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Inokuchi-Sakata S, Narita R, Takahashi Y, Ishiuji Y, Asahina A, Kato F. Region-specific activation in the accumbens nucleus by itch with modified scratch efficacy in mice - a model-free multivariate analysis. Mol Brain 2024; 17:27. [PMID: 38783364 PMCID: PMC11119306 DOI: 10.1186/s13041-024-01101-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Accepted: 05/15/2024] [Indexed: 05/25/2024] Open
Abstract
Itch is a protective/defensive function with divalent motivational drives. Itch itself elicits an unpleasant experience, which triggers the urge to scratch, relieving the itchiness. Still, it can also result in dissatisfaction when the scratch is too intense and painful or unsatisfactory due to insufficient scratch effect. Therefore, it is likely that the balance between the unpleasantness/pleasure and satisfaction/unsatisfaction associated with itch sensation and scratching behavior is determined by complex brain mechanisms. The physiological/pathological mechanisms underlying this balance remain largely elusive. To address this issue, we targeted the "reward center" of the brain, the nucleus accumbens (NAc), in which itch-responsive neurons have been found in rodents. We examined how neurons in the NAc are activated or suppressed during histamine-induced scratching behaviors in mice. The mice received an intradermal injection of histamine or saline at the neck, and the scratching number was analyzed by recording the movement of the bilateral hind limbs for about 45 min after injection. To experimentally manipulate the scratch efficacy in these histamine models, we compared histamine's behavioral and neuronal effects between mice with intact and clipped nails on the hind paws. As expected, the clipping of the hind limb nail increased the number of scratches after the histamine injection. In the brains of mice exhibiting scratching behaviors, we analyzed the expression of the c-fos gene (Fos) as a readout of an immediate activation of neurons during itch/scratch and dopamine receptors (Drd1 and Drd2) using multiplex single-molecule fluorescence in situ hybridization (RNAscope) in the NAc and surrounding structures. We performed a model-free analysis of gene expression in geometrically divided NAc subregions without assuming the conventional core-shell divisions. The results indicated that even within the NAc, multiple subregions responded differentially to various itch/scratch conditions. We also found different clusters with neurons showing similar or opposite changes in Fos expression and the correlation between scratch number and Fos expression in different itch/scratch conditions. These regional differences and clusters would provide a basis for the complex role of the NAc and surrounding structures in encoding the outcomes of scratching behavior and itchy sensations.
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Affiliation(s)
- Sanae Inokuchi-Sakata
- Department of Dermatology, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
- Department of Neuroscience, The Jikei University School of Medicine, Minato-ku, Tokyo, 105-8461, Japan
| | - Ryo Narita
- Department of Neuroscience, The Jikei University School of Medicine, Minato-ku, Tokyo, 105-8461, Japan
- Center for Neuroscience of Pain, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
| | - Yukari Takahashi
- Department of Neuroscience, The Jikei University School of Medicine, Minato-ku, Tokyo, 105-8461, Japan
- Center for Neuroscience of Pain, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
| | - Yozo Ishiuji
- Department of Dermatology, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
- Center for Neuroscience of Pain, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
| | - Akihiko Asahina
- Department of Dermatology, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan
| | - Fusao Kato
- Department of Neuroscience, The Jikei University School of Medicine, Minato-ku, Tokyo, 105-8461, Japan.
- Center for Neuroscience of Pain, The Jikei University School of Medicine, Minato-Ku, Tokyo, 105-8461, Japan.
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Poddar S, Mondal H, Podder I. Aetiology, pathogenesis and management of neuropathic itch: A narrative review with recent updates. Indian J Dermatol Venereol Leprol 2024; 90:5-18. [PMID: 37317726 DOI: 10.25259/ijdvl_846_2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Accepted: 02/17/2023] [Indexed: 06/16/2023]
Abstract
Neuropathic itch is a relatively common yet under-reported cause of systemic pruritus. It is a debilitating condition often associated with pain, which impairs the patient's quality of life. Although much literature exists about renal and hepatic pruritus, there is a dearth of information and awareness about neuropathic itch. The pathogenesis of neuropathic itch is complex and can result from an insult at any point along the itch pathway, ranging from the peripheral receptors and nerves until the brain. There are several causes of neuropathic itch, many of which do not produce any skin lesions and are thus, often missed. A detailed history and clinical examination are necessary for the diagnosis, while laboratory and radiologic investigations may be needed in select cases. Several therapeutic strategies currently exist involving both non-pharmacological and pharmacological measures, the latter including topical, systemic, and invasive options. Further research is ongoing to clarify its pathogenesis and to design newer targeted therapies with minimal adverse effects. This narrative review highlights the current understanding of this condition, focusing on its causes, pathogenesis, diagnosis, and management, along with newer investigational drugs.
