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The Journal of Neuroscience, August 6, 2003, 23(18):7176-7182
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Functional Changes of Glial Glutamate Transporter GLT-1 during Ischemia: An In Vivo Study in the Hippocampal CA1 of Normal Mice and Mutant Mice Lacking GLT-1
Akira Mitani1 and
Kohichi Tanaka2,3
1College of Medical Technology, Kyoto University,
Shogoin, Sakyo-ku, Kyoto 606-8507, Japan, 2Laboratory
of Molecular Neuroscience, School of Biomedical Science and Medical Research
Institute, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8579,
Japan, and 3Precursory Research for Embryonic Science
and Technology, Japan Science and Technology Corporation, Kawaguchi, Saitama
332-0012, Japan
Glutamate transporters remove glutamate from the extracellular space and
maintain it below neurotoxic levels under normal conditions. However, the
dynamics under ischemic conditions remain to be determined. In the present
study, we evaluated the function of the glial glutamate transporter (GLT-1)
during brain ischemia by using an in vivo brain microdialysis
technique in GLT-1 mutant mice. A microdialysis probe was placed in the
hippocampal CA1 of GLT-1 mutant and wild-type mice, and glutamate levels were
measured during 5 and 20 min ischemia. The glutamate levels in mice lacking
GLT-1 were significantly higher than the corresponding glutamate levels in
wild-type mice during 5 min ischemia. Delayed neuronal death was induced in
the CA1 of the mice lacking GLT-1 but not in the CA1 of the wild-type mice.
When ischemia was elongated to the duration of 20 min, the glutamate levels in
wild-type mice were significantly higher than the corresponding glutamate
levels in mice lacking GLT-1 during the last 12.5 min of 20 min ischemia.
Acute neuronal death was also observed in the CA1 of wild-type mice. These
results suggest that GLT-1 takes up extracellular glutamate to protect neurons
in the early stage of ischemia and then releases glutamate, triggering acute
neuronal death, when ischemic conditions are elongated. The function of GLT-1
may change from neuroprotective to neurodegenerative during ischemia.
Key words: glutamate transporter; glia; GLT-1; knock-out mouse; hippocampal CA1; ischemia; neuronal death; microdialysis
Received Mar. 17, 2003;
revised Jun. 5, 2003;
accepted Jun. 12, 2003.
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