A correlative study of internode proportions and sensitivity to procaine in regenerated frog sciatic nerves

A comparison of regenerated and normal frog sciatic nerves showed a marked reduction in conduction velocity from 37.5 to 15.2 m/s with little change in the absolute refractory period. Changes in conduction velocity corresponded to a reduced mean axon caliber (4.8 versus 6.6 micron). Regenerated nerves also had markedly foreshortened internodes (mean of 309 versus 1236) micron) and thinner sheaths than controls. The geometric proportions of internode length/fiber caliber (l/d) was reduced to approximately one-third of normal. Regenerated nerves were more easily blocked by exposure to 3 mmol/liter procaine than controls, showing greater increase in the absolute refractory, or decreases, respectively, in the peak of the alpha-wave and the area of the compound action potential; the effect of procaine on conduction velocity was less marked. Exposure of various lengths of nerves in chambers of 1, 3, or 20 mm length revealed greater differences for the shorter chambers. The data indicated that some effects could be attributed to the foreshortening of the regenerated internodes. The main difference between normal and regenerated nerves, however, had to be attributed to changes in the nodal membrane characteristics of the latter.