Auditory Brainstem Response
Materials and Methods
Smart EP High Frequency System, Intelligent Hearing System, Inc.
(includes: USB Notebook Computer System, DSP hardware, 2-channel amplifier,
SmartEP software, SmartEP high frequency option, needle electrodes (box of 10),
insert earphones, high frequency speakers for animals [2], booster cable
Heating Pad, Baxter K Mod 100, Baxter Laboratory Equipment
Electrodes, F-E2, platinum sub-dermal needle electrodes
Astro-Med, Inc., Grass Product Group, Warwick, RI
Tribromoethanol, Sigma, USA
Working Solution: 2% Tribromoethanol in saline
The mice are injected intraperitoneally with 2% Tribromoethanol and placed on the heating pad (1000 F). The equipment is prepared, the settings are adjusted [171]: Filters should be set to exclude signals above 3000 and below 100 Hz, amplification at 200K, analysis time at 10msec (averaged responses are digitized and displayed on PC screen).
After the anesthetic has taken effect, the electrodes are inserted subcutaneously and
the program is started:
First stimulus presentation consists of a click (2-8 kHz) at 70 dB, and, depending on the response, is followed by increasing or decreasing the volume initially in 10 and subsequently in 5 dB steps to determine the auditory threshold; the series is repeated for pure-tone stimuli of 8, 16 and 32 kHz (duration 3msec, 1.5msec rise and fall time).
Mice that show no responses are determined to be deaf. Those with elevated thresholds (strain and age-dependent) will be retested to confirm the findings. Following confirmation of the results these mice are maintained and tested at later intervals to evaluate progressive hearing loss.
