Nakata N, Kato H, Kogure K
Department of Neurology, Tohoku University School of Medicine, Sendai, Japan.
Stroke. 1993 Mar;24(3):458-63; discussion 463-4. doi: 10.1161/01.str.24.3.458.
To clarify the role of elevated extracellular amino acid concentrations during ischemia on the cumulative neuronal damage after repeated cerebral ischemic insults, using a microdialysis technique we measured concentrations of the amino acids glutamate, glutamine, glycine, taurine, and gamma-aminobutyric acid in the gerbil hippocampus over three 2-minute forebrain ischemic insults induced at 1-hour intervals.
Under light anesthesia, the bilateral common carotid arteries were occluded with aneurysm clips at 1-hour intervals. Samples were collected by microdialysis at 10-minute intervals, and the amino acid concentrations were determined using a high-performance liquid chromatography system.
During and immediately after the first ischemic insult, concentrations of glutamate, glycine, and taurine, but not glutamine, increased significantly. Glutamate and taurine concentrations rose again during the second and third ischemic insults, but the increases were smaller than those during the first insult. By contrast, glutamine concentrations increased slightly but significantly during the second and third ischemic insults. The extracellular concentration of gamma-aminobutyric acid before the ischemic insults was below the level of detectability but increased markedly during each ischemic insult, with similar declines in the amounts released during later insults. Concentrations of all amino acids returned to baseline after 10 minutes of reperfusion and remained at baseline until the subsequent ischemic insult was induced.
It is well established that glutamate released during ischemia plays a crucial role in ischemia-induced neuronal death. However, the present results indicate that cumulative neuronal damage following sublethal ischemic insults is not caused by an exaggerated release of excitatory amino acids during subsequent ischemic insults but strongly suggest that increased intracellular reactions leading to cell death play a major role.
为阐明缺血期间细胞外氨基酸浓度升高对反复脑缺血损伤后累积神经元损伤的作用，我们采用微透析技术，测定了沙鼠海马体中谷氨酸、谷氨酰胺、甘氨酸、牛磺酸和γ-氨基丁酸在3次间隔1小时、每次持续2分钟的前脑缺血损伤过程中的浓度。
在轻度麻醉下，每隔1小时用动脉瘤夹夹闭双侧颈总动脉。每隔10分钟通过微透析收集样本，并用高效液相色谱系统测定氨基酸浓度。
在首次缺血损伤期间及损伤后即刻，谷氨酸、甘氨酸和牛磺酸的浓度显著升高，而谷氨酰胺浓度未升高。在第二次和第三次缺血损伤期间，谷氨酸和牛磺酸浓度再次升高，但升高幅度小于首次损伤。相比之下，谷氨酰胺浓度在第二次和第三次缺血损伤期间略有但显著升高。缺血损伤前γ-氨基丁酸的细胞外浓度低于可检测水平，但在每次缺血损伤期间显著升高，且在后续损伤期间释放量有类似下降。再灌注10分钟后，所有氨基酸浓度均恢复至基线水平，并维持在基线直至诱导下一次缺血损伤。
缺血期间释放的谷氨酸在缺血诱导的神经元死亡中起关键作用，这一点已得到充分证实。然而，目前的结果表明，亚致死性缺血损伤后的累积神经元损伤并非由后续缺血损伤期间兴奋性氨基酸的过度释放所致，而是强烈提示导致细胞死亡的细胞内反应增强起主要作用。
