Hypothermia and chloropent anesthesia differentially affect the flash evoked potentials of hooded rats

Anesthetics and body temperature alterations are both known to alter parameters of sensory-evoked responses. However few studies have quantitatively assessed the contributions of hypothermia to anesthetic-induced changes. Two experiments were performed. In the first, chronically implanted rats were injected with either 0, 0.05, 0.10 or 0.20 ml Chloropent/100 g b.w., while body temperature was maintained. Flash evoked potentials recorded 30 min later showed increased latencies but only minor (not statistically significant) changes in amplitude. In the second experiment the same rats were anesthetized with 0.35 ml Chloropent/100 g b.w. and rectal temperature was systematically varied between 31 degrees C and 37 degrees C. Over the ranges of temperature and anesthetic employed, latencies increased more extensively with hypothermia than with anesthesia. P1N1 amplitude doubled when temperature was lowered to 31C, but P2N2 and N2P3 amplitudes declined over the same temperature range. Anesthetic-induced changes in peak-to-peak amplitude did not reach statistical significance when body temperature was constant. The findings suggest that previously reported alterations in evoked potentials following anesthesia may have been confounded with hypothermia.