Inhibiting effect of moderate hypothermia on cell apoptosis after diffuse brain injury in rats

To explore the variant processes of cell apoptosis and the inhibiting effect of moderate hypothermia on cell apoptosis after diffuse brain injury.

Models of diffuse brain injury were induced by the trauma device reported by Marmarou. A total of 128 Wistar rats were divided into 4 groups: the uninjured group (Group A, n=8), the severely injured group (Group B, n=60), the mildly injured group (Group C, n=30) and the mild hypothermia group (Group D, n=30). In Group D, the severely injured rats were treated with moderate hypothermia to keep the rectal temperature at 32 degrees C (standard deviation for 0.1 degree C) for 6 hours. Then the morphology, the characteristics and the quantity of apoptotic cells in the cerebral cortex and in the hippocampus regions after different severities of craniocerebral injuries were observed and compared under an electronic microscope, with terminal deoxynucleotidyl nick end labeling (TUNEL) in DNA fragmentation and with agarose gel electrophoresis.

TUNEL showed apoptotic cells increased according to the injury severity, and they peaked at 48 hours after injury and then declined. In Group C, apoptosis was located in the CA(2) and CA(3) areas of the hippocampus. And in Group B, apoptosis increased evidently, and located in the whole hippocampus and in the frontal and parietal cortex regions. The hypothermia-treated rats had some apoptotic cells, too. However, even at 24, 48 and 72 hours after injury there were significantly fewer apoptotic cells in the cortex and in the hippocampus in Group D than that in the non-treated groups. Electron microscopy showed that the apoptotic cells were round and shrunken in morphology and the nuclei were round and condensed at 24 and 48 hours after injury. And the apoptosis at 48 hours was more severe than that at 24 hours. The hypothermia-treated rats had no apoptotic cells. Gel electrophoresis showed that characteristic DNA "ladders" were observed in the cortex and in the hippocampus at 48 hours after severe injury. But there was no DNA "ladder" at other time points in the severely injured group, in the mildly injured group and in the hypothermia-treated group.

It suggests that apoptosis occurs after diffuse brain injury and apoptotic cells increase with the injury severity. Moderate hypothermia has a specific inhibiting effect on cell apoptosis after diffuse brain injury in rats.