Characteristic findings of auditory brainstem response and otoacoustic emission in the Bronx waltzer mouse

Auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) were evaluated serially from 1 to 22 months in Bronx waltzer homozygotes (bv/bv), heterozygotes (+/bv) and control (+/+) mice, which were differentiated by means of PCR of marker DNA (D5Mit209). The wave IV threshold of the click-evoked ABR was higher than the DPOAE threshold with the DP growth method in each bv/bv, although the two thresholds were almost the same in the +/+ group. The DP value at 2f₁ ? f₂ in the bv/bv showed an apparent decrease at 2 to 3 months of age with 80 dB SPL stimulation using f₂ frequency 7996 Hz and frequency ratio f₂/f₁ = 1.22, compared to control or heterozygote mice. It was characteristic that the 2f₂ ? f₁ DP signal-to-noise ratio (SNR) value was more preserved from 80 to 60 dB SPL than the 2f₁ ? f₂ DP value at f₂ frequency 7996 Hz in most bv/bv, however, control mice showed almost the same levels of 2f₁ ? f₂ and 2f₂ ? f₁ SNR value at both f₂ frequencies of 6006 and 7996 Hz. The preservation of a substantial 2f₂ ? f₁ DP suggested that it would be generated basal to the primary-tone place on the basilar membrane and there might be a reflection of the unique function of the remaining outer hair cells in the Bronx waltzer mice. These findings suggest that combination of ABR with DPOAE could offer useful information about differentiating the mechanism of hair cell dysfunction of the hereditary hearing impairment in the clinical fields.