Spatial and temporal profile of apoptosis following lateral fluid percussion brain injury in rat

Objective To investigate the spatial and temporal profile of apoptotic neural cells apoptosis following TBI. Methods In addition to morphological evidence of apoptosis, TUNEL histochemistry was used to identify DNA fragmentation in situ at both light and electronmicroscopic levels, whereas characteristic internucleosomal DNA fragmentation of apoptosis was demonstrated by DNA gel electrophoresis. Results Using TUNEL method, we detected massive cells with extensive DNA fragmentation in different regions of the brains of rats subjected to experimental traumatic brain injury. Compared with the sham controls, in the injured cortex, the apoptotic cells were detectable for up to 24 h and reached a peak 1 week after injury. The number of apoptotic cells in the white matter had a significant increase as early as 12h after injury and with a peak at 1 week. An increase in apoptotic cells was observed in the hippocampus at 48 h, whereas in the thalamus, the apoptotic response was delayed, peaking at 2 weeks after injury. By 2 months, the number of apoptotic cells in most regions had returned to uninjured levels. Gel electrophoresis of DNA extracted from affected areas of the injured brain revealed only internucleosomal fragmentation at 185 bp intervals, a feature originally described in apoptotic cell death. And no DNA ladder was detectable in the cortex and hippocampus contralateral to the injured hemisphere. Conclusion These data suggest that, in addition to the well described necrotic cell death, a temporal course of apoptotic cell death is initiated after brain trauma in selected brain regions. The apoptotic response to trauma is regionally distinct and may be involved in both acute and delayed patterns of cell death after TBI.