title: Effects of dose and infusion delay on cocaine self-administration choice in rhesus monkeys.
abstract: BACKGROUND
  Drug abuse is often considered a problem related to impulse-control disorders, but little is known about the factors that determine the choice to self-administer a drug in a self-control/impulsivity paradigm.
  
  
  OBJECTIVE
  The objective of the present study was to evaluate choice between a low dose of cocaine administered after a relatively short delay (impulsive option) and a high dose of cocaine following a relatively longer delay (self-control option).
  
  
  METHODS
  Rhesus monkeys self-administered intravenous cocaine in a discrete-trials choice procedure. First, choice was between different 3:1 doses (0.3/0.1 and 0.1/0.03 mg/kg per injection) following equal 30-s delays to infusion. Second, choice was between equal doses (0.1 mg/kg per injection) following 3:1 delays (30 s/10 s, 90 s/30 s, 270 s/90 s, 810 s/270 s). Third, choice was between 0.1 or 0.03 mg/kg per injection after the same 3:1 delays with the larger dose following the longer delay and the smaller dose following the shorter delay. Fourth, the same 3:1 delays were used to study choice between 0.3 and 0.1 mg/kg per injection.
  
  
  RESULTS
  With equal delays, the larger dose of cocaine was chosen almost exclusively, and with equal doses, the shorter delay was chosen almost exclusively. When both dose and delay were manipulated, mean large-dose (0.1 mg/kg per injection) choices for three of four subjects was 98% when the delays were the shortest (30 s/10 s), but this preference reversed as the delays increased, so that 74% of choices were for the smaller dose (0.03 mg/kg per injection) at the longest delays (810 s/270 s). This systematic decrease in large-dose choices as the absolute, but not relative, values of the delays were increased, was also observed with the higher dose combination.
  
  
  CONCLUSIONS
  Delay discounting was supported by the present findings in that the value of a large reinforcer (higher cocaine dose) was decreased as its delay to presentation was increased. The importance of not only relative, but absolute, values of delays to drug reinforcement in determining drug choice was also demonstrated. Thus, a self-control/impulsivity paradigm can be extended to conditions with non-human subjects and drug reinforcers.
authors.affiliation: Department of Psychiatry and Human Behavior, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216, USA. kanderson@psychiatry.umsmed.edu
authors.forename: Karen G
authors.initials: KG
authors.lastname: Anderson
authors.forename: William L
authors.initials: WL
authors.lastname: Woolverton
mesh_terms: D000818:Animals; D002755:Choice Behavior / Q000187:drug effects*; D003042:Cocaine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D007175:Impulsive Behavior; D007262:Infusions, Intravenous; D008253:Macaca mulatta; D008297:Male; D012055:Reinforcement Schedule; D012646:Self Administration; D013997:Time Factors
chemical_list: D003042:Cocaine