Hair cell and supporting cell response to acoustic trauma in the chick cochlea.

Damage to the chick cochlea in response to progressively increased periods of noise exposure was studied with scanning electron microscopy. Ten day-old chick hatchlings were exposed to a 1500 Hz pure tone at 120 dB SPL for 4, 8, 12, 24, and 48 h. Measurements of hair cell and supporting cell surface areas within a defined region of the cochlea showed that the average hair cell surface area decreased over the first 12 h of exposure. Between 12 h and 48 h there was no significant change in hair cell surface area. Supporting cells showed a corresponding increase in surface area over the same period. Noise damage first appeared after 4 h of exposure as a localized expansion of supporting cell surfaces near the inferior edge of the basilar papilla (BP). Between 8 and 12 h of exposure the supporting cell surface area increased dramatically and was visible throughout the noise damaged region. Hair cell expulsion was first seen after 12 h. Exposure to noise for 24-48 h resulted in further expansion of supporting cells, extensive expulsion of hair cells from the BP, and the appearance of a strip of noise damage along the superior, edge of the BP.