Scientists have found why some people are unable to get rid of their tobacco addiction, thus opening the door for new anti-smoking treatments.
A team at the Scripps Research Institute has identified a brain pathway which when defective leads to an uncontrollable desire to smoke, reports the Scotsman.
It involves a component, or 'subunit', of a receptor protein sensitive to nicotine.
Normally, the pathway dampens the urge to consume more nicotine when levels of the drug become critical. However, in some the mechanism is faulty, causing them to become hooked on tobacco.
"If the pathway isn't functioning properly, you simply take more," said lead researcher Christie Fowler.
"Our data may explain recent human data showing that individuals with genetic variation in the alpha5 nicotinic receptor subunit are far more vulnerable to the addictive properties of nicotine, and far more likely to develop smoking-associated diseases," said Fowler.
The scientists carried out tests on animals with a genetic mutation that leaves them without the receptor subunit. They found that the animals consumed far more nicotine than normal.
Major addictive component of tobacco smoke- Nicotine-acts in the brain by stimulating proteins called nicotinic acetylcholine receptors (nAChRs).
The nAChRs are made up of different types of subunits, one of which is alpha5.
When the subunit was 'knocked out' in mutant mice and rats, the animals were much more determined to seek out higher doses of nicotine. Animals with unaltered alpha5 showed more restraint.
The findings were reported in the journal Nature.