Epilepsy is a devastating neurological condition that affects over 3 million adults in the U.S. alone. The most common form of epilepsy is temporal lobe epilepsy (TLE). TLE is characterized by an initial seizure or injury, followed by a latent period, during which the disease symptoms are hidden. It then progresses to chronic and recurrent seizures that often begin in the hippocampus and propagate throughout the brain. 30% of TLE cases become drug-resistant and cause chronic suffering from seizures, mood disorders, memory loss, severe injury, and increased risk of sudden death. Accordingly, the long-term goal of this work is to develop new treatments for neurological disorders characterized by abnormal hippocampal activity. Understanding how TLE develops in the brain poses a complex challenge to the medical community because it can develop anytime in the days to years that follow the brain injury or initial seizure, and for some patients, it does not develop at all. In the epileptic brain, the hippocampus is hyperactive. However, it is unclear how the hippocampus converts to this state after the initial event, and if variability in this process explains why some patients develop TLE, while others do not. Previous studies in mice suggest that the hyperexcitability accrues in the dentate gyrus (DG) subregion of hippocampus, and that this phenomenon is related to a process called adult neurogenesis. Adult neurogenesis is a hallmark feature of the healthy DG, whereby adult-born granule cells (abGCs) continuously integrate into the existing circuit and form connections with mature cells. As TLE develops, the process of neurogenesis is disrupted. As a result, abGCs born near the time of the initial injury often show developmental abnormalities and do not integrate properly into the DG circuit. These changes enable them to amplify seizure activity in the hippocampus. Therefore, the overall objective of this proposal is to prevent chronic seizures in mice by protecting abGCs from developing features and connections that promote seizures. The specific aims are designed to understand and prevent circuit-level changes in vivo in a mouse model of TLE and will be conducted under the guidance of an expert mentoring team. Aim 1 will use nonlinear microscopy to record the brain activity of mature and adult-born DG neurons throughout the progression of pilocarpine-induced epilepsy. We expect to find that changes to these circuit dynamics, caused by pathological maturation of abGCs, will predict the severity and frequency of chronic seizures. Aim 2 will also use nonlinear microscopy to compare the efficacy of different therapeutic interventions in preventing chronic seizures from developing. These interventions are hypothesized to counteract hyperexcitability and protect abGCs from developing pathological features. This work will provide the first strategy to predict chronic seizures and will compare the efficacy of preventive interventions. Therefore, these indep...