The War of the Soups and the Sparks: The Discovery of Neurotransmitters and the Dispute Over How Nerves Communicate

World War I began only a few months after Henry Dale had left the Wellcome Laboratories to start working at the Institute for Medical Research. As did most of the leading British scientists, he spent much of the next four years working on war-related problems. When the war ended, Dale was increasingly burdened with administrative responsibilities and committees like the one he headed for the League of Nations on drug standardization. He was, however, able to continue his research on histamine and to make important contributions to our knowledge of this substance.

As noted in chapter 4, Dale and his colleagues had described the capacity of the substance later identified as histamine to produce a profound vasodilation and lowering of blood pressure. Histamine was not, however, clearly known to be present as a natural substance in the body of animals. There had been some earlier reports of finding a suspected histamine-like substance in the body, but it was generally thought to have been there as a result of some bacterial contamination. In 1927 Dale and his colleagues isolated a substance from fresh samples of the liver and lungs of animals that produced a profound and immediate vasodilation.² The same year others clearly established that this substance was histamine. It had previously been called the “H-substance” because it produced effects similar to histamine, but it was not clear if the two substances were identical. Dale summarized much of this work in the three Croonian lectures he delivered in 1929.³ Finding that histamine was a natural substance in the body may well have stimulated Dale to start thinking about whether acetylcholine was also a natural substance in animals.

Following his major paper on acetylcholine published in 1914, Dale did not do any research on that substance for fifteen years. Although he certainly was aware of Loewi’s series of publications on neurohumoral transmission through much of the 1920s, it was not until 1929 that Dale’s interest in acetylcholine was reawakened. He subsequently made clear that it was Loewi’s research on neurohumoral transmission that: “had given such ideas for the first time an experimental reality…. And thus it was not until 1929, after an interval of some fifteen years, but then in a new atmosphere of generally awakened interest in its possible significance that my direct participation in experiments with acetylcholine was awakened.”⁴

In 1929 Dale wrote to a friend: “I am more and more convinced that the thing [acetylcholine] is there to be found, if only we can overcome the technical difficulties.”⁵ That same year Dale and Harold Dudley found acetylcholine and also histamine in the spleen of the ox and the horse, and later in human placenta.⁶ How they were able to do this has been described by the neuroscience historian Stanley Finger:

Dale and Dudley had picked the spleen to study because they had previously found that an unidentified substance extracted from this organ produced effects similar to acetylcholine. In their article, they pointed out that prior to this work, acetylcholine had been considered “only as a synthetic curiosity, or as an occasional constituent of certain plant extracts. It appears to us that the case for acetylcholine as a physiological agent is now materially strengthened by the fact that we have now been able to isolate it from an animal organ and thus to show that it is a natural constituent of the body.”⁸

Dale and Dudley reviewed all the similar effects produced by acetylcholine and parasympathetic stimulation. Even though they had not found acetylcholine in nerves, they wrote cautiously that finding it to be a natural constituent of the body increased the possibility that a “substance indistinguishable from acetylcholine by its action” has a “physiological role” to play.

By 1930 Loewi’s conclusion that the vagus nerve secretes acetylcholine when innervating the heart had started to gain acceptance. However, evidence that acetylcholine is secreted at other sites had not yet been demonstrated. This started to change as a result of research by several investigators. In 1931, for example, Erich Engelhart, working in Loewi’s laboratory, reported finding acetylcholine in the aqueous humor of the eye after stimulating the oculomotor nerve. The aqueous humor was later shown to be capable of evoking a vagus-like slowing of a tortoise’s heart.⁹ The next year, Canadian investigators reported that when they stimulated the chorda tympani nerve on one side of the body of a cat, causing the salivary gland on that side to secrete saliva, the salivary gland on the opposite side also secreted saliva after a delay even though it was denervated.¹⁰ It was presumed that the delay was necessary to allow diffusion of the released acetylcholine from one side to the other through capillaries. Similar reports from others began to provide evidence that not only is acetylcholine secreted by the vagus nerve, but it might be more generally involved in mediating responses evoked by other parasympathetic nerves.

In 1930 Dale and John Gaddum began to investigate whether chemical mediation is involved in activating skeletal muscles. Exploring a phenomenon studied earlier by Charles Sherrington and others before him, they confirmed that a denervated skeletal muscle contracted if a nearby parasympathetic nerve, not connected to the muscle, was stimulated.¹¹ Dale and Gaddum hypothesized that the denervated muscle might become more sensitive to acetylcholine and that therefore a small amount released by stimulating a parasympathetic nerve could reach the muscle through the blood and cause it to contract. They demonstrated that a skeletal muscle contracted when even a small amount of acetylcholine is injected into its vascular system.¹² Although this demonstrated that skeletal muscles can respond to circulating acetylcholine, it did not prove that these muscles are normally stimulated that way or that the nerves secrete acetylcholine.

