Brain: A study suggests it is only a messenger.

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 Caroline.

Dopamine, 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 probing 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. 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 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 Prof. Anthony Grace of the University of
Pittsburgh.