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Dopamine is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the human brain and body, as well as elsewhere in biology. Its name is derived from its chemical structure: it is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which occurs in human brain cells and adrenal cells. In the brain, dopamine functions as a neurotransmitter—a chemical released by nerve cells to send signals to other nerve cells. In brain cells, it is transported to synaptic sites and packaged into vesicles for release, which occurs during synaptic transmission. After release, free dopamine is either reabsorbed into the presynaptic terminal for reuse, or broken down by the enzymes monoamine oxidase or COMT, producing a variety of degradation metabolites, whose end products are ultimately excreted in the urine. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior. Most types of reward increase the level of dopamine in the brain, and most addictive drugs increase dopamine neuronal activity. Other brain dopamine systems are involved in motor control and in controlling the release of various hormones.

Outside the nervous system, dopamine functions in several parts of the body as a local chemical messenger. In blood vessels, it inhibits norepinephrine release and acts as a vasodilator (at normal concentrations); in the kidneys, it increases sodium excretion and urine output; in the pancreas, it reduces insulin production; in the digestive system, it reduces gastrointestinal motility and protects intestinal mucosa; and in the immune system, it reduces the activity of lymphocytes. With the exception of the blood vessels, dopamine in each of these peripheral systems is synthesized locally and exerts its effects near the cells that release it.

Several important diseases of the nervous system are associated with dysfunctions of the dopamine system, and some of the key medications used to treat them work by altering the effects of dopamine. Parkinson's disease, a degenerative condition causing tremor and motor impairment, is caused by loss of dopamine-secreting neurons in a midbrain area called the substantia nigra. Its metabolic precursor L-DOPA is the most widely used treatment for the condition. There is evidence that schizophrenia involves altered levels of dopamine activity, and most antipsychotic drugs that are frequently used to treat it have a primary effect of reducing dopamine activity.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Similar dopamine antagonist drugs are also some of the most effective anti-nausea agents. Attention deficit hyperactivity disorder (ADHD) and restless legs syndrome are associated with decreased dopamine activity.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Dopaminergic stimulants can be addictive in high doses, but some are used at lower doses to treat ADHD. Dopamine itself is available for intravenous injection: although it cannot reach the brain from the bloodstream, its peripheral effects make it useful in the treatment of heart failure or shock, especially in newborn babies.


Dopamine sections
Intro  Structure  Biochemistry  Functions  Medical uses  Pharmacology  Diseases and disorders  Comparative biology and evolution  History and development  See also   References   

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{{#invoke:Hatnote|hatnote}} {{ safesubst:#invoke:Unsubst||$N=Use dmy dates |date=__DATE__ |$B= }}

Dopamine is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the human brain and body, as well as elsewhere in biology. Its name is derived from its chemical structure: it is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which occurs in human brain cells and adrenal cells. In the brain, dopamine functions as a neurotransmitter—a chemical released by nerve cells to send signals to other nerve cells. In brain cells, it is transported to synaptic sites and packaged into vesicles for release, which occurs during synaptic transmission. After release, free dopamine is either reabsorbed into the presynaptic terminal for reuse, or broken down by the enzymes monoamine oxidase or COMT, producing a variety of degradation metabolites, whose end products are ultimately excreted in the urine. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior. Most types of reward increase the level of dopamine in the brain, and most addictive drugs increase dopamine neuronal activity. Other brain dopamine systems are involved in motor control and in controlling the release of various hormones.

Outside the nervous system, dopamine functions in several parts of the body as a local chemical messenger. In blood vessels, it inhibits norepinephrine release and acts as a vasodilator (at normal concentrations); in the kidneys, it increases sodium excretion and urine output; in the pancreas, it reduces insulin production; in the digestive system, it reduces gastrointestinal motility and protects intestinal mucosa; and in the immune system, it reduces the activity of lymphocytes. With the exception of the blood vessels, dopamine in each of these peripheral systems is synthesized locally and exerts its effects near the cells that release it.

Several important diseases of the nervous system are associated with dysfunctions of the dopamine system, and some of the key medications used to treat them work by altering the effects of dopamine. Parkinson's disease, a degenerative condition causing tremor and motor impairment, is caused by loss of dopamine-secreting neurons in a midbrain area called the substantia nigra. Its metabolic precursor L-DOPA is the most widely used treatment for the condition. There is evidence that schizophrenia involves altered levels of dopamine activity, and most antipsychotic drugs that are frequently used to treat it have a primary effect of reducing dopamine activity.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Similar dopamine antagonist drugs are also some of the most effective anti-nausea agents. Attention deficit hyperactivity disorder (ADHD) and restless legs syndrome are associated with decreased dopamine activity.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Dopaminergic stimulants can be addictive in high doses, but some are used at lower doses to treat ADHD. Dopamine itself is available for intravenous injection: although it cannot reach the brain from the bloodstream, its peripheral effects make it useful in the treatment of heart failure or shock, especially in newborn babies.


Dopamine sections
Intro  Structure  Biochemistry  Functions  Medical uses  Pharmacology  Diseases and disorders  Comparative biology and evolution  History and development  See also   References   

PREVIOUS: IntroNEXT: Structure
<<>>