Early microfilament reorganization in injured auditory epithelia.

Microfilaments (MFs) play an important role in wound healing and other regenerative events. The purpose of this study was to characterize changes in the distribution of MFs in traumatized auditory epithelia and compare these changes between avian (regenerating) and mammalian (nonregenerating) ears. Chicks and guinea pigs were acoustically overstimulated and their auditory epithelia analyzed fluorescence microscopy with phalloidin as a MF-specific marker. Immediately or several hours after overstimulation, we observed a substantial reduction of MFs in stereocilia and the cuticular plate. The circumferential belt of MF which is associated with the adherens junctional complex was constricted in damaged hair cells (HCs) as early as 1 day after the exposure. Concomitant with the junctional constriction, the apical surface area of supporting cells was increased relative to normal, whereas the surface area of HCs was decreased. We conclude the changes in the amount and distribution of MFs which characterize early responses to acoustic damage are similar in avian (regenerating) and mammalian (nonregenerating) auditory epithelia. We hypothesize that changes in MF-mediated tensile forces trigger the process of tissue repair in auditory epithelia in response to insult. In mammals the reorganization of MFs may help maintain the integrity of the reticular lamina and thereby prevent further damage. In contrast, early changes in MFs in chicks may play a role in regulating regenerative tissue responses.