Effects of aging and chronic arterial hypertension on the cell populations in the neocortex and archicortex of the rat

Summary

Quantitative histological techniques were used to evaluate the effects of chronic arterial hypertension on the changes which occur during aging of the cerebral cortex and hippocampus. Normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were killed at 3 or 22–27 months of age. In the cerebral cortex, the numerical density of neurons decreased by 29.7% in aged WKY (mean age: 25.5 months) and by 31.6% in aged SHR (mean age: 23.3 months). The volume density of neuronal cell bodies decreased from 3.54% in young WKY and 3.68% in young SHR to 2.74% in the aged rats of both strains. No significant alterations in the population of cortical neuroglial cells were observed as a result of either aging or hypertension. No differences in the number of capillaries, volume density of blood vessels or number of pericytes were observed among the four experimental groups. The normotensive rats exhibited an increase in the number of venules with age. Aged hypertensive rats had significantly (23.3%) fewer endothelial cells than young SHR, while the 9.1% loss of endothelial cells in aged WKY was not statistically significant. In the CA1 zone of the hippocampus, the number of pyramidal neurons per millimeter decreased by 32.0% in aged (mean age: 25.0 months) WKY and by 34.1% in aged (mean age: 23.0 months) SHR as compared with their corresponding values at 3 months of age. These results indicate that the numerical density of neurons in the neocortex and archicortex decreases by nearly onethird between 3 and 23–25 months of age in both normotensive and hypertensive strains of rats. Chronic hypertension does not significantly alter the apparent loss of neurons from the cerebral cortex and hippocampus with advancing age.