Aβ in aging Tg2576 brain. Aβ42 (A, C) and Aβ40 (B,D) were analyzed in Tg2576 brains sequentially extracted in 2% SDS (A, B) and 70% formic acid (C, D). The ELISA assay was 3160/BC05 for Aβ42 and 3160/BA27 for Aβ40. Note that the y-axes are logarithmic and that there was no detectable Aβ40 or Aβ42 in the formic acid extract of young (2–5 months) Tg2576 mice.