高血糖对树鼩脑皮层局灶性缺血时海马微环境离子稳态及神经元继发性损伤的影响

Effects of hyperglycemia on ionic homeostasis in hippocampal microenvironment and secondary neuronal injury after focal ischemia in cerebral cortex of tree shrews

目的:研究高血糖对树鼩脑皮层血栓性缺血时海马微环境离子稳态的影响,探讨高血糖在缺血后神经元继发性损伤中的作用及机制。方法:用链脲佐菌素复制树鼩高血糖模型,并用光化学方法诱导脑皮层局部血栓性缺血,用单泵等速微灌流系统和离子分析仪测定缺血4 h、24 h及72 h海马离子微环境(细胞外pH值、K+、Na+、Ca2+、Cl-)的动态变化,并观察脑组织的病理形态学改变及海马神经元密度变化。结果:树鼩脑皮层缺血后,其海马微环境内出现了pH值、Na+、Ca2+及Cl-含量的降低,K+含量升高,变化以缺血后4 h为著,24 h次之,72 h无显著差异;高血糖加缺血进一步加重离子稳态的紊乱,缺血后4 h的pH值、K+和Ca2+含量,以及缺血后24 h的pH值和Na+含量与正常血糖缺血组同期值相比,变化显著(P<0.05)。形态学观察显示,光化学反应后4 h照射区皮层可见梗死灶,且患侧海马CA1区也存在缺血损伤性改变;24 h病损达高峰;72 h伴随胶质细胞增生等修复性反应。相应时点高血糖加缺血组皮层及海马的损伤均大于缺血组,以缺血后24 h(P<0.01)和72 h(P<0.05)尤为显著。结论:树鼩脑皮层血栓性缺血形成后,缺血中心区扩布所导致的微环境内酸碱平衡及离子稳态性异常可能是海马神经元继发性损伤的重要原因,高血糖可加剧缺血脑区离子微环境的紊乱。

AIM： To observe the effects of hyperglycemia on the ionic homeostasis in hippocampal microenvironment after thrombotic cortical ischemia in tree shrews, and to explore the action and mechanisms of hyperglycemia in secondary neuronal injury after ischemia. METHODS： High blood glucose in tree shrews was induced by intraperitoneal injection of streptozocin. Focal thrombotic cortical ischemia was induced by photochemical method in tree shrews. At 4, 24 and 72 h after ischemia, the changes of pH, K ＋ , Na ＋ , Ca2 ＋ and Cl- in the ipsilateral ischemic hippocampal microenvi- ronment were tested by a single-pumped push-pull microdialysis system and an ion analyzer. The histopathological changes and hippocampal neuronal density were also examined. RESULTS： After cortical ischemia in tree shrews, the pH and the concentrations of Na＋, Ca2＋ and Cl- in the hippocampal microenvironment decreased, while the concentration of K＋ creased. These differences were the most significant at 4 h, the second at 24 h and insignificant at 72 h. Combination of hyperglycemia and cerebral ischemia worsened the turbulence of ionic homeostasis. Compared with the normoglycemic is- chemic animals, the changes of pH, K ＋ and Ca2＋ concentrations at 4 h as well as pH and Na＋ at 24 h in the hyperglycemic ischemic animals were more significant （P 〈 0.05 ）. The results of histopathological examination showed that there was ischemic neuronal damage in the exposed cerebral cortex and the ipsilateral hippocampal CA1 region at 4 h after photochemical reaction, and the damage was the most severe at 24 h, subsequently accompanied with glial proliferation at 72 h. The hyperglycemic ischemic animals suffered from greater neuronal injury in the cortex and hippocampus than the normoglycemic ischemic animals, especially at 24 h （P 〈 0.01 ） and 72 h （P 〈 0.05 ）. CONCLUSION： The disturbance of acid-base equilibrium and ionic homeostasis in hippocampal microenvironment, following the spreading of the microenvironment in ischemic core, may be an important reason for secondary neuronal injury in the hippocampus after thrombotic cortical ischemia in tree shrews. Hyperglycemia aggravates the turbulence of ischemic ionic microenvironment. [