Approximately 14.8 million American adults suffer from depression, as shown by R.C. Kessler, Ph.D., in a study published in June 2005 in the journal Archives of General Psychiatry. Although there are numerous reasons why a person begins to suffer from depression, chemical imbalances in the brain have a major impact on this condition. Neurotransmitters, or messengers, are responsible for sending messages from neurons to other cells. Several of them have been linked to depression. It seems that depressed people oftentimes do not have enough of certain neurotransmitters.
Serotonin
Serotonin has many important tasks, such as controlling body temperature and appetite and regulating mood. Besides depression, serotonin also plays a role in eating disorders, anxiety and bipolar disorders. Serotonin is both a hormone and a neurotransmitter. Low levels of the hormone have been commonly reported in depressed individuals. It is also possible that a person has too-short serotonin receptor sites. This causes them to absorb the available serotonin too rapidly. These kinds of receptors are also unable to release serotonin back to the space between two neurons quick enough, causing a serotonin shortage. Many antidepressants work by preventing the serotonin receptor sites from absorbing serotonin too quickly. Low serotonin levels seem to be linked to irritability, poor impulse control, decreased appetite and low sex drive.
Norepinephrine
In the 1960s, Joseph Schildkraut, from Harvard University, and William Bunney and John Davis, from the National Institute of Mental Health, stated in the now famous "catecholamine" hypothesis that depression was associated with a deficiency of norepinephrine, or NE. Later, NE was also associated with anxiety. It does not seem to explain the depression in every patient, but NE medication tends to help some patients. In fact, decreased levels of this neurotransmitter seem to cause depression only in patients who are already predisposed to depression. Low NE levels are linked to poor attention and memory, and decreased concentration. It seems that neither NE nor serotonin deficiency can fully explain depression. It is when the levels of both of these neurotransmitters are low when the person is most likely to get depressed.
Dopamine
Dopamine is a neurotransmitter that is associated with reward and reinforcement. Decreased levels of this neurotransmitter have been linked with depression. Dopamine is also associated with addictions since, for example, alcohol, opium and cocaine increase dopamine production. This might explain why addictions are so common among depressed individuals. Interestingly, abnormally high levels of dopamine have been linked to such disorders as schizophrenia, and attention deficit hyperactivity disorder, or ADHD.
References
- "The Neurobiology of Depression"; Nemeroff; 2000
- The American Journal of Psychiatry; The Catecholamine Hypothesis of Affective Disorders: A Review of Supporting Evidence; Schildkraut; 1965
