Serotonin - Wikipedia Serotonin For other uses, see Serotonin ( disambiguation ). Serotonin Clinical data Synonyms 5 - HT, 5 - Hydroxytryptamine, Enteramine, Thrombocytin, 3 - ( β - Aminoethyl ) - 5 - hydroxyindole, Thrombotonin Physiological data Source tissues raphe nuclei, enterochromaffin cells Target tissues system - wide Receptors 5 - HT, 5 - HT, 5 - HT, 5 - HT, 5 - HT, 5 - HT, 5 - HT Agonists SSRIs, MAOIs ( indirectly ) Precursor 5 - HTP Biosynthesis Aromatic L - amino acid decarboxylase Metabolism MAO Identifiers IUPAC name 3 - ( 2 - Aminoethyl ) - 1H - indol - 5 - ol CAS Number 50 - 67 - 9 PubChem CID 5202 IUPHAR / BPS 5 ChemSpider 5013 KEGG C00780 PDB ligand SRO ( PDBe, RCSB PDB ) ECHA InfoCard 100.000. 054 Serotonin Names IUPAC names 5 - Hydroxytryptamine or 3 - ( 2 - Aminoethyl ) indol - 5 - ol Other names 5 - Hydroxytryptamine, 5 - HT, Enteramine ; Thrombocytin, 3 - ( β - Aminoethyl ) - 5 - hydroxyindole, Thrombotonin Identifiers CAS Number 50 - 67 - 9 3D model ( JSmol ) Interactive image ChEBI CHEBI : 28790 ChEMBL ChEMBL39 ChemSpider 5013 ECHA InfoCard 100.000. 054 IUPHAR / BPS 5 KEGG C00780 MeSH Serotonin PubChem CID 5202 UNII 333DO1RDJY InChI InChI = 1S / C10H12N2O / c11 - 4 - 3 - 7 - 6 - 12 - 10 - 2 - 1 - 8 ( 13 ) 5 - 9 ( 7 ) 10 / h1 - 2, 5 - 6, 12 - 13H, 3 - 4, 11H2 Key : QZAYGJVTTNCVMB - UHFFFAOYSA - N InChI = 1 / C10H12N2O / c11 - 4 - 3 - 7 - 6 - 12 - 10 - 2 - 1 - 8 ( 13 ) 5 - 9 ( 7 ) 10 / h1 - 2, 5 - 6, 12 - 13H, 3 - 4, 11H2 Key : QZAYGJVTTNCVMB - UHFFFAOYAX SMILES c1cc2c ( cc1O ) c ( c ( nH ) 2 ) CCN Properties Chemical formula Molar mass 176.215 g / mol Appearance White powder Melting point 167.7 ° C ( 333.9 ° F ; 440.8 K ) 121 -- 122 ° C ( ligroin ) Boiling point 416 ± 30 ° C ( at 760 Torr ) Solubility in water slightly soluble Acidity ( pK ) 10.16 in water at 23.5 ° C Dipole moment 2.98 D Hazards Safety data sheet External MSDS Lethal dose or concentration ( LD, LC ) : LD ( median dose ) 750 mg / kg ( subcutaneous, rat ), 4500 mg / kg ( intraperitoneal, rat ), 60 mg / kg ( oral, rat ) Except where otherwise noted, data are given for materials in their standard state ( at 25 ° C ( 77 ° F ), 100 kPa ). Y verify ( what is ? ) Infobox references Serotonin ( / ˌsɛrəˈtoʊnɪn, ˌsɪərə - / ) or 5 - hydroxytryptamine ( 5 - HT ) is a monoamine neurotransmitter. Biochemically the indoleamine molecule is derived from the amino acid tryptophan. Serotonin is primarily found in the enteric nervous system located in the gastrointestinal tract ( GI tract ). However, it is also produced in the central nervous system ( CNS ), specifically in the Raphe nuclei located in the brainstem. Additionally, serotonin is stored in blood platelets and is released during agitation and vasoconstriction, where it then acts as an agonist to other platelets. Serotonin is popularly thought to be a contributor to feelings of well - being and happiness. Approximately 90 % of the human body 's total serotonin is located in the enterochromaffin cells in the GI tract, where it is used to regulate intestinal movements. The serotonin is secreted luminally and basolaterally which leads to increased serotonin uptake by circulating platelets and activation after stimulation, which gives increased stimulation of myenteric neurons and gastrointestinal motility. The remainder is synthesized in serotonergic neurons of the CNS, where it has various functions. These include the regulation of mood, appetite, and sleep. Serotonin also has some cognitive functions, including memory and learning. Modulation of serotonin at synapses is thought to be a major action of several classes of pharmacological antidepressants. Serotonin secreted from the enterochromaffin cells eventually finds its way out of tissues into the blood. There, it is actively taken up by blood platelets, which store it. When the platelets bind to a clot, they release serotonin, where it can serve as a vasoconstrictor or a vasodilator while regulating hemostasis and blood clotting. In high concentrations, serotonin acts as a vasoconstrictor by contracting endothelial smooth muscle directly or by potentiating the effects of other vasoconstrictors ( e.g. angiotensin II, norepinephrine ). The vasoconstrictive property is mostly seen in pathologic states affecting the endothelium such as atherosclerosis or chronic hypertension. In physiologic states, vasodilation occurs through the serotonin mediated release of nitric oxide from endothelial cells. Additionally, it inhibits the release of norepinephrine from adrenergic nerves. Serotonin is also a growth factor for some types of cells, which may give it a role in wound healing. There are various serotonin receptors. Serotonin is metabolized mainly to 5 - HIAA, chiefly by the liver. Metabolism involves first oxidation by monoamine oxidase to the corresponding aldehyde. This is followed by oxidation by aldehyde dehydrogenase to 5 - HIAA, the indole acetic acid derivative. The latter is then excreted by the kidneys. Aside from mammals it is found in all bilateral animals including worms and insects, as well as in fungi and plants. Serotonin 's presence in insect venoms and plant spines serves to cause pain, which is a side - effect of serotonin injection. Serotonin is produced by pathogenic amoebae, and its effect in the human gut is diarrhea. Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds. Contents 1 Functions 1.1 Perception of resource availability 1.2 Cellular effects 1.2. 1 Receptors 1.2. 2 Termination 1.2. 3 Serotonylation 1.3 Nervous system 1.3. 1 Ultrastructure and Function 1.3. 2 Microanatomy 1.3. 3 Psychological influences 1.4 Outside the nervous system 1.4. 1 In the digestive tract ( emetic ) 1.4. 2 Bone metabolism 1.4. 3 Organ development 1.4. 4 Cardiovascular growth factor 2 Pharmacology 2.1 Psychedelic drugs 2.2 Antidepressants 2.2. 1 Serotonin syndrome 2.3 Antiemetics 2.4 Other 2.5 Methyl - tryptamines and hallucinogens 3 Comparative biology and evolution 3.1 Unicellular organisms 3.2 Plants 3.3 Invertebrates 3.4 Insects 3.5 Growth and reproduction 3.6 Aging and age - related phenotypes 4 Biochemical mechanisms 4.1 Biosynthesis 4.2 Effects of food content 5 History and etymology 6 See also 7 Notes 8 References 9 Further reading 10 External links Functions Serotonin is a neurotransmitter and is found in all bilateral animals including insects. Serotonin is also present in plants ( phytoserotonin ). Perception of resource availability Serotonin mediates the animal 's perceptions of resources ; In less complex animals, such as some invertebrates, resources simply mean food availability. In plants serotonin synthesis seems to be associated with stress signals. In more complex animals, such as arthropods and vertebrates, resources also can mean social dominance. In response to the perceived abundance or scarcity of resources, an animal 's growth, reproduction or mood may be elevated or lowered. This may somewhat depend on how much serotonin the organism has at its disposal. Cellular effects Receptors Main article : 5 - HT receptor The 5 - HT receptors, the receptors for serotonin, are located on the cell membrane of nerve cells and other cell types