Analysis of NMDA Receptor Localization at the Mossy Fiber-Granule Cell Synapse in the Cerebellum

NMDA receptors are critical for synaptic plasticity and neuronal development. They are complexes consisting of the GluRζ1 (NR 1) subunits and one or more GluRε (ε 1-4 or NR 2 A-D) subunits. Although their synaptic localization is physiologically important in neural activities, the mechanism underlying synaptic targeting, subcellular localization, and cell surface expression remains largely unknown. To understand the synaptic localization of the NMDA receptor in cerebellum, I generated mutant mice lacking both GluRε1and ε3subunits, and made immunohistochemical and biochemical analysis in the cerebellum. There was little immunoreactivity for the GluR g 1 subunit in the granular layer of GluRε 1/ε3 mutant cerebellum, while the GluRζ1, ε1, and ε3 subunits were found to be localized at the cerebellar glomerulus in wildtype mouse. The amount of GluRζ1 protein in the GluRε1/ε3 mutant cerebellum was greatly reduced and hardly enriched in PSD fraction. These results indicate that the GluR e subunits serve as determinants of synaptic localization and protein stabilization of the GluRζ1 subunit in vivo