Rapid acquisition of oral phencyclidine self-administration in food-deprived and food-satiated rhesus monkeys: Concurrent phencyclidine and water choice

Eight rhesus monkeys were trained to self-administer orally-delivered phencyclidine, with water concurrently available, under a fixed ratio (FR) schedule during daily 3-hr sessions. Liquid deliveries (0.55 ml) were contingent upon lip-contact responses on solenoid-operated drinking spouts. During the sessions, phencyclidine and water were available under FRs ranging from 1 to 16. Water was always available between sessions (FR 1), and food initially was available 24 hr/day. In Experiment 1 the monkeys initially were given access to water (FR 1) during the 3-hr sessions. Subsequently, phencyclidine (0.25 mg/ml) was substituted for water, and the monkeys were reduced to 85 percent of their free-feeding weights. The FR value was then increased from 1 to 8. Next, the monkeys received concurrent access to water from one spout and phencyclidine from the other (each under the FR 8 schedule), then the FR value was increased to 16 for both drug and water. Orally-delivered phencyclidine was rapidly demonstrated to function as a reinforcer (37.2 sessions) without using food to induce drinking. In Experiment 2 a similar procedure was used for another group of monkeys, except the monkeys remained food satiated throughout the acquisition phase. Phencyclidine was rapidly demonstrated to function as a reinforcer (25.9 sessions), although intakes were lower than in Experiment 1. After concurrent phencyclidine- and water-maintained performance stabilized at FR 16, the monkeys were food deprived, and phencyclidine intake increased to the levels reported in Experiment 1. Food deprivation greatly enhanced the reinforcing effect of phencyclidine and changed the temporal pattern of responding, but neither food deprivation nor food-induced drinking were necessary conditions to demonstrate the drug's reinforcing effects.