NEW YORK (Reuters Health) - Scientists in the UK, searching for the cause behind ongoing spontaneous pain, have found evidence that it's the undamaged nerve fibers that cause the pain, not those that are damaged by injury or disease.

　　Ongoing pain is characterized by a burning or sharp stabbing or shooting pain that can occur spontaneously after nerve injury. Unlike "evoked" pain caused, for example, by hitting your thumb with a hammer, ongoing pain frequently reduces quality of life and is difficult to treat with currently available painkillers.

　　Previous research into ongoing chronic pain has largely focused on the damaged nerve fibers after injury or disease and overlooked the healthy intact nerve fibers.

　　The unexpected role of the healthy nerve fibers in chronic pain may help pharmaceutical companies develop novel painkillers.

　　Dr. Laiche Djouhri and colleagues from the University of Bristol, UK, report their discovery in The Journal of Neuroscience.

　　They showed that spontaneous pain (as measured by spontaneous foot lifting in animal models) is caused by spontaneous firing in "nociceptive" or damage-detecting neurons in the body. There are thousands of these neurons in the human body.

　　"The cause of spontaneous firing in the uninjured nerve fibers appears to be inflammation within the nerves or tissues, caused by dying or degeneration of the injured nerve fibers within the same nerve," Djouhri told Reuters Health.

　　"It remains to be established how generally the mechanism described following nerve injury and tissue inflammation may also contribute to ongoing pain associated with a wide variety of other chronic pain diseases, such as back pain, arthritis, post-operative pain due to damage to nerves or tissues, trauma, especially injury to nerves, or inflammation and interstitial cystitis," Djouhri added.