Like cracking the genetic code, like the creation of the atomic bomb, the discovery of how the brain’s system of neurons communicates is one of the fundamental science developments of the twentieth century.
Nerves signal sensations to the brain; the brain flashes back commands to muscles and organs through nerves. But how? Otto Loewi’s discovery of neurotransmitters (the chemicals that make this communication possible) revolutionized the way scientists think about the brain and even what it means to be human. Neurotransmitters control memory, learning, thinking, behavior, sleep, movement, and all sensory functions. This discovery was one of the keys to understanding brain function and brain organization.
In 1888 German anatomist Heinrich Walder-Hartz was the first to propose that the nervous system was a separate network of cells. He named these nerve fibers neurons. He concluded that the ends of individual nerve cells approached each other closely, but didn’t actually touch. In 1893 Italian scientist Camillo Colgi used a new method for staining cells that brought out exceptionally fine detail under a microscope and proved that Walder-Hartz was correct.
Walder-Hartz’s discovery, however, created a scientific controversy. If neurons didn’t actually touch, how did they communicate? Some scientists argued that signals had to be sent electrically, since electrical currents existed in the brain. Some argued that nerve signals had to be sent chemically since there were no solid electrical connections between individual neurons. Neither side could prove its position.
Otto Loewi was born in Frankfurt, Germany, in 1873. He wanted to become an art historian but buckled under family pressure and agreed to attend medical school. After barely passing his medical examination, Loewi worked in the City Hospital in Frankfurt. However, he became depressed by the countless deaths and great suffering of tuberculosis and pneumonia patients left to die in crowded hospital wards because there was no therapy for them.
Loewi quit medical practice and turned to pharmacological research (the study of drugs and their effects on human organs). Over the next 25 years (1895 to 1920) he studied how different human organs responded to electrical and chemical stimuli. His papers reported on many human organs including the kidney, pancreas, liver, and brain.
By 1920 Loewi was focusing much of his attention on nerves. He was convinced that chemicals carried signals from one nerve fiber to the next. But, like other researchers, he couldn’t prove it.
Loewi later said that the answer came to him in a dream. It was the night before Easter Sunday, 1921. Loewi woke up with a start around midnight and scribbled notes about the dream’s idea. The next morning he was unable to read his scrawled notes. Nor could he remember what the dream had been about. All he could remember was that the notes and the dream were critical.
The next night he awoke at 3:00 A.M. from the same dream, remembering it clearly. He didn’t dare go back to sleep. He rose and drove to his lab, where he performed the simple experiment from his dream, an experiment that has become famous.
Loewi surgically removed the still-beating hearts from two frogs and placed each in its own container of saline (salt) solution. He left the autonomic nerve (the Vagus nerve) attached to heart number one, but not to the second heart. When he applied a tiny electrical current to heart number 1’s Vagus nerve, the heart slowed down. When he then allowed some saline solution from container 1 to flow into container 2, the second heart slowed down to match the slower rate of the first heart.
Electricity could not have affected the second heart. It had to be some chemical released into the saline solution by heart 1’s Vagus nerve that then communicated with and controlled heart 2. Loewi had proved that nerve cells communicate with chemicals. Loewi called this chemical vagusstoff.
A friend of Loewi’s, Englishman Henry Dale, was the first to isolate and decode this chemical’s structure, which we now call acetylcholine. Dale coined the name neurotransmitters for this group of chemicals that nerves use for communication.
The longest nerve cell in your body, the sciatic nerve, runs from your lower spine to your foot, roughly two to three feet in length.