Neuroplasticity of auditory neurons in conductive hearing loss

Abstract

　　We investigated the neuroplasticity of auditory neurons (ANs) in adult mice with conductive hearing loss (CHL). Eight-week-old male C57BL/6 mice were bilaterally earplugged for 4 weeks (CHL (+) group) and allowed to survive for a further 4 weeks after removal of the earplugs (CHL (+/－) group). The control mice (CHL (－) group) did not undergo the earplugging process. The ABR threshold was significantly elevated across all tested frequencies in the earplugged mice. After removal of the earplugs, the threshold shifts recovered fully. The ABR amplitude of peak 1 significantly decreased and the latency significantly increased for all tested frequencies in the CHL (+) mice as compared to the CHL (－) mice. These changes were only partially restored in the CHL (+/－) mice. Auditory deprivation had no significant impact on the survival of the hair cells and ANs. However, the synapses and myelin were significantly damaged, and the neuronal sizes of the ANs were significantly decreased in the CHL (+) mice. These changes also recovered only partially in the CHL (+/－) mice as compared to the CHL (+) mice. These results suggest that auditory activities are required to maintain peripheral auditory synapses and myelination.