Functional independence of endogenous µ- and δ-opioid receptors co-expressed in cholinergic interneurons

  1. Seksiri Arttamangkul  Is a corresponding author
  2. Emily J Platt
  3. James Carroll
  4. David Farrens
  1. Oregon Health and Science University, United States

Abstract

Class A G protein-coupled receptors (GPCRs) normally function as monomers, although evidence from heterologous expression systems suggests they may sometimes form homodimers and/or heterodimers. This study aims to evaluate possible functional interplay of endogenous µ- and d-Opioid receptors (MORs and DORs) in mouse neurons. Detecting GPCR dimers in native tissues however has been challenging. Previously, MORs and DORs co-expressed in transfected cells have been reported to form heterodimers, and their possible co-localization in neurons has been studied in knock-in mice expressing genetically engineered receptors fused to fluorescent proteins. Here we find that single cholinergic neurons in the mouse striatum endogenously express both MORs and DORs. The receptors on neurons from live brain slices were fluorescently labeled in live brain slices with a ligand-directed labeling reagent, NAI-A594. The selective activation of MORs and DORs, with DAMGO (µ-agonist) and deltorphin (d-agonist) inhibited spontaneous firing in all cells examined. In the continued presence of agonist, the firing rate returned to baseline as the result of receptor desensitization with the application of deltorphin but was less observed with the application of DAMGO. In addition, agonist-induced internalization of DORs but not MORs was detected. When MORs and DORs were activated simultaneously with [Met5]-enkephalin, desensitization of MORs was facilitated but internalization was not increased. Together, these results indicate that while MORs and DORs are expressed in single striatal cholinergic interneurons, the two receptors function independently.

Data availability

All data generated or analyzed during this study are included in the manuscript.

Article and author information

Author details

  1. Seksiri Arttamangkul

    Vollum Institute, Oregon Health and Science University, Portland, United States
    For correspondence
    arttaman@ohsu.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8815-5124
  2. Emily J Platt

    Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8128-4751
  3. James Carroll

    Surgery, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9264-4502
  4. David Farrens

    Department of Biochemistry and Molecular Biology, School of Medicine, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.

Funding

National Institute on Drug Abuse (DA048136)

  • Seksiri Arttamangkul

National Institute on Drug Abuse (DA048136)

  • David Farrens

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: All animal uses were conducted in accordance with the National Institutes of Health guidelines and with approval from the Institutional Animal Care and Use Committee (IACUC) protocol #IP00000160 of the Oregon Health & Science University. Rats and mice were anesthetized with isofluorane before euthanized with minimal suffering.

Reviewing Editor

  1. Julie A Kauer, Stanford University, United States

Publication history

  1. Preprint posted: April 24, 2021 (view preprint)
  2. Received: May 17, 2021
  3. Accepted: August 31, 2021
  4. Accepted Manuscript published: September 3, 2021 (version 1)
  5. Version of Record published: December 30, 2021 (version 2)

Copyright

© 2021, Arttamangkul et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Seksiri Arttamangkul
  2. Emily J Platt
  3. James Carroll
  4. David Farrens
(2021)
Functional independence of endogenous µ- and δ-opioid receptors co-expressed in cholinergic interneurons
eLife 10:e69740.
https://doi.org/10.7554/eLife.69740

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