Age-related loss of distortion product otoacoustic emissions in four mouse strains

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 study age-related hearing loss, were evaluated serially as a function of age with 2f(1)-f(2) distortion-product otoacoustic emissions (DPOAEs). DPOAE levels in response to equilevel primary tones for geometric-mean (GM) frequencies from 5.6 to 48.5 kHz were recorded systematically as DP-grams and response/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, CBAs showed robust and unchanged DPOAEs far all tested frequencies, while BALBs, C57s, and WBs showed strain-specific, age-related decreases in DPOAEs that 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 mice supports the notion that they represent unique animal models of age-related changes in cochlear function. In contrast, the unchanging DPOAEs for CBAs over the same time period indicate that this strain makes an effective control for normal cochlear function in the mouse, at least, up to 15 months of age. (C) 1999 Elsevier Science B.V. All rights reserved.