New means to erase pain devised

It is possible to relieve pain hypersensitivity using a new method that involves rekindling pain so that it can subsequently be erased, according to a new study.
The discovery could lead to novel means to alleviate chronic pain, researchers said.
The researchers were inspired by previous work on memory conducted some fifteen years ago. These studies had revealed that when a memory is reactivated during recall, its neurochemical encoding is temporarily unlocked.
Simultaneous administration of a drug that blocks neurochemical reconsolidation of the memory results in its erasure.
The investigators wanted to see whether a similar mechanism was at play during neurochemical encoding of pain sensitisation.

They injected capsaicin in the foot of mice. Capsaicin, the pungent chemical in chili pepper, triggers a burning sensation.

The procedure, which causes no physical damage, triggers pain hypersensitivity through a process of protein synthesis in the spinal cord.
After capsaicin injections, the mechanical pressure at which mice would flinch was about a third of that in the normal situation.
Three hours later, the researchers administered a second dose of capsaicin and, at the same time, a drug that blocks protein synthesis.
The hypersensitivity then vanished rapidly. Within less than 2 hours, the pressure tolerated by the mice was back to 70 per cent of normal.

"When the protein synthesis inhibitor is administered alone, the hypersensitivity remains. The second injection of capsaicin is necessary to render the sensitivity to pain unstable and be able to interfere with its neurochemical reconsolidation," said Yves De Koninck from Universite Laval in Canada.
The study was published in the journal Nature Neuroscience.