The ISF Aβ40 levels in APP/PS1 mice expressing apoE3 (A-B, APP/iE3; n=8/group) or apoE4 (C–D, APP/iE4; n=4/group) at the age of 3–4 months were analyzed. To assess Aβ40 half-life, the mice were treated with a γ-secretase inhibitor, and the hippocampal ISF Aβ40 levels were monitored. The slope from the individual linear regressions from log (% ISF Aβ40) versus time for each mouse was used to calculate the mean half-life (t1/2) of elimination for Aβ from the ISF (B, D). Data represent mean ± SEM. *, p<0.05; N.S., not significant.