Smokers will not believe this but nicotine exposure actually promotes alcohol dependence, says a research.

In lab experiments, the researchers also found that the combination of nicotine and alcohol activated a unique group of neurons, giving positive reinforcement to continue alcohol and nicotine use.

"It is a vicious cycle. Nicotine makes individuals crave alcohol to ‘reward’ the brain and reduce stress," said biologist and senior study author Oliver George from California-based The Scripps Research Institute (TSRI).

The team tested whether nicotine exposure could affect alcohol-drinking behaviour in two groups of male rats. Both groups were given access to alcohol to establish the baseline of how much they would drink.

After this, they used alcohol vapour to induce alcohol dependence in one group of rats. Dependence developed in about two months.

The second group of rats were exposed to both nicotine and alcohol vapour. These rats developed alcohol dependence much faster – and they began drinking the equivalent of a six-pack in just three weeks.

"We had never seen such a rapid escalation of alcohol drinking before," George noted. The researchers then offered the rats alcohol with the bitter compound quinine.

Most rats decreased their alcohol consumption to avoid the bitter taste, but the nicotine-exposed rats just kept drinking. This indicated that their behaviour was compulsive, much like alcoholism in humans.

Nicotine activates certain "reward" neurons in the brain — giving positive reinforcement to keep smoking. At the same time, nicotine activates "stress" neurons in the brain, giving negative reinforcement.

This stress can lead individuals to crave alcohol to both activate the reward system and calm the stress system.

"The compulsive alcohol consumption and neurological pathways seen in the new study suggest that alcohol works with nicotine to further activate the brain’s reward system and dampen the stress of nicotine exposure," the authors concluded.

The paper appeared in the Journal of Neuroscience.