According to the American Heart Association about 795,000 people suffer a stroke each year. Of those strokes almost 140,000 are fatal; this makes Stroke the third leading cause of death in the United States behind coronary heart disease and cancer. Hemorrhagic strokes are caused when an artery in the brain ruptures, such as a ruptured aneurysm. One possible treatment for cerebral aneurysm is a porous tubular structure, similar to a stent, called a flow diverter. A flow diverter can be placed across the neck of a cerebral aneurysm to induce the cessation of flow and initiate the formation of an intra-aneurysmal thrombosis. This excludes the aneurysm from the parent artery and returns the flow of blood to normal. The process of flow diversion alone has been shown to take months to fully exclude the aneurysm. It is possible however with an adjuvant therapy called photothrombosis to accelerate this process so that the aneurysm is excluded within minutes. Previous flow diverting devices have been analyzed to determine optimal characteristics, such as braiding angle and wire diameter. From this information a new optimized device was designed and is now in the process of being tested. In order to evaluate the effect of the device, a model must be created. One such model is the rabbit elastase induced aneurysm, which was characterized so that elastomer models could be created for in vitro studies. Particle Image Velocimetry (PIV) is a method of analysis that utilizes very small glass spheres (between 8 mu m and 12 mu m in diameter) to determine the velocity vectors of fluid flow in an in vitro model. These velocities can be used to calculate hydrodynamic circulation and kinetic energy inside an elastomer model of the elastase induced aneurysm. By comparing these values inside the aneurysm with values for previously developed diverters and a control without a diverter, it can be shown that despite changes in the braiding angle and individual wire thickness that the behavior of the devices is not significantly different (P > 0.05). Flow diversion is also being used in concert with photothrombosis. A flow diverter is used to exclude the neck remnant from the parent vessel and to provide a scaffold for the remodeling of the neck. This combination of techniques allows for very fast and near complete occlusion of the aneurysm thereby excluding the aneurysm from the parent vessel and eliminating the risk of a rupture.

Background: Ischemic stroke ranks as the third major cause of clinical mortality and the leading cause of handicap in adults. Each year, stroke occurs in about 30,000 Swedes. The severity of an acute ischemic stroke depends mainly on the degree and duration of local cerebral blood flow (lCBF) reduction. Prompt reperfusion improves neurological deficits, spontaneous electrical activity, energy metabolism, cerebral protein synthesis (CPS), and tissue repair, among which cell proliferation (neurogenesis, gliosis) and revascularization (angiogenesis) may have important functional and therapeutic implications. Aims of the thesis: (1) To establish the photothrombotic ring stroke(PRS) model with late spontaneous reperfusion in adult mice; (2) To explore angiogenesis and neurogenesis in adult brain after focal cerebral ischemia. Materials and Methods: The PRS model in C57 BL adult mice and the middle cerebral artery suture occlusion (MCAO) model in adult Wistar rats were used. The 5-bromodeoxyuridine (BrdU) was delivered into animal after stroke induction to label DNA duplication. CBF, CPS and adenosine triphosphate (ATP) were measured by laser-Doppler flowmetry (LDF), [14C]–Iodoantipyrine and [3H]-Leucine double tracer autoradiography, and bioluminescence, respectively. Immunocytochemistry / immunofluoresence were performed to detect different proteins. The cell marker colocalization was analyzed by three-dimension (3-D) confocal. The cell counting was performed with a stereological counting system. Results: The PRS model was established in adult mice by irradiating the exposed skull with a 514.5 nm argon laser ring beam (3 mm diameter, 0.21 mm thick) at an intensity of 0.65 W/cm2 for 60s, with concurrent erythrosin B (4.25 mg/kg) intravenous infusion for 15s. The central cortical region within the ring locus was progressively encroached by an annular ring-shaped perfusion deficit, where lCBF LDF declined promptly to 43% of the baseline value at 30 min post irradiation. The lCBF-IAP amounted to 46-17-58 ml/100g/min, where CPS varied from 57-38-112% at 4h-48h-7days post ischemia. ATP