[The effect of hypothermia on CSD propagation in rats]

In the cortical zone surrounding an ischemic or traumatic focus, CSD is a transient phenomenon involving interstitial ions, blood flow and metabolism and is believed to be completely reversible. However, it may extend to secondary brain injuries because CSD releases excitatory amino acids into the extracellular space. In order to prevent secondary brain injuries, it may be effective to block repeated CSD. This study was designed to determine whether hypothermia can block CSD propagation and whether this study is a potentially useful means for preventing secondary brain injuries. Male wistar rats weighing 270 g on average were used for the experiments. The animals were divided into two groups: hypothermic rats (33.5-34 degrees C, rectal temp.) and normothermic rats (37-37.5 degrees C). The changes in rCBF (regional Cerebral Blood Flow) were monitored in order to observe CSD. LDF (Laser Doppler Flowmetry) was used to measure rCBF. The two LDF probes were placed on the parietal cortex (4 mm apart). To elicit CSD, a needle stab injury was made on the cortex or a piece of paper soaked with 10% KCl was applied on the cortex. The velocity of CSD propagation was more prolonged in the hypothermic rats than in the normothermic rats (p < 0.01). There were smaller numbers of repeated CSD in the hypothermic rats than in the normothermic rats. Histological examination of the cerebral cortex revealed shrinkage neurons more distinctly in the normothermic rats than in hypothermic rats. From these results, we can speculate that hypothermic may block CSD propagation and that hypothermic therapy has the potential to prevent secondary brain injuries.