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J Occup Health year 2008 volume 50 number 5 page 373 - 379
Classification Originals
Title Changes in Guinea Pig Cochlear Hair Cells after Sound Conditioning and Noise Exposure 
Author Hongyan ZUO, Bo CUI, Xiaojun SHE and Mingquan WU
Organization Department of Occupational Hygiene, Institute of Health and Environmental Medicine of Tianjin, PR China
Keywords Sound conditioning, Cochlear hair cell, Noise-induced hearing loss
Correspondence M. Wu, Department of Occupational Hygiene, Institute of Health and Environmental Medicine of Tianjin, 1, Dali Road, Heping District, Tianjin 300050, PR China (e-mail: tjwmq@126.com)
Abstract Changes in Guinea Pig Cochlear Hair Cells after Sound Conditioning and Noise Exposure: Hongyan ZUO, et al. Department of Occupational Hygiene, Institute of Health and Environmental Medicine of Tianjin, PR China-Sound conditioning has reduced noise-induced hearing loss in experimental mammalian animals and in clinical observation. Forty guinea pigs were grouped as: A, control; B, conditioning noise exposure group; C, high level noise exposure group; and D, conditioning noise exposure followed by a high level noise exposure group. Auditory brainstem response thresholds were measured. The cochlear sensory epithelia surface was observed microscopically. Calmodulin, F-actin and heat shock protein 70 (HSP70) in hair cells were immunohistochemistrically stained. The intracellular free calcium was stained for confocal microscopy. The ABR threshold shift after noise exposure was higher in group C than D, and showed a quicker and better recovery in group D than C. Stereocilia loss and the disarrangement of outer hair cells were observed, with the greatest changes seen in group C, followed by groups D and B. The most intensive immunohistochemical intracellular expressions of calmodulin, F-actin, and HSP70 were found in group D, followed by groups C, B and A. The highest intensity of the fluorescent intracellular free Ca2+ staining in the isolated outer hair cells was observed in group C. The ABR and morphological studies confirmed the protective effect from noise trauma of sound conditioning. The protective mechanism of hair cells during sound conditioning was enforced through the increase of cellular cytoskeleton proteins and through the relieving of intracellular calcium overloading caused by the traumatic noise.