The levels of Aβ in the plasma of the APP23 Tg mice and control littermates. The measurements of these peptides were made in the 3- to 8-kDa FPLC formic acid-separated fractions at 2, 4, 9, 12, 14, and 20 months of age. Solid and broken lines correspond to the Tg mice and control mice, respectively. (A) Aβ40. (B) Aβ42. (C) the sum of Aβ40 and Aβ42. There were no significant differences between the Tg and non-Tg mice.