Journal
NEUROBIOLOGY OF LEARNING AND MEMORY
Volume 92, Issue 3, Pages 439-450Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.nlm.2009.06.003
Keywords
Opioid system; Incentive contrast; Consummatory successive negative contrast; Appetitive extinction; Naloxone; Naltrindole; DPDPE; Rats
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Previous research has shown that opioid blockage enhances consummatory successive negative contrast (cSNC)-a suppression of consummatory behavior following a downshift from 32% to 4% sucrose solution. In Experiment 1, administration of the nonselective opioid receptor antagonist naloxone (2 mg/kg, ip) distorted the comparison between expected and received incentives. The results of Experiment 2 discarded the alternative that naloxone enhances cSNC by inducing a conditioned taste aversion. The results of Experiments 3a-3c provided no evidence that opioid administration after the first downshift trial modulated subsequent consummatory performance. The opioids tested included naloxone (2 mg/kg, ip), the delta-opioid receptor selective antagonist naltrindole (1 mg/kg, ip), and the delta-opioid receptor selective agonist DPDPE (24 mu g/kg, ip). The selected doses have proven in earlier experiments to be effective when administered before training. Experiments 4-5 failed to uncover any effects of posttraining opioid blockage with naloxone in an appetitive extinction task (autoshaping with lever-food pairings). These results add to our previous understanding of opioid function in situations involving incentive downshifts, suggesting a role in the comparison process that triggers cSNC, but no apparent function in memory consolidation related to the downshift event. (C) 2009 Elsevier Inc. All rights reserved.
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