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, neutrophil response, and vascular occlusion after permanent and transient middle 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 permanent MCA occlusion (n = 29), and (2) and those having the arterial occlusion 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 evaluation. Initially, the cortical lesion was smaller in rats subjected to transient MCA occlusion than in rats subjected to permanent MCA occlusion (p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration into tissue and the time of peak neutrophil infiltration occurred earlier after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, the number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time interval between 12-48 h (p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and the chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significant differences in the size of the brain lesion disappeared 48 h after onset of ischemia.