learned to expect a dose after a light flashed. The timid bLR rats learned to accept cocaine daily.

After the rats were addicted to cocaine, the bHR group exhibited the same levels of D2 as bLRs. After a month of abstinence, bHRs relapsed into addictive behavior after receiving a cocaine injection.

Meanwhile, the bLR rats showed no signs of drug dependence and never relapsed after a period of abstinence.

Flagel and her team noted the “addiction-resilient” rats began the experiment with lower levels of genetic information needed for making FGF2, a molecule that regulates stem cell homeostasis. They felt this might help protect the rats from becoming addicted.

In specially-bred rats, this experiment is the first time researchers have determined that addiction is linked to differences in gene expression in specific molecules. Flagel hopes her experiment could help people understand and sympathize with people currently addicted to drugs.

“I do these studies in terms of helping the greater good. This is just further evidence that addiction is a disease, it has a neurobiological basis and a component like many other illnesses and diseases,” Flagel said.