[Ultrastructural studies on the lipofuscin in the cerebral cortex of aged men and rats].

The ultrastructural features of lipofuscins in the cerebral cortex in both aged men and rats were observed with an electron microscope and the author discussed the significance of morphological differences of the lipofuscins in both specimens. The lipofuscins observed in aged men consist of an electron dense structure with or without vacuoles, and each of the lipofuscin is enveloped by a single unit membrane. The inside of the vacuole is homogeneous and structureless. The electron dense area of the lipofuscin shows fine granular structures with various degrees of electron density. The lipofuscin observed in aged rats (730 days) shows roughly the same appearance essentially as those in aged men, but reveals more complex internal structure. Therefore, the lipofuscins in aged rats can be classified into four types as follows: Type 1: finely granular type consisting of fine granules of almost uniform size. Type 2: coarsely granular type consisting of both fine granules and coarse granules; each of the coarse granules is 200 to 600 A in diameter. Type 3: lamellated type consisting of both fine granules and lamellae; the lamellae are 130 A in width with a repeated pattern of five bands. Type 4: mixed type consisting of fine granules, coarse granules and lamellae. In addition, it was observed that lipofuscins rarely existed in both 12-day and 25-day rats, but that the all four types of lipofuscins existed in 85-day rats. The cause of the morphological difference between lipofuscins in aged men and aged rats is still unknown. However, it has been reported that the rats and degree of autophagocytosis differs between different species of animals, even in same cell types, the author therefore considered that such a difference in intracellular metabolic processes could be one of the factors causing the morphological difference of lipofuscins in old men and old rats.