Apoptotic morphology of dentate gyrus granule cells following experimental cortical impact injury in rats: possible role in spatial memory deficits.

Loss of hippocampal neurons as a result of traumatic brain injury (TBI) is thought to contribute to the observed spatial memory deficits. Using a rodent model of experimental brain injury, we have examined the nature of hippocampal cell death following TBI. Light microscope examination of stained sections showed the presence of a large number of hyperchromatic and dystrophic neurons in the dentate gyrus of the hippocampus. These cells appeared to be undergoing nuclear condensation. Electron microscope examination demonstrated the presence of cell shrinkage, condensed chromatin, nuclear segmentation, and cytoplasmic vacuolization. Detection of a DNA ladder and in situ labeling (TUNEL) were also consistent with the process of apoptosis. However, in some dystrophic neurons these morphologies were also accompanied by the presence of swollen mitochondria and a lack of distinctive rough endoplasmic reticulum which are typically associated with necrosis. These findings show that cortical impact injury produces cell death in the hippocampus which has both apoptotic and necrotic features.