Mouse Model of Microembolic Stroke and Reperfusion

Abstract

Background and Purpose-To test the role of fibrinolysis in stroke, we used a mouse model in which preformed 2.5-to 3-m-diameter fibrin microemboli are injected into the cerebral circulation. The microemboli lodge in the downstream precapillary vasculature and are susceptible to fibrinolysis. Methods-We injected various doses of microemboli into the internal carotid artery in mice and characterized their distribution, effects on cerebral blood flow, neurological deficit, infarct area, and spontaneous dissolution. By comparing wild-type and tissue plasminogen activator (tPA) knockout (tPA Ϫ/Ϫ ) mice, we analyzed the role of endogenous tPA in acute thrombotic stroke. Results-Microemboli cause dose-dependent brain injury. Although moderate doses of microemboli are followed by spontaneous reperfusion, they result in reproducible injury. Gene knockout of tPA markedly delays dissolution of cerebral emboli and restoration of blood flow and aggravates ischemic thrombotic infarction in the brain. Conclusions-We describe a microembolic model of stroke, in which degree of injury can be controlled by the dose of microemboli injected. Unlike vessel occlusion models, this model can be modulated to allow spontaneous fibrinolysis. Application to tPA Ϫ/Ϫ mice supports a key role of endogenous tPA in restoring cerebral blood flow and limiting infarct size after thrombosis.

Mouse Model of In Situ Thromboembolic Stroke and Reperfusion

“…22 In a photochemical vascular injury model, the outcome of tPA-deficient mice depended on the severity of injury. 16 Finally, in a mouse model of microembolic stroke, 14 tPA-deficient animals displayed a delayed dissolution of the cerebral emboli and an aggravated ischemic infarct. It is possible that differences in clot structure, dependent on the model used, may determine outcome of rtPA treatment.…”

“…9,10 Other workers have used a second type of model involving injection of autologous or heterologous preformed fibrin, blood clots, 11,12,13 including microemboli, 14 or in situ clot formation by using rose Bengal. 15,16 Although these last models are closer to what happens in patients with stroke, they lack reproducibility and uniformity in the resulting infarct volume, the location of the lesion, 17,18 and/or display a high degree of mortality 19 rendering the statistical analysis of the data confusing (for review, 20 ).…”

Delivery of Anti-Platelet-Endothelial Cell Adhesion Molecule Single-Chain Variable Fragment-Urokinase Fusion Protein to the Cerebral Vasculature Lyses Arterial Clots and Attenuates Postischemic Brain Edema

“…Immediately after intravascular injection, the fibrin microemboli form aggregates invested with blood elements, which lodge in the downstream vasculature . Previous studies showed that within 5 min after injection, the chosen dose of emboli (ϳ1.4 ϫ 10 6 particles) causes ϳ80% cessation of blood flow in the MCA, leading to an extensive ipsilateral cerebral infarction, similar to that caused by 20 h of mechanical MCA occlusion in the standard filament model (Atochin et al, 2004).…”

“…We studied the effect of scFv-uPA in a mouse model of cerebrovascular thrombosis induced by injecting 125 I-labeled fibrin emboli (ϳ3 m in diameter, prepared as described previously; Atochin et al, 2004;Ding et al, 2005), into the middle cerebral artery (MCA). Immediately after intravascular injection, the fibrin microemboli form aggregates invested with blood elements, which lodge in the downstream vasculature .…”

“…Drugs (uPA, scFv-uPA, or PBS placebo) were injected in a standard 120-l volume (PBS) via polyethylene catheters inserted into the right femoral vein. Ten minutes after injection of fibrinolytics in anesthetized mice, a suspension of 125 I-fibrin emboli was injected via the right MCA, as described previously (Atochin et al, 2004). One hour later, mice were sacrificed, and the 125 I content of the brain was measured to determine extent of cerebrovascular thrombolysis based on the amount of residual radiolabeled clots residing in the brain (Atochin et al, 2004).…”