The tensor tympani muscle reflex in the mouse.

Click evoked electromyographic (EMG) recordings were made from the contralateral tensor tympani muscle of anaesthetised mice. The mean threshold of the EMG response was around 50 dB SPL (peak equivalent) with a mean latency close to 4 ms. The mean amplitude of the response increased over a range of 70 dB to reach a level of around 150 microV with a mean latency around 3.5 ms. The tensor tympani muscle activity was investigated also in profoundly hearing-impaired mutant mice with either cochlear dysfunction (deafness) or brainstem dysfunction (quivering). No evoked EMG activity was detected in either group of hearing-impaired mutants. The data suggest that EMG activity in the mouse can provide a sensitive monitor of auditory function. The study of reflex activity in further mouse mutants is likely to provide information on the vulnerability of the reflex to different types of naturally occurring cochlear and brainstem pathology.