ESR imaging of the rat brain with a nitroxide radical perfused by in vivo microdialysis

We report here our investigation of the spatial distribution of free radicals using an electron spin resonance (ESR)-imaging system combined with an in vivo brain microdialysis method, which was performed in the resonator of the ESR-imaging system. A nonmagnetic cannula, newly developed in this study, was used for the perfusion of the exogenous free radicals agent. A nitroxide, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl PROYXL), was used as the imaging agent in saline solution at a concentration of 0.3 M, which was perfused into the right caudate putamen of the rat at 2 μl/min by a microinfusion pump. Two-dimensional ESR projection of the Z-X plane, which was clearly distinguished (about φ 10 mm) from the nonperfused brain area, was obtained 6 h after the beginning of perfusion of carbamoyl PROXYL. The present method is considered to be a useful tool to introduce stable free radicals into a specific area of the brain.