Dopamine is a neurotransmitter, a chemical that facilitates transmission of signals between brain cells, or neurons, by binding to neuron receptors. The chemical is involved in controlling emotions, pleasure, movement and incoming information. The chemical is also sometimes called the "reward hormone," because its release is associated with extreme pleasure that makes people want to repeat the activity that led to that feeling. For this reason, dopamine-releasing activities such as sex, obsession, love, gambling and certain drugs can be highly addictive.
Parkinson's disease is a degenerative disease that is associated with a breakdown of dopamine-releasing neurons. The lack of dopamine causes tremor, muscular paralysis, slow movement and difficulty initiating movement. Parkinson's disease is hard to diagnose, and even harder to predict before the main diagnostic symptoms set in. However, in a publication released in the July 28, 2010, online issue of "Neurology," a research team reports that they found an early predictor of both Parkinson's disease and dementia. The predictor is the so-called "REM sleep disorder," in which people violently kick or punch their bed partners during REM sleep.
Restless Legs Syndrome
In restless legs syndrome, people jerk their legs around during sleep. Restless legs syndrome is a predictor of impaired dopamine production in the brain, which can lead to disorders such as social phobia and attention deficit hyperactivity disorder. It is also a predictor of cardiovascular disease, reports a Harvard research team in the January 1, 2008, issue of "Neurology." People with restless legs syndrome make 200 to 300 leg movements every night, note the researchers. These movements are accompanied by an acute, rapid increase in heart rate and blood pressure. Over time this can cause cardiovascular disease.
Highly creative people often have a low density of dopamine receptors in the brain, reports a Karolinska research team in the May 2010 issue of "PLoS ONE." While highly creative people produce enough dopamine, they have fewer dopamine D2 receptors in the thalamus. In this respect, their brains resemble people with schizophrenia. Schizophrenics also have a low density of D2 receptors in the thalamus. This results in a tendency to make highly unusual associations, which the researchers believe explain the creativity of both healthy creative people and schizophrenics. A low density of D2 receptors in the thalamus affects people's ability to filter out information. With more information coming in from the thalamus, it is possible for creative people to see unusual connections that other people don't see. This can be a gift in a problem-solving situations, but it can also result in a misinterpretation of other people's intentions.
Street drugs, such as meperidine, sometimes contain the toxic chemical 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, or MPTP, which causes a breakdown of dopamine-expressing neurons, resulting in low dopamine levels, reports Spencer Cole, the author of "New Research on Street Drugs." In contrast, cocaine, amphetamine and drugs used to treat narcolepsy increase dopamine levels. Cocaine acts as a dopamine reuptake inhibitor, preventing dopamine from breaking down. Amphetamine and narcolepsy drugs increase dopamine production. With repeated use of these drugs, however, the brain will reduce the number of dopamine receptors, and receptors gradually become less sensitive to dopamine. So, with repeated use of cocaine and amphetamine or narcolepsy drugs, desensitization, also called tolerance, occurs, which means that more of the same drug is required to achieve the same effect, Cole says. With sudden withdrawal from the drug, there will be fewer and less sensitive neurons for the brain's natural resources of dopamine to bind to, which can cause Parkinson-like symptoms.