title: Sweet taste pleasantness is modulated by morphine and naltrexone.
abstract: Rodent models highlight the key role of μ-opioid receptor (MOR) signaling in palatable food consumption. In humans, however, the effects of MOR stimulation on eating and food liking remain unclear.
  
  
  
  Here, we tested sweet pleasantness experience in humans following MOR drug manipulations. We hypothesized that behaviors regulated by the endogenous MOR system would be enhanced by MOR agonism and decreased by antagonism. In line with rodent findings, we expected the strongest drug effects for the sweetest (high-calorie) sucrose stimuli. As very sweet stimuli are considered aversive by many people (called sweet dislikers), we also assessed whether MOR manipulations affect pleasantness ratings of sucrose-water stimuli differently depending on subjective and objective value.
  
  
  
  In a bidirectional psychopharmacological cross-over study, 49 healthy men underwent a sweet taste paradigm following double-blind administration of the MOR agonist morphine, placebo, and the opioid antagonist naltrexone.
  
  
  
  As hypothesized, MOR stimulation with morphine increased pleasantness of the sweetest of five sucrose solutions, without enhancing pleasantness of the lower-sucrose solutions. For opioid antagonism, an opposite pattern was observed for the sweetest drink only. The observed drug effects on pleasantness of the sweetest drink did not differ between sweet likers and dislikers.
  
  
  
  The bidirectional effect of agonist and antagonist treatment aligns with rodent findings showing that MOR manipulations most strongly affect the highest-calorie foods. We speculate that the MOR system promotes survival in part by increasing concordance between the objective (caloric) and subjective (hedonic) value of food stimuli, so that feeding behavior becomes more focused on the richest food available.
authors.affiliation: Norwegian Center for Addiction Research (SERAF), University of Oslo, PO BOX 1039 Blindern, 0315, Oslo, Norway. m.h.eikemo@medisin.uio.no.|Division of Mental Health and Addiction, Oslo University Hospital, Oslo, Norway. m.h.eikemo@medisin.uio.no.|Department of Psychology, University of Oslo, Oslo, Norway. m.h.eikemo@medisin.uio.no.
authors.forename: Marie
authors.initials: M
authors.lastname: Eikemo
authors.affiliation: Department of Psychology, University of Oslo, Oslo, Norway.
authors.forename: Guro E
authors.initials: GE
authors.lastname: Løseth
authors.affiliation: School of Psychology and CLS, University of Reading, Reading, UK.
authors.forename: Tom
authors.initials: T
authors.lastname: Johnstone
authors.affiliation: Norwegian Institute of Occupational Health (STAMI), Oslo, Norway.|Department of Basic Medical Sciences, University of Oslo, Oslo, Norway.
authors.forename: Johannes
authors.initials: J
authors.lastname: Gjerstad
authors.affiliation: Department of Basic Medical Sciences, University of Oslo, Oslo, Norway.
authors.forename: Frode
authors.initials: F
authors.lastname: Willoch
authors.affiliation: Department of Psychology, University of Oslo, Oslo, Norway.|The Intervention Center, Oslo University Hospital, Oslo, Norway.
authors.forename: Siri
authors.initials: S
authors.lastname: Leknes
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000494:pharmacology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004435:Eating / Q000187:drug effects; D004644:Emotions / Q000187:drug effects; D005518:Food Preferences / Q000187:drug effects; D006801:Humans; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors; D013395:Sucrose; D013549:Sweetening Agents; D013649:Taste / Q000187:drug effects*; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; C485764:OPRM1 protein, human; D017450:Receptors, Opioid, mu; D013549:Sweetening Agents; D013395:Sucrose; D009271:Naltrexone; D009020:Morphine
keywords: Food; Human; Morphine; Naltrexone; Opioid system