title: Continuous opioid agonist treatment dose-dependently regulates mu-opioid receptors and dynamin-2 in mouse spinal cord.
abstract: Continuous opioid agonist treatment produces tolerance and in some cases mu opioid receptor (muOR) down-regulation. Previous studies indicate that down-regulation of muOR is more likely with high-efficacy opioid agonists (e.g., etorphine), whereas lower efficacy agonists (e.g., morphine) do not regulate muOR density. It has been suggested that muOR down-regulation may depend upon increases in Dynamin-2 (DYN-2) proteins. Therefore, the present study examined the effect of various infusion doses of etorphine on muOR density, DYN-2 protein, and DYN-2 mRNA abundance in mouse spinal cord. Mice were implanted sc with an osmotic pump that infused etorphine (50-250 microg/kg/day). Controls were implanted with inert placebo pellets. At the end of 7 days, mice were sacrificed, spinal cord removed and processed for radioligand binding, quantitative Western blotting, or RT-PCR assay. Results indicate that etorphine induced dose-dependent regulation of muOR density, DYN-2 proteins, and mRNA abundance in mouse spinal cord. Higher infusion doses significantly down-regulated muOR density, increased DYN-2 protein abundance, and decreased DYN-2 mRNA. Analysis of these results indicated a significant correlation between muOR down-regulation and DYN-2 abundance in mouse spinal cord. Taken together, muOR regulation may depend on changes in DYN-2 abundance induced by high-efficacy opioid agonists in mouse spinal cord.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, St. John's University, Queens, New York 11439, USA.
authors.forename: Qiuyu
authors.initials: Q
authors.lastname: Zhang
authors.forename: Vishal
authors.initials: V
authors.lastname: Purohit
authors.forename: Byron C
authors.initials: BC
authors.lastname: Yoburn
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D034285:Dynamin II / Q000378:metabolism*; D005048:Etorphine / Q000008:administration & dosage; D008297:Male; D051379:Mice; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D017450:Receptors, Opioid, mu; D005048:Etorphine; D034285:Dynamin II