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An augmented acoustic environment delays age-related hearing loss in C57BL/6J mice as revealed by DPOAEs and cochlear histopathology.
Martin GK; Candreia C; Bohne BA; Harding GW; Stagner BB; Lonsbury-Martin BL;
Abstr 25th Midwinter Res Meet 2002 Jan; 27:69-70
Willott and Turner (Hear Res, 1999) reported that an augmented acoustic environment (AAE) delayed age-related hearing loss (AHL) in C57BL/6J (C57) mice. The present study assessed cochlear function at the outer hair cell (OHC) level by measuring distortion-product otoacoustic emissions (DPOAEs) in both AAE and control mice. These results were subsequently correlated with cochlear histopathology. Beginning at 25 d of age, C57 mice were exposed nightly, for 12 h, to a 70-dB SPL broadband AAE (200-ms pulses at 2/s), centered at 10 kHz. DPOAEs were recorded in the form of DP-grams (DPOAE level as a function of primary-tone frequency), with geometric-mean (GM) frequencies ranging from 5.6-48.5 kHz (f2=6.3-54.2 kHz), in 0.1-oct steps. DP-grams were collected at three primary-tone levels (L1=L2=55, 65, 75 dB SPL). ABRs were recorded at 6, 8, 12, 16, 24, and 32 kHz to confirm the AAE effect. At 6 mo of age, both cochleas from 4 control and 3 AAE mice were post-fixed in OsO4, dehydrated, embedded in plastic and dissected as flat preparations. Hair-cell, supporting-cell and nerve-fiber losses were determined from apex to base and cytocochleograms prepared for all cochleas. Function-structure correlations were made by overlaying the final DP-gram on the cytocochleogram. By 4 mo of age, clear differences between AAE and control DPOAEs were observed. Control C57s showed average DPOAEs that were near noise-floor levels between GM frequencies of 25-48.5 kHz, while the AAE ears exhibited moderately reduced DPOAEs over a restricted range of GM frequencies between 25-35 kHz. The functional data matched well with the histopathology in all ears. As a group, the controls had worse function and more hair-cell loss than the AAE mice. However, in both groups, there was large variability across mice. The ears of the AAE mice were more variable than the controls and 2/3 had pronounced asymmetries between ears.
Noise-exposure; Exposure-levels; Noise-induced-hearing-loss; Noise-exposure; Noise; Hearing; Hearing-disorders; Hearing-loss; Laboratory-animals; Animals; Cell-damage; Cellular-reactions; Nerve-damage; Nerve-fibers; Age-groups; Histopathology; Animal-studies
Abstracts of the 25th Midwinter Research Meeting
FL; NJ; MO; CO
Washington University, St. Louis
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