The N-methyl-D-aspartate receptor (NMDA receptor) – a type of ionotropic glutamate receptor – is a ligand-gated ion channel that is gated by the simultaneous binding of glutamate and a co-agonist (i.e., either D-serine or glycine). Studies show that the NMDA receptor is involved in regulating synaptic plasticity and memory.
The name "NMDA receptor" is derived from the ligand N-methyl-D-aspartate (NMDA), which acts as a selective agonist at these receptors.  When the NMDA receptor is activated by the binding of two co-agonists, the cation channel opens, allowing Na and Ca to flow into the cell, in turn raising the cell's electric potential. Thus, the NMDA receptor is an excitatory receptor. At resting potentials, the binding of Mg or Zn at their extracellular binding sites on the receptor blocks ion flux through the NMDA receptor channel. "However, when neurons are depolarized, for example, by intense activation of colocalized postsynaptic AMPA receptors, the voltage-dependent block by Mg is partially relieved, allowing ion influx through activated NMDA receptors. The resulting Ca influx can trigger a variety of intracellular signaling cascades, which can ultimately change neuronal function through activation of various kinases and phosphatases". Ligands include:
* Primary endogenous co-agonists: glutamate and either D-serine or glycine
* Other agonists : aminocyclopropanecarboxylic acid; D-cycloserine; L-aspartate; quinolinate, etc.
* Partial agonists : N-methyl-D-aspartic acid (NMDA); NRX-1074; 3,5-dibromo-L-phenylalanine, etc.
* Antagonists: ketamine, PCP, dextropropoxyphene, ketobemidone, tramadol, kynurenic acid (endogenous), etc.