RATIONALE: Animal models that identify the effects of self-administration histories on subsequent patterns, levels of intake, and other aspects of reinforcement will help clarify the controlling variables of human drug use. OBJECTIVE: Identify the effects of extended-access to cocaine and 1 or 7 days of deprivation on cocaine-maintained breakpoints on a progressive ratio (PR) schedule of reinforcement. METHODS: Male, Sprague-Dawley rats were trained to self-administer intravenous cocaine (expt 1: 1.5 mg/kg per infusion; expt 2: 0.75 mg/kg per infusion), and then given various histories of self-administration and deprivation. Breakpoints, the number of infusions self-administered on a PR schedule, were assessed following the deprivation period. RESULTS: Rates of cocaine intake increased when access to cocaine was extended to 6 h/day. From day 1 to day 14, daily intake increased from 92 (+/-2.5) to 101 (+/-2.8) mg/kg in expt 1, and from 55 (+/-4) to 78 (+/-2.2) mg/kg in expt 2. Total intake across this 2-week period was approximately 1260 and 970 mg/kg in expts 1 and 2. Breakpoints were not different following this escalation period. The introduction of a 7-day deprivation period failed to alter breakpoints. CONCLUSIONS: There is dissociation between changes in rate of cocaine intake (or consumption) and breakpoints maintained on a PR schedule. Extended-access to cocaine produced increases in rate of intake without altering breakpoints. Depending on the experimental question, extended-access conditions may prove useful for studying changes in certain aspects of reinforcement, such as consumption, but not others, such as the strength of a drug as a reinforcer.
RATIONALE: Animal models that identify the effects of self-administration histories on subsequent patterns, levels of intake, and other aspects of reinforcement will help clarify the controlling variables of human drug use. OBJECTIVE: Identify the effects of extended-access to cocaine and 1 or 7 days of deprivation on cocaine-maintained breakpoints on a progressive ratio (PR) schedule of reinforcement. METHODS: Male, Sprague-Dawley rats were trained to self-administer intravenous cocaine (expt 1: 1.5 mg/kg per infusion; expt 2: 0.75 mg/kg per infusion), and then given various histories of self-administration and deprivation. Breakpoints, the number of infusions self-administered on a PR schedule, were assessed following the deprivation period. RESULTS: Rates of cocaine intake increased when access to cocaine was extended to 6 h/day. From day 1 to day 14, daily intake increased from 92 (+/-2.5) to 101 (+/-2.8) mg/kg in expt 1, and from 55 (+/-4) to 78 (+/-2.2) mg/kg in expt 2. Total intake across this 2-week period was approximately 1260 and 970 mg/kg in expts 1 and 2. Breakpoints were not different following this escalation period. The introduction of a 7-day deprivation period failed to alter breakpoints. CONCLUSIONS: There is dissociation between changes in rate of cocaine intake (or consumption) and breakpoints maintained on a PR schedule. Extended-access to cocaine produced increases in rate of intake without altering breakpoints. Depending on the experimental question, extended-access conditions may prove useful for studying changes in certain aspects of reinforcement, such as consumption, but not others, such as the strength of a drug as a reinforcer.
Authors: Chesley J Christensen; Alan Silberberg; Steven R Hursh; Mary E Huntsberry; Anthony L Riley Journal: Psychopharmacology (Berl) Date: 2008-03-20 Impact factor: 4.530
Authors: Richard M Allen; Kristina A Uban; Elizabeth M Atwood; David S Albeck; Dorothy J Yamamoto Journal: Pharmacol Biochem Behav Date: 2007-07-21 Impact factor: 3.533
Authors: Kathleen M Kantak; Nicole Barlow; David H Tassin; Madeline F Brisotti; Chloe J Jordan Journal: Psychopharmacology (Berl) Date: 2014-05-07 Impact factor: 4.530