Propagation of recurrent depolarization in the penumbra in the rat—use of in vivo cortical NADH fluorescence

To elucidate the propagation of recurrent depolarization in the penumbra, the fluorescence of cortical NADH was observed in rats that had been subjected to focal ischemia. A large cranial window was made on the left parietal-temporal bone to observe almost the entire left cortical hemisphere. The cortical surface was illuminated using a UV lamp (366 nm), and images of NADH fluorescence were taken every 17 s using a CCD camera with a 460 nm band-pass filter. During a 3-h period of ischemia, 220 recurrent depolarizations were observed in 45 animals as waves of high signal intensity that originated at the edge of the ischemic core and moved along the round margin of the ischemic core. Recurrent depolarizations were classified into two types: “spread-out type (86%)” in which recurrent depolarization spread out and did not increase the area of the ischemic core, and “expansion type (14%)” in which recurrent depolarization merged with the ischemic core and increased the area of the ischemic core. Histological examination revealed that neuronal injury occurred in the penumbral region, in which “spread-out type” of recurrent depolarization was observed, and that infarction occurred in the ischemic core, in which “expansion type” of recurrent depolarization was observed.