1. Neuroscience
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Contribution of dorsal horn CGRP-expressing interneurons to mechanical sensitivity

  1. Line S Löken  Is a corresponding author
  2. Joao M Braz
  3. Alexander Etlin
  4. Mahsa Sadeghi
  5. Mollie Bernstein
  6. Madison Jewell
  7. Marilyn Steyert
  8. Julia Kuhn
  9. Katherine Hamel
  10. Ida J Llewellyn-Smith
  11. Allan Basbaum  Is a corresponding author
  1. University of California, San Francisco, United States
  2. University of California San Francisco, United States
  3. Flinders University, Australia
Research Article
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Cite this article as: eLife 2021;10:e59751 doi: 10.7554/eLife.59751

Abstract

Primary sensory neurons are generally considered the only source of dorsal horn calcitonin gene-related peptide (CGRP), a neuropeptide critical to the transmission of pain messages. Using a tamoxifen-inducible CalcaCreER transgenic mouse, here we identified a distinct population of CGRP-expressing excitatory interneurons in lamina III of the spinal cord dorsal horn and trigeminal nucleus caudalis. These interneurons have spine-laden, dorsally-directed, dendrites and ventrally-directed axons. As under resting conditions, CGRP interneurons are under tonic inhibitory control, neither innocuous nor noxious stimulation provoked significant Fos expression in these neurons. However, synchronous, electrical non-nociceptive Aβ primary afferent stimulation of dorsal roots depolarized the CGRP interneurons, consistent with their receipt of a VGLUT1 innervation. On the other hand, chemogenetic activation of the neurons produced a mechanical hypersensitivity in response to von Frey stimulation whereas their caspase-mediated ablation led to mechanical hyposensitivity. Finally, after partial peripheral nerve injury, innocuous stimulation (brush) induced significant Fos expression in the CGRP interneurons. These findings suggest that CGRP interneurons become hyperexcitable and contribute either to ascending circuits originating in deep dorsal horn or to the reflex circuits in baseline conditions, but not in the setting of nerve injury.

Data availability

All data generated or analysed during this study are included in the manuscript and supporting files. Source data file is available for figure 6.

Article and author information

Author details

  1. Line S Löken

    Anatomy, University of California, San Francisco, San Francisco, United States
    For correspondence
    linesofieloken@gmail.com
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-6762-9717
  2. Joao M Braz

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  3. Alexander Etlin

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  4. Mahsa Sadeghi

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9769-4082
  5. Mollie Bernstein

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  6. Madison Jewell

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  7. Marilyn Steyert

    Anatomy, University of California, San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  8. Julia Kuhn

    Anatomy, University of California San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  9. Katherine Hamel

    Anatomy, University of California San Francisco, San Francisco, United States
    Competing interests
    No competing interests declared.
  10. Ida J Llewellyn-Smith

    Cardiovascular Medicine and Human Physiology, College of Medicine and Public Health, Flinders University, Bedford Park, Australia
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4269-6846
  11. Allan Basbaum

    Anatomy, University of California San Francisco, San Francisco, United States
    For correspondence
    allan.basbaum@ucsf.edu
    Competing interests
    Allan Basbaum, Reviewing editor, eLife.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-1710-6333

Funding

Sir Henry Wellcome Fellowship (092208/Z/10/Z)

  • Line S Löken

Ake Wiberg Foundation

  • Line S Löken

NIH Blueprint for Neuroscience Research (R35NS097306)

  • Allan Basbaum

Wellcome Trust (A102645)

  • Allan Basbaum

Open Philanthropy Project

  • Allan Basbaum

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

Ethics

Animal experimentation: Mice were housed in cages on a standard 12:12 hour light/dark cycle with food and water ad libitum. Permission for all animal experiments was obtained and overseen by the Institutional Animal Care and Use Committee (IACUC) at the University of California San Francisco. All experiments were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the recommendations of the International Association for the Study of Pain. Ethical approval number: AN183265; expires Feb. 26, 2023.

Reviewing Editor

  1. Rohini Kuner, Universität Heidelberg, Germany

Publication history

  1. Received: June 7, 2020
  2. Accepted: May 29, 2021
  3. Accepted Manuscript published: June 1, 2021 (version 1)

Copyright

© 2021, Löken 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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