The Nobel Prize in Physiology or Medicine 1936.
"for their discoveries relating to chemical transmission of nerve impulses"
Sir Henry Hallett Dale (1875 - 1968) and Otto Loewi (1873 - 1961) won the Noble Prize in 1936 for discovering the role of chemicals, especially acetycholine, in transmitting nerve impulses.
Today we take it for granted that chemicals are involved at the synapses but in the beginning of the 20th century this wasn't obvious. The impact of this work is apparent from the Presentation Speech.
It was generally thought that impulses in the nerves act directly on the muscles or glands bringing about a change in their activity. But as early as 1904, Elliott presented a different interpretation. From the medulla of the adrenal glands, which, as embryonic development shows, is related with the sympathetic nervous system, a substance can be produced, i.e. adrenaline, the effect of which is remarkably similar to that produced by increased activity in the sympathetic system. Elliott therefore supposed that the impulses in the sympathetic nerves produced a release of adrenaline in the nerve endings which would then be the real vehicles of the stimulation effect. Ten years later, Dale published a comprehensive investigation of another substance, acetylcholine, for which he found a corresponding conformity with the effect of the parasympathetic stimulation. As, however, at that time acetylcholine had not been met with in the body, there was not sufficient basis for a discussion as to whether it normally transmitted impulses.
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[Photo Credits: Henry Hallett Dale: Jamd; Otto Loewi: ©Copyright Encyclopedia of Austria]