Gamma-aminobutyric acid

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Gamma-aminobutyric acid (usually abbreviated to GABA) is an inhibitory neurotransmitter found in the nervous systems of widely divergent species. It is the chief inhibitory neurotransmitter in the central nervous system and also in the retina.

Gamma-aminobutyric acid

General
Systematic name	4-aminobutanoic acid
Other names	GABA
Molecular formula	C₄H₉NO₂
SMILES	C(CC(=O)O)CN
Molar mass	103.12 g/mol
Appearance	white solid
CAS number	56-12-2
Properties
Density and phase	? g/cm³, ?
Solubility in water	? g/100 ml (? °C) or 0.5 M (20 °C)
Melting point	203°C (476 K)
Boiling point	? °C (? K)
Acidity (pK_a)	10.43
Basicity (pK_b)	9.77
Chiral rotation [α]_D	?°
Viscosity	? cP at ? °C
Structure
Molecular shape	?
Coordination geometry	?
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	?
NFPA 704
Flash point	? °C
R/S statement	R: ? S: ?
RTECS number	?
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	?
Other cations	?
Related ?	?
Related compounds	?
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

1 Action and receptors
2 Synthesis
3 Pharmacology
4 See also
5 External links

[edit] Action and receptors

In vertebrates, GABA acts at inhibitory synapses in the brain. GABA acts by binding to specific transmembrane receptors in the plasma membrane of both pre- and postsynaptic neurons. This binding causes the opening of ion channels to allow either the flow of negatively-charged chloride ions into the cell or positively-charged potassium ions out of the cell. This will typically result in a negative change in the transmembrane potential, usually causing hyperpolarization.

Three general classes of GABA receptor are known. These include GABA_A and GABA_C ionotropic receptors, which are ion channels themselves, and GABA_B metabotropic receptors, which are G protein-coupled receptors that open ion channels via intermediaries (G proteins).

Neurons that produce GABA as their output are called GABAergic neurons, and have chiefly inhibitory action at receptors in the adult vertebrate. Medium Spiny Cells are a typical example of inhibitory CNS GABAergic cells. GABA exhibits excitatory actions in insects, mediating muscle activation at synapses between nerves and muscle cells and also the stimulation of certain glands. In hippocampus and neocortex of the mammalian brain, GABA has primarily excitatory effects early in development, and is in fact the major excitatory neurotransmitter in many regions of the brain prior to the maturation of glutamate synapses. developing cortex. Whether GABA is excitatory or inhibitory depends on the direction (into or out of the cell) and magnitude of the ionic currents controlled by the GABA_A receptor. When net positive ionic current is directed into the cell, GABA is excitatory, when the net positive current is directed out of the cell, GABA is inhibitory. A developmental switch in the molecular machinery controlling the polarity of this current is responsible for the changes in the functional role of GABA between the neonatal and adult stages.

[edit] Synthesis

Organisms synthesize GABA from glutamate using the enzyme L-glutamic acid decarboxylase and pyridoxal phosphate as a cofactor. It is worth noting that this involves converting the principal excitatory neurotransmitter (glutamate) into the principal inhibitory one (GABA).

[edit] Pharmacology

Drugs that act as agonists of GABA receptors (known as GABA analogues or GABAergic drugs) or increase the available amount of GABA typically have relaxing, anti-anxiety and anti-convulsive effects. Many of the substances below are known to cause short-term memory loss and retrograde amnesia.

GABA has been purported to increase the amount of the Human Growth Hormone. The results of those studies have been seldom replicated and have recently been in question since it is unknown if GABA can pass the blood-brain barrier.

Drugs that affect GABA receptors: