SEM assessment of acoustically damaged cochleas

Cochleas from chinchillas exposed to a 1‐kHz pure tone stimulus were examined with the scanning electron microscope (SEM). Exposures to the 1‐kHz tone ranged in intensity and duration from 120 dB for 15 min to 90 dB for 3 h. Cochleas were examined at periods from immediately after exposure to nine months postexposure. Both permanent and temporary damage is demonstrated. Permanent lesions were confined to lower middle and upper basal turns. In some animals, sacrificed immediately after exposure, stereocilia of first and second row outer hair cells were found to be agglutinated and undergoing autolysis at focal points of lesion areas. In some cases stereocilia were already consumed leaving only stumps. No perforations into the fluid spaces of the organ of Corti could be found in animals examined either immediately after exposure or at later periods. The only change seen in some animals exposed to 120‐dB stimulation and examined immediately after exposure was a collapse o[ patches of stereocilia of inner hair cells and first row of outer hair cells. Some animals exposed to 90‐dB stimulation showed only a collapse of patches of stereocilia of the first outer row of hair cells immediately after exposure. The collapsed stereocilia of inner hair cells appeared to return to an upright position within 24 h, while those of the first row outer hair cells required periods in excess of two days.