Chemical Boosts Marijuana-Like Substance in Brain
by Amy Norton
NEW YORK, May 3, 2000 (Reuters Health) - A chemical that boosts a
marijuana-like substance in the brain may inspire new treatments for
brain disorders such as schizophrenia, Parkinson's
disease, and attention-deficit/hyperactivity disorder (ADHD).
Researchers at the University of California, Irvine, have developed a
compound--dubbed
AM404--that bolsters the natural function of anandamide, a brain
chemical that acts on the
same brain receptors as marijuana does. Experiments in rats show that
anandamide normally
inactivates another brain chemical called dopamine, which has been
implicated in a number
of brain disorders. Daniele Piomelli, a professor of pharmacology, and
colleagues report
their findings in the May issue of the Journal of Neuroscience.
In the case of PARKINSON'S disease, patients have too little dopamine,
while people with
ADHD, schizophrenia or Tourette's syndrome may have too much.
The hope is that AM404 will lay the groundwork for a new class of drugs
that either boost or block dopamine, without the side effects linked to
current treatments, Piomelli told
Reuters Health in an interview.
"Our results are interesting," he said, "because they show that you can
modulate dopamine without acting on the dopamine system."
This is important, Piomelli noted, because Parkinson's, schizophrenia,
Tourette's syndrome
and other disorders are all currently treated with drugs that act
directly on the dopamine
system. These drugs, he added, carry side effects such as lethargy and
impaired sexual
activity.
Last year, Piomelli and his colleagues showed for the first time that in
rats, anandamide
naturally counters dopamine. Usually, though, anandamide is inactive in
the brain. The
California team's latest experiments in rats reveal that AM404 stops
anandamide from being
"drained from the brain," which allows it to suppress dopamine.
Although dopamine's role in brain disorders is not completely
understood, an elevated level
is a "common element" in conditions such as ADHD, schizophrenia and
Tourette's
syndrome, Piomelli explained. These disorders are all marked by
hyperactive "intrusions"
into normal brain function, he said. For example, people with Tourette's
experience physical
"tics," while schizophrenics suffer from delusions.
The potential for anandamide-boosting drugs to work against these
disorders has some
anecdotal backing. Anandamide's counterpart, marijuana, is used by many
schizophrenics
who report that it relieves their symptoms, Piomelli noted.
"But," he said, "we are not implying that marijuana is useful for these
conditions."
Marijuana, according to Piomelli, is far less selective than anandamide
in activating brain
cells. Because pot smoking overstimulates the brain, he said, cells
eventually become
desensitized to any benefits the drug initially brings.
SOURCE: Journal of Neuroscience May 2000.
Copyright © 2000 Reuters Limited.
--
Judith Richards, London, Ontario, Canada
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