Fractalkine activity

Background N-Methyl-d-aspartate receptors (NMDARs) play fundamental roles in basic brain functions such as excitatory neurotransmission and learning and memory processes. Their function is largely regulated by factors released by glial cells, including the coagonist d-serine. We investigated whether the activation of microglial CX.sub.3CR1 induces the release of factors that modulate NMDAR functions. Methods We recorded the NMDAR component of the field excitatory postsynaptic potentials (NMDA-fEPSPs) elicited in the CA1 stratum radiatum of mouse hippocampal slices by Shaffer collateral stimulation and evaluated d-serine content in the extracellular medium of glial primary cultures by mass spectrometry analysis. Results We demonstrated that CX.sub.3CL1 increases NMDA-fEPSPs by a mechanism involving the activity of the adenosine receptor type A2 (A.sub.2AR) and the release of the NMDAR coagonist d-serine. Specifically (1) the selective A.sub.2AR blocker 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261) and the genetic ablation of A.sub.2AR prevent CX.sub.3CL1 action while the A.sub.2AR agonist 5-(6-amino-2-(phenethylthio)-9H-purin-9-yl)-N-ethyl-3,4-dihydroxytetrahydrofuran-2-carboxamide (VT7) mimics CX.sub.3CL1 effect, and (2) the selective blocking of the NMDAR glycine (and d-serine) site by 5,7-dicholorokynurenic acid (DCKA), the enzymatic degradation of d-serine by d-amino acid oxidase (DAAO) and the saturation of the coagonist site by d-serine, all block the CX.sub.3CL1 effect. In addition, mass spectrometry analysis demonstrates that stimulation of microglia and astrocytes with CX.sub.3CL1 or VT7 increases d-serine release in the extracellular medium. Conclusions CX.sub.3CL1 transiently potentiates NMDAR function though mechanisms involving A.sub.2AR activity and the release of d-serine. Keywords: CX.sub.3CL1, NMDAR, Microglia, Hippocampus, d-serine, Adenosine receptors