DOCTORS FIND A KEY MOLECULE IN NICOTINE ADDICTION

LONDON (Reuters) - Scientists have identified a chemical compound which
explains how nicotine becomes addictive and could help point the way to new
drugs for people who want to stop smoking.

``For the first time, one particular molecule has been shown to be critical
for the events leading up to nicotine addiction,'' Marina Picciotto told
Reuters.

She and colleagues at the Pasteur Institute in Paris, the Karolinska
Institute in Stockholm and the research arm of Glaxo-Wellcome in Geneva
found the first of 11 subunits, or molecules, of the nicotine receptor in
the brain of mice. Humans have the same so-called b2 subunit.

``It's the first step in identifying the other components of that receptor
and that pathway (that triggers addiction),'' she added.

Because the habit-forming properties of nicotine are similar to those of
other drugs such as cocaine and heroin, the finding could also have
important implications for treating drug abuse.

Like many drugs, the addictive elements of nicotine are connected with the
release of the neurotransmitter dopamine in the brain. People get addicted
because of the rapid activation that leads to the dopamine release.

The discovery could lead to the development of a drug that would block the
receptor responsible for addiction or activate it in a slower way.

``The idea is that the more you know about exactly which molecules are
important to nicotine addiction, the more you can intelligently design a
drug that would interrupt specifically that molecule and not other nicotine
receptors,'' she added

In a report in the scientific journal Nature, the scientists described how
they found that nicotine stimulated the release of dopamine in the brains
of normal mice but not the brains of mutant mice lacking the b2 subunit. In
a series of experiments they discovered that the mutant mice did not react
to nicotine.

The study also showed that nicotine improved the performance of mice on
avoidance-learning tests, which could explain why some smokers claim it
enhances their concentration and memory.

``There are some good things that nicotine does,'' said Picciotto, adding
that clinical trials have shown that it enhances memory in Alzheimer's
patients.

The 11 receptor subunits are similar in structure but have different
functions. Scientists have some ideas of what the subunits do what are only
at the very beginning of identifying which molecule does what.

``We think the endogenous role of this receptor is not to make you
addictive to nicotine but to regulate dopamine release in the brain under
normal circumstances,'' Picciotto explained.

The scientists are already doing experiments to see how their finding could
influence the addictive properties of other drugs.