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- Title
Effects of extended-access self-administration and deprivation on breakpoints maintained by cocaine in rats.
- Authors
Yu Liu; Roberts, David C. S.; Morgan, Drake
- Abstract
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.
- Subjects
DRUG administration; DRUG abuse; COCAINE; DEPRIVATION (Psychology); NARCOTICS
- Publication
Psychopharmacology, 2005, Vol 179, Issue 3, p644
- ISSN
0033-3158
- Publication type
Article
- DOI
10.1007/s00213-004-2089-y