Changes in the compound action current amplitudes in relation to the conduction velocity and functional recovery in the reconstructed peripheral nerve

The average axon diameter in the proximal segment of a transected and recon structed peripheral nerve will decrease shortly after the transection and i ncrease again when the regenerating axons make contact with their targets. The magnetically recorded nerve compound action current (NCAC) amplitude an d the conduction velocity (CV) are directly related to the axon diameters. in this experiment, the peroneal nerve was unilaterally transected and reco nstructed in 42 rabbits. After 3, 4.5, 6, 8, 12, 20, and 36 weeks of regene ration time, hind leg motor function recovery, NCAC amplitude, and CV1st pe ak were studied. Our results demonstrate a significant decrease in signal a mplitude 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 amplitu des do not. Based on the correlation of the CV and signal amplitude with ax on diameter, they would both be expected to increase with recovering functi on. As an explanation for this lack of increase of signal amplitude, we sug gest that, at the same time as some axons reach their target organs and sta rt 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 decre ase in compound signal amplitude, which cancels out the expected increase i n NCAC amplitude, due to axonal maturation. (C) 1999 John Wiley & Sons, Inc .