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Yarmolinsky DA, Zeng X, MacKinnon-Booth N, Greene C, Kim C, Woolf CJ. Selective modification of ascending spinal outputs in acute and neuropathic pain states. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.08.588581. [PMID: 38645252 PMCID: PMC11030409 DOI: 10.1101/2024.04.08.588581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Pain hypersensitivity arises from the plasticity of peripheral and spinal somatosensory neurons, which modifies nociceptive input to the brain and alters pain perception. We utilized chronic calcium imaging of spinal dorsal horn neurons to determine how the representation of somatosensory stimuli in the anterolateral tract, the principal pathway transmitting nociceptive signals to the brain, changes between distinct pain states. In healthy conditions, we identify stable, narrowly tuned outputs selective for cooling or warming, and a neuronal ensemble activated by intense/noxious thermal and mechanical stimuli. Induction of an acute peripheral sensitization with capsaicin selectively and transiently retunes nociceptive output neurons to encode low-intensity stimuli. In contrast, peripheral nerve injury-induced neuropathic pain results in a persistent suppression of innocuous spinal outputs coupled with activation of a normally silent population of high-threshold neurons. These results demonstrate the differential modulation of specific spinal outputs to the brain during nociceptive and neuropathic pain states.
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Xu JF, Liu L, Liu Y, Lu KX, Zhang J, Zhu YJ, Fang F, Dou YN. Spinal Nmur2-positive Neurons Play a Crucial Role in Mechanical Itch. THE JOURNAL OF PAIN 2024:104504. [PMID: 38442838 DOI: 10.1016/j.jpain.2024.02.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 02/23/2024] [Accepted: 02/29/2024] [Indexed: 03/07/2024]
Abstract
The dorsal spinal cord is crucial for the transmission and modulation of multiple somatosensory modalities, such as itch, pain, and touch. Despite being essential for the well-being and survival of an individual, itch and pain, in their chronic forms, have increasingly been recognized as clinical problems. Although considerable progress has been made in our understanding of the neurochemical processing of nociceptive and chemical itch sensations, the neural substrate that is crucial for mechanical itch processing is still unclear. Here, using genetic and functional manipulation, we identified a population of spinal neurons expressing neuromedin U receptor 2 (Nmur2+) as critical elements for mechanical itch. We found that spinal Nmur2+ neurons are predominantly excitatory neurons, and are enriched in the superficial laminae of the dorsal horn. Pharmacogenetic activation of cervical spinal Nmur2+ neurons evoked scratching behavior. Conversely, the ablation of these neurons using a caspase-3-based method decreased von Frey filament-induced scratching behavior without affecting responses to other somatosensory modalities. Similarly, suppressing the excitability of cervical spinal Nmur2+ neurons via the overexpression of functional Kir2.1 potassium channels reduced scratching in response to innocuous mechanical stimuli, but not to pruritogen application. At the lumbar level, pharmacogenetic activation of these neurons evoked licking and lifting behaviors. However, ablating these neurons did not affect the behavior associated with acute pain. Thus, these results revealed the crucial role of spinal Nmur2+ neurons in mechanical itch. Our study provides important insights into the neural basis of mechanical itch, paving the way for developing novel therapies for chronic itch. PERSPECTIVE: Excitatory Nmur2+ neurons in the superficial dorsal spinal cord are essential for mechanical but not chemical itch information processing. These spinal Nmur2+ neurons represent a potential cellular target for future therapeutic interventions against chronic itch. Spinal and supraspinal Nmur2+ neurons may play different roles in pain signal processing.
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Affiliation(s)
- Jun-Feng Xu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Lian Liu
- Department of Endocrinology and Metabolic Diseases, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China
| | - Yuan Liu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, Shanghai, China; School of Life Science and Technology, ShanghaiTech University, Shanghai, China; Lingang Laboratory, Shanghai, China
| | - Ke-Xing Lu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Jun Zhang
- Department of Anesthesiology, Daping Hospital, Army Medical University, Chongqing, China
| | - Yan-Jing Zhu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Fang Fang
- Department of Endocrinology and Metabolic Diseases, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China
| | - Yan-Nong Dou
- Institute of Neuroscience, State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
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Ding H, Zhou L, Zhou J, Feng J. Peripheral Mechanisms of Mechanical Itch. J Invest Dermatol 2024:S0022-202X(23)03204-9. [PMID: 38206270 DOI: 10.1016/j.jid.2023.10.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/25/2023] [Accepted: 10/31/2023] [Indexed: 01/12/2024]
Abstract
Mechanical itch, which is defined as an itch sensation caused by innocuous mechanical force, may warn of the potential risk in the skin. The increased mechanosensitivity in sensory neurons may cause scratch-induced itch and promote the transition from acute itch to chronic itch. Recent studies have not only expanded our knowledge about the neuronal circuits in the CNS but have also highlighted the importance of the peripheral epithelia-immune-neuronal crosstalk in the development of mechanical itch. In this review, we will summarize related findings about the molecular and cellular mechanisms of mechanical itch in the skin.
