Editing Serotonin (section)

===Unicellular organisms===
Serotonin is used by a variety of single-cell organisms for various purposes. [[SSRIs]] have been found to be toxic to algae.<ref name="pmid16753215">{{cite journal | vauthors = Johnson DJ, Sanderson H, Brain RA, Wilson CJ, Solomon KR | title = Toxicity and hazard of selective serotonin reuptake inhibitor antidepressants fluoxetine, fluvoxamine, and sertraline to algae | journal = Ecotoxicology and Environmental Safety | volume = 67 | issue = 1 | pages = 128–139 | date = May 2007 | pmid = 16753215 | doi = 10.1016/j.ecoenv.2006.03.016 | bibcode = 2007EcoES..67..128J }}</ref> The gastrointestinal parasite ''[[Entamoeba histolytica]]'' secretes serotonin, causing a sustained secretory diarrhea in some people.<ref name="pmid6308760">{{cite journal | vauthors = McGowan K, Kane A, Asarkof N, Wicks J, Guerina V, Kellum J, Baron S, Gintzler AR, Donowitz M | title = Entamoeba histolytica causes intestinal secretion: role of serotonin | journal = Science | volume = 221 | issue = 4612 | pages = 762–764 | date = August 1983 | pmid = 6308760 | doi = 10.1126/science.6308760 | bibcode = 1983Sci...221..762M }}</ref><ref name="pmid2861068">{{cite book | vauthors = McGowan K, Guerina V, Wicks J, Donowitz M | chapter = Secretory Hormones of ''Entamoeba histolytica'' | title = Ciba Foundation Symposium | volume = 112 | pages = 139–154 | year = 1985 | pmid = 2861068 | doi = 10.1002/9780470720936.ch8 | series = Novartis Foundation Symposia | isbn = 978-0-470-72093-6 }}</ref> Patients infected with ''E. histolytica'' have been found to have highly elevated serum serotonin levels, which returned to normal following resolution of the infection.<ref name = "Banu_2005">{{cite journal | vauthors = Banu N, Zaidi KR, Mehdi G, Mansoor T | title = Neurohumoral alterations and their role in amoebiasis | journal = Indian Journal of Clinical Biochemistry | volume = 20 | issue = 2 | pages = 142–145 | date = July 2005 | pmid = 23105547 | pmc = 3453840 | doi = 10.1007/BF02867414 }}</ref> ''E. histolytica'' also responds to the presence of serotonin by becoming more virulent.<ref name="pmid2561282">{{cite journal | vauthors = Acharya DP, Sen MR, Sen PC | title = Effect of exogenous 5-hydroxytryptamine on pathogenicity of Entamoeba histolytica in experimental animals | journal = Indian Journal of Experimental Biology | volume = 27 | issue = 8 | pages = 718–720 | date = August 1989 | pmid = 2561282 }}</ref> This means serotonin secretion not only serves to increase the spread of [[entamoeba]]s by giving the host diarrhea but also serves to coordinate their behaviour according to their population density, a phenomenon known as [[quorum sensing]]. Outside the gut of a host, there is nothing that the entamoebas provoke to release serotonin, hence the serotonin concentration is very low. Low serotonin signals to the entamoebas they are outside a host and they become less virulent to conserve energy. When they enter a new host, they multiply in the gut, and become more virulent as the enterochromaffine cells get provoked by them and the serotonin concentration increases.

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