Tolerance to Naloxone-Induced Suppression of Intake: Learning and Cross-Tolerance to Cholecystokinin in Rats

Experiments were conducted to evaluate the contribution of conditioning to tolerance to the meal-suppressive effect of naloxone (Nx) in rats. The results indicated (a) Nx suppresses consumption in a dose-dependent manner; (b) tolerance to this suppression of intake is "contingent" (the rat must eat in conjunction with drug administration for tolerance to develop); (c) tolerance is displayed only in the context of environmental cues previously …