Age Changes in Cerebellar Oligodendrocytes: The Appearance of Nuclear Filaments and Increase in the Volume Density of the Nucleus and in the Number of Dark Cell Forms

A qualitative and quantitative ultrastructural study (volume density of the nucleus and cell countings) on age-related changes occurring in neocerebellar oligodendrocytes of the granular layer was carried out in female albino rats aged 2-24 months. Taking into account the cytological features, two types of oligodendrocytes could be discerned, designated as Type I and Type II. Observations showed that, from 18 months onwards, the appearance of bundles of nuclear filaments running throughout the euchromatin areas are common occurrence in Type II oligodendrocytes. The lowest and highest mean volume density of the nucleus is achieved, respectively, at 2 months (50.67%) and at 21 months (64.93%); the analysis of variance of the parameter with ageing displays a most statistically significant result. There is also a positive and linear correlation between the volume density and age. The percentage of Type I oligodendrocytes (out of the total of counted oligodendrocytes) predominates from 2 to 15 months; after being even at 18 months, the percentage of Type II oligodendrocytes preponderates at 21 and 24 months. Although oligodendrocytes are capable of undergoing mitosis, it is concluded that they are prone to morphological changes with ageing, a warning that the physiology of oligodendrocytes may be eventually affected.