The N-methyl-D-aspartate (NMDA) receptor channel has been shown to be involved in long-term potentiation, an activity-dependent increase in the efficiency of synaptic transmission thought to underlie certain kinds of memory and learning. Functional NMDA receptors appear to be composed (minimally) of an invariant subunit (NMDAR1) and 1 of several variable subunits . Each of the variable subunits exhibits a distinct distribution in the adult brain. For example, postnatally, NMDA receptors containing the NMDAR2B
subunit are primarily localized to the hippocampus and forebrain. The sequence of the predicted 1,484-amino acid human protein is 98% and 96% identical to the sequences of the rat and mouse Nmdar2b proteins, respectively.