Age-related loss of distortion product otoacoustic emissions in four mousestrains

Changes in cochlear function in four inbred strains of mice, CBA/CaJ (CBA), C57BL/6J (C57), BALB/cByJ (BALB), and WB/ReJ (WB), previously used to stud y age-related hearing loss, were evaluated serially as a function of age wi th 2f(1)-f(2) distortion-product otoacoustic emissions (DPOAEs). DPOAE leve ls in response to equilevel primary tones for geometric-mean (GM) frequenci es from 5.6 to 48.5 kHz were recorded systematically as DP-grams and respon se/growth or input/output (I/O) functions at monthly intervals from about 2 to 15 months of age. Over the approximate 13-month measurement period, CBA s showed robust and unchanged DPOAEs far all tested frequencies, while BALB s, C57s, and WBs showed strain-specific, age-related decreases in DPOAEs th at progressed systematically from the high to low frequencies. Specifically , for the youngest WBs at 2 months of age, no DPOAEs were recordable for GM frequencies greater than or equal to 32 kHz, while C57s and BALBs reached the identical stage of cochlear dysfunction by 5 and 8 months, respectively . The differential decline in DPOAE activity shown for WE, C57, and BALE mi ce supports the notion that they represent unique animal models of age-rela ted changes in cochlear function. In contrast, the unchanging DPOAEs for CB As over the same time period indicate that this strain makes an effective c ontrol for normal cochlear function in the mouse, at least, up to 15 months of age. (C) 1999 Elsevier Science B.V. All rights reserved.