PECAM1 and Cerebral ischemia: Confocal microscopic studies revealed that the immunoreactivity for CD31 volume per unit volume on the border area within the ischemic core defined as microtubule-associated protein 2 (MAP2)-negative area decreased at 1 day after cerebral ischemia and reached a minimum level at 3 days after cerebral ischemia compared to sham-operated rats (all P < 0.001) (Fig. 1B).