Increased phencyclidine self-administration due to food deprivation: Interaction with concentration and training conditions

Six monkeys were trained to self-administer orally delivered phencyclidine (0.25 mg/ml) under a fixed-ratio 16 (FR-16) schedule. Water was concurrently available under an FR-16 schedule. During initial phencyclidine training, three monkeys were allowed free access to food (food satiation) and three were maintained at 85% of their free-feeding body weights (food deprivation). At the end of the training phase, the food-satiated monkeys were food-deprived. After behavior was stable for ten sessions, all monkeys were food-satiated and tested with a range of phencyclidine concentrations (0.0625-1 mg/ml). They were subsequently food-deprived and tested with concentrations of 0.0312-1 mg/ml, and then they were again food-satiated and tested with 0.0312 and 0.25 mg/ml. The monkeys that were trained to self-administer phencyclidine-maintained responding at lower drug concentrations when later tested while food-satiated. In contrast, monkeys that were trained while food-deprived did not respond for phencyclidine in excess of water at the lower concentrations when later tested while food-satiated. Drug-maintained performance during food deprivation did not change systematically as a function of training condition (food deprivation versus food satiation). These results illustrated a marked interaction between drug concentration and the feeding condition and this interaction was modified by training history.