The average axon diameter in the proximal segment of a transected and reconstructed peripheral nerve will decrease shortly after the transection and increase again when the regenerating axons make contact with their targets. The magnetically recorded nerve compound action current (NCAC) amplitude and the conduction velocity (CV) are directly related to the axon diameters. In this experiment, the peroneal nerve was unilaterally transected and reconstructed in 42 rabbits. After 3, 4.5, 6, 8, 12, 20, and 36 weeks of regeneration time, hind leg motor function recovery, NCAC amplitude, and CV(1st peak) were studied. Our results demonstrate a significant decrease in signal amplitude and CV in the first 8 weeks after reconstruction. These decreases are related (P < 0.05). After 8 weeks of regeneration time, motor function and the CV of the recorded signals start to recover, but the signal amplitudes do not. Based on the correlation of the CV and signal amplitude with axon diameter, they would both be expected to increase with recovering function. As an explanation for this lack of increase of signal amplitude, we suggest that, at the same time as some axons reach their target organs and start to mature, a number of the axons which have not reached a proper target organ will lose their signal-conducting capability. This will cause a decrease in compound signal amplitude, which cancels out the expected increase in NCAC amplitude, due to axonal maturation.
Copyright 1999 John Wiley & Sons, Inc.