Accumulation of M/LMW Aβ42 peptides in dendrites correlates with reduced MAP2 in Tg2576 mouse brain by immuno-EM.

<p>(A) Representative image from an area not adjacent to amyloid plaques in a 26-month-old Tg2576 mouse. Marked M/LMW Aβ42 peptide (gold particles, white arrowheads) accumulation was locally associated with reduced MAP2 (immunoperoxidase, white thin arrows) staining in a postsynaptic compartment (plus), while a strongly MAP2 labeled dendritic postsynaptic compartment revealed no Aβ42 labeling (black arrowheads). Moreover, another synaptic compartment revealed intermediate levels of both M/LMW Aβ42- and MAP2-immunoreactivities (asterisk). Synaptic compartments are clearly recognizable because of the presence of postsynaptic densities (black thin arrows). (B) Adjacent to dystrophic neurites (asterisk), M/LMW Aβ42 peptide (gold particles, white arrowheads) accumulation is apparent in dendrites (thick black arrows) with reduced labeling of MAP2 (immunoperoxidase, white thin arrows). (C) Aβ42 peptide (gold particles, white arrowheads) associated with dark fibril-like material (black thin arrow) attach to an abnormal appearing multivesicular body (thick black arrow) in a weak MAP2-labeled dendrite. (D) Marked accumulation of Aβ42-immunoreactivity (gold particles, white arrowheads) in degenerated pre- and postsynaptic compartments without any obvious cytoskeletal structure (thick black arrows) close to amyloid fibers (asterisk). In contrast, a normal MAP2-labeled postsynaptic compartment without M/LMW Aβ42 peptide labeling is located nearby (black arrowheads). Scale bars: 500 nm.