THE EFFECTS OF DELAY OF REINFORCEMENT AND DOSE ON THE SELF-ADMINISTRATION OF COCAINE AND PROCAINE IN RHESUS-MONKEYS

Delays of reinforcement were imposed while three rhesus monkeys intrav enously self-administered either cocaine or procaine to determine whet her the magnitude of delay-induced reductions in infusion frequency we re dose- or drug-dependent. Drug-maintained baselines demonstrating th e greatest resistance to change under delay conditions might be concep tualized as involving the greatest strength of responding and include drug reinforcers with the greatest efficacy. Under baseline conditions , cocaine or procaine was infused contingent upon lever pressing accor ding to fixed ratio 10 schedules during daily, 1-h experimental sessio ns. Under delay conditions, a 120-s delay of reinforcement was inserte d between the completion of each fixed ratio contingency and infusion delivery. Tests under baseline and delay conditions alternated until s everal doses of cocaine (3, 10, 33, 100, and 300 mu g/kg), and subsequ ently, of procaine (33, 100, 300, 1000, and 3000 mu g/kg) were tested. The results indicated that during both baseline and delay conditions increases in dose of either drug resulted in increases followed by dec reases in the number of infusions obtained. Introducing delays of rein forcement resulted in decreases in the number of infusions obtained at a given dose. Generally, however, when reinforcement delays were impo sed the decreases in infusion number, as a percentage of baseline numb er, were less at the higher doses of both drugs. The doses of procaine which were maximally effective as reinforcers (i.e. during which infu sion number was minimally reduced by delay) were as effective as the m aximally effective doses of cocaine: These results suggest that drug p reparations and routes of administration which, in fact, maximize unit dose delivery would also maximize the likelihood that drug-maintained behavior will be; resistant to theraputic intervention.