Dynamic changes of cortical NADH fluorescence in rat focal ischemia: Normothermia vs. hypothermia

[INTRODUCTION] Preischemic hypothermia has been suggested to reduce infarct volume. However, the dynamics of the growth of infarct volume during hypothermia has not been observed. In this study, we examined differences in expansion of the ischemic core in normothemic and hypothermic groups using a cortical NADH fluorescence imaging technique described by Higuchi et al. (1) [METHODS] Nine male spontaneous hypertensive rats weighing 300±20 g were used in this study. Permanent occlusion of the left common carotid and middle cerebral arteries was performed. In the hypothermic group (n=4), hypothermia was induced before ischemia, and then the animals were kept at 30-31°C for two hours and rewarmed to 36.5°C over a period of 60 minutes. In the normothermic group (n=5), the animals were kept at 37.0±0.5°C. A large cranial window was made on the left parietal-temporal bone, and cortical NADH fluorescence in this window was examined. The infarct volumes were measured 24 hours after onset of ischemia. [RESULTS] The areas of the ischemic core in the normothermic and hypothermic groups had increased to a maximal level at about 30 minutes and 60 minutes respectively. The areas of the ischemic core at 15, 30, 60 and 120 minutes after onset of ischemia and at the end of rewarming were significantly reduced in the hypothermic groups compared to those in the normothermic group.(see figure) The infarct volumes were also significantly reduced in the hypothermic group (P<0.05). [CONCLUSION] We could elucidate differences between growth of the ischemic core in the normothermic group and that in the hypothermic group using cortical NADH fluorescence images. The results of this study suggested that preischemic hypothermia not only reduced area of the ischemic core but also delayed expansion of the ischemic core, resulting in reduction of infarct volume. Cortical NADH fluorescence imaging is useful for real-time monitoring of growth of the ischemic core in focal ischemic rat models.