The quantification and mRNA expression levels of cochlear synapses in C57BL/6j mice following repeated exposure to noise

Purpose: This study aimed to examine the impact of repeated noise exposure on the quantification and mRNA expression levels of cochlear synapses.

Methods: Measurements were conducted at baseline, 1 day, and 14 days post-exposure to 88 or 97 dB SPL noise (2 h/day for 7 days, frequency range 2-20 kHz). Auditory brainstem responses (ABRs), immunofluorescence and quantitative real-time PCR (qRT-PCR) were used to examine the results.

Results: 1. Exposure to 88 dB SPL caused minimal changes in ABRs, ribbon morphology and medial olivocochlear (MOC) efferent synapses; elevation of synaptophysin(SYP) and α9α10 nAchR mRNA levels were observed. 2. Exposure to 97 dB SPL caused threshold shift and synaptopathy of ribbon and MOC; downregulation of α10nAchR, SYP and ctbp2 mRNA levels were observed.

Conclusion: Noise-induced cochlear synaptic degeneration involves both afferent and efferent synaptopathy.