Summary: Human consciousness and cognitive function are governed by a complex brain circuitry made up of neural connections regulated by an integrated multicellular network. Glial make up 90% of all cells in the brain and play dynamic and active roles in neuronal signaling, where astrocytes and microglia regulate synaptic transmission and plasticity. In the past decade, increasing evidence suggests that the principal co-agonist for N-methyl-D- Aspartate receptors (NMDARs) is the D-amino acid, D-serine, rather than glycine; however, few studies have examined its role in CNS pathologies. To address this gap, we have recently identified a novel mechanism of synaptic damage, where glia within the tripartite synapse uniquely synthesize and release D-serine following the onset of pathological events. We hypothesize that microglia are a key source of pathological D-serine that hyperactivates extrasynaptic NMDAR subunits to initiate synaptic damage as a result of microglia targeting and pruning of dendritic spines. Our proposed experiments will examine (1) the mechanisms of D-serine release from microglia; (2) the mechanisms of synaptic damage and microglia targeting & pruning; (3) transcriptomic analysis of brain injury in both murine and human models. We will achieve this by employing both genetic and pharmacological approaches to dissect the mechanism of microglial action within the complexity of brain injury using state-of-the-art transcriptomic, imaging, and genetic techniques. Our studies will result in a better understanding of the mechanisms that regulate synaptic damage and dysfunction, but also will start to define novel therapeutics for patient interventions.