Neuroglial cells in the cerebral cortex of rats from young adulthood to old age: An electron microscope study

Summary

Neuroglial cells were examined in the rat auditory cerebral cortex to determine the effects of aging on astrocytes, oligodendrocytes and microglia. The animals ranged in age from 3 months to 29.5 months. Over this age range of 26.5 months none of the neuroglial cells exhibit striking abnormalities in the morphology or the number of their organelles other than each of these cell types accumulates a distinct membrane-bound inclusion material. Astrocytes accumulate considerably more of this material than oligodendrocytes, and demonstrate earlier and more frequent signs of it. Microglia show the most striking alterations in regard to the inclusion material and in animals of increasing age microglial cells engorged with the heterogeneous material become increasingly common. Concurrently there is a slow transformation of the microglial population from an array of multipolar forms to larger, elongated or spherical forms which contain variable amounts of the dense membrane-bound material. These alterations in the microglial cell population do not occur at a chronologically uniform rate, and in animals 18 months and older, examples of the multipolar, the elongated, and the engorged spherical forms of microglia may be encountered.

The total number of neuroglial cells increases with age. However, the numbers of the various types do not increase by similar proportions. While there is little change in the populations of astrocytes and oligodendrocytes in rats between the ages of 3 and 27 months, in the same animals the number of microglia increases by about 65%.