N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ionotropic glutamate receptors that mediate excitatory synaptic transmission and are important for many aspects of nervous system function including: synaptic plasticity; learning and memory; neuronal development and circuit formation. NMDARs have also been implicated in various neuronal disorders. NMDARs are heteromers consisting of an obligate NR1 and most commonly one or two kinds of NR2 subunits or occasionally NR3 subunits.

The NR3 isoform, NR3B, is abundantly expressed in α-motoneurones and at a lower level in the forebrain (including hippocampus, cerebral cortex, caudoputamen, and nucleus accumbens), and in the cerebellum. mRNA for the NR3B subunit is first detected during the second postnatal week, it then increases and peaks at postnatal day 21. NR3B is a dominant-negative receptor subunit since its presence in NMDA receptors results in a reduction in cellular NMDA receptor activity, calcium permeability, and whole-cell currents.

NR3B plays a role in determining the morphology of dendrites of spinal motor neurones and the proper maturation of motor behaviour. The involvement of NMDAR in the central nervous system (CNS) has become a focus area for neurodegenerative diseases such as Alzheimer’s disease, epilepsy and ischemic neuronal cell death.