Pubdate: 3 Mar 1999
Source: Reuters
Copyright: 1999 Reuters Limited.
Author: Patricia Reaney

NEW CLUES ABOUT WHAT TRIGGERS PLEASURE IN BRAIN

LONDON, March 3 (Reuters) - Feelings of pleasure generated in the human
brain appear to be the result of several mechanisms rather than one
well-known chemical, American researchers said on Wednesday.

Animal studies by scientists at the University of North Carolina showed
that dopamine, associated with pleasure and with drug addiction, is
probably only one of many "neurotransmitters" that reward certain kinds of
behaviour and generate euphoria.

"Our data suggests that dopamine is part of the alerting response that
something rewarding is going to happen but it is not part of the continuous
reward. It is not the thing that makes you feel good continuously," Mark
Wightman said in a telephone interview.

Wightman and his colleagues developed technology to map the circuitry of
the brain. Their findings could be the first step in unravelling the
mysteries of how people react to drugs and why they become addicted.

"What one would like to do is understand all that circuitry that gets
activated in the brain during drug abuse so you can perhaps figure out a
way to intervene and stop it," he said.

"Understanding the overall circuitry is important and I think what our work
does is refine and add to our knowledge of how the brain processes
rewarding signals."

Cocaine and amphetamines directly stimulate nerve cells that produce
dopamine. Alcohol and nicotine have also been linked to changes in brain
dopamine levels, leading scientists to suspect it causes the feelings of
pleasure.

But Wightman and his colleagues discovered that dopamine may not be the
reward itself, but could be involved in an early stage of the process
triggering expectation of the reward.

The researchers measured levels of dopamine in rats taught to press a lever
to electrically stimulate their own dopamine-releasing neurons.

When the rats pressed the lever, dopamine levels decreased. But when the
scientists pressed it for the rats, it came as a surprise and dopamine
levels rose.

"The brain reward system is extremely complicated so it is extremely
unlikely that it would be associated with one single molecule. That's what
our research dramatically illustrates," Wightman said. 
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MAP posted-by: Mike Gogulski