Immunohistochemical distribution of delta opioid receptors in the rat central nervous system: Evidence for somatodendritic labeling and antigen-specific cellular compartmentalization

Many studies have reported on the distribution of delta opioid receptors (d elta OR) in the mammalian central nervous system (CNS) by using a variety o f techniques. However, no general consensus has emerged with regards to the localization of this receptor due to inconsistencies in the immunohistoche mical literature. In the present study, we analyzed the cellular and subcel lular distribution of immunoreactive delta OR in the rat CNS using two diff erent antibodies (directed against a sequence in the C-terminus or N-termin us of the rat delta OR). By using Western blotting, these two antibodies re cognized similar forms of the delta OR in COS-7 cells transfected with this receptor, but distinct forms in membranes from the rat spinal cord. By usi ng light microscopic immunohistochemistry, both antibodies recognized ident ical populations of nerve cell bodies throughout the CNS; the distribution of these cell bodies conformed to that of delta OR mRNA-expressing cells de tected by in situ hybridization. However, whereas the C-terminus-directed a ntibody recognized predominantly perikarya and proximal dendrites, the N-te rminus-directed antibody also labeled extensively dendritic and terminal ar bors. Furthermore, by using electron microscopy, the two antibodies were fo und not only to label differentially somatodendritic versus axonal compartm ents, but also plasma membrane versus cytoplasmic ones, suggesting that dis tinct immunological forms of the receptor are being targeted preferentially to different cellular and subcellular domains. (C) 2001 Wiley-Liss, Inc.