title: The effect of heroin dependence on resumption of heroin self-administration in rats.
abstract: BACKGROUND
  It has been proposed that relapse vulnerability in previously dependent individuals results from augmentation of drug-induced reinforcement due to repeated associations between the interoceptive properties of the drug and reduction of acute withdrawal distress.
  
  
  METHODS
  To test this hypothesis, male Sprague-Dawley rats self-administered 0.05 mg/kg/inf heroin on continuous reinforcement (CR) and progressive ratio (PR) schedules. During this period, they also received injections of vehicle or escalating doses of heroin. Following tests of naloxone-precipitated withdrawal, as well as a drug-free period (4 days), and extinction (9 sessions), they were pre-treated with vehicle or yohimbine (0.5mg/kg, IV) and tested for resumption of heroin self-administration (0.05 mg/kg/inf) on CR and PR schedules, or tested for reinstatement in extinction conditions.
  
  
  RESULTS
  Increased self-administration on the CR schedule was observed in the heroin-injected rats, but no group differences were observed on the PR schedule, in spite of greater signs of withdrawal precipitated by naloxone in the heroin-injected rats. More importantly, there were no group differences in resumption of heroin self-administration, and this was not altered by yohimbine.
  
  
  CONCLUSIONS
  These results suggest that relapse vulnerability cannot be uniquely ascribed to enhanced reinforcing action of drugs; contextual and other conditioning factors must play a role in modulating resumption of drug intake after abstinence.
authors.affiliation: Department of Psychology, University of Guelph, Ontario, Canada, N1G 2W1.
authors.forename: Meenu
authors.initials: M
authors.lastname: Minhas
authors.affiliation: Department of Psychology, University of Guelph, Ontario, Canada, N1G 2W1. Electronic address: fleri@uoguelph.ca.
authors.forename: Francesco
authors.initials: F
authors.lastname: Leri
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005108:Extinction, Psychological; D003932:Heroin / Q000008:administration & dosage*; D006556:Heroin Dependence / Q000523:psychology*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D012055:Reinforcement Schedule; D012646:Self Administration; D013375:Substance Withdrawal Syndrome / Q000523:psychology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D015016:Yohimbine; D009270:Naloxone; D003932:Heroin
keywords: Heroin; Progressive ratio; Reinstatement; Resumption; Withdrawal; Yohimbine