The brain is part of the central nervous system and plays a crucial role in regulating the body's metabolism and nearly all of its functions. Brain cells, or neurons, use chemical messenger molecules called neurotransmitters for communication. Dysfunction in one or more of the neurotransmitter systems in the brain is believed to contribute to mental illness and depression.
Dopamine Function
Dopamine is a neurotransmitter synthesized from an enzymatic modification of an amino acid called tyrosine. Dopamine's function in the brain is associated with motivation, attention, reward and feelings of pleasure. Dopamine is also involved in the regulation of motor activity; the loss of dopamine-secreting cells adversely affects the control of voluntary movement, causing the tremors seen in Parkinson's disease. In some cells of the brain, dopamine is further enzymatically modified to produce another neurotransmitter called norepinepherine.
Depression
Feelings of sadness, loss of interest in formerly pleasurable activities, changes in appetite and sleep patterns, feelings of worthlessness and thoughts of death are all symptoms of a depressive disorder. People suffering from depression have a greatly reduced quality of life, and depressive disorders are estimated to be the leading cause of disability world-wide.
Antidepressant Medications
The drugs used to treat depression typically target a class of neurotransmitters known as monoamines. These include: serotonin, dopamine, histamine, epinephrine and norepinepherine. For example, fluoxetine, also known as Prozac, is a selective serotonin re-uptake inhibitor, or SSRI. These drugs are thought to work by inhibiting the metabolism of serotonin by neurons. Other drugs used to treat depression include: serotonin norepinepherine re-uptake inhibitors, or SNRIs; monoamine oxidase inhibitors, or MAOIs; norepinepherine re-uptake inhibitors, or NRIs, and tricyclic anti-depressants.
Dopamine Levels and Depression
Deficiency in dopamine function has been associated with several symptoms of depressive disorders, including lack of motivation and inability to experience pleasure. Additionally, some antidepressant drugs appear to improve the function of dopaminergic neurons. These findings suggest that low levels of dopamine function may contribute to depression.
Considerations
Dopamine function refers to the ability of the neurotransmitter dopamine to effectively communicate with neurons. Cells that are capable of receiving dopaminergic messages have special proteins on their membranes called dopamine receptors. These receptors must be functional in order for the proper message to be conveyed. Additionally, dopamine is metabolized by enzymes or packaged into tiny structures called vesicles where they are taken back into the cell to be used again. Proper dopamine function requires these mechanisms to be working. Finally, deficiency may be the result of some impairment in the cells that synthesize dopamine.
References
- "Molecular Neuropharmacology" ; Nestler, Hyman, and Malenka; 2009
- "Nature Medicine"; The global burden of disease, 1990-- 2020; AD Lopez and CC Murray; November 1998;
- "The Dopamine Receptors (2nd Edition)"; Kim Neve; 2010
