Tolerance to an environmental cold challenge in rats is eliminated when cold exposure occurs in a context different from the adaptation context, indicating that learning mechanisms playa role in thermoregulation (Riccio, MacArdy, & Kissinger, 1991). This finding, analogous to outcomes obtained with drug tolerance, was investigated in the present study. Experiment 1 demonstrated that a change in both proximal and distal contextual cues disrupts an established cold adaptation, an outcome consistent with the view that associative processes contribute to the tolerance. In Experiment 2, although cold tolerance persisted over a 7-day retention interval, the disruption of tolerance by a shift in context was attenuated with the delay of testing. This finding suggests that the precise stimulus attributes of the context were forgotten over the interval. Experiment 3 demonstrated that cold-tolerance disruption is due to the actual change in context and not to novelty of the test context. Experiment 4 showed that changing the context associated with each cold exposure impaired the development oftolerance. The results of these experiments provide additional evidence that cold tolerance is regulated at least partially by associative learning processes.

Learning processes have been implicated in drug tolerance, but the role of associative mechanisms in adaptation to stressors has not previously been determined. Rats that received daily brief cold exposures demonstrated adaptation to the cold as measured by an attenuation of hypothermia. Tolerance to the cold was disrupted by changing the context in which the subject experienced the cold. These findings provide evidence of associative processes in adaptation to cold exposure and illustrate that these processes are not limited to drug tolerance.

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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.A now substantial body of evidence implicates associative processes in the development of tolerance to morphine and other drugs (for review, see Siegel, 1989). An early study reported that tolerance to the analgesic effects of morphine could be disrupted if rats were tested for tolerance in an environment that had not been previously paired with morphine administration, suggesting that tolerance to morphine is modulated, in part, by non pharmacological mechanisms (Siegel,1975). This disruption of tolerance resulting from a change in context conflicts with the We thank Dr. Ralph R. Miller for calling our attention to the possible "occasion setting" role of context. The research reported here was supported in part by

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