Background and Purpose-A reversible model of focal thrombotic stroke was developed in the rat and examined for histological evidence of reperfusion injury after clinically relevant times of recanalization. Methods-The distal middle cerebral artery of 28 male Sprague-Dawley rats was occluded by 562-nm laser-driven photothrombosis for 0.5, 2, and 3 hours or permanently (each nϭ7) and was recanalized by 355-nm UV laser irradiation. Occlusive material was examined by transmission electron microscopy. Cortical cerebral blood flow was monitored by laser-Doppler flowmetry. Brain infarcts were examined histologically at 3 days. Results-After occlusion, cortical cerebral blood flow was reduced to 33Ϯ4% of baseline for all groups and was restored to 82Ϯ9%, 75Ϯ3%, and 93Ϯ7% of baseline for the 0.5-, 2-, and 3-hour groups, respectively, following recanalization after 29Ϯ8, 38Ϯ20, and 70Ϯ33 minutes of UV laser irradiation. The thrombotic occlusion contained compactly aggregated platelets but no fibrin, with length (1.2 to 1.8 mm) proportional to the ischemic period. During recanalization, microchannels containing erythrocytes and scattered leukocytes and bordered by intact disaggregated platelets infiltrated the thrombus. Infarct volumes (mm 3 ) at 3 days were 12Ϯ3 for the permanent case and 8Ϯ4, 24Ϯ3, and 30Ϯ9 for the 0.5-, 2-, and 3-hour cases, respectively, thus demonstrating reperfusion injury histologically in the latter 2 groups. No hemorrhage was seen. Conclusions-UV laser-facilitated dissolution of a conventionally refractory platelet thrombus provides a novel and effective method for restoring blood flow without hemorrhagic complications during thrombotic stroke. This was the first observation of histologically confirmed reperfusion injury in such a model.

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