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Hao S, Shi W, Liu W, Chen QY, Zhuo M. Multiple modulatory roles of serotonin in chronic pain and injury-related anxiety. Front Synaptic Neurosci 2023; 15:1122381. [PMID: 37143481 PMCID: PMC10151796 DOI: 10.3389/fnsyn.2023.1122381] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Accepted: 04/03/2023] [Indexed: 05/06/2023] Open
Abstract
Chronic pain is long-lasting pain that often persists during chronic diseases or after recovery from disease or injury. It often causes serious side effects, such as insomnia, anxiety, or depression which negatively impacts the patient's overall quality of life. Serotonin (5-HT) in the central nervous system (CNS) has been recognized as an important neurotransmitter and neuromodulator which regulates various physiological functions, such as pain sensation, cognition, and emotions-especially anxiety and depression. Its widespread and diverse receptors underlie the functional complexity of 5-HT in the CNS. Recent studies found that both chronic pain and anxiety are associated with synaptic plasticity in the anterior cingulate cortex (ACC), the insular cortex (IC), and the spinal cord. 5-HT exerts multiple modulations of synaptic transmission and plasticity in the ACC and the spinal cord, including activation, inhibition, and biphasic actions. In this review, we will discuss the multiple actions of the 5-HT system in both chronic pain and injury-related anxiety, and the synaptic mechanisms behind them. It is likely that the specific 5-HT receptors would be new promising therapeutic targets for the effective treatment of chronic pain and injury-related anxiety in the future.
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Affiliation(s)
- Shun Hao
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao, Shandong, China
- Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China
- International Institute of Brain Research, Forevercheer Medicine Pharmac Inc., Qingdao, Shandong, China
| | - Wantong Shi
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
| | - Weiqi Liu
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
| | - Qi-Yu Chen
- International Institute of Brain Research, Forevercheer Medicine Pharmac Inc., Qingdao, Shandong, China
- The Brain Cognition and Brain Disease Institute, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Min Zhuo
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao, Shandong, China
- Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China
- International Institute of Brain Research, Forevercheer Medicine Pharmac Inc., Qingdao, Shandong, China
- Center for Neuron and Disease, Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an, Shaanxi, China
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- *Correspondence: Min Zhuo,
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Gupta S, Kawaguchi R, Heinrichs E, Gallardo S, Castellanos S, Mandric I, Novitch BG, Butler SJ. In vitro atlas of dorsal spinal interneurons reveals Wnt signaling as a critical regulator of progenitor expansion. Cell Rep 2022; 40:111119. [PMID: 35858555 PMCID: PMC9414195 DOI: 10.1016/j.celrep.2022.111119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 04/12/2022] [Accepted: 06/28/2022] [Indexed: 11/03/2022] Open
Abstract
Restoring sensation after injury or disease requires a reproducible method for generating large quantities of bona fide somatosensory interneurons. Toward this goal, we assess the mechanisms by which dorsal spinal interneurons (dIs; dI1-dI6) can be derived from mouse embryonic stem cells (mESCs). Using two developmentally relevant growth factors, retinoic acid (RA) and bone morphogenetic protein (BMP) 4, we recapitulate the complete in vivo program of dI differentiation through a neuromesodermal intermediate. Transcriptional profiling reveals that mESC-derived dIs strikingly resemble endogenous dIs, with the correct molecular and functional signatures. We further demonstrate that RA specifies dI4-dI6 fates through a default multipotential state, while the addition of BMP4 induces dI1-dI3 fates and activates Wnt signaling to enhance progenitor proliferation. Constitutively activating Wnt signaling permits the dramatic expansion of neural progenitor cultures. These cultures retain the capacity to differentiate into diverse populations of dIs, thereby providing a method of increasing neuronal yield.
