Drug addiction is a complex process that involves numerous biological and environmental factors, but a central element is how the drugs affect the activity of dopamine, the chemical that regulates pleasure and reward in the brain.

To get a real-time sense of dopamine activity, Joanna Fowler and her colleague Gene-Jack Wang at Brookhaven, along with Nora Volkow, Director of the National Institute on Drug Abuse, combined positron emission tomography (PET), a medical imaging technology useful for identifying brain diseases, with special radioactive tracers that bind to dopamine receptors. The PET scan highlights the movement of the tracers in the brain, and can be used to reconstruct real-time 3D images of the dopamine system in action.

The scientists tested this procedure on several drug-addicted volunteers as well as age-matched healthy control subjects and found that people with addictions in general have 15-20 percent fewer dopamine receptors than normal and thus cannot bind to a lot of the dopamine released in response to the drugs or natural reinforcers like food.

ÒThese addicted individuals all had a blunted dopamine response,Ó noted Fowler, a senior scientist in BrookhavenÕs medical department. ÒThis reinforces the idea that drug addicts experience diminished feelings of pleasure, which drives their continual drug use.Ó

Fowler added that the study looked at multiple recreational drugs and found similar results. ÒSo, while various drugs operate by unique mechanisms, they all share a commonality in that the dopamine receptors in the brains of addicted individuals show an under-stimulated reward system.Ó

In an interesting correlation, Fowler noted that Gene-Jack Wang also used the dopamine PET scans on obese individuals and found highly similar patterns of low dopamine receptors-validating that at least in some cases, obesity can also be considered a disease of addiction.

A potential valuable application of observing dopamine activity in real-time, Fowler noted, involves not looking at addicted individuals while they use drugs, but rather when they donÕt.

ÒWe can examine individuals as they use different coping strategies to try to suppress their desires for drugs or food,Ó she said, Òand see in the scans which approach work best.Ó

ÒWe still have a lot of research to do before we fully understand why people take drugs,Ó Fowler continued, Òbut with this new PET scan application, we might help more people stop.Ó

The highlights of this study were recently presented in FowlerÕs talk, ÒImaging Brain Chemistry in Diseases of Addiction,Ó at the American Society for Biochemistry and Molecular BiologyÕs annual meeting, which took place April 26 in Anaheim, CA.