Imagine an epidural or a shot of Novocain that doesn’t paralyze your legs or make you numb yet totally blocks your pain. This type of pain management is now within reach. As a result, childbirth, surgery, and trips to the dentist might be less traumatic in the future, thanks to researchers at Massachusetts General Hospital (MGH) and Harvard Medical School (HMS) who have succeeded in selectively blocking pain-sensing neurons in rats without interfering with other types of neurons.
The pint-sized subjects received injections near their sciatic nerves, which run down their hind limbs, and subsequently lost the ability to feel pain in their paws. But they continued to move normally and react to touch. The injections contained QX-314, a normally inactive derivative of the local anesthetic lidocaine, and capsaicin, the active ingredient in hot peppers. In combination, these chemicals targeted only pain-sensing neurons, preventing them from sending signals to the brain.
“We’ve introduced a local anesthetic selectively into specific populations of neurons,” explains HMS Professor Bruce Bean, an author on the paper, which appears in Nature today (Oct. 4). “Now we can block the activity of pain-sensing neurons without disrupting other kinds of neurons that control movements or nonpainful sensations.”
“We’re optimistic that this method will eventually be applied to humans and change our experience during procedures ranging from knee surgery to tooth extractions,” adds Clifford Woolf of MGH, who is senior author on the study.
Harvard researchers have discovered that combining the ‘hot’ ingredient in chili peppers with anesthesia dulls pain nerves without dulling all the surrounding nerves. 
