Delayed cell death in neonatal mouse hippocampus from hypoxia-ischemia is neither apoptotic nor necrotic

Hypoxic-ischemic (HI) injury in neonatal mice is associated with significan t cell loss in hippocampus, striatum and deep layers of the cortex. The pat tern of cell death in hippocampus after a moderate focal ischemic-global hy poxic insult is studied through morphologic changes in dying neurons at bot h the light and ultrastructural levels. Light microscopy at 24 h showed a n umber of injured neurons, as evidenced by dark, round, condensed nuclei, pr imarily in CA1 through CA3. Nuclei appeared punctate and cytoplasm vacuolat ed. Electron microscopy revealed that the punctate appearance of the nuclei corresponded to clumped chromatin. At 7 days after HI, injured neurons wer e shrunken and had a uniformly dark, angular appearance. While dying cells had an appearance consistent with apoptosis on light microscopy, cells were neither necrotic nor apoptotic at the ultrastructural level. (C) 2001 Else vier Science Ireland Ltd. All rights reserved.