In 1952, enteromin was shown to be the same substance as serotonin, and as the broad spectrum of physiological roles was elucidated, the abbreviation 5-HT of the true chemical name 5-hydroxytryptamine became the preferred name in the pharmacological field.  Synonyms for serotonin include: 5-hydroxytriptamine, thrombotin, enteramine, substance DS and 3-(β-aminoethyl)-5-hydroxyindole.  In 1953, Betty Twarog and Page discovered serotonin in the central nervous system.  Page considered Erspamer`s work on Octopus vulgaris, Discoglossus pictus, Hexaplex trunculus, Bolinus brandaris, Sepia, Mytilus and Ostrea to be valid and fundamental to understanding this newly identified substance, but considered his earlier results in various models – particularly from rat blood – too confused by the presence of other MAs, including other vasoactive substances.  Serotonin, which is excreted from enterochromaffin cells, eventually makes its way from tissue into the bloodstream. There it is actively absorbed by platelets, which store it. When platelets bind to a clot, they release serotonin, where it can serve as a vasoconstrictor or vasodilator while regulating hemostasis and blood clotting. At high concentrations, serotonin acts as a vasoconstrictor by directly contracting the smooth muscles of the endothm or potentiating the action of other vasoconstrictors (e.g. angiotensin II, noradrenaline). The vasoconstrictor property is manifested mainly in pathological conditions affecting the endothelium – such as atherosclerosis or chronic hypertension. In physiological states, vasodilation occurs through the release of serotonin-mediated nitric oxide from endothelial cells. In addition, it inhibits the release of noradrenaline by adrenergic nerves.  Serotonin is also a growth factor for certain types of cells, which may give it a role in wound healing.
There are different serotonin receptors. Like non-placental vertebrates, teleost fish also possess 5-HT cells in other parts of the brain, including the basal forebrain.  Danio rerio (zebrafish) is a type of teleost fish often used to study serotonin in the brain. Although much is unknown about serotonergic systems in vertebrates, its importance in moderating stress and social interaction is well known.  AVT and CRF are believed to cooperate with serotonin in the hypothalamic-pituitary-interrenal axis.  These neuropeptides affect the plasticity of the teleost and affect its ability to change and respond to its environment. Subordinate fish in social media show a drastic increase in 5-HT concentrations.  High concentrations of 5-HT influence long-term inhibition of aggression in subordinate fish.  In July 2006, the FDA issued a warning that a life-threatening condition called serotonin syndrome can occur when SSRIs such as Prozac or norepinephrine reuptake inhibitors (SNRIs) are taken with triptans. Triptans are also known as 5-hydroxytryptamine receptor agonists. Symptoms of serotonin syndrome include: For example, in the roundworm Caenorhabditis elegans, which feeds on bacteria, serotonin is released as a signal in response to positive events, such as looking for a new food source or in males finding a female to mate with.
 When a well-nourished worm detects bacteria on its cuticle, dopamine is released, which slows it down; When starving, serotonin is also released, which further slows down the animal. This mechanism increases the time animals spend in the presence of food.  The serotonin released activates the muscles used for eating, while octopamine suppresses them.   Serotonin diffuses into serotonin-sensitive neurons that control the animal`s perception of nutrient availability. Serotonin is known to regulate aging, learning, and memory. The first evidence comes from the study of longevity in C. elegans.  During the first phase of aging, serotonin levels increase [vaguely], altering movement patterns and associative memory.  The effect is restored by mutations and drugs (including mianserin and methiothepine) that inhibit serotonin receptors. The observation does not contradict the idea that serotonin levels decline in mammals and humans, which is typically seen in the late, but not early, phase of aging. The quotes below are publications that use Tocris products. Extremely high serotonin levels can cause a condition known as serotonin syndrome, with toxic and life-threatening effects.