title: Escalation of cocaine consumption in short and long access self-administration procedures.
abstract: BACKGROUND
  Escalation of consumption is a hallmark of cocaine addiction. Many animal models reveal escalation by increasing the duration of drug access (e.g., 6-24 h/day) after longer histories of self-administration. We recently developed a method that reveals escalation early post-acquisition under shorter access conditions. However, whether or not rats will escalate cocaine consumption both early post-acquisition under short access (2 h/day) conditions, and later under long access (6 h/day) conditions, has not been demonstrated.
  
  
  METHODS
  All rats acquired cocaine self-administration (0.8 mg/kg, i.v.) under 2 h conditions, and then continued 2h self-administration for an additional 13 sessions. Then, rats were assigned either to 2 or 6h conditions, and self-administered cocaine (0.8 mg/kg, i.v.) for an additional 19 sessions. In addition, four cocaine-induced locomotor activity measurements were taken for each rat: before cocaine exposure, after non-contingent cocaine administration, and after escalation in the short and long access experimental phases.
  
  
  RESULTS
  Following acquisition, rats displayed a robust escalation of intake during 2 h sessions. Rats that self-administered cocaine in continued 2h sessions exhibited stable intake, whereas rats that self-administered cocaine in 6h sessions further escalated intake. Despite the second escalation in 6h rats, cocaine-induced locomotor activity did not differ between 2 and 6h rats.
  
  
  CONCLUSIONS
  Escalation of cocaine self-administration can occur in the same rats both early post-acquisition, and later under long access conditions. Importantly, this early post-acquisition period provides a new opportunity to determine the mechanisms first involved in the escalation phenomenon.
authors.affiliation: Department of Psychology, University of Colorado Denver, Denver, CO 80217, United States. Electronic address: bruce.mandt@ucdenver.edu.
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Mandt
authors.affiliation: Department of Psychology, University of Colorado Denver, Denver, CO 80217, United States.
authors.forename: Leland I
authors.initials: LI
authors.lastname: Copenhagen
authors.affiliation: Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045, United States.
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Zahniser
authors.affiliation: Department of Psychology, University of Colorado Denver, Denver, CO 80217, United States.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Allen
mesh_terms: D000818:Animals; D003042:Cocaine / Q000008:administration & dosage* / Q000494:pharmacology; D008124:Locomotion / Q000187:drug effects; D008297:Male; D051381:Rats; D012646:Self Administration; D013997:Time Factors
chemical_list: D003042:Cocaine
keywords: Addiction; Animal model; Cocaine self-administration; Escalation; Sensitization