The Effects of Normal Aging on Primate Cerebral Hemispheres


Rhesus monkeys live to a maximum of about 35 years (Tigges et al., 1988), and since humans live to be about 100 years of age, then one monkey year is equivalent to about 3 human years. An advantage of studying the effects of age on the brains of rhesus monkeys is that these primates have complex behavior patterns that approach those of humans and their cognitive status can be accurately assessed before their brains are preserved for structural evaluations. The different kinds of structural alterations that have occurred with age can then be examined to determine whether the frequency of a particular type of the structural alteration correlates with the cognitive decline. The other advantage of using the rhesus monkey to study normal aging is that these primates do not develop Alzheimer’s disease, so that the effects of aging are not confounded by changes related to Alzheimer’s disease pathology. Senile plaques do occur in the cerebral cortices of rhesus monkeys, but the plaques are few in number and their frequency does not correlate with cognitive decline (Sloane et al., 1997).

The normal appearance of these cells in young animals is illustrated in the book, “The Fine Structure of the Nervous System: Neurons and Their Supporting Cells” 1991, by Alan Peters, Sanford L. Palay and Henry deF. Webster. 3rd Edition, Oxford University Press.

The tissue used in this presentation has been fixed by perfusion of aldehyde containing solutions through the heart. Tissue blocks were then osmicated and embedded in Araldite for thin sectioning. The thin sections were stained with lead citrate and uranyl acetate, before being photographed in an electron microscope. The sheet film negatives were then scanned at high resolution and stored in a computer. Some of the scanned images have been colored using Photoshop to show the distribution of the various components of the neuropil, and as far as possible a standardized color scheme has been used throughout.

This research was supported by  the Institute on Aging of the National Institute of Health through Program Project grant  number P 01-AG 000001. The authors would like to thank Charmian Proskauer and Dr. R. Jarrett Rushmore for their suggestions regarding the final editing of this site.