Characterization of a New Model of Thromboembolic Stroke in C57 black/6J mice

This study characterizes a new model of thromboembolic stroke of the middle cerebral artery in C57 black/6J mice, thus offering an opportunity to use the model for studying ischemic stroke in transgenic mice. Thromboembolic stroke was induced by local injection of either 1.5 or 3.0 UI of thrombin directly into the right MCA of C57 black/6J mice. Cerebral blood flow (CBF) velocity was measured continuously by laser Doppler flowmetry, which allowed documentation of both MCA occlusion and of spontaneous recanalization. After 24 h, all animals were euthanized. Cryosections were cut at 400-mu m intervals and silver stained with the high-contrast method for volumetric assessment of infarct size. Interleukin (IL)-6, tumor necrosis factor-alpha (TNF-alpha), caspase-3 and hsp 70 protein levels were investigated by immunofluorescence. Thrombin injection resulted in clot formation in all animals. Cortical infarction occurred in 63 % of the mice while 37 % had a spontaneous MCA recanalization during the first 20 min following thrombin injection. In cases of successful MCA occlusion with consequent infarction, the clot was stable up to 2 h after formation. Subsequently, 20 % recanalized spontaneously. Infarctions were restricted to the cortex with a mean lesion volume of 36 +/- 5 for 1.5 UI and 56 +/- 8 for 3.0 UI thrombin. Protein levels of IL-6, TNF-alpha, caspase-3, and hsp 70 were significantly increased after MCAO. The results demonstrate that the mouse thromboembolic stroke model produces cortical infarctions of consistent size in C57 black/6J mice, which is dependent upon the amount of thrombin used for clot formation. Spontaneous MCA recanalization occurs after 2 h of ischemia in 20 % of mice. Thus, the thromboembolic model is an applicable stroke model for C57 black/6J mice, which mimics many of the features of human stroke, including spontaneous recanalization. However, strain differences between Swiss and C57 black/6J mice must be taken into account when using the model.