树鼩脑缺血时海马微环境与血脑屏障通透性改变的可能机制

目的观察树鼩血栓性脑缺血时海马血脑屏障（blood-brain barrier，BBB）通透性的变化，并探讨其与微环境相互作用的可能机制。方法通过光化学反应诱导树鼩血栓性脑缺血模型，采用单泵等速微灌流系统及荧光分光法检测脑缺血后4、24及72h海马细胞外液异硫氰基荧光素标记的葡聚糖（fluorescein thiocarbamoyl dextrans，FITC-D）含量及血浆FITC-D的清除率（Clearancerate of FITC-D，Cf），Cf的高低反映海马BBB的通透性。用高效液相色谱技术检测海马灌流液的氨基酸递质水平，并观察缺血海马微血管超微结构。结果树嗣血栓性脑缺血后4h海马BBB通透性开始升高，缺血24h最为明显，Cf=（0．526±0．130）／μl（P〈0．01），72h通透性有所恢复。脑缺血后24h海马细胞外Glu及GABA水平明显升高，分别为（5．71±0．39）μmol·L^-1和（3．81±0．14）μmol·L^-1，均具有统计学意义（P〈0．01）。海马微血管超微结构观察显示星形胶质细胞肿胀，毛细血管周围水肿形成。结论脑缺血可导致海马BBB通透性增高，而海马微环境紊乱对BBB通透性具有促进作用。

Possible Mechanism of the Hippocampus BBB Permeability and Microenvironment after Photochemistry Induced Thrombotic Cerebral Ischemia in Tree Shrews

Objective To observe the dynamic changes of blood-brain barrier（BBB） permeability and explore the correlation between BBB dysfunction and the changes of ischemic microenvironment. Methods The cerebral ischemic model was induced by photochemical reaction in Tree Shrews. Using a kind of single- pumped push-pull perfusing system, the ischemia hippocampus was perfused and fluorescein thiocarbamoyl dextran（molecular weight 70K Dalton, FITC-Do70K） from the ischemic microenvironment and plasma samples were detected with fluorescent spectrophotometer and then the unit volume clearance rate of FITC-D-70K（ Cf） was estimated respectively, which is defined as the BBB permeability coefficient. The concentrations of amino acidic neurotransmitters in the perfusates were detected with high performance liquid chromatography （HPLC） method. And the morphocytological changes of hippocampus microvascular were observed with electronic mi- croscope 24h after cerebral ischemia. Results Compared with the sham group, BBB permeability of the ischemic hippocampus started to increase at 4h and reached the peak at 24h（0.526±0. 130μl, P 〈0.01）. glutamate（Glu） and gamma-aminobutyric acid（GABA） contents（5.71±0.39μmol·L^-1 and 3.81 ±0.14μmol·L^-1, respectively） in the microenvironment increased （P 〈0.01） at 24h after cerebral ischemia. Conclusion The increase of BBB permeability in the hippocampus may follow the thrombotic cerebral ischemia, and microenvironment deterioration may promote BBB destruction.