Mild as well as severe insults produce necrotic, not apoptotic, cells: evidence from 60-min seizures.

We tested the hypothesis that mild insults produce apoptotic, and severe insults necrotic, cells by subjecting adult Wistar rats to 60-min instead of 3-h generalized seizures. Rats' brains were evaluated 6 and 24h later for evidence of neuronal necrosis by light and electron microscopy, the presence of TUNEL staining and active caspase-3 immunoreactivity, and for evidence of DNA laddering 24h after seizures. Apoptotic neurons from the retrosplenial cortex of postnatal day 8 rat pups served as positive controls. Six and 24h after seizures, 16 and 15 brain regions respectively out of 24 showed significant numbers of acidophilic neurons by hematoxylin and eosin stain. Three brain regions had significant numbers of TUNEL-positive neurons 24h after seizures. No neurons showed active caspase-3 immunoreactivity. Acidophilic neurons were necrotic by electron-microscopic examination. Ultrastructurally, they were shrunken and electron-dense, with shrunken, pyknotic nuclei and swollen mitochondria with disrupted cristae. Nuclei did not contain the irregular chromatin clumps found after 3-h seizures. None of the six brain regions studied ultrastructurally that show DNA laddering 24h after 3-h seizures showed DNA laddering 24h after 60-min seizures, probably because there were too few damaged neurons, although the lack of chromatin clumping might have been a contributing factor. Following seizures, a mild as well as a severe insult produces caspase-3-negative necrotic neurons. These results do not support the hypothesis that mild insults produce apoptotic, and severe insults, necrotic, cells.