Ultrastructural morphological changes are not characteristic of apoptotic cell death following focal cerebral ischaemia in the rat.

We have used a permanent middle cerebral artery occlusion (MCAO) model in the rat to ascertain if the DNA fragmentation seen in nuclei, shows the characteristic ultrastructural features of apoptosis. Results from light and electron microscopic studies were compared with those from a neonatal model of excitotoxic cell death in which classical apoptotic changes were seen in a subpopulation of cells. At 6 and 24 h following occlusion, cells were either swollen or dark and shrunken showing a disordered cytosol. At 24 h survival a high number of cells in the lesion core and lesion border showed internucleosomal DNA breaks, which were detected in sections using terminal dUTP nick-end-labelling (TUNEL). Electron microscopy of cells with TUNEL positive spherical structures of condensed chromatin in the lesion core showed an advanced stage of cellular disintegration as opposed to an apoptotic morphology of a subpopulation of cells with chromatin condensation in the cortex and mammillary body of N-methyl-D-aspartate (NMDA) treated neonatal rats. We conclude that in focal cerebral ischaemia internucleosomal DNA fragmentation associated with chromatin condensation is a late consequence of ischaemic cell death rather than a hallmark of apoptosis.