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Affiliation(s)
- Shreya Poddar
- Department of Dermatology, Asansol District Hospital, Asansol, West Bengal, India
| | - Himel Mondal
- Department of Physiology, All India Institute of Medical Sciences (AIIMS), Deoghar, Jharkhand, India
| | - Indrashis Podder
- Department of Dermatology, College of Medicine & Sagore Dutta Hospital, Kolkata, West Bengal, India
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Chen WZ, Shen TY, Wang M, Yuan L, Wang LH, Ding WQ, Shi XX, Wang XF, Bo BS, Liang ZF, Sun YG. An atlas of itch-associated neural dynamics in the mouse brain. Cell Rep 2023; 42:113304. [PMID: 37862165 DOI: 10.1016/j.celrep.2023.113304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 08/07/2023] [Accepted: 10/04/2023] [Indexed: 10/22/2023] Open
Abstract
The itch-scratching cycle is mediated by neural dynamics in the brain. However, our understanding of the neural dynamics during this cycle remains limited. In this study, we examine the neural dynamics of 126 mouse brain areas by measuring the calcium signal using fiber photometry. We present numerous response patterns in the mouse brain during the itch-scratching cycle. Interestingly, we find that a group of brain areas exhibit activation only at the end of histamine-induced scratching behavior. Additionally, several brain areas exhibit transient activation at the onset of scratching induced by chloroquine. Both histamine- and chloroquine-induced itch evoke diverse response patterns across the mouse brain. In summary, our study provides a comprehensive dataset for the diverse activity pattern of mouse brain during the itch-scratching cycle, paving the way for further exploration into the neural mechanisms underlying the itch-scratching cycle.
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Affiliation(s)
- Wen-Zhen Chen
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; University of Chinese Academy of Sciences, 19A Yu-quan Road, Beijing 100049, China
| | - Ting-Yu Shen
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; University of Chinese Academy of Sciences, 19A Yu-quan Road, Beijing 100049, China
| | - Meng Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; University of Chinese Academy of Sciences, 19A Yu-quan Road, Beijing 100049, China
| | - Lin Yuan
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; Department of Orthopaedic Surgery, The First Affiliated Hospital of Fujian Medical University, Fuzhou, China
| | - Lin-Han Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; University of Chinese Academy of Sciences, 19A Yu-quan Road, Beijing 100049, China
| | - Wen-Qun Ding
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China; University of Chinese Academy of Sciences, 19A Yu-quan Road, Beijing 100049, China
| | - Xiao-Xue Shi
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Xiao-Fei Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Bin-Shi Bo
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Zhi-Feng Liang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China
| | - Yan-Gang Sun
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science & Intelligence Technology, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China.
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Mahmoud O, Oladipo O, Mahmoud RH, Yosipovitch G. Itch: from the skin to the brain - peripheral and central neural sensitization in chronic itch. Front Mol Neurosci 2023; 16:1272230. [PMID: 37849619 PMCID: PMC10577434 DOI: 10.3389/fnmol.2023.1272230] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 09/05/2023] [Indexed: 10/19/2023] Open
Abstract
Similar to chronic pain, chronic itch is frequently linked to neural sensitization, a phenomenon wherein the nervous system becomes hypersensitive to stimuli. This process of neural sensitization of chronic itch is orchestrated by various signaling pathways and mediators in both the peripheral and central nervous systems. At the level of the peripheral nervous system, inflammation and neuroimmune interactions induce plastic changes to peripheral nerve fibers, thereby amplifying the transmission of itch signaling. Neural sensitization in the central nervous system occurs at both the spinal cord and brain levels. At the level of the spinal cord, it involves hyperactivity of itch-activating spinal pathways, dysfunction of spinal inhibitory circuits, and attenuation of descending supraspinal inhibitory pathways. In the brain, neural sensitization manifests as structural and functional changes to itch-associated brain areas and networks. Currently, we have a diverse array of neuroimmune-modulating therapies targeting itch neural sensitization mechanisms to help with providing relief to patients with chronic itch. Itch research is a dynamic and continually evolving field, and as we grow in our understanding of chronic itch mechanisms, so will our therapeutic toolbox. Further studies exploring the peripheral and central neural sensitization mechanisms in the context of chronic itch are needed.
