Fig. 1

Cerebral injury dependence on recovery time between recurrence of mild transient ischemic insults. Representative cerebral cortical micrographs of sections at low and high magnification (scale bar of 25 µm) stained with: hematoxylin and eosin (a–h), ED1 for activated macrophages/microglia (j–m), and GFAP for reactive astrocytes (o–r). Brain was perfusion fixed and processed 7 days following the last insult. Cerebral cortex contralateral to the transient middle cerebral artery occlusion (MCAO) is normal (A,C). Within cerebral cortex (b, d) after a mild transient MCAO followed by a recurrent MCAO at 1 day there is extensive pannecrosis (p). Selective necrosis (s) is common following a mild transient MCAO followed by a recurrent MCAO at 3 days (e, g). Selective necrosis also occurs in rats with a sham surgery followed 1 day later by transient MCAO (f, h). Semiquantitative assessment of injury scores indicated greater damage with 1 day compared to 3 days recurrence in the H&E sections (i). Immunohistochemical staining with ED1 antibody demonstrated an increase in activated macrophages/microglia following recurrent MCAO produced at either 1 or 3 days after an initial MCAO (j–m). The mean number of cells per field with ED1 staining demonstrating a difference between 1 and 3 days recurrent MCAO groups (n). GFAP staining of astrocytes was increased with recurrent MCAO at 1 or 3 days (o–r). The median score for altered GFAP staining reflected greater injury and astrocytic changes in brains of animals with recurrent MCAO at 1 day than 3 days (s). n = 6/group. *P < 0.05; **P < 0.006, Ipsilateral different from contralateral; ^†P < 0.05; ^††P < 0.006, different from 1 day Recurrent MCAO. ^‡P < 0.01, different from Sham