title: A new animal model of placebo analgesia: involvement of the dopaminergic system in reward learning.
abstract: We suggest a new placebo analgesia animal model and investigated the role of the dopamine and opioid systems in placebo analgesia. Before and after the conditioning, we conducted a conditioned place preference (CPP) test to measure preferences for the cues (Rooms 1 and 2), and a hot plate test (HPT) to measure the pain responses to high level-pain after the cues. In addition, we quantified the expression of tyrosine hydroxylase (TH) in the ventral tegmental area (VTA) and c-Fos in the anterior cingulate cortex (ACC) as a response to reward learning and pain response. We found an enhanced preference for the low level-pain paired cue and enhanced TH expression in the VTA of the Placebo and Placebo + Naloxone groups. Haloperidol, a dopamine antagonist, blocked these effects in the Placebo + Haloperidol group. An increased pain threshold to high-heat pain and reduced c-Fos expression in the ACC were observed in the Placebo group only. Haloperidol blocked the place preference effect, and naloxone and haloperidol blocked the placebo analgesia. Cue preference is mediated by reward learning via the dopamine system, whereas the expression of placebo analgesia is mediated by the dopamine and opioid systems.
authors.affiliation: Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea.|Department of Internal Medicine: Psychosomatic Medicine and Psychotherapy, University of Tübingen, Tübingen, Germany.|Institute for Medical Psychology, fMEG Center, University of Tübingen, Tübingen, Germany.|IMPRS for Cognitive and Systems Neuroscience, University of Tübingen, Tübingen, Germany.
authors.forename: In-Seon
authors.initials: IS
authors.lastname: Lee
authors.affiliation: Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea.
authors.forename: Bombi
authors.initials: B
authors.lastname: Lee
authors.affiliation: Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea.
authors.forename: Hi-Joon
authors.initials: HJ
authors.lastname: Park
authors.affiliation: Center for Social and Affective Neuroscience, Linköping University.
authors.forename: Håkan
authors.initials: H
authors.lastname: Olausson
authors.affiliation: Department of Internal Medicine: Psychosomatic Medicine and Psychotherapy, University of Tübingen, Tübingen, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Enck
authors.affiliation: Acupuncture and Meridian Science Research Center, College of Korean Medicine, Kyung Hee University, Seoul, Korea.
authors.forename: Younbyoung
authors.initials: Y
authors.lastname: Chae
mesh_terms: D000698:Analgesia / Q000379:methods*; D000818:Animals; D018492:Dopamine Antagonists / Q000494:pharmacology; D006179:Gyrus Cinguli / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D006220:Haloperidol / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D023421:Models, Animal; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010146:Pain / Q000378:metabolism / Q000473:pathology*; D017288:Pain Threshold / Q000502:physiology; D015990:Placebo Effect; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology
chemical_list: D018492:Dopamine Antagonists; D009292:Narcotic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D009270:Naloxone; D014446:Tyrosine 3-Monooxygenase; D006220:Haloperidol