Tip link loss and recovery on chick short hair cells following intense exposure to sound.

Stereocilia tip links on chick short hair cells (SHCs) were counted in the 'patch' lesion produced by acoustic overstimulation. Tip links were also counted on tall hair cells (THCs) immediately superior to the lesion. Eight groups were studied with three exposed to intense sound for differing durations. Three other groups were allowed to recover from the longest exposure for different time periods. Tip link counts from non-exposed control hair cells came from two other groups. Chicks exposed for 4, 24 or 48 h to a 120-dB SPL 0.9-kHz pure tone showed SHC tip link loss of 30.3, 40.6, and 35.5%, respectively. Chicks exposed for 48 h were allowed to recover for 24, 96 or 288 h, and showed systematic tip link recovery to control levels. Tip link loss and recovery in THCs adjacent to the patch lesion were identical to that seen in SHCs. After 288 h of recovery, surviving SHCs were distinguished from newly regenerated SHCs in the patch lesion. A comparison of tip link presence in the surviving (74%) and regenerated (84%) SHCs revealed a significant difference. These results suggest that the process of tip link destruction and recovery following acoustic overstimulation is the same for THCs and SHCs. This observation is surprising based on differences in the degree of acoustic injury to THC and SHC regions of the papillae, and the difference between THC and SHC sensory hair bundle stimulation.