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Affiliation(s)
- Sandeep Gupta
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| | - Riki Kawaguchi
- Department of Psychiatry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Eric Heinrichs
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Genetics and Genomics Graduate Program, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Salena Gallardo
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Molecular Biology Interdepartmental Graduate Program, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Stephanie Castellanos
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, Los Angeles, CA 90095, USA; CIRM Bridges to Research Program, California State University, Northridge, Los Angeles, CA, USA
| | - Igor Mandric
- Department of Computer Science, Samueli School of Engineering, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Bennett G Novitch
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, Los Angeles, CA 90095, USA; Intellectual & Developmental Disabilities Research Center, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Samantha J Butler
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, Los Angeles, CA 90095, USA; Intellectual & Developmental Disabilities Research Center, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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Chen J, Li Q, Saliuk G, Bazhanov S, Winston JH. Estrogen and serotonin enhance stress-induced visceral hypersensitivity in female rats by up-regulating brain-derived neurotrophic factor in spinal cord. Neurogastroenterol Motil 2021; 33:e14117. [PMID: 33705592 DOI: 10.1111/nmo.14117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Revised: 02/08/2021] [Accepted: 02/15/2021] [Indexed: 12/20/2022]
Abstract
BACKGROUND We previously reported that female offspring of dams subjected to chronic prenatal stress (CPS) develop enhanced visceral hypersensitivity (VHS) following exposure to chronic stress in adult life that is mediated by up-regulation of spinal cord BDNF. The aims of this study were to examine the roles of estrogen receptor alpha (ERα) and an increase in spinal serotonin signaling in promoting this enhanced VHS in female rats and up-regulation of spinal cord BDNF transcription. METHODS Pregnant dams were exposed to chronic stress from E11 until delivery. At 8 weeks, a chronic adult stress (CAS) protocol was applied for nine days. KEY RESULTS Ovariectomy before CAS or treatment with letrozole before and during CAS significantly prevented the development of enhanced VHS in female CPS+CAS rats. Intrathecal application of ERα siRNA significantly reduced VHS, decreased lumbar-sacral spinal cord expression of both ERα and BDNF, and reversed pro-transcriptional epigenetic modifications at BDNF promoter lX. Cerebrospinal fluid serotonin levels and 5HT3A receptor expression in the LS spinal cord were both significantly increased in female CPS+CAS rats. During CAS, intrathecal infusion of alosetron significantly decreased VHS, reduced BDNF and ERα expression in the LS spinal cord, and attenuated RNA pol II and ERα binding to the BNDF core promoter IX. CONCLUSIONS & INFERENCES Serotonin-mediated activation of 5HT3A receptors in the spinal cord drives the development of enhanced female-specific VHS in our two hit CPS+CAS through up-regulation of spinal cord ERα.
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Affiliation(s)
- Jinghong Chen
- Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Psychotic Disorders, Shanghai, China
| | - Qingjie Li
- Division of Gastroenterology and Hepatology, Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA
| | - Genevieve Saliuk
- Division of Gastroenterology and Hepatology, Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA
| | - Sonia Bazhanov
- Division of Gastroenterology and Hepatology, Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA
| | - John H Winston
- Division of Gastroenterology and Hepatology, Internal Medicine, University of Texas Medical Branch, Galveston, TX, USA
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Moriya S, Yamashita A, Masukawa D, Sakaguchi J, Ikoma Y, Sameshima Y, Kambe Y, Yamanaka A, Kuwaki T. Involvement of A5/A7 noradrenergic neurons and B2 serotonergic neurons in nociceptive processing: a fiber photometry study. Neural Regen Res 2021; 17:881-886. [PMID: 34472489 PMCID: PMC8530127 DOI: 10.4103/1673-5374.322465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
