Five animals for each mouse strain were used for ABR recordings. The mouse was anesthetized with a mixture of ketamine/xylazine (ketamine 100 mg/kg; xylazine 15 mg/kg; ip), and supplemented as needed. ABRs were recorded in response to tone bursts of 2, 4, 8, 16, 22, and 32 kHz using standard procedures previously described [25 (link),26 (link)]. Tone pipe with 1 ms rise cosine on/off ramps were generated digitally using a clock rate of 125 kHz and 16-bit D/A converters. Stimulus levels were calibrated using a 1/8 inch B & K microphone (Model 4138) and were presented as sound pressure levels measured in decibels (dB SPL: referenced to 20 mPa). ABR signals were collected with subcutaneous platinum needle electrodes placed at the vertex, mastoid prominence, and shoulder. Response signals were amplified (100,000x), filtered, and acquired by TDT Workstations (Tucker-Davis Technologies). Each averaged response was based on 200 stimulus repetitions. During the procedure, the body temperature was maintained at 37°C with a heating pad. All records were obtained in a sound-attenuating chamber.
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