Ana Clara Bobadilla hypothesized the experiment would go the same way it had for other researchers.
Bobadilla was giving rats cocaine in an attempt to learn more about the effect of a certain protein on their addiction. Her lab at the Medical University of South Carolina wanted to know what would happen if they gave the rats an injection after taking away the drugs while other researchers had given the rats the injection at other stages of their addiction.
But a funny thing happened: The rats did the opposite of what Bobadilla expected.
"We did the experiment again and again to make sure it wasn’t a mistake," she said.
Bobadilla was able to stop the rats from relapsing on cocaine. Though still in very early stages, the research could one day have implications for addiction treatment in people.
Rats could access the cocaine by pressing a lever; they knew the drugs would be there when there was a light and tone. But the researchers took away the drug for about 10 days. If the rodents pressed the lever during that time, nothing came out. Then came the injection of the protein called "brain-derived neurotropic factor" to a cluster of nerve cells deep in the brain that controls reward-seeking behaviors.
The researchers then turned on the cue again. Bobadilla and her team hypothesized the rats would again start pressing the levers like crazy, hoping to get more of the drug they had learned to crave. Peter Kalivas, who runs the lab at MUSC where Bobadilla works, explained this mirrors triggers in humans that can lead to relapsing on their drug of choice.
"It’s like the person who’s driving home from the bar," Kalivas said. "Well for the rats, it’s seeing this light and tone that they learned means drugs are going to be around."
But, researchers showed, the injection had the opposite effect. The rats didn't want the drug anymore, even when they got the cue they had associated with cocaine.
The MUSC's researchers' findings in the rodents don't mean a treatment for cocaine relapse in humans is necessarily on the way.
One ethics review published in 2015 estimated that upwards of 96 percent of drugs that pass animal-based and other preliminary tests never make it to the market.
But it may open an interesting line of research, and one that could be important given persistently high rates of cocaine abuse in South Carolina.
Heroin and prescription painkillers have been the focus of policymakers in the last year, as the number of deaths from overdose mount and addictions burden the health care system.
Meanwhile, law enforcement officers are seizing cocaine more than any other drug in South Carolina, according to a recent report by the Drug Enforcement Agency. The drug is smuggled from Mexico. Some is then converted to crack cocaine by local dealers.
The amount of cocaine seized in this state has been ticking up slightly for years, according to the DEA. On a nationwide scale, cocaine is the No. 2 killer among overdose deaths, and still disproportionately affects the African-American population, according to the Centers for Disease Control and Prevention.
Cocaine was an easy drug for the researchers to begin with because it is highly addictive. The researchers tried sucrose, too, but didn't see the same effect. They plan to find out more about whether their findings are specific to cocaine.
Bobadilla and Kalivas said the research is one step toward understanding how the protein they are studying affects the brain, and how it could be significant for addiction research.