59-427: Serotonin ( / ˌ s ɛr ə ˈ t oʊ n ɪ n , ˌ s ɪər ə -/ ) or 5-hydroxytryptamine ( 5-HT ) is a monoamine neurotransmitter . Its biological function is complex, touching on diverse functions including mood , cognition , reward , learning , memory , and numerous physiological processes such as vomiting and vasoconstriction . Serotonin is produced in the central nervous system (CNS), specifically in
118-434: 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. Several classes of drugs target
177-484: A class of antidepressants . Monoamine neurotransmitter systems occur in virtually all vertebrates, where the evolvability of these systems has served to promote the adaptability of vertebrate species to different environments. A recent computational investigation of genetic origins shows that the earliest development of monoamines occurred 650 million years ago and that the appearance of these chemicals, necessary for active or participatory awareness and engagement with
236-503: 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 – the biological function after which serotonin
295-437: A serotonin 5-HT 2A receptor agonist, is thought to be non-hallucinogenic. The hallucinogenic effects of serotonergic psychedelics appear to be mediated specifically by activation of serotonin 5-HT 2A receptors expressed in a population of cortical neurons in the medial prefrontal cortex (mPFC). These serotonin 5-HT 2A receptors, unlike most serotonin and related receptors, are expressed intracellularly . In addition,
354-465: A 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 1B receptors , it negatively regulates bone mass, while it does so positively through 5-HT 2B receptors and 5-HT 2C receptors . There is very delicate balance between physiological role of gut serotonin and its pathology. Increase in
413-419: A two-carbon chain (such as -CH 2 -CH 2 -). Examples are dopamine , norepinephrine and serotonin . All monoamines are derived from aromatic amino acids like phenylalanine , tyrosine , and tryptophan by the action of aromatic amino acid decarboxylase enzymes . They are deactivated in the body by the enzymes known as monoamine oxidases which clip off the amine group. Monoaminergic systems, i.e.,
472-470: A vasoconstrictor by contracting endothelial smooth muscle directly or by potentiating the effects of other vasoconstrictors (e.g. angiotensin II and norepinephrine). The vasoconstrictive property is mostly seen in pathologic states affecting the endothelium – such as atherosclerosis or chronic hypertension . In normal physiologic states, vasodilation occurs through the serotonin mediated release of nitric oxide from endothelial cells, and
531-455: Is a naturally occurring endogenous compound in the body. In relation to the fact that serotonin itself is unable to activate intracellular serotonin 5-HT 2A receptors, it is possible that DMT might be the endogenous ligand of these receptors rather than serotonin. Monoamine neurotransmitter Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by
590-456: Is also found to be more resilient against depression and anxiety. Besides their use in treating depression and anxiety, certain serotonergic antidepressants are also approved and used to treat fibromyalgia , neuropathic pain , and chronic fatigue syndrome . Azapirone anxiolytics like buspirone and tandospirone act as serotonin 5-HT 1A receptor agonists . Many antipsychotics bind to and modulate serotonin receptors , including
649-461: Is due to the selective activity of the plasma membrane monoamine transporter (PMAT) which actively transports the molecule across the membrane and back into the presynaptic cell. In contrast to the high affinity of SERT, the PMAT has been identified as a low-affinity transporter, with an apparent K m of 114 micromoles/l for serotonin, which is approximately 230 times higher than that of SERT. However,
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#1732909326310708-449: Is found in platelets and 1–2% in the CNS. 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, including
767-474: Is involved in numerous physiological processes, including sleep , thermoregulation , learning and memory , pain , (social) behavior, sexual activity , feeding, motor activity, neural development, and biological rhythms . In less complex animals, such as some invertebrates , serotonin regulates feeding and other processes. In plants serotonin synthesis seems to be associated with stress signals. Despite its longstanding prominence in pharmaceutical advertising,
826-891: Is produced by pathogenic amoebae, causing diarrhea in the human gut. Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds. Biochemically, the indoleamine molecule derives from the amino acid tryptophan , via the (rate-limiting) hydroxylation of the 5 position on the ring (forming the intermediate 5-hydroxytryptophan ), and then decarboxylation to produce serotonin. Preferable conformations are defined via ethylamine chain, resulting in six different conformations. Serotonin crystallizes in P2 1 2 1 2 1 chiral space group forming different hydrogen-bonding interactions between serotonin molecules via N-H...O and O-H...N intermolecular bonds. Serotonin also forms several salts, including pharmaceutical formulation of serotonin adipate. Serotonin
