Posted by: faithful | September 6, 2012

what is serotonin?

Serotonin

What it is:

Serotonin is a monoamine neurotransmitter that is primarily found in the gastrointestinal (GI) tract and central nervous system (CNS) and influencing the functioning of the neuronal, cardiovascular, renal, immune, and gastrointestinal systems.

Approximately 80 percent of the human body’s total serotonin is located in the enterochromaffin cells in the gut, where it is used to regulate intestinal movements.

The remainder is synthesized in serotonergic neurons in the Central Nervous System where it has various functions, including the regulation of mood, appetite, sleep, muscle contraction, and some cognitive functions including memory and learning; and in blood platelets where it helps to regulate hemostasis and blood clotting.

In addition to humans and animals, serotonin is also found in fungi and plants.

Serotonin is used by a variety of single-cell organisms for various purposes.

History:

Serotonin was originally discovered by Italian Vittorio Erspamer in Rome in 1935 and American scientists in the late 1940s. Isolated and named in 1948 by Maurice M. Rapport, Arda Green, and Irvine Page of the Cleveland Clinic, the name ”serotonin” is something of a misnomer and reflects the circumstances of the compound’s discovery. It was initially identified as a vasoconstrictor substance in blood serum – hence ”serotonin”, a serum agent affecting vascular tone. This agent was later chemically identified as 5-hydroxytryptamine (5-HT) by Rapport, and, as the broad range of physiological roles were elucidated, 5-HT became the preferred name in the pharmacological field.

Biology:

Serotonin, a hormone in the pineal gland, also known as 5-hydroxytryptamine  is a monoamine neurotransmitter. Biochemically derived from tryptophan, it is  found in the digestive tract, the central nervous system, and blood platelets. A hormone is a substance our body produces that regulates and controls the activity of certain cells or organs.

The molecular formula of serotonin is C10H12N2O.

Serotonin is a neurotransmitter – this is a chemical substance that transmits nerve impulses across the space between nerve cells or neurons. We call these spaces synapses.  Here is a model image of how the SSRI (Selective Serotonin Reuptake Inhibitor) effects serotonin reception at the brain synapse):

Serotonin plays an important part in the regulation of learning, mood, sleep and vasoconstriction. Experts believe serotonin also has a role in anxiety, migraine, vomiting and appetite.

For some types of cells, serotonin is a growth factor – and it may have a role in wound healing.

According to Medilexicon:

A vasoconstrictor, liberated by blood platelets, that inhibits gastric secretion and stimulates smooth muscle; present in relatively high concentrations in some areas of the central nervous system (hypothalamus, basal ganglia), and occurring in many peripheral tissues and cells and in carcinoid tumors.

Any disruption in the synthesis, metabolism or uptake of this neurotransmitter has been found to be partly responsible for certain manifestations of schizophrenia, depression, compulsive disorders and learning problems.

Bi-Polar vs. Non Bi-Polar Brain

serotonin pet scan depressed vs not depressed

Serotonin originates in neurons deep in the midline of the brainstem. Because these neurons profile diffusely throughout the brain, serotonin can affect various brain functions.

serotonin 1A receptor (5-HT1A) image pet scan

The diffuse connections of serotonin allow it to affect many basic psychological functions such as anxiety mechanisms and the regulation of mood, thoughts, aggression, appetite, sex drive and the sleep/wake cycle.

Seretonin interacts with many other neurotransmitters, either directly through neurons that use both serotonin and another neurotransmitter, or by serotonin neurons influencing neurons that primarily use these other transmitters.

In depression, the principal biochemical abnormality appears to be impaired metabolism of one or more central amines or peptide neurotransmitters and their receptor sites. SSRIs inhibit the reuptake of serotonin and, thus, increase the concentration of this neurotransmitter in the central nervous system.

The precise mechanism of action of antidepressants is largely unknown. In depression, the principal biochemical abnormality appears to be impaired metabolism of one or more central amines or peptide neurotransmitters and their receptor sites. SSRIs inhibit the reuptake of serotonin and, thus, increase the concentration of this neurotransmitter in the central nervous system.

In humans, serotonin levels are affected by diet. An increase in the ratio of tryptophan to phenylalanine and leucine will increase serotonin levels. Fruits with a good ratio include dates, papayas and bananas. Foods with a lower ratio inhibit the production of serotonin. These include whole wheat and rye bread. Research also suggests eating a diet rich in carbohydrates and low in protein will increase serotonin by secreting insulin, which helps in amino acid competition.However, increasing insulin for a long period may trigger the onset of insulin resistance, obesity, type 2 diabetes, and lower serotonin levels. Muscles use many of the amino acids except tryptophan, allowing more muscular individuals to produce more serotonin. Myoinositol, a carbocyclic polyol present in many foods, is known to play a role in serotonin modulation.

The mechanism of action for the SSRIs is the blocking of the uptake pump action on the presynaptic neuron. This increases the amount of serotonin in the synaptic cleft and at the postsynaptic serotonin receptor site, resulting in greater postsynaptic serotonin stimulation.

In addition to animals, serotonin is found 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 amoebas, and its effect on the gut causes diarrhea. Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds.

Biosynthesis:

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) and amino acid decarboxylase (DDC). 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 brain-specific isoform.

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, can and do 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.

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