Studies on trafficking of endogenous opioid receptors in vivo are subject of the present review. In many of the in vivo studies, the use of semi-quantitative immuno-electron microscopy is the approach of choice. Endogenous opioid receptors display differential subcellular distributions with μ opioid receptor (MOPR) being mostly present on the plasma membrane and δ- and κ-opioid receptors (DOPR and KOPR, respectively) having a significant intracellular pool. Etorphine and DAMGO cause endocytosis of the MOPR, but morphine does not, except in some dendrites. Interestingly, chronic inflammatory pain and morphine treatment promote trafficking of intracellular DOPR to the cell surface which may account for the enhanced antinociceptive effects of DOPR agonists. KOPR has been reported to be associated with secretory vesicles in the posterior pituitary and translocated to the cell surface upon salt loading along with the release of vasopressin. The study of endogenous opioid receptors using in vivo models has produced some interesting results that could not have been anticipated in vitro. In vivo studies, therefore, are essential to provide insight into the mechanisms underlying opioid receptor regulation.
Recommended CitationWang, Yulin; Van Bockstaele, Elisabeth J.; and Liu-Chen, Lee-Yuan, "In vivo trafficking of endogenous opioid receptors" (2008). Department of Neurosurgery Faculty Papers. Paper 4.