BY LAUREL HAMERS
Using opioids gives some brain cells a
call to action.
Opioid addicts’ brains, examined after
death, contained about 50 percent more
nerve cells that release a molecule called
hypocretin compared with brains of people who didn’t use the drugs, a study finds.
Giving morphine to mice induced similar
changes in their brains. Once-dormant
nerve cells, or neurons, appear to rev up
their hypocretin machinery in response
to the drugs, researchers report in the
June 27 Science Translational Medicine.
The findings fit with a growing body of
research suggesting that hypocretin — a
brain chemical that regulates wakefulness
and arousal and has been linked to narcolepsy — may be involved in addiction.
“There is extensive evidence now
that shows that the hypocretin neurons
are supporting motivated behavior
in general,” and addiction falls under
that umbrella, says Rodrigo España, a
neurobiologist at Drexel University in
Philadelphia who wasn’t involved in the
study. His lab recently showed that rats
with a weaker brain response to hypo-
cretin showed less motivation to seek
out cocaine rewards.
The new study comes from the opposite angle, showing changes in hypocretin
neurons in response to drug use. “It
does suggest the possibility that part of
the reason it’s so hard to get off drugs is
there’s this massive change in the brain,”
says UCLA neuroscientist Jerome Siegel.
Siegel and colleagues discovered hypo-
cretin’s potential link to addiction while
investigating narcolepsy. People with
the sleep disorder have about 90 percent
fewer hypocretin-producing neurons
than normal. While examining brains as
part of a narcolepsy study, Siegel’s group
got a surprise: a supposedly healthy brain
with an unexpectedly large number of
hypocretin neurons. That person had
been a heroin addict.
Now, an analysis of four more brains
from people addicted to heroin or other
opioids suggests that the elevated number of hypocretin neurons in the first
brain was not a fluke.
Addicts’ brains had 54 percent more
hypocretin-producing neurons, on average, than healthy brains, the team found.
In experiments, two weeks of receiving
morphine increased the number of active
hypocretin-producing neurons in mice’s
brains. Narcoleptic mice’s muscle weakness, a symptom of the disorder, even
reversed with morphine injections.
With proper dosing and monitoring,
opioids might be an effective treatment
for narcolepsy, Siegel says. Further testing is needed to determine whether opioids are more effective than other, less
addictive drugs for the sleep disorder. s
BODY & BRAIN
Narcolepsy molecule tied to addiction
Opioids boost a brain chemical that regulates wakefulness
www.sciencenews.org | July 21, 2018 11