title: Touch Perception Altered by Chronic Pain and by Opioid Blockade.
abstract: Touch plays a significant role in human social behavior and social communication, and its rewarding nature has been suggested to involve opioids. Opioid blockade in monkeys leads to increased solicitation and receipt of grooming, suggesting heightened enjoyment of touch. We sought to study the role of endogenous opioids in perception of affective touch in healthy adults and in patients with fibromyalgia, a chronic pain condition shown to involve reduced opioid receptor availability. The pleasantness of touch has been linked to the activation of C-tactile fibers, which respond maximally to slow gentle touch and correlate with ratings of pleasantness. We administered naloxone to patients and healthy controls to directly observe the consequences of µ-opioid blockade on the perceived pleasantness and intensity of touch. We found that at baseline chronic pain patients showed a blunted distinction between slow and fast brushing for both intensity and pleasantness, suggesting reduced C-tactile touch processing. In addition, we found a differential effect of opioid blockade on touch perception in healthy subjects and pain patients. In healthy individuals, opioid blockade showed a trend toward increased ratings of touch pleasantness, while in chronic pain patients it significantly decreased ratings of touch intensity. Further, in healthy individuals, naloxone-induced increase in touch pleasantness was associated with naloxone-induced decreased preference for slow touch, suggesting a possible effect of opioid levels on processing of C-tactile fiber input. These findings suggest a role for endogenous opioids in touch processing, and provide further evidence for altered opioid functioning in chronic pain patients.
authors.affiliation: National Center for Complementary and Integrative Health, NIH , Bethesda, Maryland 20892.
authors.forename: Laura K
authors.identifier: 0000-0003-3730-2451
authors.initials: LK
authors.lastname: Case
authors.affiliation: National Center for Complementary and Integrative Health, NIH , Bethesda, Maryland 20892.
authors.forename: Marta
authors.identifier: 0000-0001-8679-8145
authors.initials: M
authors.lastname: Čeko
authors.affiliation: National Center for Complementary and Integrative Health, NIH , Bethesda, Maryland 20892.
authors.forename: John L
authors.initials: JL
authors.lastname: Gracely
authors.affiliation: National Center for Complementary and Integrative Health, NIH , Bethesda, Maryland 20892.
authors.forename: Emily A
authors.initials: EA
authors.lastname: Richards
authors.affiliation: Department of Clinical and Experimental Medicine, Center for Social and Affective Neuroscience, Linköping University , Linköping, S-581 83 Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Olausson
authors.affiliation: National Center for Complementary and Integrative Health, NIH , Bethesda, Maryland 20892.
authors.forename: M Catherine
authors.identifier: 0000-0001-5207-9767
authors.initials: MC
authors.lastname: Bushnell
mesh_terms: D000293:Adolescent; D000328:Adult; D059350:Chronic Pain / Q000503:physiopathology* / Q000523:psychology; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D010812:Physical Stimulation; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000502:physiology*; D055698:Touch Perception / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
chemical_list: D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009270:Naloxone
keywords: C-tactile fibers; affective touch; chronic pain; fibromyalgia; opioids; somatosensation