2009). …”