CHEMICAL MECHANISM OF NERVE ACTIVITY 



By David Nachmansohn* 



Department oj Neurology, College of Physicians and Surgeons, Columbia Uni- 

 versity, New York, N. Y. 



INTRODUCTION 



The electrical signs of nervous action were, for a century, the only 

 manifestations studied by neurophysiologists. But the function of a 

 living cell cannot be conceived in purely physical terms. This was 

 clearly expressed by Gasser, when he compared the electric spikes to 

 the ticks of the clock, both being only signs of activity.^ For a thor- 

 ough understanding of the mechanism of nerve activity, a knowledge 

 of the chemical reactions involved is essential. Biophysics and bio- 

 chemistry are, consequently, of equal importance and inseparable in 

 any attempt to solve the problem. 



The special function of the nervous system is that of carrying mes- 

 sages from one distant point of the body to another. This process 

 may be subdivided into three successive phases: First, a stimulus 

 reaching a neuron has to initiate an impulse. Second, the impulse once 

 initiated has to be propagated along the axon. Finally, the impulse 

 arriving at the nerve ending has to be transmitted either to a second 

 neuron or to an effector cell. Early in this century, T. R. Elliot 

 had the idea that the third phase, namely, the transmission of 

 the nerve impulse from the nerve ending to the effector cell, may be 

 carried out by a chemical compound released from the nerve ending and 

 acting directly on the second unit. Elliot suggested that adrenaline 

 may be the transmitter of the impulse from the sympathetic nerve end- 

 ing to the effector cell.- He based this idea on the similarity between 

 the action of adrenaline and the effect of stimulation of sympathetic 

 nerves on the effector organ. Similar ideas were advanced subsequently 

 by Dixon and Howell. 



In 1921, Otto Loewi found that, following vagus stimulation of an 

 isolated frog's heart, a compound appeared in the perfusion fluid which, 

 when transmitted to a second heart, produced an effect similar to that 

 of vagus stimulation. Accepting the basic idea of Elliot, Otto Loewi 

 concluded that this compound, which was later identified with acetyl- 



* Most of the work described in this lecture has been supported by grants from the Josiah Macy, 

 Jr., Foundation and the Dazian Foundation for Medical Research. 



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