Science Pick of the Week is a new column co-written by Max Enger and Frankie Lewis dedicated to analyzing science news relevant to the University of Oregon campus community.
Max Egener is an Arts & Culture writer at the Daily Emerald covering documentary films and food. He has a bachelor’s of science in environmental science from Dickinson College in Carlisle, Pennsylvania, and is a graduate student of journalism at UO. Frankie Lewis is a senior writer at the Daily Emerald covering campus culture. He is also an undergraduate biology major and anthropology minor at UO.
Many high school counselors have warned of the dangers of alcohol abuse. One of their classic arguments is that the alcohol use will lead an individual to try riskier behaviors, such as abusing highly addictive drugs like cocaine or heroin. While alcohol certainly leads to questionable decision making, no data has ever been presented that suggests alcohol could have a “gateway drug” effect.
A study published in Science Advances on Nov. 1 may display a connection between alcohol and future drug use. Researchers at Columbia University demonstrated that prior alcohol consumption by laboratory mice increased the mice’s likelihood of becoming addicted to cocaine.
Researchers created three mice groups: alcohol primed, alcohol concurrent and alcohol naive. The alcohol primed mice had voluntary access to alcohol for ten days prior to 21 days of voluntary access to cocaine injection. Alcohol concurrent mice could simultaneously access alcohol and cocaine for 31 days. The final (control) group, alcohol naive mice, had water ten days prior to voluntary access to cocaine for 21 days.
The study found that the alcohol primed mice exhibited significantly more addiction-like behaviors than the other two groups. The alcohol primed mice also demonstrated a willingness to seek out cocaine despite negative consequences. Analysis of the chemical pathways involved in the cocaine reward system in the mice’s brains found that prior alcohol use inhibits proteins involved in regulating reward responses to cocaine.
To test the mice’s level of cocaine dependence, the researchers set up a lever-pressing mechanism that automatically injected the mouse with cocaine. Once the mice had become conditioned — in other words, addicted — to the cocaine injection, they removed the injection from the mechanism, leaving just the lever. Then, they monitored how many times each group of mice tried the lever before giving up.
When the alcohol-primed mice were deprived of access to cocaine, they pushed the lever that had administered the cocaine in the first stage of the study an average of 563 times before giving up. The alcohol naive and alcohol concurrent groups pushed the lever an average of 310 times and 317 times respectively before giving up. The alcohol-primed mice showed a greater persistence and motivation for cocaine than the control groups.
In order to test whether mice in any of the groups would continue using cocaine despite negative consequences, the researchers shocked the mice’s feet when they began pushing the lever that administered the cocaine. The alcohol-primed mice showed a significantly greater resilience to each of three increasingly intense shocks than mice in the other groups. The alcohol primed mice were more willing to take negative consequences as a result of their cocaine use.
These results were also not reversible. When mice were primed with cocaine prior to alcohol using the same experimental design, they did not exhibit addiction-like behavior for alcohol. This test showed that specifically alcohol creates these conditions in the brain.
The researchers found that these groups didn’t differ in their ability to figure out the mechanism that administered the cocaine injection, and there was no difference in the sheer amount of cocaine that these groups consumed daily. In short, individuals are more likely to develop an addiction to cocaine after alcohol consumption, not more prone to trying cocaine for the first time or indulging in large doses.
While a study of this type is unlikely to ever be tried on humans for ethical reasons, it is significant because it is the first observed case of a direct “gateway drug” effect. Not only did the researchers show how previous alcohol abuse caused the mice to have a greater craving for cocaine, the alcohol primed mice displayed a clear disregard for a harmful side-effect in order to consume the drug. If the findings are expanded upon and one day applied to humans, it could change the way we think about and regulate alcohol and drug consumption.