AD phenotypes first appear in female B6. APBTgmice between 4–6 months of age. To determine the ideal ages at which to perform gene expression profiling we assessed plaque formation in brains from female B6.APBTg mice between 2–6 months of age. Plaques were visualized using Thioflavin T (Thio T, blue). The earliest detectable plaques occurred in the cortex of 4 months old mice. No plaques were observed in 2 months old mice. As expected, plaques were more apparent in brains from 6 months old mice. Arrows in the upper panels indicate the region shown in the lower panels. Scale bars; upper panels = 100 μm, lower panels = 50 μm.