title: Chronic Morphine Reduces Surface Expression of δ-Opioid Receptors in Subregions of Rostral Striatum.
abstract: The delta opioid receptor (DOPr), whilst not the primary target of clinically used opioids, is involved in development of opioid tolerance and addiction. There is growing evidence that DOPr trafficking is involved in drug addiction, e.g., a range of studies have shown increased plasma membrane DOPr insertion during chronic treatment with opioids. The present study used a transgenic mouse model in which the C-terminal of the DOPr is tagged with enhanced-green fluorescence protein to examine the effects of chronic morphine treatment on surface membrane expression in striatal cholinergic interneurons that are implicated in motivated learning following both chronic morphine and morphine sensitization treatment schedules in male mice. A sex difference was noted throughout the anterior striatum, which was most prominent in the nucleus accumbens core region. Incontrast with previous studies in other neurons, chronic exposure to a high dose of morphine for 6 days had no effect, or slightly decreased (anterior dorsolateral striatum) surface DOPr expression. A morphine sensitization schedule produced similar results with a significant decrease in surface DOPr expression in nucleus accumbens shell. These results suggest that chronic morphine and morphine sensitisation treatment may have effects on instrumental reward-seeking behaviours and learning processes related to drug addiction, via effects on striatal DOPr function.
authors.affiliation: Discipline of Pharmacology, University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Leah
authors.affiliation: Brain and Mind Research Institute, University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Emily M L
authors.initials: EM
authors.lastname: Heath
authors.affiliation: Brain and Mind Research Institute, University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Bernard W
authors.initials: BW
authors.lastname: Balleine
authors.affiliation: Discipline of Pharmacology, University of Sydney, Sydney, NSW, 2006, Australia. mac.christie@sydney.edu.au.
authors.forename: Macdonald J
authors.initials: MJ
authors.lastname: Christie
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D008297:Male; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000235:genetics / Q000378:metabolism*; D012737:Sex Factors
chemical_list: D000697:Central Nervous System Stimulants; D017465:Receptors, Opioid, delta; D009020:Morphine
keywords: Delta opioid receptor; Morphine; Nucleus accumbens; Receptor trafficking; Sensitization; Striatum