The changes of the peripheral nervous system caused by the aging are difficult to be studied in humans because of the difficulties in approaching the different parts of it in vivo.

For this reason experimental animals have been used in order to clarify the nature of changes in peripheral nervous system caused by aging. Most of the animals which have been used are rats of different ages and the results of different studies are reviewed in the present article.

Neurophysiological studies have shown age related reduction of conduction velocities of the peripheral nerves which varies in different nerves. Well protected nerves likes phrenic nerve, do not show any age related change of conduction velocities.

Pathological studies have shown that the most dramatic change is myelin distruption and formation of myelin bubbles with the resultant segmental demyelination and remyelination. The frequency and the size of myelin bubbles differ in different parts of the peripheral nervous system. Simultaneously loss of neurons is appeared which is different in various nerves and is more pronounced in the distal parts of them.

Electron microscopy studies have shown increased numbers of Hirano bodies and Reich granules in the Schwann cells cytoplasm. Neurons often contain inclusions mainly glycogen and Lafora bodies, the frequency of which is also different in various nerves.

The changes seen in axons and myelin with aging might be the result of alterations of both slow and fast axonal transport systems. The end plate shows signs of degeneration, an increase of synaptic delay and width of synaptic cleft. The muscles show reduction of fiber diameter, group atrophy and gradual replacement of the muscle with fatty tissue. Neuronal degeneration have been also described in central processes of dorsal root ganglion cells and posterior column fibers.

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Hellenic Archives of Pathology, 1994, 8(3): 133-139