Unitary ototoxic gentamicin exposure may not disrupt the function of cochlear outer hair cells in mice

Abstract

Background: Previous study showed that mild ototoxic exposure could induce a reversible hearing impairment, and the loss and secondary incomplete recovery of cochlear ribbon synapses could be responsible for the hearing loss. However, it remains unclear whether cochlear outer hair cells’ (OHCs) functions are affected.

Objective: To verify whether the function of OHCs are also affected significantly after the ototoxic exposure.

Methods: Mice were injected intraperitoneally with 100 mg/kg concentration of gentamicin daily for 14 days. Distortion Product of Oto-acoustic Emission (DPOAE) was detected at control (pre-treatment), Day 0, day 4, day 7, day 14 and day 28 after the ototoxic exposure, respectively. In addition, the morphology of OHCs was observed by electron microscopy, OHCs has been counted by light microscopy, and the hearing thresholds were detected by auditory brain response (ABR).

Results: No significant changes have been found in OHC and OHC stereocilia among the experimental groups (p > .05). Further, no significant changes or loss was found in the morphology of OHCs either. However, we found ABR threshold elevations occurred after ototoxic exposure.

Conclusions: Unitary ototoxic gentamicin exposure may not disrupt the function of cochlear OHCs in mice, regardless of hearing loss identified in this ototoxic exposure.

Chinese abstract

背景: 以前的研究表明轻度耳毒性暴露可以诱导可逆性听力损伤, 耳蜗带突触的毁损和二次不完全恢复可能是听力损失的原因。然而, 仍然不清楚耳蜗外毛细胞 (OHCs) 功能是否受到影响。

目的: 验证在耳毒性接触后, OHCs的功能是否也受到显著影响。

方法: 每天给小鼠腹腔内注射浓度为100mg/kg的庆大霉素, 持续14天。分别对对照组 (预处理) 以及耳毒性接触后第0天、第4天、第7天、第14天和第28天检测耳声发射 (DPOAE) 的畸变产物。此外, 通过电子显微镜观察OHCs的形态, 通过光学显微镜计数OHCs, 并通过听觉脑反应 (ABR) 检测听力阈值。

结果: 在实验组中没有发现OHC和OHC毛细胞静纤毛的显著变化 (p> 0.05) 。此外, 也没有发现OHC的形态发生过显著变化或损失。然而, 我们发现ABR阈值升高发生于耳毒性接触之后。

结论: 单一耳毒性庆大霉素接触可能不会破坏小鼠耳蜗OHCs的功能, 尽管在这种耳毒性接触中发现到听力损失。

Keywords:

• Ototoxicty
• hearing loss
• distortion product of otoacoustic emission
• cochlea
• outer hair cells

Acknowledgements

This work was supported by the National High-Tech R&D Program of China for Young, the Beijing Municipal Commission of Education (TJSHG 201510025004), and the National Natural Science Foundation of China (NSFC) (81503372, 81271720). Also, this work was supported by the Youth Cultivation Project of Military Medical Science (16QNP133).

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was supported by the National High-Tech R&D Program of China for Young, the Beijing Municipal Commission of Education (TJSHG 201510025004), and the National Natural Science Foundation of China (NSFC) (81503372, 81271720). Also, this work was supported by the Youth Cultivation Project of Military Medical Science (16QNP133).