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US: Marijuana may make your brain grow

Geoff Brumfiel

Nature

Monday 17 Oct 2005

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Cannabinoid injections sprout new neurons in mice.

Most addictive drugs inhibit the growth of new brain cells. But
injections of a cannabis-like chemical seem to have the opposite
effect in mice, according to new research. Experts say that the
results, if borne out by further studies, could have far-reaching
implications for addiction research and the application of marijuana
in medicine.

For several years now, researchers have been interested in how drugs
affect a part of the brain known as the hippocampus. This region is
unusual in that it can grow new neurons throughout a person's
lifetime. Researchers have theorized that these new cells help to
improve memory while combating depression and mood disorders.

Many drugs, such as heroin, cocaine and alcohol, inhibit the growth
of new cells in the hippocampus, which scientists believe could
emotionally destabilize addicts. Understanding how drugs affect the
hippocampus may have a critical role in treating addiction.

Neuropsychologist Xia Zhang and a team of researchers based at the
University of Saskatchewan in Saskatoon, Canada, aimed to find out
just how marijuana-like drugs, known collectively as cannabinoids,
act on the brain.

Expanding the mind

The researchers injected rats with HU210, a synthetic drug that is
about one-hundred times as powerful as THC, the high-inducing
compound naturally found in marijuana. They then used a chemical
tracer to watch new cells growing in the hippocampus.

They found that HU210 seemed to induce new brain cell growth, just as
some antidepressant drugs do, they report in the Journal of Clinical
Investigation1. This suggests that they could potentially be used to
reduce anxiety and depression, Zhang says. He adds that the research
might help to create new cannabinoid-based treatments.

"I think it's a very exciting study," says Amelia Eisch, an addiction
researcher at the University of Texas Southwestern Medical Center in
Dallas. "It makes marijuana look more like an antidepressant and less
like a drug of abuse."

Eisch adds that much more work must be done before scientists can
reach any definitive conclusions about the benefits and costs of
marijuana. First and foremost, researchers need to establish that THC
has the same positive effects as the synthetic HU210. Then they must
develop more sophisticated experiments to firm up the correlation
between neuron growth in the hippocampus and emotional balance.

Finally, she says, scientists must understand why cannabinoids have a
different effect on the brain than other addictive drugs.

Although his findings point to potential benefits of smoking pot,
Zhang says that he does not endorse its use. "Marijuana has been used
for medicine and recreation for thousands of years," he says. "But it
can also lead to addiction."

He says his group's next studies will examine this more unpleasant
side of the drug. Other addiction researchers will be keenly
interested in the results, because this cannibinoid acts so
differently on the hippocampus than other drugs.

References
1. Jiang W., et al. J. Clin. Invest., (published online) doi:
10.1172/JCI25509(2005). | PubMed |




 

 

 

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