It is widely accepted that even a single acute noise exposure at moderate intensity that induces temporary threshold shift (TTS) can result in permanent loss of ribbon synapses between inner hair cells and afferents. However, effects of repeated or chronic noise exposures on the cochlear synapses especially medial olivocochlear (MOC) efferent synapses remain elusive. Based on a weeklong repeated exposure model of bandwidth noise over 2-20 kHz for 2 hours at seven intensities (88 to 106 dB SPL with 3 dB increment per gradient) on C57BL/6J mice, we attempted to explore the dose-response mechanism of prolonged noise-induced audiological dysfunction and cochlear synaptic degeneration. In our results, mice repeatedly exposed to relatively low-intensity noise (88, 91, and 94 dB SPL) showed few changes on auditory brainstem response (ABR), ribbon synapses, or MOC efferent synapses. Notably, repeated moderate-intensity noise exposures (97 and 100 dB SPL) not only caused hearing threshold shifts and the inner hair cell ribbon synaptopathy but also impaired MOC efferent synapses, which might contribute to complex patterns of damages on cochlear function and morphology. However, repeated high-intensity (103 and 106 dB SPL) noise exposures induced PTSs mainly accompanied by damages on cochlear amplifier function of outer hair cells and the inner hair cell ribbon synaptopathy, rather than the MOC efferent synaptic degeneration. Moreover, we observed a frequency-dependent vulnerability of the repeated acoustic trauma-induced cochlear synaptic degeneration. This study provides a sight into the hypothesis that noise-induced cochlear synaptic degeneration involves both afferent (ribbon synapses) and efferent (MOC terminals) pathology. The pattern of dose-dependent pathological changes induced by repeated noise exposure at various intensities provides a possible explanation for the complicated cochlear synaptic degeneration in humans. The underlying mechanisms remain to be studied in the future.
机构:
The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
LIU Ke
ZHAO Ning
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机构:
The Department of Otolaryngology, The First Affiliated Hospital of China Medical University
China Medical UniversityThe Institute of Otolaryngology, PLA General Hospital
ZHAO Ning
SHI Chuang
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机构:
The Department of Otolaryngology, The First Affiliated Hospital of China Medical University
China Medical UniversityThe Institute of Otolaryngology, PLA General Hospital
SHI Chuang
WU Nan
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The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
WU Nan
LIU Huizhan
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机构:
The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
LIU Huizhan
ZHANG Yue
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The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
ZHANG Yue
YANG Weiyan
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机构:
The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
YANG Weiyan
YANG Shiming
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机构:
The Institute of Otolaryngology, PLA General HospitalThe Institute of Otolaryngology, PLA General Hospital
机构:
Department of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
Department of Otolaryngology Head and Neck surgery,Shiyan Taihe HospitalDepartment of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
SHI Chuang
SHI Lei
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机构:
Department of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical UniversityDepartment of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
SHI Lei
JIANG Xuejun
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Department of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical UniversityDepartment of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
JIANG Xuejun
YANG Shiming
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机构:
Department of Otolaryngology Head and Neck surgery,Institute of Otolaryngology,Chinese PLA General HospitalDepartment of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
YANG Shiming
LIU Ke
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机构:
Department of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University
Department of Otolaryngology Head and Neck surgery,Institute of Otolaryngology,Chinese PLA General HospitalDepartment of Otolaryngology Head and Neck Surgery,The First Affiliated Hospital of China Medical University