The structural and functional aspects of hair cell regeneration in the chick as a result of exposure to intense sound.

This paper summarizes the structural and functional damage caused by intense sound exposure in neonatal chicks. Scanning electron microscopy has been used to follow the structural changes to the papilla and their subsequent repair. Pure-tone exposures produced a localized lesion consisting of tectorial membrane destruction, changes in surface organization of the papilla, and hair cell loss. The papilla underwent significant repair following the exposure and new hair cells could be identified on the sensory surface after 4 days of recovery. In addition, various evoked-potential methods provided an objective assessment of auditory function and demonstrated that the peripheral ear was severely impaired by overstimulation. Auditory function returned to near normal levels within 3 days postexposure. The inescapable conclusion from these observations was that hair cell regeneration had little to do with the functional recovery observed during the first 3 days. Tectorial membrane regeneration and the restoration of cochlear micromechanics were combined to form a hypothesis to account for the restoration of auditory function.