Effects of aging on the neuroglial cells and pericytes within area 17 of the rhesus monkey cerebral cortex

Abstract

An electron microscopic analysis has been carried out to compare the neuroglial cells and pericytes within the primary visual cortex, area 17, of young (5-6 years) and old (25-35 years) rhesus monkeys. All of the neuroglial cell types accumulate inclusions within their cytoplasm as they age, and the inclusions within the astrocytes and oligodendrocytes are essentially characteristic of those cell types. The astrocytes probably acquire their inclusions by phagocytosis, and it is suggested that the inclusions in the oligodendrocytes are caused by an age-related degeneration of the myelin sheaths they produce. The inclusions within the microglia are very heterogeneous. They are more massive than in the other neuroglial cells, so that their inclusions may almost fill the microglia. Pericytes also accumulate inclusions with age and there is evidence to suggest that they empty the contents of their inclusions vacuoles directly into the capillaries. On the basis of counts of the numbers of profiles of neuroglial cells displaying nuclei in thin sections, the only cells to increase in number with age are the microglia. They show an increase of about 44% when the cortices of young and old monkeys are compared.

Light microscopic quantification of morphological changes during aging in neurons and glia of the rat parietal cortex

“…In specific cell types, different authors have reported both hyperplasia of human and rat astrocytes (Lolova, 1991;Amenta et al, 1994) and also hypertrophy of these cells. Increases with age have also been described in glial size (Björklund et al, 1985) and in the number of filaments within astrocytes (Peters et al, 1991). Increases with age in microglial cells and oligodendrocytes have been also reported in the frontal cortex of the rhesus monkey (Peters et al, 1994).…”

“…Other non-neuronal cells such as pericytes and endothelial vascular cells were carefully excluded (Ling and Leblond, 1973;Curcio and Coleman, 1982;O'Kusky and Colonnier, 1982;Sturrock, 1983;Peters et al, 1991).…”

“…However, Haug et al (1983) failed to detect changes with age in glial cells in the frontal and visual areas of the human brain. Studies of areas 1, 3, and 4 (Brizzee, 1975;Brizzee et al, 1976), the visual cortex (Peters et al, 1991), and the frontal cortex (Peters et al, 1994) of the rhesus monkey reported a significant increase in the neuroglial cell population with age. In aged rats, increased numbers of microglial cells were reported in the auditory cortex (Vaughan and Peters, 1974), and astrocyte hypertrophy and astrogliosis have been described in the hippocampus (Landfield et al, 1981) and frontal cortex (Amenta et al, 1994).…”

Preservation of hippocampal neuron numbers in aged rhesus monkeys

“…As far as nonhuman primates are concerned, stereological analyses of various brain structures strongly indicate that neuron numbers do not decline with age. Although the primary visual cortex of aged rhesus monkeys showed no electron microscopical sign of neuron loss, various types of neuroglial cells and pericytes were affected by age [45]. Also, in nonhuman primates, a decrease in white matter volume, as measured with magnetic resonance imaging, was correlated with an overall cognitive impairment [47].…”

Neuronal density in the human retinal ganglion cell layer from 16-77 years

“…For example, the visual system of the monkey, from ganglion cell layer to primary visual cortex, shows no neuronal loss due to aging (Kim et al, 1996(Kim et al, , 1997Peters et al, 1997;Ahmad and Spear, 1993;Peters and Sethares, 1993;Vincent et al, 1989). The main changes due to aging in the monkey brain appear to be a degeneration of myelin and various glial cell types (Peters et al, 1989(Peters et al, , 1991(Peters et al, , 1994.…”