885-399: Is released into the synapse, or space between neurons, and diffuses over a relatively wide gap (>20 nm) 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,
944-434: 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. There are often serotonin abnormalities in gastrointestinal disorders such as constipation and irritable bowel syndrome. If irritants are present in the food, the enterochromaffin cells release more serotonin to make
1003-433: 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 found that a significant portion of 5-HT's synaptic clearance
1062-436: Is the tryptophan derivative serotonin , a neurotransmitter involved in mood and sleep . Another example of an indolamine is melatonin . In biochemistry , indolamines are substituted indole compounds that contain an amino group. Examples of indolamines include the lysergamides . Indolamines are biologically synthesized from the essential amino acid tryptophan . Tryptophan is synthesized into serotonin through
1121-466: The brainstem 's raphe nuclei , the skin's Merkel cells , pulmonary neuroendocrine cells and the tongue's taste receptor cells . Approximately 90% of the serotonin the human body produces is in the gastrointestinal tract 's enterochromaffin cells , where it regulates intestinal movements. Additionally, it is stored in blood platelets and is released during agitation and vasoconstriction, where it then acts as an agonist to other platelets. About 8%
1180-627: 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 in the brain as subordinate males and females (measured by the concentration of 5-HIAA in the cerebrospinal fluid (CSF)). Dominance status and CSF 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
1239-616: The indole acetic-acid derivative. The latter is then excreted by the kidneys. 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 psychedelic drugs . Except for the 5-HT 3 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. Serotonergic action
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#17329093263101298-481: The nausea and vomiting that occur during anticancer chemotherapy using cytotoxic drugs . Another application is in the treatment of postoperative nausea and vomiting . Some serotonin releasing agents , serotonin reuptake inhibitors , and/or serotonin 5-HT 2C receptor agonists , such as fenfluramine , dexfenfluramine , chlorphentermine , sibutramine , and lorcaserin , have been approved and used as appetite suppressants for purposes of weight loss in
1357-545: The serotonin receptors and mediate their hallucinogenic effects specifically by activation of the serotonin 5-HT 2A receptor . This is evidenced by the fact that serotonin 5-HT 2A receptor antagonists and so-called " trip killers " like ketanserin block the hallucinogenic effects of serotonergic psychedelics in humans, among many other findings. Some serotonergic psychedelics, like psilocin and DMT, are substituted tryptamines and are very similar in chemical structure to serotonin. Serotonin itself, despite acting as
1416-525: The triptans like sumatriptan act as agonists of the serotonin 5-HT 1B , 5-HT 1D , and/or 5-HT 1F receptors . Earlier antimigraine agents were the ergoline derivatives and ergot -related drugs such as ergotamine , dihydroergotamine , and methysergide , which act as non-selective serotonin receptor agonists . Some serotonin 5-HT 3 receptor antagonists , such as ondansetron , granisetron , and tropisetron , are important antiemetic agents. They are particularly important in treating
1475-546: 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 that the administration of SSRIs such as fluoxetine and sertraline may be associated with an inhibitory effect on PMAT activity when used at higher than normal dosages ( IC 50 test values used in trials were 3–4 fold higher than typical prescriptive dosage). Serotonin can also signal through
1534-534: The SERT in these medial prefrontal cortex neurons resulted in the serotonin releasing agent para -chloroamphetamine (PCA), which does not normally show psychedelic-like effects, being able to produce psychedelic-like effects in animals. Although serotonin itself is non-hallucinogenic, administration of very high doses of a serotonin precursor , like tryptophan or 5-hydroxytryptophan (5-HTP), or intracerebroventricular injection of high doses of serotonin directly into
1593-659: The brain, can produce psychedelic-like effects in animals. These psychedelic-like effects can be abolished by indolethylamine N -methyltransferase (INMT) inhibitors , which block conversion of serotonin and other endogenous tryptamines into N - methylated tryptamines, including N -methylserotonin (NMS; norbufotenin), bufotenin (5-hydroxy- N , N -dimethyltryptamine; 5-HO-DMT), N -methyltryptamine (NMT), and N , N -dimethyltryptamine (DMT). These N -methyltryptamines are much more lipophilic than serotonin and, in contrast, are able to diffuse into serotonergic neurons and activate intracellular serotonin 5-HT 2A receptors. DMT
1652-478: The brainstem. The serotonergic pathway is 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 suggests that serotonergic activity increases with motor activity while firing rates of serotonergic neurons increase with intense visual stimuli. Animal models suggest that kainate signaling negatively regulates serotonin actions in
