Hypothermia protects the cochlea from noise damage

Thresholds of the cochlear action potential were obtained from rodents at euthermic (38 degrees C) and hypothermic (30 degrees and 25 degrees C) rectal temperatures. In the gerbil, low and middle frequency (1-8 kHz) thresholds increased an average of 2.3 dB per degrees C decrease of body temperature; at 16 kHz, 3.5 dB/degrees C; and at 32 kHz, an increase of 4.4 dB/degrees C. In the mouse, these values were: 2-16 kHz, 1.4 dB increase per degrees C decrease; 32 kHz, 2.7 dB/degrees C; 64 kHz, 3.8 dB/degrees C. When subjects maximally susceptible to permanent threshold shift (PTS) at low and middle frequencies (anesthetized, immature mice) were exposed to 115 dB noise, hypothermia reduced PTS at these most susceptible frequencies (2-16 kHz). When awake adult mice were exposed to this noise, hypothermia protected them from PTS at their most vulnerable frequency (32 kHz).