Patterns of hair cell loss in chick basilar papilla after intense auditory stimulation. Exposure duration and survival time.
Ten-day-old chicks were exposed to a pure tone (1.5 kHz) or white noise at 125 dB SPL avg. RMS for 4 to 24 hours, and were sacrificed either 10, 30 or 60 days after exposure. The basilar papillae were embedded in plastic, sectioned, and hair cells were counted at 100-micrometer intervals throughout the length of the papilla. As sound exposure duration increased, both the maximum number of hair cells lost, and the extent of the damaged area along the basilar membrane increased. Short hair cells situated on the free area of the basilar papilla were more susceptible to damage than were tall hair cells. The location of hair cell loss varied as a function of frequency band of exposure; the pure tone produced a well localized basal lesion, while wide-band noise produced a more general lesion which extending toward the apex. Degeneration continued with increased survival time up to 30 days. It is concluded that avians respond to acoustic overstimulation in a manner very similar to mammals. The convenience of this preparation along with the relative simplicity of its cochlea may render it useful for future investigations of the mechanisms of acoustic trauma.