in animals, and mediate the effects of serotonin as the endogenous ligand and of a broad range of pharmaceutical and hallucinogenic drugs. Except for the 5 - HT receptor, a ligand - gated ion channel, all other 5 - HT receptors are G - protein - coupled receptors ( also called seven - transmembrane, or heptahelical receptors ) that activate an intracellular second messenger cascade. Termination Serotonergic action is terminated primarily via uptake of 5 - HT from the synapse. This is accomplished through the specific monoamine transporter for 5 - HT, SERT, on the presynaptic neuron. Various agents can inhibit 5 - HT reuptake, including cocaine, dextromethorphan ( an antitussive ), tricyclic antidepressants and selective serotonin reuptake inhibitors ( SSRIs ). A 2006 study conducted by the University of Washington suggested that a newly discovered monoamine transporter, known as PMAT, may account for `` a significant percentage of 5 - HT clearance ''. Contrasting with the high - affinity SERT, the PMAT has been identified as a low - affinity transporter, with an apparent K of 114 micromoles / l for serotonin ; approximately 230 times higher than that of SERT. However, the PMAT, despite its relatively low serotonergic affinity, has a considerably higher transport ' capacity ' than SERT, `` resulting in roughly comparable uptake efficiencies to SERT in heterologous expression systems. '' The study also suggests some SSRIs, such as fluoxetine and sertraline anti-depressants, inhibit PMAT but at IC values which surpass the therapeutic plasma concentrations by up to four orders of magnitude. Therefore, SSRI monotherapy is `` ineffective '' in PMAT inhibition. At present, no known pharmaceuticals are known to appreciably inhibit PMAT at normal therapeutic doses. The PMAT also suggestively transports dopamine and norepinephrine, albeit at K values even higher than that of 5 - HT ( 330 -- 15,000 μmoles / L ). Serotonylation Main article : Serotonylation Serotonin can also signal through a nonreceptor mechanism called serotonylation, in which serotonin modifies proteins. This process underlies serotonin 's effects upon platelet - forming cells ( thrombocytes ) in which it links to the modification of signaling enzymes called GTPases that then trigger the release of vesicle contents by exocytosis. A similar process underlies the pancreatic release of insulin. The effects of serotonin upon vascular smooth muscle tone ( this is the biological function from which serotonin originally got its name ) depend upon the serotonylation of proteins involved in the contractile apparatus of muscle cells. Binding profile of serotonin Receptor K ( nM ) Receptor function 5 - HT receptor family signals via G inhibition of adenylyl cyclase. 5 - HT 3.17 Memory ( agonists ↓ ) ; learning ( agonists ↓ ) ; anxiety ( agonists ↓ ) ; depression ( agonists ↓ ) ; positive, negative, and cognitive symptoms of schizophrenia ( partial agonists ↓ ) ; analgesia ( agonists ↑ ) ; aggression ( agonists ↓ ) ; dopamine release in the prefrontal cortex ( agonists ↑ ) ; serotonin release and synthesis ( agonists ↓ ) 5 - HT 4.32 Vasoconstriction ( agonists ↑ ) ; aggression ( agonists ↓ ) ; bone mass ( ↓ ). Serotonin autoreceptor. 5 - HT 5.03 Vasoconstriction ( agonists ↑ ) 5 - HT 7.53 5 - HT 10 5 - HT receptor family signals via G activation of phospholipase C. 5 - HT 11.55 Psychedelia ( agonists ↑ ) ; depression ( agonists & antagonists ↓ ) ; anxiety ( antagonists ↓ ) ; positive and negative symptoms of schizophrenia ( antagonists ↓ ) ; norepinephrine release from the locus coeruleus ( antagonists ↑ ) ; glutamate release in the prefrontal cortex ( agonists ↑ ) ; urinary bladder contractions ( agonists ↑ ) 5 - HT 8.71 Cardiovascular functioning ( agonists increase risk of pulmonary hypertension ), empathy ( via the spindle neurons or Von Economo neurons ) 5 - HT 5.02 Dopamine release into the mesocorticolimbic pathway ( agonists ↓ ) ; acetylcholine release in the prefrontal cortex ( agonists ↑ ) ; appetite ( agonists ↓ ) ; antipsychotic effects ( agonists ↑ ) ; antidepressant effects ( agonists & antagonists ↑ ) Other 5 - HT receptors 5 - HT 593 Emesis ( agonists ↑ ) ; anxiolysis ( antagonists ↑ ). 5 - HT 125.89 Movement of food across the GI tract ( agonists ↑ ) ; memory & learning ( agonists ↑ ) ; antidepressant effects ( agonists ↑ ). Signalling via G activation of adenylyl cyclase. 5 - HT 251.2 Memory consolidation. Signals via G inhibition of adenylyl cyclase. 5 - HT 98.41 Cognition ( antagonists ↑ ) ; antidepressant effects ( agonists & antagonists ↑ ) ; anxiogenic effects ( antagonists ↑ ). G signalling via activating adenylyl cyclase. 5 - HT 8.11 Cognition ( antagonists ↑ ) ; antidepressant effects ( antagonists ↑ ). Acts by G signalling via activating adenylyl cyclase. Nervous system Serotonin system, contrasted with the dopamine system The neurons of the raphe nuclei are the principal source of 5 - HT release in the brain. There are nine raphe nuclei, designated B1 - B9, which contain the majority of serotonin - containing neurons ( some scientists chose to group the nuclei raphes lineares into one nucleus ), all of which are located along the midline of the brainstem, and centered on the reticular formation. Axons from the neurons of the raphe nuclei form a neurotransmitter system reaching almost every part of the central nervous system. Axons of neurons in the lower raphe nuclei terminate in the cerebellum and spinal cord, while the axons of the higher nuclei spread out in the entire brain. Ultrastructure and function The serotonin nuclei may also be divided into two main groups, the rostral and caudal containing three and four nuclei respectively. The rostral group consists of the caudal linear nuclei ( B8 ), the dorsal raphe nuclei ( B6 and B7 ) and the median raphe nuclei ( B5, B8 and B9 ), that project into multiple cortical and subcortical structures. The caudal group consists of the nucleus raphe magnus ( B3 ), raphe obscurus nucleus ( B2 ), raphe pallidus nucleus ( B1 ), and lateral medullary reticular formation, that project into the brainstem. Serotonergic pathway are involved in sensorimotor function, with pathways projecting both into cortical ( Dorsal and Median Raphe Nuclei ), subcortical, and spinal areas involved in motor activity. Pharmacological manipulation suggest that serotonergic activity increases with motor activity, while firing rates of serotonergic neurons increase with intense visual stimuli. The descending projections form a pathway that inhibits pain called the `` descending inhibitory pathway '' that may be relevant to disorder such as fibromyalgia, migraine and other pain disorders, and the efficacy of antidepressants in them. Serotonergic projections from the caudal nuclei are involved in regulating mood, emotion and hypo or hyperserotonergic states may be involved in depression and sickness behavior. Microanatomy Serotonin is released into the synapse, or space between neurons, and diffuses over a relatively wide gap ( > 20 μm ) to activate 5 - HT receptors located on the dendrites, cell bodies and presynaptic terminals of adjacent neurons. When