Auditory Brainstem Responses to clicks and tone bursts in C57 BL/6J mice

In auditory research, hearing function of mouse mutants is assessed in vivo by evoked potential recording. Evaluation of the response parameters should be performed with reference to the evoked responses recorded from mice of wild-type strain. This study reports normative data calculated on Auditory Brainstem Responses (ABRs) obtained from twenty wild-type C57 BL/6J mice at postnatal age between 21 and 45 days. Acoustic stimuli consisted of tone bursts at 8, 14, 20, 26, 32 kHz, and of clicks. Each stimulus was delivered in free field at stimulation intensity starting from a maximum of 100 dB peak equivalent SPL (dB peSPL) at decreasing steps of 10 dB with a repetition rate of 13/s. Evoked responses were recorded by means of needle electrodes inserted subcutaneously. At high intensity stimulation five response waveforms, each consisting of a positive peak and a subsequent negative valley, were identified within 7 ms, and were labelled with sequential capital Roman numerals from I to V. Peak IV was the most robust and stable at low intensities for both tone burst and click stimuli, therefore it has been utilized to estimate hearing thresholds. Both latencies and amplitudes of ABR peaks showed good reproducibility with acceptable standard deviations. Mean wave IV thresholds as measured across all animals ranged from a maximum of 23 dB peSPL for clicks to a minimum of 7 dB peSPL for 20 kHz-tone burst stimuli. Statistical analysis of the distribution of latencies and amplitudes of peaks from I to V performed for each stimulus type, yielded a normative data set which was utilized to obtain the most consistent fitting-curve model. This could serve as a reference for further studies on murine models of hearing loss.