<Li> Increase of NR2A diluting the number of NR2B without the decrease of the latter . </Li> <P> The NR2B and NR2A subunits also have differential roles in mediating excitotoxic neuronal death . The developmental switch in subunit composition is thought to explain the developmental changes in NMDA neurotoxicity . Disruption of the gene for NR2B in mice causes perinatal lethality, whereas the disruption of NR2A gene produces viable mice, although with impaired hippocampal plasticity . One study suggests that reelin may play a role in the NMDA receptor maturation by increasing the NR2B subunit mobility . </P> <P> Granule cell precursors (GCPs) of the cerebellum, after undergoing symmetric cell division in the external granule - cell layer (EGL), migrate into the internal granule - cell layer (IGL) where they downregulate NR2B and activate NR2C, a process that is independent of neuregulin beta signaling through ErbB2 and ErbB4 receptors . </P> <P> NMDA receptors have been implicated by a number of studies to be strongly involved with excitotoxicity . Because NMDA receptors play an important role in the health and function of neurons, there has been much discussion on how these receptors can affect both cell survival and cell death . Recent evidence supports the hypothesis that overstimulation of extrasynaptic NMDA receptors has more to do with excitotoxicity than stimulation of their synaptic counterparts . In addition, while stimulation of extrasynaptic NMDA receptors appear to contribute to cell death, there is evidence to suggest that stimulation of synaptic NMDA receptors contributes to the health and longevity of the cell . There is ample evidence to support the dual nature of NMDA receptors based on location, and the hypothesis explaining the two differing mechanisms is known as the "localization hypothesis". </P>

What is the difference between ampa receptors and nmda receptors