PROJECT SUMMARY Stroke in pregnancy is a major health problem in the US, with an incidence that is 3-fold higher than stroke rates in comparable nonpregnant women. Pregnancy-related stroke has a profound and devastating impact on a women’s life and her ability to care for her child or children. Complicating the public health concerns even more is the fact pregnancy-related strokes in the United States is on the rise. The increased risk of stroke in pregnancy is largely driven by the comorbidity of preeclampsia (PE), a hypertensive disorder that complicates up to 10% of all pregnancies. In fact, greater than 1/3 of women with pregnancy-related stroke have comorbid PE, increasing the risk of stroke 6-fold vs. women without PE. Relevant to this proposal, stroke in pregnancy is largely unstudied. Pregnant women have been excluded from randomized stroke clinical trials and therefore nothing is known about treatment and outcome in this population. This R21 proposal is to provide critically needed information on stroke injury and outcome in pregnancy and PE. Our overall hypothesis is that the maternal brain is more susceptible to ischemia and reperfusion injury than age-matched nonpregnant females and that this susceptibility is further exacerbated by PE. This hypothesis is based on our published and preliminary data demonstrating increased neuronal excitability and brain injury in a rat model of normal pregnancy that is further increased in a model of PE. In addition, PE is a state of high oxidative stress and neuroinflammation that could exacerbate stroke injury. Remarkably, it is unknown how pregnancy and PE affect stroke outcome. Aim 1 will use a model of transient focal ischemia in nonpregnant, normal pregnant and PE rats to determine stroke outcome (infarct, cellular injury, neurologic deficit and mortality) as well as contributors to injury, including perfusion deficit, collateral flow and reperfusion injury (edema and hemorrhagic transformation). Aim 2 will acutely treat with clinically relevant doses of magnesium sulfate (MgSO4), a safe and effective treatment in pregnancy that has been used for decades to prevent brain hyperexcitability and seizure. MgSO4 is a calcium antagonist that prevents glutamate-induced excitotoxic injury and may be beneficial in preventing stroke injury in pregnancy and PE, an excitotoxic state. Importantly, we will use MgSO4 in combination with tissue plasminogen activator (tPA) since tPA has been shown to interfere with stroke treatment. tPA alone will also be studied since it is standard of care yet the safety and therapeutic window is not known in pregnancy or PE. It is our hope that the results of this project will lead to better treatment of stroke in pregnancy.