title: Endocannabinoid regulation of nausea is mediated by 2-arachidonoylglycerol (2-AG) in the rat visceral insular cortex.
abstract: Cannabinoid (CB) agonists suppress nausea in humans and animal models; yet, their underlying neural substrates remain largely unknown. Evidence suggests that the visceral insular cortex (VIC) plays a critical role in nausea. Given the expression of CB1 receptors and the presence of endocannabinoids in this brain region, we hypothesized that the VIC endocannabinoid system regulates nausea. In the present study, we assessed whether inhibiting the primary endocannabinoid hydrolytic enzymes in the VIC reduces acute lithium chloride (LiCl)-induced conditioned gaping, a rat model of nausea. We also quantified endocannabinoid levels during an episode of nausea, and assessed VIC neuronal activation using the marker, c-Fos. Local inhibition of monoacylglycerol lipase (MAGL), the main hydrolytic enzyme of 2-arachidonylglycerol (2-AG), reduced acute nausea through a CB1 receptor mechanism, whereas inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of anandamide (AEA), was without effect. Levels of 2-AG were also selectively elevated in the VIC during an episode of nausea. Inhibition of MAGL robustly increased 2-AG in the VIC, while FAAH inhibition had no effect on AEA. Finally, we demonstrated that inhibition of MAGL reduced VIC Fos immunoreactivity in response to LiCl treatment. Taken together, these findings provide compelling evidence that acute nausea selectively increases 2-AG in the VIC, and suggests that 2-AG signaling within the VIC regulates nausea by reducing neuronal activity in this forebrain region.
authors.affiliation: Dept. of Psychology and Collaborative Neuroscience Program, University of Guelph, Guelph, Ontario, Canada; Hotchkiss Brain Institute, Dept. of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada. Electronic address: martin.sticht@ucalgary.ca.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Sticht
authors.affiliation: Dept. of Psychology and Collaborative Neuroscience Program, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Limebeer
authors.affiliation: Dept. of Psychology and Collaborative Neuroscience Program, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Benjamin R
authors.initials: BR
authors.lastname: Rafla
authors.affiliation: Dept. of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Rehab A
authors.initials: RA
authors.lastname: Abdullah
authors.affiliation: Dept. of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Justin L
authors.initials: JL
authors.lastname: Poklis
authors.affiliation: Hotchkiss Brain Institute, Dept. of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Winnie
authors.initials: W
authors.lastname: Ho
authors.affiliation: The Skaggs Institute for Chemical Biology and Dept. of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA.
authors.forename: Micah J
authors.initials: MJ
authors.lastname: Niphakis
authors.affiliation: The Skaggs Institute for Chemical Biology and Dept. of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA.
authors.forename: Benjamin F
authors.initials: BF
authors.lastname: Cravatt
authors.affiliation: Hotchkiss Brain Institute, Dept. of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Sharkey
authors.affiliation: Dept. of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: Aron H
authors.initials: AH
authors.lastname: Lichtman
authors.affiliation: Dept. of Psychology and Collaborative Neuroscience Program, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Parker
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D002219:Carbamates / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D063388:Endocannabinoids / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism*; D009325:Nausea / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism
chemical_list: D001095:Arachidonic Acids; D002219:Carbamates; D063388:Endocannabinoids; D005989:Glycerides; C000592052:JZL195; D010879:Piperazines; D016760:Proto-Oncogene Proteins c-fos; D043884:Receptor, Cannabinoid, CB1; C094503:glyceryl 2-arachidonate
keywords: 2-arachidonoylglycerol (2-AG); 25154867); Anandamide (PubChem CID: 5281969); Endocannabinoid; Insular cortex; JZL195 (PubChem CID: 46232606); Lithium chloride (PubChem CID: 433294); MJN110 (PubChem CID: N/A); Monoacylglycerol lipase (MAGL); Nausea; Oleoylethanolamide (PubChem CID: 5283454); PF3845 (PubChem CID:; Palmitoylethanolamide (PubChem CID: 4671); Saccharin (PubChem CID: 5143); Tween 80 (PubChem CID: 5281955); URB597 (PubChem CID: 1383884); c-Fos