Genetically-altered mice may be able to resist one of the addictive effects of tobacco, suggests research.

A team from the Institute of Psychiatry in London is unlocking the reasons why nicotine is rated as one of the most addictive chemicals.

Its research comes as another leading expert warned a European conference about an impending world cancer catastrophe caused by smoking.

Professor Julian Peto, from the Institute of Cancer Research in Surrey, said that death rates were set to increase tenfold unless more people were persuaded to give up smoking.

The Institute of Psychiatry research, presented at a seminar on smoking at the ECCO Conference in Lisbon, could one day contribute to drugs or treatments aimed at weaning hardened smokers away from the habit.

Professor Ian Stolerman, leading the team has, since the 1970s, been carrying out animal experiments to test the effects of nicotine on the brain.

Blocking the buzz

He has identified "receptors" on brain cells which appear to be key to the "head-rush" felt by smokers.

These role of these receptors, called alpha-4 beta-2, were identified using rats and mice which had been trained to respond when they felt the effects of a nicotine injection.

The team found that when they used drugs which "blocked" these particular receptors, the response to nicotine was muted.

However, in mice which had been altered so that the gene needed to make the receptors was missing, then this response was even less.

There was still some response, suggesting the presence of other types of nicotine receptor, but showed that this particular receptor plays is of primary importance.

Professor Stolerman said: "This is the best evidence to date for the involvement of the beta-2 receptors in the response to this substance."

However, he said it could be five years before the role of all the receptors was understood - pointing to a long wait before gene technology could boost anti-smoking therapies.

The research also adds weight to the theory that susceptability to smoking addiction may have a heriditary root.

Timebomb of disease

Professor Peto told the meeting that while lung cancer deaths had fallen sharply in the UK over the past few decades, other countries had yet to approach the peak in smoking-related deaths.

Because a lifetime of smoking is needed to kill - even giving up in middle age is highly beneficial - countries where smoking was still growing faced a huge upsurge in disease over the next century.

During the entire 20th century, there were approximately 100m smoking-related deaths worldwide.

However, he said this would grow quickly, with 150m just in the next quarter-century, and 500m between 2050 and 2100, unless smoking rates were drastically cut.

"These statistics are very very depressing for people such as myself," he said.