Editing Dopamine (section)

==Comparative biology and evolution==
===Microorganisms===
There are no reports of dopamine in [[archaea]], but it has been detected in some types of [[bacteria]] and in the [[protozoa]]n called ''[[Tetrahymena]]''.<ref>{{cite book | vauthors = Roshchina VV |year=2010 |chapter=Evolutionary considerations of neurotransmitters in microbial, plant, and animal cells |title=Microbial Endocrinology |pages=17–52 | veditors = Lyte M, Primrose PE |publisher=Springer |location=New York |isbn=978-1-4419-5576-0}}</ref> Perhaps more importantly, there are types of bacteria that contain [[homology (biology)|homologs]] of all the enzymes that animals use to synthesize dopamine.<ref name=Iyer/> It has been proposed that animals derived their dopamine-synthesizing machinery from bacteria, via [[horizontal gene transfer]] that may have occurred relatively late in evolutionary time, perhaps as a result of the [[symbiotic]] incorporation of bacteria into [[eukaryote|eukaryotic]] cells that gave rise to [[mitochondrion|mitochondria]].<ref name=Iyer>{{cite journal | vauthors = Iyer LM, Aravind L, Coon SL, Klein DC, Koonin EV | title = Evolution of cell-cell signaling in animals: did late horizontal gene transfer from bacteria have a role? | journal = Trends in Genetics | volume = 20 | issue = 7 | pages = 292–99 | date = July 2004 | pmid = 15219393 | doi = 10.1016/j.tig.2004.05.007 }}</ref>

===Animals===
Dopamine is used as a neurotransmitter in most multicellular animals.<ref name=Barron/> In [[sponge]]s there is only a single report of the presence of dopamine, with no indication of its function;<ref>{{cite journal |year=2004 |title=Isolation of Araguspongine M, a new stereoisomer of an Araguspongine/Xestospongin alkaloid, and dopamine from the marine sponge ''Neopetrosia exigua'' collected in Palau |journal=Marine Drugs |volume=2 |issue=4 |pages=154–63 |vauthors=Liu H, Mishima Y, Fujiwara T, Nagai H, Kitazawa A, Mine Y, etal |doi=10.3390/md204154|pmc=3783253 |doi-access=free }}</ref> however, dopamine has been reported in the nervous systems of many other [[symmetry in biology#radially symmetric|radially symmetric]] species, including the [[cnidarian]] [[jellyfish]], [[hydra (genus)|hydra]] and some [[coral]]s.<ref>{{cite journal | vauthors = Kass-Simon G, Pierobon P | title = Cnidarian chemical neurotransmission, an updated overview | journal = Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology | volume = 146 | issue = 1 | pages = 9–25 | date = January 2007 | pmid = 17101286 | doi = 10.1016/j.cbpa.2006.09.008 }}</ref> This dates the emergence of dopamine as a neurotransmitter back to the earliest appearance of the nervous system, over 500 million years ago in the [[Cambrian]] Period. Dopamine functions as a neurotransmitter in [[vertebrate]]s, [[echinoderm]]s, [[arthropod]]s, [[mollusca|molluscs]], and several types of [[worm]].<ref name="Cottrell">{{cite journal | vauthors = Cottrell GA | title = Occurrence of dopamine and noradrenaline in the nervous tissue of some invertebrate species | journal = British Journal of Pharmacology and Chemotherapy | volume = 29 | issue = 1 | pages = 63–69 | date = January 1967 | pmid = 19108240 | pmc = 1557178 | doi = 10.1111/j.1476-5381.1967.tb01939.x }}</ref><ref>{{cite journal | vauthors = Kindt KS, Quast KB, Giles AC, De S, Hendrey D, Nicastro I, Rankin CH, Schafer WR | s2cid = 2092645 | title = Dopamine mediates context-dependent modulation of sensory plasticity in C. elegans | journal = Neuron | volume = 55 | issue = 4 | pages = 662–76 | date = August 2007 | pmid = 17698017 | doi = 10.1016/j.neuron.2007.07.023 | doi-access = free }}</ref>

