Traumatic brain injury (TBI) is a leading cause of mortality and disability. The goals of this proposal are to: 1) establish the role of elevated interstitial concentrations of excitatory amino acids (EAAs) and the formation of reactive oxygen species (ROS) in posttraumatic pathophysiology, 2) understand the mechanism responsible for increased interstitial concentrations of these molecules and 3) elucidate the relationship between EAA and ROS in the production of degenerative change. Using a controlled cortical contusion model, we will establish whether the TBI-induced elevations in interstitial concentrations of EAA ([EAA]i) is attributable to diminished reversed uptake by both characterizing the effect of a blocker of voltage-dependent Na+ channels and by determining the effect of glucose (plus/minus and inhibitor of EAA uptake) on the posttraumatic elevation in [EAA]i. The relative contribution of EAA release will be assessed by comparing the effect of these treatments on TBI- and K+-induced elevation in [EAA]i. The role of ROS in RBI will be assessed by determining the influence of TBI on interstitial concentrations of dihydroxybenzoic acid (formed by the reaction between salicylate and hydroxyl radicals) and malondialdehyde (a product of lipid peroxidation). The involvement of ROS in human brain injury will be assessed by determining the concentrations of ascorbate and malondialdehyde in serial samples of ventricular CSF from patients with severe closed head injury. In addition, the lesion caused by intracortical injection of iron will be compared with that produced by controlled cortical contusion using glial fibrillary acid protein immunohistochemistry. We will also determine the effectiveness of both a ROS scavenger and a chelator of iron in reducing the magnitude of the TBI-induced lesion, as assessed by magnetic resonance imaging (edema and lesion volume) and histology (lesion volume). We have established that moderate hypothermia reduces the amount of tissue damage caused by TBI. The mechanism that underlies this cytoprotective action will be assessed by comparing TBI-induced changes in fos gene expression, interstitial concentrations of malondialdehyde and dihydroxybenzoic acid in animals maintained normothermic or hyperthermic (32degreesC). The effect of sustained (24 h) hypothermia on malondialdehyde concentration will also be assessed in the ventricular CSF of head-injured humans. A possible secondary (delayed) posttraumatic elevation in [EAA]i and [ROS]i will be assessed by microdialysis in posttraumatic freely moving animals. The locus of reactive oxygen species formation will be assessed by removing blood from the posttraumatic animals and measuring the formation of dihydroxybenzoic acid in interstitial fluid and also by determining the effect MK-801 treatment on dialysate concentration of MDA posttrauma. Finally, the possibility that EAA and ROS cooperate in this process will be assessed by comparing the effectiveness of MK-801 therapy to reduce the severity of injury (assessed longitudinally by magnetic resonance imaging and finally by histology) when administered alone and in combination with a free radical scavenger and a chelator of iron.
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