Your brain uses chemicals called neurotransmitters to send messages across brain cells. One such neurotransmitter is called dopamine. Only about 0.3% of the cells in your brain use dopamine; however, it plays a vital role in many body functions and illnesses. Since researchers cannot directly measure the levels of dopamine in someone's brain, they rely on dopamine markers that give an indirect measure of dopamine levels.
Your brain uses dopamine as a chemical messenger to communicate between brain cells and brain areas. According to the McGill University website, “The Brain from Top to Bottom,” the release of dopamine in your brain relates to feelings of reward. Dopamine also helps regulate your attention and to control your body’s movements.
A dopamine marker helps researchers to understand the levels of dopamine in someone's brain. Researchers may want to know whether a person’s brain produces more dopamine that normal. For example, according to Oliver Howes and Shitij Kapur in a March 2009 article in the journal "Schizophrenia Bulletin," many researchers study whether high amounts of dopamine cause schizophrenia. Researchers can use dopamine markers to ascertain whether people who suffer from schizophrenia do in fact have higher levels of dopamine than normal.
Researchers use a variety of methods as dopamine markers. For example, in an October 2004 article for the journal, “Annals of Neurology,” Dr. N. D. Volkow and colleagues examined two different kinds of dopamine markers: presynaptic and postsynaptic markers. Presynaptic markers are chemicals that gather up dopamine after it gets released. Volkow and colleagues also used dopamine receptors as postsynaptic markers of dopamine levels. Volkow and colleagues were able to use dopamine markers to determine that people tend to lose both dopamine transporters and receptors as they age.
People who suffer from Parkinson’s disease have lower than average levels of dopamine in a brain area called the substantia nigra. Therefore, uncovering easily measurable markers of dopamine levels makes it easier for physicians to diagnose Parkinson’s disease. In a 1995 article in the “Journal of Neural Transmission,” D. A. Loeffler and colleagues examined the properties of the cerebral spinal fluid of rabbits as an indirect measure of dopamine levels.
Dopamine markers measure the levels of dopamine in the brain indirectly. This leads to problems with the accuracy of researcher's measurements. For example, in an October 2009 article in the journal "Neuroscience Letters," J. R. Cannon and J. T. Greenamyre say that a protein that researchers often use as a dopamine marker, neuron-specific nuclear protein, does not always increase and decrease with dopamine levels. Cannon and Greenamyre suggest that neuron-specific nuclear protein may in fact not be a useful dopamine marker.