What is serotonin?:
Serotonin, and 5-hydroxytryptamine (5-HT) or Enteramin is a tissue hormone and neurotransmitter that is found among others in the central nervous system, intestinal nervous system, cardiovascular system and blood. The name of this biogenic amine is derived from its effect on blood pressure from: Serotonin is a component of the serum, which regulates the tone (tension) of blood vessels. It also affects the gastro-intestinal activity and signal transmission in the central nervous system.
In the human body has a variety of serotonin functions in particular the cardiovascular system, the gastrointestinal tract and nervous system. At the molecular level, the functions of serotonin on at least 14 different serotonin receptors (5-HT receptors) proteins, which are grouped into seven families: 5-HT1 to 5-HT7. The 5-HT3 receptors consist of ion channels, all other known 5-HT receptors are G protein-coupled receptors.  With this large number of serotonin receptors, the tissue also, are distributed cell type and konditionsabhängig is the organism in a position to respond to different serotonin concentrations and to start different signal transduction pathways. These are the main cause for the often conflicting functions of serotonin in the body. In addition, serotonin is capable of an intracellular modification of proteins known as Serotonylierung signaling pathways to control.
Serotonin and appetite:
Serotonin is a neurotransmitter, its distribution in the brain is indirectly associated with the food. One factor is the concentration of free tryptophan in blood plasma. Carbohydrate-rich diet leads to insulin secretion via an increase in tryptophan intake in the brain, which increased with a serotonin synthesis is associated.
Serotonin is associated with a particular appetite-suppressing effect in combination. In obese people the tryptophan levels in blood plasma and the serotonin levels are reduced in the brain. Drugs that increase, as the selective serotonin reuptake inhibitors, serotonin concentration in the brain leading to a loss of appetite as a side effect. Selective activation of serotonin receptor subtype 5-HT1A, primarily as autoreceptors controlling the release of serotonin is through inhibition of serotonin from nerve endings to an increased appetite. The actual appetitsenkende effect of serotonin is largely due to the serotonin receptors 5-HT1B or 5-HT2C
Serotonin sexual behavior:
Serotonin, which is distributed among other things, at the time of ejaculation in the hypothalamus showing primarily an inhibitory effect on sexual behavior and sexual function. Serotonin acts as an antagonist of dopamine. Drug substances, which increase as selective serotonin reuptake inhibitors increase serotonin concentration in the brain may result in addition to a reduction of the sexual need for men in particular to a limited capacity for erection, or to an inhibition of ejaculation.
Serotonin and sleep-wake rhythm:
The effects of serotonin on sleep are partially contradictory and depend crucially on the part of the brain and the role of serotonin receptors involved used.The as antagonists of catecholamines in the initiation of sleep has been known since the 1950s. A serotonin release was therefore associated with the paradoxical sleep (REM sleep). Surgical removal of the serotoninhaltigen raphe nuclei and inhibitors of serotonin synthesis, such as p-Chlorphenylalanin lead in experimental animals to sleep, which can be treated successfully by microinjection of serotonin or 5-hydroxytryptophan in the Hypnogen zones. Also an increased intake of the amino acid tryptophan, can be formed from serotonin in the brain indicates sleep-effect. In contrast, an increased activity of the raphe nuclei and increased serotonin secretion observed during the recovery period.
Serotonin and central nervous system:
Serotonin, which is located in the central nervous system in the somata (cell bodies) serotoninergic nerves in raphe nuclei, emit their axons to all parts of the brain that affects directly or indirectly, almost all brain functions. The main functions of serotonin in the brain that can cross the blood-brain barrier and are formed so the spot has to include the control or influence the perception of sleep, temperature regulation, sensory, pain perception and processing, of appetite, sexual behavior and hormone secretion. Serotonin acts both as a neurotransmitter in the synaptic gap, and is diffusely distributed on the other hand, free nerve endings.