In every type of animal that has been examined, dopamine has been seen to modify motor behavior.<ref name="Barron">{{cite journal | vauthors = Barron AB, Søvik E, Cornish JL | title = The roles of dopamine and related compounds in reward-seeking behavior across animal phyla | journal = Frontiers in Behavioral Neuroscience | volume = 4 | pages = 163 | year = 2010 | pmid = 21048897 | pmc = 2967375 | doi = 10.3389/fnbeh.2010.00163 | doi-access = free }}</ref> In the [[model organism]], [[nematode]] ''[[Caenorhabditis elegans]]'', it reduces [[animal locomotion|locomotion]] and increases food-exploratory movements; in [[flatworm]]s it produces "screw-like" movements; in [[leech]]es it inhibits swimming and promotes crawling. Across a wide range of vertebrates, dopamine has an "activating" effect on behavior-switching and response selection, comparable to its effect in mammals.<ref name=Barron/><ref>{{cite journal | vauthors = Kalivas PW, Stewart J | s2cid = 10775295 | title = Dopamine transmission in the initiation and expression of drug- and stress-induced sensitization of motor activity | journal = Brain Research. Brain Research Reviews | volume = 16 | issue = 3 | pages = 223–44 | date = 1 September 1991 | pmid = 1665095 | doi = 10.1016/0165-0173(91)90007-U }}</ref>

Dopamine has also consistently been shown to play a role in reward learning, in all animal groups.<ref name=Barron/> As in all vertebrates – [[invertebrate]]s such as [[Nematodes|roundworms]], [[flatworm]]s, [[mollusc]]s and [[Drosophila melanogaster|common fruit flies]] can all be trained to repeat an action if it is consistently followed by an increase in dopamine levels.<ref name="Barron"/> In [[Drosophila melanogaster|fruit flies]], distinct elements for reward learning suggest a modular structure to the insect reward processing system that broadly parallels that in the mammalian one.<ref>{{cite journal | vauthors = Perry CJ, Barron AB | s2cid = 19678766 | title = Neural mechanisms of reward in insects | journal = Annual Review of Entomology | volume = 58 | issue = 1 | pages = 543–62 | date = 2013 | pmid = 23020615 | doi = 10.1146/annurev-ento-120811-153631 | url = http://pdfs.semanticscholar.org/5526/26c5fe0572b4d6419555a1976877c757b0da.pdf | archive-url = https://web.archive.org/web/20200605184440/http://pdfs.semanticscholar.org/5526/26c5fe0572b4d6419555a1976877c757b0da.pdf | url-status = dead | archive-date = 2020-06-05 }}</ref> For example, dopamine regulates short- and long-term learning in monkeys;<ref>{{cite journal | vauthors = Takikawa Y, Kawagoe R, Hikosaka O | title = A possible role of midbrain dopamine neurons in short- and long-term adaptation of saccades to position-reward mapping | journal = Journal of Neurophysiology | volume = 92 | issue = 4 | pages = 2520–29 | date = October 2004 | pmid = 15163669 | doi = 10.1152/jn.00238.2004 | s2cid = 12534057 | url = http://pdfs.semanticscholar.org/b8a6/84a6d815d43db0b2491e4d3db5c664970e6e.pdf | archive-url = https://web.archive.org/web/20190302163535/http://pdfs.semanticscholar.org/b8a6/84a6d815d43db0b2491e4d3db5c664970e6e.pdf | url-status = dead | archive-date = 2019-03-02 }}</ref> in fruit flies, different groups of dopamine neurons mediate reward signals for short- and long-term memories.<ref>{{cite journal | vauthors = Yamagata N, Ichinose T, Aso Y, Plaçais PY, Friedrich AB, Sima RJ, Preat T, Rubin GM, Tanimoto H | title = Distinct dopamine neurons mediate reward signals for short- and long-term memories | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 2 | pages = 578–83 | date = January 2015 | pmid = 25548178 | doi = 10.1073/pnas.1421930112 | pmc = 4299218 | bibcode = 2015PNAS..112..578Y | doi-access = free }}</ref>

