EVIDENCE OF NUCLEAR-DNA FRAGMENTATION FOLLOWING HYPOXIA-ISCHEMIA IN THE INFANT RAT-BRAIN, AND TRANSIENT FOREBRAIN ISCHEMIA IN THE ADULT GERBIL

Wistar rats, eight days old, were subjected to permanent bilateral for ebrain ischemia, followed by hypoxia for 15 minutes. A cerebral infarc t, mainly involving the cerebral neocortex, hippocampus, amygdala, str iatum and subcortical white matter was produced. Neurons and glia show ing punctate chromatin condensation and karyorrhectic cells were obser ved 12 hours after hypoxia-ischemia. Their number increased during the first two days and recruitment of cells with degenerating nuclei occu rred until day five. In situ labeling of nuclear DNA fragmentation sta ined many normal-appearing nuclei, as well as punctate chromatin conde nsations and nuclear fragments in karyorrhectic cells. Delayed neurona l death in the CA1 area of the hippocampus was observed after 20 minut es of transient forebrain ischemia in the adult gerbil. In situ labeli ng of nuclear DNA fragmentation demonstrated stained punctate chromati n condensation in a few degenerating cells at 48 hours post-ischemia. Substantial labeling of CA1 neurons occurred in the fourth day. Agaros e gel electrophoresis of extracted brain DNA from ischemic infant rats and adult gerbils showed a ladder-type pattern which is typical of nu clear DNA fragmentation into oligonucleosomal fragments (internucleoso mal cleavage). These findings suggest that endonuclease(s) activation may play a role in cell death induced by different forms of hypoxia-is chemia.