TRANSIENTLY CATECHOLAMINERGIC CELLS IN THE FETAL-RAT EXPRESS MESSENGER-RNA FOR THE GLUTAMATE NMDAR(1) RECEPTOR

The N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor has been shown to be vital to the development of the central nervous syste m. The purpose of this study was to determine if the neural crest-deri ved precursors which migrate to the primitive gut contain mRNA encodin g for the NMDA receptor. Many of these enteric precursors briefly elab orate tyrosine hydroxylase (TH) and have been termed transiently catec holaminergic (TC) cells. TH-like immunoreactivity (TH-ir) serves as a marker for them. Immunocytochemistry combined with NMDAR(1) in situ hy bridization revealed that TH-ir cells in Day 14 rat embryos do express mRNA coding for the NMDAR(1) receptor. However, the TC cells did not contain detectable levels of immunoreactivity for the NMDAR(1) recepto r peptide. The absence of detectable NMDAR(1)-like immunoreactivity mi ght reflect some form of transcriptional or translational regulation, such that the onset of functional receptor activity is delayed until d ifferentiation and/or synaptogenesis commence. Whether TC cell migrati on is glutamate-mediated remains unclear, since some of them successfu lly reached the gut without expressing NMDAR(1) message. Characterizin g TC cell NMDA receptor activity and determining exactly when it ensue s will be of paramount importance to defining the role(s) of this rece ptor in ENS development. In conclusion, the expression of NMDAR(1) mRN A by TH-ir cells suggests a possible developmental role for this recep tor.