Curare is a poison obtained from different species of plants in South America, which was used in arrows by the natives. Its lethal paralyzing potential and mechanism of action began to be explored in the 19th century. In this article, we highlight the research on this poison and the fruitful exchanges between the Brazilian Emperor Dom Pedro II and the researchers João Baptista de Lacerda, Louis Couty and Alfred Vulpian who contributed to the development of experimental neurophysiology in Brazil. Vulpian found that curare does not affect the nerve itself, but acts between the nerves and the muscle, through a "ligand substance" - this Vulpian's pioneering concept is often wrongly attributed to Claude Bernard. These prestigious scientists contributed to the transnational circulation of knowledge that later yielded in the preparation of curare purified extract used for convulsive therapy and anesthesia.