title: Role of the opioid system in incentive downshift situations.
abstract: 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 (2mg/kg, ip), the delta-opioid receptor selective antagonist naltrindole (1 mg/kg, ip), and the delta-opioid receptor selective agonist DPDPE (24 microg/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.
authors.affiliation: Department of Psychology, Texas Christian University, Fort Worth, TX 76129, USA.
authors.forename: Alan M
authors.initials: AM
authors.lastname: Daniel
authors.forename: Leonardo A
authors.initials: LA
authors.lastname: Ortega
authors.forename: Mauricio R
authors.initials: MR
authors.lastname: Papini
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D003214:Conditioning, Classical / Q000187:drug effects; D019422:Dietary Sucrose / Q000008:administration & dosage*; D004327:Drinking Behavior / Q000187:drug effects*; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects; D005247:Feeding Behavior / Q000187:drug effects; D005260:Female; D006040:Goals; D008297:Male; D009042:Motivation; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D011897:Random Allocation; D051381:Rats; D020318:Rats, Long-Evans; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors; D055697:Taste Perception / Q000187:drug effects; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D019422:Dietary Sucrose; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009270:Naloxone; D009271:Naltrexone; D020881:Enkephalin, D-Penicillamine (2,5)-; C055382:naltrindole