title: Lack of endogenous opioid release during sustained visceral pain: a [11C]carfentanil PET study.
abstract: Opioidergic neurotransmission in the central nervous system is involved in somatic pain, but its role in visceral pain remains unknown. We aimed to quantify endogenous opioid release in the brain during sustained painful gastric distension. Therefore, 2 dynamic [11C]carfentanil positron emission tomography scans were performed in 20 healthy subjects during 2 conditions: sustained (20 minutes) painful proximal gastric balloon distension at predetermined individual discomfort threshold (PAIN) and no distension (NO PAIN), in counterbalanced order. Pain levels were assessed during scanning using visual analogue scales and after scanning using the McGill Pain Questionnaire. Emotional state was rated after scanning using the Positive and Negative Affect Schedule. Distribution volume ratios in 21 volumes of interest in the pain matrix were used to quantify endogenous opioid release. During the PAIN compared to the NO PAIN condition, volunteers reported a significantly higher increase in negative affect (5.50±1.29 versus 0.10±1.08, P=.0147) as well as higher pain ratings (sensory: 74.05±9.23 versus 1.50±0.95, P<.0001; affective: 91.42±8.13 versus 4.33±6.56, P<.0001). No difference in endogenous opioid release was demonstrated in any of the volumes of interest. Thus, contrary to its somatic counterpart, no opioid release is detected in the brain during sustained visceral pain, despite similar pain intensities. Endogenous opioids may play a less important role in visceral compared to somatic pain.
authors.affiliation: Department of Clinical and Experimental Medicine, Translational Research Center for Gastrointestinal Diseases (TARGID), University of Leuven, Belgium Department of Neurosciences, Division of Experimental Neurology, Laboratory for Cognitive Neurology, University of Leuven, Belgium Department of Medical Diagnostic Sciences, Medical Imaging Research Center, University of Leuven, Belgium Department of Medical Diagnostic Sciences, Nuclear Medicine Section, University of Leuven, Belgium Faculty of Pharmaceutical Sciences, Laboratory for Radiopharmacy, University of Leuven, Belgium University Psychiatric Centre, Liaison Psychiatry, University Hospital Gasthuisberg, Leuven, Belgium.
authors.forename: Huynh Giao
authors.initials: HG
authors.lastname: Ly
authors.forename: Patrick
authors.initials: P
authors.lastname: Dupont
authors.forename: Brecht
authors.initials: B
authors.lastname: Geeraerts
authors.forename: Guy
authors.initials: G
authors.lastname: Bormans
authors.forename: Koen
authors.initials: K
authors.lastname: Van Laere
authors.forename: Jan
authors.initials: J
authors.lastname: Tack
authors.forename: Lukas
authors.initials: L
authors.lastname: Van Oudenhove
mesh_terms: D000293:Adolescent; D000328:Adult; D002250:Carbon Radioisotopes; D005260:Female; D005283:Fentanyl / Q000031:analogs & derivatives*; D006801:Humans; D008297:Male; D018847:Opioid Peptides / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000379:methods; D016037:Single-Blind Method; D013997:Time Factors; D059265:Visceral Pain / Q000000981:diagnostic imaging*; D055815:Young Adult
chemical_list: D002250:Carbon Radioisotopes; D018847:Opioid Peptides; C017114:carfentanil; D005283:Fentanyl
keywords: Endogenous opioid release; Positron emission tomography; Visceral pain; [(11)C]carfentanil