Effects of hyperthermia on the auditory-evoked brainstem responses in mice.

This study investigated the effects of increased body temperature on the latencies and amplitudes of the auditory-evoked brainstem response (ABR) in mice. Six eleven-week-old male CBA/CaJ mice were anesthetized with pentobarbital and screened for normal hearing. Hyperthermia was induced by placing the animal in a thermostatically controlled chamber; a thermistor connected to a digital thermometer measured the rectal temperature. ABRs were evoked with broad-band clicks presented at repetition rates of 21.1/s and 61.1/s. The latencies and amplitudes of waves I-V were measured at 1-degree and/or 0.5-degree intervals between 37 and 42 degrees C. Temperature elevation between 37 and 41 degrees C shortened the latencies of all the ABR waves, the effect being linear and cumulative across the time window. Change in this trend occurred between 41 and 42 degrees C, whereby the latencies of all the waves stabilized or showed minimal prolongation. Amplitudes of the most robust waves I and II showed a trend similar to the latencies, whereas the later waves showed erratic and uninterpretable changes. These findings in the mouse may be indicative of the physiological limit of thermal tolerance and as such may be regarded as a premonitory signal of permanent damage.