Researchers from the University of Michigan Medical School identified several genetic markers that may determine one’s vulnerability to cocaine addiction and relapse. The researchers assert that their study, published on April 25 in the Proceedings of the National Academy of Sciences, was only done on rats and cannot explain all the factors of human addiction, but this shows that addiction stems from genes and brain changes.

Initially, the research team observed the rat’s genetic instructions needed to make the pleasure receptor called D2. D2 enables the brain cells to receive signals sent by using cocaine and the neurotransmitter dopamine.

Those rats that are more predisposed to addiction had lower D2 genetic instruction levels. The researchers explain that the animals’ low D2 levels are caused by the presence of a DNA tag called an epigenetic marker or H3K9me3.

cocaine addiction

In these images of rat brains, differences in gene expression of genes for fibroblast growth factor 2 (FGF2, top set) and dopamine 2 receptor (D2, bottom sett) can be seen in rats of two breeds before (left) and after (right) cocaine exposure. The addiction-prone bHR rats differed significantly in several ways from the timid bLR rats. Credit: Flagel Lab, University of Michigan

However, when the addiction-prone rats became addicted to cocaine, their D2 levels became similar with those of rats less prone to addiction. One week after the researchers stopped administering cocaine, the rats with the epigenetic tag were more likely to experience relapse.

On the other hand, those rats less vulnerable to addiction had lower levels needed to make the gene FGF2, which has been known to play a part in addiction. The addiction-resilient rats were also more likely to carry the epigenetic tag that kept them from reading the addiction gene.

Nevertheless, the results have been limited to rats so these do not necessarily explain human addiction. Still, the researchers believe that their study could support further explorations on drug addiction.

“It is likely that the propensity to seek drugs and become addicted to them involves numerous genes,” says senior author Huda Akil. “Moreover, factors beyond novelty-seeking including stress and depression can lead to substance use in some individuals.”

The research team is currently employing broad-based genotyping to determine other genes that encourage drug addiction.  The results of this investigation could pave the way for targeted drug abuse and addiction treatment strategies.