Several prominent neurophysiologists criticized Dale and Gaddum’s suggestion that skeletal muscles normally contract in response to “the peripheral liberation of acetylcholine” by spinal nerves.¹³ They argued that it had not been proven that spinal nerves actually secrete acetylcholine, and they pointed out that acetylcholine might come from some other organ, as it had recently been found in organs as diverse as the placenta and the cornea as well as the spleen. Some neurophysiologists were willing to concede that acetylcholine might play an ancillary role in the response of skeletal muscles, but they insisted that the normal mode of innervation was electrical.

What was needed to bolster the argument was a method for detecting the small amounts of acetylcholine that were presumed to be secreted at nerve terminals. Neither Dale nor Loewi had developed such a technique. However, the leech muscle preparation developed by Bruno Minz in Wilhelm Feldberg’s laboratory in Berlin proved to be just the method needed at this time. Minz had first described the technique in 1932, and Feldberg subsequently used the method in several studies that demonstrated that acetylcholine was secreted by the vagus and other nerves in mammals.¹⁴ Several of these experiments were done in collaboration with Otto Krayer, who later became head of pharmacology at Harvard.¹⁵ Krayer had developed a good technique for drawing venous blood, and Feldberg had the leech muscle preparation. Together they demonstrated that after the nerve was stimulated the blood drawn from the vein surrounding that nerve terminal contained acetylcholine. It was this technique that Feldberg brought to Dale’s laboratory in 1933, and during the next three years it played a major role in proving that acetylcholine is secreted at many different peripheral synapses. The political events that were responsible for Feldberg leaving Germany and working in Dale’s laboratory are an important part of this history.

Wilhelm Feldberg (1900–1993) was born in Hamburg into a Jewish family. His father and uncle had gone into business selling women’s clothing, and they expanded this into a highly successful department store. This financial success made it possible for the family to indulge their interest in the arts, and Feldberg’s sister later became a successful artist. Because of the family’s wealth, Feldberg was later able to select positions based solely on his interest, regardless of whether any salary was included. Although he did keep abreast of the family business, it was an older brother who took it over while he studied medicine in Heidelberg and Munich, and completed the medical degree at the University of Berlin.

Feldberg received his medical degree in 1925, but, like both Dale and Loewi, he preferred research to practicing medicine, and he joined the laboratory of Professor E. Schilf at the University of Berlin. That same year he married Katherine Scheffler, the daughter of Karl Scheffler, a noted art historian. Katherine had studied literature and anthropology and worked as a translator, but she also showed a lively interest in her husband’s research and career, an interest that was responsible for Feldberg first meeting Dale.

Feldberg met Dale only a few months after he and Katherine were married. Feldberg’s family was close-knit, and it was expected that he would spend much of every weekend with them. However, Katherine recognized that this was interfering with her husband’s work. Together, they decided that the least offensive way to terminate the family weekend visits was to get away for awhile. Feldberg’s mentor, Schilf, had previously translated Langley’s book The Autonomic Nervous System into German and was able to arrange for Feldberg to spend 1925 in Langley’s laboratory in Cambridge.

Feldberg had been in Cambridge for only six months when Langley died unexpectedly. Dale then invited him to spend the remaining time in his laboratory in London. Feldberg later described how both Langley and then Dale urged him to take great care before publishing any experimental results. Langley’s advice was to repeat experiments many times: “if you obtain a result in five consecutive experiments, but not on the sixth, you must do another twelve experiments.” Dale’s advice was to concentrate on perfecting the experimental methodology: “Feldberg, you must work like an astronomer. Prepare for weeks, for months, if necessary for years, until your method is working to perfection, then do one experiment, perhaps two—and publish the results.”¹⁶

Not only did Feldberg profit from the time he spent with English physiologists and pharmacologists, but the period away was successful in enabling him to discontinue the “required” weekend family visits and to spend the time instead doing research. Feldberg studied the action of histamine, and in 1930 he coauthored with Schilf a 600-page book on the pharmacology and physiology of histamine. The book was dedicated to “H. H. Dale, In Dankbarkeit und Verehring” (In gratitude and admiration).¹⁷

In 1932 Dale and Feldberg met again in Germany. The occasion was a meeting of the German Pharmacological Society in Wiesbaden. The meeting was followed by the Internisten Kongress, where Dale was the invited lecturer. Dale attended both, and Feldberg later described their meeting:

Dale was anxious to hear more about the leech technique, and he arranged to have lunch with Feldberg. At a lull in their conversation, Dale asked Feldberg what he thought about Hitler, whose Nazi party was rapidly gaining strength in Germany. Feldberg replied: “Sir Henry [Dale had been knighted that year], you need not worry, he will never win, and if he should, he will cook with water only,” using the German expression that meant nothing will come of it. Dale, who paid more attention to political events, replied: “Feldberg, you had better stick to your experiments.”

