New Study Refutes Role of Dopamine in Cocaine Addiction

Scientists have long struggled with the mystery behind why some are more vulnerable to cocaine abuse than others. Finally, new research might offer some insight.

A research team from the University of Geneva (UNIGE) investigated the complicated relationship between one’s personality and brain chemistry. More specifically, the university researchers wanted to focus on the role of impulsivity and how dopamine production might work together to shape the threat of cocaine abuse in a given individual.

The researchers published their findings in the January edition of eNeuro, and revealed new data that might better explain individual vulnerabilities to drug abuse. The scientists suggest that their results could inform the development of more targeted interventions for at-risk individuals.

“Our study reveals that dopamine synthesis does not predict impulsivity or vulnerability to cocaine, nor is it affected by chronic drug exposure,” the authors wrote. “Our results suggest that the heightened presynaptic function underlying impulsivity and the cocaine-induced tolerance to drugs depend on alternative mechanisms to dopamine synthesis, such as those controlling dopamine reactivity to stimulation and dopamine reuptake.”

Exploring the Origins Of Cocaine Addiction

Scientists have long since established that drug consumption produces a surge in dopamine production. It’s that rush of dopamine that produces the “high.”

Similarly, repeated drug use leads to diminishing returns. The dopamine surges taper off, which can lead to more drug consumption. This cycle can vary between individuals. Some appear to be more vulnerable to the addictive high. Others seem to be immune to it.

To shed some light on these disparities, the UNIGE researchers, led by Associate Professor Nathalie Ginovart and PhD student Ginna Paola Urueña-Méndez, examined two groups of rats. One group consisted of impulsive specimens, while the other group included less impulsive rats. The team trained the rats to self-administer cocaine at a high enough dose to “trigger dopamine neuroadaptations without harming their health.”

To start, the scientists trained the animals in a gambling task to measure a pair of impulsive behaviors:

• Impulsive action, marked by an inability to control automatic actions.
• And risky decision-making, defined by embracing greater risk during decision-making.

Scientists then measured the level of dopamine synthesis using a non-invasive neuroimaging technique before and after cocaine intake in both groups. The scientists found that impulsive action, not risky decision-making, forecasted “a greater number of cocaine injections and faster cocaine use.”

A Notable Difference Emerges

The researchers identified no difference in the rats’ ability to produce dopamine between the highly impulsive and less impulsive animals.

“In other words, impulsivity and vulnerability to cocaine abuse might not be linked to dopamine production, but to mechanisms controlling its release,’’ Urueña-Méndez explained.

The team then took a closer look at the impact of repeated cocaine use on the animals.

‘‘Until now, the idea that regular cocaine consumption could reduce the ability to produce dopamine was accepted,” Ginovart added. “Our results contradict this assumption as both populations of rats retained the same capacity to produce dopamine, despite chronic consumption.”

Other Factors At Play?

Based on these results, the researchers hint that “dopamine synthesis is probably not the main driver of impulsivity or vulnerability to cocaine use.” These results also appear to counter the prevailing theory that cocaine use might directly hinder dopamine production.

Consequently, this research suggests a new approach to drug treatment might be possible.

“This variation in vulnerability could be linked to differences in the relative reactivity of dopaminergic neurons, so that certain stimuli, including drugs, are more salient for more impulsive animals,’’ the researchers wrote.

Further Reading

Prescription Opioid Use and Motivations for Misuse Among US Adults

Substance Use Before Suicide Attempts

Anger and Impulsivity Among Adolescents