title: Cue-induced reinstatement of alcohol-seeking behavior is associated with increased ERK1/2 phosphorylation in specific limbic brain regions: blockade by the mGluR5 antagonist MPEP.
abstract: Relapse to alcohol use after periods of abstinence is a hallmark behavioral pathology of alcoholism and a major clinical problem. Emerging evidence indicates that metabotropic glutamate receptor 5 (mGluR5) antagonists attenuate relapse to alcohol-seeking behavior but the molecular mechanisms of this potential therapeutic effect remain unexplored. The extracellular signal-regulated kinase (ERK1/2) pathway is downstream of mGluR5 and has been implicated in addiction. We sought to determine if cue-induced reinstatement of alcohol-seeking behavior, and its reduction by an mGluR5 antagonist, is associated with changes in ERK1/2 activation in reward-related limbic brain regions. Selectively-bred alcohol-preferring (P) rats were trained to lever press on a concurrent schedule of alcohol (15% v/v) vs. water reinforcement. Following 9 days of extinction, rats were given an additional extinction trial or injected with the mGluR5 antagonist MPEP (0, 1, 3, or 10mg/kg) and tested for cue-induced reinstatement. Brains were removed 90-min later from the rats in the extinction and MPEP (0 or 10mg/kg) conditions for analysis of p-ERK1/2, total ERK1/2, and p-ERK5 immunoreactivity (IR). Cue-induced reinstatement of alcohol-seeking behavior was associated with a three to five-fold increase in p-ERK1/2 IR in the basolateral amygdala and nucleus accumbens shell. MPEP administration blocked both the relapse-like behavior and increase in p-ERK1/2 IR. p-ERK1/2 IR in the central amygdala and NAcb core was dissociated with the relapse-like behavior and the pharmacological effect of mGluR5 blockade. No changes in total ERK or p-ERK5 were observed. These results suggest that exposure to cues previously associated with alcohol self-administration is sufficient to produce concomitant increases in relapse-like behavior and ERK1/2 activation in specific limbic brain regions. Pharmacological compounds, such as mGluR5 antagonists, that reduce cue-induced ERK1/2 activation may be useful for treatment of relapse in alcoholics that is triggered by exposure to environmental events.
authors.affiliation: Department of Psychiatry, Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Thurston-Bowles Building; CB #7178, Chapel Hill, NC 27599, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Schroeder
authors.forename: Marina
authors.initials: M
authors.lastname: Spanos
authors.forename: Jennie R
authors.initials: JR
authors.lastname: Stevenson
authors.forename: Joyce
authors.initials: J
authors.lastname: Besheer
authors.forename: Michael
authors.initials: M
authors.lastname: Salling
authors.forename: Clyde W
authors.initials: CW
authors.lastname: Hodge
mesh_terms: D019973:Alcohol-Related Disorders / Q000523:psychology*; D000438:Alcohols / Q000008:administration & dosage*; D000818:Animals; D001522:Behavior, Animal; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism; D003216:Conditioning, Operant / Q000187:drug effects*; D003463:Cues; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005108:Extinction, Psychological / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D048054:Mitogen-Activated Protein Kinase 7 / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000502:physiology; D012646:Self Administration / Q000379:methods
chemical_list: D000438:Alcohols; D018691:Excitatory Amino Acid Antagonists; C578937:Grm5 protein, rat; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C121465:6-methyl-2-(phenylethynyl)pyridine; D048052:Mitogen-Activated Protein Kinase 3; D048054:Mitogen-Activated Protein Kinase 7