Only months later, on January 30, 1933, the Nazis took over the government after the Reichstag fire incident, and the first anti-Semitic laws were promulgated shortly thereafter. Feldberg was working in Paul Trendelenburg’s Institute of Physiology in Berlin. In April of that year, while in the midst of an experiment, he was called to the director’s office and told that he had to leave the institute by noon that day. Feldberg later described his first reaction as “idiotic,” as he only thought to ask: “But what about my experiment today?” The director consented to allow him to finish the experiment, but made it clear that he had no choice and Feldberg had to leave permanently by the end of the day.

Feldberg called his wife to inform her about what had happened, and she volunteered to come to the laboratory to help him finish the experiment. It was after midnight before they were ready to leave. Feldberg later wrote that his departure would have been totally ignored except for two visiting Japanese colleagues who had heard of his dismissal and were waiting patiently at the door for his departure. The Japanese colleagues bowed silently as they left and bowed once again when Feldberg and his wife turned back.¹⁹

During 1933 roving bands of brownshirts were roughing up Jews in broad daylight, and 100,000 Germans, Jews, and political leftists were put in hastily built camps or taken into police custody on fabricated charges. At the time it was still possible for Jews to leave Germany, providing they left most of their assets behind. The Rockefeller Foundation had begun to provide grants to institutions that would offer positions to eminent scientists and intellectuals who had lost their positions because of the German Nazi government. The grants were barely adequate, but they could be renewed for up to three years.²⁰

Feldberg had heard about the Rockefeller Foundation program, and in May he sought out Dr. Robert Lambert, assistant director of the Rockefeller medical science division in Europe, who was in Berlin at the time.²¹ Feldberg’s name was not on his list, but Lambert said it sounded familiar and after searching through his diary he declared: “Here it is. I have a message for you from Sir Henry Dale whom I met a fortnight ago in London.” Lambert reported that Dale had said that if by any chance he should meet Feldberg in Berlin, and he had been dismissed, to tell him that Dale would like him to come to London to work with him there. Lambert’s report to the Rockefeller Foundation indicated that he had had a conversation with Feldberg on May 24 and was “very favorably impressed with his personality and with the importance of his investigations.” He also reported that although Feldberg had some private means, the Germans would permit him to take very little money out of the country. Feldberg had requested an annual stipend of 300 pounds, but Dale had informed Lambert that a family needed a minimum of 600 pounds to live in London.

Dale had written several letters to Lambert and others at the Rockefeller Foundation about Feldberg, as well as on behalf of other German scientists he knew were in difficulty. In a letter dated May 3, Dale wrote to Lambert, mentioning his high opinion of Feldberg and adding that: “of all the people I have had in my own laboratory, he is the one who has most directly continued to work in the field to which his association with me first introduced him. From my point of view, there is nobody whom I would more willingly have working with me.”²²

Technically Feldberg’s situation did not meet the Rockefeller Foundation’s conditions for support. Feldberg had taken a position as a private docent at the Institute of Physiology because it allowed him to devote full time to research with no teaching or other nonresearch duties required. However, because he had no salary it meant that he had not technically been fired and had not, therefore, met this Rockefeller Foundation requirement for support. Feldberg not only did not have a salary, but even paid for his assistant and the research expenses from his own money. It took several letters from Dale to finally work out an arrangement whereby the Rockefeller Foundation granted funds to support a specific research project that included money in the budget for a subsistence wage for Feldberg.²³

Feldberg left Germany, arriving in England on July 7, 1933. Feldberg’s wife, Katherine, who was not Jewish, had insisted that he leave Germany immediately, while she remained behind in Berlin with their two children to pack their personal belongings. The first question Dale asked Feldberg after welcoming him to England was: “Feldberg, what do you think now about Hitler?” The only answer he could think of was: “Sir Henry, can I help it that history made a mistake?”

