MITOCHONDRIAL ACCUMULATION OF Sr²⁺ SUPPORTED BY PYRUVATE IN THE CEREBELLAR CORTEX OF THE RAT. CELLULAR VARIATIONS DURING AGING

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The mitochondrial metabolism of pyruvate has been studied in the cerebellar cortex at an ultrastructural level in rats 3 to 36 months old using the technique of the accumulation of Sr²⁺ (15, 17). Shape, size and number of the reaction products were the basis to distinguish the types of mitochondria related to the distinct activity levels of the enzyme pyruvate dehydrogenase. Important differences were detected between: 1) different types of neuronal and glial cells; 2) different neuronal parts (soma, dendrites and axons); and 3) neurons and filial cells of young (3 to 6 months old) and senile animals (24 to 36 months old). Animals 3 to 18 months old presented a constant activity pattern for each cell type and for the different cytoplasmatic regions studied. Purkinje cells, in animals of this age group, are the most active and display a high intensity in their soma with a progressive diminution towards the endings of the dendrites. Granule cells present an intermediate intensity in soma and dendrites. Remaining neurons exhibit low somatic intensities. Axons of short axon cells were usually negative, but afferent fibers were positive. Mossy fibers display various types of reaction products.
Animals 24 to 36 months old maintain this reaction pattern, but the mitochondrial reaction pattern, but the mitochondrial reaction is heterogenous. Purkinje and granule cells exhibit the greatest amount of diminution. Some cells and cellular regions (granule dendrites and astrocytes) may show a stronger reaction than in young animals. Results are related to the pre-or post-synaptic location of the reaction product, mitochondrial and cellular involution, and reactive and plastic phenomena of aging.