Can alcohol be a gateway drug? Well, according to a new study from Columbia University's Mailman School of Public health, early exposure to alcohol can increase the likelihood that someone will develop an addiction to cocaine later in life.
This is problematic because it's common for adolescents to experiment with alcohol during the teen years. The study at Columbia showed that mice who were exposed to alcohol had chemical changes in their brain. These changes led to disruption in gene expression. Genes in the brain's reward centers allowed the mice to develop drug-seeking behavior.
The researchers worked from known statistics on cocaine addiction. Currently, the CDC estimates that about 21% of those who experiment with cocaine will become addicted to it. That means that most who try it will not have an issue, so the team at Columbia wondered what it was that caused that 21% to go on to have a problem. Two substances that most cocaine users have been exposed to are nicotine and alcohol. In the study, the mice who were "primed" with either substance and then had cocaine available were much more likely to keep going for the cocaine with a fierce determination.
The study began with exposing the mice to alcohol in their water bottles for two hours per day over an 11 day period. After that, cocaine was made available at different intervals over a 32 day period. Getting the cocaine required the mice to push a lever. As the study went on, more effort was needed to get a cocaine-laced food pellet. The mice who had been exposed to alcohol continued to do the work required to get the cocaine. These mice pressed the lever an average of 563 times, compared to the sober mice who only pressed it about 310 times.
Eventually, the researchers ended the access to cocaine, meaning even if the mice pressed the correct lever, they would not get any of the drugs. Eventually, some of the mice figured out that the party was over and stopped pressing the lever. To add another layer to the study, after the cocaine was no longer available, pressing the lever would earn a mouse a small electrical shock. The current increased and at the end of the study only about 15% of the sober mice were continuing to press the lever after being zapped. In the mice who had been given alcohol, 29% of them continued to seek the cocaine by pushing the lever, even when the maximum electrical current in the shock had been reached.
The behavior of the mice was not the only finding of the study. On examination, the brains of the mice that had been exposed to alcohol had chemical differences in the nucleus accumbens, a region of the brain involved in reward behavior. The changes happened in the epigenome of the brain, in effect, changing the genetic expression via the neurotransmitting chemical messaging system that controls rewards.
The work mirrored earlier research by the same group who had looked at the use of nicotine, conducting a similar study with mice. The chemical changes in the brains of mice exposed to nicotine, the addictive ingredient in cigarettes,where the same type that had happened in the study using alcohol.
Denise Kandel, PhD, professor of Sociomedical Sciences at the Mailman School of Public Health and research scientist at the New York State Psychiatric Institute and a co-author on the study explained, "The findings demonstrate how an early exposure to a drug like alcohol can increase a person's vulnerability to developing an addiction to cocaine and other drugs. Our research further indicates the importance of targeting intervention programs in earlier stages of development – adolescence and young adulthood. Since alcohol and nicotine use take place before cocaine use in adolescence and early adulthood you have to begin studying these early developmental stages." Take a look at this video from the team at Columbia to hear more about this research.