Homeostatic regulation and Pavlovian conditioning in tolerance to amphetamine-induced anorexia.

A series of experiments on the role of Pavlovian processes in tolerance to amphetamine-induced anorexia in rats was conducted. In Experiment 1A, tolerance to the suppressant effect of d-amphetamine (4.0 mg/kg) on milk consumption was substantially diminished in an environment not previously associated with drug administration. Experiment 1B supported the interpretation that Pavlovian compensatory conditioning rather than a nonassociative mechanism mediated this phenomenon. Experiment 2 examined the hypothesis that "contingent tolerance" results from an inadvertent manipulation of Pavlovian cues. As in previous research, tolerance was contingent in that it did not develop if the rats were not exposed to food under the influence of the drug. Tolerance developed only if access to food occurred under the influence of amphetamine, but as in Experiment 1A, it was substantially diminished in an environment not previously associated with drug administration. Thus, tolerance to amphetamine-induced anorexia was shown to be both contingent on previous experience with food in the drugged state and subject to Pavlovian control. No current explanation for the occurrence of contingent tolerance or for the control of tolerance by Pavlovian processes can at once account for both of these findings. Experiment 3 confirmed the hypothesis that interaction with the food stimulus would be necessary to extinguish tolerance. This finding is also problematic for any current behavioral theory of tolerance. It is proposed that interaction with food is necessary for the homeostatic regulation of disturbances in eating caused by amphetamine. When activated, this regulatory process operates by means of Pavlovian conditional compensatory processes.