Bruno Minz, who had taken the lead in Feldberg’s laboratory in developing the leech muscle technique for detecting acetylcholine, was not as fortunate as Feldberg in finding a place to continue his work. Minz, who was also Jewish, had to flee Berlin. He had obtained a temporary position in Paris. However, he eventually had to flee Paris also, ending up in Algeria, where he found work as a physician in a military hospital. Attempts to find a position for him in the United States were unsuccessful. After the war Minz was able to pursue his research career at the Sorbonne in Paris, where he made a number of important contributions.²⁴

During his first weeks in London, Feldberg was in constant fear that his wife and children might not be permitted to leave Germany. There were stories of passengers being taken off the trains at the Dutch frontier. Katherine managed, however, to get on a boat in Holland. Hours before the boat was due in England, even before the custom officials had arrived, Feldberg was at the dock, pacing up and down. Finally, the boat arrived and Katherine and the children disembarked. An immigration official, who had been observing Feldberg’s pacing and his agitated state, said to Katherine as he handed back her landing permit: “Mrs. Feldberg, you must never again leave your husband alone.”

Feldberg later commented that the immigration officer’s remark was typical of the compassion that most English had for the refugees from Germany. This compassion was typical of many, but not all. While English scientists generally welcomed the persecuted German scientists into their laboratories as colleagues, many English physicians perceived German doctors as competitors, and the major medical organizations opposed their admission. Employment of the refugee physicians was generally restricted and existed only on a limited scale. Lord Dawson, the president of the Royal College of Physicians, for example, sent a memorandum to the home office in 1933 stating “that the number of German physicians who could teach us anything could be counted on the fingers of one hand.” This was at a time when German medicine was arguably the best in the world.

The Feldbergs rented a two-room furnished flat only a ten-minute walk from the institute at Hampstead. This enabled Feldberg to spend the maximum amount of time working in the laboratory. Katherine would generally walk with him to the institute in the morning, wish him good luck on the experiment scheduled for that day, and assure him that he need not worry if he had to work late. Feldberg would typically call Katherine when he was ready to leave, and they would meet halfway.

One day, when Feldberg and his wife had stopped to admire some lobsters in a fish market, Lady Dale walked by and asked what they were doing. Katherine explained that her husband loved lobsters and whenever an experiment had gone well in Germany, they would celebrate with a lobster dinner. When Henry Dale arrived at his office the next morning, he told Feldberg that from now on “lobster experiments would be celebrated in [his] house.” Sometimes, after Dale had been away attending a meeting, he would come to the laboratory in the evening and ask: “A lobster experiment today?” Feldberg’s presence obviously brought about a change in Dale, who for some time had been pulled away from the laboratory by administrative responsibilities. The potential of the leech preparation, however, had motivated him to return to the laboratory. Lady Dale told Katherine that she was so pleased they had come, because her husband was once again excited about doing experiments.

There is no doubt that Feldberg made a major contribution to the ongoing research in the laboratory, but Dale also helped many German scientists get positions in other laboratories in Great Britain besides his own. He was aware of the danger of the Nazi movement before most were, and he was genuinely concerned about those who were being persecuted.

Hitler’s Gift

During the first year after the Nazis came to power, 2,600 scientists left Germany.²⁵ As these included some of the most eminent scientists, it had an enormous impact on science in Germany, a country where science had been preeminent. From 1901, the first year the Nobel Prize was awarded, to 1932, German scientists had received one-third (33 out of 100) of the prizes in science. Great Britain received 18, and United States scientists were awarded only 6. Those figures were turned on their head after the war ended.²⁶

Twenty of the refugees from Hitler’s regime later received the Nobel Prize, and fifty who emigrated to Great Britain became fellows of the Royal Society. Twenty-five percent of German physicists left the country, and the majority of the scientists working on the atomic bomb were refugees from the Nazis, not all of them German and not all of them Jewish. Among the scientists working on synaptic transmission and neurochemistry who left Germany between 1933 and 1937 were Hermann Blaschko, Edith Bülbring, Wilhelm Feldberg, Bernard Katz, Otto Krayer, David Nachmanson, and Marthe Vogt. There were many more who left countries other than Germany because of the Nazis. Among these were Otto Loewi and Stephen Kuffler, both of whom left Austria after the Germans annexed that country. Kuffler, who worked for awhile on synaptic transmission with John Eccles and Bernard Katz in Australia, became a member of the National Academy of Sciences in the United States, and a foreign member of the Royal Society. A few examples that illustrate Dale’s consideration for others are described below.

Although the father of Edith Bülbring (1903–1990) was German, her mother was a Dutch Jew. Bülbring was working in Berlin, doing research with Professor Friedmann, a noted authority on infectious diseases. Friedmann was Jewish, and in 1933 he was dismissed from the hospital along with all the other Jewish doctors. Bülbring, who had a German name and was registered as a Protestant, was safe for a time, but one day she was summoned by the hospital authorities and told that because of her Jewish mother she could no longer work there. At the time her sister was taking a trip to England and Edith joined her there, in part to visit Professor Friedmann, who was working in the National Institute for Medical Research, which Dale was then heading.

