Soluble and insoluble amyloid peptides in brain of aging APP/V717I transgenic mice. Concentrations of soluble (A) and precipitated or plaque-associated (B) amyloid peptides, i.e., Aβ40 (gray bars) and Aβ42 (black bars), were measured by specific ELISA, and results are expressed as nanogram peptide per gram brain tissue. The ratio of the concentrations, i.e., Aβ42/Aβ40 of both soluble and precipitated amyloid peptides, was calculated (A andB, right). All histograms represent the mean with SEM of at least four transgenic mice in each age group.