Immunolocalization of NR1, NR2A, and PSD-95 in rat hippocampal subregions during postnatal development.

Although the expression of NMDARs and synaptic-associated proteins has been widely studied, the temporospatial distribution of NMDAR subunits and synaptic proteins in different hippocampal subregions during postnatal development still lacks detailed information, and the relationship between NR1 or NR2 subunits and PSD-95 family proteins is controversial. In this study, we used immunofluorescent staining to assess NR1 or NR2A and PSD-95 expressions and the relationship between them in CA1, CA3, and DG of rat hippocampus on postnatal (P) days: P0, P4, P7, P10, P14, P21, P28, P56. The results showed that from P0 to P56, NR1, NR2A, and PSD-95 expressions increased gradually, and the time points of their expression peak differed in CA1, CA3, and DG during postnatal development. Interestingly, although the expression of PSD-95 was positively correlated to both NR1 and NR2A, the NR1 and PSD-95 coexpressed puncta were greatest in CA3, while NR2A and PSD-95 coexpressed puncta were greatest in CA1, compared to other subregions. Surprisingly, at P21, among different strata of CA1, the area of highest expression of NR2A was dramatically changed from stratum pyramidale to stratum polymorphum and stratum moleculare, and returned to stratum pyramidale gradually on the later observed days again, indicating that P21 may be one critical timepoint during postnatal development in CA1. The specific temporospatial distribution pattern of NR1, NR2A, and PSD-95 might be related to the different physiological functions during postnatal development. Discovering the alteration of the relationship between PSD-95 and NMDAR subunits expression may be helpful for understanding mechanisms and therapy of neurodegenerative diseases.