Impact Of Microhemorrhages On Brain Cell Function

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A stroke is defined as abnormal brain functionality due to a disruption in the blood supply produced by a hemorrhage or clot. They can be classified as symptomatic or asymptomatic. In this dissertation I imaged deep into the brains of live rodents using two-photon excited fluorescence microscopy to study hemorrhagic asymptomatic strokes. We focused high-energy lasers on the surface of a particular blood vessel to rupture its endothelium to cause bleeding. The damage was only confined to the focus of the laser (~1 [MICRO SIGN]m2 ). Employing these methods, we investigated two issues that could advance stroke treatments. First, we evaluated the use of blood breaking drugs or anticoagulants on the effect of hemorrhage size. We examined tissue plasminogen activator (tPA), the only FDA approved drug to dissolve blood clots, and the following anticoagulants: dabigatran etexilate (DE), warfarin and heparin. We found that DE and tPA treated mice developed hemorrhages of comparable size than control mice (treated with saline). In contrast, mice treated with warfarin and heparin (anticoagulants) developed larger hemorrhages. It is relevant to characterize the size of brain hemorrhages since it correlates with patient prognosis. The study suggests that tPA and DE do not exacerbate damage from hemorrhaging and they present a lower risk for bleeding complications when compared to warfarin and heparin. In the second part of this dissertation, we analyzed neuronal activity around microhemorrhages to characterize the resulting region of damage. We compared calcium transient responses to a peripheral stimulus from cortical neurons and neuropil. We found that calcium transient responses obtained after a microhemorrhage were inhibited or had smaller amplitudes than responses obtained before microhemorrhage induction. In addition, the amplitude of the responses is correlated with the distance from the edge of the hemorrhage. Furthermore, calcium transient responses improved over four hours after a hemorrhage, returning to normal responses (i.e. comparable to control experiments) one day after initial onset. This dissertation provides a better understanding of microhemorrhage pathophysiology.
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stroke; hemorrhages; calcium imaging; neural activity; two-photon microscopy; laser ablation; chronic imaging
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Schaffer, Chris
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Linster, Christiane
Van Der Meulen, Marjolein C.H.
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Biomedical Engineering
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Ph. D., Biomedical Engineering
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Doctor of Philosophy
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Government Document
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dissertation or thesis
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