Wallerian Degeneration in the Rat the Effect of Age on the Concentration of Nucleic Acid and Phospholipid in Intact and Sectioned Nerves

If a peripheral nerve is cut, that portion of the nerve distal to the point of section undergoes a series of changes characteristic of Wallerian degeneration. Logan, Mannell & Rossiter (1952 a) showed that in the peripheral segment of the sciatic nerve of the cat degenerating after nerve section there is an increase in the concentration of nucleic acid. This change, which is probably related to the cellular proliferation that accompanies Wallerian degeneration, involves both pentosenucleic acid (PNA) and deoxypentosenucleic acid (DNA), although the increase in the two nucleic acids is disproportionate, resulting in an increase in the PNA/DNA ratio. Johnson, McNabb & Rossiter (1949 a) and Brante (1949) showed that there is also a later decrease in the concentration of myelin lipid, related to the destruction of the myelin sheath. Mannell (1952) reported similar changes for the sciatic nerve of the rat, although in this species all the processes are considerably speeded up in time. By observing changes in the concentration of nucleic acid and phospholipid, the study of Wallerian degeneration may be placed upon a quantitative basis. Changes in the concentration of nucleic acid give an indication of the number of cells throughout the length of a given portion of nerve. Such a determination is less time-consuming than the method of nuclear counting devised by Abercombie (1946), a method that* gives the density of cell nuclei at one or more selected levels in the nerve. Changes in the concentration of phospholipid give an indication of the amount of myelin material present in the nerve, an estimate difficult to obtain by microscopic examination, for in degenerating nerve the configuration and staining properties of the myelin are quite variable. In none of the studies mentioned above, with the exception of that of Mannell (1952), was the age of the animals controlled. Preliminary experiments by Mannell & Rossiter (1952) with two groups of rats of different ages suggested that the chemical composition of the sciatic nerve was dependent upon the age of the animal. Not only were the concentrations of nucleic acid and phospholipid greater in nerves of younger animals, but the rates at which the concentration of nucleic acid increased and the concentration of phospholipid decreased after nerve section were also much greater. That Wallerian degeneration takes place more rapidly in younger animals is stated frequently in the older writings on nerve degeneration (Ramon y Cajal, 1928, for references), but …