title: Activation of the opioidergic descending pain control system underlies placebo analgesia.
abstract: Placebo analgesia involves the endogenous opioid system, as administration of the opioid antagonist naloxone decreases placebo analgesia. To investigate the opioidergic mechanisms that underlie placebo analgesia, we combined naloxone administration with functional magnetic resonance imaging. Naloxone reduced both behavioral and neural placebo effects as well as placebo-induced responses in pain-modulatory cortical structures, such as the rostral anterior cingulate cortex (rACC). In a brainstem-specific analysis, we observed a similar naloxone modulation of placebo-induced responses in key structures of the descending pain control system, including the hypothalamus, the periaqueductal gray (PAG), and the rostral ventromedial medulla (RVM). Most importantly, naloxone abolished placebo-induced coupling between rACC and PAG, which predicted both neural and behavioral placebo effects as well as activation of the RVM. These findings show that opioidergic signaling in pain-modulating areas and the projections to downstream effectors of the descending pain control system are crucially important for placebo analgesia.
authors.affiliation: Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. f.eippert@uke.uni-hamburg.de
authors.forename: Falk
authors.initials: F
authors.lastname: Eippert
authors.forename: Ulrike
authors.initials: U
authors.lastname: Bingel
authors.forename: Eszter D
authors.initials: ED
authors.lastname: Schoell
authors.forename: Juliana
authors.initials: J
authors.lastname: Yacubian
authors.forename: Regine
authors.initials: R
authors.lastname: Klinger
authors.forename: Jürgen
authors.initials: J
authors.lastname: Lorenz
authors.forename: Christian
authors.initials: C
authors.lastname: Büchel
mesh_terms: D000328:Adult; D000698:Analgesia / Q000379:methods*; D000701:Analgesics, Opioid / Q000494:pharmacology / Q000627:therapeutic use; D004311:Double-Blind Method; D006801:Humans; D008297:Male; D009270:Naloxone / Q000494:pharmacology / Q000627:therapeutic use; D010146:Pain / Q000503:physiopathology* / Q000517:prevention & control; D010147:Pain Measurement / Q000187:drug effects / Q000379:methods*; D015990:Placebo Effect; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology*; D011957:Receptors, Opioid / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D011957:Receptors, Opioid; D009270:Naloxone