Amyloid histology in cortical (first and third rows) and hippocampal (second and fourth rows) sections from untreated tTA/APP mice shows a dramatic progression of pathology between 6 and 9 mo of age. Suppression of transgenic APP expression arrests this progression, although without any sign of plaque clearance (6 mo + 3 mo dox). Hirano silver stain (top panels); thioflavin-S (bottom panels).