Immunohistochemical investigations of excitotoxicity in experimental spinal cord trauma

The concept of "excitotoxicity" assumes that high concentration of glutamate (main excitatory neuromediator) acting through specific receptors leads to damage of cells due to an influx of calcium ions. Proteins called "excitatory amino acid transporters" (EAATs), present in astroglia, play important role in the removal of glutamate. We investigated the expression of GluR2 (glutamate receptor), EAAT1, and EAAT2 by immunohistochemistry in formalin-fixed, paraffin-embedded rat spinal cords, previously subjected to experimental mechanical trauma. In the injured spinal cords, an elevated immunoreactivity of GluR2 was noted even 10 min after trauma and was still observed 2 days after injury. Strong immunoreactivity was observed not only in many cells in gray matter but also in some cells in white matter (probably glial cells). In the injured spinal cords, we observed stronger (as compared with controls) expression of EAATs in the white matter, especially 6 hours after injury. The results support the role of excitotoxicity in mechanical trauma of spinal cord suggesting a possibility of long lasting elevated expression of glutamate receptor. It may help to understand and to explain beneficial action of "anti-glutamate" drugs, reported by other investigators.