Morphological changes in the ears of noise-exposed parakeets

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Abstract
Parakeets exposed to 13-octave bands of noise for 12 or more hours sustain asymptotic threshold shifts (Dooling and Saunders). The ears of three parakeets from the Dooling and Saunders study were prepared for phase-contrast microscopic examination as embedded whole mounts after final audiograms had been obtained. Findings in these ears were then compared to ears of other parakeets exposed for 12 hours to a 13-octave band of noise centered at 2 kHz with a sound pressure level of 76, 86, or 106 dB. The ears of half the parakeets were prepared for microscopic examination 30 minutes following exposure, while the rest were prepared after the birds had recovered from their ATS. Preliminary findings in parakeet ears with ATS include: no sensory cell loss, no tectorial membrane displacement, no reticular lamina breakage, and no abnormalities in the stereocilia. In addition, the cytoplasm of some tall hair cells bulged from the surface of the basilar papilla, thus separating nerve endings from the hair cell bases. This latter feature was not present in parakeet ears which had recovered from ATS.

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