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Scientists find that nicotine use promotes alcohol dependence

Posted April 16, 2015

It has been noticed that there is a connection between bad habit of smoking and consuming alcohol long ago. But now team of scientists at The Scripps Research Institute have described this relation. They found that nicotine use increases compulsive alcohol consumption. Furthermore, smokers have a five to ten times greater risk of developing alcohol dependence than non-smokers.

It is difficult for smokers to quit drinking, and vice versa, because nicotine creates craving for alcohol as a reward and alcohol reliefs stress. Image credit: Kelly via Wikimedia, Public Domain

It is difficult for smokers to quit drinking, and vice versa, because nicotine creates craving for alcohol as a reward and alcohol reliefs stress. Image credit: Kelly via Wikimedia, Public Domain

Question whether smokers have a greater tendency toward addiction in general or does nicotine somehow reinforce alcohol consumption was puzzling scientists for quite some time. Now scientists did some research with rat models and found out that nicotine exposure actually promotes alcohol dependence. Biologist Olivier George, who was leading the study, described this as a “vicious cycle”. Nicotine creates craving for alcohol as a reward and stress relieving substance

In an earlier study scientists discovered that the combination of nicotine and alcohol activates a unique group of neurons, giving positive reinforcement to continue alcohol and nicotine use.  It was already known how addiction for these habits is created, but it is new that addiction is stronger when both substances are used in combination. Methodology of this new study was pretty simple and, as usual, rats were used to conduct the experiment.

Scientists started with two groups of male rats. At first they wanted to test whether nicotine exposure could affect alcohol-drinking behaviour in rat models. At first they were given alcohol just to establish the baseline of how much they would drink. The rats did drink a little bit – about the equivalent of one or two beers for a human. They stopped before showing any signs of drunkenness. Then scientists spent two months inducing alcohol addiction in one of the groups by using alcohol vapour. After dependence was developed, rats would drink equivalent of a six-pack of beer and had blood alcohol levels close to three times the legal limit for humans.

At the meantime, second group of rats was affected by both nicotine and alcohol vapour. They developed same kind of addiction in just three weeks. Such rapid acceleration of the dependence on alcohol was unexpected. Then scientists tried giving rats alcohol with the bitter compound quinine added to see if they could stop the rats from drinking. Most of the rats tried to avoid the bitter taste and consumed less alcohol. But rats affected by nicotine just kept drinking at the same levels. This indicated that their behaviour was compulsive, much like alcoholism in humans.

This can be explained through the activation of “stress” and “reward” pathways in the brain. Previous studies have shown that nicotine activates so called “reward” neurons in the brain and it gives positive reinforcement to keep smoking. However, at the same time nicotine activates “stress” neurons as well, which give negative reinforcement. It can lead individuals to crave alcohol to both activate the reward system and calm the stress system. It means that alcohol works with nicotine to activate the brain’s reward system and dampen the stress of nicotine exposure.

According to World health organization, globally individuals above 15 years of age drink on average 6.2 litres of pure alcohol per year, but different regions consume different amounts of alcohol. The worst situation in this regard is in former Soviet countries, while smallest amount of alcohol per capita is consumed in so Middle East and North Africa. Such variation is mostly dictated by different culture and religion, but alcohol problem remains one of the biggest challenges in Eastern Europe.

This newly discovered interaction may explain why it is difficult for smokers to quit drinking, and vice versa. Now, when scientists know the mechanisms involved better, they are hoping to try to find compounds that will specifically inactivate those neurons involved and help people get rid of alcohol and nicotine dependencies.

Sources: Scripps, WHO

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