Aging brain lesions of a 60-year-old Bornean orangutan (Pongo pygmaeus)

A female Bornean orangutan (Pongo pygmaeus) raised in a zoo died at 60 years of age. The animal showed no clinical signs besides decreased gait speed. Pathological examination revealed small hemorrhagic foci in the cerebral cortex and liver fibrosis with fatty degeneration of the hepatocytes. To evaluate aging lesions, the brain was examined histologically and immunohistochemically. Severe amyloid β (Aβ) deposition was observed in the cerebral cortex and vascular walls. Parenchymal Aβ deposits in the cerebral cortex appeared as diffuse plaques. Loss of smooth muscle was observed in the vascular walls affected by Aβ deposition. In contrast, only a few phosphorylated tau aggregates were observed. This report describes severe Aβ deposition in the brain of the oldest orangutan ever reported, which did not exhibit significant tau pathologies.