Distribution, progression and chemical composition of cortical amyloid-beta deposits in aged rhesus monkeys: similarities to the human.

A comprehensive investigation of the incidence, distribution, progression and chemical composition of Abeta deposits in the brains of two young (5 years) and seven aged (25-30 years) rhesus monkeys was conducted to determine the similarity of this phenomenon to that in the human. The brains of the young rhesus were devoid of Abeta deposits. In contrast, Abeta deposits were observed within the cerebral cortex of all aged animals. In animals with mild Abeta burden, deposits were observed primarily in association cortical zones. In animals with moderate Abeta burden, many paralimbic cortical zones also contained Abeta deposits. Finally, in an animal with a heavy burden of Abeta, core limbic cortical zones were also involved. The primary sensory and motor cortices were relatively free of Abeta deposits. A higher proportion of plaques contained Abeta40 as compared with Abeta42. Abeta deposits contained a number of other constituents. Cholinesterases were present in nearly 50% of plaques and displayed the exact same biochemical characteristics as those in the human. Nearly 20% of Abeta deposits also contained apolipoprotein E and a smaller proportion contained heparin sulfate proteoglycans and alpha1-anti-chymotrypsin. The latter three chemicals were present in many compact plaques. These results indicate that the distribution, progression and chemical composition of plaques in the aged rhesus monkey display many similarities to those observed in the aged human and Alzheimer's disease. Therefore, despite some differences from the human, the aged rhesus may be a good model for studies of the pathological effects of Abeta in the primate brain.