Glycine receptors (GlyRs) are pentameric ligand-gated chloride channels (pLGICs) which mediate inhibitory neurotransmission. They are abundantly expressed throughout the central nervous system and are found primarily in the spinal cord, brain stem, and retina. In the spinal cord, postsynaptic GlyRs are important in regulating motor reflexes and controlling movement. Presynaptic GlyRs are found at glutamatergic and glycinergic synapses and play a pivotal role in modulating neurotransmitter release. The GlyRs belong to the superfamily of Cys-loop pLGICs. In vertebrates, this superfamily of pLGICs can be classified into two categories: cation selective receptors, which include 5-HT 3 serotonin receptors and nicotinic acetylcholine receptors (nAChRs), and anion selective receptors, which contain GABA and glycine receptors. Structurally, as with other pLGICs, the GlyR is a pentameric assembly of five homologous or heterologous subunits.