不同程度缺氧缺血对新生大鼠脑损伤的影响及机制探讨

目的比较不同程度的缺氧缺血(hypoxia-ischemia,HI)对新生大鼠脑损伤的影响,探讨胶质细胞活化和细胞因子所起的作用。方法 120只7日龄Wistar大鼠随机分为对照组、轻度HI组和重度HI组。两组HI大鼠行右颈总动脉结扎,分别置于含8%氧的密闭氧舱内34.5℃,40min和35.5℃,65min。用MRI、微管相关蛋白(MAP2)和TUNEL染色评估脑损伤;免疫组化法检测巨噬细胞激活抗原(ED1)、TNF-α和硝基酪氨酸(NT)表达的变化。结果轻度HI组大鼠MRI显示缺血侧皮质T2强度轻度下降,皮层下白质T2值增加,皮质MAP2染色中度下降,皮层下白质TUNEL阳性细胞数量明显增多;重度HI组大鼠缺血侧半球的大部分T2值均增加,皮质与白质MAP2染色均明显减少,TUNEL阳性细胞数量均明显增加。轻度HI后ED1、TNF-α与NT表达仅在急性期增加,且多局限于皮层下白质;而重度HI后其增加出现得较晚且持久,见于整个缺血侧半球。结论轻度HI可引起相对选择性的白质损伤,重度HI则引起缺血侧半球的广泛损伤,胶质细胞活化和细胞因子异常表达可能起了一定作用。

Effects of different severities of hypoxia-ischemia on brain injury in neonatal rats

Objective To compare the features of brain injury in neonatal rats with different severities of hypoxia-ischemia(HI),and explore the role of microglial activation and cytokines.Methods One hundred and twenty 7-day-old rats were randomized to three groups:sham control,mild HI,and severe HI.The rats in the HI groups were subjected to right carotid artery occlusion and 8% oxygen hypoxia exposure(40 minutes,34.5℃ in the mild HI group;65 minutes,35.5℃ in the severe HI group).MRI,microtubule associated protein(MAP2)and TUNEL staining were used to confirm the severity of brain injury.Changes in expression of activated microglia(ED1)and signs of cytokine involvement or oxidative stress(TNF-α,nitrotyrosine)were assessed immunohistochemically.Results In the mild HI group,MRI scans demonstrated increased T2 values in the ipsilateral subcortical white matter and a slight loss of T2 values in the cortex,corresponding to a medium loss of MAP2 in the ipsilateral cortex.There was an increase in the number of TUNEL positive cells compared to the control group within the subcortical white matter.In the severe HI group,the T2 value increased in the majority of the hemisphere,corresponding to a severe loss of staining for MAP2 in the ispilateral hemisphere.The number of TUNEL positive cells significantly increased in the ipsilateral cortex and white matter.In the mild HI group,ED1,TNF-α and nitrotyrosine expression increased only in the acute stage and was only observed in subcortical white matter.In contrast,after severe HI,the increase in ED1,TNF-α and nitrotyrosine expression was observed in the whole ipsilateral hemisphere and prolonged for weeks.Conclusions Following a mild HI a relatively selective white matter injury compares to the pannecrosis in the cortex and white matter following a severe HI.Microglial activation and over-expression of cytokines might contribute to the development of hypoxic-ischemic brain damage.