NMDA receptors (NMDARs) are members of the glutamate-gated ion-channel family and function in synaptic plasticity, neuronal development and excitotoxicity. NMDARs are heteromeric complexes of multiple subunits: NR1, which occurs as eight distinct isoforms as the result of alternate splicing; NR2 (NR2A, B, C and D are encoded by four related genes, several of which also display multiple splice forms); and NR3 (NR3A and B also have several splice forms). The particular combination of subunits determines the functional characteristics of the receptor.