Hippocampal aging in rats: a morphometric study of multiple variables in semithin sections.

Quantitative analyses of pyramidal cells, astrocytes, dark glia (microglia and dark oligodendrocytes), lipofuscin accumulation and astrocyte reactivity were carried out in semithin sections from field CA3 of the hippocampus of rats in 3 age groups (4-7 mo., 13-15 mo., 25-28 mo.). A decrease in neuronal density (approximately 25%) and an increase in dark glia were found in the oldest group. The astrocyte population was stable with age. Lipofuscin increased by 13-15 mo. and increased further by 25-28 mo. Qualitative examples of several kinds of glial reactivity are also described. Our observations indicate that hippocampal changes in aging rats exhibit some similarities to brain changes reported in other mammalian species, and also illustrate the value of semithin sections for examining neuromorphologic correlates of brain aging.