Effects of a combination of BACE1 haploinsufficiency and neprilysin overexpression on memory deficits and cholinergic neuron loss in 12-month-old 5XFAD mice. (A, B) Mice were trained with a CS-US pairing for contextual fear conditioning (n = 6–11 mice per group). 5XFAD mice showed significantly lower levels of contextual freezing than wild-type mice when tested 24 h after training. NEP · 5XFAD and BACE1+/− · NEP · 5XFAD mice are rescued almost completely back to wild-type control levels of contextual memory. (C) Brain sections were immunostained for the cholinergic marker ChAT. Shown are representative photomicrographs of ChAT-immunoreactive neurons in the medial septum of mice. Scale bar = 200 μm. (D) The number of ChAT-positive neurons in the medial septum and the vertical limb of the diagonal band (Ch1/2), which provide the cholinergic innervation to the hippocampus, was counted for quantification (n = 2–5 mice per group). Cholinergic neuronal death associated with 5XFAD is prevented in NEP · 5XFAD and BACE1+/− · NEP · 5XFAD mice. * p < 0.05 vs. wild-type, #
p < 0.05 vs. 5XFAD. All data are presented as mean ± SEM.