The overall goal of the proposed research for this K22 award is to test the hypothesis that P2Y12 receptors regulate prime microglial cell function during normal development and contribute to physiological neuronal excitability and consequently outcomes from a developmental seizure disorder. In the mentored Phase I, I will develop technical skill in (i) high resolution two photon in vivo imaging techniques in and (ii) electroencephalogram (EEG) implantation seizure measurement in developing mice. Having developed these techniques, in the independent Phase II, I will address the specific aims of this proposal including determining the role of P2Y12 receptors in microglial colonization and phagocytosis in the developing brain (Aim 1); determining the role of microglial P2Y12 receptors in synaptic structure and function (Aim 2); and determining any contributions of microglial P2Y12 receptors in the seizure phenotypes and outcomes in a developmental seizure model of Dravet Syndrome. When completed, this proposal will provide an understanding of P2Y12 receptor roles in microglial activities and its consequences on neuronal maturation and seizure phenotypes that could inform future therapeutic approaches.