February 16, 2006

Cause of ongoing pain elucidated

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

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

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

"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.

SOURCE: The Journal of Neuroscience January 25, 2006.