Amyloid Deposition and Dendritic Complexity of Corticocortical Projection Cells in Five Familial Alzheimer's Disease Mouse.

In Alzheimer's disease and related dementias, amyloid beta (Aβ) and amyloid plaques can disrupt long-term synaptic plasticity, learning and memory and cognitive function. Plaque accumulation can disrupt corticocortical circuitry leading to abnormalities in sensory, motor, and cognitive processing. In this study, using 5xFAD (five Familial Alzheimer's Disease - FAD - mutations) mice, we evaluated amyloid plaque formation in different cortical areas, and whether differential amyloid accumulation across cortical fields correlates with changes in dendritic complexity of layer 3 corticocortical projection neurons and functional responses in the primary somatosensory cortex following whisker stimulation. We focused on three cortical areas: the primary somatosensory cortex (S1), the primary motor cortex (M1), and the prefrontal cortex (PFC including the anterior cingulate, prelimbic, and infralimbic subdivisions). We found that Aβ and amyloid plaque accumulation is not uniform across 5xFAD cortical areas, while there is no expression in littermate controls. We also found that there are differential layer 3 pyramidal cell dendritic complexity changes across the three areas in 5xFAD mice, compared to same age controls, with no apparent relation to differential amyloid accumulation. We used voltage-sensitive dye imaging (VSDi) to visualize neural activity in S1, M1 and PFC following whisker activation. Control mice show normal physiological responses in all three cortical areas, whereas 5xFAD mice only display physiological responses in S1. Taken together our results show that 5xFAD mutation affects the overall dendritic morphology of layer 3 pyramidal cells across sensory-motor and association cortex irrespective of the density and distribution of the Aβ amyloid proteins. Corticocortical circuitry between the sensory and motor/association areas is most likely disrupted in 5xFAD mice as cortical responses to whisker stimulation are altered.