Cannabinoid injections sprout new neurons in mice.

Published online: 13 October 2005
doi:10.1038/news051010-12

Marijuana may make your brain grow

Cannabinoid injections sprout new neurons in mice.
Geoff Brumfiel

One synthetic cannibinoid has the same effect on part of the
brain as antidepressants.

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.

It makes marijuana look more like an antidepressant and less
like a drug of abuse.

Amelia Eisch
University of Texas Southwestern Medical Centre, Dallas


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