Natural Occurrence of Amyloid-Aβ Deposits in the Brain of Young Common Marmosets (Callithrix jacchus): A Morphological and Immunohistochemical Evaluation

The spontaneous incidence and distribution of β-amyloid (Aβ) peptide and argyrophilic deposits were extensively investigated in the common marmoset (Callithrix jacchus). In 12 young marmosets, up to 67 coronal step sections were evaluated in the brain. One brain hemisphere was stained by a silver method and also immunohistochemically with a primary antibody directed against Aβ. Argyrophilic deposits were observed in 4 (33%) of 12 animals with silver stain, and Aβ was seen in 4 (33%) of 12 animals with anti-4G8 antibody. The overall incidence was 6 (50%) of 12 affected animals. These results show that the young marmoset brain displays Aβ deposits at a low incidence and that immunohistochemistry is more suitable than silver staining to reveal rare amyloid plaques. These findings also provide evidence for the early onset of amyloid deposits in marmoset brain.