A recent study in mice identified a biological mechanism that could help determine how tobacco products could act as a gateway drug, increasing the future likelihood of drug abuse.

The study by researchers at Columbia University in New York City is the first to show that nicotine might prime the brain to enhance the behavioral effects of cocaine, according to the National Institute on Drug Abuse (NIDA), part of the National Institute on Health.

The gateway drug model is based on epidemiological evidence that most unauthorized drug users report use of tobacco products or alcohol prior to illicit drug use. The model has generated significant controversy over the years about whether or not prior drug exposure to nicotine, alcohol, or marijuana is related to later drug use.

The new study in mice found that nicotine exposure could increase vulnerability to illicit drug abuse.

The study took mice and exposed them to nicotine in their drinking water for at least 7 days, in turn the mice exposed to nicotine showed an increased response to cocaine.

The study found that nicotine – which is one of the most commonly used addictive drugs in the U.S. – could alter the mice’s genetics and their responsive to cocaine.

The effect depended on a previously unrecognized effect of nicotine on gene expression. Nicotine changes the structure of the DNA molecule and reprograms the expression pattern of specific genes, in particular the FosB gene that has been related to addiction, ultimately altering the behavioral response to cocaine.

The findings in mice suggest that if nicotine has similar effects in humans, changing their DNA structure, changing their expression pattern in specific genes related to addiction, and altering their response to cocaine, then effective smoking prevention efforts would not only prevent the negative health consequences associated with smoking but could also decrease the possible risk of addiction to cocaine and possibly other illicit drug use.

"Now that we have a mouse model of the actions of nicotine as a gateway drug this will allow us to explore the molecular mechanisms by which alcohol and marijuana might act as gateway drugs," said Eric Kandel, M.D., of Columbia University Medical Center and a senior author of the study. "In particular, we would be interested in knowing if there is a single, common mechanism for all gateway drugs or if each drug utilizes a distinct mechanism."