Relation of Chemically Induced Activity in Nerve to Changes in Demarcation Potential. ∗

Abstract

Repetitive activity often develops in mammalian nerves as a result of a localized injury (Adrian). 1 The phenomenon has been explained by assuming that circulating currents set up between the depolarized region of injury and the normal nerve result in periodic stimulation, at a frequency which depends on the rate of recovery of the normal nerve surface and the strength of the circulating currents. Recently, Fessard 2 has shown that repetitive activity can result when crystals of certain salts are applied to a nerve trunk, and that the region thus treated may be either positive or negative to the untreated parts. In recent work we have made an extended investigation of chemical activation of nerve, using isotonic solutions containing various effective salts applied to single active fibers dissected from the sciatic nerve of the frog. In these experiments the impulses were recorded at the treated region. This is an ideal preparation for studying the relation between chemically induced activity and changes in demarcation potential.

The present experiments were undertaken (1) to observe the impulse discharge and the change in demarcation potential by simultaneous measurement of the two through the same pair of matched electrodes, (2) to measure the effect of anions on the demarcation potential of a single fiber, since this has never been observed in studies on the sheathed frog nerve (Wilbrandt, 3 for discussion), and (3) to test our hypothesis that chemically induced activity results only during the period of active exchange of ions in a nerve, and that the degree of activity depends upon the rate of this exchange.