Glossary of Physiology Terms

γ-Aminobutyric acid

GABA

GABA is an inhibitory amino acid neurotransmitter in the central and peripheral nervous systems. It is the most abundant inhibitory neurotransmitter in the nervous system. During embryonic development, GABA acts as an excitatory neurotransmitter at some central synapses. GABA is a classical neurotransmitter. Its action is exerted via the activation of GABA_A, GABA_B, and GABA_C receptors. GABA_A and GABA_C receptors are ligand-gated chloride channels, whereas GABA_B receptors are G protein coupled receptors. At GABAergic synapses, the action of GABA is terminated by GABA transporters (GAT), which transport GABA from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.

Glycine

Glycine (Gly, G) is one of the standard twenty (20) amino acids. At a molecular weight of 75.07 g/mol, it is the smallest of the 20 amino acids used by cells to synthesize peptides, polypeptides, and proteins.

In the nervous system, glycine is also an inhibitory amino acid neurotransmitter. Glycinergic synapses are most commonly found in brain stem and spinal cord circuits. Glycine is a classical neurotransmitter. Its action is exerted via the activation of ionotropic glycine receptors (GlyR), which are ligand-gated chloride channels. At glycinergic synapses, the action of glycine is terminated by glycine transporters (GlyT), which transport glycine from the extracellular space in synaptic and extrasynaptic regions into neurons and glia.