Fig. 6

Dual staining with BSB and MCAAD-3 detected subtle pathology in the background parenchyma of human AD brain. (A,D) Representative spectral micrographs of frontal cortex (Brodmann area 9) from sporadic AD and non-AD controls labeled with 300 nM BSB and 1000 nM MCAAD-3. Only the dim background pixels were selected for phasor analysis, leading to a similar appearance for both control and AD plots (B,E). The ROI on the phasor plot was the same as in mouse samples (Fig. 5), and selected the majority of background pixels shown in blue in C, F. r*θ metrics revealed significant differences between control and AD background ((G), p = 0.025 Wilcoxon signed-rank test), which were completely abolished by formic acid hydrolysis (H). The average emission spectra of the kernels enclosed by the ROI showed a subtle red-shift of the AD background parenchyma compared to controls due to a relatively higher MCAAD-3 peak (I, arrow), which was reduced by formic acid treatment (J). Taken together, as in 5xFAD mouse background, these results are consistent with a subtle but widespread amyloid deposition in the non-plaque human AD parenchyma. Scale bars: 50 μm, error bars indicate SEM