Heterogeneity and death of Purkinje cells of rat neocerebellum (Crus I and Crus II): hypothetic mechanisms based on qualitative and quantitative microscopical data.

: The morphological changes that take place with ageing in the soma of what we call clear Purkinje cells (CP cells) are examined by light and electron microscopy. Besides the very obvious lipofuscin accumulation, another kind of space consuming structures become greater in number and complexity, i.e., the occurrence of very pleomorphic degenerating focal zones. Apart from CP cells, dark Purkinje cells (DP cells) indeed appear in increasing numbers with ageing; one subtype (DP-1 cells) has medium dark density revealing dumbbell-shaped mitochondria, ring-shaped Golgi apparatus and lamellated bodies; the other subtype (DP-2 cells) has very dark density presenting pycnotic nuclei with complete nucleolar regression and degenerating mitochondria, but with well developed Nissl bodies and Golgi apparatus. The possibility of DP cells not being technical artifacts is discussed. Quantitative studies are also carried out in Purkinje cell somata: mean volume, surface-to-volume ratio, absolute volume occupied with lipofuscin dense bodies as well as the linear density (number per mm) and percentage of CP and DP cells out of the total population of Purkinje cells. Statistically significant linear trends with age are found for absolute volume of lipofuscin in CP cells and for the linear densities and percentages of either CP or DP cells. The concatenation of qualitative and quantitative data suggests that Purkinje cells of Crus I and Crus II undergo an age-related fall-out. Some clear Purkinje cells may become DP-1 cells and others DP-2 cells. The former reveal signs of slow cellular damage; the latter are suggestively very damaged or even dead cells probably on account of having exceeded the critical threshold of the surface-to-volume ratio leading to asphyxia; indeed, their stout structure does not match slow damage.