Photomicrographs of sections from APP23 Tg mice brains. Images A through H were stained with thioflavine S and photographed using scanning laser confocal microscopy. Images A through D illustrate the progressive accumulation of cortical plaques with increasing age of the Tg animal, representing mice aged 9, 12, 14, and 20 months, respectively. Calibration bar in A equals 500 µm and serves for A–D. Images E through G depict the typical increase in plaque size with increasing age. Nine-, 12-, and 20-month-old animals are represented in E, F, and G, respectively. Image H shows two blood vessels with intense thioflavine fluorescence of their walls as well as exophytic growths of amyloid extending from the vessel wall into the adjacent neuropil (arrow). Calibration bar in E equals 50 µm and serves for E–H. Photomicrographs I through L show immunohistochemical staining of cortical plaques with antibodies to Aβ (I–K) and ApoE (L). Sections I–K were counterstained with neutral red. Antibody 6E10, against Aβ1–17, stains both amyloid cores (I, lower arrow) and diffuse-type plaques (I, upper arrow). The end-specific antibody against Aβ N-40, R163, stains cores intensely (J, arrow), but does not stain diffuse plaques. The end-specific antibody directed at Aβ N-42, R165, stains diffuse plaques (K, arrow), but cores are stained poorly. Calibration bar in I equals 100 mm and serves for I–K. Staining for ApoE revealed plaques in numbers and morphology similar to that seen with thioflavine S staining (L); calibration bar equals 75 µm. Photomicrographs M through P are included to show intracellular findings with Aβ and APP antibodies. The sections were counterstained for cellular detail with neutral red. Antibody 6E10 reveals intracytoplasmic granules within large cortical pyramidal neurons (M, arrows). Sections stained with the end-specific antibodies R163 and R165, against carboxy terminal residues of Aβ40 and Aβ42, respectively, did not show any intracellular reaction product (staining with R165 is shown in N; staining with R163 was similar but is not shown). The sections seen in O and P were stained with the 22C11 and R37 antibodies for the N- and C-termini of APP, respectively. Note the presence of abundant intraneuronal granular reaction product. The calibration bar in M equals 15 mm and serves for M–P.