For light microscopy, the animals were reanesthetized with 4% isoflurane and transcardially perfused with 4% paraformaldehyde in 0.1 mol/L phosphate-buffered saline (pH 7.4). The fixed brains were removed and kept in 4% paraformaldehyde for 6 h. A coronal slab of brain tissue containing the center of the lesion was cut, embedded in paraffin, sectioned, and prepared for hematoxylin and eosin staining. Electron microscopy was also performed on caudate tissue from the rats at 4 h after photothrombosis. The animals underwent transcardiac perfusion with 4% glutaraldehyde. Specimens containing the photothrombosis-induced lesion were excised, embedded in epon, and prepared for ultrastructural examination. For the assessment of blood–brain barrier change, the animals were anesthetized and injected with Evans Blue solution (2 mL/kg, 2% in saline). After 1 h, brains were removed and cut coronally (1-mm-thick) on a brain-slicing matrix at the level of optic fiber implantation. The coronal section was stained with 2,3,5-triphenyl tetrazolium chloride to visualize the area of mitochondrial dysfunction and Evans blue leakage.

Neurological deficits were examined in gerbils by the recording of open field locomotion. The animals were placed in an open field 90 cm  ×  90 cm in size and their spontaneous locomotion was traced with a video-tracking system (PanLab, Barcelona, Spain) for 5 min, and length of stay in the center and the periphery, both equal to 50% of total area, of open field was calculated.

In our hands, the mortality rate was zero in these stroke models. The blood gases and blood pressure were stable and within the normal range. At 24 h after light exposure in the basal ganglia model, an oval, lightly stained, ischemic lesion was present in the caudate around the tip of the optic fiber (Fig. 2a, b). Histologically, the lesion was an ischemic infarction (Fig. 2c). Four hours after photothrombosis, many thrombosed microvessels with pyknotic and eosinophilic neurons and numerous microvacuoles were seen in the lesion (Fig. 2d, f). Electron microscopy revealed platelet thrombus formation within parenchymal small vessels (Fig. 2e). The lesion became infarcted at 24 h after photothrombosis.

Histological changes after cortical photothrombosis were identical to caudate photothrombosis (Fig. 3). Control animals developed no tissue injury except for that caused by the needle track.

Recording of locomotion in gerbil after photothrombosis revealed different pattern and distribution between caudate and cortical lesioning. The trace showed circulation after caudate photothrombosis (Fig. 4a). The animal moved evenly both in the center and periphery of the open field. After cortical photothrombosis, the animal developed linear locomotion mainly in the periphery of the open field (Fig. 4b).

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