Myelin damage and transmission of auditory signals


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The link between exposure to excessive noise and hearing loss has been clearly established. However, the mechanisms underlying this effect are not yet well understood.

A team of researchers from the Department of Cell Physiology and Pharmacology, and Electron Microscopy Facility at the University of Leicester (United Kingdom) studied how damage to the myelin sheaths of the auditory nerve (AN), after acoustic overexposure (AOE), affects the transmission of auditory signals in a rat model. The study was led by Dr Martine Hamann, lecturer in Neurosciences at the university, and was part of a 3-year PhD studentship.

Study rats were anesthetized and exposed to 110 dB SPL single-tone frequency sound for a total of 9 hours; 3 hours per day over 3 consecutive days. Age-matched control animals from the same litter were similarly anesthetized but were not exposed to AOE. Hearing threshold elevations were determined in tested animals following exposure, and myelin sheaths were examined microscopically. According to the authors, their findings provide evidence for dysmyelination of AN axons that contributes to impaired action potential propagation.

“This new study is particularly important because it allows us to understand the pathway from exposure to loud sound leading to the hearing loss. We now have a better idea about the mechanisms behind the auditory signals failing to get transmitted accurately from the cochlea to the brain. Consequently, targeting myelin and promoting its repair after exposure to loud sound could be proven effective in noise-induced hearing loss,” Dr Hamann explains.

Source: Eurekalert; Tagoe T et al. Auditory nerve perinodal dysmyelination in noise-induced hearing loss. The Journal of Neuroscience. 2014;34(7):2684-8.