1711-466: 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
1770-508: The claim that low serotonin levels cause depression is not supported by scientific evidence. Serotonin primarily acts through its receptors and its effects depend on which cells and tissues express these receptors. Metabolism involves first oxidation by monoamine oxidase to 5-hydroxyindoleacetaldehyde (5-HIAL). The rate-limiting step is hydride transfer from serotonin to the flavin cofactor. There follows oxidation by aldehyde dehydrogenase (ALDH) to 5-hydroxyindoleacetic acid ( 5-HIAA ),
1829-433: The effect of monoamine neurotransmitters are used to treat patients with psychiatric and neurological disorders, including depression , anxiety , schizophrenia and Parkinson's disease . Specific transporter proteins called monoamine transporters that transport monoamines in or out of a cell exist. These are the dopamine transporter (DAT), serotonin transporter (SERT), and the norepinephrine transporter (NET) in
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1888-525: The environment, coincides with the emergence of bilaterian or “mirror” body in the midst of (or perhaps in some sense catalytic of?) the Cambrian Explosion. Indoleamine Indolamines are a family of neurotransmitters that share a common molecular structure (namely, indolamine). Indolamines are a classification of monoamine neurotransmitter , along with catecholamines and ethylamine derivatives. A common example of an indolamine
1947-456: The extracellular content of serotonin results in a complex relay of signals in the osteoblasts culminating in FoxO1/ Creb and ATF4 dependent transcriptional events. Following the 2008 findings that gut serotonin regulates bone mass, the mechanistic investigations into what regulates serotonin synthesis from the gut in the regulation of bone mass have started. Piezo1 has been shown to sense RNA in
2006-431: The gut and relay this information through serotonin synthesis to the bone by acting as a sensor of single-stranded RNA (ssRNA) governing 5-HT production. Intestinal epithelium-specific deletion of mouse Piezo1 profoundly disturbed gut peristalsis, impeded experimental colitis, and suppressed serum 5-HT levels. Because of systemic 5-HT deficiency, conditional knockout of Piezo1 increased bone formation. Notably, fecal ssRNA
2065-405: 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 . Thus, drugs and toxins stimulate serotonin release from enterochromaffin cells in
2124-464: The gut release serotonin. Their function is probably vasoconstriction during hypoxia . Serotonin is also produced by Merkel cells which are part of the somatosensory system. 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
2183-590: The gut wall can induce emesis. 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. The lung , including that of reptiles, contains specialized epithelial cells that occur as solitary cells or as clusters called neuroepithelial bodies or bronchial Kulchitsky cells or alternatively K cells . These are enterochromaffin cells that like those in
2242-571: The inhibition of 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 . Biochemically, the indoleamine molecule derives from the amino acid tryptophan . Serotonin is metabolized mainly to 5-hydroxyindoleacetic acid (5-HIAA), chiefly by the liver . Several classes of antidepressants , such as selective serotonin reuptake inhibitors (SSRIs) and serotonin–norepinephrine reuptake inhibitors (SNRIs), interfere with
2301-434: 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. The serotonin nuclei may also be divided into two main groups,
2360-603: The neonatal period. Human serotonin can also act as a growth factor directly. Liver damage increases cellular expression of 5-HT 2A and 5-HT 2B receptors , mediating liver compensatory regrowth (see Liver § Regeneration and transplantation ) Serotonin present in the blood then stimulates cellular growth to repair liver damage. 5-HT 2B receptors also activate osteocytes , which build up bone However, serotonin also inhibits osteoblasts , through 5-HT 1B receptors. Serotonin, in addition, evokes endothelial nitric oxide synthase activation and stimulates, through
2419-429: The networks of neurons that use monoamine neurotransmitters, are involved in the regulation of processes such as emotion, arousal, and certain types of memory. It has also been found that monoamine neurotransmitters play an important role in the secretion and production of neurotrophin-3 by astrocytes, a chemical which maintains neuron integrity and provides neurons with trophic support. Drugs used to increase or reduce
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2478-776: The neurons containing them lack expression of the serotonin transporter (SERT), which normally transports serotonin from the extracellular space to the intracellular space within neurons. Serotonin itself is too hydrophilic to enter serotonergic neurons without the SERT, and hence these serotonin 5-HT 2A receptors are inaccessible to serotonin. Conversely, serotonergic psychedelics are more lipophilic than serotonin and readily enter these neurons. In addition to explaining why serotonin does not show psychedelic effects, these findings may explain why drugs that increase serotonin levels, like selective serotonin reuptake inhibitors (SSRIs) and various other types of serotonergic agents, do not produce psychedelic effects. Artificial expression of
