Journal
NEUROBIOLOGY OF LEARNING AND MEMORY
Volume 93, Issue 2, Pages 248-260Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.nlm.2009.10.005
Keywords
Heroin; Cocaine; Naloxone; Reacquisition; Conditioned place preference; Ventral tegmental area; Memory consolidation; Rat
Funding
- Natural Sciences and Engineering Research Council of Canada
- Canada Foundation for Innovation
- Ontario Innovation Trust
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To investigate the effect of naloxone on a putative memory consolidation process underlying reacquisition of heroin and cocaine conditioned place preference, four studies were conducted in male Sprague-Dawley rats using a common procedure involving: place conditioning (0.3 or 1 mg/kg heroin or 20 mg/kg cocaine; x 4 sessions), extinction (vehicle x 4 sessions), and reconditioning (0 or 1 mg/kg heroin or 20 mg/kg cocaine; x 1 session). Systemic naloxone injections (0, 1 and 3 mg/kg) or bilateral intra-ventral tegmental area (VTA) naloxone methiodide infusions (2 nmol in 0.5 mu l x side) were administered at different times following reconditioning. Post-reconditioning administration of naloxone dose-dependently blocked, attenuated and had no effect on reacquisition of heroin CPP when administered immediately, 1 h and 6 h after reconditioning, respectively. The highest dose of naloxone also blocked reacquisition of cocaine CPP, and did not produce a conditioned place aversion in heroin-naive and heroin pre-treated animals. Post-reconditioning infusions in the VTA, but not in adjacent structures, blocked reacquisition of heroin CPP when administered immediately, but not 6 h, after reconditioning. These data suggest that reacquisition of drug-cues associations involves a memory consolidation process sensitive to manipulations of the endogenous opioid system, and indicate that opioid receptors in the VIA may be critically involved in the re-emergence of drug seeking behavior. (C) 2009 Elsevier Inc. All rights reserved.
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