Intravital oxygen radical imaging in normal and ischemic rat cortex

We examined reactive oxygen species (ROS) generation on cerebral ischemia/reperfusion by intravital fluorescence imaging.

In anesthetized adult rats, a fluorescent dye (5 microL), MitoSOX (5 micromol/L) for superoxide radical (.O2-), and hydroxyphenyl fluorescein (20 micromol/L) for hydroxyl radical (.OH), was injected into cortices by a pressurized bolus. Through a closed cranial window, fluorescent images were taken with a confocal microscope on 10-minute forebrain ischemia. Because hemoglobin absorbs excitation and emission lights, ischemia may affect the change in fluorescence intensity (FI) inside the brain. To examine the effects of ischemia on the FI change, fluoromicrospheres (0.2-microm diameter) were used to mimic a dye and FI was analyzed in the same manner as when using ROS indicators. Their FI increased to 129% during ischemia (n=3/mimicking each dye), and based on the results, FI of ROS indicators was corrected.

After correcting the FI of MitoSOX and hydroxyphenyl fluorescein, they showed no change during ischemia, whereas the raw data showed the increase. In the early period of reperfusion, FI significantly (n=5/each, P<.01) increased (to 183% in MitoSOX and to 189% in hydroxyphenyl fluorescein), and these increases were significant in the areas adjacent to the arteries. To test the feasibility of our imaging, edaravone (3.0 mg/kg) was used. The treatment completely scavenged .OH, but did not do so in .O2- generation.

ROS production increased in the early period of reperfusion but not during ischemia, which was location selective, being significant in the areas adjacent to the arteries. Our method was useful for investigating intracellular in situ ROS production.