ABSTRACT
<p><b>AIM</b>To study the effects of hyperthermia on brainstem auditory evoked potentials (BAEP) and middle latency response (MLR) in rats.</p><p><b>METHODS</b>BAEP and MLR were recorded at the skull surface of rats. The body temperature of anesthetized rats increased gradually with a physical method and was detected by a digital thermometer inserted into the rectum. The peak latency (PL), interpeak latency (IPL), wave amplitude and the critical body temperature at which BAEP and MLR completely lost had been observed.</p><p><b>RESULTS</b>All PL and I - II, I - III and I -IV IPL of BAEP shortened more and more as the body temperature increased step by step from 37 degrees C to 41.5 degrees C. But all PL and I - II and I -IV IPL did not shortened further and prolonged a little contrary as the body temperature at 42 degrees C and over 42 degrees C. All PL and P1-P3 and P2-P3 IPL of MLR also shortened as the body temperature increased from 37 degrees C to 43 degrees C. The wave amplitudes of BAEP and MLR decreased as the body temperature increased, especially as the body temperature over 42 degrees C. BAEP and MLR lost completely and synchronously at the body temperature (43.1 +/- 0.5) degrees C, which was not reversed as the body temperature returning to normal by cooling.</p><p><b>CONCLUSION</b>There were obvious effects of hyperthermia on both BAEP and MLR in rats, and irreversible impairments appeared at a critical body temperature.</p>