While Bülbring was visiting Friedmann, Dale engaged her in a long conversation about her work and then asked her whom she would like to work with in England. Actually, her plan was to try to secure a position in Holland, but when Dale put the question to her, she replied spontaneously that she would like to work with him. Dale said that he already had fifteen people from the Continent working at the institute, but he would make a call to see what could be arranged. Dale was able to arrange a position for Edith Bülbring in a new pharmacology laboratory in London. She later moved to Oxford University, where her important contributions to smooth muscle physiology were recognized with many awards and honors, including election to the Royal Society.

The story of Marthe Vogt, who was born in 1903 and is still alive in 2004, living in California, illustrates that of a number of scientists who left Germany not because they were Jewish, but because they could not tolerate the Nazi regime. She was the daughter of the renowned neuroanatomists Cecile and Oskar Vogt. At a time when it was quite unusual for a woman to obtain a medical degree, Marthe Vogt had both the M.D. and Ph.D. degrees. While the Vogts were not Jewish, they had many Jewish friends and colleagues. Oskar Vogt had helped the Soviet government establish a brain research institute in Moscow and had advised Soviet physicians on the preservation of Lenin’s brain. All of these activities and contacts made the Nazis suspect Oskar and Cecile Vogt, and they were discharged from their position at the Max Planck Institute. They might have been arrested had not the powerful Krupp family, several of whom had been patients of the Vogts, interceded on their behalf.

By 1935 Marthe Vogt had become head of the chemical division of the Kaiser Wilhelm Institüt für Hirnforschung (Institute for Brain Science), but had made up her mind to get out of Germany. With Rockefeller Foundation support, Dale was able to accommodate her in his laboratory. In 1936 Marthe Vogt, with Dale and Feldberg, was the first to prove that spinal motor nerves secrete acetylcholine.²⁷ After the war, Marthe Vogt and Feldberg traced the distribution of acetylcholine in the brain. Their report on the location of acetylcholine in the brain raised the possibility that this substance might also be a brain neurotransmitter. Marthe Vogt later moved to Cambridge University and then to the pharmacology department of Edinburgh University. In 1954 she published a paper on the regional distribution of sympathin (a name used at the time for adrenaline and noradrenaline together) in the brain, providing more suggestive evidence that brain neurons might secrete neurotransmitters.²⁸ Before she retired, Marthe Vogt received many awards from physiological and pharmacological societies around the world and she was also elected a fellow of the Royal Society.

Otto Krayer was another German who was not Jewish but left Germany because of the Nazi regime. Krayer was a relatively young pharmacologist at the University of Berlin and had collaborated with Feldberg in a study demonstrating that the mammalian vagus nerve secretes acetylcholine. After Hitler came to power, Krayer was offered the position of chair of pharmacology in Düsseldorf to replace Philipp Ellinger, who had been dismissed because he was Jewish. Krayer’s ethical principles would not allow him to accept the position under those conditions, and he wrote a letter explaining why he thought such dismissals were wrong. This took a lot of courage, and Krayer was dismissed from his position in Berlin.

Krayer was not able to emigrate immediately, but with help from a Rockefeller Foundation fellowship he obtained temporary employment at University College in London. He refused to return to Germany when the fellowship period ended, and he accepted a position at the American University of Beirut. When Reid Hunt was approaching retirement as professor of pharmacology at Harvard, Walter Cannon, professor of physiology there, recommended Krayer for the position. Dale also wrote in support of Krayer, who was given the position. Krayer became enormously popular with students and faculty at Harvard, where he built a leading department of pharmacology.

Immediately after arriving in England, Feldberg set up the leech muscle preparation for detecting acetylcholine. The untreated leech muscle is not especially reactive to acetylcholine, but if eserine (physostigmine) is added to the bath, its sensitivity is increased more than a million fold.²⁹ Essentially, the technique involved perfusing leech muscle suspended in a saline-eserine bath with blood drawn from a vein that drained the region surrounding the nerve terminal under study. A strain gauge attached to the leech muscle was used to detect any contraction that occurred when the blood was added to the bath.

As is the case with any biological technique, there were some “tricks” that had to be learned to make it reliable. First of all, because the muscles from all leeches are not equally sensitive to acetylcholine, the right strain of leeches had to be used.³⁰ It was also necessary to adjust the amount of eserine (physostigmine) added to the saline solution, because every muscle has a different baseline sensitivity to acetylcholine. Moreover, the experimental animal (usually a cat or dog) must be injected with eserine and an anticoagulant such as heparin. The eserine protected the acetylcholine collected in the blood from degradation by cholinesterase, while the anticoagulant prevented the blood from clotting. Finally, before the blood was injected into the saline-eserine bath it had to be passed through a cooling jacket to adjust its temperature to a level suitable for the cold-blooded leech.

