Abstract
In the previous study we reported electrophysiological phenomenon of hypothermia on the cochlea of guinea pigs. The most interesting finding was a transient increase of AP amplitude evoked by a click up to 28°C, followed by gradual decrease with the further temperature decline. The purpose of the present study is to clarify the mechanism of this transient increase of AP amplitude. Narrow band analysis, AP tuning curve, thresholds of AP and CM were determined using 30 normal guinea pigs. The AP and CM thresholds and the tip of AP tuning curves were elevated as the temperature was lowered and this tendency was the most remarkable in the responses at 12kHz. Narrow band-APs above 8kHz obviously demonstrated the transient increase in amplitude, although those below 8kHz showed the linear decrease with the temperature decline. These findings suggest that there are differences in sensitivity and response to hypothermia between the basal turn and second turn, and the transient increase in AP amplitude is due to the increased response originating from the basal turn.
