Action of Veratrine on Medullated Nerve

Abstract

Fromherz 1 has recently investigated the effect of veratrine and other drugs upon the electrical response of medullated nerve, using a moving coil galvanometer as a measuring instrument. He detects little difference in response between normal and veratrinized nerve, if the nerve is suspended in oxygen throughout. If, however, veratrinized nerve be asphyxiated and allowed to recover in oxygen, he finds that the after-potential after a single shock or short tetanus may last as long as 10 minutes. We have reinvestigated the action of veratrine on the sciatic nerve of R. pipiens with the cathode ray oscillograph, and find that if the concentration is suitably adjusted to the temperature, typical veratrine after-potentials as measured out to one-half second can be obtained whether the nerve is in air or in oxygen. The results of Graham and Gasser 2 are therefore not due to partially asphyxial conditions, as suggested by Fromherz 1 and Hill. 5

In order to study the after-potential throughout its course we have modified the usual oscillographic technique by employing a voltage amplifier of the direct-coupled type, especially designed to avoid amplifier drift (the theory of this amplifier has been published by Schmitt 3 and the details of the circuit as modified for electrophysiological use will be published elsewhere). By this method the resting potential is followed continuously so that due allowance for drift in resting potential can be made in estimating the duration of the after-potential. After a shock the potential changes can be followed for the first 3-4 seconds by photographing a slow sweep of the oscillograph beam; thereafter the potential may be measured every few seconds for as long as desired by reading the balancing potentiometer, using the oscillograph at high amplification as a null instrument. Preliminary experiments have revealed after-potentials lasting as long as 6 minutes after a single stimulation of veratrinized nerve in oxygen after previous asphyxiation. Without asphyxiation the potential seldom lasts longer than 10-30 seconds.