Rhythmic Activity of Single Nerve Fibers Induced by Low Calcium

Abstract

In the course of certain experiments on the chemical excitation of nerve we have observed the development of rhythmic volleys of impulses in the individual fibers which recur at regular intervals for long periods of time. Because of the possible relation of such a phenomenon to the mechanism of rhythmic activity of the nervous system in normal and pathological states we have studied this type of response in some detail.

All of the experiments have been performed on the sciatic nerve of the frog. In order to facilitate the penetration of the solution used for stimulation the sheath of the excised nerve was removed for a length of about one cm. and here the fibers were carefully separated so as to form a large number of small bundles. The region thus treated with the solution was usually at one end, but it was equally satisfactory to do so anywhere along the course of the nerve. A single fiber was then isolated at the other end of the nerve and placed on non-polarizable electrodes leading to an amplifier and oscillograph.

Partial removal of the ionized calcium in the nerve by sodium citrate or a reduction of its concentration by bathing the fiber bundles in calcium-free Ringer's fluid initiates a continuous train of impulses from the treated end at the rate of about 1001 per sec. When the nerve fiber has been brought into this condition which causes a sustained discharge of impulses we find that the substitution of normal Ringer's fluid for the citrate or the calcium-free solution ultimately transforms the discharge into a series of rhythmic volleys. The continuous discharge goes on for a time which is variable from preparation to preparation and then suddenly stops, followed after an interval of a few seconds by a burst of impulses.