IS ACQUIRED TOLERANCE TO HYPOTHERMIA SUSCEPTIBLE TO EXTINCTION

Studies examining adaptation to thermoregulatory challenges have shown that tolerance to hypothermia is mediated, in part, by associative (P avlovian) learning mechanisms. This study examined whether acquired to lerance to deep body cooling (hypothermia) could be extinguished by co nditions in which presentations of the environmental cues were present ed in the absence of hypothermia treatment. The results of Experiment 1 indicate that five extinction exposures in which the context was pre sented alone were not sufficient to extinguish established hypothermia tolerance in rats. Experiment 2 demonstrated that tripling the number of daily extinction exposures from 5 to 15 also did not disrupt adapt ation to cold, and further demonstrated that the presentation of a cha llenge condition (heat exposure) over the 15-day extinction phase of t he experiment had no effect on established cold tolerance. Furthermore , Experiment 2 confirmed associative control of tolerance by demonstra ting a context shift effect in resistance to cold. The lack of an exti nction effect in these two experiments suggests that the environmental context may be acting as an occasion setter.