RESEARCHERS: ABILITY TO ENDURE PAIN MAY BE GENETICALLY LINKED.

Byline: Robert S. Boyd Knight-Ridder News Wire

Thanks to new tools and techniques, scientists are beginning to unravel the mystery of pain - why such a terrible thing exists and what can be done to relieve it.

Using modern electronic scanning devices, they can watch individual nerve cells, or neurons, in the living brains of people and animals react to painful stimuli.

As they gain understanding, they hope to discover new ways to prevent, control or end unnecessary or excessive pain.

At a meeting of the Society for Neuroscience in Washington this week, researchers noted that the capacity to suffer pain, despite its evil reputation, is built into our genes because it has survival value.

``Pain says, `there is something wrong with your body,''' said A.D. (Bud) Craig, a researcher at the Barrow Neurological Institute in Phoenix. ``It stirs up memories and emotions that drive an animal to locate, remember and avoid harm.''

The same thing happens in humans as pain reinforces learning. ``A child doesn't have to learn twice not to touch a hot stove,'' said Steven Hyman, director of the National Institute of Mental Health.

The neuroscientists described pain as a complex phenomenon, involving various parts of the brain governing emotions, memories and involuntary movements as well as physical sensations.

Their new knowledge comes primarily from experiments with positron emission tomography (PET) and magnetic resonance imaging (MRI), which use electronic devices that allow researchers to observe the brain while it is experiencing pain.

The first PET images of pain in humans were made five years ago by Gary Duncan of the University of Montreal. Now many laboratories are performing similar experiments on animals and humans.

Different regions of the brain, the scientists have found, handle different aspects of pain.

For example, Duncan reported that a sharp jab to the skin causes reactions in the cortex, the highest level of the brain, which controls thought and perception, and also in lower regions that govern feelings, memories and motions.

``If you are stabbed with needle, you perceive a sharp stimulus, you recall memories of past pain, you may feel anger, withdraw from the source, sweat, maybe faint,'' Duncan said.

In the last couple years, neuroscientists have traced two separate pain ``pathways'' - bundles of nerve fibers that transmit signals from the skin through the spinal column and up into the brain. When these fibers are damaged, the sensation of pain is lost.

In addition, Casey said there are three distinct ``pain centers'' in the cortex, each with a different function.

One region of the cortex collects information on the location, duration and intensity of a painful event. Another records feelings of unpleasantness and a drive to escape whatever is causing pain. A third reflects the emotions, like anger or grief, that accompany pain.

Still other parts of the brain handle involuntary responses, such as blood flow and heart rate, or control muscles that cause you to run or jerk your hand away.

Michael Gabriel, a neuroscientist at the University of Illinois in Champaign-Urbana, trains rabbits to jump off a wheel when they hear a tone warning them that they are about to receive an electric shock. Gabriel said he can see physical changes taking place in the rabbits' brain cells as they learn to recognize and respond to the pain signal.

``The cortex reflects the behavior training of the animal,'' he said. ``These internal signals help animals avoid painful situations.''

The goal, the neuroscientists say, is not just to understand pain, but to use their knowledge to develop better methods of controlling pain - with drugs, surgery or psychological techniques.