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Spurges (of the Euphorbia genus, of which there are 2300 species) are
plants with a yellowish green inflorescence, known as cyathia, arranged into
umbels. Each inflorescence consists of one female flower with three styles
surrounded by male flowers with a single anther, all in a bowl formed by two bracts
plus four or five glands in the shape of retorts. When broken, the stem leaks a
white or yellow latex. The dried latex of Euphorbia resinifera, known as
euphorbium, has been in medicinal use since the earliest times of recorded
history. Pliny, in his Natural History, ascribes their name to Euphorbus, a
physician to King Juba II of Mauritania.
The active molecule in the latex belongs to the family of diterpenes and is
named resiniferatoxin. It was first isolated in 1975 and it has since
become a tool of the first importance for research on pain. It is an analog,
physologically, of capsaicin, the pungent principle in hot chili peppers,
but it is 100-10,000 times more potent than capsaicin. The euphorbia toxin binds
to a specific membrane recognition site, known as the vanilloid receptor,
associated with neurons responsible for the feeling of pain. Resiniferatoxin
works by opening an ion channel in the plasma membrane of sensory neurons,
making it permeable to cations, the calcium cation in particular; this
causes a powerful irritation. Desensitization to resiniferatoxin is a promising
approach to mitigate neuropathic pain and other pathologies in which sensory
neuropeptides released from capsaicin-sensitive neurons play a crucial
role.