Cellular and subcellular distribution of NMDA receptor subunit NR2B in the retina

Immunocytochemical studies showed the presence of staining for the N-methyl-D-aspartate (NMDA)-R2B glutamate receptor subunit at multiple sites in the cat retina. Reaction product in photoreceptor cells was localized at the inner/outer segment junction and in the axon terminals. Staining within the inner retina was limited to ganglion cells and their dendrites ramifying throughout the inner plexiform layer. These cells were seen to receive synaptic input from cone bipolar cells in both sublaminae. As with other glutamate receptor subunits, this immunoreactivity was typically confined to a single postsynaptic element at a cone bipolar dyad complex. Immunocytochemical localization of the NMDA-R1 subunit, considered to be an essential component of functional receptors, showed a widespread distribution across the retina including all the sites where NMDA-R2B staining was seen. Immunoprecipitation and Western blot analysis were used to confirm the presence of the NR2B receptor protein and its association with the NR1 subunit in both proximal and distal retinal layers. The findings suggest that NMDA-R2B subunits are positioned for multiple functions within the retina.