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Serotonin and dopamine are both neurotransmitters found in abundance within the human brain and throughout the human body. Both classified as biogenic amines, they are among the group of psychoactive chemicals responsible for the proper functioning of the central nervous system. Their close relationship is an important aspect in research within the psychiatric spectrum. The importance of the connection between these two substances stems from the balance that must be maintained within the body to keep a person's mood stable.
Serotonin and dopamine are both needed in various quantities throughout the body. Their metabolism, synthesis, and uptake pathways are intertwined. Serotonin and dopamine are both metabolized by the same enzyme, MAO, and sometimes compete for the attention of this chemical. Serotonin is synthesized from the amino acids tryptophan and 5-Hydroxytryptophan (5-HTP), whereas dopamine is synthesized from the amino acids tyrosine and L-Dopa. When one of these neurotransmitter precursors is out of balance, metabolism, synthesis, and uptake of either neurotransmitter can be impaired.
When either serotonin or dopamine becomes depleted within the system, disturbances in mood and cognitive function become apparent. Biological pathways that regulate things such as appetite, libido, and the circulatory system can be affected, as well. The imbalance of these two chemicals, sometimes in addition to other chemical imbalances and triggers from the outside environment, leads to illness.
While the neurotransmitters have a symbiotic relationship within the body, they act independently of each other and regulate specific functions of the brain. Serotonin depletion is responsible for some forms of major depression and feelings of anxiety and aggression. Dopamine depletion is responsible for lack of motivation, and for anhedonia, the inability to feel pleasure. When there is an imbalance with either one, there is an increased chance of the other becoming unbalanced as a result of their interdependent nature. This leads to a cyclic disease model.
Balancing serotonin, dopamine, and other biogenic amines such as norepinephrine is the focus of research into treating many mood disorders. The monoamine hypothesis, which points to serotonin as the main culprit in most mood disorders, is becoming obsolete as researchers discover new layers in the complicated relationship between serotonin and many of the brain's other psychoactive chemical compounds. Dopamine is proving to be as important as serotonin when researching psychiatric disease. Medications used to treat chemical imbalance are becoming more effective, because newer drugs take into account the complicated connection between serotonin and dopamine.