By William Allen
Of the Post-Dispatch

Feb. 21, 2000

Edited by Virginia Baldwin Gilbert

Just because you have a low tolerance for pain doesn't mean you're a wimp.

You can blame it on your genes.

That's one conclusion reported by researchers Sunday at the annual meeting in Washington of the American Association for the Advancement of Science.

"People who are 'whiners' may actually be in more pain," said one of the researchers, Jeffrey Mogil of the University of Illinois at Urbana-Champaign.

Mogil and other scientists who study the nature of pain say human variation in pain tolerance is based largely on our genetic blueprint. In other words, some of us inherit biochemical mechanisms that make us more susceptible to feeling pain than others.

This finding is important because it can help researchers improve ways of treating pain, a complex system involving such biochemical players as nerve impulses, amplifiers and inhibitors. Persistent pain affects an estimated 100 million Americans in forms that include chronic headaches, lower back pain and neuropathic pain, which plagues an injured site long after damaged nerves have healed.

The new research holds promise for one day developing more-potent drugs precisely targeted at specific kinds of pain.

First, basic researchers must figure out why some people respond to certain painkillers but others don't.

Mogil studies the response of different breeds of mice and rats to hot water on their tails. Some breeds tolerate the heat well, and some don't. Although mice aren't humans, the results translate roughly to us because the nervous systems of the two species are similar.

He found that the more sensitive a mouse is to pain, the less the pain is alleviated by analgesic drugs, such as morphine.

He also found that males tolerate pain better than females and that the difference is based on genetic differences.

"Both (males and females) feel pain, but they are responding differently," Mogil said.

Catherine Bushnell, a researcher at McGill University in Montreal, uses brain-imaging technology to "look" inside the brain when a person is subjected to nondamaging burning pain.

"There is huge variation in the way individuals experience pain and in the parts of the brain that respond," she said.

Some people experience pain when their skin is touched lightly, while others can tolerate ample burning.

"Ultimately, a common circuit is involved," she said.

In experiments on humans, Bushnell found that simple distractions can reduce brain activity related to pain "the same as if you had given the patient morphine or some other analgesic."

She discovered this while playing sounds for people at the same time they were exposed to nondamaging burns. Apparently thinking about something else can ease pain.

"This doesn't make the pain disappear," she said, but it does show that people can do something about their pain by occupying their minds with something else.

The genetic basis for variation in pain response means that somewhere within our genes is a "volume knob" that turns pain sensitivity up in some people and down in others, Mogil said. Among the implications:

* The real differences in the way people respond to pain "should lead to a destigmatization toward people who are pain sensitive," he said.

* Scientists may be able to develop a pre-surgery genetic test to help d etermine a patient's response to pain. This might enable doctors to develop better strategies for treating postoperative pain.