Marijuana munchies are all in the brain,
U.S. study finds
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[February 19, 2015]
By Sharon Begley
NEW YORK (Reuters) - If recent laws
legalizing marijuana in more U.S. states also boost sales of potato
chips and brownies, scientists will know why: A study in mice published
on Wednesday found, unexpectedly, that the active ingredients in pot
essentially make appetite-curbing regions of the brain reverse
functions.
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When that happens, neurons that ordinarily transmit a signal that
means, "you're full, stop eating," instead give the brain the
munchies, neurobiologists reported in the journal Nature.
The fact that smoking marijuana makes users crave salty, crunchy or
sweet snacks has long been enshrined in popular lore and comedy. But
how that happens has been a scientific enigma.
One idea had involved heightened sensory perception. A 2014 study by
neuroscientists in Europe, for instance, found that the active
ingredients in marijuana, cannabinoids, affect the olfactory center
in the brains of mice. As a result, the animals better smell food,
which can stimulate appetite.
But that didn't explain the marijuana-fueled appeal of foods without
much aroma.
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In their study, scientists led by Tamas Horvath of Yale University
focused on molecules called receptors that cannabinoids bind to and
activate in the brains of both mice and men. They expected to find
that when cannabinoids did so, the receptors sent out a signal
quieting nearby neurons that suppress appetite. That could lead to
the munchies.
To their surprise, Horvath said, they found that activating the
cannabinoid receptors in mice's brains instead increased, not
decreased, the activity of appetite-suppressing neurons.
The reason that did not suppress appetite was that the neurons,
instead of emitting their usual appetite-killing neurochemicals,
emitted completely different ones. Called endorphins, they traveled
to the brain's appetite-control region, the hypothalamus,
stimulating the mice's desire to eat.
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"Neurons that normally shut down eating instead promoted it, even
when the mice were full," Horvath said in an interview. "Marijuana
fools the brain's feeding system."
It does not fool the brain into eating just anything, however.
Smoking marijuana rarely leads to a craving for broccoli. Instead,
he said, the brain mechanisms create a desire for calorie-dense
foods like salty, fatty chips and rich sweets.
There are likely additional brain pathways by which marijuana causes
the munchies, which could be tapped for one of the drug's medical
uses: increasing appetite in cancer patients and others who have
lost the desire to eat.
(Reporting by Sharon Begley; Editing by Cynthia Osterman)
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