低温对小鼠缺氧缺血性脑损伤的保护作用

目的：低温对脑损伤的保护作用与抑制细胞凋亡有关并取决于低温开始的时间与脑的发育成熟程度,该研究探讨不同年龄阶段的小鼠在缺氧缺血性脑损伤过程中温度的改变对脑损伤的影响。方法：结扎7日龄(P7)和21日龄(P21)C57/BL6小鼠左侧颈总动脉后分别在34℃和36℃恒温箱吸入10%氧气50min制成脑缺氧缺血(HI)模型,在HI后24h及7d取脑进行免疫组化染色和Western蛋白印迹测定。结果：常温组(36℃)在HI后7dHI侧大脑多个部位可见明显损伤,其中P7小鼠大脑皮层可见液化空洞,而P21小鼠大脑皮层成层状梗塞。低温组(34℃)在HI后7d,P7小鼠未见明显的皮层梗塞,海马仍可见明显萎缩,但神经病理学积分在低温组均明显低于常温组(P<0.01);P21小鼠除皮层损伤较常温组明显减轻外(P<0.01),其他部位损伤如海马、纹状体和丘脑与常温组无明显差别。免疫组化染色显示P7小鼠HI后24h大脑皮层活性半胱天冬酶3,凋亡诱导因子(AIF)的阳性细胞数每高倍视野在低温组分别是:7.0±5.6和3.7±6.2,明显低于常温组的51.5±23.2和31.8±22.4(P<0.01),而在海马CA1区活性半胱天冬酶3和AIF的阳性细胞数在低温组与常温组之间无明显差别。Western蛋白印迹显示HI后激活的Akt表达明显减少,低温干预能减少激活的Akt下降(P<0.05)。结论：低温对缺氧缺血性脑损伤的保护作用与脑发育的成熟程度有关,对未成熟脑损伤的保护作用优于对成熟脑损伤的脑保护作用。

Neuroprotective effect of hypothermia on hypoxic-ischemic brain injury in mice

OBJECTIVE: The study was to investigate the effect of different temperatures during hypoxia on brain injury in mice of different ages. METHODS: Newborn C57/BL6 mice at 7 days or 21 days of life were subjected to left carotid artery ligation followed by exposure with 10% oxygen. The mice were kept in a incubator with a predetermined, constant temperature, either 34 degrees centigrade (Hypothermia group) or 36 degrees centigrade (Normothermia group). Brain injury was evaluated 7 days after hypoxia-ischemia (HI). Active caspase-3 and apoptosis-inducing factor (AIF) expressions in the brain tissue were detected by immunohistochemistry and Western Blot was used to evaluate the phosphor-Akt (P-Akt) expression in the brain tissue at 24 hrs post-HI. RESULTS: Brain injuries, including the cortex, hippocampus, striatum and thalamus injuries, occurred in the Normothermia group at 7 days post-HI. The brain cortex showed cystic cavitation in the postnatal day (P)7 pups mice and laminar infarct of the brain cortex was observed in P21 mice. In the Hypothermia group, the P7 mice did not present with laminar infarct of the cortex and had lower scores of neuropathological lesions in cortex, hippocampus, striatum and thalamus than P7 mice from the Normothermia group (P < 0.01); the cortex injuries were significantly relieved but the injuries of hippocampus, striatum and thalamus in P21 mice were similar to those from the Normothermia group. Active caspase-3 (7.0 +/- 5.6) and AIF positive cells (3.7 +/- 6.2) in the cortex of P7 mice from the Hypothermia group were significantly lower than those of the Normothermia group (51.5 +/- 23.2 and 31.8 +/- 22.4) at 24 hrs post-HI (P < 0.01). Wetstern Blot showed the P-Akt expression was obviously decreased in the ipsilateral hemisphere to the occlusion compared with that of the contralateral hemisphere after HI in the Normothermia group (P < 0.05), while in the Hypothermia group the P-Akt expression was not significantly different between the two hemispheres. CONCLUSIONS: Hypothermia has protective effects against HI insults. The protection was more pronounced for the immature brain than the mature brain.