TEMPORAL PROFILE OF ISCHEMIC TISSUE-DAMAGE, NEUTROPHIL RESPONSE, AND VASCULAR PLUGGING FOLLOWING PERMANENT AND TRANSIENT (2H) MIDDLE CEREBRAL-ARTERY OCCLUSION IN THE RAT

We investigated the temporal profile of ischemic tissue damage, neutro phil response, and vascular occlusion after permanent and transient mi ddle cerebral artery occlusion in the rat. Focal cerebral ischemia was induced by advancing a nylon monofilament to occlude middle cerebral artery (MCA). Two groups of rats were investigated: (1) those with per manent MCA occlusion (n = 29), and (2) and those having the arterial o cclusion released after 2 h (n = 34). Experiments were terminated at 6 , 12, 24, 48, 72, 96 and 168 h after the onset of ischemia, and brain sections were stained with hematoxylin and eosin for histological eval uation. Initially, the cortical lesion was smaller in rats subjected t o transient MCA occlusion than in rats subjected to permanent MCA occl usion (p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration i nto tissue and the time of peak neutrophil infiltration occurred earli er after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, t he number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time i nterval between 12-48 h (p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and t he chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significan t differences in the size of the brain lesion disappeared 48 h after o nset of ischemia.