title: Effects of amphetamine and methylphenidate on delay discounting in rats: interactions with order of delay presentation.
abstract: BACKGROUND
  Drug effects on delay discounting are thought to reflect changes in sensitivity to reinforcer delay, although other behavioral mechanisms might be involved. One strategy for revealing the influence of different behavioral mechanisms is to alter features of the procedures in which they are studied.
  
  
  OBJECTIVE
  This experiment examined whether the order of delay presentation under within-session delay discounting procedures impacts drug effects on discounting.
  
  
  METHODS
  Rats responded under a discrete-trial choice procedure in which responses on one lever delivered one food pellet immediately and responses on the other lever delivered three food pellets either immediately or after a delay. The delay to the larger reinforcer (0, 4, 8, 16, and 32 s) was varied within session and the order of delay presentation (ascending or descending) varied between groups.
  
  
  RESULTS
  Amphetamine (0.1-1.78 mg/kg) and methylphenidate (1.0-17.8 mg/kg) shifted delay functions upward in the ascending group (increasing choice of the larger reinforcer) and downward in the descending group (decreasing choice of the larger reinforcer). Morphine (1.0-10.0 mg/kg) and delta-9-tetrahydrocannabinol (0.32-5.6 mg/kg) tended to shift the delay functions downward, regardless of order of delay presentation, thereby reducing choice of the larger reinforcer, even when both reinforcers were delivered immediately.
  
  
  CONCLUSIONS
  The effects of amphetamine and methylphenidate under delay discounting procedures differed depending on the order of delay presentation, indicating that drug-induced changes in discounting were due, in part, to mechanisms other than altered sensitivity to reinforcer delay. Instead, amphetamine and methylphenidate altered responding in a manner consistent with increased behavioral perseveration.
authors: Departments of Pharmacology (TT, DRM, CH, CPF) and Psychiatry (CPF), University of Texas Health Science Center, San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA.
authors: Takayuki
authors: T
authors: Tanno
authors: David R
authors: DR
authors: Maguire
authors: Cedric
authors: C
authors: Henson
authors: Charles P
authors: CP
authors: France
mesh_terms: D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D019540:Area Under Curve; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D003627:Data Interpretation, Statistical; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology; D006213:Hallucinogens / Q000494:pharmacology; D008297:Male; D008774:Methylphenidate / Q000494:pharmacology*; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012201:Reward
chemical_list: D000697:Central Nervous System Stimulants; D006213:Hallucinogens; D009294:Narcotics; D008774:Methylphenidate; D009020:Morphine; D013759:Dronabinol; D000661:Amphetamine
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