Developmental expression, subcellular localization, and tyrosine phosphorylation of NR2A and NR2B in the rat brain

We carried out quantitative analyses of the developmental expression, subcellular localization of the N-methyl-D-aspartate receptor subunit 2A (NR2A) and 2B (NR2B), and tyrosine phosphorylation of NR2B. Immunoblot analyses showed that NR2A was not detected during the embryonic period and the first postnatal week but its expression reached 63.90% of adult at P14 and continued to increase until the fourth week, reaching a maximum at P30 (110% of adult). The NR2B was detected from as early as E14 (2.65% of adult) and its expression was transiently elevated at birth (43.73% of adult), decreasing for the first postnatal week, and then increased again rapidly in the second week (105.45% of adult at P14) with a maximum at P30 (123.34% of adult). There were 2.26 +/- 0.40-fold more NR2B than NR2A proteins in the forebrain PSD fractions, and NR2A and NR2B were enriched 2.75 +/- 0.35 and 4.65 +/- 0.25 fold, respectively, in the synaptosome, and 13.75 +/- 0.80 and 16.04 +/- 0.25-fold, respectively, in the PSD fraction from brain homogenate. The tyrosine phosphorylation of NR2B reached an adult level at around birth declining in the first postnatal week but recovered to the adult level by the end of the second week, while the amount of the protein itself increased 2.28-fold after birth, indicating that only a fraction of the proteins are phosphorylated in vivo. Our results indicate that expression and tyrosine phosphorylation of NR2B might be important for NMDA receptor functions in embryonic and early postnatal development.