Yaël: Uhm. Don? You're drooling.

Don: Oops! Thanks, Yaël! I just came from the dentist. My mouth is still numb from the      shot of anesthesia she gave me. But I guess being numb and drooling is better than      being in pain.

Y: I hear that hot peppers might be the key to a new type of anesthetic that blocks pain      without making you numb or paralyzed?

D: Hot peppers? Seems like they'd cause pain rather than block it!

Y: You'd think so, but researchers in San Francisco discovered that capsaicin, the      compound that gives hot peppers their heat, binds to certain ion channels on the      surface of pain-sensing neurons called nociceptors.

     Most local anesthetics work by blocking the activity of all neurons, including      nociceptors, but also neurons that sense touch or control muscles. So the pain      sensation is effectively blocked, but so is all the feeling in that area.

     A later study at Harvard Medical School found that when capsaicin is bound to the      channels on nociceptors, it causes those channels to open like pores in the neuron's      membrane. They discovered that the pores were just large enough for molecules of      an anesthetic called QX-314 to enter and block the neuron's activity.

D: So by injecting both capsaicin and the anesthetic, only the pain-sensing neurons are      deactivated? I could be pain-free but not totally numb and drooling?

Y: That's the idea. The capsaicin and QX-314 combo was successfully tested in mice,      but scientists are still not sure if it will work for humans. They hope that this discovery      will ultimately lead to a way for doctors to block pain without generalized numbness      or paralysis.  

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