Reduced Levels of mGlu2 Receptors within the Prelimbic Cortex Are Not Associated with Elevated Glutamate Transmission or High Alcohol Drinking

Alcohol Clin Exp Res. 2017 Nov;41(11):1896-1906. doi: 10.1111/acer.13488. Epub 2017 Oct 3.


Background: A Grm2 cys407* stop codon mutation, which results in a loss of the metabotropic glutamate 2 (mGlu2) receptor protein, was identified as being associated with high alcohol drinking by alcohol-preferring (P) rats. The objectives of the current study were to characterize the effects of reduced levels of mGlu2 receptors on glutamate transmission and alcohol drinking.

Methods: Quantitative no-net-flux microdialysis was used to test the hypothesis that basal extracellular glutamate levels in the prelimbic (PL) cortex and nucleus accumbens shell (NACsh) will be higher in P than Wistar rats. A lentiviral-delivered short-hairpin RNA (shRNA)-mediated knockdown was used to test the hypothesis that reduced levels of mGlu2 receptors within the PL cortex will increase voluntary alcohol drinking by Wistar rats. A linear regression analysis was used to test the hypothesis that there will be a significant correlation between the Grm2 cys407* mutation and level of alcohol intake.

Results: Extracellular glutamate concentrations within the PL cortex (3.6 ± 0.6 vs. 6.4 ± 0.6 μM) and NACsh (3.2 ± 0.4 vs. 6.6 ± 0.6 μM) were significantly lower in female P than female Wistar rats. Western blot detected the presence of mGlu2 receptors in these regions of female Wistar rats, but not female P rats. Micro-infusion of shRNAs into the PL cortex significantly reduced local mGlu2 receptor levels (by 40%), but did not alter voluntary alcohol drinking in male Wistar rats. In addition, there was no significant correlation between the Grm2 mutation and alcohol intake in 36 rodent lines (r = 0.29, p > 0.05).

Conclusions: Collectively, these results suggest a lack of association between the loss of mGlu2 receptors and glutamate transmission in the NACsh and PL cortex of female P rats, and between the level of mGlu2 receptors in the PL cortex and alcohol drinking of male Wistar rats.

Keywords: Alcohol-Preferring P Rat; Glutamate; Prelimbic Cortex; mGlu2 Receptor.

MeSH terms

  • Alcohol Drinking / metabolism*
  • Animals
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism*
  • Ethanol / administration & dosage
  • Female
  • Glutamic Acid / metabolism*
  • Male
  • Microdialysis / methods
  • Nucleus Accumbens / drug effects
  • Nucleus Accumbens / metabolism*
  • Rats
  • Rats, Wistar
  • Receptors, Metabotropic Glutamate / metabolism*
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*


  • Receptors, Metabotropic Glutamate
  • metabotropic glutamate receptor 2
  • Ethanol
  • Glutamic Acid