Depression of the guinea pig cochlear temperature caused by anesthesia and ventral-approach ear surgery

A chronic implant of a thermocouple, on the round window membrane of the guinea pig cochlea, was used to determine the cochlear temperature in awake, anesthetized, and surgically dissected animals. The normal cochlear temperature was equal to the core (rectal) temperature of the guinea pig (38.5 degrees C) and, in the intact animal, exactly tracks changes in core temperature at least down to the 33 degrees C level tested here. Ventral surgery to expose the cochlea results in a decrease, to a low value of 31 degrees C, in cochlear temperature because of the removal of tissue mass overlying the auditory bulla. Effective use of a heating pad and blanket cover, over the body of the guinea pig, will regulate core temperature but the exposed cochlea will always have a lower value than either the temperature measured rectally or in the orophraynx.