In the central nervous system, the A6 noradrenaline (NA) and the B3 serotonin (5-HT) cell groups are well-recognized players in the descending antinociceptive system, while other NA/5-HT cell groups are not well characterized. A5/A7 NA and B2 5-HT cells project to the spinal horn and form descending pathways. We recorded G-CaMP6 green fluorescence signal intensities in the A5/A7 NA and the B2 5-HT cell groups of awake mice in response to acute tail pinch stimuli, acute heat stimuli, and in the context of a non-noxious control test, using fiber photometry with a calcium imaging system. We first introduced G-CaMP6 in the A5/A7 NA or B2 5-HT neuronal soma, using transgenic mice carrying the tetracycline-controlled transactivator transgene under the control of either a dopamine β-hydroxylase or a tryptophan hydroxylase-2 promoters and by the site-specific injection of adeno-associated virus (AAV-TetO(3G)-G-CaMP6). After confirming the specific expression patterns of G-CaMP6, we recorded G-CaMP6 green fluorescence signals in these sites in awake mice in response to acute nociceptive stimuli. G-CaMP6 fluorescence intensity in the A5, A7, and B2 cell groups was rapidly increased in response to acute nociceptive stimuli and soon after, it returned to baseline fluorescence intensity. This was not observed in the non-noxious control test. The results indicate that acute nociceptive stimuli rapidly increase the activities of A5/A7 NA or B2 5-HT neurons but the non-noxious stimuli do not. The present study suggests that A5/A7 NA or B2 5-HT neurons play important roles in nociceptive processing in the central nervous system. We suggest that A5/A7/B2 neurons may be new therapeutic targets. All performed procedures were approved by the Institutional Animal Use Committee of Kagoshima University (MD17105) on February 22, 2018.
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Affiliation(s)
- Shunpei Moriya
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Akira Yamashita
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Daiki Masukawa
- Department of Molecular Pharmacology and Neurobiology, Yokohama City University Graduate School of Medicine, Yokohama, Japan
| | - Junichi Sakaguchi
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Yoko Ikoma
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Yoshimune Sameshima
- Department of Pharmacology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Yuki Kambe
- Department of Pharmacology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
| | - Akihiro Yamanaka
- Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan
| | - Tomoyuki Kuwaki
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima, Japan
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Li X, Zhang ZH, Zabed HM, Yun J, Zhang G, Qi X. An Insight into the Roles of Dietary Tryptophan and Its Metabolites in Intestinal Inflammation and Inflammatory Bowel Disease. Mol Nutr Food Res 2021; 65:e2000461. [PMID: 33216452 DOI: 10.1002/mnfr.202000461] [Citation(s) in RCA: 52] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 10/14/2020] [Indexed: 12/11/2022]
Abstract
Inflammatory bowel disease (IBD) is complex, chronic, and relapsing gastrointestinal inflammatory disorders, which includes mainly two conditions, namely ulcerative colitis (UC) and Crohn's disease (CD). Development of IBD in any individual is closely related to his/her autoimmune regulation, gene-microbiota interactions, and dietary factors. Dietary tryptophan (Trp) is an essential amino acid for intestinal mucosal cells, and it is associated with the intestinal inflammation, epithelial barrier, and energy homeostasis of the host. According to recent studies, Trp and its three major metabolic pathways, namely kynurenine (KYN) pathway, indole pathway, and 5-hydroxytryptamine (5-HT) pathway, have vital roles in the regulation of intestinal inflammation by acting directly or indirectly on the pro/anti-inflammatory cytokines, functions of various immune cells, as well as the intestinal microbial composition and homeostasis. In this review, recent advances in Trp- and its metabolites-associated intestinal inflammation are summarized. It further discusses the complex mechanisms and interrelationships of the three major metabolic pathways of Trp in regulating inflammation, which could elucidate the value of dietary Trp to be used as a nutrient for IBD patients.
