Resiniferatoxin (RTX) is a naturally occurring chemical found in resin spurge (Euphorbia resinifera), a cactus-like plant commonly found in Morocco, and in Euphorbia poissonii found in northern Nigeria. It is an ultrapotent analog of capsaicin, the active ingredient in chili pepper. It activates the vanilloid receptor in a subpopulation of primary afferent sensory neurons involved in nociception (the transmission of physiological pain). RTX causes an ion channel in the plasma membrane of sensory neurons — the transient receptor potential vanilloid 1 — to become permeable to cations, most particularly the calcium cation; this evokes a powerful irritant effect followed by desensitization and analgesia. Research has been conducted at the National Institutes of Health and the University of Pennsylvania[9] to design a novel class of analgesics from the latex of Euphorbia resinifera.
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