Ischemia-induced glutamate release in the dentate gyrus. A microdialysis study in the gerbil

The levels of extracellular glutamate were measured in the dentate gyrus by using an in vivo brain microdialysis method to determine whether the ische mia-induced glutamate release might be correlated with the neuronal vulnera bility to ischemia. A microdialysis membrane was placed in CA4 (vulnerable to ischemia) and the molecular and granule cell layers of the dentate gyrus (resistant to ischemia) of gerbils. A significant increase in glutamate le vels was induced in the normal dentate gyrus during 10-min ischemia. The in crease was completely suppressed during the first 5 min of ischemia when CA 4 neurons were eliminated. Thus, it was indicated that during the first 5 m in of ischemia glutamate was released mostly from CA4 neurons but not from granule cells of the dentate gyrus. During the second half of 10-min ischem ia, a significant increase in glutamate release was induced even in the den tate gyrus where CA4 neurons were eliminated; this increase was significant ly suppressed by inhibiting proliferation of astrocytes. A large part of gl utamate that was released during the second half of 10-min ischemia was con sidered to be attributable to glutamate release from astrocytes. (C) 1999 E lsevier Science Ireland Ltd. All rights reserved.