1936 - Sir Henry Hallett Dale & Otto Loewi

Is the transmission of nerve impulses mediated by chemical substances, and if yes - which chemicals? It was generally thought that impulses in the nerves act directly on muscles or glands. In a very simple but ingenious experiment Loewi proved that certain substances can lead to nerve stimulation. Electrically stimulating an isolated frog heart placed in nutrient fluid, he altered heart beats. Transferring the fluid which was pumped in and out of the heart into another similarly prepared heart, he found that the fluid itself can produce changes in the heart activity. While the substance of acetylcholine was not yet recognized in the body, Dale found that it leads to effects corresponding to those done by parasympathetic stimulation. Later, using very sensitive methods, he proved that acetylcholine produces muscular contractions by the motor nerves, and that infinitely small quantities of acetylcholine are needed to cause such muscle contractions. These observations are fundamental for our interpretation of the physiological processes of the nervous system.