Figure 1

Auditory brainstem responses in dearisch mice. (a) The distribution of click thresholds of mice in the dearisch colony born between 2009 and 2011 (n = 250). The majority of mice hear normally; however, there is a second peak of mice with a spread of thresholds between 50 and 80 dB SPL. (b) The audiograms of mice examined with the long ABR protocol at 12 weeks of age (n = 16). The mean thresholds at each frequency and standard deviation at each frequency for the mice with an ABR click threshold above 50 dB SPL (affected) and below 30 dB SPL (unaffected) are shown in red and blue, respectively. The shape of the mean affected audiogram is similar to the unaffected audiogram with approximately 40 dB increase in threshold (hearing loss) at each frequency, consistent with a conductive hearing impairment. (c) Growth of ABR wave 1 amplitude with increasing stimulus intensity, plotted as dB above threshold (sensation level, dB SL), is similar in affected and unaffected mice, consistent with a purely conductive defect; n = 13 affected mice (in red) and 13 unaffected mice (in blue). (d) Reduction in latency to the first peak of the ABR waveform with increasing stimulus intensity above threshold (dB SL) is similar in affected and unaffected mice, consistent with a conductive defect; n = 13 affected mice (in red) and 13 unaffected mice (in blue).(e) Measurement of click-evoked ABR thresholds with recovery allowing repeated ABR measurements in individual mice with increasing age from 3 to 28 weeks. From 8 to 28 weeks 16 mice underwent recurrent recordings and 9 mice underwent single recordings. Between 3 and 8 weeks a different set of mice (n = 66) underwent one or two click ABR recordings. Although there is some variability in thresholds, most mice could hear normally, while a few mice have raised thresholds from as early as 3 weeks. In general, thresholds are stable, not increasing with age.