Increases in the reinforcing efficacy of cocaine after... : Behavioural Pharmacology (original) (raw)
Research Papers
Increases in the reinforcing efficacy of cocaine after particular histories of reinforcement
Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
Correspondence to Drake Morgan, Department of Physiology and Pharmacology Wake Forest University School of Medicine, Winston-Salem, NC 27157-1083, USA. E-mail: [email protected]
*Current address: Department of Psychiatry, University of British Columbia, Vancouver, BC, V6 T 2A1, Canada.
†Current address: Department of Psychiatry, Yale University School of Medicine, New Haven, CT 06520-8068, USA.
Received 2 July 2002 accepted as revised 23 July 2002
Abstract
In humans, the progression to cocaine addiction presumably involves increases in the effectiveness of cocaine to function as a reinforcer. Here we use breakpoints assessed using the progressive ratio (PR) schedule as an index of the efficacy of cocaine as a reinforcer. To date, no preclinical studies have demonstrated an increase in breakpoint as a consequence of self-administration history. In the current study, baseline performances on fixed ratio (FR) and PR schedules were determined. Rats were then exposed to different self-administration histories and deprivation periods, and responding under FR and PR schedules was reassessed. Exposure to a discrete-trials procedure (access to cocaine 4 times/hour, 24 hours/day; DT4) for 7 or 10 days, coupled with a deprivation period of 7 days, resulted in increases in breakpoint on a PR schedule, with no change in FR1 schedule responding. Exposure to an FR1 schedule for 72 consecutive hours followed by 7 days of deprivation, failed to change breakpoints, but increased rates of intake assessed with an FR1 schedule. Thus, the type of self-administration history and the length of deprivation experienced contribute to changes in the reinforcing efficacy of cocaine as measured by a PR schedule.
© 2002 Lippincott Williams & Wilkins, Inc.