Neuroplasticity of auditory neurons in cochlear damage

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K24052
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0906:Surgery related to the biological and sensory functions and related fields
• Research Institution: National Defense Medical College (2020); Kitasato University (2019)
• Principal Investigator: Takaomi Kurioka 防衛医科大学校(医学教育部医学科進学課程及び専門課程、動物実験施設、共同利用研究施設、病院並びに防衛, 耳鼻咽喉科学, 講師 (30842728)
• Project Period (FY): 2019-08-30 – 2021-03-31
• Keywords: 内耳障害 / シナプス / 髄鞘 / 蝸牛神経 / 難聴

Outline of Final Research Achievements

We investigated the neuroplasticity of auditory neurons（ANs）in adult mice with conductive hearing loss（CHL）. Eight―week―old male 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 ABR threshold was sgnificantly elevated across all tested frequencies in the earplugged mice. After removal of the earplugs, the threshold shifts recovered fully. The ABR amplitude significantly decreased and the latency significantly increased for all tested frequencies in 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.

Free Research Field

耳科学

Academic Significance and Societal Importance of the Research Achievements

伝音難聴には真珠腫性中耳炎や慢性中耳炎などがあり，薬物治療や外科的治療が聴力回復に有用と考えられている。薬物治療や外科治療が伝音難聴の治療に有効であることは変わりないものの，長期間の伝音難聴に伴う蝸牛神経への電気刺激の減少は，不可逆的な蝸牛シナプス障害をきたす可能性がある。従って，臨床における伝音難聴においても，長期に放置した場合には蝸牛神経の機能が低下する懸念があることから，早期に外科的治療や補聴器装用で神経活動を維持することが重要であると考える。