GluN2B (GRIN2B) forms a di-heterotetramer with GluN1 (GRIN1). The tetramer includes two molecules of GluN1 and two molecules of GluN2B. GluN2B expression starts during embryonic development and continues in adult brain (Monyer et al. 1992, Sheng et al. 1994). The tetrameric structure is deduced from the crystal structure of the rat GluN1:GluN2B (Grin1:Grin2b) NMDA receptor (Karakas and Furukawa 2014) and the Xenopus GluN1:GluN2B NMDA receptor (Lee et al. 2014).