NEW YORK, Jul 13 (Reuters Health) - Brain cell targets called mu-opioid receptors play a key role in the way we perceive pain, say researchers from the University of Michigan in Ann Arbor.

Pain is a complex experience encompassing sensation, perception and interpretation, according to Dr. Jon-Kar Zubieta and associates, who present their findings in the July 13th issue of Science.

The investigators used special imaging called PET (positron emission tomography) to examine how mu-opioid receptors behave in the brain during the experience of prolonged pain in 20 healthy volunteers. These receptors are activated by the body's own pain relievers, called endogenous opioids.

Sustained pain applied to the jaw muscle activated mu-opioid receptors in brain areas associated with the body's attempt to minimize the experience of pain, a reaction known as the antinociceptive response, the authors report.

Receptor activation and pain experience, as might be expected, varied widely among the 20 study participants, the report indicates.

However, the more mu-opioid receptors that were activated, the lower were the pain scores reported by the volunteers, the team found.

Zubieta and colleagues conclude that activation of these receptors controls the brain's anti-pain, or antinociceptive, responses. Individual differences in these receptors probably also account for individual differences in the experience of pain.

"These types of studies provide the bases for further understanding of the brain chemical mechanisms that control the pain experience," Zubieta told Reuters Health. "We can now examine methods that would regulate, possibly enhance, the natural anti-pain systems in humans.

"We are learning more about how individuals experience pain or other stimuli, and relate their experiences to chemical changes inside our bodies, effectively providing a window into the chemical functioning of our bodies," Zubieta added. "Further developments in this area will hopefully provide us with objective, effective ways to move basic research findings into the clinical arena."

From ReutersHealth.com