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Affiliation(s)
- Xiaolan Li
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
| | - Zhi-Hong Zhang
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
| | - Hossain M Zabed
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
| | - Junhua Yun
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
| | - Guoyan Zhang
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
| | - Xianghui Qi
- School of Food and Biological Engineering, Jiangsu University, Zhenjiang, Jiangsu, 212013, China
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Heijmans L, Mons MR, Joosten EA. A systematic review on descending serotonergic projections and modulation of spinal nociception in chronic neuropathic pain and after spinal cord stimulation. Mol Pain 2021; 17:17448069211043965. [PMID: 34662215 PMCID: PMC8527581 DOI: 10.1177/17448069211043965] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Revised: 08/01/2021] [Accepted: 08/16/2021] [Indexed: 12/11/2022] Open
Abstract
Chronic neuropathic pain is a debilitating ordeal for patients worldwide and pharmacological treatment efficacy is still limited. As many pharmacological interventions for neuropathic pain often fail, insights into the underlying mechanism and role of identified receptors is of utmost importance. An important target for improving treatment of neuropathic pain is the descending serotonergic system as these projections modulate nociceptive signaling in the dorsal horn. Also with use of last resort treatments like spinal cord stimulation (SCS), the descending serotonergic projections are known to be involved in the pain relieving effect. This systematic review summarizes the involvement of the serotonergic system on nociceptive modulation in the healthy adult rodent and the chronic neuropathic rodent and summarizes all available literature on the serotonergic system in the SCS-treated neuropathic rodent. Medline, Embase and Pubmed databases were used in the search for articles. Descending serotonergic modulation of nociceptive signaling in spinal dorsal horn in normal adult rat is mainly inhibitory and mediated by 5-HT1a, 5-HT1b, 5-HT2c, 5-HT3 and 5-HT4 receptors. Upon injury and in the neuropathic rat, this descending serotonergic modulation becomes facilitatory via activation of the 5-HT2a, 5-HT2b and 5-HT3 receptors. Analgesia due to neuromodulatory intervention like SCS restores the inhibitory function of the descending serotonergic system and involves 5-HT2, 5-HT3 and 5-HT4 receptors. The results of this systematic review provide insights and suggestions for further pharmacological and or neuromodulatory treatment of neuropathic pain based on targeting selected serotonergic receptors related to descending modulation of nociceptive signaling in spinal dorsal horn. With the novel developed SCS paradigms, the descending serotonergic system will be an important target for mechanism-based stimulation induced analgesia.
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Affiliation(s)
- Lonne Heijmans
- Department of Anesthesiology and Pain Management, Maastricht
University Medical Centre, the Netherlands
- Department of Translational Neuroscience, School of Mental
Health and Neuroscience, Maastricht University, the Netherlands
| | - Martijn R Mons
- Department of Anesthesiology and Pain Management, Maastricht
University Medical Centre, the Netherlands
- Department of Translational Neuroscience, School of Mental
Health and Neuroscience, Maastricht University, the Netherlands
| | - Elbert A Joosten
- Department of Anesthesiology and Pain Management, Maastricht
University Medical Centre, the Netherlands
- Department of Translational Neuroscience, School of Mental
Health and Neuroscience, Maastricht University, the Netherlands
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7
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Drozd US, Shaburova EV, Dygalo NN. Genetic approaches to the investigation of serotonergic neuron functions in animals. Vavilovskii Zhurnal Genet Selektsii 2019. [DOI: 10.18699/vj19.513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The serotonergic system is one of the most important neurotransmitter systems that take part in the regulation of vital CNS functions. The understanding of its mechanisms will help scientists create new therapeutic approaches to the treatment of mental and neurodegenerative diseases and find out how this neurotransmitter system interacts with other parts of the brain and regulates their activity. Since the serotonergic system anatomy and functionality are heterogeneous and complex, the best tools for studying them are based on manipulation of individual types of neurons without affecting neurons of other neurotransmitter systems. The selective cell control is possible due to the genetic determinism of their functions. Proteins that determine the uniqueness of the cell type are expressed under the regulation of cell-specific promoters. By using promoters that are specific for genes of the serotonin system, one can control the expression of a gene of interest in serotonergic neurons. Here we review approaches based on such promoters. The genetic models to be discussed in the article have already shed the light on the role of the serotonergic system in modulating behavior and processing sensory information. In particular, genetic knockouts of serotonin genes sert, pet1, and tph2 promoted the determination of their contribution to the development and functioning of the brain. In addition, the review describes inducible models that allow gene expression to be controlled at various developmental stages. Finally, the application of these genetic approaches in optogenetics and chemogenetics provided a new resource for studying the functions, discharge activity, and signal transduction of serotonergic neurons. Nevertheless, the advantages and limitations of the discussed genetic approaches should be taken into consideration in the course of creating models of pathological conditions and developing pharmacological treatments for their correction.
