Temporary focal cerebral ischemia results in swollen astrocytic end-feet that compress microvessels and lead to focal cortical infarction

We examined the mechanisms underlying the abrupt onset of the focal infarction in disseminated selective neuronal necrosis (DSNN) after temporary ischemia. Stroke-positive animals were selected according to their stroke-index score during the first 10 minutes after left carotid occlusion performed twice at a 5-hour interval. The animals were euthanized at various times after the second ischemia. Light- and electron-microscopical studies were performed chronologically on the coronal-cut surface of the cerebral cortex at the chiasmatic level, where focal infarction evolved in the maturing DSNN. We counted the number of neurons, astrocytes, and astrocytic processes (APs); measured the areas of end-feet and astrocytes; and counted the numbers of obstructed microvessels and carbon-black-suspension-perfused microvessels (CBSPm). Between 0.5 and 5 hours after ischemia, DSNN matured, with the numbers of degenerated and dead neurons increasing, and those of APs cut-ends decreasing; whereas the area of the end-feet and the numbers of obstructed microvessels increased and those of CBSPm decreased. At 12 and 24 hours after ischemia, the infarction evolved, with the area of end-feet and astrocytic number decreased; whereas the numbers of obstructed microvessels decreased and the CBSPm number increased. The focal infarction evolved by temporary microvascular obstruction because of compression by swollen end-feet.