The mGluR5 antagonist MPEP selectively inhibits the onset and maintenance of ethanol self-administration in C57BL/6J mice.
BACKGROUND
Many of the biochemical, physiological, and behavioral effects of ethanol are known to be mediated by ionotropic glutamate receptors. Emerging evidence implicates metabotropic glutamate receptors (mGluRs) in the biobehavioral effects of ethanol and other drugs of abuse, but there is little information regarding the role of mGluRs in the reinforcing effects of ethanol.


METHODS
Male C57BL/6J mice were trained to lever-press on a concurrent fixed ratio 1 schedule of ethanol (10% v/v) vs water reinforcement during 16-h sessions. Effects of mGluR1, mGluR2/3, and mGluR5 antagonists were then tested on parameters of ethanol self-administration behavior.


RESULTS
The mGluR5 antagonist MPEP (1-10 mg/kg, i.p.) dose-dependently reduced ethanol-reinforced responding but had no effect on concurrent water-reinforced responding. Analysis of the temporal pattern of responding showed that MPEP reduced ethanol-reinforced responding during peak periods of behavior occurring during the early hours of the dark cycle. Further analysis showed that MPEP reduced the number of ethanol response bouts and bout-response rate. MPEP also produced a 13-fold delay in ethanol response onset (i.e., latency to the first response) with no corresponding effect on water response latency or locomotor activity. The mGluR1 antagonist CPCCOEt (1-10 mg/kg, i.p.) or the mGluR2/3 antagonist LY 341495 (1-30 mg/kg, i.p.) failed to alter ethanol- or water-reinforced responding.


CONCLUSIONS
These data indicate that mGlu5 receptors selectively regulate the onset and maintenance of ethanol self-administration in a manner that is consistent with reduction in ethanol's reinforcement function.
Hodge
Clyde W
CW
Department of Psychiatry, Bowles Center for Alcohol Studies School of Medicine, CB#7178, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7178, USA. chodge@med.unc.edu
Miles
Michael F
MF
Sharko
Amanda C
AC
Stevenson
Rebekah A
RA
Hillmann
Jennie R
JR
Lepoutre
Veronique
V
Besheer
Joyce
J
Schroeder
Jason P
JP
D000428:Alcohol Drinking / Q000523:psychology; D000818:Animals; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology*; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors*; D012054:Reinforcement, Psychology; D012646:Self Administration
D002492:Central Nervous System Depressants; 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