Neuronal regression during ageing: an ultrastructural study of the human cortex.

Neuronal regression has been ultrastructurally investigated in a neuronal sampling of the ageing human cerebral cortex. Even though the number of specimens examined is limited, there is an indication of an age-related regression involving the intraneuronal "nucleus-ribosome system". Such regressive signs are characterized by the polymorphous outline, invagination, reduced size of the nucleus, and in the nucleolar texture. Recognizable changes in the cytoplasm are, alterations in the density and distribution of free ribosomes and in the structure and organization of the rough endoplasmic reticulum cisternae. Furthermore light cytoplasmic areas, and increased number of microtubules and the gradual congestion of the perikaryon by age pigments are reliable criteria for identifying the sequence of morphologic events that occur during neuronal ageing. The above data provide some insight into the neuronal process and adding to a previous proposed model of neuronal maturation.