Evidence for supporting cell mitosis in response to acoustic trauma in the avian inner ear

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Abstract
Acoustic overstimulation can lead to sensory cell (hair cell) loss in the auditory epithelium. Damaged hair cells in the organ of Corti (the mammalian auditory end-organ) degenerate and are replaced by non-sensory cells (supporting cells) which construct an irreversible scar. In birds, however, auditory hair cells which are damaged by acoustic trauma or ototoxic drugs may be replaced by new hair cells. As first step in determining the mechanism of hair cell regeneration, we developed an assay for cell divisions in the auditory epithelium after acoustic trauma. The results of these experiments demonstrate that supporting cells in damaged regions of the auditory epithelium incorporate the DNA-specific marker bromodeoxyuridine as early as one day after noise exposure. We provide direct evidence that following acoustic insult to the avian inner ear, supporting cells which reside within the sensory epithelium divide near the luminal surface and repopulate the epithelium. These results suggest that supporting cells participate in scar formation during hair cell degeneration, and produce new cells for regeneration.