- In the stoner stereotype, pot smokers and dying brain
cells go hand in hand. However, new research suggests the situation may
be more uplifting than that. A drug that functions as concentrated marijuana
does may spur neurogenesis, the process by which the brain gives birth
to new nerve cells.
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- Previous research had suggested that neurogenesis happens
only in select locations in the brain, such as the hippocampus, a region
involved in learning and memory. Some studies have shown that this process
is inhibited by most illicit drugs, such as cocaine, heroin, and methamphetamine.
However, says Xia Zhang of the University of Saskatchewan in Saskatoon,
marijuanas effect on neurogenesis has not been clear.
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- He and his colleagues started investigating this mystery
by searching cell surfaces in live, cultured slices of rat hippocampus
for receptors that respond to marijuana and a few other similar drugs,
called cannabinoids. They reasoned that if marijuana affected neurogenesis
in the hippocampus, then cells in that area must have a way to recognize
the drug. Sure enough, 95 percent of hippocampus cells responsible for
neurogenesis showed evidence of cannabinoid 1 (CB1) receptors, one of two
receptors that respond to cannabinoid drugs.
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- Next, Zhangs team incubated samples of rat hippocampus
with a solution containing HU210, a drug that stimulates CB1 receptors
with a strength 100 times greater than that of pot. Other rat-hippocampus
cells were incubated with the same solution minus the drug or with AM281,
a drug that blocks CB1 receptors. After 2 days, the researchers found a
significant increase in the number of new brain cells in the samples incubated
with HU210, but no significant increase of such cells in the other samples.
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- Finally, the researchers injected adult rats with various
doses of HU210. A single high-dose injection seemed to make no significant
difference in the number of new nerve cells. However, animals injected
with high daily doses of the drug over the course of 2 weeks had about
30 percent more newborn nerve cells than did rats given AM281 or a solution
without either drug.
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- Animals given the 2-week course of HU210 also showed
less anxiety and depressionlike behavior than did rats not given the drug.
When the researchers irradiated the rats hippocampi with X rays, which
kill off new neurons, animals given HU210 responded to these tests much
as did animals that didnt receive the drug. These results suggest that,
while these new neurons probably dont increase intelligence, they could
be responsible for antianxiety and antidepressive effects, says Zhang.
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- He and his team report their findings in the November
Journal of Clinical Investigation.
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- While data suggesting that cannabinoid drugs can accelerate
neurogenesis are "interesting and potentially promising," its
too early to tell whether high doses of marijuana over long periods have
a similar effect on depression and anxiety in people, says Ron Duman, a
neuroscientist at Yale University. "There is very little clinical
evidence demonstrating that cannabinoid administration produces an antidepressant
response," he says.
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