Ultrastructure of osmiophilic bodies identified as lipofuscin granules occurring at extraneuronal sites in the brain tissue of both young and old monkeys was studied. The present work revealed that lipofuscin granules were detected normally in the neuroglia cells, phagocytic cells and pericytes surrounding the blood capillaries, as well as in the capillary endothelium. However, their presence in these sites was more marked in young animals. The findings presented in this report are strongly suggestive of the normal removal of lipofuscin from the nerve cells to the capillary endothelium, and suggest further that the phagocytic cells as well as the glia cells participate in this removal mechanism. Being a more active process during youth, few lipofuscin granules are present in neurones from young animals. Failure of the removal mechanism due to diminished activity of the participating cells with ageing, is probably the cause of lipofuscin accumulation in senescent neurones.
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