Association of NR3A with theN-Methyl-d-aspartate Receptor NR1 and NR2 Subunits

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Abstract
The NR3A subunit of the N-methyl-d-aspartate receptor has been shown to form glutamatergic receptor complexes with NR1 and NR2 subunits and excitatory glycinergic receptor complexes with NR1 alone. We developed an antibody to NR3A and, using quantitative immunoblotting techniques, determined the degree of association between the NR3A subunit and the NR1 and NR2 subunits as well as changes in these associations during development. NR3A expression peaks between postnatal days 7 and 10 in the cortex, midbrain, and hippocampus and reaches higher maximal expression levels in these areas than in the olfactory bulb and cerebellum. Immunoprecipitation experiments with an anti-NR1 antibody demonstrated that the majority of NR3A is associated with NR1 in postnatal day 10 rat cortex (80 ± 8%), decreasing by half (38 ± 4%) in the adult rat cortex. Using the anti-NR3A antibody in immunoprecipitation studies, we find that 9.7 ± 0.8% of NR1, 8.7 ± 1.8% of NR2A, and 5.0 ± 0.6% of NR2B are associated with NR3A at postnatal day 10. These values decrease by about half in adult rat cortex. The results of this study demonstrate that NR3A is expressed, distributed, and associated with other subunits in a manner that supports its role in synaptic transmission throughout the rat brain, perhaps playing different roles during development.