Spurge

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.