Amino Acid Neurotransmitters
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 signaling 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.
Glutamate
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 overexciting 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)
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.
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.
Glycine
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 [i] 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
L-Arginine [ii] 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. [iii]
[i] Nong Y; Huang YQ; Ju W; Kalia LV; Ahmadian G; Wang
YT; Salter MW. Glycine binding primes NMDA receptor internalization. Nature 2003
Mar 20;422(6929):302-7Programme in Brain and Behaviour,
Hospital for Sick Children, , University of Toronto, Toronto, Ontario M5G 1X8,
Canada.
[ii] L-arginine induces nitric
oxide-dependent vasodilation in patients with critical limb ischemia. A
randomized, controlled study. Bode-Böger SM; Böger RH; Alfke H; Heinzel D;
Tsikas D; Creutzig A; Alexander K; Frölich JC Circulation, 93: 1, 1996 Jan 1,
85-90
[iii] Anonymous. Drink reduces movement
disorder symptoms in men. Medical Post June 25 2002;13-16. Tarvil was reported
to cost $100 USD for 30 packets of 6 Gms. The product is licensed to SHS North
America, Rockville Md.