Figure 6.1 The leech muscle technique introduced by Bruno Minz and Wilhelm Feldberg. The response of the leech muscle is extremely sensitive to the presence of acetylcholine. Drawing by Professor Michael Myslobodsky.

Blood was withdrawn from the vein before and after the nerve under study was stimulated. The stimulated nerve was suspended on a thread that lifted it away from the surrounding tissue. This precaution prevented the surrounding tissue from being stimulated and possibly being the source of any acetylcholine detected. When all of these conditions were met, the leech muscle could respond to a dilution of only one part of acetylcholine in 500 million parts of the bath solution. By systematically diluting solutions containing an unknown amount of acetylcholine and comparing their effects to standard solutions of acetylcholine it was even possible to achieve a reasonable quantitative estimate of the amount of this substance present in any solution.³¹

In less than three years, between 1933 and 1936, Feldberg published twenty-five experimental papers, with Dale and with various members of the exceptional group of colleagues working in the laboratory.³² It can be argued that Dale would not have shared the Nobel Prize with Otto Loewi in 1936, had it not been for Feldberg’s contribution. However, Feldberg always minimized his own role, saying that he “may have brought a key capable of opening some doors, but it was Sir Henry and John Gaddum [another of Dale’s collaborators] who knew what doors needed to be opened.” This was too self-effacing, as even before he had joined Dale’s laboratory Feldberg had used the leech preparation in Germany to demonstrate that acetylcholine is secreted by different nerves. Not only had he demonstrated that the vagus nerve secretes acetylcholine in mammals, but he and Otto Krayer showed that the lingual nerve, which innervates the tongue, also secrets acetylcholine. Moreover, Feldberg and Minz had used the leech muscle preparation to demonstrate that the splanchnic nerve secretes acetylcholine when innervating the adrenal medulla.³³ This finding was important because the splanchnic nerve is a sympathetic preganglionic nerve that innervates the adrenal medulla without terminating on a postganglionic fiber, and served as an early hint of what was later proven, namely that all preganglionic nerves—sympathetic as well as parasympathetic—secrete acetylcholine. Even before joining Dale’s laboratory in 1933, Feldberg was well on the way to demonstrating that acetylcholine is secreted by many autonomic nerves. The importance of Feldberg’s many contributions was later recognized, and in 1947 he was elected a fellow of the Royal Society.³⁴

The first experiment with the leech preparation in Dale’s laboratory demonstrated that acetylcholine is secreted by other branches of the vagus nerve, in addition to the branch innervating the heart. After Dale and Feldberg reported in 1934 that acetylcholine is secreted by all the branches of the vagus nerve, including the one innervating the stomach, Dale proposed that all branches of a nerve secrete the same chemical substance.³⁵ It was the neurophysiologist John Eccles who first referred to this as “Dale’s Principle” or “Dale’s Law.” It was accepted as a basic principle of neural functioning until relatively recently, when it had to be modified after the discovery that neurons are capable of secreting several different neurotransmitters.

Dale and Feldberg reported an exception to what seemed, at the time, to be the general rule that postganglionic sympathetic nerves always secrete an adrenaline-like substance. They found that the postganglionic sympathetic nerve that innervates the sweat glands on a cat’s paws secretes acetylcholine.³⁶ To avoid confusing the pharmacological and anatomical classification, Dale recommended that autonomic synapses should be referred to as either cholinergic or adrenergic, a designation still used today. Dale summarized the conclusion he reached from the many studies he did with Feldberg and other collaborators in his laboratory in the following statement:

Feldberg and Gaddum demonstrated that acetylcholine is secreted at sympathetic ganglia synapses as well as at parasympathetic ganglia.³⁸ To do this, they drew blood from the vessels surrounding the superior cervical ganglion region, where some pre- and postganglionic sympathetic nerves synapse. The technique for doing this had recently been described by A. W. Kibjakow, a Russian working in Kazan.³⁹ By drawing blood before and after stimulating preganglionic sympathetic nerves, Feldberg and Gaddum could demonstrate that acetylcholine is secreted by the nerve. This demonstration was especially significant because it showed for the first time that neurotransmitters were secreted not only to innervate smooth muscles and glands, but also at synapses between neurons. Up to this point there had remained the possibility, although the evidence was piling up against it, that the acetylcholine detected might come from the innervated muscle rather than the nerve. But at the ganglionic synapses there was no muscle involved. Despite this demonstration, the concept of neurohumoral transmission at synapses between two neurons was particularly resisted by neurophysiologists.⁴⁰ Dale later commented that John Eccles “continued for some time to dig his toes in firmly in opposition to any suggestion of a cholinergic transmission at synapses in ganglia, still maintaining that it must be electrical. One could hardly avoid a suspicion that he must still be unconsciously influenced by the somewhat closer analogy between these peripheral interneuronal synapses and those of the central grey matter [the spinal cord and the brain].”⁴¹

