Recovery of auditory structure and function in neonatal chicks exposed to intense sound for 8 days

This paper describes hearing loss and recovery as well as cochlear damage in chicks, after a 200-h exposure to an intense pure tone, and compares the results to similar data following a 48-h exposure to the same sound. The results revealed that the magnitude of initial hearing loss and the rate of recovery were nearly the same for both exposures. The initial cochlear damage produced by the 200-h exposure, however, was less severe than that seen after the 48-h exposure. In addition, new hair cells were observed in the lesion area immediately after the 200-h exposure. However, after the 48-h exposure, they were first identified after several days of recovery. These observations were consistent with the conclusion that cochlear repair began during the longer exposure itself. The fact that hearing loss and recovery was the same for the two exposure conditions, while the level of cochlear damage differed, suggests that functional recovery depended on processes other than the regeneration or repair of hair cells and supporting cells. These other processes are considered.