Conclusion: These results suggest that noise induces free radical formation in the cochlea and that, in the guinea pig, heme oxygenase-1 (HO-1) may play an important role in the recovery from noise trauma in the organ of Corti. Objective: Free radicals are involved in noise-induced hearing loss. It has been demonstrated that the induction of HO-1 may protect cells exposed to oxidative challenge. The present study was designed to investigate the effect of intense noise exposure on HO-1 induction. Materials and methods: A total of 25 adult guinea pigs (body weight 200-300 g) with a normal Preyers's reflex were used as subjects. Based on preliminary tests, the appropriate intensities and durations of noise were determined that were adequate to induce apparent threshold shifts and lead to various recovery patterns to initial thresholds. The sound was routed through a power amplifier to a speaker, which was positioned directly over the animals in a sound chamber. Auditory brainstem response (ABR) testing, Western blot analysis for HO-1, and immunohistochemical testing were done. Results: Exposure of the guinea pigs to 115 dB SPL octave band noise for 5 h induced HO-1 expression in the organ of Corti. In the organ of Corti, HO-1 expression increased mainly in the outer hair cells. Some expression of HO-1 was observed before and after noise exposure in the supporting cells. HO-1 expression in the organ of Corti was definitely increased in guinea pigs with an intense noise exposure which causes a temporary threshold shift.
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