Morphological Change of Mouse Inner Ear Hair Cells after Noise Exposure

BACKGROUND AND OBJECTIVES: Mechanism of inner ear hair cell distortion after noise exposure has been well described. The present study was designed to determine the response to the auditory system of a genetically well-defined laboratory mouse in preparation for examining the effect of noise on mice with specific genetic mutations. So it is important to recognize the relationship between noise exposure duration and hair cell morphological changes. We try to reveal the hearing loss and inner ear hair cell morphological changes after applying the noise protocol. SUBJECTS AND METHOD: The mice were BALB/c hybrids and aged 8 weeks. Six mice served as non-noise-exposed controls and 8 mice were exposed for 3 hours per day to white band noise with a center frequency from 0.2 kHz to 70 kHz and a sound pressure level of 120 dB. And we divided the noise exposure group into 3 subgroups(1 day, 3 day, 5 day noise exposure group). We checked the photographs of FITC phalloidin stain and scanning electron microscopy of cochlea after noise exposure. RESULTS: The hearing level of mice decreased after noise exposure. We could see the stereocilia damage in cochlea after FITC phalloidin stain in cochlea and sterocilia loss was more severe in basal turn. In scanning electron microscopy, morphological changes of stereocilia were observed to be more severe in the cochlear basal turn than other area. Significant hair cell loss in the cochlear basal turn could be calculated using cochleocytogram. CONCLUSION: 120dB broad white band noise can damage the hair cell of cochlea in mice. These changes were especially severe in the cochlear basal turn. Noise exposure duration is the other important factor in damaging cochlear hair cells. Therefore, we can guess that harmful noise level and noise exposure duration are the main risk factors that injure the inner ear hair cell