humans smell food, dopamine is released to increase the appetite. But, unlike in worms, serotonin does not increase anticipatory behaviour in humans ; instead, the serotonin released while consuming activates 5 - HT2C receptors on dopamine - producing cells. This halts their dopamine release, and thereby serotonin decreases appetite. Drugs that block 5 - HT receptors make the body unable to recognize when it is no longer hungry or otherwise in need of nutrients, and are associated with weight gain, especially in people with a low number of receptors. The expression of 5 - HT receptors in the hippocampus follows a diurnal rhythm, just as the serotonin release in the ventromedial nucleus, which is characterised by a peak at morning when the motivation to eat is strongest. In macaques, alpha males have twice the level of serotonin released in the brain than subordinate males and females ( as measured by the levels of 5 - Hydroxyindoleacetic acid ( 5 - HIAA ) in the cerebro - spinal fluid ). Dominance status and cerebro - serotonin levels appear to be positively correlated. When dominant males were removed from such groups, subordinate males begin competing for dominance. Once new dominance hierarchies were established, serotonin levels of the new dominant individuals also increased to double those in subordinate males and females. The reason why serotonin levels are only high in dominant males but not dominant females has not yet been established. In humans, levels of 5 - HT receptor activation in the brain show negative correlation with aggression, and a mutation in the gene that codes for the 5 - HT receptor may double the risk of suicide for those with that genotype. Serotonin in the brain is not usually degraded after use, but is collected by serotonergic neurons by serotonin transporters on their cell surfaces. Studies have revealed nearly 10 % of total variance in anxiety - related personality depends on variations in the description of where, when and how many serotonin transporters the neurons should deploy. Psychological influences Serotonin has been implicated in cognition, mood, anxiety and psychosis, but strong clarity has not been achieved. Outside the nervous system In the digestive tract ( emetic ) The gut is surrounded by enterochromaffin cells, which release serotonin in response to food in the lumen. This makes the gut contract around the food. Platelets in the veins draining the gut collect excess serotonin. If irritants are present in the food, the enterochromaffin cells release more serotonin to make the gut move faster, i.e., to cause diarrhea, so the gut is emptied of the noxious substance. If serotonin is released in the blood faster than the platelets can absorb it, the level of free serotonin in the blood is increased. This activates 5 - HT3 receptors in the chemoreceptor trigger zone that stimulate vomiting. The enterochromaffin cells not only react to bad food but are also very sensitive to irradiation and cancer chemotherapy. Drugs that block 5HT3 are very effective in controlling the nausea and vomiting produced by cancer treatment, and are considered the gold standard for this purpose. Bone metabolism In mice and humans, alterations in serotonin levels and signalling have been shown to regulate bone mass. Mice that lack brain serotonin have osteopenia, while mice that lack gut serotonin have high bone density. In humans, increased blood serotonin levels have been shown to be significant negative predictor of low bone density. Serotonin can also be synthesized, albeit at very low levels, in the bone cells. It mediates its actions on bone cells using three different receptors. Through 5 - HT receptors, it negatively regulates bone mass, while it does so positively through 5 - HT receptors and 5 - HT receptors. There is very delicate balance between physiological role of gut serotonin and its pathology. Increase in the extracellular content of serotonin results in a complex relay of signals in the osteoblasts culminating in FoxO1 / Creb and ATF4 dependent transcriptional events. These studies have opened a new area of research in bone metabolism that can be potentially harnessed to treat bone mass disorders. Organ development Since serotonin signals resource availability it is not surprising that it affects organ development. Many human and animal studies have shown that nutrition in early life can influence, in adulthood, such things as body fatness, blood lipids, blood pressure, atherosclerosis, behavior, learning and longevity. Rodent experiment shows that neonatal exposure to SSRI 's makes persistent changes in the serotonergic transmission of the brain resulting in behavioral changes, which are reversed by treatment with antidepressants. By treating normal and knockout mice lacking the serotonin transporter with fluoxetine scientists showed that normal emotional reactions in adulthood, like a short latency to escape foot shocks and inclination to explore new environments were dependent on active serotonin transporters during the neonatal period. Human serotonin can also act as a growth factor directly. Liver damage increases cellular expression of 5 - HT2A and 5 - HT2B receptors, mediating liver compensatory regrowth ( see Liver § Regeneration and transplantation ) Serotonin present in the blood then stimulates cellular growth to repair liver damage. 5HT2B receptors also activate osteocytes, which build up bone However, serotonin also inhibits osteoblasts, through 5 - HT1B receptors. Cardiovascular growth factor Main article : Cardiac fibrosis Serotonin, in addition, evokes endothelial nitric oxide synthase activation and stimulates, through a 5 - HT1B receptor - mediated mechanism, the phosphorylation of p44 / p42 mitogen - activated protein kinase activation in bovine aortic endothelial cell cultures. In blood, serotonin is collected from plasma by platelets, which store it. It is thus active wherever platelets bind in damaged tissue, as a vasoconstrictor to stop bleeding, and also as a fibrocyte mitotic ( growth factor ), to aid healing. Pharmacology Several classes of drugs target the 5 - HT system, including some antidepressants, antipsychotics, anxiolytics, antiemetics, and antimigraine drugs, as well as the psychedelic drugs and empathogens. Psychedelic drugs The psychedelic drugs psilocin / psilocybin, DMT, mescaline, psychedelic mushroom and LSD are agonists, primarily at 5HT receptors. The empathogen - entactogen MDMA releases serotonin from synaptic vesicles of neurons. Antidepressants Main articles : SSRI and MAOI Drugs that alter serotonin levels are used in treating depression, generalized anxiety disorder and social phobia. Monoamine oxidase inhibitors ( MAOIs ) prevent the breakdown of monoamine neurotransmitters ( including serotonin ), and therefore increase concentrations of the neurotransmitter in the brain. MAOI therapy is associated with many adverse drug reactions, and patients are at risk of hypertensive emergency triggered by foods with high tyramine content, and certain drugs. Some drugs inhibit the re-uptake of serotonin, making it stay in the synaptic cleft longer. The tricyclic