Quantification Of Cerebral Blood Flow In Mouse Models Of Hematological Disease

Abstract

The investigation of cerebral microcirculation is challenging due to the complex three-dimensional structure of the brain and the requirement to maintain subject physiology to ensure an adequate blood supply. We developed an algorithm to capture blood flow dynamics with high temporal and spatial resolution when coupled with two-photon excited fluorescence microscopy imaging. Using these techniques and chronic craniotomy surgical preparations, we focused our attention on myeloproliferative neoplasms and their impacts on cortical circulation. These rheological conditions exhibit an excessive amount of red blood cells, leukocytes, and/or platelets, resulting in abnormal, prothrombotic flow conditions. Although no direct evidence has indicated microvascular flow disruptions in the brain, cognitive dysfunction is reported among myeloproliferative neoplasm patients. Because neurological impairment is linked to cerebral microcirculation problems, we looked for direct confirmation in animal models of the diseases-essential thrombocythemia and polycythemia vera, specifically. We found cerebral microvessels in the subjects to be largely occluded by leukocytes and platelets, which adhered tightly to the endothelium. In the case of essential thrombocythemia, ~20% of the stalled vessels by platelets remain blocked for over two hours, while the rest of the micro-occlusions resolved and reestablished flow on their own. The adherence of leukocytes and platelets is a result of cellular activation due to enhanced cell-to-cell interactions in the high hematocrit flow regime as well as the triggering of platelet aggregation by injured endothelial cells. We concluded that there is a need for targeted therapy to resolve cerebral microcirculation disruption, and that clinicians should include a careful cognitive evaluation when treating patients with myeloproliferative neoplasms. In future work, we are interested in identifying the mechanism of thrombosis in sickle cell disease where patients are severely anemic but prone to thrombosis, nevertheless. Two-photon excited fluorescence microscopy also has many other applications. We exercised one by using second harmonic generation imaging to observe collagen fibers in cardiac tissue in vitro. In this study, collagen fibers were presented with cyclic anisotropic strain that led to tissue alignment and remodeling. We identified that anisotropy of biaxial strain causes fiber alignment along the principal directions of strain and concluded that strain field anisotropy is an independent regulator of fibroblast cell phenotype, turnover, and reorganization.