Is Acquired Tolerance to Hypothermia Susceptible to Extinction?

Abstract

Studies examining adaptation to thermoregulatory challenges have shown that tolerance to hypothermia is mediated, in part, by associative (Pavlovian) learning mechanisms. This study examined whether acquired tolerance to deep body cooling (hypothermia) could be extinguished by conditions in which presentations of the environmental cues were presented in the absence of hypothermia treatment. The results of Experiment 1 indicate that five extinction exposures in which the context was presented 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 adaptation to cold, and further demonstrated that the presentation of a challenge condition (heat exposure) over the 15-day extinction phase of the experiment had no effect on established cold tolerance. Furthermore, Experiment 2 confirmed associative control of tolerance by demonstrating a context shift effect in resistance to cold. The lack of an extinction effect in these two experiments suggests that the environmental context may be acting as an occasion setter.