Targeted anatomical and functional identification of antinociceptive and pronociceptive serotonergic neurons that project to the spinal dorsal horn

Abstract

Spinally-projecting serotonergic neurons play a key role in controlling pain sensitivity and can either increase or decrease nociception depending on physiological context. It is currently unknown how serotonergic neurons mediate these opposing effects. Utilizing virus-based strategies and Tph2-Cre transgenic mice, we identified two anatomically separated populations of serotonergic hindbrain neurons located in the lateral paragigantocellularis (LPGi) and the medial hindbrain, which respectively innervate the superficial and deep spinal dorsal horn and have contrasting effects on sensory perception. Our tracing experiments revealed that serotonergic neurons of the LPGi were much more susceptible to transduction with spinally injected AAV2retro vectors than medial hindbrain serotonergic neurons. Taking advantage of this difference, we employed intersectional chemogenetic approaches to demonstrate that activation of the LPGi serotonergic projections decreases thermal sensitivity, whereas activation of medial serotonergic neurons increases sensitivity to mechanical von Frey stimulation. Together these results suggest that there are functionally distinct classes of serotonergic hindbrain neurons that differ in their anatomical location in the hindbrain, their postsynaptic targets in the spinal cord, and their impact on nociceptive sensitivity. The LPGi neurons that give rise to rather global and bilateral projections throughout the rostrocaudal extent of the spinal cord appear to be ideally posed to contribute to widespread systemic pain control.

Data availability

All data generated or analysed during this study are included in the manuscript. Raw data acquired in these experiments are uploaded to www.datadryad.org and are available for download.

The following data sets were generated

Article and author information

Author details

  1. Robert Philip Ganley

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8502-9870
  2. Marilia Magalhaes de Sousa

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  3. Kira Werder

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  4. Tugce Öztürk

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  5. Raquel Mendes

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  6. Matteo Ranucci

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  7. Hendrik Wildner

    Institute for Pharmacology and Toxicology, University of Zürich, Zurich, Switzerland
    Competing interests
    The authors declare that no competing interests exist.
  8. Hanns Ulrich Zeilhofer

    Institute for Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
    For correspondence
    zeilhofer@pharma.uzh.ch
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-6954-4629

Funding

Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (310030_197888)

  • Hanns Ulrich Zeilhofer

Olga Mayenfisch Stiftung

  • Hendrik Wildner

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

Ethics

Animal experimentation: Permission to perform these experiments was obtained from the Veterinäramt des Kantons Zürich (154/2018 and 063/2016)

Reviewing Editor

  1. David D Ginty, Harvard Medical School, United States

Version history

  1. Received: March 16, 2022
  2. Preprint posted: March 18, 2022 (view preprint)
  3. Accepted: February 6, 2023
  4. Accepted Manuscript published: February 8, 2023 (version 1)
  5. Version of Record published: February 21, 2023 (version 2)

Copyright

© 2023, Ganley 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.

Metrics

  • 1,311
    Page views
  • 236
    Downloads
  • 2
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Robert Philip Ganley
  2. Marilia Magalhaes de Sousa
  3. Kira Werder
  4. Tugce Öztürk
  5. Raquel Mendes
  6. Matteo Ranucci
  7. Hendrik Wildner
  8. Hanns Ulrich Zeilhofer
(2023)
Targeted anatomical and functional identification of antinociceptive and pronociceptive serotonergic neurons that project to the spinal dorsal horn
eLife 12:e78689.
https://doi.org/10.7554/eLife.78689

Further reading

    1. Chromosomes and Gene Expression
    2. Neuroscience
    Alan E Murphy, Nurun Fancy, Nathan Skene
    Research Article

    Mathys et al. conducted the first single-nucleus RNA-seq (snRNA-seq) study of Alzheimer’s disease (AD) (Mathys et al., 2019). With bulk RNA-seq, changes in gene expression across cell types can be lost, potentially masking the differentially expressed genes (DEGs) across different cell types. Through the use of single-cell techniques, the authors benefitted from increased resolution with the potential to uncover cell type-specific DEGs in AD for the first time. However, there were limitations in both their data processing and quality control and their differential expression analysis. Here, we correct these issues and use best-practice approaches to snRNA-seq differential expression, resulting in 549 times fewer DEGs at a false discovery rate of 0.05. Thus, this study highlights the impact of quality control and differential analysis methods on the discovery of disease-associated genes and aims to refocus the AD research field away from spuriously identified genes.

    1. Neuroscience
    Josue Haubrich, Karim Nader
    Research Article

    The strength of a fear memory significantly influences whether it drives adaptive or maladaptive behavior in the future. Yet, how mild and strong fear memories differ in underlying biology is not well understood. We hypothesized that this distinction may not be exclusively the result of changes within specific brain regions, but rather the outcome of collective changes in connectivity across multiple regions within the neural network. To test this, rats were fear conditioned in protocols of varying intensities to generate mild or strong memories. Neuronal activation driven by recall was measured using c-fos immunohistochemistry in 12 brain regions implicated in fear learning and memory. The interregional coordinated brain activity was computed and graph-based functional networks were generated to compare how mild and strong fear memories differ at the systems level. Our results show that mild fear recall is supported by a well-connected brain network with small-world properties in which the amygdala is well-positioned to be modulated by other regions. In contrast, this connectivity is disrupted in strong fear memories and the amygdala is isolated from other regions. These findings indicate that the neural systems underlying mild and strong fear memories differ, with implications for understanding and treating disorders of fear dysregulation.