Human amyloid precursor protein transgene expression is readily detectable within the pyramidal cell layer of 3xTg-AD mouse hippocampus from 2 to 26 months of age. Coronal mouse brain sections (30 μm) were prepared from 3xTg-AD mice sacrificed at 2 (A, I, Q), 3 (B, J, R), 6 (C, K, S), 9 (D, L, T), 12 (E, M, U), 15 (F, N, V), 18 (G, O, W), and 26 months of age (H, P, X) and were processed for immunohistochemistry to detect human amyloid precursor protein (hAPP) A4 using the Y188 monoclonal antibody. CA1 hippocampal sections at Bregma -1.8 mm (A–H), at Bregma -2.5 mm (I-P), and at Bregma -2.8 mm (Q-X), were examined for regional and temporal patterns of hAPPswe transgene expression and photomicrographs were obtained at 10×. The inset in panel X represents a 40× digitally magnified image of the photomicrograph for better visualization of stained cell morphology. Scale bar in D represents 200 μm.