PROJECT SUMMARY/ABSTRACT Hypoxic-ischemic brain injury (HI) complicates 2-6 per 1,000 term births and is associated with significant mortality and poor neurologic outcomes. HI is also the leading cause of neonatal seizures (NS). Current treatments are both ineffective and potentially harmful. The central hypothesis of this proposal is that neonatal seizures independently worsen brain injury after neonatal HI. Whether neonatal seizures are a critical second hit after HI or just a biomarker of injury severity has been a long-debated question and we now have the technologies available to address it at the temporal and cellular resolution necessary to answer it. Specifically, in vivo real-time monitoring of seizures and neuronal death overcomes many of the limitations of past studies to enable a more rigorous understanding of these dynamic processes. The immediate goals of this proposal are to validate two-photon imaging methods for in vivo real-time seizure and cell death monitoring in a neonatal pup and to define the relationship between neuronal seizure burden and the probability of cell death in a neonatal HI model. Transgenic mouse lines expressing neuronal fluorescent proteins and calcium indicators will undergo neonatal HI and be followed with chronic time-lapse two-photon imaging. The experiments proposed will generate high-resolution correlational data between seizure burden and the probability of neuronal death. The long-term goal is to obtain definitive data indicating whether NS are independently harmful or not after HI, which is essential to determine how aggressively to treat patients and how to prioritize research efforts to develop improved NS treatment strategies. The techniques and data acquired in this proposal will be applied to future NIH-funded studies by the applicant to examine these processes and test treatments in this clinically relevant pathophysiologic condition. This proposal combines innovative and rigorous methodologies with directly translational implications, excellent mentorship in science and career development in the laboratory as well as through the applicant's scientific advisory committee, and extensive institutional resources at Massachusetts General Hospital and Harvard Medical School. Completing the proposed aims in conjunction with the applicant's career development plan will lead to the independence of the applicant as a clinician-scientist by the end of the award period. The proposal closely reflects the applicant's research and clinical interests and provides key training to accomplish the applicant's long-term career goal to become an expert in the clinical care of neonates and infants with epilepsy while conducting laboratory-based research into mechanisms of and therapeutic strategies for brain injury, seizures, and epileptogenesis in the developing brain.