302 Acta Neuropathol (2011) 122:293–311 Fig. 5 Diffuse and vascular Ab deposits induce astrocyte endfeet retraction and swelling in TG arcAb mice, starting at early-stage pathology. a Representative confocal microscopy images of cortical brain sections of an early-stage TG arcAb mouse triple-stained for GFAP, laminin and Ab/APP. At this age, TG arcAb mice have only few diffuse Ab plaques and very little CAA but the structural appearance of these Ab deposits is similar to that in mid-stage and late-stage animals, albeit less dense and restricted in size. Astrocytes (GFAP) surrounding these plaques show swollen endfeet (a, arrows to their NTG littermates (Fig. 7). The clear and typically- shaped endothelial imprints as seen in the NTG littermates (Fig. 7a, arrow) were malformed and often abolished in the TG mice (Fig. 7b, arrow). Furthermore, the vessel walls of these arteries and arterioles had a tree bark-like appearance (Fig. 7b, arrow). Severe vessel constrictions, appearing as stenoses, were found on numerous arteries and arterioles (Fig. 7b, asterisks and inset). Protrusions of the perfusion resin were found both on arterioles and capillaries of TG animals, indicating leakage of the vessel walls (Fig. 7c). In addition to these changes in vessel morphology, gaps in the vascular bed were uniquely present in the TG animals (Fig. 7d). Cerebrovascular morphology of early and mid- stage TG animals was not altered as compared to their NTG littermates (data not shown). Cerebral hypoperfusion and small cerebral vessel leakages without signiﬁcant haemorrhaging in late-stage arcAb mice Mouse brains perfused with casting resin and processed for histological analyses, showed that the presence of vessel 123 and asterisk) and loss of endfeet contact at CAA-affected vessels (laminin was used as vessel marker). b Arrows in sections show close endfeet—vessel interactions at a non-CAA-affected vessel in a late- stage TG arcAb mouse brain. The same endfeet retractions and swellings as can be seen in a were observed for astrocytes within and surrounding diffuse Ab plaques (b, asterisk). Scale bar a 30 lm; b 150 lm. Hue settings of ﬂuorescence for Ab were altered for more contrast effect explaining the blue colour leakages was paralleled by CAA in the TG animals (Fig. 8b, asterisks). These leakages appeared as ball- shaped structures protruding out of the vessel wall, similar to the structures observed in the SEM pictures (Fig. 7d). Resin protrusions were not found on vessels of NTG lit- termates (Fig. 8a). The number of vessels perfused with ﬂuorescent casting resin was lower in the TG animals (Fig. 8b, frame and Fig. 8c) as compared to their NTG littermates (Fig. 8a, frame and Fig. 8c). This was not accompanied by a reduction in vascular density (Fig. 8b GLUT1, frame and Fig. 8d) indicating that the decrease in vascular casting resin penetration was most likely due to the pathological cerebral hypoperfusion in the TG animals. Decreased cerebral perfusion could also explain the gaps in the vascular bed in the TG mice as observed with SEM (Fig. 7d). To assess if casting resin protrusions could be a sign of BBB compromise, TG and arcAb NTG mice were intraperitoneally injected with Trypan Blue. Unlike the results seen with the vascular casting resin (Fig. 8) such Trypan Blue-albumin (TBA) extravasations were mainly found around small vessels (Fig. 9a, asterisks). Bigger arterioles and arteries showed a mere accumulation of TBA