- NEW YORK (Reuters Health)
- New research hints at why it's so hard to quit smoking. In a mouse study,
Pennsylvania researchers found that nicotine affects the brain through
the same mechanism as heroin and other opiate drugs.
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- What's more, when nicotine-addicted mice were placed
in the same cage where they had received nicotine before, the same signals
in the brain were set off as when mice were actually given nicotine --
showing that certain cues reinforce the addiction.
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- But a drug that reverses the effects of narcotic drugs
blocked both the effect of nicotine in the brain and the similar effect
set off when mice were in the cage they associated with nicotine.
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- Anyone who has tried to quit smoking knows that nicotine
is extremely addictive, and that certain situations trigger the desire
to smoke.
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- Part of nicotine's hold on smokers is believed to be
due to its effect on brain levels of dopamine, which is associated with
feelings of well-being. But there is evidence from several studies that
nicotine also causes a rise in levels of opioids -- naturally occurring
chemicals that are similar to opiate drugs.
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- Now, Dr. Julie A. Blendy and colleagues at the University
of Pennsylvania in Philadelphia indeed found that nicotine affects the
brain pathway activated by heroin and other opiate drugs, at least in mice.
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- In the experiments, mice that were given nicotine showed
a rise in levels of a protein called CREB. This protein is thought to be
involved in the brain's response to many drugs of abuse.
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- But levels of this protein rose not only when mice were
given nicotine but also when they were in placed in a location where they
had previously received nicotine, Blendy and her colleagues report in the
journal Neuron.
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- These effects were absent in mice that lacked opioid
receptors, which respond to the body's natural painkillers as well as to
drugs such as heroin and morphine.
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- A single dose of the drug naloxone, which reverses the
effect of heroin and other similar drugs, blocked both responses -- to
nicotine and to being in a place associated with nicotine.
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- The results raise the possibility of using opioid-blocking
drugs to treat nicotine addiction.
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- In past studies, opioid-blocking drugs have not been
effective at helping people quit smoking. But Blendy and her colleagues
note that these studies were carried out in hospitals or in labs, not in
places where people normally light up. It might make more sense, according
to the researchers, to study the effects of these drugs when taken just
before people are placed in situations when they may be tempted to smoke.
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- SOURCE: Neuron, June 16, 2005.
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