الفهرس 
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Abstract
Serotonin was known to be synthesised from tryptophan early on its existence and the sequence of steps shown to be hydroxylation followed by decarboxylation.
Serotonergic signaling plays an important role in the modulation of human mood, anger and aggression. Serotonin has broad activities in the brain, and genetic variation in serotonin receptors and the serotonin transporter, which facilitates re-uptake of serotonin into presynapses, have been implicated in neuropsychiatric diseases. Drugs targeting serotonin-induced pathways are being used in the treatment of many psychiatric disorders. One focus of clinical research is the influence of genetics on serotonin action and metabolism in psychiatric settings. Such studies have revealed that the variation in the promoter region of the serotonin transporter protein accounts for nearly 10% of total variance in anxiety-related personality, and the effect of this gene on depression was found to interact with the environment. Serotonin also has effects on appetite, sleep and general metabolism. In the blood, the major storage site is platelets, which collect serotonin from plasma. Bleeding causes serotonin release which constricts blood vessels.
Serotonin receptors are a group of G protein-coupled receptors (GPCRs) and ligand-gated ion channels (LGICs) found in the central and peripheral nervous system. They mediate both excitatory and inhibitory neurotransmission. The serotonin receptors are activated by the neurotransmitter serotonin, which acts as their endogenous ligand. The serotonin receptors modulate the release of many neurotransmitters, including glutamate, GABA, dopamine, epinephrine/norepinephrine, and acetylcholine, as well as many hormones, including oxytocin, prolactin, vasopressin, cortisol, corticosterone, corticotropin, and substance P, among others. The serotonin receptors influence various biological and neurological processes such as aggression, anxiety, appetite, cognition, learning, memory, mood, nausea, sleep, and thermoregulation. The serotonin receptors are the target of a variety of pharmaceutical and illicit drugs, including many antidepressants, antipsychotics, anorectics, antiemetics, gastroprokinetic agents, antimigraine agents, hallucinogens, and entactogens
Extremely high levels of serotonin can have toxic and potentially fatal effects, causing a condition known as serotonin syndrome. In practice, such toxic levels are essentially impossible to reach through an overdose of a single anti-depressant 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 non-toxic levels
The development of the idea that 5-HT has a major role in the action of antidepressant treatments is an interesting amalgam of information being obtained from pharmacology, clinical biochemistry and psychiatry together.
What is perhaps demoralising is our inability to use all the new information to treat psychiatric illness, particularly depression more effectively. The key involvement of 5-HT in this illness had long been known, but our pharmacological treatment of it has improved only modestly over the last 40 years. The current drugs are much better than the old tricyclic compounds in terms of producing far fewer adverse effects. The newer compounds are also much safer in overdose. However, in terms of the percentage of patients who are resistant to treatment, this figure stubbornly refuses to decrease markedly, particularly when treating the elderly.
The speed with which biomedical research is advancing makes any attempt to predict the future a foolhardy exercise. In just over 10 years we went from knowing about perhaps two 5-HT receptors in the brain to 21 and much of this was due to molecular biological techniques. and we still await a good understanding of the action of many of these receptors. However, this knowledge will come with the availability of receptor-selective drugs.
One has to hope that consolidation of existing knowledge and the new drugs that will come out of that knowledge will improve the treatment of psychiatric patients in the next few years.