[Ultrastructural study of the neurons of the spinal ganglia during aging in the rat].

The chronology of the alterations impairing the cytology of the spinal ganglion neurons was analysed in 3- to 32-month-old male rats. A type neurons are impaired earlier and more severely than B neurons. Ageing alterations occur during two successive periods. During the first period, beginning at about 3 months, lipofuscin pigments gradually accumulate in the neurons. During the second period, beginning at about 24 months, various kinds of inclusions appear (granulofilamentous bodies, nematosomes,...); some of which could be originating from altered microtubules and/or filaments. At the same time, lipofuscin pigments are more heterogeneous. This period might be the onset of real senescence and of the gradual deterioration of the neuronal function.