Acute occlusion of a major brain artery causes a stereotyped sequel of morphological alterations which evolve over a protracted period and which depend on the topography, severity and duration of ischemia [31, 32]. The most sensitive brain cells are neurons, followed - in this order - by oligodendrocytes, astro-cytes and vascular cells. The most vulnerable brain regions are hippocampal subfield CA1, neocortical layers 3, 5 and 6, the outer segment of striate nucleus, and the Purkinje and basket cell layers of cerebellar cortex. If blood flow decreases below the threshold of energy metabolism, the primary pathology is necrosis of all cell elements, resulting in ischemic brain infarct. If ischemia is not severe enough to cause primary energy failure, or if it is of so short duration that energy metabolism recovers after reperfusion, a delayed type of cell death may evolve which exhibits
the morphological characteristics of necrosis, apop-tosis or a combination of both. In the following, primary and delayed cell death will be described separately.
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