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Affiliation(s)
- Huijuan Ding
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, China
| | - Liqin Zhou
- State Key Laboratory of Chemical Biology, Shanghai Institute of Materia Medica, Chinese Academy of Science, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China
| | - Jiaying Zhou
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, China
| | - Jing Feng
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, China; State Key Laboratory of Chemical Biology, Shanghai Institute of Materia Medica, Chinese Academy of Science, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China.
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Sheahan TD, Warwick CA, Cui AY, Baranger DA, Perry VJ, Smith KM, Manalo AP, Nguyen EK, Koerber HR, Ross SE. Identification of a convergent spinal neuron population that encodes itch. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.29.560205. [PMID: 37873278 PMCID: PMC10592866 DOI: 10.1101/2023.09.29.560205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Itch is a protective sensation that drives scratching. Although specific cell types have been proposed to underlie itch, the neural circuit basis for itch remains unclear. Here, we used two-photon Ca2+ imaging of the dorsal horn to visualize the neuronal populations that are activated by itch-inducing agents. We identify a convergent population of spinal neurons that is defined by the expression of GRPR. Moreover, we discover that itch is conveyed to the brain via GRPR-expressing spinal output neurons that target the lateral parabrachial nucleus. Further, we show that nalfurafine, a clinically effective kappa opioid receptor agonist, relieves itch by inhibiting GRPR spinoparabrachial neurons. Finally, we demonstrate that a subset of GRPR spinal neurons show persistent, cell-intrinsic Ca2+ oscillations. These experiments provide the first population-level view of the spinal neurons that respond to pruritic stimuli, pinpoint the output neurons that convey itch to the brain, and identify the cellular target of kappa opioid receptor agonists for the inhibition of itch.
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Affiliation(s)
- Tayler D. Sheahan
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Co-first authors
| | - Charles A. Warwick
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Co-first authors
| | - Abby Y. Cui
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - David A.A. Baranger
- Department of Psychological and Brain Sciences, Washington University in St. Louis, St. Louis Missouri, USA
| | - Vijay J. Perry
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Kelly M. Smith
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Current Address: Biohaven Pharmaceuticals, LTD, Pittsburgh, Pennsylvania, USA
| | - Allison P. Manalo
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Eileen K. Nguyen
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Current Address: Department of Anesthesiology and Perioperative Care, University of California, Los Angeles, Los Angeles, California, USA
| | - H. Richard Koerber
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Sarah E. Ross
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Lead contact
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Follansbee T, Dong X. A tactile twist: decoding the phenomena of mechanical itch and alloknesis. Front Mol Neurosci 2023; 16:1278151. [PMID: 37771556 PMCID: PMC10523328 DOI: 10.3389/fnmol.2023.1278151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 08/30/2023] [Indexed: 09/30/2023] Open
Abstract
Itch is a sensation in the skin which provokes the desire to scratch. In the past few decades there has been a significant elucidation of the immune and neural pathways which underly the sensation of itch. An interesting divergence in the itch pathway relates to the type of stimulation used to evoke an itchy sensation. Commonly, chemical mediators of itch such as histamine are injected into the skin where they activate their cognate receptors on sensory neurons. Another way to evoke itch, particularly in patients with chronic itch, is to use light mechanical stimulation. Investigation into these pathways utilizing the mouse model have shown that the neuronal pathways which underly chemical itch are distinct from those which mediate itch in response to mechanical stimulation. Specific populations of primary sensory neurons, spinal interneurons and transmission neurons have been identified which suggests a labeled line for itch transmission. Additionally, Piezo channels, which underly mechanosensation, were discovered to play an important role in the mechanical itch pathway. Given these novel findings relating to the mechanical itch pathway, the purpose of this review is to summarize the reports from human subjects and animal studies to highlight the advances in our understanding of mechanical itch and alloknesis.
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Affiliation(s)
- Taylor Follansbee
- Department of Neuroscience, Howard Huges Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Xinzhong Dong
- Department of Neuroscience, Howard Huges Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD, United States
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