According to the Centers for Disease Control and Prevention, as of 2008, approximately one in every 10 American adults reports that they suffer with depression. One of the current theories concerning the reason for depression suggests that people who are depressed have abnormally low levels of serotonin, norepinephrine or dopamine.
What is Dopamine?
Dopamine is a neurotransmitter, or a chemical substance used by the nerves to send signals so they can communicate with each other. It is made at the end of a nerve from the amino acid tyrosine, as explained by David Standaert, M.D., Ph.D., Associate Professor of Neurology at Harvard Medical School in "Goodman & Gilman's The Pharmacological Basis of Therapeutics." When the nerve releases dopamine, it crosses a very small gap called a synapse, and then attaches to a dopamine receptor on the next nerve.
Dopamine Receptors
Receptors are proteins that are located on the membrane of a cell, and sometimes within a cell, that act after they have been told what to do. There are dopamine receptors in several locations including the pituitary gland, blood vessels of the kidneys, heart and the nerves, writes Paul Fitzgerald, M.D., Clinical Professor of Medicine at the University of California in "Greenspan's Basic & Clinical Endocrinology." There are five subtypes of dopamine receptors, named D1 through D5, which are all involved in one way or another with sending signals.
MAOIs and Depression
MAOI is the abbreviation for monoamine oxidase inhibitor. Monoamine oxidase is an enzyme, a protein that speeds up the amount of time that a reaction will take. This enzyme specifically speeds up the time that it takes for the monoamine chemicals to break down, as written by William Coryell, M.D., Professor of Psychiatry at the University of Iowa in "The Merck Manual for Healthcare Professionals." The monoamine chemicals are serotonin, norepinephrine and dopamine. According to one theory, people are depressed because they do not have enough serotonin, norepinephrine or dopamine. Taking an MAOI will increase the levels of these chemicals.
Bupropion and Dopamine Receptors
Normally after dopamine is released by a nerve, it crosses a gap to attach to a dopamine receptor on the next nerve. Bupropion is a medication that, in animal studies, interferes with a nerve taking norepinephrine and dopamine after it crosses that gap, according to Charles DeBattista, M.D., Professor of Psychiatry and Behavioral Science at Stanford University School of Medicine in "Basic & Clinical Pharmacology." In medical terminology, bupropion interferes with the reuptake of dopamine at the dopamine receptor. Dopamine stays in the gap longer and keeps stimulating the next nerve.
Clinical Trial on Dopamine Receptors
As of 2010, the National Institute of Mental Health is conducting a study so they can understand more about how dopamine receptors function in people who have depression. The scientists at the Institute also want to see if genetics has a role in the way that the receptors function in people who are depressed. Those participating in the study will have MRI and PET scan images of the brain, as well as genetic screening using the DNA obtained from a blood sample.
References
- "Basic & Clinical Pharmacology"; Bertram Katzung, M.D., Ph.D., Susan Masters, Ph.D., Anthony Trevor, Ph.D.; 2009
- Centers for Disease Control and Prevention: National Depression Screening Day
- "Goodman & Gilman's The Pharmacological Basis of Therapeutics"; Laurence Brunton, Ph.D.; 2006
- "Greenspan's Basic & Clinical Endocrinology"; David Gardner, M.D., Dolores Shoback, M.D.; 2007
- National Institute of Mental Health: Dopamine Receptor Imaging in Mood Disorders
- The Merck Manual for Healthcare Professionals: Depressive Disorders
