Phenotypic patterns of distortion product otoacoustic emission in inbred and F1 hybrid hearing mouse strains

Assessment of cochlear function in mice: distortion-product otoacoustic emissions

Distortion-product otoacoustic emissions (DPOAEs) can be measured in the ear canal following the presentation of two tones. These emissions are generated by the outer hair cells (OHCs) of the inner ear and they are reduced or absent when the OHCs are damaged by, for example, exposure to excessive noise or ototoxic drugs. Consequently, DPOAEs provide a powerful and noninvasive means to assess the robustness of OHC function. A detailed method is described for measuring DPOAEs to assess cochlear function in mice. Recommendations are given for the required equipment and instructions are presented for setting up a DPOAE system. Also, a protocol is outlined for measuring DPOAEs in mice and troubleshooting tips are provided. Examples of data analysis procedures following noise exposure in mice are included, as well. These methods are not only applicable to mice, but can be performed using essentially all small laboratory animals.

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 for 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 > or = 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 WB, C57, and BALB 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.

Low intensities and 1.3 ratio produce distortion product otoacoustic emissions which are larger in heterozygous (+/dn) than homozygous (+/+) mice

The f2/f1 frequency ratio of 1.3 in combination with stimulus levels of L1/L2 = 50/60 and 50/50 dB SPL produced a higher level of distortion product otoacoustic emissions (DPOAE) in the heterozygous (+/dn) mice than in the homozygous (+/+) mice. These results suggest that the dn gene carriers have a unique cochlear trait which may be related to the dn gene locus and expressed via a frequency- and intensity-dependent DPOAE function.