Cited by 507Neurotransmitter Receptor Influence on BehaviorNeuroscience and Neuropharmacology ResearchMemory and Neural Mechanisms

The DOI matches its Crossref record; 73 of the 73 references it cites were found in a registry or an index; none of the 40 sources its claims cite is checked for support yet.

Anatomically Defined and Functionally Distinct Dorsal Raphe Serotonin Sub-systems

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Abstract

Summary The dorsal raphe (DR) constitutes a major serotonergic input to the forebrain and modulates diverse functions and brain states including mood, anxiety, and sensory and motor functions. Most functional studies to date have treated DR serotonin neurons as a single population. Using viral-genetic methods, we found that subcortical- and cortical-projecting serotonin neurons have distinct cell body distributions within the DR and differentially co-express a vesicular glutamate transporter. Further, amygdala- and frontal cortex-projecting DR serotonin neurons have largely complementary whole-brain collateralization patterns, receive biased inputs from presynaptic partners, and exhibit opposite responses to aversive stimuli. Gain- and loss-of-function experiments suggest that amygdala-projecting DR serotonin neurons promote anxiety-like behavior, whereas frontal cortex-projecting neurons promote active coping in the face of challenge. These results provide compelling evidence that the DR serotonin system contains parallel sub-systems that differ in input and output connectivity, physiological response properties, and behavioral functions.

Overview

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Written from the paper’s full text.

TL;DR

The dorsal raphe (DR) serotonin system contains anatomically and functionally distinct sub-systems, with cortical- and subcortical-projecting neurons differing in location, Vglut3 co-expression, collateralization, inputs, physiological responses, and behavior. Amygdala-projecting DR serotonin neurons promote anxiety-like behavior, whereas frontal cortex-projecting neurons promote active coping.

Key findings

  • DR serotonin neurons projecting to subcortical regions localized more dorsally, while olfactory bulb and cortical-projecting neurons localized more ventrally; the subcortical and anterior cortical clusters overlapped by 17.4% and 39.6% of their volumes, respectively. Vglut3&Tph2 neurons overlapped 66%±0.6% with the anterior cortical cluster but only 19%±1.1% with the subcortical cluster.
  • OFC- and CeA-projecting DR serotonin neurons showed largely complementary whole-brain collateralization patterns; many known DR targets were innervated by neither subpopulation. cTRIO input mapping found starter cells were predominantly serotonin neurons (97%±2% for OFC-projecting, 94%±4% for CeA-projecting), with OFC-projecting neurons receiving proportionally more input from lateral hypothalamus, lateral habenula, and most medulla nuclei, while CeA-projecting neurons received more input from CeA, BNST, PVH, and nucleus of the solitary tract.
  • Both OFC- and CeA-projecting DR serotonin neurons were activated by reward, but OFC-projecting neurons showed significant pre-lever-press ramping compared with CeA-projecting neurons. To foot-shock, all 7 OFC-projecting mice showed long-lasting Ca2+ reduction, whereas all 8 CeA-projecting mice showed transient elevation.
  • Chemogenetic activation of either OFC- or CeA-projecting neurons decreased locomotion. CeA-projecting neuron activation promoted anxiety-like behavior and Tph2 depletion was anxiolytic; OFC-projecting neuron Tph2 depletion enhanced anxiety-like behavior. OFC-projecting neuron activation enhanced escape behavior in the forced-swim test, and Tph2 deletion increased immobility; CeA-projecting neuron activation did not affect immobility, while Tph2 depletion reduced it.

Methods

  • Viral-genetic retrograde tracing combined with Tph2/Vglut3 staining and registration to the Allen reference brain was used to map cell-body distributions of DR serotonin neurons projecting to eight target regions (PVH, CeA, LHb, dLGN, OB, OFC, PIR, ENT; n=4 per region).
  • iDISCO+ whole-brain clearing and light-sheet imaging mapped collateralization of OFC- and CeA-projecting DR serotonin neurons; cTRIO rabies tracing identified monosynaptic inputs to these subpopulations.
  • Fiber photometry with GCaMP6m recorded reward and foot-shock responses; gain- and loss-of-function experiments used hM3Dq chemogenetic activation and conditional Tph2 knockout, followed by open field, elevated plus maze, auditory fear conditioning, and forced-swim tests.

Limitations

  • Stated: dual-color retrograde tracing had low co-labeling efficiency, preventing strong conclusions about individual DR serotonin neurons targeting multiple areas; subdivisions are not absolute, and each characterized sub-system may still be heterogeneous, with DRSert→OB possibly better described by a two-cluster model.
  • Stated: Tph2 depletion is irreversible and compensatory circuit changes may occur before behavioral testing, so it may not reveal the full function of serotonin release; a small fraction of OFC- and CeA-projecting Tph2+ neurons came from median raphe, which may contribute to loss-of-function phenotypes.
  • Stated: CeA-projecting Tph2 depletion’s forced-swim effect cannot be ruled out as secondary to movement; cTRIO counts did not adjust for possible double counting across consecutive sections and may underestimate posterior thalamic subregions. Evident from the text: fiber photometry during the manipulated behaviors was technically difficult, and many DR targets were not innervated by either OFC- or CeA-projecting subpopulation, implying additional uncharacterized sub-systems.