antidepressants ( TCAs ) inhibit the reuptake of both serotonin and norepinephrine. The newer selective serotonin reuptake inhibitors ( SSRIs ) have fewer side - effects and fewer interactions with other drugs. Certain SSRI medications have been shown to lower serotonin levels below the baseline after chronic use, despite initial increases. The 5 - HTTLPR gene codes for the number of serotonin transporters in the brain, with more serotonin transporters causing decreased duration and magnitude of serotonergic signaling. The 5 - HTTLPR polymorphism ( l / l ) causing more serotonin transporters to be formed is also found to be more resilient against depression and anxiety. Serotonin syndrome Main article : Serotonin syndrome Extremely high levels of serotonin can cause a condition known as serotonin syndrome, with toxic and potentially fatal effects. In practice, such toxic levels are essentially impossible to reach through an overdose of a single antidepressant drug, but require a combination of serotonergic agents, such as an SSRI with an MAOI. The intensity of the symptoms of serotonin syndrome vary over a wide spectrum, and the milder forms are seen even at nontoxic levels. Antiemetics Some 5 - HT antagonists, such as ondansetron, granisetron, and tropisetron, are important antiemetic agents. They are particularly important in treating the nausea and vomiting that occur during anticancer chemotherapy using cytotoxic drugs. Another application is in the treatment of postoperative nausea and vomiting. Other Some serotonergic agonist drugs cause fibrosis anywhere in the body, particularly the syndrome of retroperitoneal fibrosis, as well as cardiac valve fibrosis. In the past, three groups of serotonergic drugs have been epidemiologically linked with these syndromes. These are the serotonergic vasoconstrictive antimigraine drugs ( ergotamine and methysergide ), the serotonergic appetite suppressant drugs ( fenfluramine, chlorphentermine, and aminorex ), and certain anti-Parkinsonian dopaminergic agonists, which also stimulate serotonergic 5 - HT receptors. These include pergolide and cabergoline, but not the more dopamine - specific lisuride. As with fenfluramine, some of these drugs have been withdrawn from the market after groups taking them showed a statistical increase of one or more of the side effects described. An example is pergolide. The drug was declining in use since it was reported in 2003 to be associated with cardiac fibrosis. Two independent studies published in the New England Journal of Medicine in January 2007, implicated pergolide, along with cabergoline, in causing valvular heart disease. As a result of this, the FDA removed pergolide from the United States market in March 2007. ( Since cabergoline is not approved in the United States for Parkinson 's Disease, but for hyperprolactinemia, the drug remains on the market. Treatment for hyperprolactinemia requires lower doses than that for Parkinson 's Disease, diminishing the risk of valvular heart disease ). Methyl - tryptamines and hallucinogens For details on tryptamine neurotransmitters in humans, see Trace amine. Several plants contain serotonin together with a family of related tryptamines that are methylated at the amino ( NH ) and ( OH ) groups, are N - oxides, or miss the OH group. These compounds do reach the brain, although some portion of them are metabolized by monoamine oxidase enzymes ( mainly MAO - A ) in the liver. Examples are plants from the genus Anadenanthera that are used in the hallucinogenic yopo snuff. These compounds are widely present in the leaves of many plants, and may serve as deterrents for animal ingestion. Serotonin occurs in several mushrooms of the genus Panaeolus. Comparative Biology and evolution Unicellular organisms Serotonin is used by a variety of single - cell organisms for various purposes. SSRIs have been found to be toxic to algae. The gastrointestinal parasite Entamoeba histolytica secretes serotonin, causing a sustained secretory diarrhea in some people. Patients infected with E. histolytica have been found to have highly elevated serum serotonin levels, which returned to normal following resolution of the infection. E. histolytica also responds to the presence of serotonin by becoming more virulent. This means serotonin secretion not only serves to increase the spread of enteamoebas 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 entoamoebas provoke to release serotonin, hence the serotonin concentration is very low. Low serotonin signals to the entoamoebas 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. Plants In drying seeds, serotonin production is a way to get rid of the buildup of poisonous ammonia. The ammonia is collected and placed in the indole part of L - tryptophan, which is then decarboxylated by tryptophan decarboxylase to give tryptamine, which is then hydroxylated by a cytochrome P450 monooxygenase, yielding serotonin. However, since serotonin is a major gastrointestinal tract modulator, it may be produced by plants in fruits as a way of speeding the passage of seeds through the digestive tract, in the same way as many well - known seed and fruit associated laxatives. Serotonin is found in mushrooms, fruits and vegetables. The highest values of 25 -- 400 mg / kg have been found in nuts of the walnut ( Juglans ) and hickory ( Carya ) genera. Serotonin concentrations of 3 -- 30 mg / kg have been found in plantains, pineapples, banana, kiwifruit, plums, and tomatoes. Moderate levels from 0.1 -- 3 mg / kg have been found in a wide range of tested vegetables. Serotonin is one compound of the poison contained in stinging nettles ( Urtica dioica ), where it causes pain on injection in the same manner as its presence in insect venoms ( see below ). It is also naturally found in Paramuricea clavata, or the Red Sea Fan. Serotonin and tryptophan have been found in chocolate with varying cocoa contents. The highest serotonin content ( 2.93 μg / g ) was found in chocolate with 85 % cocoa, and the highest tryptophan content ( 13.27 -- 13.34 μg / g ) was found in 70 -- 85 % cocoa. The intermediate in the synthesis from tryptophan to serotonin, 5 - hydroxytryptophan, was not found. Invertebrates Serotonin functions as a neurotransmitter in the nervous systems of most animals. For example, in the roundworm Caenorhabditis elegans, which feeds on bacteria, serotonin is released as a signal in response to positive events, such as finding a new source of food or in male animals finding a female with which to mate. When a well - fed worm feels bacteria on its cuticle, dopamine is released, which slows it down ; if it is starved, serotonin also is released, which slows the animal down further. This mechanism increases the amount of time animals spend in the presence of food. The released serotonin activates the muscles used for feeding, while octopamine suppresses them. Serotonin diffuses to serotonin - sensitive neurons, which control the animal 's perception of nutrient availability. If lobsters are injected with serotonin, they behave like dominant individuals whereas octopamine causes subordinate behavior. A crayfish