dopamine

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dopamine

(dōp`əmēn), one of the intermediate substances in the biosynthesis of epinephrineepinephrine
, hormone important to the body's metabolism, also known as adrenaline. Epinephrine, a catecholamine, together with norepinephrine, is secreted principally by the medulla of the adrenal gland.
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 and norepinephrine. See catecholaminecatecholamine
, any of several compounds occurring naturally in the body that serve as hormones or as neurotransmitters in the sympathetic nervous system. The catecholamines include such compounds as epinephrine, or adrenaline, norepinephrine, and dopamine.
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.

Dopamine

A catecholamine neurotransmitter that is synthesized by certain neurons in the brain and interacts with specific receptor sites on target neurons.

Dopamine is manufactured inside dopamine neurons in a controlled manner from the amino acid precursor l -tyrosine, which mammals obtain through the normal diet. Dopamine is then stored in vesicles within the nerve terminals, which may fuse with the cell membrane to release dopamine into the synapse.

The release of neurotransmitter is controlled by a variety of factors, including the firing rate of the dopamine nerve cell (termed impulse-dependent release) and the release- and synthesis-modulating presynaptic dopamine receptors located on the dopamine nerve terminals. Since presynaptic dopamine receptors are sensitive to the cell's own neurotransmitter, they are called dopamine autoreceptors. Once released, dopamine also acts at postsynaptic receptors to influence behavior. The actions of dopamine in the synapse are terminated primarily by the reuptake of neurotransmitter into the presynaptic terminal by means of an active dopamine transporter. Dopamine may then be either repackaged into synaptic vesicles for rerelease or degraded by the enzyme monoamine oxidase. The dopamine transporter is an important site of action of the drugs cocaine and amphetamine. See Synaptic transmission

Although it was first thought that dopamine occurred only as an intermediate product formed in the biosynthesis of two other catecholamine neurotransmitters, norepinephrine and epinephrine, dopamine is now recognized as a neurotransmitter in its own right. Several distinct dopamine neuronal systems have been identified in the brain. These include systems within the hypothalamus and the pituitary gland; systems within the midbrain that project to a variety of cortical and limbic regions and basal ganglia; the retinal system; and the olfactory system. See Brain, Epinephrine, Noradrenergic system

The midbrain dopamine neurons which project to a variety of forebrain structures are critically involved in normal behavioral attention and arousal; abnormalities in the normal functioning of these systems have been implicated in a variety of disorders. For example, Parkinson's disease involves a degeneration of the midbrain dopamine neurons. This condition is often successfully treated by providing affected individuals with l -dopa, which is readily converted to dopamine in the brain. Attention deficit disorder, which is usually first diagnosed in childhood, is thought to involve dopamine systems, because the treatment of choice, methylphenidate, binds to the dopamine transporter and alters dopamine levels in the synapse. See Parkinson's disease

Drugs used to treat the major symptoms of schizophrenia are potent dopamine receptor antagonists. It is possible that certain schizophrenias are the result of increased activity in dopamine neuronal systems, but this has not as yet been conclusively demonstrated. A similar involvement of midbrain dopamine systems has been implicated in the multiple tic disorder Tourette's syndrome, which is treated, often successfully, with dopamine receptor antagonists. See Neurobiology, Schizophrenia

Dopamine

 

3,4-dihydroxyphenethylamine, hydroxytyra-mine, C6H3(OH)2CH2(CH)2(NH2), an intermediate in the biosynthesis of catecholamines, produced by the decarboxylation of dihydroxyphenylalanine (dopa).

A number of organs and tissues (for example, the liver, lungs, and intestine) contain an abundance of dopamine. Along with epinephrine and norepinephrine, dopamine is secreted in small amounts by the adrenals, an indication that dopamine may have an independent hormonal function. Dopamine is present in the central nervous system, mainly in the motor centers, where it acts as a mediator. Healthy persons excrete an average of between 210 and 255 μg of dopamine daily with urine.

dopamine

[′dō·pə‚mēn]
(biochemistry)
C8H11O2N An intermediate in epinephrine and norepinephrine biosynthesis; the decarboxylation product of dopa.
References in periodicals archive ?
During exercise, the increase in the activity of the dopaminergic system in the preoptic area seems to influence tolerance to heat stress.
The increase in locomotor activity could be caused by the effects on the dopaminergic system of NMDA receptors.
Thus, acute pharmacological adjunctive treatment should consist of preferential blocking of postsynaptic NAc DA receptors (D1-D5), whereas long-term activation of the mesolimbic dopaminergic system should involve activation and/or release of DA at the NAc site.
To verify the effect of FRA's antidepression over serotonergic, noradrenergic and dopaminergic system, the anti-immobility effect of FRA in FST was prevented by pre-treatment of rat with their receptor antagonists.
It is generally accepted that the central dopaminergic system is implicated in the pathogenesis of schizophrenia.
In addition to the foregoing, there is another evidence suggesting that the dopaminergic system may also be implicated in the physiopathology of depression, given that in some depressed patients with notorious psychomotor retard and suicidal behavior, the plasmatic concentrations of dopamine and some of its metabolites, such as the dihydroxyphenylacetic acid, are reduced.
In conclusion, our data show that heavy metals polluting the environment can cause subtle effects on the children's renal and dopaminergic systems.
On theoretical grounds, the effects of atypicals on the serotonergic and dopaminergic systems would suggest antidepressant activity for the class in general, he said.
1993); this contrasts with the increase in activity and dopaminergic systems associated with PD-like mechanisms.
The drug, which was formerly known as tomoxetine, is a highly selective presynaptic norepinephrine transporter blocker with no apparent effect on dopaminergic systems.
Collectively, these studies demonstrate that ATR can produce neurotoxicity in dopaminergic systems that are critical to the mediation of movement as well as cognition and executive function.
For example, there is preliminary evidence that a bacterial stimulus (endotoxin) can produce cytokines that impair the development of the mesencephalic dopaminergic systems during pregnancy.