Concurrent progressive-ratio schedules to compare reinforcing effectiveness of different phencyclidine (PCP) concentrations in rhesus monkeys.
BACKGROUND
Progressive ratio (PR) schedules have become well accepted for testing the reinforcing effectiveness of drugs. This study extends the methods to concurrent PR schedules with different concentrations of orally delivered phencyclidine (PCP).


OBJECTIVE
The sensitivity of the procedure is tested by presenting different PCP concentrations with independently-operating PR schedules.


METHODS
PCP self-administration was investigated in seven rhesus monkeys. Six different PCP concentrations (0.03-1.0 mg/ml) and water were randomly paired (21 pairings). Liquid delivery (24 ml) was contingent upon lip-contact responses on solenoid-operated drinking spouts; whereby, the response requirement or fixed-ratio (FR) increased (from 8 to 16, 32, 64, 128... to 4096) after each successful completion of a previous FR and subsequent liquid delivery. Monkeys self administered PCP during daily 3-h sessions, and each pair of concentrations was held constant until behavior had stabilized for at least 4 days.


RESULTS
The higher of the two PCP concentrations always maintained greater responding, PR break point (BP), or the last ratio completed, and liquid deliveries than did the lower concentration. However, the monkeys did not exclusively respond on the drinking spout that yielded the higher drug concentration. When examined across all drug pairings, the percentage of total available deliveries of the higher concentration was significantly greater than those of the lower concentration. The monkeys maximized the amount (mg) consumed for the response output. Responding, BPs and liquid deliveries maintained by 0.12 and 0.25 mg/ml PCP were significantly greater than other PCP concentrations; however, drug intake (mg) increased directly with PCP concentration.


CONCLUSIONS
These results indicate that concurrent PR schedules using oral drug self-administration and a concurrent choice paradigm reliably provide an estimation of relative reinforcing strength, and behavior maintained by these schedules is sensitive to small changes in PCP concentration.
Department of Psychiatry, University of Minnesota, Minneapolis 55455, USA.
J S
JS
Rodefer
M E
ME
Carroll
D000284:Administration, Oral; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D006213:Hallucinogens / Q000008:administration & dosage* / Q000494:pharmacology; D008253:Macaca mulatta; D008297:Male; D010622:Phencyclidine / Q000008:administration & dosage* / Q000494:pharmacology; D012055:Reinforcement Schedule
D006213:Hallucinogens; D010622:Phencyclidine