Combined effects of buprenorphine and an alternative nondrug reinforcer on phencyclidine self-administration in rhesus monkeys

Six rhesus monkeys self-administered orally delivered phencyclidine (PCP; 0.25 mg/ml) with saccharin (0.3% or 0.03% wt/vol) or water under concurrent fixed-ratio (FR) schedules. During daily 3-hr sessions, subjects had concurrent access to 2 liquids: PCP versus water, PCP versus saccharin, or saccharin versus water. The FR of both liquids was varied (4, 8, 16, 32, and 64) in nonsystematic order and when behavior was stable at each FR, buprenorphine (0.005 mg/kg) was injected intramuscularly for 5 days. Buprenorphine treatment decreased PCP deliveries by 16-65% across the range of FR values when compared with the no-treatment baseline, and concurrent saccharin reduced PCP deliveries from 34-63%. Combining buprenorphine treatment and concurrent availability of saccharin produced decreases in PCP deliveries of 70-87% from the no-treatment baseline across the FR values. Greater reductions were found at the highest FR values. P(max) values were shifted to the left under all treatment conditions, suggesting that the reinforcing efficacy of the drug was reduced. These findings suggest that pharmacological and behavioral treatments produce additive reductions in drug self-administration.