CHEMICAL MECHANISM OF NERVE ACTIVITY

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.l For a thorough understanding of the mechanism of nerve activity, a knowledge of the chemical reactions involved is essential. Biophysics and biochemistry 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 messages 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 ending to the effector 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 Maey, Jr., Foundation and the Dazian Foundation for Medical Research.