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））的增加参与了缺血-再灌注期间脑损伤的机制。为此，采用微透析生物传感器和微透析技术，在体内测定大鼠前脑等血再灌注模型中细胞外谷氨酸释放和一氧化氮生成。双侧颈动脉闭塞（10分钟），控制出血性低血压（MAP = 30 mmHg），进行前脑缺血再灌注。通过测量NO最终产物（亚硝酸盐和硝酸盐）来测定NO的生成。高压氧（HBO）对NO和ROS生成的影响也在大鼠模型中测定，认为NO和ROS增加（内毒素注射、失血性休克和高压氧CNS氧毒性）。1)细胞外谷氨酸和NO释放及NO合成酶（NOS）抑制剂（L-NAME）的作用a)纹状体、海马和前脑皮层的细胞外谷氨酸水平在缺血时呈双相升高，最高可达6倍左右，再灌注后30 mm内恢复到基线水平。b)亚硝酸盐在缺血期间和再灌注后40 min增加，而硝酸盐则相反。c) L-NAME对NOS的抑制作用不能阻止缺血诱导的谷氨酸释放，并能增加再灌注时谷氨酸水平。2)高压氧对一氧化氮和ROSa生成的影响)高压氧不抑制内毒素处理大鼠血浆一氧化氮终产物（亚硝酸盐、硝酸盐）水平的升高。高压氧可显著提高失血性休克大鼠血浆亚硝酸盐和硝酸盐水平，其方法是先取血至MAP = 40 mmHg，持续30 mm，然后用血浆扩张剂替代。然而，与对照大鼠相比，HBO延长了生存时间。b)通过NO和ROS相关制剂的实验结果表明，NO和ROS的生成增加参与了HBO诱导的ONS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.