title: Reduction of conditioned pain modulation in humans by naltrexone: an exploratory study of the effects of pain catastrophizing.
abstract: The current study tested the hypothesis that conditioned pain modulation is mediated by the release of endogenous opioids with a placebo-controlled (sugar pill) study of naltrexone (50 mg) in 33 healthy volunteers over two counter-balanced sessions. Pain modulation consisted of rating of heat pain (palm) during concurrent cold water immersion (foot). Compared to baseline heat pain ratings, concurrent foot immersion lowered pain intensity ratings, which suggests an inhibitory effect, was reduced with naltrexone, suggesting at least partial dependence of inhibition on endogenous opioids. An exploratory analysis revealed that individual differences in catastrophizing moderated the effects of naltrexone; endogenous opioid blockade abolished modulation in subjects lower in catastrophizing while modulation was unaffected by naltrexone among high catastrophizers. The results suggest a role of endogenous opioids in endogenous analgesia, but hint that multiple systems might contribute to conditioned pain modulation, and that these systems might be differentially activated as a function of individual differences in responses to pain.
authors.affiliation: Department of Community Dentistry and Behavioral Science, College of Dentistry, University of Florida, 1329 SW 16th St, Gainesville, FL 32610-3628, USA. cking@dental.ufl.edu
authors.forename: Christopher D
authors.initials: CD
authors.lastname: King
authors.forename: Burel
authors.initials: B
authors.lastname: Goodin
authors.forename: Lindsay L
authors.initials: LL
authors.lastname: Kindler
authors.forename: Robert M
authors.initials: RM
authors.lastname: Caudle
authors.forename: Robert R
authors.initials: RR
authors.lastname: Edwards
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Gravenstein
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Riley
authors.forename: Roger B
authors.initials: RB
authors.lastname: Fillingim
mesh_terms: D000328:Adult; D058443:Catastrophization / Q000503:physiopathology* / Q000523:psychology*; D003214:Conditioning, Classical / Q000187:drug effects* / Q000502:physiology*; D018592:Cross-Over Studies; D059328:Diffuse Noxious Inhibitory Control / Q000187:drug effects* / Q000502:physiology*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007206:Individuality; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D018847:Opioid Peptides / Q000502:physiology; D010146:Pain / Q000503:physiopathology* / Q000523:psychology*; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D009271:Naltrexone