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Hair-cell-membrane changes in the cochlea following noise.
Schmitt-N; Hsu-K; Bohne-BA; Harding-GW
Abstr 27th Midwinter Res Meet 2004 Feb; 27:132
The morphological correlates of temporary threshold shift (TTS) remain controversial. Mulroy et al ('98) provided indirect evidence that alligator lizards with noise-induced TTS have microlesions in hair-cell plasma membranes. To test this hypothesis directly, chinchillas were exposed for 24 hrs to a 4-kHz OBN at 92 dB SPL. ABR & DPOAE testing were carried out pre- & post-exposure. Three hrs post-exposure, 3 chinchillas had EP measured & carbon particles injected into the endolymphatic space before fixation. Two chinchillas recovered for 1 or 2 wks before EP measurement, carbon injection & cochlear fixation. Two controls underwent EP measurement (74 & 89 mV), carbon injection & cochlear fixation. Cochleas were embedded in plastic, dissected as flat preparations & missing cells counted. Cytocochleograms were prepared with functional data overlaid according to the chinchilla frequencyplace map. Thin sections of the OC were cut in the region of maximum threshold shift (TS) for TEM. Immediately post-exposure, all animals had an ABR TS of 20-60 dB over a frequency range of 1-16 kHz & a DPOAE level shift (LS) of 10-50 dB over 2-16 kHz; EP was 21, 49 & 79 mV in the three 0-d-recovery animals. Most hair cells were present & had normal shapes by phase contrast microscopy; by TEM, OHC stereocilia were slightly disarrayed but the plasma membranes were intact. The 1-wk-recovery animal had an ABR TS of 10-20 dB for 1-16 kHz, a DPOAE LS of 12-30 dB for 3-12 kHz & an EP of 83 mV. The 2-wk-recovery animal had an ABR TS of 10-20 dB for 3-6 kHz, a DPOAE LS of 12-23 dB for 3-12 kHz & an EP of 80 mV. In the 1-wk-recovery animal, one region of the OC contained about 20% degenerating OHCs. By TEM, the apical membranes of some degenerating hair cells contained microlesions. We conclude that hair cells do not develop microlesions in noise-exposed mammalian cochleas unless the cells are degenerating.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals; Cell-damage; Cellular-reactions; Animal-studies
Abstracts of the 27th Midwinter Research Meeting
FL; NJ; MO
Washington University, St. Louis
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