title: The mGluR5 antagonist 6-methyl-2-(phenylethynyl)pyridine decreases ethanol consumption via a protein kinase C epsilon-dependent mechanism.
abstract: Glutamatergic neurotransmission plays a critical role in addictive behaviors, and recent evidence indicates that genetic or pharmacological inactivation of the type 5 metabotropic glutamate receptor (mGluR5) reduces the self-administration of cocaine, nicotine, and alcohol. Because mGluR5 is coupled to activation of protein kinase C (PKC), and targeted deletion of the epsilon isoform (PKCepsilon) in mice reduces ethanol self-administration, we investigated whether there is a functional link between mGluR5 and PKCepsilon. Here, we show that acute administration of the mGluR5 agonist (R,S)-2-chloro-5-hydroxyphenylglycine to mice increases phosphorylation of PKCepsilon in its activation loop (T566) as well as in its C-terminal region (S729). Increases in phospho-PKCepsilon are dependent not only on mGluR5 stimulation but also on phosphatidylinositol-3 kinase (PI3K). In addition, the selective mGluR5 antagonist 6-methyl-2-(phenylethynyl)pyridine (MPEP) reduced basal levels of phosphorylation of PKCepsilon at S729. We also show that MPEP dose dependently reduced ethanol consumption in wild-type but not in PKCepsilon-null mice, suggesting that PKCepsilon is an important signaling target for modulation of ethanol consumption by mGluR5 antagonists. Radioligand binding experiments using [(3)H]MPEP revealed that these genotypic differences in response to MPEP were not a result of altered mGluR5 levels or binding in PKCepsilon-null mice. Our data indicate that mGluR5 is coupled to PKCepsilon via a PI3K-dependent pathway and that PKCepsilon is required for the ability of the mGluR5 antagonist MPEP to reduce ethanol consumption.
authors.affiliation: Ernest Gallo Clinic and Research Center, Department of Neurology, University of California at San Francisco, 5858 Horton St., Suite 200, Emeryville, CA 94608, USA. folive@itsa.ucsf.edu
authors.forename: M Foster
authors.initials: MF
authors.lastname: Olive
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McGeehan
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Kinder
authors.forename: Thomas
authors.initials: T
authors.lastname: McMahon
authors.forename: Clyde W
authors.initials: CW
authors.lastname: Hodge
authors.forename: Patricia H
authors.initials: PH
authors.lastname: Janak
authors.forename: Robert O
authors.initials: RO
authors.lastname: Messing
mesh_terms: D000428:Alcohol Drinking / Q000188:drug therapy* / Q000378:metabolism*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000008:administration & dosage / Q000037:antagonists & inhibitors; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011493:Protein Kinase C / Q000502:physiology*; D051744:Protein Kinase C-epsilon; D011725:Pyridines / Q000494:pharmacology* / Q000627:therapeutic use; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D018691:Excitatory Amino Acid Antagonists; C578936:Grm5 protein, mouse; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D000431:Ethanol; C121465:6-methyl-2-(phenylethynyl)pyridine; C497256:Prkce protein, mouse; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon