deposition is not immunohistochemically detectable in male 3xTg-AD mouse hippocampus until 15 months of age. A monoclonal antibody specific for human Aβ1–42 (12F4; Signet) was incubated with 20 month-old 3xTg-AD mouse brain sections alone (A), or with a 200-fold molar excess of the cognate reverse peptide (B), forward peptide (C), or no-primary control (D) according to a protocol designed to detect extracellular Aβ1–42. Coronal mouse brain sections (30 μm) were prepared from 3xTg-AD mice sacrificed at 2 (E, M, U), 3 (F, N, V), 6 (G, O, W), 9 (H, P, X), 12 (I, Q, Y), 15 (J, R, Z), 18 (K, S, AA), and 26 months of age (L, T, AB) and were processed for immunohistochemistry using the 12F4 antibody to detect extracellular Aβ1–42 peptide accumulation. CA1 hippocampal sections at Bregma -1.8 mm (E-L), at Bregma -2.5 mm (M-T), and at Bregma -2.8 mm (U-AB), were examined for regional and temporal patterns of extracellular Aβ1–42 deposition and photomicrographs were obtained at 10×. The inset in panel AB represents a 40× digitally magnified image of the photomicrograph for better visualization of stained cell morphology. Scale bar in D represents 200 μm.