Electrophysiological evidence for an increase in the number of ventral root afferent fibers after neonatal peripheral neurectomy in the rat.

Our recent study has shown that many afferent fibers in the ventral root are third branches of dorsal root ganglion cells in addition to their processes in the peripheral nerve and the dorsal root. From results of this study, we hypothesized that most of the afferent fibers in the normal ventral root are extra processes of certain dorsal root ganglion cells. To accommodate experimental findings by others, we formulated several working hypotheses in the present study as an extension of our previous hypothesis: these afferent processes in the ventral root are of varying length; they end bluntly along the length of the root; and in an event such as peripheral neurectomy in the neonatal stage, these fibers sprout at the blunt endings along the length of the ventral root. We tested the above hypotheses using electrophysiological methods. The sciatic nerve on one side in neonatal rats was cut. After the rat was fully grown, volleys of neural activity were recorded along the length of the ventral root while stimulating the dorsal root of the same segment. There was a great increase in the size of compound action potentials in the ventral root on the sciatic nerve-lesioned side. Various lines of evidence suggest that this enhancement of the evoked potentials is likely to be due to an increase in the number of afferent fibers in the ventral root in response to neonatal peripheral nerve injury. The results are consistent with our hypotheses.