Nicotine withdrawal might take over your
body, but it doesn't take over your brain. The symptoms of nicotine withdrawal
are driven by a very specific group of neurons within a very specific brain
region, according to a report in Current Biology, a Cell Press
Although caution is warranted, the researchers
say, the findings in mice suggest that therapies directed at this group of
neurons might one day help people quit smoking.
"We were surprised to find that one
population of neurons within a single brain region could actually control
physical nicotine withdrawal behaviours," says Andrew Tapper of the
Brudnick Neuropsychiatric Research Institute at the University of Massachusetts
Tapper and his colleagues first obtained
mice addicted to nicotine by delivering the drug to mice in their water for a
period of 6 weeks.
Then they took the nicotine away. The mice
started scratching and shaking in the way a dog does when it is wet. Close
examination of the animals' brains revealed abnormally increased activity in
neurons within a single region known as the interpeduncular nucleus.
Molecular targets of nicotine
When the researchers artificially
activated those neurons with light, animals showed behaviours that looked like
nicotine withdrawal, whether they had been exposed to the drug or not. The
reverse was also true: treatments that lowered activity in those neurons
alleviated nicotine withdrawal symptoms.
That the interpeduncular nucleus might
play such a role in withdrawal from nicotine makes sense because the region
receives connections from other areas of the brain involved in nicotine use and
response, as well as feelings of anxiety.
The interpeduncular nucleus is also
densely packed with nicotinic acetylcholine receptors that are the molecular
targets of nicotine.
It is much less clear whether the findings
related to nicotine will be relevant to other forms of addiction, but there are
some hints that they may.
"Smoking is highly prevalent in
people with other substance-use disorders, suggesting a potential interaction
between nicotine and other drugs of abuse," Tapper says. "In
addition, naturally occurring mutations in genes encoding the nicotinic
receptor subunits that are found in the interpeduncular nucleus have been
associated with drug and alcohol dependence."