Extracellular glutamate changes in rat striatum during ischemia determinedby a novel dialysis electrode and conventional microdialysis

Our newly developed method using a dialysis electrode has made it possible to perform real time monitoring of extracellular glutamate concentration ([ Glu]e) utilizing the oxygen-independent reaction with glutamate oxidase and ferrocene. In this study, we therefore, investigated [Glu]e changes during brain ischemia using both the conventional microdialysis method and the di alysis electrode method. A comparison between our newly developed dialysis electrode and conventional microdialysis methods provided the following res ults. When the conventional microdialysis method was employed: (1) the elev ation of [Glu]e during complete global ischemia was delayed; and (2) the el evation of concentration and reuptake of glutamate were delayed during 10-m in transient ischemia, and the elevation of [Glu]e reached a maximum later using conventional microdialysis than using our dialysis electrode. (3) The biphasic [Glu]e elevation of glutamate concentration detected using the di alysis electrode method was not observed using the conventional microdialys is method. It was additionally investigated why the conventional microdialy sis method provides inferior time resolution. In this study, we also demons trated with the chromatographic SMART((TM)) procedure coupled to UV detecti on that biogenic substances, i.e. low molecular weight proteins and peptide s, are released during ischemic injury, and they may cause a delay in the t ime resolution in the microdialysis method. (C) 2001 Elsevier Science Ltd. All rights reserved.