beta-Amyloid (Abeta) accumulation and aggregation are hallmarks of Alzheimer's disease (AD). High-resolution three-dimensional (HR-3D) volumetric imaging allows for better analysis of fluorescence confocal microscopy and 3D visualization of Abeta pathology in brain. Early intraneuronal Abeta pathology was studied in AD transgenic mouse brains by HR-3D volumetric imaging. To better visualize and analyze the development of Abeta pathology, thioflavin S staining and immunofluorescence using antibodies against Abeta, fibrillar Abeta, and structural and synaptic neuronal proteins were performed in the brain tissue of Tg19959, wild-type, and Tg19959-YFP mice at different ages. Images obtained by confocal microscopy were reconstructed into three-dimensional volumetric datasets. Such volumetric imaging of CA1 hippocampus of AD transgenic mice showed intraneuronal onset of Abeta42 accumulation and fibrillization within cell bodies, neurites, and synapses before plaque formation. Notably, early fibrillar Abeta was evident within individual synaptic compartments, where it was associated with abnormal morphology. In dendrites, increasing intraneuronal thioflavin S correlated with decreases in neurofilament marker SMI32. Fibrillar Abeta aggregates could be seen piercing the cell membrane. These data support that Abeta fibrillization begins within AD vulnerable neurons, leading to disruption of cytoarchitecture and degeneration of spines and neurites. Thus, HR-3D volumetric image analysis allows for better visualization of intraneuronal Abeta pathology and provides new insights into plaque formation in AD.
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