Study opens door for anti-smoking drug
Paris - Scientists have pinpointed a source of nicotine craving in the brain, opening up a new path towards drug treatments to help smokers kick their habit.
A study released on Sunday show that tobacco killed more than five million people every year and accounts for nearly one-in-10 adult deaths, 90% of them due to lung cancer.
In experiments with mice and rats, the researchers mapped the functioning of a gene called CHRNA5 that has been previously fingered in nicotine addiction.
The gene controls a receptor - an entry point on the surface of brain cells - which responds to nicotine molecules.
With a normal version of this gene, anything more than a tiny dose of nicotine triggers a message to the brain which says, in effect, "stop consuming," the scientists found.
Larger doses unleash a sense of repulsion, similar to "bad-tasting food or drink," lead researcher Paul Kenny at the Scripps Research Institute in Florida said in an e-mail exchange.
But the effect was quite different in mice in which a tiny sub-unit of the receptor, known as alpha5, had been knocked out.
The negative message was never sent - and as a result, the rodents couldn't get enough of the potent drug.
A similar scenario occurs naturally in some humans, the researchers believe.
Genome-wide screening studies have identified genetic alterations which impair the alpha5 unit's functioning.
Between 30 and 35% of the population in the United States is thought to have a form of the CHRNA5 gene that encourages unbridled nicotine craving.
"Our data probably explain the fact that individuals with this genetic variation have increased vulnerability to developing tobacco addiction," Kenny said.
"They are likely to be far less sensitive to the averse properties of the drug, and are thus more likely to acquire a nicotine habit."