title: Second-order schedules of intravenous drug self-administration in rhesus monkeys.
abstract: Lever-pressing behavior was generated and maintained in 3 rhesus monkeys by intravenous infusions of morphine or cocaine under a second-order schedule of reinforcement. Under this schedule, every tenth lever-press response (FR 10) during a fixed interval of time produced a 2 sec stimulus light. The first FR 10 completed after a 60 min interval had elapsed produced the stimulus light and an intravenous infusion of morphine or cocaine. The stimulus light remained on for the duration of the drug infusion (50-60 sec). Sessions of morphine or cocaine presentation, each with distinct stimulus light conditions, alternated on a daily basis. Under this schedule, single doses of morphine from 0.125 to 1.0 mg/kg maintained high overall response rates (maximum of 40 Rs/min) in the pattern characteristic of fixed interval (FI) schedules of reinforcement. There was no functional relationship between the response-rates and the doses of morphine tested. The simultaneous infusion of naloxone (0.125 mg/kg/) with morphine (0.25 mg/kg) markedly decreased response rates. However, the infusion of the same dose of naloxone five min after the presentation of morphine failed to suppress self-administration behavior. Naloxone had no effects on cocaine-reinforced responding.
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant; D000882:Haplorhini; D006801:Humans; D008253:Macaca mulatta; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D012055:Reinforcement Schedule; D012646:Self Administration; D019966:Substance-Related Disorders
chemical_list: D009270:Naloxone; D009020:Morphine; D003042:Cocaine