Morphology changes in the cochlea of impulse noise-induced hidden hearing loss

Abstract

Background

This study was focused on impulse noise induces hidden hearing loss.

Objectives

This study was designed to determine the morphology changes of noise-induced hidden hearing loss (NIHHL).

Method

Fifteen guinea pigs were divided into three groups: noise-induced hidden hearing loss (NIHHL) group, noise-induced hearing loss (NIHL) group, and normal control group. For the NIHHL group, guinea pigs were exposed to 15 times of impulse noise with peak intensity of 163 dB SPL at one time. For the NIHL group, animals were exposed to two rounds of 100 times impulse noise, and the time interval is 24 h. Auditory brain response (ABR) was tested before, immediately, 24 h, one week, and one month after noise exposure to evaluate cochlear physiology changes. One month after noise exposure, all guinea pigs in three groups were sacrificed, and basement membranes were carefully dissected immediately after ABR tests. The cochlea samples were observed by transmission electron microscopy (TEM) to find out the morphology changes.

Result

The ABR results showed that 15 times of impulse noise exposure could cause NIHHL in guinea pigs and 200 times could cause completely hearing loss. Impulse noise exposure could cause a dramatic increase of mitochondria in the inner hair cell. The structures of ribbon synapse and heminode were also obviously impaired compared to the normal group. The nerve fiber and myelin sheath remained intact after impulse noise exposure.

Conclusion

This research revealed that impulse noise could cause hidden hearing loss, and the changes in inner hair cells, ribbon synapse, and heminode all played a vital role in the pathogenesis of hidden hearing loss.

Chinese Abstract

背景：这项研究的重点是脉冲噪声引起的隐性听力损失。

目的：本研究旨在确定噪声引起的隐性听力损失（NIHHL）的形态变化。

方法：15只豚鼠分为三组：噪声引起的隐性听力损失(NIHHL) 组、噪声引起的听力损失 (NIHL) 组和正常对照组。对于 NIHHL组, 豚鼠暴露于 15 次脉冲噪声, 一次峰值强度为 163 dB SPL 。对于 NIHL 组, 动物暴露于两轮 100 次的脉冲噪声中, 时间间隔为 24 小时。听觉大脑反应 (ABR) 在噪声暴露之前、立即、24 小时、一周和一个月后进行测试, 以评估耳蜗生理变化。噪声暴露一个月后, 将三组豚鼠全部处死, ABR测试后立即仔细解剖基底膜。通过透射电子显微镜（TEM）观察耳蜗样品以找出形态变化。

结果：ABR结果显示, 15次脉冲噪声暴露可导致豚鼠的NIHHL, 200次可能导致完全听力损失。脉冲噪声暴露可能导致内毛细胞中线粒体的急剧增加。带状突触和半结的结构与正常组相比也明显受损。神经纤维和髓鞘脉在冲噪声暴露后保持完好。

结论：这项研究表明, 脉冲噪声可能导致隐性听力损失, 而内毛细胞、带状突触和半结的变化都在隐性听力损失发病机制中起重要作用。

Keywords:

• Hidden hearing loss
• inner hair cell
• ribbon synapse
• heminode
• impulse noise
• transmission electron microscopy

Acknowledgments

We would like to thank the Center for Biological Imaging (CBI), Institute of Biophysics, Chinese Academy of Sciences for the transmission electric microscope (TEM, FEI Tecnai Spirit120kV), and we are grateful to Professor Xixia Li for her help in making TEM samples and analyzing images.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This article was funded by the Active Health Project of the Ministry of Science and Technology [2020YFC2004001], NSFC grant [81470700], Special Youth Project of the PLA General Hospital [QNC19051], and Beijing Natural Science Foundation [7222185].