Changes in Glutamate and Gliotransmitter Adenosine Triphosphate Signalsin the Extracellular Space after Traumatic Brain Injury, and Association with Neuronal Cell Death

Abstract

Background: Glutamate is a fundamental neurotransmitter in the brain, and the gliotransmitter adenosine triphosphate (ATP) acts as a paracrine signal to communicate with the surrounding astrocytes, synapses, and microglia.The present study investigated the relationship between glutamate and ATP signaling in the extracellular spaceafter traumatic brain injury.Material and Methods: Rat stab wound injury models were used to measure the changes in ATP and glutamateconcentrations (ΔGlutamate and ΔATP) in the extracellular space using biosensors. The cellular responses wereevaluated by histopathological staining and Western blotting of glial fibrillary acidic protein (GFAP) as an astrocytic marker and CD11b as a microglial marker. Neuronal cell death was assessed by Fluoro-Jade C staining.Results: ATP and glutamate were released into the extracellular space after injury. ATP and glutamate levelspeaked within 1 second. Apyrase and tetrodotoxin are inhibitors of glia and neurons, respectively. The apyrase andtetrodotoxin groups showed significantly decreased ΔATP and Δglutamate compared to the control group. On theother hand, the apyrase and tetrodotoxin groups showed no significant difference between groups. Furthermore,Western blotting showed that GFAP and CD11b significantly decreased in the apyrase group compared to the control group on days 3, 7, and 28. The apyrase and tetrodotoxin groups suffered significantly decreased neuronal celldeath compared to the control group.Conclusion: This study indicated that apyrase decreased glutamate changes in the extracellular space and reducedneuronal cell death by suppressing ATP signaling. Knowledge of these interactions