A SINGLE BRAIN-STEM SUBSTRATE MEDIATES THE MOTIVATIONAL EFFECTS OF BOTH OPIATES AND FOOD IN NONDEPRIVED RATS BUT NOT IN DEPRIVED RATS

Drug-naive and morphine-dependent rats both preferred places paired with morphine over unfamiliar neutral places. Morphine-dependent, but not naive, rats avoided places paired with the lack of morphine (i.e., withdrawal). Food-sated and food-deprived rats both preferred places paired with food over unfamiliar neutral places. Food-deprived, but not sated, rats avoided places paired with the lack of food (i.e., hunger). Lesions of the tegmental pedunculopontine nucleus (TPP) blocked the morphine- and food-conditioned place preferences in drug-naive and food-sated rats, respectively. TPP lesions failed to block morphine- and food-conditioned place preferences as well as morphine withdrawal-conditioned and hunger-conditioned place aversions in morphine-dependent and food-deprived rats, respectively. These results suggest that separate neural mechanisms subserve deprivation- and non-deprivation-induced motivation.