that is frightened may flip its tail to flee, and the effect of serotonin on this behavior depends largely on the animal 's social status. Serotonin inhibits the fleeing reaction in subordinates, but enhances it in socially dominant or isolated individuals. The reason for this is social experience alters the proportion between serotonin receptors ( 5 - HT receptors ) that have opposing effects on the fight - or - flight response. The effect of 5 - HT receptors predominates in subordinate animals, while 5 - HT receptors predominates in dominants. Insects Serotonin is evolutionary conserved and appears across the animal kingdom. It is seen in insect processes in roles similar to in the human central nervous system, such as memory, appetite, sleep, and behavior. Locust swarming is mediated by serotonin, by transforming social preference from aversion to a gregarious state that enables coherent groups. Learning in flies and honeybees is affected by the presence of serotonin. Insect 5 - HT receptors have similar sequences to the vertebrate versions, but pharmacological differences have been seen. Invertebrate drug response has been far less characterized than mammalian pharmacology and the potential for species selective insecticides has been discussed. Wasps and hornets have serotonin in their venom, which causes pain and inflammation. as do scorpions. If flies are fed serotonin, they are more aggressive ; flies depleted of serotonin still exhibit aggression, but they do so much less frequently. Growth and reproduction In the nematode C. elegans, artificial depletion of serotonin or the increase of octopamine cues behavior typical of a low - food environment : C. elegans becomes more active, and mating and egg - laying are suppressed, while the opposite occurs if serotonin is increased or octopamine is decreased in this animal. Serotonin is necessary for normal nematode male mating behavior, and the inclination to leave food to search for a mate. The serotonergic signaling used to adapt the worm 's behaviour to fast changes in the environment affects insulin - like signaling and the TGF beta signaling pathway, which control long - term adaption. In the fruit fly insulin both regulates blood sugar as well as acting as a growth factor. Thus, in the fruit fly, serotonergic neurons regulate the adult body size by affecting insulin secretion. Serotonin has also been identified as the trigger for swarm behavior in locusts. In humans, though insulin regulates blood sugar and IGF regulates growth, serotonin controls the release of both hormones, modulating insulin release from the beta cells in the pancreas through serotonylation of GTPase signaling proteins. Exposure to SSRIs during Pregnancy reduces fetal growth. Genetically altered C. elegans worms that lack serotonin have an increased reproductive lifespan, may become obese, and sometimes present with arrested development at a dormant larval state. Aging and age - related phenotypes Serotonin is known to regulate aging, learning and memory. The first evidence comes from the study of longevity in C. elegans. During early phase of aging, the level of serotonin increases, which alters locomotory behaviors and associative memory. The effect is restored by mutations and drugs ( including mianserin and methiothepin ) that inhibit serotonin receptors. The observation does not contradict with the notion that the serotonin level goes down in mammals and humans, which is typically seen in late but not early phase of aging. Biochemical mechanisms Biosynthesis The pathway for the synthesis of serotonin from tryptophan. In animals including humans, serotonin is synthesized from the amino acid L - tryptophan by a short metabolic pathway consisting of two enzymes : tryptophan hydroxylase ( TPH ), aromatic amino acid decarboxylase ( DDC ) and the coenzyme pyridoxal phosphate. The TPH - mediated reaction is the rate - limiting step in the pathway. TPH has been shown to exist in two forms : TPH1, found in several tissues, and TPH2, which is a neuron - specific isoform. Serotonin can be synthesized from tryptophan in the lab using Aspergillus niger and Psilocybe coprophila as catalysts. The first phase to 5 - hydroxytryptophan would require letting tryptophan sit in ethanol and water for 7 days, then mixing in enough HCl ( or other acid ) to bring the pH to 3, and then adding NaOH to make a pH of 13 for 1 hour. Asperigillus niger would be the catalyst for this first phase. The second phase to synthesizing tryptophan itself from the 5 - hydroxytryptophan intermediate would require adding ethanol and water, and letting sit for 30 days this time. The next two steps would be the same as the first phase : adding HCl to make the pH = 3, and then adding NaOH to make the pH very basic at 13 for 1 hour. This phase uses the Psilocybe coprophila as the catalyst for the reaction. Serotonin taken orally does not pass into the serotonergic pathways of the central nervous system, because it does not cross the blood -- brain barrier. However, tryptophan and its metabolite 5 - hydroxytryptophan ( 5 - HTP ), from which serotonin is synthesized, does cross the blood -- brain barrier. These agents are available as dietary supplements, and may be effective serotonergic agents. One product of serotonin breakdown is 5 - hydroxyindoleacetic acid ( 5 - HIAA ), which is excreted in the urine. Serotonin and 5 - HIAA are sometimes produced in excess amounts by certain tumors or cancers, and levels of these substances may be measured in the urine to test for these tumors. Effects of food content See also : Tryptophan Consuming purified tryptophan increases brain serotonin whereas eating foods containing tryptophan does not. This is because the transport system which brings tryptophan across the blood - brain barrier is also selective for the other amino acids contained in protein sources. High plasma levels of other large neutral amino acids compete for transport and prevent the elevated plasma tryptophan from increasing serotonin synthesis. History and etymology In 1935, Italian Vittorio Erspamer showed an extract from enterochromaffin cells made intestines contract. Some believed it contained adrenaline, but two years later, Erspamer was able to show it was a previously unknown amine, which he named `` enteramine ''. In 1948, Maurice M. Rapport, Arda Green, and Irvine Page of the Cleveland Clinic discovered a vasoconstrictor substance in blood serum, and since it was a serum agent affecting vascular tone, they named it serotonin. In 1952, enteramine was shown to be the same substance as serotonin, and as the broad range of physiological roles was elucidated, the abbreviation 5 - HT of the proper chemical name 5 - hydroxytryptamine became the preferred name in the pharmacological field. Synonyms of serotonin include : 5 - hydroxytriptamine, thrombotin, enteramin, substance DS, and 3 - ( β - Aminoethyl ) - 5 - hydroxyindole. In 1953, Betty Twarog and Page discovered serotonin in the central nervous system. See also 5 - HT2c receptor agonist Notes Jump up ^ References are ignored for the functions of these receptors due to the fact they appear on the wikipedia pages for the specific receptor in question References Jump up ^ Calculated using Advanced Chemistry Development ( ACD / Labs ) Software V11. 