Subtle behavioral changes and increased prefrontal-hippocampal network synchronicity in APPNL-G-F mice before prominent plaque deposition

Amyloid-beta (A beta) peptides occur in the brains of patients with Alzheimer's disease (AD), but their role in functional impairment is still debated. High levels of APP and APP fragments in mice that overexpress APP might confound their use in preclinical research. We examined the occurrence of behavioral, cognitive and neuroimaging changes in APP(NL-G-F) knock-in mice that display A beta 42 amyloidosis in the absence of APP over-expression. Female APP(NL-G-F) mice (carrying Swedish, Iberian and Arctic APP mutations) were compared to APP(NL) mice (APP Swedish) at 3, 7 and 10 months. Mice were subjected to a test battery that referred to clinical AD symptoms, comprising cage activity, open field, elevated plus maze, social preference and novelty test, and spatial learning, reversal learning and spatial reference memory performance. Our assessment confirmed that behavior at these early ages was largely unaffected in these mice in accordance with previous reports, with some subtle behavioral changes, mainly in social and anxiety-related test performance. Resting-state functional MRI (rsfMRI) assessed connectivity between hippocampal and prefrontal regions with an established role in flexibility, learning and memory. Increased prefrontal-hippocampal network synchronicity was found in 3-month-old APP(NL-G-F) mice. These functional changes occurred before prominent amyloid plaque deposition.