LOCALIZATION AND REGULATION OF THE DELTA-OPIOID RECEPTOR IN DORSAL-ROOT GANGLIA AND SPINAL-CORD OF THE RAT AND MONKEY - EVIDENCE FOR ASSOCIATION WITH THE MEMBRANE OF LARGE DENSE-CORE VESICLES

Using immunohistochemistry and immunoelectron microscopy, the localiza tion and regulation of delta-opioid receptor-like immunoreactivity wer e studied in dorsal root ganglia and spinal cord of normal rat and mon key, and after peripheral axotomy. delta-Opioid receptor-like immunore activity was observed in many small dorsal root ganglion neurons, and in the rat most of them contained substance P and calcitonin gene-rela ted peptide. At the ultrastructural level, delta-opioid receptor-like immunoreactivity was localized in the Golgi complex, on the membrane o f the large dense-core vesicles and on the membrane of and/or inside a type of large Vesicle with an interior of low electron density. The l atter vesicles were often in contact with multivesicular bodies. In th e superfacial dorsal horn of the spinal cord, most delta-opioid recept or-positive nerve fibers contain substance P and/or calcitonin gene-re lated peptide, both in rat and monkey. Also, in these nerve endings de lta-opioid receptor-like immunoreactivity was found on the membrane of large dense-core vesicles and on the membrane of, or in, the lucent v esicles. Occasionally, delta-opioid receptor-like immunoreactivity was observed on the plasmalemma of the terminals, particularly when the v esicles were in exocytotic contact with the plasmalemma. Peripheral ax otomy induced a decrease in delta-opioid receptor-like immunoreactivit y both in cell bodies in the dorsal root ganglia and in terminals in t he dorsal horn. These data suggest that the F-opioid receptor may be a constituent of the membrane of large dense-core vesicles storing and releasing neuropeptides. It is suggested that upon exocytotic release of substance P and calcitonin gene-related peptide from large dense-co re vesicles, there is a transient modification of the surface of the p rimary afferent terminals which leads to exposure of the receptor prot ein so that enkephalin released from adjacent terminals can activate t he receptor. The decrease in delta-opioid receptors after axotomy indi cates that delta-opioid receptor-mediated inhibitory effects are atten uated at the spinal level both in the rat and monkey. (C) 1997 IBRO. P ublished by Elsevier Science Ltd.