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Curious About Curare

How did a substance found in plants in the Amazon revolutionize the way we look at anaesthesia?

Olivia Fraser Barsby is a biology and anthropology student at McGill University, specializing in conservation, ecology, evolution and behaviour. 

Blowdart poison and modern anaesthesia: at first glance, you might not think they have much in common. And that’s fair—their connection runs further and deeper than I’d ever imagined. But hey, surgery would look a heck of a lot different today without this relationship—all thanks to “curare.”

Indigenous natives in Ecuador—specifically, the Achuar and Canelos Quichua peoples—have long used blowdarts to hunt in the rainforests of the Amazon. What makes this practice so effective, though, is the dipping of the darts in a poison that kills their targets. Curare is an umbrella term for certain extracts of tropical plants with paralytic properties and is thought to come in a host of regional preparations. While normally harmless when ingested, curare immobilizes its target when injected (i.e., via a blowdart)—perfect for hunting.

Curare (pronounced khyr-rah-ree) acts as a muscle relaxant—its active ingredient is a chemical compound called D-tubocurarine. Normally, our muscles contract thanks in part to a chemical messenger called acetylcholine, which delivers messages from motor neurons—the cells that tell our muscles what to do—to the muscles themselves. For this delivery to happen, acetylcholine has to bind to special receptors. However, D-tubocurarine also binds to these receptors, essentially blocking acetylcholine from telling your muscles to contract and paralyzing them temporarily.

This can be seen to have a practical use in medicine pretty quickly—surgery is a lot easier when muscles are in a relaxed state. Take, for example, a relatively common procedure like an appendectomy. In order to get to your inflamed appendix, surgeons will have to slice through your abdominal muscles. We don’t all have abs of steel, but it’s still easier to cut through relaxed muscle tissue than muscles that are tensed.

Though curare has been described for centuries, and experimental work with the compound began in the 1700s, we might have one particular individual to thank for its introduction into a clinical context. Richard C. Gill was born into a family of doctors in Washington, D.C. in 1901. He followed in their footsteps and began to study medicine at Cornell until he was bitten by a travel bug and dropped out after his second year. After going back to finish a B.A. in 1927, Gill worked for the American Rubber Company in Peru for two years before he and his wife Ruth bought land in Ecuador and decided to make a permanent move.

At the age of 31, while back visiting the States, Gill fell off a horse and began experiencing a host of neurological symptoms, including a tremor. Other sources state that he had multiple sclerosis that manifested around this time. Either way, Gill was determined to find a way to treat his condition. His neurologist suggested travelling back to Central America in search of a plant that he thought might be able to help. Gill was finally well enough to travel back to Ecuador in 1936 and eventually came back to the U.S. with 100 pounds of plant product two years later—25 pounds of paste that he would give to a pharmaceutical company called E.R. Squibb & Sons for research purposes and 75 pounds of botanicals that he would give to the New York Botanical Garden.

Back when they first moved to Ecuador, the Gills built a hacienda—a colonial estate, basically—and began farming on the land they had bought. They developed relationships and trading affiliations with the Canelos Quichua and Achuar peoples in Pacayacu and Sarayacu that would prove critical for the transportation of all that curare back to the U.S. After the two-year long expedition, D-tubocurare was isolated from the imported curare and synthetic forms were made and sold. However, E.R. Squibb & Sons didn’t get much attention from practicing anaesthesiologists at the time.

Gill became frustrated with this lack of interest, which he thought stemmed from curare’s historical unpredictability. Before his expedition, the curare involved in research was trickling out of the Amazon in tiny amounts and differing combinations. Scientific attitudes created harmful misconceptions around its traditional blowdart hunting use. Because there was no effort to understand the distinctive regional types of curare—remember, it’s a general term used to refer to a host of plants with the same active ingredient that are sometimes combined in different amounts—the research surrounding it wasn’t valued.

In the end though, all it took was one medical team to try: Harold Griffith and Enid Johnson at the Homeopathic Hospital in Montreal. On a winter day in early 1942, Griffith and Johnson used curare to supplement their use of an anaesthetic called cyclopropane. The combination worked wonders—the patient’s muscles were relaxed enough to make the surgery and recovery processes that much simpler. Though neither cyclopropane (too flammable) nor curare (effective synthetic versions are now available) are directly used in clinical settings today, they helped to form the basis for current anaesthetic practices: a triple cocktail of narcotics, analgesics and muscle relaxants.

Anaesthesiologist Merlin Larson argues that a personality like Gill’s was necessary to advance the use of curare in a clinical context. His connection to the Achuar and Canelo peoples in Ecuador was necessary in order to realize the potential role of muscle relaxants in contemporary anaesthetic practices. Interestingly, Gill never revealed the names of the ingredients, nor the locations of his teachers, perhaps because he did not want to exploit these relationships or go back on any deal that had been made. It is important to recognize and reflect on the fact that European and North American settlers continue to benefit from the discovery of curare, a compound made by Indigenous peoples on their traditional lands. Surgical practices would not have evolved the same way without them and their knowledge.

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