Detection of delta opioid receptor and N-methyl-D-aspartate receptor-like immunoreactivity in retinoic acid-differentiated neuroblastoma x glioma (NG108-15) cells

NG108‐15 neuroblastoma cells differentiated with 0.1 M of all‐trans retinoic acid (RA) were processed for immunohistochemical analysis using polyclonal antisera against the delta opioid receptor (DOR) and the N‐Methyl‐D‐Aspartate receptor (NMDAR1) to determine the cellular sites for possible functional associations between DOR and NMDAR1 receptors. In this study, 6 days of RA treatment resulted in prominent morphological differentiation characterized by the appearance of numerous axon‐ and dendrite‐like processes and formation of networks between the cell clusters. An immunocytochemical approach allowed the demonstration of antibody concentration‐dependent differences, not evident in ligand binding studies, in the distribution of DOR and NMDA receptor protein between cell soma and processes. RA‐differentiated cultures showed positive DOR‐like immunostaining (DOR‐LI) throughout the cell bodies as well as on the newly acquired processes. In contrast, NMDAR1‐like immunoreactivity (NMDAR1‐LI) in the RA‐treated cells was detected in the cell soma and processes only with the higher concentration of the antiserum. With the lower concentration of the antibody the NMDAR1‐LI was not detected in the processes and was limited to a punctuate subcellular distribution in the soma. The DOR‐LI pattern of distribution in NG108‐15 cells differentiated with RA appeared to be consistent with the DOR‐LI detected in the CNS. The NMDAR1‐LI distribution in these cells is similar to brain tissue with respect to its presence on the newly acquired processes. However, it differed from brain in that a much higher abundance of NMDAR1 receptors was observed in the cell soma. This differential distribution of DOR and NMDAR1 receptors in the RA‐treated NG108‐15 cells could provide a basis for future studies of drug‐induced changes in these two receptors. J. Neurosci. Res. 47:83–89, 1997. © 1997 Wiley‐Liss, Inc.