Cellular and subcellular localization of the 2B-subunit of the NMDA receptor in the adult rat telencephalon.

NMDA receptors (NR) are encoded by a family of genes including those of the NR1 and NR2A-D subunits. In situ hybridization has revealed that NR1, comprising eight splice variants, is ubiquitously expressed in the central nervous system (CNS) while the expression of NR2 isoforms is restricted to particular CNS regions. We report on the cellular and ultrastructural distribution of the NR2B polypeptide in rat telencephalon. In the telencephalon, the hippocampus represented the most intensively immunolabeled region. Here, predominantly the CA pyramidal neurons were heavily stained. Intense immunoreactivity (IR) was also detected in cortical neurons, in particular in pyramidal-like ones of layers II/III and V. On the ultrastructural level, the NR2B subunit was present not only in synaptic complexes where it usually was present in postsynaptic sites but in addition could be located at extrasynaptic sites. Furthermore, preliminary evidence indicates a presynaptic location of NR2B in some rare cases. NR2B antigen distribution is consistent with that of corresponding transcripts. Indeed, NR2B immunoreactivity coincides largely with that for NR1, indicating that both subunits are coexpressed in numerous cortical and hippocampal neurons.