2537-402: 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 1A receptor inhibition in the brain show negative correlation with aggression, and a mutation in the gene that codes for the 5-HT 2A receptor may double
2596-427: The normal reabsorption of serotonin after it is done with the transmission of the signal, therefore augmenting the neurotransmitter levels in the synapses . Besides mammals, serotonin is found in all bilateral animals including worms and insects, as well as in fungi and in plants . Serotonin's presence in insect venoms and plant spines serves to cause pain, which is a side-effect of serotonin injection. Serotonin
2655-426: The outer cell membrane and the vesicular monoamine transporter ( VMAT1 and VMAT2 ) in the membrane of intracellular vesicles . After release into the synaptic cleft , monoamine neurotransmitter action is ended by reuptake into the presynaptic terminal. There, they can be repackaged into synaptic vesicles or degraded by the enzyme monoamine oxidase (MAO), which is a target of monoamine oxidase inhibitors ,
2714-500: The postsynaptic receptor to induce a nerve impulse on the postsynaptic neuron. Serotonin can also bind to auto-receptors on the presynaptic neuron to regulate the synthesis and release of serotonin. Normally serotonin is taken back into the presynaptic neuron to stop its action, then reused or broken down by monoamine oxidase. Drugs that alter serotonin levels are used in treating depression , generalized anxiety disorder , and social phobia . Monoamine oxidase inhibitors (MAOIs) prevent
2773-466: The potential for serotonin research to treat bone mass disorders. 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 SSRIs makes persistent changes in
2832-436: The regulation of mood, appetite , and sleep . 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
2891-517: The retina, with possible implications for the control of the visual system. The descending projections form a pathway that inhibits pain called the "descending inhibitory pathway" that may be relevant to a 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 and emotion, and hypo- or hyper-serotonergic states may be involved in depression and sickness behavior. Serotonin
2950-625: 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
3009-465: 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. Serotonin regulates gastrointestinal (GI) function. The gut
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#17329093263103068-454: 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
3127-424: 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
3186-441: The serotonin 5-HT 1A , 5-HT 2A , 5-HT 2B , 5-HT 2C , 5-HT 6 , and 5-HT 7 receptors , among others. Activation of serotonin 5-HT 1A receptors and blockade of serotonin 5-HT 2A receptors may contribute to the therapeutic antipsychotic effects of these agents, whereas antagonism of serotonin 5-HT 2C receptors has been especially implicated in side effects of antipsychotics. Antimigraine agents such as
3245-440: 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 2C 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 2C receptors in
3304-426: The serotonin system, including some antidepressants , anxiolytics , antipsychotics , analgesics , antimigraine drugs , antiemetics , appetite suppressants , and anticonvulsants , as well as psychedelics and entactogens . At rest, serotonin is stored within the vesicles of presynaptic neurons. When stimulated by nerve impulses, serotonin is released as a neurotransmitter into the synapse, reversibly binding to
3363-849: The treatment of overweightness or obesity . Several of the preceding agents have been withdrawn from the market due to toxicity , such as cardiac fibrosis or pulmonary hypertension . Although it was previously withdrawn from the market as an appetite suppressant, fenfluramine was reintroduced as an anticonvulsant for treatment of seizures in certain rare forms of epilepsy like Dravet syndrome and Lennox–Gastaut syndrome . Selective serotonin 5-HT 2C receptor agonists, like lorcaserin, bexicaserin , and BMB-101 , are also being developed for this use. Serotonergic psychedelics , including drugs like psilocybin (found in psilocybin mushrooms ), dimethyltryptamine (DMT) (found in ayahuasca ), lysergic acid diethylamide (LSD), and mescaline (found in peyote cactus ), are non-selective agonists of
3422-449: Was identified as a natural Piezo1 ligand, and ssRNA-stimulated 5-HT synthesis from the gut was evoked in a MyD88/TRIF-independent manner. Colonic infusion of RNase A suppressed gut motility and increased bone mass. These findings suggest gut ssRNA as a master determinant of systemic 5-HT levels, indicating the ssRNA-Piezo1 axis as a potential prophylactic target for treatment of bone and gut disorders. Studies in 2008, 2010 and 2019 have opened
3481-443: Was originally named – depend upon the serotonylation of proteins involved in the contractile apparatus of muscle cells. 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
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