EPR imaging for in vivo analysis of the half-life of a nitroxide radical in the hippocampus and cerebral cortex of rats after epileptic seizures

Recently, we developed an in vivo temporal electron paramagnetic resonance (EPR) imaging technique to be applied to the brain of a rat, into which a b lood-brain barrier (BBB)-permeable nitroxide radical, 3-methoxycarbonyl-2,2 ,5,5-tetramethylpyrrolidine-1-oxyl (PCAM) was injected intraperitoneally. T his imaging technique made it possible to measure decay rates of a nitroxid e radical in multiple regions of the brain simultaneously. Using this techn ique, the half-life of PCAM was estimated from the exponential decay of the signal intensity derived from the temporal EPR images in the hippocampus a nd cerebral cortex of rats after a kainic acid (KA)-induced seizure. The hi ppocampal half-life of PCAM after KA-induced seizures was significantly pro longed (p < .01), whereas the prolongation of the cortical half-life was no t significant. These findings suggest that following a KA-seizure, the intr ahippocampal ability to reduce the nitroxide radical is impaired, but the a bility is intact in the cerebral cortex, This is the first in vivo quantita tive EPR imaging study that has a bearing on the pathogenesis of KA-induced seizures in the brain. (C) 1999 Elsevier Science Inc.