Distinct distributions of five N‐methyl‐D‐aspartate receptor channel subunit mRNAs in the forebrain

Abstract

The distributions of five NMDA receptor channel subunit mRNAs in the mouse forebrain at postnatal day 21 were semiquantitatively examined by in situ hybridization with subunit‐specific oligonucleotide probes. In contrast to ubiquitous distribution of the ζ1 subunit mRNA throughout the forebrain, distributions of four ϵ subunit mRNAs were highly variable from nucleus to nucleus. The telencephalon (except for the septum) expressed the ϵ1 and ϵ2 subunit mRNAs. Various combinations of the ϵ1, ϵ2, ϵ3, and ϵ4 subunit mRNAs were present in different nuclei of the septum, the olfactory bulb, and the thalamus. In the hypothalamus, the suprachiasmatic nucleus expressed distinct signals for the ϵ3 subunit mRNA alone, whereas other nuclei showed faint signals for the ϵ1, ϵ2, and ϵ4 subunit mRNAs. Moreover, different signal levels of the ϵ subunit mRNAs were found in various regions. The hippocampal CA1 region expressed higher signals for the ϵ1 and ϵ2 subunit mRNAs than the CA3 region and the dentate gyrus. In the cerebral cortex, signal levels of the ϵ1 subunit mRNA were higher in the laminae II/III, IV, and VI than the lamina V, whereas those of the ϵ2 subunit mRNA were highest in laminae II/III and lowest in laminae IV and V. Different signal levels between the ϵ1 and ϵ2 subunit mRNAs were also discerned in the amygdala, the caudate‐putamen, and the thalamus. The distinct anatomical distributions and differential signal levels of the ϵ subunit mRNAs strongly suggest different subunit organizations of the NMDA receptor channel in different forebrain neurons, which may result in functional diversity of the channel in vivo.