Dale and his colleagues began to investigate whether neurohumoral transmission exists outside the autonomic nervous system. Although neurophysiologists offered many reasons why chemical mediation is too slow for the innervation of skeletal muscles, there was, as mentioned in the last chapter, some indirect evidence that spinal nerves might secrete acetylcholine.⁴² The leech muscle preparation made it possible in 1936 to demonstrate much more persuasively that spinal nerves also secrete acetylcholine.⁴³

A few years earlier, George Lindor Brown, a neurophysiologist, had joined Dale’s laboratory. He was the only neurophysiologist to work in the laboratory, and the circumstances of his being there are somewhat ironic. Brown had been working in John Eccles’ laboratory when Dale heard him present a paper at a meeting in Oxford. Dale was impressed with Brown and invited him to join his laboratory. Using essentially the same techniques he had been using in Eccles’ laboratory, Brown stimulated spinal motor nerve with a brief, weak electric pulse. Under this condition, the innervated muscle received only a single neuronal impulse and it responded only feebly with a short-lasting contraction. However, when eserine was applied at the point of the synapse, a vigorous, repetitive firing of the muscle fibers occurred.⁴⁴ Since eserine facilitates only the response to acetylcholine, this demonstration provided additional evidence that acetylcholine was being used as a chemical transmitter by spinal motor neurons. Because these neurons originate in the spinal cord they are considered central nervous system neurons, and therefore the demonstration provided support for the idea that neurohumoral transmission exists outside the autonomic nervous system.

The controversy continued, but by 1936 Dale and his collaborators had extended Loewi’s work by providing persuasive evidence—if not completely convincing to everyone—that neurotransmitters were secreted at all peripheral synapses, not just at the synapse between the vagus nerve and the heart. They had provided evidence both that all autonomic preganglionic nerves secrete acetylcholine and, although its significance was still contested, that the spinal motor nerves innervating skeletal muscle also secrete acetylcholine. With only a few exceptions, postganglionic parasympathetic synapses were shown to be cholinergic, whereas postganglionic sympathetic synapses were demonstrated to be adrenergic.

In 1936 Loewi and Dale shared the Nobel Prize in Physiology or Medicine for demonstrating neurohumoral transmission. The citation for the award was written by Gorän Liljestrand of the Royal Karolinska Institute:

Liljestrand got it just about right. It was Loewi who had made the speculative leap based on his initial experiment. He was guided toward this leap, at least partly, by the evidence that Dale had collected earlier. Loewi, who was at first hesitant to extend his conclusions beyond the nerves regulating heart rate, was convinced by the evidence from Dale’s laboratory to change his mind. In his 1936 Nobel Lecture, Loewi stated that: “The total result of the many different, resultant investigations on various organs can be summarized by saying that up until now no single case is known in which the effect of the stimulation of the parasympathetic nerves was not caused by the release of acetylcholine.”

In a tribute to Dale on his eighty-fifth birthday, Loewi reminded his audience that in 1933 he had said that: “I personally do not believe in a humoral transmission in the case of striated muscle.” He continued by noting that: “Within the next year Dale demonstrated the chemical nature of transmission from spinal nerves to striated muscles. It was a discovery that made me happy, which may seem strange in view of the sentence just quoted. But it was not strange at all, for the fact stood forth that physiology owed and still owes to Dale the knowledge that the transmission of impulses from all peripheral, efferent nerves to the effector organs is of a chemical nature. “⁴⁵

Liljestrand also wrote in the Nobel citation that, in addition to contributing to our understanding of synaptic transmission, neurohumoral transmission was beginning to have practical implications. He noted: “Certain observations made during recent years point to practical consequences which will be of value in combating a number of pathological conditions.” Liljestrand probably had in mind some work that followed the observation of Mary Walker at the Alfege Hospital in Greenwich, England. Walker had reported that hypodermic injections of physostigmine (eserine) had “a striking though temporary effect” in increasing muscle strength in a patient suffering from myasthenia gravis, and it also improved the patient’s swallowing and respiration. Walker and others had been encouraged to administer physostigmine because its well-established ability to block the action of cholinesterase might potentiate acetylcholine’s ability to activate skeletal muscles.⁴⁶

Figure 6.2 Sir Henry Dale and Professor Otto Loewi in Stockholm in 1936 on the occasion of the awarding of their Nobel Prize. Courtesy of the Wellcome Trust.

