Death pathways in noise-exposed outer hair cells.
Bohne-BA; Harding-GW; Lee-SC
Abstr 30th Midwinter Res Meet 2007 Feb; 30:113
Using morphological criteria, death pathways in OHCs were determined in Organs of Corti (OC) exposed to an octave band of noise (OBN) with a center frequency of either 0.5 or 4 kHz at a moderate sound pressure level (SPL). The specimens were part of our collection of plastic-embedded flat preparations of chinchilla cochleae. Three death pathways were identified: 1) oncosis - OHCs were swollen & pale-staining with a swollen nucleus; 2) apoptosis - OHCs were shrunken & dark-staining with a pyknotic nucleus; & 3) a third death pathway - OHCs had no basolateral plasma membrane, a nucleus deficient in nucleoplasm & cellular debris arranged in the shape of an intact OHC. To minimize the secondary loss of OHCs that occurs post-exposure, the specimens used for quantitative analysis of death pathways had the following characteristics: a) the level to which they were exposed was < 95 dB SPL; b) the exposure duration was 6-216 h; c) the cochleae were fixed in-vivo 1-2 h post-exposure; & d) there were no focal OHC lesions in the OC. Fifty-eight noise-exposed cochleae in our collection met these criteria. The specimens had a variable amount of OHC loss, minimal IHC loss, rare pillar loss, & no spiral ganglion cell loss. The cochleae were grouped by total exposure energy [E = log2 (Pa2 seconds)] into 7 Groups with energies ranging from 7.77-17.74 for the 0.5-kHz OBN & 6 Groups with energies ranging from 5.11-14.75 for the 4- kHz OBN. In all specimens, degenerating & missing OHCs were classified as to which death pathway the cells were following. Nine non-noise-exposed cochleae were also evaluated for OHC death pathways. The number of OHCs following the third death pathway was significantly greater in the noise-exposed cochleae than the non-noise-exposed cochleae for total exposure energies greater than that produced by a 0.5-kHz OBN at 75 dB SPL for 216 h (i.e., 13.26) or a 4-kHz OBN at 57 dB SPL for 48 h (i.e., 5.11). In cochleae exposed to either octave band, OHCs dying by oncosis or apoptosis were uncommon. Further work must be done on cell-death pathways in the noise-damaged cochlea to determine how the prevalence of the different pathways changes with exposure parameters.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals
Abstracts of the 30th Midwinter Research Meeting
Washington University, St. Louis