What scientists learned about addiction by giving rats cocaine

A new study of laboratory rats given cocaine is shedding new light on the cognition of addiction.

Identifying populations vulnerable to substance use disorder is a growing focus for prevention strategies, yet scientists have long struggled to understand why some people develop disorders while others do not.

The focus of this latest round of research was aversive cues, the unpleasant experiences that often accompany the consumption of addictive substances. These include but are not limited to bitter taste, smoke inhalation and needle use.

Researchers say the initial reaction to these experiences can help determine an individual’s susceptibility to addiction.

“Aversive cues matter from the first exposure,” said study author and University of Texas at El Paso biologist Travis Moschak, Ph.D. He explained that while previous studies have explored the link between aversive cues and drug use, this is the first to study them as a paired experience from the first instance of drug use.

In the new study, published Wednesday in the journal Drug and Alcohol Dependence, nearly 30 lab rats were given the opportunity to self-administer small doses of cocaine by sticking their noses into a designated hole. Each hit of cocaine was preceded by a dose of bitter-tasting quinine.

Moshak and his team measured the rats’ response to this mixed positive-negative experience to assess whether their aversion to quinine outweighed the joy of a high.

Three distinct patterns emerged among the cocaine-addicted rats—and the third wasn’t what they expected.

One group expressed a strong aversion to quinine and stopped taking cocaine altogether. Moshak compares this response to a person who tries a drug, has a negative experience, and never does it again.

A second group started with low shock doses before gradually increasing their intake, suggesting that quinine’s bitterness wasn’t enough of a deterrent to get them to stop. The sweet high was worth the bitter evil, so to speak.

A third surprise group started with heavy cocaine use that gradually tapered off.

“The third group surprised us,” Moschak said. “They seemed to have overindulged and the combination of too much cocaine and a very aversive stimulus took over.”

Moschak said these findings may help explain why some individuals develop patterns of addiction.

He added that future research will focus on brain regions activated during the paired experience of drugs and aversive cues. He hopes this information will help his team and others better understand the genetic and biological differences that inform substance use and abuse.

Cocaine deaths soared in 2022 – increasing by more than 12% in just one year.

“This is a fascinating study with great potential to help us better understand and treat drug abuse in humans,” said Robert Kirken, Ph.D., dean of the College of Science. “With further study, this research could lead to better ways to prevent and treat addiction.”

If you’re curious about where the rodents got their nose candy, it was procured through the National Institute on Drug Abuse’s Drug Supply Program, which supplies restricted substances for research purposes. At the conclusion of the study, the revived rats were weaned off the cocaine and were, according to the team, unharmed by the experience.