One right or left area 4 of each of 19 rhesus monkeys, ranging in age from 1 day to 35 years, was processed (frozen sectioned at 30 or 40 microns) for light microscopic analysis to assess age-related changes in the neuronal population. All neurons were examined regardless of their size. In addition, Betz cells were analyzed separately; to be regarded as Betz cells, pyramidal somata had to display a minimum height of 38 microns. A significant loss of approximately one-third was observed in the total number of neurons in maturing monkeys (less than 5.5 years). In contrast, in maturing rhesus monkeys significant increases with age were observed in the mean number of Betz cells, and in the means of Betz cell area, height, width, perimeter, and estimated volume. In adult monkeys (greater than 4.5 years), no age-associated loss of neurons was observed. Also, no loss of Betz cells occurred, although the perimeter, area, and estimated volume of Betz cells decreased slightly, but significantly, with increasing age in adult monkeys. Lipofuscin granules were discernable in Betz cells beginning at the age of 5 years and their number increased with increasing age. In the older rhesus monkeys, the lipofuscin granules were so large and numerous that in some Betz cell somata they displaced the nucleus from its usual location in the center of the cell. No age-related change in thickness of area 4 was found.

Aging↗

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The stability of synaptic measures in cortex and hippocampus.

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Aging↗

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A beta40 is a major form of beta-amyloid in nonhuman primates.

Because aged nonhuman primates show beta-amyloid (A beta) deposition in senile plaques and blood vessels similar to that seen in human aging and AD, we used C-terminal specific antibodies to A beta40 and A beta42 to investigate A beta peptide length in the brains of 11 aged rhesus monkeys and a 59-year-old chimpanzee. In contrast to AD, where the earliest and most prominent form of A beta in senile plaques is A beta42, in the monkey, A beta40-positive plaques predominated. The ratio of A beta40:A beta42-positive plaques averaged 2.08 in the monkey, as compared to a mean ratio of 0.37 in 68 human AD subjects (p < 0.001). A beta40 was also more prominent in the chimpanzee than in humans. Possible explanations for these findings include species differences in the cleavage of A beta from the amyloid precursor protein or in the activity of a putative carboxy peptidase forming A beta40 from A beta42 in situ.

Aging↗