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Integrity signals

Registry

Crossref · 10.1016/j.cell.2018.07.043

Cites

73 of 73 references verified0 citation errors · 0 not checkable

Statistics

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Verification

Claims the paper makes

0 of 40 cited sources checked · 0 supported · 0 flagged

  • It may state two separate claims as one. 36
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 31
61 of 61
  • The paper relies on this without support.

    Tph2 staining reliably identifies serotonin-producing neurons.

    “Co-staining of DR sections with tryptophan hydroxylase 2 (Tph2) revealed that serotonin neurons projecting to specific output sites have stereotyped cell body locations in the DR.”
  • The paper relies on this without support.

    Avoidance of the center in the open field and of the open arms in the elevated plus maze indicates anxiety-like behavior.

    “Excessive avoidance of the center in the open field or the open arms of the elevated plus maze (EPM) are widely used as indications of anxiety-like behavior.”
  • The paper relies on this without support.

    Immobility and struggle in the forced-swim test indicate passive and active coping, respectively.

    “Immobility and struggle (escape behavior) in the forced-swim test are often used as indications of passive and active coping in the face of challenge, respectively.”
  • The paper relies on this without support.

    Mild electrical foot-shock is an aversive or punishing stimulus.

    “we recorded responses to punishment by subjecting the same set of mice to mild electrical shocks.”
  • The paper relies on this without support.

    Sucrose water is a rewarding stimulus.

    “we trained mice to lever press for a sucrose water reward in a fixed-ratio paradigm.”
  • The paper relies on this without support.

    The behavioral paradigms used engage the DR serotonin system.

    “We subjected the same sets of mice to a series of behavioral paradigms known to engage the DR serotonin system in a fixed sequence (STAR Methods).”
  • The paper relies on this without support.

    Median raphe serotonin neurons make only a small contribution to the loss-of-function phenotypes.

    “Although the vast majority of Tph2+ neurons that project to OFC and CeA were from DR, a small fraction were from median raphe (Figure S5E); thus median raphe serotonin neurons may have a small contribution to the loss-of-function phenotypes described below.”
  • The authors state this as an assumption.

    The sectioning angle is parallel for each brain.

    “we assumed a parallel sectioning angle for each brain.”
  • The paper relies on this without support.

    A large fraction of DR serotonin neurons likely co-release glutamate.

    “since a large fraction of DR serotonin neurons likely co-releases glutamate, Tph2 depletion specifically addresses the function of serotonin in these neurons.”
  • The paper relies on this without support.

    Chemogenetic silencing requires a higher CNO concentration than chemogenetic activation.

    “First, chemogenetic silencing requires a higher CNO concentration than does chemogenetic activation; as the active component of CNO may be clozapine (Gomez et al., 2017), which engages several serotonin receptors at high concentrations (Meltzer, 1994), this strategy may ectopically affect serotonin-related behavior.”
  • The paper relies on this without support.

    1 mg/kg clozapine increases locomotor activity in the open field test.

    “far below 1 mg/kg clozapine that has been reported to elevate locomotor activity in the open field test.”
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Metadata

Authors
Ren, J., Friedmann, D., Xiong, J., Liu, C. D., Ferguson, B. R., Weerakkody, T., DeLoach, K. E., Ran, C., Pun, A., Sun, Y., Weissbourd, B., Neve, R. L., Huguenard, J., Horowitz, M. A., & Luo, L.
Affiliations
  • Howard Hughes Medical Institute (US)
  • Stanford University (US)
  • Stanford Medicine (US)
  • Massachusetts General Hospital (US)
Corresponding author
Luo, Liqun
Venue
Cell
Publisher
Elsevier BV
Published
2018-10
Volume
175
Issue
2
Pages
472-487.e20
ISSN
0092-8674 (ISSN-L)
OpenAlex
W2888526386
Cited by
498
References
72
Citations by year
2026: 61 · 2025: 71 · 2024: 73 · 2023: 74 · 2022: 45 · 2021: 59 · 2020: 66 · 2019: 43 · 2018: 5
FWCI
19.82
Type
journal article
Language
en
Open access
Locations
  • Cell (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
  • BRAIN initiative
  • National Institutes of Health (R01 NS104698)
  • National Science Foundation (NeuroNex)
  • HHMI
Topics
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neurotransmitter Receptor Influence on Behavior
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Memory and Neural Mechanisms
Keywords
dorsal raphe nucleus, serotonergic neurons, vesicular glutamate transporter, amygdala projections, presynaptic input, anxiety-like behavior, active coping, aversive stimuli
MeSH terms
Adaptation, Psychological, Amygdala, Animals, Anxiety, Brain, Female, Frontal Lobe, Male, Mice, Inbred C57BL, Neurons, Serotonin, Mice, Dorsal Raphe Nucleus

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