Figure 4.

Extended sonication increases β-amyloid-inducing activity. Brain extracts [10% (w/v)] from aged APP23 mice (Tg extract) were subjected to additional sonication (3 × 20 s). A, Immunoblot analysis with an antibody specific to human Aβ reveals no change in total Aβ between the original Tg extract (−) and the extract with extended sonication (+). However, more Aβ was found in the supernatant (SN) of the extra-sonicated extract after ultracentrifugation (100,000 × g; 1 h) (long exposure). B, C, In vivo seeding activity of the original and extra-sonicated extracts was tested by intrahippocampal injections into young, pre-depositing APP23 mice. Brains were immunohistochemically analyzed for Aβ deposition 4 months after injection. Shown is the dentate gyrus of the hippocampus. Injection of original Tg extract (B) induced robust congophilic Aβ deposition with a filamentous and dense pattern, while Aβ induction with the extra-sonicated Tg extract generated more punctate and small deposits (C). The inset shows double labeling of Aβ immunoreactivity and Congo red binding of the induced β-amyloid. Scale bars: 200 μm and 20 μm. D, Stereological quantification of Aβ load in the hippocampus revealed a significant increase in β-amyloid induction by extended sonication (n = 5–6 mice per group; mean ± SEM, t₍₉₎ = 3.188; *p < 0.05).