Bipolar disorder, also known as manic-depressive disorder, refers to a group of mood disorders that varies in the severity of episodes of mania and depression and the predominant type of episode. Certain chemicals, also called neurotransmitters, act as messengers between neurons in the brain. A study in the October 2000 issue of the “American Journal of Psychiatry” reports that several neurotransmitters have been implicated as causal of the disease, but additional factors contribute to the disorder, including structural differences in areas of the brain. Also, genetic and environmental triggers contribute to the development of bipolar disorder. The neurotransmitters suspected of being involved in mediating the symptoms of bipolar disorder regulate mood, stress, pleasure, reward, sleep, arousal, concentration and attention, among other higher cognitive functions.
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Serotonin is a neurotransmitter that is synthesized from the amino acid tryptophan. Decreased levels of serotonin are commonly found in patients with bipolar disorder and depression. Many antidepressant medications, including monoamine oxidase inhibitors, selective serotonin reuptake inhibitors and tricyclic antidepressants reduce the symptoms of depression by increasing the concentration of serotonin in the brain.
The amino acid glutamate is the most abundant excitatory neurotransmitter in the brain. A study published in the December 2007 issue of “Biological Psychiatry” reports that glutamate levels are higher in certain regions of the brain in patients with bipolar disorder. Many mood-stabilizing drugs used to treat bipolar disorder are known to decrease the excitatory actions of glutamate.
Gamma-amino butyric acid, or GABA, is an inhibitory neurotransmitter synthesized from the amino acid glutamate. GABA modulates the activity of several other neurotransmitters, including dopamine, serotonin and norepinephrine. An article in the July 2001 issue of “Neuropsychopharmacology” states that the actions of GABA in the brains of bipolar patients are significantly blunted.
Dopamine is a neurotransmitter synthesized from the amino acid tyrosine. It is known to affect the reward centers of the brain and also is involved in regulating sleep, motivation, attention and learning. A review in a 2007 issue of the journal “Acta Psychiatrica Scandinavica Supplementum” concludes that dopamine plays a role in the cyclical shifts from mania to depression in patients with bipolar disorder. This review notes that several studies provide evidence that dopamine levels are high during manic episodes and depression is initiated upon the subsequent down-regulation of dopamine.
Norepinephrine is a neurotransmitter that is synthesized from dopamine and is released by neurons in the brain in response to stress. Patients with bipolar disorder commonly have decreased levels of norepinephrine in the brain.
Melatonin is a hormone derived from the amino acid tryptophan. It is secreted by the pineal gland in the brain, and many of its actions are the result of it acting similar to a neurotransmitter. Melatonin regulates sleep-wake cycles, and its circulating levels vary throughout the day and night. In addition, melatonin modulates the activities of GABA and dopamine. A study in the January 2001 issue of the journal “Frontiers of Neuropharmacology” reports that the release of melatonin is altered in patients with bipolar disorder.