Fig. 5

Hypoxia-induced endothelial proliferation in the brain occurs preferentially in white matter tracts. Frozen brain sections taken from mice exposed to normoxia or hypoxia (8% O₂) for 4 days were stained for CD31 (AlexaFluor-488), Ki67 (Cy-3), and DAPI (blue) (A, cerebellum and D, forebrain) or fluoromyelin (red) and Ki67 (AlexaFluor-488) (B, cerebellum and E, forebrain). Scale bars = 500 μm except for high power (HP) images where scale bars = 200 μm. White dotted line demarcates the WM corpus callosum (CC, inside) from the surrounding cerebral cortex (CX) grey matter. C and F. Quantification of the number of proliferating endothelial cells/unit area in the cerebellum (C) or cerebral cortex/corpus callosum areas (F) after 0- or 4-days hypoxia. Results are expressed as the mean ± SEM (n = 5–6 mice/group). *** p < 0.001. Note that in both brain areas, most of the hypoxia-induced endothelial proliferation occurs in the WM tracts