Title

Characterization of age- and noise-induced cochlear changes with distortion product otoacoustic emissions in four inbred strains of mice

Date of Award

2000

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Neuroscience

First Committee Member

Brenda L. Lonsbury-Martin, Committee Chair

Abstract

Measures of distortion-product otoacoustic emissions (DPOAEs) were used to track changes in cochlear function due to the effects of age and sound over-exposure in four inbred strains of mice, CBA/CaJ (CBA), C57BL/6J (C57), BALB/cByJ (BALB), and WB/ReJ (WB). Pilot DPOAE studies established that the optimal parameters were the 2f1--f2 DPOAE measured over a geometric mean (GM) frequency range of 5.6--48.5 kHz with a primary-tone ratio of f2/f1 = 1.25, at three equilevel primary tones, i.e., L1 = L2 = 55, 65, and 75 dB SPL. Using these parameters, DPOAEs were recorded as DP-grams and input/output (I/O) functions, at monthly intervals from 2 to 15 mo of age. Over this measurement period, CBAs exhibited robust and unchanged DPOAEs for all tested frequencies, while BALBs, C57s, and WBs showed strain-specific, age-related DPOAE decreases that progressed systematically from the high to low frequencies. Specifically, for WBs at 2 mo of age, no DPOAEs were recordable for GM frequencies ≥32 kHz, while C57s and BALBs reached the identical stage of cochlear dysfunction by 5 and 8 mos, respectively. In addition, two cohorts of mice, at either 2.5 or 6 mos of age, were exposed to a tonal exposure paradigm, allowed to recover, and then re-exposed to an octave band noise (OBN), at 3 or 7 mos. Although the tonal paradigm resulted in temporary DPOAE decreases for all strains, at both ages, the 2.5-mo BALBs exhibited the most susceptibility to the tonal-exposure, while the 2.5-mo WBs showed the least. In contrast, the OBN paradigm resulted in a permanent decrease in DPOAEs for the WB, C57, and BALB strains, while the CBA recovered to baseline levels by about 1 mo post-exposure. These data show that the parameters used in the present study are adequate for tracking age-related and noise-induced cochlear changes. In addition, the early onset AHL strains, can be used in combination, as the bases of 'impaired' ears, to set up a database to which other strains can be compared, where as, the CBA strain can be used, at least up to 15 mos, not only as a control for the 'normal' ears, but as a serial control in aging and noise studies.

Keywords

Health Sciences, Audiology; Biology, Neuroscience; Health Sciences, Medicine and Surgery

Link to Full Text

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