Don’t Give Your Rat a Drink Before Giving Him Cocaine

A study shows how compulsive cocaine use is caused: the breakdown of key proteins in the brain, which can be caused by alcohol

A razor blade divides the contents of a five-dollar vile of crack, Bronx, New York, 1989.
Mark Lennihan / AP

If you’re going to give your rat cocaine, don’t make him drunk or smoke beforehand. Science has discovered that an alcohol habit enhances the propensity to become addicted to cocaine. At least in rodents. Specifically, giving rats alcohol for 10 days before giving them cocaine enhanced their addictive tendency, an American-Swedish study shows.

It appears that like many a human, rats really like coke. Alcohol-addled rodents would even continue to paw for cocaine despite receiving electric shocks when they did so, the researchers say. Rats not inebriated before the coke didn’t do that.

Alcohol and cigarettes seem to affect the brain in similar ways: Both increase the likelihood that cocaine use will become compulsive.

The problem apparently lies in the brain region involved in reward-based memory, the nucleus accumbens (which just means in Latin the nucleus next to the septum). Alcohol leads certain proteins there to break down, the scientists say.

It has been discovered before that cocaine addiction is sometimes preceded by other habits, from cigarettes to marijuana to alcohol. Cause and effect are another kettle of rats, though. Are smokers or drinkers more likely to try cocaine because their personalities are like that, or do so-called gateway drugs have a biochemical effect?

At this point, it appears that about 21 percent of cocaine users progress to compulsive use, the researchers say. It is therefore commonly thought that both environmental and hereditary factors play roles in addiction to coke, they add.

While alcohol made the rats somehow more susceptible to compulsive coke use, the converse was not found. A cocaine habit didn’t make the rats more likely to drink alcohol. Intuitively, perhaps that may not be surprising.

The teams evaluated cocaine-seeking behaviors in three groups of rats. One had been imbibing alcohol for 10 days before receiving cocaine. One was given coke and alcohol concurrently. The third group had never been exposed to the demon drink.

Rats with longer-term prior alcohol exposure were more persistent in seeking cocaine, the researchers state.

The numbers tell it all. Rats exposed to long-term alcohol pressed the legendary lever to get cocaine 58 times on average during a period of the experiment when no drugs were released to the rodents. Rats with no alcohol exposure were evidently less stressed about it, pressing the lever 18 times on average.

Why would long-term alcohol use have this effect? Well, the researchers discovered that alcohol exacerbated the degradation of two proteins in the rats’ brains (histone deacetylases 4 and 5). The breakdown of these proteins creates a permissive environment for cocaine-induced gene expression, they explain.

They say this protein discovery indicates that alcohol and nicotine act through similar molecular mechanisms to increase vulnerability to cocaine.