title: Delay discounting of oral morphine and sweetened juice rewards in dependent and non-dependent rats.
abstract: BACKGROUND
  Opioid-dependent humans are reported to show accelerated delay discounting of opioid rewards when compared to monetary rewards. It has been suggested that this may reflect a difference in discounting of consumable and non-consumable goods not specific to dependent individuals. Here, we evaluate the discounting of similar morphine and non-morphine oral rewards in dependent and non-dependent rats
  
  
  METHODS
  We first tested the analgesic and rewarding effects of our morphine solution. In a second experiment, we assigned rats randomly to either dependent or non-dependent groups that, 30 min after daily testing, received 30 mg/kg subcutaneous dose of morphine, or saline, respectively. Delay discounting of drug-free reward was examined prior to initiation of the dosing regimen. We tested discounting of the morphine reward in half the rats and retested the discounting of the drug-free reward in the other half. All tests were run 22.5 h after the daily maintenance dose.
  
  
  RESULTS
  Rats preferred the morphine cocktail to the drug-free solution and consumed enough to induce significant analgesia. The control quinine solution did not produce these effects. Dependent rats discounted morphine rewards more rapidly than before dependence and when compared to discounting drug-free rewards. In non-dependent rats both reward types were discounted similarly.
  
  
  CONCLUSIONS
  These results show that morphine dependence increases impulsiveness specifically towards a drug reward while morphine experience without dependence does not.
authors.affiliation: Department of Psychology, McGill University, Montreal, QC, H3A 1B1, Canada.
authors.forename: Colin
authors.initials: C
authors.lastname: Harvey-Lewis
authors.forename: Johnna
authors.initials: J
authors.lastname: Perdrizet
authors.forename: Keith B J
authors.initials: KB
authors.lastname: Franklin
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001628:Beverages; D002755:Choice Behavior / Q000187:drug effects; D065786:Delay Discounting / Q000187:drug effects*; D007175:Impulsive Behavior / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009021:Morphine Dependence / Q000523:psychology*; D051381:Rats; D020318:Rats, Long-Evans; D012201:Reward; D013549:Sweetening Agents / Q000008:administration & dosage
chemical_list: D000701:Analgesics, Opioid; D013549:Sweetening Agents; D009020:Morphine