BRAIN CHEMICAL DOPAMINE MAY NOT BE ADDICTION KEY

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, 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 antipsychotic 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 that casts doubt on that approach.

The 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. That's something that's a real topic of
investigation," said Anthony Grace, a professor of neuroscience and
psychiatry at the University of Pittsburgh who was not involved in the study.

Grace said that even if dopamine is not the ultimate reward for the brain,
it might still be the key to curing addiction.

Some researchers now complain that dopamine's activity in the brain has
been overstated. Alan Leshner, director of the National Institute on Drug
Abuse, has criticized what he called "the dopamine religion" among some
scientists.

Marc Caron, a professor of cell biology at the Duke University Medical
Center, found evidence last year that the effects of cocaine are not solely
controlled by dopamine. Caron created specially bred mice without dopamine
transporters, and found they still wanted cocaine.

Medications that block the transporters in humans, however, might be
effective if they could block the desire for cocaine long enough to break
the addiction, Grace said.