Research Application of Laser-Induced Shock Wave for Studying Blast-Induced Cochlear Injury

Summary

Here, we describe experimental protocols for creating an animal model of blast-induced cochlear injury using laser-induced shock wave (LISW). Exposure of the temporal bone to LISW allows the reproduction of blast-induced cochlear pathophysiology. This animal model could be a platform for elucidating cochlear pathology and exploring potential treatments for blast injuries.

Abstract

The ear is the organ most susceptible to explosion overpressure, and cochlear injuries frequently occur after blast exposure. Blast exposure can lead to sensorineural hearing loss (SNHL), which is an irreversible hearing loss that negatively affects the quality of life. Detailed blast-induced cochlear pathologies, such as the loss of hair cells, spiral ganglion neurons, cochlear synapses, and disruption of stereocilia, have been previously documented. However, determining cochlear sensorineural deterioration after a blast injury is challenging because animals exposed to blast overpressure usually experience tympanic membrane perforation (TMP), which causes concurrent conductive hearing loss. To evaluate pure sensorineural cochlear dysfunction, we developed an experimental animal model of blast-induced cochlear injury using a laser-induced shock wave. This method avoids TMP and concomitant systemic injuries and reproduces the functional decline in the SNHL component in an energy-dependent manner after LISW exposure. This animal model could be a platform for elucidating the pathological mechanisms and exploring potential treatments for blast-induced cochlear dysfunction.

Introduction

Hearing loss and tinnitus are among the most prevalent disabilities, reported in up to 62% of veterans¹. Several blast-induced auditory complications, including sensorineural hearing loss (SNHL) and tympanic membrane perforation (TMP), have been reported in individuals exposed to blast overpressure². Moreover, research on individuals exposed to blasts suggests that blast exposure frequently results in defects in auditory temporal resolution, even when the hearing thresholds are within normal range, which is known as "hidden hearing loss (HHL)"³. It is well established that there is a subst....

Protocol

All experimental procedures were approved by the Institutional Animal Care and Use Committee of the National Defense Medical College (approval #18050) and performed in accordance with the guidelines of the National Institutes of Health and the Ministry of Education, Culture, Sports, Science, and Technology of Japan. All efforts were made to minimize the number of animals and their suffering.

1. Animals

1. Use 8-week-old male CBA/J mice to follow this protocol. Before the experiment, subject the mice to a hearing function test and endoscopic observation of the tympanic membrane to ensure normality.
2. Divide ....

Results

LISW waveform
The reproducibility of the LISW pressure waveform was measured 5x at 2.0 J/cm² as follows. The waveforms were generally similar and stable and showed a sharp increase with time width, peak pressure, and impulse of 0.43±0.4 µs, 92.1 ± 6.8 MPa, and 14.1 ± 1.9 Pa∙s (median ± SD), which corresponds to SW characteristics (Figure 1B). LISWs are characterized by a fast rise time, high peak pressure, short duration, and p.......

Discussion

This study aimed to validate a mouse model of blast-induced cochlear damage using LISW. Our findings demonstrated that following LISW application through the temporal bone, the exposed mice ear exhibited a consistent pathological and physiological decline in the cochlea, which was accompanied by an increase in LISW overpressure. These results indicate that this mouse model is appropriate for replicating various cochlear pathologies by adjusting the LISW output. Specifically, this LISW-induced cochlear dysfunction mouse m.......

Materials

Name	Company	Catalog Number	Comments
532 nm Q-switched Nd:YAG laser	Quantel	Brilliant b
ABR peak analysis software	Mass Eye and Ear	N/A	EPL Cochlear Function Test Suite
Acrylic resin welding adhesive	Acrysunday Co., Ltd	N/A
confocal fluorescence microscopy	Leica	TCS SP8
cryosectioning compound	Sakura	Tissue-Tek O.C.T
CtBP2 antibody	BD Transduction	#612044
Dielectric multilayer mirrors	SIGMAKOKI CO.,LTD	TFMHP-50C08-532	M1-M3
Digital oscilloscope	Tektronix	DPO4104B
Earphone	CUI	CDMG15008-03A
Hydrophone	RP acoustics e.K.	FOPH2000
Image J software plug-in	NIH	measurement line	https://myfiles.meei.harvard.edu/xythoswfs/webui/_xy-e693768_1-t_wC4oKeBD
Light microscope	Keyence Corporation	BZ-X700
Myosin 7A antibody	Proteus Biosciences	#25–6790
Neurofilament antibody	Sigma	#AB5539
Plano-convex lens	SIGMAKOKI CO.,LTD	SLSQ-30-200PM
Prism software	GraphPad	N/A	ver.8.2.1
Scanning electron microscope	JEOL Ltd	JSM-6340F
Small digital endoscope	AVS Co. Ltd	AE-C1
Ultrasonic jelly	Hitachi Aloka Medical	N/A
Variable attenuator	Showa Optronics Co.	N/A	Currenly avaiable successor: KYOCERA SOC Corporation, RWH-532HP II
Water-soluble encapsulant	Dako	#S1964