Figure 5.

Impairment of the BBB in the Cld5 ^−/− brains of 18.5-d embryos. Primary amine-reactive biotinylation reagent (443 D) was perfused from the heart of resuscitated embryos. After a 5-min incubation, sagittal frozen sections from the whole body (a and a′) or the brain (b, b′, c, and c′) were incubated with HRP-conjugated streptavidin to localize the biotinylation reagent by peroxidase activity. At a low magnification in the wild-type mouse (a), the reagent was completely excluded from the brain (arrow) and the spinal cord (arrowhead); in sharp contrast, in the Cld5 ^−/− mouse (a′), the CNS showed intense peroxidase activity. At a higher magnification, in the Cld5 ^−/− (b′ and c′) but not in the wild-type brain (b and c), the reagent infiltrated abundantly into the parenchyma. Bars: (a and a′) 2 mm; (b and b′) 40 μm; (c and c′) 10 μm.