Hydroxyl Radicals Generated In Vivo Kill Neurons in the Rat Spinal Cord: Electrophysiological, Histological, and Neurochemical Results

Abstract: We have used microdialysis to establish an experimental model to characterize mechanisms whereby released substances cause secondary damage in spinal cord injury. We use this model here to characterize damaging effects of the hydroxyl radical (OH') in vivo in the spinal cord. OH'was generatad in vivo by pumping H₂O₂ and FeCI₂/EDTA through parallel microdialysis fibers inserted into the spinal cord. These agents mixed in the tissue to produce OH'by Fenton's reaction. Two types of control experiments were also conducted, one administering only 5 m M H₂O₂ and the other only 0.5 m M FeCI₂/0.82 m M EDTA. During administration of these chemicals, electrical conduction was recorded as one test for deterioration. OH'blocked conduction completely in 2.5-5 h and Fe²⁺/EDTA partly blocked conduction, but H₂O₂ alone did not cause detectable blockage. Histological examination supported the hypothesis that neurons were killed by OH', as Fe²⁺/EDTA and H₂O₂ alone did not destroy significant numbers of neurons. OH', H₂O₂, and Fe²⁺ all caused gradual increases in extracellular amino acid levels. These results are consistent with Fe²⁺-catalyzed free radical generation playing a role in tissue damage upon spinal cord injury.