Hyperthermia exacerbates and hypothermia protects from noise-induced threshold elevation of the cochlear nerve...

The scalp-recorded cochlear nerve envelope response (CNER) reflects the ability of high frequency cochlear nerve axons to fire in a phase-locked fashion to low frequency modulations of the acoustic envelope of high frequency stimuli. This property might be useful in evaluating the adverse effects of noise exposure on the ability of the ear to detect acoustic changes characteristic of vocalizations and speech. Hyperthermia (40 degrees C rectal) per se had no observable influence on the CNER in C57BL/6 mice. Hypothermia (30 degrees C) elevated CNER thresholds elicited by high frequency stimuli, although these stimuli still generated an auditory brainstem response. Mice exposed to noise when hyperthermic had greater threshold elevations than those exposed when euthermic (36 degrees C); those exposed when hypothermic had smaller threshold elevations than those exposed when euthermic. These observations were discussed in terms of the interaction of temperature and noise on oxidative processes within the cochlea.