CHANGES IN THE EXTRACELLULAR GLUTAMATE CONCENTRATIONS IN THE RAT CORTEX FOLLOWING LOCALIZED HYPERTHERMIA

The mechanisms involved in cellular injury caused by hyperthermia in the central nervous system (CNS) remain unknown. In order to test the hypothesis that glutamate excitotoxicity may play a role in hyperthermia-induced CNS injury, we measured the extracellular glutamate concentrations, using intracerebral microdialysis, in the rat brain following localized hyperthermia. The glutamate concentration in the dialysate was not increased by mild hyperthermia (41 degrees C), but it reached 250% of the control level 40 min after a 20-min period of moderate hyperthermia (43 degrees C) and then decreased rapidly. When severe hyperthermia (45 degrees C) was induced, the glutamate concentration reached approximately 300% of the control level and was maintained at that level for 100 min after hyperthermia cessation. The elevated extracellular glutamate concentrations by local hyperthermia reached neurotoxic levels. The results presented here suggest that a glutamate-mediated, 'excitotoxic' process plays an important role in hyperthermia-induced cellular injury in the CNS.