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

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Brenda L. Lonsbury-Martin - Committee Chair


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.


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

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