A STUDY OF NERVE DEGENERATION AND REGENERATION

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Abstract
For the most part, the prepn. used has been the phrenic nerve of the dog with two of its roots of origin. One of the roots is crushed; the fibers of the other, remaining intact, serve as the control. Movable stimulating electrodes are applied to the nerve proper and fixed leads are taken from each of the roots separately. The results so obtained are expressed as ratios, degenerated (or regenerated) over normal X 100. Degeneration is complete in 4 days over lengths that have exceeded 200 mm. At 3 days the changes in action potential areas are such as to indicate that 30-40 mm. from the lesion only about 1/4th of the degenerating fibers still conduct to the central lead; and there is a further decrease in action potential area as the distance of conduction increases, but excitability and conduction rate in the fastest fibers still are normal, at least in the more central regions. The results are compatible with abrupt failure of conduction at random loci increasing in frequency peripheralwards, or possibly with failure proceeding centripetally. The histological evidence is reviewed that would account for the premised type of failure. At 3 days the only change in the response of degenerating fibers to high rates of stimulation is such as to indicate some prolongation of the relatively refractory period. In regenerating nerves the excitability at about 30 days delcines with the distance from a value of 5 to about 1, the normal being 100 + ; it becomes approximately uniform the length of the nerve at about 130 days, but continues to increase through about 343 days, when it attains a value of about 45. Conduction velocity at 31 days falls off markedly with the distance; it becomes linear after about 190 days; but at 343 days it has attained only 60% of the normal. The results indicate that conduction rate and excitability may never return to normal. Area ratios indicate that by 50 days less than half of the central fibers have grown out to reach the peripheral end of the prepn. and that the number is approaching 100% after about 100 days.

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