Radiculoneuropathy of ageing rats: a quantitative study

: A quantitative and morphometric study has been done on the effects of age on myelinated nerve fibres of the sciatic nerve of rats ranging from 100 to 824 days of age. Using 1.0 micron semi-thin sections and a particle size analyser (TGA 10, Zeiss) it was found that both myelin sheaths and their associated axons grew in diameter until about 400 days of age, but massive destruction and disappearance of myelinated nerve fibres became manifest only after 700 days of age. In addition, onset, development and distribution of degenerative changes of nerve fibres were studied in spinal roots, lumbar plexus and sciatic nerves. Analysis of the observed data suggests that two independent mechanisms are involved in the degenerative changes of myelinated peripheral nerve fibres with age: one is axonal atrophy or loss and the other is vacuole forming, segmental demyelination and remyelination. The former begins very early in a limited number of nerve fibres and in more distal parts of the nerve, while the latter begins at a significantly later age and from the most proximal (spinal root) region.