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Affiliation(s)
- U. S. Drozd
- Novosibirsk State University; Institute of Cytology and Genetics, SB RAS
| | - E. V. Shaburova
- Novosibirsk State University; Institute of Cytology and Genetics, SB RAS
| | - N. N. Dygalo
- Novosibirsk State University; Institute of Cytology and Genetics, SB RAS
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Gautier A, Geny D, Bourgoin S, Bernard J, Hamon M. Differential innervation of superficial versus deep laminae of the dorsal horn by bulbo-spinal serotonergic pathways in the rat. IBRO Rep 2017; 2:72-80. [PMID: 30135935 PMCID: PMC6084826 DOI: 10.1016/j.ibror.2017.04.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 03/28/2017] [Accepted: 04/07/2017] [Indexed: 01/04/2023] Open
Abstract
Convergent data showed that bulbo-spinal serotonergic projections exert complex modulatory influences on nociceptive signaling within the dorsal horn. These neurons are located in the B3 area which comprises the median raphe magnus (RMg) and the lateral paragigantocellular reticular (LPGi) nuclei. Because LPGi 5-HT neurons differ from RMg 5-HT neurons regarding both their respective electrophysiological properties and responses to noxious stimuli, we used anatomical approaches for further characterization of the respective spinal projections of LPGi versus RMg 5-HT neuron subgroups. Adult Sprague-Dawley rats were stereotaxically injected into the RMg or the LPGi with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The precise location of injection sites and RMg vs LPGi spinal projections into the different dorsal horn laminae were visualized by PHA-L immunolabeling. Double immunofluorescent labeling of PHA-L and the serotonin transporter (5-HTT) allowed detection of serotonergic fibers among bulbo-spinal projections. Anterograde tracing showed that RMg neurons project preferentially into the deep laminae V-VI whereas LPGi neuron projections are confined to the superficial laminae I-II of the ipsilateral dorsal horn. All along the spinal cord, double-labeled PHA-L/5-HTT immunoreactive fibers, which represent only 5-15% of all PHA-L-immunoreactive projections, exhibit the same differential locations depending on their origin in the RMg versus the LPGi. The clear-cut distinction between dorsal horn laminae receiving bulbo-spinal serotonergic projections from the RMg versus the LPGi provides further anatomical support to the idea that the descending serotonergic pathways issued from these two bulbar nuclei might exert different modulatory influences on the spinal relay of pain signaling neuronal pathways.
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Affiliation(s)
| | | | | | | | - M. Hamon
- INSERM UMR 894 - Centre de Psychiatrie et Neurosciences, Université Paris Descartes, 75014, Paris, France
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The developmental emergence of differential brainstem serotonergic control of the sensory spinal cord. Sci Rep 2017; 7:2215. [PMID: 28533557 PMCID: PMC5440407 DOI: 10.1038/s41598-017-02509-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 04/12/2017] [Indexed: 12/29/2022] Open
Abstract
Descending connections from brainstem nuclei are known to exert powerful control of spinal nociception and pain behaviours in adult mammals. Here we present evidence that descending serotonergic fibres not only inhibit nociceptive activity, but also facilitate non-noxious tactile activity in the healthy adult rat spinal dorsal horn via activation of spinal 5-HT3 receptors (5-HT3Rs). We further show that this differential serotonergic control in the adult emerges from a non-modality selective system in young rats. Serotonergic fibres exert background 5-HT3R mediated facilitation of both tactile and nociceptive spinal activity in the first three postnatal weeks. Thus, differential descending serotonergic control of spinal touch and pain processing emerges in late postnatal life to allow flexible and context-dependent brain control of somatosensation.
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