EPR imaging to estimate the in vivo intracerebral reducing ability of mature rats after neonatal hypoxic–ischemic brain injury

A rat model of neonatal hypoxic–ischemic encephalopathy (Riceʹs model) was obtained by unilateral ligation of the common carotid artery of 7-day-old rats with hypoxia (exposure to 8% oxygen). To estimate the in vivo intracerebral reducing ability of the mature rats (8 weeks old) of Riceʹs model, temporal electron paramagnetic resonance (EPR) imaging of the brain of a rat receiving a blood–brain barrier-permeable nitroxide radical, 3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, was performed. In this imaging technique, the decay rate of the EPR signal intensity in a selected region of the brain is indicative of region-specific reducing ability. The effect of neonatal treatment of an antioxidant agent, 3-methyl-1-phenyl-2-pyrazolin-5-one (MCI-186), after a hypoxic–ischemic insult was also tested. It was found that the reducing ability had been depleted in the contralateral hemisphere of Riceʹs model rats; this depletion was suppressed by administering MCI-186.