Washington, Aug 12 - Researchers have come up with evidence that acupuncture affects the brain's long-term ability to regulate pain.

Researchers at the University of Michigan (U-M) Chronic Pain and Fatigue Research Centre showed acupuncture increased the binding availability of mu-opoid receptors (MOR) in regions of the brain that process and dampen pain signals - specifically the cingulate, insula, caudate, thalamus and amygdala.

Opiod painkillers, such as morphine, codeine and other medications, are thought to work by binding to these opioid receptors in the brain and spinal cord.

'The increased binding availability of these receptors was associated with reductions in pain,' said Richard E. Harris, researcher and assistant professor of anesthesiology at the U-M.

One implication of this research is that patients with chronic pain treated with acupuncture might be more responsive to opioid medications since the receptors seem to have more binding availability, Harris said.