DOUBT CAST ON BRAIN CHEMICAL ROLE OF DOPAMINE NOT SO `FEEL-GOOD'

Dopamine may not be the brain's "feel-good" chemical after all, a study
found, suggesting that scientists trying to unlock the secrets of drug
addiction may have been off-target for the past two decades.

The naturally produced brain chemical, rather than being the key player in
the pleasure process, is only a messenger and one of several factors,
according to the study, being published today in the journal Nature.

"It certainly says the picture is much more complicated than being just
dopamine alone, and it will lead to the search for other chemical
substances in the brain," said the study's author, chemist R. Mark Wightman
of the University of North Carolina-Chapel Hill.

Dopamine, first discovered in 1957, came into prominence in the early 1960s
when scientists discovered that several anti-psychotic drugs targeted it.
In the late 1970s, researchers began looking into its role in drug
addiction and found that cocaine, heroin and other addictive drugs increase
levels of dopamine in the body.

Since then, some scientists have tried to develop a medication that would
cure cocaine addiction by blocking dopamine.

The latest study is another in a series that have cast doubt on that approach.

Researchers attached electrodes to the brains of rats, which produced
dopamine when they were shocked. The rats were then trained to shock
themselves.

As the rats continued to shock themselves, however, the researchers
discovered that the amount of dopamine produced by their brains decreased
- -- even though they continued to seek pleasure by pressing the lever that
electrically stimulated their brains.

Dopamine appears to be related to "novelty, predictability or some other
aspect of the reward process, rather than to hedonism itself," the
researchers reported.

What chemical or process is ultimately responsible for the pleasure is "not
really clear right now," said Anthony Grace, a professor of neuroscience
and psychiatry at the University of Pittsburgh, who was not involved in the
study.

Francis White, chairman of cellular and molecular pharmacology at the
Chicago Medical School, said the study adds to the growing belief that the
pleasure process has been oversimplified.