Understanding the brain in relation to addictive substances

New research published in the American Journal of Psychiatry is furthering our understanding of what happens in the brain in relation to heavy cocaine use and possibly other addictive substances.

Dr. Clifford Cassidy
Dr. Clifford Cassidy

Dr. Clifford Cassidy, a scientist at The Royal’s Institute of Mental Health Research (IMHR) and his team used neuromelanin-sensitive MRI (NM-MRI) to investigate dopamine function in the human brain. Neuromelanin can serve as a non-invasive proxy measure of dopamine function and integrity.
Dopamine is a neurotransmitter in the brain that plays a powerful role in regulating how rewards (i.e. pleasurable feelings) associated with things like food, sex, and substance use, are reinforced. Significant changes in the dopamine system are observed during the development of addiction that track the individual’s loss of control over the use of substances such as cocaine.
“The benefit of this method is that it’s a simple way to track imbalance in the dopamine system in addiction,” says Cassidy. “This new method is more accessible than the more standard neuroimaging tools used to examine the dopamine system.”
These latest findings could eventually inform strategies for drug treatment. It could also be a marker of risk for addiction. It’s something that Cassidy would like to investigate further.

The research project, titled “Evidence for dopamine abnormalities in the substantia nigra in cocaine addiction revealed by neuromelanin-sensitive MRI,” was a collaboration with Columbia University.

Dopamine imbalance in addiction is one of the most well-established biological findings in psychiatry.
“[These studies] have been replicated many times, it is clear that there is less dopamine release and fewer dopamine receptors in people with every kind of addiction,” he explains. “The reason we care so much about chemical imbalances in psychiatric disorders is because we can treat them with drugs. But despite the evidence of low dopamine, there’s no evidence that drugs that mimic the actions of dopamine in the body are useful for any addiction. It makes you wonder why that is.”
Cassidy’s team discovered that individuals who use cocaine heavily have an “altered signal” in a specific part of their brains where dopamine cells are located. “We can understand something about dopamine imbalance in these people from that signal,” says Cassidy.
One interpretation of the findings is that it may be that there’s not too little dopamine in people with addiction, but that the dopamine is in the wrong place.
“These chemicals have to be trafficked from one area to another, some of them are floating around freely, some of them are packaged in preparation to serve their function as neurotransmitters. The previous evidence suggests there is too little of this packaged dopamine while our new evidence suggests that this may be because too much dopamine is stuck in the free floating pool.”
The research team chose to study the effects of cocaine instead of other substances because it acts directly on the dopamine system.
Whether chronic cocaine use causes the altered signal or not requires more research.

“Our work can help to refine our understanding of how the dopamine system is changed in people with addiction, perhaps it is not simply too much or too little dopamine. A more subtle understanding of this question could help us come up with better strategies to treat addiction.”