Dition, GluD1 and GluD2 seem incapable of forming receptors that can be activated by any known agonists (see section V.A). Whether GluD1 and GluD2 can form heteromeric receptors is unresolved. Functional NMDA receptors require assembly of two GluN1 subunits together with either two GluN2 subunits or a combination of GluN2 and GluN3 subunits (Monyer et al., 1992; Schorge and Colquhoun, 2003; Ulbric