title: Discrete-trial control of morphine self-injection behaviour in monkeys: effects of injection dose and trials per session.
abstract: Responding for intravenous injections of morphine was studied using a discrete-trials procedure in squirrel monkeys. For one group, each session consisted of 10 trials at an inter-trial interval of 15 min; for the second group, each session consisted of 100 trials at an inter-trial interval of 1.5 min. When different injection doses of morphine (1-1000 mug/kg per injection), including saline as a control procedure, were substituted at random for blocks of five consecutive sessions, the frequency of morphine self-administration was found to be an inverted U-shaped function of the injection dose. This relationship was observed in each group of monkeys, despite a 10-fold difference in the total amount of the drug which was available for self-administration per session when a given injection dose was substituted for both groups. The results show that the injection dose of morphine acted as a primary determinant of response probability, even under circumstances in which trial spacing imposed a significant delay between consecutive opportunities for drug self-administration,
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D000882:Haplorhini; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D012453:Saimiri; D012646:Self Administration
chemical_list: D009020:Morphine