Biochemical characterization of pre-plaque McGill-Thy1-APP-TG rat brain. (a) Immunohistochemical staining with 6E10 (red), a monoclonal antibody to the N-terminal region of Aß in APP, illustrates the lack of extracellular deposits in the hippocampus of a 5 month-old TG rat. Sections were co-stained with the neuronal marker NeuN (green). Left hand panel shows low power view with NeuN staining. The boxed areas are shown in high power in the right hand panels. Several cell bodies had overlapping intracellular staining (yellow in overlay, Ovl) indicating intracellular reactivity in both hippocampal (CA1 area) and cortical neurons. The 6E10 staining that did not co-localize with NeuN staining was caused by non-specific staining of blood vessels. Scale bars: overview 500 μm, insets 100 μm. (b,c) Characterization by Western blotting using the antibody 6E10 of human APP breakdown products in membrane (b) and extracellular (c) fractions of cortical extracts from 3–4 month-old TG rats. (b) The membrane fraction contained Aß monomer (1-mer), C-terminal fragment-ß (CTF-ß) and full length APP (flAPP). It also contained two other APP cleavage products (mACP 50–75 and mACP 37–50). (c) In contrast, the extracellular fraction contained mainly sAPPα with trace amounts of Aß monomer and two other APP cleavage products (eACP 50–75 and eACP 10–15). The asterisks indicate non-specific bands.