RT Journal Article
SR Electronic
T1 Differential Activation and Trafficking of μ-Opioid Receptors in Brain Slices
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 972
OP 979
DO 10.1124/mol.108.048512
VO 74
IS 4
A1 Seksiri Arttamangkul
A1 Nidia Quillinan
A1 Malcolm J. Low
A1 Mark von Zastrow
A1 John Pintar
A1 John T. Williams
YR 2008
UL http://molpharm.aspetjournals.org/content/74/4/972.abstract
AB The activation of G protein-coupled receptors results in a cascade of events that include acute signaling, desensitization, and internalization, and it is thought that not all agonists affect each process to the same extent. The early steps in opioid receptor signaling, including desensitization, have been characterized electrophysiologically using brain slice preparations, whereas most previous studies of opioid receptor trafficking have been conducted in heterologous cell models. This study used transgenic mice that express an epitope-tagged (FLAG) μ-opioid receptor (FLAGMOR) targeted to catecholamine neurons by regulatory elements from the tyrosine hydroxylase gene. Brain slices from these mice were used to study tagged MOR receptors in neurons of the locus ceruleus. Activation of the FLAGMOR with [Met5]enkephalin (ME) produced a hyperpolarization that desensitized acutely to the same extent as native MOR in slices from wild-type mice. A series of opioid agonists were then used to study desensitization and receptor trafficking in brain slices, which was monitored with a monoclonal antibody against the FLAG epitope (M1) conjugated to Alexa 594. Three patterns of receptor trafficking and desensitization were observed: 1) ME, etorphine, and methadone resulted in both receptor desensitization and internalization; 2) morphine and oxymorphone caused significant desensitization without evidence for internalization; and 3) oxycodone was ineffective in both processes. These results show that two distinct forms of signaling were differentially engaged depending on the agonist used to activate the receptor, and they support the hypothesis that ligand-specific regulation of opioid receptors occurs in neurons maintained in brain slices from adult animals. The American Society for Pharmacology and Experimental Therapeutics