Changes in neuron number and size and glia number in the young, adult, and aging rat medial occipital cortex

Abstract

We previously reported changes in the Long-Evans, male rat cerebral cortical thickness as a function of age between birth and 650 days of age [Diamond, M. C., Johnson, R. E., and Ingham, C. (1975). Behav. Biol. 14 , 163–174]. On the adjacent celloidin-embedded sections from the 26-, 41-, 108-, and 650-day age groups in that study, cell counts and measurements were taken in the present study. Neurons, astrocytes, and oligodendrocytes were counted in the medial occipital cortex sectioned at the level of the posterior commissure. In addition, comparisons were made between neuron density as a function of age in the upper and lower halves of the cortical samples. The greatest decrease in density in both neuron and astrocytes and oligodendrocytes occurs before 108 days of age, with a nonsignificant density decrease after this time until 650 days of age. The lower cortical layers indicate a greater decrease in density before 108 days of age than do the upper layers. The area of the perikarya and nuclei decreases significantly before 108 days of age but not between 108 and 650 days of age. These cell counts and neuron size measurements offer encouraging results regarding the aging mammalian cortex of an animal living in a standard laboratory environment.