Epilepsy is a chronic neurological disorder generally characterized by unprovoked recurrent seizures, and affects around 70 million people worldwide. Current treatments are based on antiepileptic drug regimens. These mostly block seizures but do not affect the underlying pathology or progression of the disorder, and are ineffective in up to 30 percent of patients, suggesting that other, possibly non-neuronal mechanisms participate in the epileptogenesis process and/or progression of the disease. Pre-clinical and clinical evidence has accumulated over the past few years to suggest that neuroinflammation, with the participation of microglia and astrocytes, has a significant role in the pathophysiology of epilepsy. Upon brain seizures microglia are known to change their morphology and to release molecules that regulate glia-neuron interactions. Some of these molecules are known to contribute to the epileptogenesis process, such as IL-1ß, TGF-ß and COX-2. On the other hand, conditional microglia/macrophage ablation before seizure leads to increased seizure symptoms, suggesting that microglia might play a protective role in epilepsy. To date it is unclear how microglia sense hyperexcitability in neurons, how this impacts on their behaviour and how, in turn, microglia influence disease progression.In this proposed research project, we aim to characterize the dynamic behaviour of microglia in the epileptic brain and their contribution to the generation and progression of seizures. We will use both chemical and genetic zebrafish models of epilepsy and perform quantitative in vivo time-lapse imaging of mobility and branching behaviour of the entire network of labelled microglia and their correlation with neuronal excitability, measured by calcium, glutamate and ATP fluxes across the brain. Moreover, we will analyse spatio-temporal relationship between neuronal apoptosis and microglial behavior, and test a possible causal effect by inhibiting key apoptotic pathways. In this project, we will take advantage of focal seizure models of epilepsy, in which epileptiform discharges occur in discrete regions of the brain, and analyse the range of attraction that these epileptic events exert on the entire microglial network. These models will be generated in the course of this proposed project, based on spatio-temporal overexpression of genes that induce spontaneous seizures, using both LexPR and optogenetic approaches. Additionally, we will characterize microglia-mediated neuroinflammatory responses in the brain and their contribution to the generation and progression of seizures, both by using microglia depletion strategies, as well as pharmacological-mediated functional inhibition.The results generated from this project will be important to further understand: (1) how microglial behaviour can be influenced by neuronal activity, (2) what is the effect of this modulation in the outcome of the epileptic disease, and (3) how the modulation of microglial activation can be used as a therapeutic approach for the treatment of drug-resistant epilepsies.