ESR spectroscopy for analysis of hippocampal elimination of a nitroxide radical during kainic acid-induced seizure in rats.

To analyze the balance between free radical production and elimination during seizure, techniques were developed to monitor the sequential changes in the level of an exogenous free radical by ESR in the brains of freely moving rats given kainic acid (KA) to induce seizures (n = 6) and control rats given saline (n = 6). The hippocampus of each rat was perfused with a nitroxide radical solution for 120 min by in vivo microdialysis. Then an intraperitoneal injection of KA or the physiological saline was given to each rat, and the perfusate was changed to Ringer's solution. ESR analysis of sequential samples of dialysate taken after injection revealed an exponential decay in signal amplitude. The median half-life of the nitroxide radical was significantly longer in the KA-treated group than in the control group (P < 0.01). This finding demonstrates a decreased capacity of the hippocampus to eliminate the nitroxide radical from the extracellular space during seizure and may help clarify the mechanism of neuronal cell vulnerability to free radicals during insult or degeneration.