Effect of Endolymphatic Hydrops on Sound Transmission in Live Guinea Pigs Measured with a Laser Doppler Vibrometer.

Chen-Ru Ding,Lin Yang,Xin-Da Xu,Xian-Hao Jia,Dong-Dong Ren,Fang-Lu Chi,Xiang Liu,Xiang Cheng,Xin-Wei Wang,Bu-Sheng Tong

doi:10.1155/2016/8648297

Abstract

Objective. This study aimed at describing the mechanism of hearing loss in low frequency and the different dynamic behavior of the umbo, the stapes head, and the round window membrane (RWM) between normal guinea pigs and those with endolymphatic hydrops (EH), using a laser Doppler vibrometer (LDV). Methods. Cochlear sections were stained with hematoxylin and eosin (HE) to evaluate the hydropic ratio (HR). Auditory brainstem responses (ABR) and whole-mount immunostaining were measured. Displacement of the umbo, stapes head, and RWM in response to ear-canal sound was evaluated using a LDV. Results. Mean HR values in EH model of all the turns are larger than the control group. The ABR threshold of the EH group was significantly higher than that of the control. Strong positive correlation was found between HR at apical turn and ABR threshold elevation at 1000 Hz and at subapical turn and ABR threshold elevation at 2000 Hz. FITC-phalloidin immunostaining of the cochlear basilar membrane in the apical, subapical, and suprabasal turns showed missing and derangement stereocilia of third-row outer hair cells. The umbo, stapes head, and RWM displacement in ears with EH was generally lower than that of normal ears. The EH-induced differences in stapes head and RWM motion were significant at 0.5 kHz. Conclusion. The LDV results suggested that the higher inner ear impedance in EH affected the dynamic behavior of the two opening windows of the cochlea and then reduced the vibration of the ossicular chain by increasing the afterload, resulting in acoustic dysfunction. The vibration reduction mainly occurred at low frequencies, which has related with the morphology changes of the apical and subapical turns in EH model.

Highlights

In mammals, sound waves stimulate the cochlea via the vibration of the ossicular chain
We reported the effect of endolymphatic hydrops of live guinea pigs on the Auditory brainstem responses (ABR) threshold, morphology changes, and movements of the umbo, stapes head, and round window membrane (RWM) under 85 dB SPL pure tone stimuli in the external auditory canal in this study
We had explored the mechanism of the hearing loss in EH model, which showed displacements reduction of the umbo, stapes head, and RWM was greater at low frequency (

Summary

Introduction

Sound waves stimulate the cochlea via the vibration of the ossicular chain. The opposite vibrating phase between the round window and the oval window causes relative motion between the endolymph and perilymph and produces displacement waves travelling on the spirally basilar membrane. Since Hallpike and Carins [4] described the presence of EH in the temporal bones of patients with Meniere’s Disease (MD) in 1938, EH has generally been accepted as the basic histopathologic sign of this disease, which is an intractable disease that results in hearing loss that is often fluctuating and initially involves the low frequencies [5]. In the study by Lee et al [3], spontaneous low frequency air-bone gaps in evaluating hearing sensitivity were found in approximately 13.9% of patients with Meniere’s Disease and may indirectly

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Discussion

Conclusion