It had long been believed that arthropods were an exception to this with dopamine being seen as having an adverse effect. Reward was seen to be mediated instead by [[octopamine]], a neurotransmitter closely related to [[norepinephrine]].<ref name=Waddell/> More recent studies, however, have shown that dopamine does play a part in reward learning in fruit flies. It has also been found that the rewarding effect of octopamine is due to its activating a set of dopaminergic neurons not previously accessed in the research.<ref name="Waddell">{{cite journal | vauthors = Waddell S | title = Reinforcement signalling in Drosophila; dopamine does it all after all | journal = Current Opinion in Neurobiology | volume = 23 | issue = 3 | pages = 324–329 | date = June 2013 | pmid = 23391527 | pmc = 3887340 | doi = 10.1016/j.conb.2013.01.005 }}</ref> Dopamine can also be found in [[cephalopod ink]].<ref>{{cite journal | vauthors = Lucero MT, Farrington H, Gilly WF | title = Quantification of L-Dopa and Dopamine in Squid Ink: Implications for Chemoreception | journal = The Biological Bulletin | volume = 187 | issue = 1 | pages = 55–63 | date = August 1994 | pmid = 29281314 | doi = 10.2307/1542165 }}</ref>

===Plants===

[[File:Bananas white background DS.jpg|thumb|right|Dopamine can be found in the [[Banana peel|peel]] and fruit pulp of [[bananas]].|alt=Photo of a bunch of bananas.]]

Many plants, including a variety of food plants, synthesize dopamine to varying degrees.<ref name=Kulma/> The highest concentrations have been observed in bananas—the fruit pulp of [[red banana|red]] and [[Cavendish banana|yellow bananas]] contains dopamine at levels of 40 to 50 parts per million by weight.<ref name=Kulma/> Potatoes, avocados, broccoli, and Brussels sprouts may also contain dopamine at levels of 1 part per million or more; oranges, tomatoes, spinach, beans, and other plants contain measurable concentrations less than 1 part per million.<ref name=Kulma>{{cite journal |vauthors=Kulma A, Szopa J |title=Catecholamines are active compounds in plants |journal=Plant Science |year=2007 |volume=172 |pages=433–40 |doi=10.1016/j.plantsci.2006.10.013 |issue=3|bibcode=2007PlnSc.172..433K }}</ref> The dopamine in plants is synthesized from the amino acid [[tyrosine]], by biochemical mechanisms similar to those that animals use.<ref name=Kulma/> It can be metabolized in a variety of ways, producing [[melanin]] and a variety of [[alkaloid]]s as byproducts.<ref name=Kulma/> The functions of plant [[catecholamine]]s have not been clearly established, but there is evidence that they play a role in the response to stressors such as bacterial infection, act as growth-promoting factors in some situations, and modify the way that sugars are metabolized. The receptors that mediate these actions have not yet been identified, nor have the intracellular mechanisms that they activate.<ref name=Kulma/>

Dopamine consumed in food cannot act on the brain, because it cannot cross the blood–brain barrier.<ref name="Nice-pharma"/> However, there are also a variety of plants that contain L-DOPA, the metabolic precursor of dopamine.<ref name=Ingle>{{cite journal | vauthors = Ingle PK |year=2003 |title=L-DOPA bearing plants |journal=Natural Product Radiance |volume=2 |pages=126–33 |url=http://nopr.niscair.res.in/bitstream/123456789/12261/1/NPR%202%283%29%20126-133.pdf |archive-url=https://web.archive.org/web/20140302114720/http://nopr.niscair.res.in/bitstream/123456789/12261/1/NPR%202%283%29%20126-133.pdf |archive-date=2014-03-02 |url-status=live |access-date=24 September 2015}}</ref> The highest concentrations are found in the leaves and bean pods of plants of the genus ''[[Mucuna]]'', especially in ''[[Mucuna pruriens]]'' (velvet beans), which have been used as a source for L-DOPA as a drug.<ref>{{cite journal |year=1993 |title=Occurrence of L-DOPA and dopamine in plants and cell cultures of ''Mucuna pruriens'' and effects of 2, 4-d and NaCl on these compounds |journal=Plant Cell, Tissue and Organ Culture |volume=33 |issue=3 |pages=259–64 |doi=10.1007/BF02319010 | vauthors = Wichers HJ, Visser JF, Huizing HJ, Pras N|s2cid=44814336 }}</ref> Another plant containing substantial amounts of L-DOPA is ''[[Vicia faba]]'', the plant that produces fava beans (also known as "broad beans"). The level of L-DOPA in the beans, however, is much lower than in the pod shells and other parts of the plant.<ref>{{cite journal | vauthors = Longo R, Castellani A, Sberze P, Tibolla M | title = Distribution of l-dopa and related amino acids in Vicia | journal = Phytochemistry | year = 1974 | volume = 13 | issue = 1 | pages = 167–71 | doi = 10.1016/S0031-9422(00)91287-1| bibcode = 1974PChem..13..167L }}</ref> The seeds of ''[[Cassia (genus)|Cassia]]'' and ''[[Bauhinia]]'' trees also contain substantial amounts of L-DOPA.<ref name=Ingle/>

