Extracellular neurotransmitter release and generation of reactive oxygen species during cerebral ischemia-reperfusion

兴奋性氨基酸如谷氨酸的过度释放和自由基如活性氧（ROS）和一氧化氮（NO）的产生增加参与缺血-再灌注期间脑损伤的机制。因此，在大鼠前脑缺血再灌注模型中，采用微透析生物传感器和微透析技术在体检测细胞外谷氨酸释放和NO生成。采用双侧颈动脉阻断（10 min）和控制性出血性低血压（MAP = 30 mmHg）进行前脑缺血再灌注。通过测量NO终产物（亚硝酸盐和硝酸盐）来确定NO生成。高压氧（HBO）对大鼠NO和ROS生成的影响也被确定，其中NO和ROS被认为是增加的（内毒素注射、失血性休克和高压CNS氧毒性）。1）细胞外谷氨酸和NO释放，以及NO合酶（NOS）抑制剂（L-NAME）的作用a）纹状体中的细胞外谷氨酸水平，海马和前脑皮质在缺血期间双相增加高达约6倍，并在再灌注后30分钟内恢复到基线水平。B）亚硝酸盐在缺血期和再灌注后40 min增加，而硝酸盐则相反。（3）L-NAME抑制NOS并不能阻止缺血再灌注时谷氨酸的释放，并增加再灌注时谷氨酸的水平。（2）HBO对NO和ROa的影响。高压氧使失血性休克大鼠血浆亚硝酸盐和硝酸盐水平显著升高，并以MAP = 40 mmHg持续放血30 min，然后用血浆扩容剂替代。然而，与对照组相比，HBO延长了存活时间。B）NO和ROS相关药物的实验结果表明，NO和ROS的产生增加参与了HBO诱导ONS的氧毒性。

Excessive release of excitatory amino acids such as glutamate and increased generation of free radicals such as reactive oxygen species (ROS) and nitric oxide (NO) are involved in mechanisms of cerebral damage during ischemia-reperfusion. Therefore extracellular glutamate release and NO generation were measured in vivo with microdialysis biosensor and microdialysis in rat forebrain isohemia - reperfusion model. Forebrain ischemia-reperfusion was performed by bilateral carotid artery occlusion (10 min) with controlled hemorrhagic hypotension (MAP = 30 mmHg). NO generation was determined by measuring NO end-products (nitrite and nitrate). The effect of hyperbaric oxygen (HBO) on generation of NO and ROS was also determined in rat model, where NO and ROS had been considered to increase (endotoxin injection, hemorrhagic shock and hyperbaric CNS oxygen toxicity).1) Extracellular glutamate and NO release, and effects of NO synthase (NOS) inhibitor (L-NAME)a) Extracellular glutamate levels in striatum, hippocampus and forebrain cortex increased biphasically upto about 6-fold during ischemia and returned to the baseline level within 30 mm after reperfusion. b) Nitrite increased during schemia and 40 min after reperfusion, however, nitrate changed in the opposite direction. c) NOS inhibition by L-NAME did not prevent ischemia-induced glutamate release, and increased glutamate level during reperfusion.2) Effect of HBO on generation of NO and ROSa) HBO did not suppress increased plasma levels of NO-endproducts (nitrite, nitrate) in endotoxin-treated rats. HBO significantly increased plasma nitrite and nitrate level in rats of hemorrhagic shock, which was induced by withdrawing blood until MAP = 40 mmHg for 30 mm and thereafter replaced by plasma expander. HBO, however, prolonged survival time compared to control rats. b) As the results of experiments using NO and ROS related agents, increased generation of NO and ROS take part in oxygen toxicity induced by HBO in ONS.