Time course of apoptotic cell death after experimental neurotrauma

Traumatic or ischemic brain injury may give rise to the development of secondary brain damage. In the present study the time course of TUNEL staining which is widely used to delineate apoptotic reaction pattern was followed after experimental neurotrauma in order to test the hypothesis that apoptotic cell death may be involved in the development of secondary brain damage. Neurotrauma was induced in male Wistar rats by applying a cold probe to the exposed dura over the temporo-parietal cortex. Animals were sacrificed between 1 and 72 hours after trauma and coronal sections prepared from the lesioned area and adjacent tissue. The TUNEL staining was employed to detect DNA-fragmentation and conventional HE staining of sequential slices to delineate the extent of the lesion. Occurrence of positively stained cells was detected by a computer-based quantification system and stored on hard disk. TUNEL-positive nuclei were observed as early as one hour after lesion and peaked at 3 hours. There after, the number of cells detected decreased steadily. Histological examination revealed two different types of morphology in TUNEL-positive cells. A small proportion termed type I-cells displayed additional signs of apoptotic cell death such as nuclear condensation and fragmentation while type-II were considered to undergo necrotic cell death. Thus, TUNEL staining proved to be an unspecific marker of apoptotic cell death in the present study. Nevertheless, the data suggest that apoptotic cell death does not contribute substantially to the final extent of cold induced brain tissue damage.