In a species of [[seawater|marine]] [[green algae]] ''[[Ulvaria obscura]]'', a major component of some [[algal bloom]]s, dopamine is present in very high concentrations, estimated at 4.4% of dry weight. There is evidence that this dopamine functions as an anti-[[herbivore]] defense, reducing consumption by snails and [[isopoda|isopods]].<ref name="pmid16489461">{{cite journal | vauthors = Van Alstyne KL, Nelson AV, Vyvyan JR, Cancilla DA | s2cid = 5029574 | title = Dopamine functions as an antiherbivore defense in the temperate green alga Ulvaria obscura | journal = Oecologia | volume = 148 | issue = 2 | pages = 304–11 | date = June 2006 | pmid = 16489461 | doi = 10.1007/s00442-006-0378-3 | bibcode = 2006Oecol.148..304V }}</ref>

===As a precursor for melanin===
{{anchor|dopamine-melanin}}

Melanins are a family of dark-pigmented substances found in a wide range of organisms.<ref name=Simon/> Chemically they are closely related to dopamine, and there is a type of melanin, known as '''dopamine-melanin''', that can be synthesized by oxidation of dopamine via the enzyme [[tyrosinase]].<ref name=Simon>{{cite journal | vauthors = Simon JD, Peles D, Wakamatsu K, Ito S | title = Current challenges in understanding melanogenesis: bridging chemistry, biological control, morphology, and function | journal = Pigment Cell & Melanoma Research | volume = 22 | issue = 5 | pages = 563–79 | date = October 2009 | pmid = 19627559 | doi = 10.1111/j.1755-148X.2009.00610.x | doi-access = free }}</ref> The melanin that darkens human skin is not of this type: it is synthesized by a pathway that uses L-DOPA as a precursor but not dopamine.<ref name=Simon/> However, there is substantial evidence that the [[neuromelanin]] that gives a dark color to the brain's substantia nigra is at least in part dopamine-melanin.<ref>{{cite journal | vauthors = Fedorow H, Tribl F, Halliday G, Gerlach M, Riederer P, Double KL | s2cid = 503902 | title = Neuromelanin in human dopamine neurons: comparison with peripheral melanins and relevance to Parkinson's disease | journal = Progress in Neurobiology | volume = 75 | issue = 2 | pages = 109–24 | date = February 2005 | pmid = 15784302 | doi = 10.1016/j.pneurobio.2005.02.001 }}</ref>

Dopamine-derived melanin probably appears in at least some other biological systems as well. Some of the dopamine in plants is likely to be used as a precursor for dopamine-melanin.<ref>{{cite journal |year=1967 |title=Melanins from DOPA-containing plants |journal=Phytochemistry |volume=6 |issue=1 |pages=13–18 |doi=10.1016/0031-9422(67)85002-7 | vauthors = Andrews RS, Pridham JB|bibcode=1967PChem...6...13A }}</ref> The complex patterns that appear on butterfly wings, as well as black-and-white stripes on the bodies of insect larvae, are also thought to be caused by spatially structured accumulations of dopamine-melanin.<ref>{{cite journal | vauthors = Beldade P, Brakefield PM | s2cid = 17417235 | title = The genetics and evo-devo of butterfly wing patterns | journal = Nature Reviews. Genetics | volume = 3 | issue = 6 | pages = 442–52 | date = June 2002 | pmid = 12042771 | doi = 10.1038/nrg818 }}</ref>