Dopamine (redirected from Dopamine hydrochloride)

dopamine (dōp`əmēn), one of the intermediate substances in the biosynthesis of epinephrine and norepinephrine. See catecholamine.

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dopamine

One of the catecholamines, widely distributed in the central nervous system. Through a series of enzymatic reactions (see enzyme) it is formed from levodopa and converted to norepinephrine and then epinephrine. It is a central nervous system neurotransmitter essential to control of motion; it also acts as a hormone. Degeneration of certain dopamine-producing brain cells results in parkinsonism.

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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