Abstract
Blast exposure can induce various types of hearing impairment, including permanent hearing loss, tinnitus, and hyperacusis. Herein, we conducted a detailed investigation of the cochlear pathophysiology in blast-induced hearing loss in mice using two blasts with different characteristics: a low-frequency dominant blast generated by a shock tube and a high-frequency dominant shock wave generated by laser irradiation (laser-induced shock wave). The pattern of sensorineural hearing loss (SNHL) was low-frequency- and high-frequency-dominant in response to the low- and high-frequency blasts, respectively. Pathological examination revealed that cochlear synaptopathy was the most frequent cochlear pathology after blast exposure, which involved synapse loss in the inner hair cells without hair cell loss, depending on the power spectrum of the blast. This pathological change completely reflected the physiological analysis of wave I amplitude using auditory brainstem responses. Stereociliary bundle disruption in the outer hair cells was also dependent on the blast’s power spectrum. Therefore, we demonstrated that the dominant frequency of the blast power spectrum was the principal factor determining the region of cochlear damage. We believe that the presenting models would be valuable both in blast research and the investigation of various types of hearing loss whose pathogenesis involves cochlear synaptopathy.
Highlights
Blast exposure can induce various types of hearing impairment, including permanent hearing loss, tinnitus, and hyperacusis
The waveform of the shock wave generated by the shock-tube system used in this study showed a steep rise in the positive peak with 25.0 kPa (Fig. 1e)
The waveform of the laser-induced shock wave (LISW) used in this study showed a steep rise with a positive peak pressure of 91.3 MPa, which was a thousand times higher than that obtained by the shock tube (Fig. 1f)
Summary
Blast exposure can induce various types of hearing impairment, including permanent hearing loss, tinnitus, and hyperacusis. The other model of unilateral hearing loss and tinnitus was generated via irradiation with a laser-induced shock wave (LISW)[19], which is our unique blast injury model of pure unilateral hearing loss and tinnitus following unilateral cochlear damage[20] This model was reported to have good reproducibility for generating mild SNHL without T MP19. The advantage of these two models for hearing-related research is that they do not cause damage to the middle ear (including TMP), making it possible to investigate pure SNHL Using these two blast-induced SNHL mouse models, this study aimed to analyze the relationship between the property of the blast shock wave and the pathophysiological effect on the inner ear after blast exposure. We investigated the relationship between the site of inner ear dysfunction physiologically and anatomically and the peak pressure of the exposed shock wave
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