Abstract
1. Excitability changes in ventral root fibers during the course of the VRP were examined with excised toad's spinal cord.
2. During the course of the VRP, an increase in the excitability was observed on the ventral root close to the cord. The time course of the excitability change was in accord with that of VRP recorded from the same spot.
3. Spatial spread of the hyperexcitability was examined along the ventral root. The largest increase in the excitability was found in close proximity to the cord, which declined exponentially as the test electrode was moved distally until it faded out somewhere about10mm apart from the cord. At a marginal region, distal from where any excitability change failed to appear, VRP was frequently recorded as a slight positive deflection. Even in this region an in creased excitability was observed. This kind of positivity in VRP was thus accounted for by the volume conductor effect of the ventral root.
4. The results were attributed to the catelectrotonic change in the root fibers which was responsible also for the potential changes in these fibers.
