After reading this story I started wondering about the main active component of chillis, capsaicin (8-Methyl-N-vanillyl-trans-6-nonenamide).
As anyone who has chopped chillis before can testify, capsaican is severe irritant to humans and other mammals and capable of causing severe pain. Interestingly birds seem unaffected by capsaicin and feed on chillis - this is a nice piece of evolution as chilli seeds don’t germinate if they’ve passed through a mammalian digestive tract but do if it’s avian.
In vivo, capsaicin binds to vanilloid receptor subtype1 (TVPR1), opening it and allows ions to flow. TVPR1 is involved in pain transmission and is also opened other stimuli such as heat or acids - hence capsaicin causes that lovely burning sensation.
Whilist writing this I stumbled across and this story. Basically inject capsaicin and an analgesic and the former will allow the latter to enter only neurons that provide pain response leaving others unaffected thus reducing numbness etc.
One small stumbling block though…
Dr Joan Hester, the president of the British Pain Society, said that while capsaicin had been used for many years to reduce skin sensitivity linked to chronic pain, it caused an unpleasant burning sensation that was too much for some patients.
This might be even more of a problem if the chemical was injected below the skin, she said.
“The technique has not yet been tried on humans, and it is hard to see how capsaicin could be used in this situation.”
I’ve add some more info on this once I’ve read the paper, apparently it’s in Nature but I can’t find it yet.
Update: the paper has been published and can be found here.
In response to PJ’s comment, they do appear to have used capsaicin and the analgesic (QX-314) alone as a controls. There is an increase in pain threshold when QX-314 injection is followed by capsaicin injection in both tests, heat and mechanical. If anyone with more knowledge of anaesthesia would like to follow up I’d be interested.
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