DEVELOPMENTAL AND REGIONAL EXPRESSION IN THE RAT-BRAIN AND FUNCTIONAL-PROPERTIES OF 4 NMDA RECEPTORS

An in situ study of mRNAs encoding NMDA receptor subunits in the devel oping rat CNS revealed that, at all stages, the NR1 gene is expressed in virtually all neurons, whereas the four NR2 transcripts display dis tinct expression patterns. NR2B and NR2D mRNAs occur prenatally, where as NR2A and NR2C mRNAs are first detected near birth. All transcripts except NR2D peak around P20. NR2D mRNA, present mainly in midbrain str uctures, peaks around P7 and thereafter decreases to adult levels. Pos tnatally, NR2B and NR2C transcript levels change in opposite direction s in the cerebellar internal granule cell layer. In the adult hippocam pus, NR2A and NR2B mRNAs are prominent in CA1 and CA3 pyramidal cells, but NR2C and NR2D mRNAs occur in different subsets of interneurons. R ecombinant binary NR1-NR2 channels show comparable Ca2+ permeabilities , but marked differences in voltage-dependent Mg2+ block and in offset decay time constants. Thus, the distinct expression profiles and func tional properties of NR2 subunits provide a basis for NMDA channel het erogeneity in the brain.