Gross-Excitation Between Mammalian Medullated Nerve Fibers After Treatment with Veratrine

Abstract

Dun and Feng 1 have demonstrated with amphibian preparations that contrary to general belief nerve fibers, but more particularly motor nerve endings after treatment with veratrine, give prolonged repetitive discharges to a single stimulus. We have extended their work and found that mammalian motor nerve endings after vera-trinization likewise show prolonged repetitive discharges which can be readily recorded from the ventral root. We have furthermore ascertained that in a cat which has received an intravenous injection of a suitable amount of veratrine, such as 2 cc of 0.1% solution, the nerve fibers in the nerve trunk can also show prolonged repetitive firing. In the course of our work we had occasion to make various control tests, some of which dealt with possibilities which at first seemed very remote. One of the tests consisted of stimulating one ventral root bundle and leading off from another ventral root bundle of the same segment and side, both bundles being sectioned centrally at their exit from the cord. In a normal cat, in view of Blair and Erlanger's work, 2 one would naturally expect to lead off nothing but stimulus artifact in this way; but in a veratrinized animal one could not be so sure. In fact we have found that in a veratrinized cat in which the motor nerve endings and the nerve fibers in the sciatic nerve trunk were giving prolonged abundant after-discharges, some discharges could generally be led off from one ventral root when another ventral root was stimulated with a single shock. Such discharges have characteristic long and rather irregular delays in their onset; their shortest latency being about 4 msec and the longest exceeding 30 msec. This long latency, in addition to other reasons, excludes the possibility that the discharges might be due to the escape of the stimulating current from one root to the other; and there is left only one reasonable interpretation that they result from cross-excitation between nerve fibers.