02 ( © 1994 -- 2011 ACD / Labs ) Jump up ^ Mazák K, Dóczy V, Kökösi J, Noszál B ( April 2009 ). `` Proton speciation and microspeciation of serotonin and 5 - hydroxytryptophan ''. 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Molecule of the Month : Serotonin at University of Bristol 60 - Second Psych : No Fair ! My Serotonin Level Is Low, Scientific American Serotonin Test Interpretation on ClinLab Navigator. Neurotransmitters Amino acid - derived Major excitatory / inhibitory systems : Glutamate system : Agmatine Aspartic acid ( aspartate ) Cycloserine Glutamic acid ( glutamate ) Glutathione Glycine GSNO GSSG Kynurenic acid NAA NAAG Proline Serine ; GABA system : GABA GABOB GHB ; Glycine system : α - Alanine β - Alanine Glycine Hypotaurine Proline Sarcosine Serine Taurine ; GHB system : GHB T - HCA ( GHC ) Biogenic amines : Monoamines : 6 - OHM Dopamine Epinephrine ( adrenaline ) NAS ( normelatonin ) Norepinephrine ( noradrenaline ) Serotonin ( 5 - HT ) ; Trace amines : 3 - Iodothyronamine N - Methylphenethylamine N - Methyltryptamine m - Octopamine p - Octopamine Phenylethanolamine Phenethylamine Synephrine Tryptamine m - Tyramine p - Tyramine ; Others : Histamine Neuropeptides : See here instead. Lipid - derived Endocannabinoids : 2 - AG 2 - AGE ( noladin ether ) 2 - ALPI 2 - OG AA - 5 - HT Anandamide ( AEA ) DEA LPI NADA NAGly OEA Oleamide PEA RVD - Hpα SEA Virodhamine ( O - AEA ) Neurosteroids : See here instead. Nucleobase - derived Nucleosides : Adenosine system : Adenosine ADP AMP ATP Vitamin - derived Cholinergic system : Acetylcholine Miscellaneous Gasotransmitters : Carbon monoxide ( CO ) Hydrogen sulfide ( H S ) Nitric oxide ( NO ) ; Candidates : Acetaldehyde Ammonia ( NH ) Carbonyl sulfide ( COS ) Nitrous oxide ( N O ) Sulfur dioxide ( SO ) Serotonin receptor modulators 5 - HT 5 - HT Agonists : 8 - OH - DPAT Adatanserin Amphetamine Antidepressants ( e.g., etoperidone, hydroxynefazodone, nefazodone, trazodone, triazoledione, vilazodone, vortioxetine ) Atypical antipsychotics ( e.g., aripiprazole, asenapine, brexpiprazole, cariprazine, clozapine, lurasidone, quetiapine, ziprasidone ) Azapirones ( e.g., buspirone, eptapirone, gepirone, perospirone, tandospirone ) Bay R 1531 Befiradol BMY - 14802 Cannabidiol Dimemebfe Dopamine Ebalzotan Eltoprazine Enciprazine Ergolines ( e.g., bromocriptine, cabergoline, dihydroergotamine, ergotamine, lisuride, LSD, methylergometrine ( methylergonovine ), methysergide, pergolide ) F - 11461 F - 12826 F - 13714 F - 14679 F - 15063 F - 15599 Flesinoxan Flibanserin Flumexadol Lesopitron LY - 293284 LY - 301317 mCPP MKC - 242 Naluzotan NBUMP Osemozotan Oxaflozane Pardoprunox Piclozotan Rauwolscine Repinotan Roxindole RU - 24969 S - 14506 S - 14671 S - 15535 Sarizotan Serotonin ( 5 - HT ) SSR - 181507 Sunepitron Tryptamines ( e.g., 5 - CT, 5 - MeO - DMT, 5 - MT, bufotenin, DMT, indorenate, N - Me - 5 - HT, psilocin, psilocybin ) TGBA01AD U-92016A Urapidil Vilazodone Xaliproden Yohimbine Antagonists : Atypical antipsychotics ( e.g., iloperidone, risperidone, sertindole ) AV965 Beta blockers ( e.g., alprenolol, carteolol, cyanopindolol, iodocyanopindolol, isamoltane, oxprenolol, penbutolol, pindobind, pindolol, propranolol, tertatolol ) BMY - 7378 CSP - 2503 Dotarizine Ergolines ( e.g., metergoline ) Flopropione GR - 46611 Isamoltane Lecozotan Mefway Metitepine ( methiothepin ) MIN - 117 ( WF - 516 ) MPPF NAN - 190 Robalzotan S - 15535 SB - 649915 SDZ 216 - 525 Spiperone Spiramide Spiroxatrine UH - 301 WAY - 100135 WAY - 100635 Xylamidine Unknown / unsorted : Acetryptine Ergolines ( e.g., ergometrine ( ergonovine ) ) 5 - HT Agonists : CGS - 12066A CP - 93129 CP - 94253 CP - 122,288 CP - 135807 Eltoprazine Ergolines ( e.g., bromocriptine, dihydroergotamine, ergotamine, methylergometrine ( methylergonovine ), methysergide, pergolide ) mCPP RU - 24969 Serotonin ( 5 - HT ) Triptans ( e.g., avitriptan, donitriptan, eletriptan, sumatriptan, zolmitriptan ) TFMPP Tryptamines ( e.g., 5 - BT, 5 - CT, 5 - MT, DMT ) Vortioxetine Antagonists : AR - A000002 Beta blockers ( e.g., alprenolol, carteolol, isamoltane, oxprenolol, penbutolol, propranolol, tertatolol ) Elzasonan Ergolines ( e.g., metergoline ) GR - 127935 Isamoltane LY - 393558 Metitepine ( methiothepin ) SB - 216641 SB - 224289 SB - 236057 Yohimbine Unknown / unsorted : Ergolines ( e.g., cabergoline, ergometrine ( ergonovine ), lisuride ) 5 - HT Agonists : CP - 122,288 CP - 135807 CP - 286601 Ergolines ( e.g., bromocriptine, cabergoline, dihydroergotamine, ergotamine, LSD, methysergide ) GR - 46611 L - 694247 L - 772405 mCPP PNU - 109291 PNU - 142633 Serotonin ( 5 - HT ) TGBA01AD Triptans ( e.g., almotriptan, avitriptan, donitriptan, eletriptan, frovatriptan, naratriptan, rizatriptan, sumatriptan, zolmitriptan ) Tryptamines ( e.g., 5 - BT, 5 - CT, 5 - Et - DMT, 5 - MT, 5 - ( nonyloxy ) tryptamine, DMT ) Antagonists : Alniditan BRL - 15572 Elzasonan Ergolines ( e.g., metergoline ) GR - 127935 Ketanserin LY - 310762 LY - 367642 LY - 393558 LY - 456219 LY - 456220 Metitepine ( methiothepin ) Mianserin Ritanserin Yohimbine Ziprasidone Unknown / unsorted : Acetryptine Ergolines ( e.g., lisuride, lysergol, pergolide ) 5 - HT Agonists : BRL - 54443 Ergolines ( e.g., methysergide ) Serotonin ( 5 - HT ) Triptans ( e.g., eletriptan ) Tryptamines ( e.g., tryptamine ) Antagonists : Metitepine ( methiothepin ) Unknown / unsorted : Ergolines ( e.g., ergometrine ( ergonovine ), lysergol, methylergometrine ( methylergonovine ) 5 - HT Agonists : BRL - 54443 CP - 122,288 Ergolines ( e.g., bromocriptine, lysergol, methylergometrine ( methylergonovine ) methysergide ) Lasmiditan LY - 334370 Serotonin ( 5 - HT ) Triptans ( e.g., eletriptan, naratriptan, sumatriptan ) Tryptamines ( e.g., 5 - MT ) Antagonists : Mianserin Metitepine ( methiothepin ) 5 - HT 5 - HT Agonists : 25H / NB series ( e.g., 25I - NBF, 25I - NBMD, 25I - NBOH, 25I - NBOMe, 25B - NBOMe, 25C - NBOMe, 25TFM - NBOMe, 2CBCB - NBOMe, 25CN - NBOH, 2CBFly - NBOMe ) 2Cs ( e.g., 2C - B, 2C - E, 2C - I, 2C - T - 2, 2C - T - 7, 2C - T - 21 ) 2C - B - FLY 2CB - Ind 5 - Methoxytryptamines ( 5 - MeO - DET, 5 - MeO - DiPT, 5 - MeO - DMT, 5 - MeO - DPT, 5 - MT ) α - Alkyltryptamines ( e.g., 5 - Cl - αMT, 5 - Fl - αMT, 5 - MeO - αET, 5 - MeO - αMT, α - Me - 5 - HT, αET, αMT ) AL - 34662 AL - 37350A Bromo - DragonFLY Dimemebfe DMBMPP DOx ( e.g., DOB, DOC, DOI, DOM ) Efavirenz Ergolines ( e.g., 1P - LSD, ALD - 52, bromocriptine, cabergoline, ergine ( LSA ), ergometrine ( ergonovine ), ergotamine, lisuride, LA - SS - Az, LSB, LSD, LSD - Pip, LSH, LSP, methylergometrine ( methylergonovine ), pergolide ) Flumexadol Jimscaline Lorcaserin MDxx ( e.g., MDA ( tenamfetamine ), MDMA ( midomafetamine ), MDOH, MMDA ) O - 4310 Oxaflozane PHA - 57378 PNU - 22394 PNU - 181731 RH - 34 Phenethylamines ( e.g., lophophine, mescaline ) Piperazines ( e.g., BZP, quipazine, TFMPP ) Serotonin ( 5 - HT ) TCB - 2 TFMFly Tryptamines ( e.g., 5 - BT, 5 - CT, bufotenin, DET, DiPT, DMT, DPT, psilocin, psilocybin, tryptamine ) Antagonists : 5 - I - R91150 5 - MeO - NBpBrT AC - 90179 Adatanserin Altanserin Antihistamines ( e.g., cyproheptadine, hydroxyzine, ketotifen, perlapine ) AMDA Atypical antipsychotics ( e.g., amperozide, aripiprazole, asenapine, blonanserin, brexpiprazole, carpipramine, clocapramine, clorotepine, clozapine, fluperlapine, gevotroline, iloperidone, lurasidone, melperone, mosapramine, ocaperidone, olanzapine, paliperidone, quetiapine, risperidone, sertindole, zicronapine, ziprasidone, zotepine ) Cinanserin CSP - 2503 Deramciclane Dotarizine Eplivanserin Ergolines ( e.g., amesergide, LY - 53857, LY - 215840, mesulergine, metergoline, methysergide, sergolexole ) Fananserin Flibanserin Glemanserin Irindalone Ketanserin KML - 010 Landipirdine LY - 393558 mCPP Medifoxamine Metitepine ( methiothepin ) MIN - 101 MIN - 117 ( WF - 516 ) Naftidrofuryl Nantenine Nelotanserin Opiranserin ( VVZ - 149 ) Pelanserin Phenoxybenzamine Pimavanserin Pirenperone Pizotifen Pruvanserin Rauwolscine Ritanserin S - 14671 Sarpogrelate Serotonin antagonists and reuptake inhibitors ( e.g., etoperidone, hydroxynefazodone, lubazodone, mepiprazole, nefazodone, triazoledione, trazodone ) SR - 46349B TGBA01AD Teniloxazine Temanogrel Tetracyclic antidepressants ( e.g., amoxapine, aptazapine, esmirtazapine, maprotiline, mianserin, mirtazapine ) Tricyclic antidepressants ( e.g., amitriptyline ) Typical antipsychotics ( e.g., chlorpromazine, fluphenazine, haloperidol, loxapine, perphenazine, pimozide, pipamperone, prochlorperazine, setoperone, spiperone, spiramide, thioridazine, thiothixene, trifluoperazine ) Volinanserin Xylamidine Yohimbine Unknown / unsorted : Ergolines ( e.g., dihydroergotamine, nicergoline ) 5 - HT Agonists : 4 - Methylaminorex Aminorex Amphetamines ( e.g., chlorphentermine, cloforex, dexfenfluramine, fenfluramine, levofenfluramine, norfenfluramine ) BW - 723C86 DOx ( e.g., DOB, DOC, DOI, DOM ) Ergolines ( e.g., cabergoline, dihydroergocryptine, dihydroergotamine, ergotamine, methylergometrine ( methylergonovine ), methysergide, pergolide ) Lorcaserin MDxx ( e.g., MDA ( tenamfetamine ), MDMA ( midomafetamine ), MDOH, ( MMDA ( drug ) Antagonists : Agomelatine Atypical antipsychotics ( e.g., amisulpride, aripiprazole, asenapine, brexpiprazole, cariprazine, clozapine, N - desalkylquetiapine ( norquetiapine ), N - desmethylclozapine ( norclozapine ), olanzapine, pipamperone, quetiapine, risperidone, ziprasidone ) Cyproheptadine EGIS - 7625 Ergolines ( e.g., amesergide, bromocriptine, lisuride, LY - 53857, LY - 272015, mesulergine ) Ketanserin LY - 393558 mCPP Metadoxine Metitepine ( methiothepin ) Pirenperone Pizotifen Propranolol PRX - 08066 Rauwolscine Ritanserin RS - 127445 Sarpogrelate SB - 200646 SB - 204741 SB - 206553 SB - 215505 SB - 221284 SB - 228357 SDZ SER - 082 Tegaserod Tetracyclic antidepressants ( e.g., amoxapine, mianserin, mirtazapine ) Trazodone Typical antipsychotics ( e.g., chlorpromazine ) TIK - 301 Yohimbine Unknown / unsorted : Ergolines ( e.g., ergometrine ( ergonovine ) ) 5 - HT Agonists : 2Cs ( e.g., 2C - B, 2C - E, 2C - I, 2C - T - 2, 2C - T - 7, 2C - T - 21 ) 5 - Methoxytryptamines ( 5 - MeO - DET, 5 - MeO - DiPT, 5 - MeO - DMT, 5 - MeO - DPT, 5 - MT ) α - Alkyltryptamines ( e.g., 5 - Cl - αMT, 5 - Fl - αMT, 5 - MeO - αET, 5 - MeO - αMT, α - Me - 5 - HT, αET, αMT ) A-372159 AL - 38022A Alstonine CP - 809101 Dimemebfe DOx ( e.g., DOB, DOC, DOI, DOM ) Ergolines ( e.g., ALD - 52, cabergoline, dihydroergotamine, ergine ( LSA ), ergotamine, lisuride, LA - SS - Az, LSB, LSD, LSD - Pip, LSH, LSP, pergolide ) Flumexadol Lorcaserin MDxx ( e.g., MDA ( tenamfetamine ), MDMA ( midomafetamine ), MDOH, MMDA ) MK - 212 Org 12962 Org 37684 Oxaflozane PHA - 57378 Phenethylamines ( e.g., lophophine, mescaline ) Piperazines ( e.g., aripiprazole, BZP, mCPP, quipazine, TFMPP ) PNU - 22394 PNU - 181731 Ro60 - 0175 Ro60 - 0213 Serotonin ( 5 - HT ) Tryptamines ( e.g., 5 - BT, 5 - CT, bufotenin, DET, DiPT, DMT, DPT, psilocin, psilocybin, tryptamine ) Vabicaserin WAY - 629 WAY - 161503 YM - 348 Antagonists : Adatanserin Agomelatine Atypical antipsychotics ( e.g., asenapine, clorotepine, clozapine, fluperlapine, iloperidone, melperone, olanzapine, paliperidone, quetiapine, risperidone, sertindole, ziprasidone, zotepine ) Captodiame CEPC Cinanserin Cyproheptadine Deramciclane Desmetramadol Dotarizine Eltoprazine Ergolines ( e.g., amesergide, bromocriptine, LY - 53857, LY - 215840, mesulergine, metergoline, methysergide, sergolexole ) Etoperidone Fluoxetine FR - 260010 Irindalone Ketanserin Ketotifen Latrepirdine ( dimebolin ) Medifoxamine Metitepine ( methiothepin ) Nefazodone Pirenperone Pizotifen Propranolol Ritanserin RS - 102221 S - 14671 SB - 200646 SB - 206553 SB - 221284 SB - 228357 SB - 242084 SB - 243213 SDZ SER - 082 Tedatioxetine Tetracyclic antidepressants ( e.g., amoxapine, aptazapine, esmirtazapine, maprotiline, mianserin, mirtazapine ) TIK - 301 Tramadol Trazodone Tricyclic antidepressants ( e.g., amitriptyline, nortriptyline ) Typical antipsychotics ( e.g., chlorpromazine, loxapine, pimozide, pipamperone, thioridazine ) Xylamidine Unknown / unsorted : Efavirenz Ergolines ( e.g., ergometrine ( ergonovine ), methylergometrine ( methylergonovine ) ) 5 - HT 5 - HT Agonists : Alcohols ( e.g., butanol, ethanol ( alcohol ), trichloroethanol ) m - CPBG Phenylbiguanide Piperazines ( e.g., BZP, mCPP, quipazine ) RS - 56812 Serotonin ( 5 - HT ) SR - 57227 SR - 57227A Tryptamines ( e.g., 2 - Me - 5 - HT, 5 - CT, bufotenidine ( 5 - HTQ ) ) Volatiles / gases ( e.g., halothane, isoflurane, toluene, trichloroethane ) YM - 31636 Antagonists : Alosetron Arazasetron AS - 8112 Atypical antipsychotics ( e.g., clozapine, olanzapine, quetiapine ) Azasetron Batanopride Bemesetron ( MDL - 72222 ) Bupropion Cilansetron CSP - 2503 Dazopride Dolasetron Galanolactone Granisetron Hydroxybupropion ICS - 205930 Lerisetron Memantine Ondansetron Palonosetron Ramosetron Renzapride Ricasetron Tedatioxetine Tetracyclic antidepressants ( e.g., amoxapine, mianserin, mirtazapine ) Thujone Tropanserin Tropisetron Typical antipsychotics ( e.g., loxapine ) Volatiles / gases ( e.g., nitrous oxide, sevoflurane, xenon ) Vortioxetine Zacopride Zatosetron Unknown / unsorted : LY - 53857 Piperazines ( e.g., naphthylpiperazine ) 5 - HT Agonists : 5 - MT BIMU8 Capeserod Cinitapride Cisapride CJ - 033466 Dazopride Metoclopramide Minesapride Mosapride Prucalopride PRX - 03140 Renzapride RS - 67333 RS - 67506 Serotonin ( 5 - HT ) Tegaserod Velusetrag Zacopride Antagonists : GR - 113808 GR - 125487 L - Lysine Piboserod RS - 39604 RS - 67532 SB - 203186 SB - 204070 5 - HT Agonists : Ergolines ( e.g., 2 - Br - LSD ( BOL - 148 ), ergotamine, LSD ) Serotonin ( 5 - HT ) Tryptamines ( e.g., 5 - CT ) Valerenic Acid Antagonists : Asenapine Latrepirdine ( dimebolin ) Metitepine ( methiothepin ) Ritanserin SB - 699551 Unknown / unsorted : Ergolines ( e.g., metergoline, methysergide ) Piperazines ( e.g., naphthylpiperazine ) 5 - HT Agonists : Ergolines ( e.g., dihydroergocryptine, dihydroergotamine, ergotamine, lisuride, LSD, mesulergine, metergoline, methysergide ) Serotonin ( 