The significance of action potentials in the isolated nerve cord of the earthworm (Lumbricus terrestris)

Abstract

There are two questions considered in tlie present study of the spontaneous potentials of the nerve cord of the earthworm. The first is the one raised by Gray and Lissman ('38), as to whether the potentials of the isolated cord have functional rneaning. They have found in the leech that there is good correlation between the muscular movements of swimming and the appearance of potentials in the cord, but were unable to observe a similar relation in the earthworm and state: "The present observations seem to give very little positive support to the view that a true ambulatory rhythm can be displayed by a nerve cord after complete isolation from all peripheral connections. " The second problcrn is whether inorganic cations and certain organic substances are able to affect the spontaneous rhythms of the isolated cord.The following experiments were undertaken in the expectation that they would furnish evidence on both questions. At the outset it seemed possible by the method of chemical stimulation to attack the general problem of whether the potentials of the isolated cord of the eartliworui have functional meaning. Potentials were recorded by means of a tu7ochannel cathode ray oscillograph. One channel provided records of nerve activity, the other was so connected as to give time marks at onefifth second intervals. The nerve cord was laid across three silver wire electrodes spaced approximately 0.5 em. apart in an electrically shielded moist chamber. One outside electrode was grounded, the other two serving as active leads from the cord. The two active leads were connected to a wide-range, highgain, push-pull amplifier, condenser coupled. Slight low-f requency and high-frequency attenuation were used to limit longtime drifts and unbalance of the amplifier on the one hand, and tube and resistor noises on the other hand. Under these conditions the amplifier was flat within one-half decibel from 60 cycles to lOOQ 1 Aided by a grant of the Resrarch Council of the Oregon State System of Higher Education. 1s1