Serotonin (5HT) is synthesized in:
- Cells in the raphe nuclei of brainstem convert L-tryptophan by tryptophan hydroxylase (TPH) to 5-hydoxytryptamine (5-HTP), and furtherly, by amino acid decarboxylase (DDC) to serotonin (5-HT). This is broken down by monoamineoxidase (MAO) to 5-HIAA. Serotonin is released into the synapse in a similar fashion to norepinephrine. Two presynaptic serotonin receptors serve as both brakes and enhancers of serotonin release when blocked by serotonin or norepinephrine, while the postsynaptic receptors regulate the release of the serotonin signal into the neuron. Serotonin producing neurons extend to the cerebellum, basal ganglia, frontal cortex, amygdala, thalamus, hypothalamus and limbic system, and down the spinal cord. TPH1 is in several tissues, and TPH2, is a brain-specific isoform. Ovarian hormones can affect the expression of TPH (postpartum depression and premenstrual stress syndrome).
- Enterochromaffin cells in the gastrointestinal tract
- Platelets
Picture 1. Serotonin synthesis
Serotonin Effects
Serotonin effects include:
- Serotonin is found in the GI tract,… from mood to anxiety to sleep (serotonin makes melatonin, which regulates sleep) to sexual response to food craving and (in)digestion.
- Intestinal serotonin may inhibit bone formation (2)
- As a neurotransmitter: modulation of anger, aggression, body temperature, mood, sleep, human sexuality, appetite, and metabolism, as well as stimulating vomiting (2).
- In platelets - post-injury vasoconstriction
- Nausea/vomiting (Dolasetron blocks serotonin so it helps in nausea)
What Affects Serotonin Release?
This:
- Serotonin transporter facilitates re-uptake of serotonin into presynapses
- Exercise
Substances with Serotogenic Action:
Serotonergic action is terminated primarily via uptake of 5-HT from the synapse. This is through the specific monoamine transporter for 5-HT, SERT, on the presynaptic neuron. Various agents can inhibit 5-HT reuptake including (2):
- The empathogen MDMA (ecstasy) releases serotonin from synaptic vesicles of neurons.
- Amphetamine
- Cocaine
- Dextromethorphan (an antitussive)
- Tricyclic antidepressants (TCAs)
- Selective serotonin reuptake inhibitors (SSRIs) (2).
- The psychedelic drugs psilocin/psilocybin, DMT, mescaline, and LSDare agonists primarily at 5-HT2A receptor.
- MAO inhibitors
- Tryptophan and5-hydroxytryptophan (5-HT) cross blood-brain barrier and are converted to serotonin
- Some cancers(carcinoid) secrete serotonin or 5-HIAA
Foods High in Serotonin
These include:
- Nuts of the walnut (Juglans) and hickory (Carya) genuses
- Plantain, pineapple, banana, kiwifruit, plums, and tomatoes.
- Fish, chicken and turkey
- Avocado
- Whole meal bread
- High-fibre cereals
- Tryptophan is found in bananas, pineapples, plums, turkey and milk
What is required to increase serotonin production is an increase in the ratio of tryptophan to phenylalanine and leucine. Fruits with a good ratio include dates, papaya and banana. Foods with a lower ratio inhibit the production of serotonin. These include whole wheat and rye bread.
Low Serotonin
- Problems with concentration and attention (1)
- Depression
- Chronic fatigue
- Nonrefreshed sleep; we can’t go to sleep at night as our mind/thought is racing ( “My mind won’t shut up!” ); early-morning awakening
- Loss of appetite and subsequent weight loss or a craving for sweets and carbohydrates when the brain is trying to make more Serotonin.
- Total loss of sexual and other interest is present. In fact, there is loss of interest in everything
- People whose serotonin levels have been artificially lowered will reject unfair offers
References:
- http://www.enotalone.com/article/4116.html
- Serotonin inhibits bone formation http://en.wikipedia.org/wiki/Serotonin
- Exercise releases serotonin (serendip.brynmawr.edu)