declined at 4h, achieved its maximum level at 48h and was markedly reduced at 7 days postischemia. Morphologically, at 4h some neurons in the region at-risk appeared swollen, at 48h the majority were severely swollen, eosinophilic and pyknotic. Tissue morphology became partly restored at 7 days post stroke, when numerous cortical cells were immunolabeled by BrdU or the mitosis-specific marker phosphorylated histone H3 (Phos-H3). Some of these cells were even doubly immunopositive to the neuron-specific marker Neu N and the astrocyte marker GFAP, as analyzed by 3-D confocal. In adult rats exposed to MCAO, widespread BrdU-immunolabeled cells appeared in the cortex, ipsilateral striatum and dentate gyrus of the hippocampus. Some of which were doubleimmunolabeled by the neuron specific markers Map-2, β-tubulin III and Neu N as analyzed by 3-D confocal. As early as 24h postischemia, BrdU-immunopositive endothelial cells were aligned as microvessels, some of which exhibited distinguishable lumens in the ischemic boundary zone, where VEGF-A, B, C proteins and their receptors flt-1, fik-1, flt-4 were overexpressed at 72h after MCAO. Conclusion: PRS model in adult mice elicits a dynamic deterioration and then restoration of local CBF, CPS, ATP and tissue morphology in the spontaneously reperfused cerebral cortex at 7d after stroke, where cortical neurogenesis and gliosis occurred. In adult rats with MCAO, neurogenesis occurred at 30 and 60d in the penumbral cortex and striatum. Angiogenesis occurred as early as 24h, which contributed to the spontaneous reperfusion frequently observed in this setting of acute ischemic stroke.

Stroke is the leading cause of long-term disability in the developed world and can have devastating effects on the health and everyday functioning of individuals. In most cases stroke is ischemic and is caused by the obstruction of blood flow due to a clot in the brain blood vessels. This initiates a cascade of events that result in tissue death and loss of behavioural function associated with the damaged region. The peri-infarct cortex is a region surrounding the infarct core that survives the ischemic event and is most susceptible to pharmacological treatments and rehabilitation. α4ß2 nicotinic acetylcholine receptor (nAChR) signalling has been implicated as a mechanism that affects cell survival and cell death in the acute response after stroke. Nicotinic receptor signalling is also involved in modulating brain excitability, which can affect neural plasticity and restoration of cortical circuits and lead to recovery of lost function after stroke. In order to elucidate the role of α4ß2 nAChRs on acute and chronic recovery after stroke, we tested two hypotheses: (1) blocking α4ß2 nAChRs triggers acute neuroprotection and (2) α4ß2 nAChRs play a role in regulating plasticity and long-term functional recovery. In the first set of experiments a new model of targeted photothrombotic stroke was induced in a distal branch of the middle cerebral artery (MCA) in awake and anaesthetized mice. Mice treated with the α4ß2 nAChR antagonist dihydro-ß-erythroidine (DHßE) showed smaller lesion sizes relative to vehicle controls and this effect was greater in mice that were awake during stroke induction. To determine the mechanism of α4ß2 nAChRmediated neuroprotection, changes in collateral flow were measured using Evans bluestained surface angiograms and laser Doppler flowmetry. Contrary to what was expected, DHßE did not appear to induce neuroprotection by altering collateral flow. In the second set of experiments, we first used confocal imaging to quantify and characterize the expression of α4ß2 nAChRs after stroke. Next, mice were induced with a targeted photothrombotic stroke in the forelimb somatosensory cortex. Mice were then chronically treated with DHßE to determine if α4ß2 nAChR antagonism could improve recovery of function. Behavioural tests showed that blocking α4ß2 nAChRs chronically had no effect on forelimb function after stroke. Voltage-sensitive dye imaging was used to measure forelimb-evoked responses in the somatosensory cortex and revealed no differences in cortical responsiveness between treated and non-treated groups. Altogether, these results show that changes in α4ß2 nAChR signalling that occur after stroke mediate ischemic cell death but do not have an effect on long-term recovery and plasticity. Moreover, they present a novel pathway for investigating stroke pathophysiology and the development of acute neuroprotective treatments. / Graduate / 0317 / aseto@uvic.ca