Amino acids are the most abundant neurotransmitters in the brain. Nichols suggested: “amino acids synapses exceed those of all the other neurotransmitters combined…amino acids are responsible for almost all the fast signalling between neurons, leaving predominantly modulatory roles for the other transmitters.” 

Glutamate is the major excitatory neurotransmitter and is distributed in all regions of the brain. Aspartate is closely related to glutamate and the two amino acids are often found together at axon terminals. Neurons synthesize glutamate and aspartate and are independent of dietary supply.

Three types of receptors for glutamate have been identified: N-methyl- D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate( KA) receptors. The three chemicals that identify glutamate receptors are also potentially neurotoxic and are routinely used in animal experiments to investigate the harmful effects of over-stimulating glutamate receptors. It is known that following brain injury, glutamate is released from injured cells and extends brain damage by over exciting neurons in the neighborhood. Neuronal death often follows overstimulation. While many chemicals used in research block this overstimulation, none are in use medically.

Gamma amino butyric acid (GABA) is the major inhibitory neurotransmitter in the brain, derived from glucose, which is transaminated in the Kreb’s cycle to glutamine and then converted to GABA by the enzyme, glutamic acid decarboxylase. The production of GABA appears to be independent of the dietary supply of glutamine but requires dietary pyridoxine.

Glycine is an inhibitory neurotransmitter found mostly in the brain stem and spinal cord. A major discovery that adds complexity to the already confusing story of neurotransmitters is that glycine acts as a co-transmitter in excitatory NMDA synapses. Nong et al    stated:” Recognition that glycine potentiates NMDAR-mediated currents as well as being a requisite co-agonist of the NMDAR subtype of 'glutamate' receptor profoundly changed our understanding of chemical synaptic communication in the central nervous system. The binding of both glycine and glutamate is necessary to cause opening of the NMDAR conductance pore.”

L-Arginine is the precursor of endogenous nitric oxide (NO), which is a vasodilator acting via the intracellular second-messenger cGMP. In healthy humans, L-arginine induces peripheral vasodilation and inhibits platelet aggregation due to an increased NO production. Prostaglandin E1 (PGE1) induces peripheral vasodilation via stimulating prostacyclin receptors.

A mixture of branch-chain amino acids, leucine, valine and isoleucine will reduce tardive dyskinesia and movement disorder that is caused by anti-schizophrenic drugs. Tarvil, has been marketed in the USA that delivers 6.0 grams of the 3 amino acids per packet. A dose of 6 gm three times a day has been recommended. 

More about Neurotransmitters

Catecholamines
Dopamine
Serotonin
More about amino acids

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Human Brain in Health and Disease

Neuroscience Notes

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