Summary This grant focuses on understanding the causes and consequences of cerebral blood flow decreases in mouse models of Alzheimer’s disease (AD). We recently showed there is increased incidence of the transient arrest of circulating neutrophils in capillaries in the brain of AD mouse models. Because blood cells flow single file in capillaries, this leads to stalled flow in the capillary segment. We serendipitously discovered that administration of antibodies against the murine neutrophil surface protein, Ly6G, rapidly interferes with this neutrophil arrest, decreasing the incidence of stalled capillaries by about two-thirds. We further found that this decrease in capillary stalling was associated with a ~30% increase in cerebral blood flow, and was accompanied by a rapid improvement (within hours) in performance on spatial and working memory tasks. In this grant, we are aiming to: • Aim 1 – understand the cellular mechanisms contributing to neutrophil arrest in capillary segments, where we test three hypotheses: capillary constrictions caused by pericytes; binding to increased adhesion molecules on the endothelial surface; binding to exposed basement membrane and adhesion molecules in the widened gap between endothelial cells. • Aim 2 – evaluate the role of reactive oxygen species produced by NAPDH oxidase as an initiating factor in the arrest of neutrophils in capillaries. • Aim 3 – assess whether improving cerebral blood flow over time decrease amyloid-beta aggregation and neuropathology, taking advantage of knock-in mouse models of AD. • Aim 4 – use three photon excited fluorescence microscopy to assess capillary stalling and blood flow in the hippocampus We have made major progress on Aims 1 and 2, with a recent publication and a second manuscript currently in revision. We are conducting experiments for Aim 3 now, and we had our first hippocampal imaging working in the last couple of months to start Aim 4. Unfortunately, we had a ~15 year old femtosecond laser system recently fail. This laser is essential for the two-photon excited fluorescence microscopy that is the dominant experimental approach we use in this work. We are requesting supplemental funding to help replace this laser.