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Affiliation(s)
| | | | | | - Gil Yosipovitch
- Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery, Miami Itch Center, University of Miami Miller School of Medicine, Miami, FL, United States
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Millard SK, Bokelmann K, Schalbroeck R, van der Wee NJA, van Loey NEE, van Laarhoven AIM. No indications for altered EEG oscillatory activity in patients with chronic post-burn itch compared to healthy controls. Sci Rep 2022; 12:5184. [PMID: 35338171 PMCID: PMC8956573 DOI: 10.1038/s41598-022-08742-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 02/14/2022] [Indexed: 11/23/2022] Open
Abstract
A large proportion of patients with burn injuries develop chronic itch, which impacts quality of life. The underlying pathophysiological mechanisms are poorly understood. This cross-sectional pilot study investigates whether altered cortical oscillatory processes are involved in chronic post-burn itch. Continuous electroencephalography (EEG) data were recorded during rest and stimulation of non-injured skin, inducing itch (histamine and electrical) and cold-pressor task pain for 15 adults with chronic post-burn itch and 15 matched healthy controls. Quantitative metrics comprised oscillatory power and peak frequencies in theta, alpha, and beta bands. No statistical differences between patients and healthy controls were found in oscillatory activity during rest or stimulation, with Bayesian analysis suggesting equivocal evidence. However, post-traumatic stress symptoms and duration of chronic itch may be associated with changes in oscillatory activity. A lack of differences in cortical oscillatory processing and itch levels at non-injured sites, suggests that itch symptoms have a localised character in this sample of patients with post-burn itch. For future studies, a biopsychological approach with integration of peripheral and central nervous system techniques, linear and non-linear EEG analysis, injured and non-injured stimulation sites, and incorporation of individual characteristics is recommended. Insight into pathophysiological mechanisms underlying chronic post-burn itch could improve diagnostics and treatments.
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Affiliation(s)
- Samantha K Millard
- Health, Medical, and Neuropsychology Unit, Faculty of Social and Behavioural Sciences, Leiden University, Wassenaarseweg 52, 2333 AK, Leiden, The Netherlands.,Centre for Pain IMPACT, Neuroscience Research Australia, 139 Barker Street, Randwick, Sydney, NSW, 2031, Australia.,School of Medical Science, Faculty of Medicine, University of New South Wales, 18 High St, Kensington, Sydney, NSW, 2052, Australia
| | - Klara Bokelmann
- Health, Medical, and Neuropsychology Unit, Faculty of Social and Behavioural Sciences, Leiden University, Wassenaarseweg 52, 2333 AK, Leiden, The Netherlands
| | - Rik Schalbroeck
- Health, Medical, and Neuropsychology Unit, Faculty of Social and Behavioural Sciences, Leiden University, Wassenaarseweg 52, 2333 AK, Leiden, The Netherlands
| | - Nic J A van der Wee
- Department of Psychiatry, Leiden University Medical Centre, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands
| | - Nancy E E van Loey
- Association of Dutch Burn Centers, Maasstad Hospital, Burn Center, Maasstadweg 21, 3079 DZ, Rotterdam, The Netherlands.,Department of Clinical Psychology, Utrecht University, Heidelberglaan 1, 3584 CS, Utrecht, The Netherlands
| | - Antoinette I M van Laarhoven
- Health, Medical, and Neuropsychology Unit, Faculty of Social and Behavioural Sciences, Leiden University, Wassenaarseweg 52, 2333 AK, Leiden, The Netherlands. .,Department of Psychiatry, Leiden University Medical Centre, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands. .,Leiden Institute for Brain and Cognition (LIBC), Leiden University, P.O. Box 9600, 2300 RC, Leiden, The Netherlands.
