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Study Investigates Cocaine's Effect on Brain Metabolism
> 2/19/2008 1:48:50 PM

Previous research on cocaine addiction has identified the neurotransmitter dopamine, which is involved in the brain's pleasure system, as a primary factor underlying addiction to cocaine. Specifically, cocaine blocks dopamine transporters, preventing reabsorption of dopamine and creating elevated levels of dopamine in the brain. This then reinforces the perception of cocaine as a pleasurable substance. In a new study, researchers from the U.S. Department of Energy's Brookhaven National Laboratory investigated cocaine's effect on forms of brain activity, finding that cocaine may influence brain metabolism through the action of dopamine as well as through other mechanisms.

The researchers used positron emission tomography (PET) to study two groups of mice: one bred not to have dopamine transporters and a control group that had normal dopamine levels. The two groups received treatment with either cocaine or saline. Using PET scanners, the researchers were able to see concentrations of glucose in various regions throughout the brain both before and after treatment, observing the effect of cocaine on brain metabolism in dopamine-transporter deficient mice and in normal mice. Cocaine caused reductions in brain metabolism in both groups, although normal mice had more significant decreases and in various brain regions. The researchers surmise that these decreases in brain metabolism are connected to cocaine blocking dopamine transporters.

Before treatment with cocaine or saline, dopamine-transporter deficient mice displayed heightened metabolic activity in the thalamus and cerebellum, areas of the brain involved in processing sensory information, learning, and motor functions, and dopamine may play an important role in regulating glucose levels in these regions. The PET scans revealed that after receiving cocaine, dopamine-transporter deficient mice had reduced metabolic activity primarily in the thalamus, an indication that cocaine affected metabolic activity in this area via another neurotransmitter, such as norepinephrine or serotonin.

While the results of this study add new evidence of dopamine's role in cocaine addiction, and of its effect on the brain's metabolic activity, it may also help shed light on ADHD. Previous studies have implicated abnormal dopamine levels in the development of ADHD, and some researchers have even pointed toward dopamine-transporter deficient mice as a potential animal model of the disorder. The researchers behind this study explain that elevated dopamine levels in the brain may contribute to symptoms of ADHD or substance abuse. Further research on the role of dopamine in these and other psychiatric disorders will allow for a better understanding of how these conditions develop and may also indicate potential targets for new treatments.

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