Effects of different food-reinforcement histories on cocaine self-administration by rhesus monkeys

The purpose of the present study was to examine whether a history of responding under food reinforcement schedules that generated either high or low response rates would influence the acquisition and maintenance of cocaine self-administration. Eight experimentally naive rhesus monkeys were initially trained to respond on the right lever under either a fixed-ratio (FR) 50 or interresponse times (IRT) > 30-s schedule of food reinforcement. After 65 sessions of food-maintained responding, monkeys were surgically prepared with indwelling intravenous catheters and cocaine 0.03 mg/kg per injection (IV) was available on the left lever under a fixed-interval (FI) 5-min schedule. After at least 60 consecutive sessions at this dose, a cocaine dose-response curve (saline, 0.01-0.3 mg/kg per injection) was determined. The FR 50 schedule generated high rates of food-maintained responding (90.1 +/- 6.2 responses/min), while response rates under the IRT > 30-s schedule were low (1.9 +/- 0.1 responses/min). Across the 60 consecutive sessions under the FI 5-min schedule, linear changes in response rates and cocaine intake were significantly different between FR- and IRT-history monkeys. FR-history monkeys responded at higher rates than IRT-history subjects, while cocaine intake during the first 15 sessions was lower in FR- compared to IRT-history monkeys. Rates of cocaine-maintained responding after food-reinforcement histories were compared to response rates of monkeys initially trained to self-administer cocaine under an FI 5-min schedule (Nader and Reboussin 1994).(ABSTRACT TRUNCATED AT 250 WORDS)