Glutamate measured by 6-s resolution brain microdialysis: capillary electrophoretic and laser-induced fluorescence...

In the present experiment the combination of brain microdialysis and CZE-LIFD permitted the measurement of glutamate in 100 nl microdialysis samples collected every 5 or 6 s. Samples were collected every 6 s, in rats anesthetized with two different anesthetic agents (ketamine and sodium thiopental). A microdialysis probe was inserted in the cortex of an anesthetized rat in the territory irrigated by the middle cerebral artery. The artery was clamped for 30 s and then released. The samples were derivatized with fluorescein isothiocyanate I (FITC) by means of a continuous-flow reactor, collected and injected into a home-made CZE-LIFD instrument. Glutamate decreased immediately after clamping the artery in ketamine anesthetized rats and increased 1 min after the onset of the ischemia in sodium thiopental anesthetized rats. In another experiment a 60 mM KCl solution was injected through a microdialysis probe inserted in the hippocampus of an anesthetized rat. In the first 5 s after the KCl solution reached the tissue, glutamate increased but gamma-aminobutytic acid and glutamine did not. The experiments show that time resolution of brain microdialysis can be reduced to a few seconds if the analytical technique is the proper one.