The Functional and Morphological Changes by Noise without Causing Hearing Loss: A Comparison between Mice and Guinea Pigs

Abstract

Noise exposure is one of the most common causes for acquired sensorineural hearing loss (SNHL). Recent studies have demonstrated that low-level noise exposure can kill spiral ganglion neurons (SGNs) without causing permanent hearing threshold shift. The present study further investigated the dynamic changes of ribbons in the cochlea of guinea pigs and the impact of the noise-induced synaptic damage and the loss of SGNs on the temporal processing of the cochlea in both mice and guinea pigs. Unlike what was reported in mice, the initial loss of ribbon in guinea pigs (>60% at high frequency region) largely recovered within one month after the noise, which was consistent with the functional recovery in auditory sensitivity and cochlear response amplitude. However, temporal processing in guinea pigs and mice remained deteriorated long after the hearing threshold was recovered.