5 - HT ) Tryptamines ( e.g., 2 - Me - 5 - HT, 5 - BT, 5 - CT, 5 - MT, Bufotenin, E-6801, E-6837, EMD - 386088, EMDT, LY - 586713, N - Me - 5 - HT, tryptamine ) WAY - 181187 WAY - 208466 Antagonists : ABT - 354 Atypical antipsychotics ( e.g., aripiprazole, asenapine, clorotepine, clozapine, fluperlapine, iloperidone, olanzapine, tiospirone ) AVN - 101 AVN - 211 AVN - 322 AVN - 397 BGC20 - 760 BVT - 5182 BVT - 74316 Cerlapirdine EGIS - 12233 GW - 742457 Idalopirdine Ketanserin Landipirdine Latrepirdine ( dimebolin ) Metitepine ( methiothepin ) MS - 245 PRX - 07034 Ritanserin Ro 04 - 6790 Ro 63 - 0563 SB - 258585 SB - 271046 SB - 357134 SB - 399885 SB - 742457 Tetracyclic antidepressants ( e.g., amoxapine, mianserin ) Tricyclic antidepressants ( e.g., amitriptyline, clomipramine, doxepin, nortriptyline ) Typical antipsychotics ( e.g., chlorpromazine, loxapine ) Unknown / unsorted : Ergolines ( e.g., 2 - Br - LSD ( BOL - 148 ), bromocriptine, lergotrile, pergolide ) Piperazines ( e.g., naphthylpiperazine ) 5 - HT Agonists : 8 - OH - DPAT AS - 19 Bifeprunox E-55888 Ergolines ( e.g., LSD ) LP - 12 LP - 44 RU - 24969 Sarizotan Serotonin ( 5 - HT ) Triptans ( e.g., frovatriptan ) Tryptamines ( e.g., 5 - CT, 5 - MT, bufotenin, N - Me - 5 - HT ) Antagonists : Atypical antipsychotics ( e.g., amisulpride, aripiprazole, asenapine, brexpiprazole, clorotepine, clozapine, fluperlapine, olanzapine, risperidone, sertindole, tiospirone, ziprasidone, zotepine ) Butaclamol DR - 4485 EGIS - 12233 Ergolines ( e.g., 2 - Br - LSD ( BOL - 148 ), amesergide, bromocriptine, cabergoline, dihydroergotamine, ergotamine, LY - 53857, LY - 215840, mesulergine, metergoline, methysergide, sergolexole ) JNJ - 18038683 Ketanserin LY - 215840 Metitepine ( methiothepin ) Ritanserin SB - 258719 SB - 258741 SB - 269970 SB - 656104 SB - 656104A SB - 691673 SLV - 313 SLV - 314 Spiperone SSR - 181507 Tetracyclic antidepressants ( e.g., amoxapine, maprotiline, mianserin, mirtazapine ) Tricyclic antidepressants ( e.g., amitriptyline, clomipramine, imipramine ) Typical antipsychotics ( e.g., acetophenazine, chlorpromazine, chlorprothixene, fluphenazine, loxapine, pimozide ) Vortioxetine Unknown / unsorted : Ergolines ( e.g., lisuride, pergolide ) Piperazines ( e.g., naphthylpiperazine ) See also : Receptor / signaling modulators Adrenergics Dopaminergics Melatonergics Monoamine reuptake inhibitors and releasing agents Monoamine metabolism modulators Monoamine neurotoxins Human trace amine - associated receptor ligands TAAR1 Agonists Endogenous Classical monoamine neurotransmitters Dopamine Histamine Norepinephrine Serotonin Trace amines 3 - Iodothyronamine 3 - Methoxytyramine N - Methylphenethylamine N - Methyltyramine m - Octopamine p - Octopamine Phenethylamine Phenylethanolamine Synephrine Tryptamine m - Tyramine p - Tyramine Synthetic Amphetamine DOB DOET 4 - Hydroxyamphetamine Isoprenaline MDA ( tenamfetamine ) MDMA ( midomafetamine ) 2 - Methylphenethylamine 3 - Methylphenethylamine 4 - Methylphenethylamine β - Methylphenethylamine Methamphetamine 3 - MMA Norfenfluramine Phentermine o - PIT Propylhexedrine RO5166017 N, N - Dimethylphenethylamine Neutral antagonists Inverse agonists EPPTB ( RO5212773 ) TAAR2 Agonists Neutral antagonists TAAR5 Agonists N, N - Dimethylethylamine Trimethylamine Neutral antagonists Inverse agonists 3 - Iodothyronamine References for all endogenous human TAAR1 ligands are provided at List of trace amines References for synthetic TAAR1 agonists can be found at TAAR1 or in the associated compound articles. For TAAR2 and TAAR5 agonists and inverse agonists, see TAAR for references. See also : Receptor / signaling modulators Tryptamines 1 - Methylpsilocin 2 - Methyl - 5 - HT 4, 5 - DHP - DMT 4, 5 - MDO - DMT 4, 5 - MDO - DiPT 4 - AcO - DALT 4 - AcO - DET 4 - AcO - DMT 4 - AcO - DiPT 4 - AcO - NMT 4 - AcO - MET 4 - AcO - DPT 4 - AcO - MiPT 4 - HO - DALT 4 - HO - DET 4 - HO - DiPT 4 - HO - DSBT 4 - HO - MET 4 - HO - MiPT 4 - HO - NMT 4 - HO - αMT 4 - Me - αET 4 - Me - αMT 4 - MeO - DiPT 4 - MeO - DMT 5 - BT 5 - Bromo - DMT 5 - CT 5 - Chloro - αMT 5 - Ethoxy - αMT 5 - Fluoro - αMT 5 - HO - αMT 5 - HO - DiPT 5 - HTP 5 - Ethoxy - DMT 5 - Ethyl - DMT 5 - Fluoro - DMT 5 - Methyl - DMT 5 - Methoxytryptamine 5 - MeO - 7, N, N - TMT 5 - Methyl - αET 5 - MeO - αET 5 - MeO - αMT 5 - MeO - DALT 5 - MeO - DET 5 - MeO - DiPT 5 - MeO - DMT 5 - MeO - DPT 5 - MeO - EiPT 5 - MeO - EPT 5 - MeO - MALT 5 - MeO - MiPT 5 - MeO - NBpBrT 5, 7 - Dihydroxytryptamine 5 - ( Nonyloxy ) tryptamine 6 - Fluoro - αMT 6 - Hydroxymelatonin 7 - Methyl - αET 7 - Methyl - DMT Acetryptine Aeruginascin αET AL - 37350A αMT BW - 723C86 Baeocystin Bufotenidine Bufotenin ( 5 - HO - DMT ) Convolutindole A DALT Desformylflustrabromine DET DiPT DMT DPT Ethocybin EiPT EMDT EPT FGIN - 127 FGIN - 143 HIOC Ibogaine Indorenate Iprocin Lespedamine Luzindole MET MiPT MPT Miprocin Melatonin MS - 245 NAS N - Feruloylserotonin NMT Norbaeocystin Normelatonin O - 4310 Oxypertine Plakohypaphorine PiPT Psilocin ( 4 - HO - DMT ) Psilocybin ( 4 - PO - DMT ) Rizatriptan Serotonin ST - 1936 Sumatriptan Tryptamine Tryptophan Yohimbine Yuremamine Zolmitriptan GND : 4054614 - 7 NDL : 00570824 Chemistry portal Biology portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Serotonin&oldid=849387307 '' Categories : Serotonin Tryptamine alkaloids Biogenic amines Neurotransmitters TAAR1 agonists Hydroxyarenes Peripherally selective drugs Hidden categories : CS1 Italian - language sources ( it ) All articles lacking reliable references Articles lacking reliable references from October 2017 CS1 maint : Extra text : authors list Articles needing more detailed references Use dmy dates from March 2016 ECHA InfoCard ID from Wikidata Articles without EBI source Chemical pages without DrugBank identifier Articles without InChI source Articles without UNII source Drugs missing an ATC code Drugs with no legal status Articles containing unverified chemical infoboxes Drugs that are a physiological drug All articles with unsourced statements Articles with unsourced statements from October 2017 All Wikipedia articles needing clarification Wikipedia articles needing clarification from March 2014 Wikipedia articles needing clarification from January 2012 Wikipedia articles needing clarification from September 2017 Wikipedia articles with GND identifiers Wikipedia articles with NDL identifiers Talk Contents About Wikipedia Asturianu Azərbaycanca تۆرکجه বাংলা Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto Estremeñu Euskara فارسی Français Gaeilge Galego 한국어 Հայերեն Hrvatski Bahasa Indonesia Italiano עברית Қазақша Кыргызча Latina Latviešu Lietuvių Magyar Македонски മലയാളം Bahasa Melayu Nederlands 日本 語 Norsk Occitan Oʻzbekcha / ўзбекча Polski Português Română Русский Scots Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Tagalog தமிழ் ไทย Türkçe Українська Tiếng Việt 中文 53 more Edit links This page was last edited on 8 July 2018, at 16 : 59 ( UTC ). 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Question: where is most of the body's serotonin located
Answer: the enteric nervous system located in the gastrointestinal tract (GI tract)