title: Opioid-receptor antagonism increases pain and decreases pleasure in obese and non-obese individuals.
abstract: Endogenous opioids inhibit nociceptive processing and promote the experience of pleasure. It has been proposed that pain and pleasure lie at opposite ends of an affective spectrum, but the relationship between pain and pleasure and the role of opioids in mediating this relationship has not been tested.
  
  
  
  Here, we used obese individuals as a model of a dysfunctional opioid system to assess the role of the endogenous opioid peptide, beta-endorphin, on pain and pleasure sensitivity.
  
  
  
  Obese (10M/10F) and age- and gender-matched non-obese (10M/10F) controls were included in the study. Pain sensitivity using threshold, tolerance, and subjective rating assessments and perceived sweet pleasantness using sucrose solutions were assessed in two testing sessions with placebo or the opioid antagonist, naltrexone (0.7 mg/kg body weight). Beta-endorphin levels were assessed in both sessions.
  
  
  
  Despite having higher levels of baseline beta-endorphin and altered beta-endorphin-reactivity to naltrexone, obese individuals reported a similar increase in pain and decrease in pleasantness following naltrexone compared to non-obese individuals. Beta-endorphin levels did not correlate with pain or pleasantness in either group, but naltrexone-induced changes in pain and pleasantness were mildly correlated. Moreover, naltrexone-induced changes in pain were related to depression scores, while naltrexone-induced changes in sweet pleasantness were related to anxiety scores, indicating that pain and pleasantness are related, but influenced by different processes.
authors.affiliation: Faculty of Medicine, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.|Alan Edwards Center for Research on Pain, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Price
authors.affiliation: McGill University Department of Surgery, Royal Victoria Hospital, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.
authors.forename: Nicolas V
authors.initials: NV
authors.lastname: Christou
authors.affiliation: McGill University Department of Anesthesia, Royal Victoria Hospital, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.
authors.forename: Steven B
authors.initials: SB
authors.lastname: Backman
authors.affiliation: Alan Edwards Center for Research on Pain, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.|Faculty of Dentistry, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada.
authors.forename: Laura
authors.initials: L
authors.lastname: Stone
authors.affiliation: Faculty of Medicine, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada. petra.schweinhadrt@mcgill.ca.|Alan Edwards Center for Research on Pain, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada. petra.schweinhadrt@mcgill.ca.|Faculty of Dentistry, McGill University, Strathcona Anatomy and Dentistry Building, Bldg Rm M/19, 3640 Rue University, Montreal, QC, H3A 0C7, Canada. petra.schweinhadrt@mcgill.ca.
authors.forename: Petra
authors.initials: P
authors.lastname: Schweinhardt
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009765:Obesity / Q000503:physiopathology*; D018847:Opioid Peptides / Q000494:pharmacology; D017288:Pain Threshold / Q000187:drug effects*; D057181:Pleasure / Q000187:drug effects*; D012684:Sensory Thresholds / Q000187:drug effects; D001615:beta-Endorphin / Q000378:metabolism
chemical_list: D009292:Narcotic Antagonists; D018847:Opioid Peptides; D009271:Naltrexone; D001615:beta-Endorphin
keywords: Anxiety; Beta-endorphin; Depression; Naltrexone; Obesity; Opioid