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Metabotropic glutamate receptors inhibit microglial glutamate release

Stephen M McMullan1, Bounleut Phanavanh1, Gary Guo Li1

  • 1*Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, U.S.A.

ASN Neuro
|July 10, 2012
PubMed

Insights

Metabotropic glutamate receptors (mGluRs) on microglia can block glutamate export, preventing excitotoxicity. This feedback mechanism involves cyclic AMP (cAMP) signaling, highlighting a neuroprotective role for microglia.

Area of Science:

  • Neuroscience
  • Neuroimmunology
  • Cellular Signaling

Background:

  • Microglia, the immune cells of the brain, release glutamate under inflammatory conditions.
  • This microglial glutamate release can cause excitotoxicity in neighboring neurons.
  • Microglia express glutamate receptors, suggesting potential autocrine or paracrine feedback mechanisms.

Purpose of the Study:

  • To investigate the role of metabotropic glutamate receptors (mGluRs) in regulating microglial glutamate export.
  • To explore the downstream signaling pathways, specifically cyclic AMP (cAMP), involved in this feedback.
  • To determine if mGluR activation can attenuate the neurotoxic potential of microglial glutamate release.

Main Methods:

  • Primary rat microglia were treated with lipopolysaccharide (LPS) to induce glutamate export.
  • Various mGluR agonists and antagonists were applied to assess their effects on glutamate release.
  • Nitric oxide (NO) production was measured to ensure specificity of mGluR effects.
  • The role of cAMP was investigated using inhibitors of protein kinase A (PKA) and phosphodiesterase (PDE), as well as cAMP mimetics.

Main Results:

  • Group-II and -III mGluR agonists (ACPD, L-AP4) completely blocked LPS-induced glutamate export without affecting NO production.
  • Group-I mGluR agonists were ineffective, while mGluR inhibition potentiated glutamate export.
  • Inhibition of PKA mimicked the effect of mGluR agonists, and this effect was reversed by increasing intracellular cAMP levels.

Conclusions:

  • Activation of group-II and -III mGluRs on microglia attenuates the export of glutamate.
  • This mGluR-mediated inhibition of glutamate export is dependent on the cAMP signaling pathway.
  • These findings suggest a neuroprotective role for activated microglia via mGluR-mediated feedback, reducing excitotoxicity.

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