Transiently catecholaminergic cells in the fetal rat express mRNA for the glutamate NMDAR 1 receptor

Abstract

The N-methyl- d-aspartate (NMDA) subtype of the glutamate receptor has been shown to be vital to the development of the central nervous system. The purpose of this study was to determine if the neural crest-derived precursors which migrate to the primitive gut contain mRNA encoding for the NMDA receptor. Many of these enteric precursors briefly elaborate tyrosine hydroxylase (TH) and have been termed transiently catecholaminergic (TC) cells. TH-like immunoreactivity (TH-ir) serves as a marker for them. Immunocytochemistry combined with NMDAR, in situ hybridization 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 receptor peptide. The absence of detectable NMDAR 1-like immunoreactivity might reflect some form of transcriptional or translational regulation, such that the onset of functional receptor activity is delayed until differentiation and/or synaptogenesis commence. Whether TC cell migration is glutamate-mediated remains unclear, since some of them successfully reached the gut without expressing NMDAR 1 message. Characterizing TC cell NMDA receptor activity and determining exactly when it is ensues will be of paramount importance to defining the role(s) of this receptor in ENS development. In conclusion, the expression of NMDAR 1 mRNA by TH-ir cells suggests a possible developmental role for this receptor.