Glutamate, aspartate, γ-aminobutyric acid (GABA), glycine, D-alanine and D-serine are amino acid neurotransmitters that act, primarily, at ionotropic receptors. Glycine, serine, alanine, aspartate and glutamate all activate the NMDA ionotropic glutamate receptor and the binding of both L-glutamate/aspartate and D-serine/D-alanine/glycine (where / means “or”) at their respective sites on the receptor is required for the receptor to be activated. AMPA and kainate receptors are also glutamate receptors and are also ionotropic receptors. Glutamate also has a number of metabotropic receptors named the metabotropic glutamate receptors and numbered 1-8 (given the abbreviation mGluR1-8). They generally act by either inhibiting and/or potentiating the activity of nearby ionotropic receptors, or regulating the release of glutamate. Glutamate’s ionotropic receptors are all excitatory, that is, they increase the electrical excitability of the neurons on which they are expressed. Glycine also has its own ionotropic receptor called the glycine receptors which are inhibitory and are found primarily in the spinal cord. GABA binds to two major receptor types: GABAA and GABAB receptors, both of which are inhibitory in nature, GABAA is an ionotropic receptor whereas GABAB is a metabotropic receptor.