PROJECT SUMMARY: Viral infections of the central nervous system (CNS) are associated with an increased risk for seizures, status epilepticus (SE), and the development of chronic epilepsy. Our collaborative group has developed the first animal model of viral-induced epilepsy. Mice (C57BL/6) who receive intra-cerebral injections of Theiler's Murine Encephalomyelitis Virus (TMEV) display acute spontaneous seizures several days after infection, survive the initial infection and go on to develop spontaneous recurrent seizures. Furthermore, our data from the last award period using C57BL/6 mice with various cytokines or cytokine receptors knocked-out have shown that manipulations in the TNF? system can significantly alter the pathologic sequelae observed following TMEV injection. Therefore, we propose to test our overall hypothesis that following TMEV infection, calcium dependent increases in production and release of TNF? from microglia activates the neuronal TNF?R1 pathway, contributing to seizure generation. The proposed experiments will lead to a greater understanding of the role of viral and immune contributions to acute seizures, altered neuronal and microglial function, and epileptogenesis. We will use a multidisciplinary approach to test our hypothesis, including, state of the art in vivo and in vitro 2 photon microscopy, calcium imaging, novel transgenic mouse models, chronic video-EEG monitoring and brain slice electrophysiology to: 1) Determine the time course and extent of physical changes, motility, and the development of spontaneous calcium transients in microglia in TMEV infected mice during the acute infection period using GCAMP5G selectively expressed in microglia; 2) Determine the mechanisms underlying calcium transients in activated microglia during the acute infection period and the role of calcium transients in cytokine production; and 3) Determine if signaling through the neuronal TNF?R1 pathway underlies hippocampal excitability and seizure activity following TMEV infection. We anticipate that these experiments will provide important new insight into the role of TNF? and it's receptor, TNF?R1 in cell death, synaptic transmission and epileptogenesis and set the stage for the development of novel therapeutic interventions for the prevention of infection induced epilepsy.