An examination of the nominations of Loewi and Dale for the 1936 Nobel Prize for Physiology or Medicine reflects the political climate of the time.⁴⁷ Normally recipients of the Nobel Prize receive many nominations from their native country. However, by 1936 the Nazi Party in Austria had become quite active and overt anti-Semitism was growing. Although Otto Loewi had been the professor of pharmacology at the University of Graz for more than twenty-five years, he received only two nominations from Austria and none from his own university. There were no nominations from Germany, his native country. One of the nominations from Austria was from Loewi’s friend Ernst von Brücke, a professor at Innsbruck, but the letter consisted of only a single paragraph.⁴⁸ The second nomination, also from Innsbruck, was submitted by A. Jarisch, who nominated both Loewi and Henry Dale.

In contrast to the few nominations Otto Loewi received from Austria (and the total absence from Germany), Henry Dale was nominated by many eminent scientists in Great Britain. The list of British scientists who wrote in support of Dale’s nomination included Sir Charles Sherrington and Sir Edgar Adrian, both of whom were Nobel Laureates. There were also nominating letters from A. V. Hill, F. G. Hopkins, J. H. Burn, and George Barger, a former collaborator.

It was actually Henry Dale who submitted the longest, most detailed, and most persuasive letter nominating Otto Loewi for the Nobel Prize. Dale described the early speculation by Thomas Elliott and Walter Dixon that chemical substances might mediate sympathetic and parasympathetic innervation, but noted that “direct experimental evidence of such process was lacking, and it was nothing more than an interesting and unfruitful speculation.” Dale described how this was changed by Loewi’s work:

Dale went on to describe in detail the evidence Loewi had collected to prove that it is acetylcholine that is secreted by the vagus nerve and to support the conclusion that a substance “probably related to adrenaline” is secreted by the sympathetic nerve innervating the heart. Throughout this highly persuasive letter nominating Loewi, Dale included several reminders, modestly presented, of his own contributions to this work. Dale made reference to his early work that had laid the foundation for Loewi’s work:

And when Dale described Loewi’s discovery of cholinesterase in heart muscle, he noted that he had anticipated the existence of such an esterase enzyme in 1914. Dale also noted in his letter that the importance of Loewi’s work had grown as a result of the demonstrations of active neurohumoral substances at all peripheral nerves, including spinal motor nerves, adding that, “Since a large part in this more recent development has been played by work in my own laboratory, I feel a special confidence in claiming that it has been made possible and has owed its original stimulus to the discovery made by Loewi in 1921.”

In nominating Loewi for the Nobel Prize and documenting his own contributions along the way, Dale had developed a strong argument for the prize to be shared between the two of them. There were several other letters that nominated both of them for the prize, but none as effective as the one Dale himself had written, although he never explicitly suggested that the prize be shared.⁴⁹

The awarding of the Nobel Prize did not end the controversy between the proponents of electrical transmission and those of chemical transmission. By this time most neurophysiologists were willing to concede that neurohumoral transmission might occur at autonomic nervous system synapses, but they opposed the idea of chemical transmission in the central nervous system. Some opposed the theory of chemical transmission not only in the brain but also at the spinal motor neuron synapses with skeletal muscles. This continuing controversy, known as the War of the Soups and the Sparks, is the subject of chapter 8.

But first it is necessary to discuss a relatively neglected side of the argument for neurohumoral transmission. Although it was the similar effects produced by adrenaline and sympathetic nerve stimulation that first raised the possibility that the neural impulse was chemically mediated, it was the work on acetylcholine that provided the most compelling evidence for neurohumoral transmission. Otto Loewi had concentrated his efforts on proving that his “Vagusstoff” was acetylcholine and did not pursue to the same degree his strong suspicion that the “Acceleranstoff” was probably adrenaline. Even in 1935 Loewi hesitated to call the sympathetic transmitter adrenaline: “In spite of analogies, however, and although personally I am convinced of the identity, I do not feel justified as yet in assuming that the sympathetic transmitter is adrenaline, and I will therefore call it ‘the adrenaline-like’ substance.”⁵⁰

When Henry Dale resumed his research in this area after having put it aside for fifteen years, it was the role of acetylcholine that he and his collaborators explored. In the meantime, the American physiologist Walter Cannon stumbled on evidence that adrenaline-like substances, which he came to call sympathin, were serving as chemical transmitters at sympathetic nerve synapses. Cannon’s many contributions to physiology and the story of how he came close to sharing the Nobel Prize with Loewi and Dale are described in the next chapter.