Study: PET imaging shows fewer dopamine receptors in drug addicts

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A PET imaging protocol that visualizes the activity of the brain's reward circuitry has been developed and will help in determining what treatment strategies might be most effective in individuals addicted to drugs, according to a presentation at the American Society for Biochemistry and Molecular Biology's annual meeting, a part of the Experimental Biology 2010 conference on Monday April 26 in Anaheim, Calif.

Joanna Fowler, PhD, senior scientist at the U.S. Department of Energy's Brookhaven National Laboratory in Upton N.Y. and her colleague, Gene-Jack Wang, MD, senior scientist at Brookhaven, along with Nora D. Volkow, MD, director of the National Institute on Drug Abuse in Bethesda, Md., combined PET with radioactive tracers that bind to dopamine receptors. The PET scan highlights the movement of the tracers in the brain, and was used to reconstruct real-time 3D images of the dopamine system in action.

The researchers performed PET scans 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 subjects and thus cannot bind to a lot of the dopamine released in response to the drugs or natural reinforcers like food.

"These addicted individuals all had a blunted dopamine response," noted Fowler. "This reinforces the idea that drug addicts experience diminished feelings of pleasure, which drives their continual drug use."

Fowler added that the study looked at multiple recreational drugs and found similar results. "[W]hile 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."

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.