The age of biosenescence and the incidence of cerebral beta-amyloidosis in aged captive rhesus monkeys.

Autopsy surveillance of 186 rhesus monkeys aged 20 to 36 years revealed that development of major geriatric diseases such as emphysema, coronary sclerosis, and cancer increased rapidly after the age of 25 years, and nearly 70% of the monkeys in each cohort group died by 30 years. According to our 12-year longitudinal survey, the age of biosenescence in captive rhesus monkeys begins around 25 years and the maximum longevity is 36 years. The incidence of cerebral beta-amyloidosis associated with plaque formation and cerebral angiopathy was observed in 51 brains of rhesus monkeys aged 25 to 36 years. Lesions were found in 31 of 51 aged brains (60%) and 6 monkeys over 34 years of age were all severely affected. Despite the size of the plaque, nearly all of them showed immunopositive beta-amyloid. Cerebral angiopathy coexisted in 10 of 31 plaque-positive brains. The basal prefrontal gyrus was the most common site and contained the highest density of plaques, followed by the amygdala region. The amyloid in the liver, spleen, adrenal and pancreatic islets in visceral amyloidosis showed no positivity to the beta-amyloid demonstrated in the brain. As in aged human brains, the incidence of age-dependent cerebral beta-amyloidosis in captive rhesus monkeys showed great individual variation.