Acta Neuropathol (2011) 122:293–311 303 within the vessel wall (Fig. 9a plus sign and arrow, respectively). Similar to the vascular resin histology (Fig. 8) these small vessel TBA extravasations and arterial/ big arteriolar TBA accumulations were only present on CAA-affected vessels (Fig. 9a). Vessels were visualised using a CD31 antibody to stain endothelial cells. b Fig. 6 Astrocytic b dystroglycan expression is signiﬁcantly decreased in late-stage TG arcAb mouse brain and paralleled by IgG extravasation. Representative images of late-stage TG (a, c, e) and arcAb NTG littermate (b, d, f) mice showing decreased expression of the astrocyte endfeet protein b dystroglycan in TG arcAb mouse brain as compared to their NTG littermates. Loss of b dystroglycan immunoreactivity was most pronounced in the cortex (a) and hippocampus (e) of TG animals. This reduced expression was paralleled by the presence of cerebral extravasation of endogenous IgG around diffuse Ab plaques (a, e, arrows). Areas of the brain (hypothalamic region) where no mouse IgG could be observed did show less pronounced loss of b dystroglycan expression (c). These areas were also not affected by diffuse Ab plaques but rather by CAA. Scale bar a 300 lm. Presence of mouse IgG was detected by the same secondary anti-mouse antibody (FITC-tagged donkey anti-mouse IgG) used to visualise primary anti-b dystroglycan antibody which was raised in mouse, explaining the presence of both b dystroglycan and endogenous mouse IgG on the same brain sections. g Signiﬁcant loss of b dystroglycan expression on blood vessels in cortex (ctx), hippocampus (hipp) and hypothalamic region (hypthal) of late-stage TG arcAb mice compared to NTG littermates. The hypothalamic region of TG arcAb mice showed signiﬁcantly more b dystroglycan expression as compared to cortex and hippocampus (p \ 0.02) but was still signiﬁcantly less than in NTG littermates (p \ 0.001). b dystroglycan immunoreactivity was calculated by measuring staining intensity using ImageJ software. Student’s t test, n = respective brain areas of 12 mice (6 TG and 6 NTG), three sections/brain area/mouse. Hue settings of ﬂuorescence for Ab were altered for more contrast effect explaining the purple colour Unlike TBA extravasations, cerebrovascular haemor- rhages as detected by Prussian Blue staining were rarely seen but likewise associated with CAA (Fig. 9b, asterisk and 9c) with brain areas presenting abundant CAA, e.g. (pre-) frontal cortex, mainly affected. However, the extent of haemorrhagic lesions did not correlate with the severity degree of CAA. Furthermore, casting resin protrusions were not chronically paralleled by haemorrhages (Fig. 9d, arrows). CAA-dependent abnormalities of vascular basement membranes and degeneration of smooth muscle cells in late-stage arcAb mice Brains from littermates of the mice used in the SEM vascular corrosion casts (Fig. 7) and which were not perfused with casting resin were processed for immu- nohistochemistry to analyse the morphological alterations found by SEM. Laminin staining (Fig. 10a) was used as VBM/vessel marker and its expression found to be sig- niﬁcantly increased on CAA-laden vessels in mid- and late-stage TG arcAb mice (Fig. 10c, d), a phenomenon underlying VBM thickening and well known to occur in AD [16]. Bulges of laminin (Fig. 10a, asterisks) resem- bling the stenoses observed in the SEM analyses (Fig. 7b, asterisks) and vessel constrictions (Fig. 7c, arrow and Fig. 10a, plus signs) were widely found in the TG animals. Moreover, these vascular malformations 123