UPTON, NY — A brain-imaging study conducted at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory provides the first definitive evidence that patients suffering from attention deficit hyperactivity disorder (ADHD) have lower-than-normal levels of certain proteins essential for experiencing reward and motivation.
"These deficits in the brain's reward system may help explain clinical symptoms of ADHD, including inattention and reduced motivation, as well as the propensity for complications such as drug abuse and obesity among ADHD patients," said lead author Nora Volkow, Director of the National Institute on Drug Abuse and a long-time collaborator on neuroimaging research at Brookhaven Lab.
The study, published in the September 9, 2009, issue of the Journal of the American Medical Association, also has important implications for treatment. "Finding ways to address the underlying reward-system deficit could improve the direct clinical outcome of ADHD, and potentially reduce the likelihood of other negative consequences of this condition," said study co-author Gene-Jack Wang, chair of Brookhaven's medical department.
Can't pay attention? It is all down to your dopamine receptors. You don't have enough of them to get rewarded for paying attention.
The scientists used positron emission tomography (PET) to measure two markers of the dopamine system — dopamine receptors, to which the chemical messenger binds to propagate the "reward" signal, and dopamine transporters, which take up and recycle excess dopamine after the signal is sent.
Lying in a PET scanner, each patient was injected with a minute amount of a "radiotracer" compound — a chemical labeled with a radioactive form of carbon and designed to bind specifically to one of the targets. Different tracers were used for each target, and patients were scanned for each at separate times. By detecting the signal from the radiotracers, the PET machine can measure the receptor and transporter locations and concentrations in various parts of the brain.
The results clearly showed that, relative to the healthy control subjects, the ADHD patients had lower levels of dopamine receptors and transporters in the accumbens and midbrain — two key regions of the brain directly involved in processing motivation and reward. In addition, the measurements of dopamine markers correlated with measures of behavior and clinical observations of ADHD symptoms, such as reduced levels of attention as measured by standard psychological tests.
A drug that would stimulate neurons to increase the synthesis of dopamine receptors would probably improve the ability of people to pay attention for longer periods of time. Do any existing drugs increase dopamine receptor synthesis?
Think about the continuing stream of discoveries about how neurotransmitter receptor concentrations alter behavior and mood. These discoveries are building up a foundation of knowledge needed to develop drugs that will alter mood, motivation, and intellectual performance. We will become more pharmacologically malleable as a result of drug development guided by these discoveries. Those new drugs might be 10 or 20 years off. But they'll come eventually.
|Share |||Randall Parker, 2009 September 08 11:25 PM Brain Performance|