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Piyush Shah D, Barik A. The Spino-Parabrachial Pathway for Itch. Front Neural Circuits 2022; 16:805831. [PMID: 35250493 PMCID: PMC8891797 DOI: 10.3389/fncir.2022.805831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Accepted: 01/03/2022] [Indexed: 11/13/2022] Open
Abstract
Itch-induced scratching is an evolutionarily conserved behavioral response that protects organisms from potential parasites/irritants in their immediate vicinity. How the exposure to a pruritogen is translated to the perception of itch and how that perception drives scratching directed towards the site of exposure remains poorly understood. In this review, we focus on the recent findings that shed light on the neural pathways in the brain that underlie itch-induced scratching. We compare the molecularly defined itch pathways with the known pain circuits as they have anatomical and functional overlap. We review the roles played by the neurons in the spinoparabrachial pathway-comprising of the neurons in the spinal cord and the parabrachial nucleus (PBN), which acts as a hub for transmitting itch information across the brain. Lastly, we deliberate on scratching as a behavioral measure of the intensity of itch and its implication in unraveling the underlying supraspinal mechanisms. In summary, we provide a resource on the recent advances and discuss a path forward on our understanding of the neural circuits for itch.
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Affiliation(s)
| | - Arnab Barik
- Centre for Neuroscience, Indian Institute of Science, Bengaluru, India
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Mu D, Sun YG. Circuit Mechanisms of Itch in the Brain. J Invest Dermatol 2021; 142:23-30. [PMID: 34662562 DOI: 10.1016/j.jid.2021.09.022] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 08/21/2021] [Accepted: 09/21/2021] [Indexed: 12/12/2022]
Abstract
Itch is an unpleasant somatic sensation with the desire to scratch, and it consists of sensory, affective, and motivational components. Acute itch serves as a critical protective mechanism because an itch-evoked scratching response will help to remove harmful substances invading the skin. Recently, exciting progress has been made in deciphering the mechanisms of itch at both the peripheral nervous system and the CNS levels. Key neuronal subtypes and circuits have been revealed for ascending transmission and the descending modulation of itch. In this review, we mainly summarize the current understanding of the central circuit mechanisms of itch in the brain.
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Affiliation(s)
- Di Mu
- Department of Anesthesiology, Shanghai General Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
| | - Yan-Gang Sun
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Center for Excellence in Brain Science and Intelligence Technology (CEBSIT), Chinese Academy of Sciences, Shanghai, China; Shanghai Center for Brain Science and Brain-Inspired Intelligence Technology, Shanghai, China.
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Mochizuki H, Kursewicz CD, Nomi JS, Yosipovitch G. The right default mode network is associated with the severity of chronic itch. J Eur Acad Dermatol Venereol 2021; 35:e819-e821. [PMID: 34242425 DOI: 10.1111/jdv.17510] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- H Mochizuki
- Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery and Miami Itch Center, Miller School of Medicine, University of Miami, Miami FL, USA
| | - C D Kursewicz
- Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery and Miami Itch Center, Miller School of Medicine, University of Miami, Miami FL, USA
| | - J S Nomi
- Department of Psychology, University of Miami, Coral Gables, FL, USA
| | - G Yosipovitch
- Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery and Miami Itch Center, Miller School of Medicine, University of Miami, Miami FL, USA
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The Skin Microbiota and Itch: Is There a Link? J Clin Med 2020; 9:jcm9041190. [PMID: 32331207 PMCID: PMC7230651 DOI: 10.3390/jcm9041190] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 04/18/2020] [Accepted: 04/20/2020] [Indexed: 02/07/2023] Open
Abstract
Itch is an unpleasant sensation that emanates primarily from the skin. The chemical mediators that drive neuronal activity originate from a complex interaction between keratinocytes, inflammatory cells, nerve endings and the skin microbiota, relaying itch signals to the brain. Stress also exacerbates itch via the skin–brain axis. Recently, the microbiota has surfaced as a major player to regulate this axis, notably during stress settings aroused by actual or perceived homeostatic challenge. The routes of communication between the microbiota and brain are slowly being unraveled and involve neurochemicals (i.e., acetylcholine, histamine, catecholamines, corticotropin) that originate from the microbiota itself. By focusing on itch biology and by referring to the more established field of pain research, this review examines the possible means by which the skin microbiota contributes to itch.
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