Qualitative and Quantitative Observations in Y oung and Senile Rats

Summary. Ultrastructural changes including reduced electron density, reduction in polysemes and cisternae of rough endoplasmic reticulum occur in the cytoplasrn of endothelial cells and pericytes in the cerebellar cortex of senile virgin female Han: WIST -rats in cornparison to 3-month old virgin rats. Processes of pericytes cover less of the capillary surface in the cerebellar cortex of senile rats; rnoreover, arithmetic and harmonic mean thickness of the endothelium and relative volume of mitochondria . in endothelial cells and pericytes are reduced, w hereas the luminal diame­ ter of the capillaries, harrnonic and arithmetic mean thickness of peri­ cytes and their processes and of the basal Iaminae between endothelial cells and astrocytes (abbreviated BAL 1), pericytes and astrocytes (BAL 2) and endothelial cells and pericytes (BAL 3) increase. The in­ crease in harrnonic mean thickness of the basal laminae is statistically significant (o:<0.05) and compensates for a decrease in thickness of capillary endothelium. Consequently, the total barrier mass and thick­ ness of cerebellar cortical capillaries in senile animals is higher than in young individuals.