TB medication offers pain relief.

A drug used nearly half a century ago to treat tuberculosis may help people who experience chronic pain. The drug, an antibiotic called D-Cycloserine, reduces chronic-pain-like symptoms in rats.

A. Vania Apkarian of Northwestern University in Evanston, Ill., and his colleagues tested the drug on rats in which the researchers had cut tissue and a major nerve in one paw. The tissue healed, but nerve damage persisted, as is often the case in chronic pain.

The team then gave oral D-Cycloserine to some rats. In others, the researchers injected the drug into the medial prefrontal cortex, a brain region that the scientists speculate is involved, in people, in emotional responses to chronic pain.

Both treatments significantly improved the rats' ability to withstand pressure on the injured paw. Oral doses repeated twice daily for 2 weeks or longer had a particularly pronounced effect, according to the report published online and in an upcoming Pain. However, D-Cycloserine injections to other brain regions didn't help the rats.

The researchers say that this supports their theory that learned emotional responses centered in the medial prefrontal cortex play a key role in the experience of chronic, or neuropathic, pain.

Previous work by Apkarian's team demonstrated that the medial prefrontal cortex in people is active in individuals who are experiencing chronic pain but not in individuals reacting to normal pain stimuli, such as a hot surface. "We think a large component of the suffering is enhanced by the [medial prefrontal cortex] of the brain," says Apkarian.

He and his team are planning to test the drug in people suffering chronic pain.--J.P.