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<p><span id="History" class="mw-headline"><font color="#000000"><font size="3"><strong>Dopamine </strong> is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. <br /><br />In the brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors—D1, D2, D3, D4, and D5—and their variants. Dopamine is produced in several areas of the brain, including the substantia nigra and the ventral tegmental area.[1] Dopamine is also a neurohormone released by the hypothalamus. Its main function as a hormone is to inhibit the release of prolactin from the anterior lobe of the pituitary. <br />
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Dopamine is available as an intravenous medication acting on the sympathetic nervous system, producing effects such as increased heart rate and blood pressure. However, because dopamine cannot cross the blood-brain barrier, dopamine given as a drug does not directly affect the central nervous system. To increase the amount of dopamine in the brains of patients with diseases such as Parkinson's disease and dopa-responsive dystonia, L-DOPA, which is the precursor of dopamine, can be given because it can cross the blood-brain barrier. <br />
<p><font color="#000000">Two major degradation pathways for dopamine exist. In most areas of the brain, including the striatum and basal ganglia, dopamine is inactivated by reuptake via the dopamine transporter (DAT1), then enzymatic breakdown by monoamine oxidase (MAOA and MAOB) into 3,4-dihydroxyphenylacetic acid. In the prefrontal cortex, however, there are very few dopamine transporter proteins, and dopamine is instead inactivated by reuptake via the norepinephrine transporter (NET), presumably on neighboring norepinephrine neurons, then enzymatic breakdown by catechol-<em>O</em>-methyl transferase (COMT) into 3-methoxytyramine.<sup id="cite_ref-3" class="reference"><font size="2"><span>[</span>4<span>]</span></font></sup> The DAT1 pathway is roughly an order of magnitude faster than the NET pathway: in mice, dopamine concentrations decay with a half-life of 200 ms in the caudate nucleus (which uses the DAT1 pathway) versus 2,000 ms in the prefrontal cortex.<sup id="cite_ref-4" class="reference"><font size="2"><span>[</span>5<span>]</span></font></sup> Dopamine that is not broken down by enzymes is repackaged into vesicles for reuse by VMAT2.</font></p>
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<h2p><span id="Functions_in_the_brain" class="mw-headline"><font color="#000000"><font size="5"><strong>Functions in the brain<br /font></spanstrong></h2font><pbr /><font colorsize="#0000003">Dopamine has many functions in the brain, including important roles in behavior and cognition, voluntary movement, motivation, punishment and reward, inhibition of prolactin production (involved in lactation and sexual gratification), sleep, mood, attention, working memory, and learning. Dopaminergic neurons (i.e., neurons whose primary neurotransmitter is dopamine) are present chiefly in the ventral tegmental area (VTA) of the midbrain, the substantia nigra pars compacta, and the arcuate nucleus of the hypothalamus.<br /font><br /p><p><font color="#000000">It has been hypothesized that dopamine transmits reward prediction error, although this has been questioned.<sup id="cite_ref-dopamine_function_5-0" class="reference"><font size="2"><span>[</span>6<span>]</span></font></sup> According to this hypothesis, the phasic responses of dopamine neurons are observed when an unexpected reward is presented. These responses transfer to the onset of a conditioned stimulus after repeated pairings with the reward. Further, dopamine neurons are depressed when the expected reward is omitted. Thus, dopamine neurons seem to encode the prediction error of rewarding outcomes. In nature, we learn to repeat behaviors that lead to maximizing rewards. Dopamine is therefore believed to provide a teaching signal to parts of the brain responsible for acquiring new behavior. Temporal difference learning provides a computational model describing how the prediction error of dopamine neurons is used as a teaching signal.<br /font><br /p><p><font color="#000000">The reward system in insects uses octopamine, which is the presumed arthropod homolog of norepinephrine,<sup id="cite_ref-octopamine-honeybee_6-0" class="reference"><font size="2"><span>[</span>7<span>]</span></font></sup> rather than dopamine. In insects, dopamine acts instead as a punishment signal and is necessary to form aversive memories.<sup id="cite_ref-pmid14627633_7-0" class="reference"><font size="2"><span>[</span>8<span>][9]<br /span></font><br /sup><sup id="cite_ref-pmid19521527_8-0" class="reference"></font size="2"><span>[</span>9<span>]</span></font></sup></font></p>
<h3><span id="Anatomy" class="mw-headline"><font color="#000000">Anatomy</font></span></h3>
<div class="rellink relarticle mainarticle"><font color="#000000">Main article: Dopaminergic pathways</font></div>
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<h2><span id="External_links" class="mw-headline">External links</span></h2>
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<li><a title="DrugBank" href="/wiki/DrugBank"><font color="#0645ad">DrugBank</font></a> <a class="external text" rel="nofollow" href="http://redpoll.pharmacy.ualberta.ca/drugbank/cgi-bin/getCard.cgi?CARD=APRD00085.txt"><font color="#3366bb">APRD00085</font></a> </li>
<li><a class="external text" rel="nofollow" href="http://druginfo.nlm.nih.gov/drugportal/dpdirect.jsp?name=Dopamine"><font color="#3366bb">U.S. National Library of Medicine: Drug Information Portal - Dopamine</font></a> </li>
<li><span class="text13">[[도파민]]<br />
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