Morphological and biochemical changes in peripheral nerves with aging.

The ulnar nerve taken at autopsy from 30 subjects aged 24-98 who died without features of clinical involvement of peripheral nerves was examined morphologically. Density of myelinated fibers (m.f) per 0.1 mm2, frequency distribution of the external diameter of m.f., and teased fiber were estimated. Besides, in 8 nerves some lipids were assessed biochemically. The study showed that the percentage of fibers with morphological changes increases with aging (7-10% in adults and even up to 35% in aged subjects). In older subjects loss of m.f. may be marked. Morphological changes in the nerves of subjects in all groups of age are unspecific (axonal degeneration, and segmental demyelination). Striking feature for the nerve is the preserved ability to repair damage of the fiber independently of the subjects' age. Accidental factors play some role as a cause of morphological changes in the nerve in all groups of age but in the elderly, aging of the neuron seems to be an important factor. Biochemical changes in the nerves with age are not prominent, and much less expressed than morphological changes.