N-methyl-D-aspartate (NMDA) receptors are a class of ionotropic glutamate receptors. NMDA receptor channels are formed from heteromers composed of three different subunits: the key receptor zeta subunit NMDAR1 (GRIN1) with an NMDAR2 epsilon subunit: NMDAR2A (GRIN2A), NMDAR2B (GRIN2B), NMDAR2C (GRIN2C), or NMDAR2D (GRIN2D) and a third subunit: GRIN3A or GRIN3B.