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Hirsch SJ, Budig A, Husam S, Birklein F. Aged females unilaterally hypersensitize, lack descending inhibition, and overexpress alpha1D adrenergic receptors in a murine posttraumatic chronic pain model. Pain 2024:00006396-990000000-00533. [PMID: 38408277 DOI: 10.1097/j.pain.0000000000003197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 01/11/2024] [Indexed: 02/28/2024]
Abstract
ABSTRACT Vulnerability to chronic pain is found to depend on age and sex. Most patients with chronic pain are elderly women, especially with posttraumatic pain after bone fracture that prevails beyond the usual recovery period and develops into a complex regional pain syndrome (CRPS). There, a distal bone fracture seems to initiate a pathophysiological process with unknown mechanism. To investigate whether sex, age, and alpha adrenergic receptors also contribute to a CRPS-like phenotype in animals, we performed experiments on tibia-fractured mice. Those mice commonly are resilient to the development of a CRPS-like phenotype. However, we found them to be vulnerable to long-lasting pain after distal bone fracture when they were of old age. These mice expressed mechanical and thermal hypersensitivity, as well as weight-bearing and autonomic impairment following bone trauma, which persisted over 3 months. Site-specific and body side-specific glycinergic and α1D-noradrenergic receptor expression in the spinal cord and the contralateral locus coeruleus were misbalanced. Aged female tibia-fractured mice lost descending noradrenergic inhibition and displayed enhanced spinal activity on peripheral pressure stimuli. Together, changes in the noradrenergic, hence, glycinergic system towards excitation in the pain pathway-ascending and descending-might contribute to the development or maintenance of long-lasting pain. Conclusively, changes in the noradrenergic system particularly occur in aged female mice after trauma and might contribute to the development of long-lasting pain. Our data support the hypothesis that some patients with chronic pain would benefit from lowering the adrenergic/sympathetic tone or antagonizing α1(D).
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Affiliation(s)
- Silke J Hirsch
- Department of Neurology, Unimedizin Mainz, Mainz, Germany
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Zhang Z, Zheng H, Yu Q, Jing X. Understanding of Spinal Wide Dynamic Range Neurons and Their Modulation on Pathological Pain. J Pain Res 2024; 17:441-457. [PMID: 38318328 PMCID: PMC10840524 DOI: 10.2147/jpr.s446803] [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: 10/26/2023] [Accepted: 01/12/2024] [Indexed: 02/07/2024] Open
Abstract
The spinal dorsal horn (SDH) transmits sensory information from the periphery to the brain. Wide dynamic range (WDR) neurons within this relay site play a critical role in modulating and integrating peripheral sensory inputs, as well as the process of central sensitization during pathological pain. This group of spinal multi-receptive neurons has attracted considerable attention in pain research due to their capabilities for encoding the location and intensity of nociception. Meanwhile, transmission, processing, and modulation of incoming afferent information in WDR neurons also establish the underlying basis for investigating the integration of acupuncture and pain signals. This review aims to provide a comprehensive examination of the distinctive features of WDR neurons and their involvement in pain. Specifically, we will examine the regulation of diverse supraspinal nuclei on these neurons and analyze their potential in elucidating the mechanisms of acupuncture analgesia.
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Affiliation(s)
- Zhiyun Zhang
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing, People’s Republic of China
| | - Hao Zheng
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing, People’s Republic of China
| | - Qingquan Yu
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing, People’s Republic of China
| | - Xianghong Jing
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing, People’s Republic of China
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Rogness VM, Juliette J, Khasabova IA, Gupta K, Khasabov SG, Simone DA. Descending Facilitation of Nociceptive Transmission From the Rostral Ventromedial Medulla Contributes to Hyperalgesia in Mice with Sickle Cell Disease. Neuroscience 2023; 526:1-12. [PMID: 37330194 PMCID: PMC10528639 DOI: 10.1016/j.neuroscience.2023.06.007] [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: 04/25/2023] [Revised: 05/26/2023] [Accepted: 06/09/2023] [Indexed: 06/19/2023]
Abstract
Sickle cell disease (SCD) is an inherited blood disorder that is associated with acute episodic and chronic pain. Mice with SCD have robust hyperalgesia mediated, in part, by sensitization of spinal dorsal horn neurons. However, underlying mechanisms are not fully understood. Since the rostral ventromedial medulla (RVM) is a major component of descending circuitry that modulates nociceptive transmission in the spinal cord, we examined if the RVM contributes to hyperalgesia in mice with SCD. Injection of lidocaine, but not vehicle, into the RVM eliminated mechanical and heat hyperalgesia in sickle (HbSS-BERK) mice without altering mechanical and heat sensitivity in naïve C57B mice. These data indicate that the RVM contributes to the maintenance of hyperalgesia in mice with SCD. In electrophysiological studies, we determined the changes in response properties of RVM neurons that might contribute to hyperalgesia in sickle mice. Recordings were made from single ON, OFF, and Neutral cells in the RVM of sickle and control (HbAA-BERK) mice. Spontaneous activity and responses of ON, OFF and Neutral cells evoked by heat (50 °C) and mechanical (26 g) stimuli applied to the hind paw were compared between sickle and control mice. Although there were no differences in the proportions of functionally-identified neurons or spontaneous activity between sickle and control mice, evoked responses of ON cells to heat and mechanical stimuli were increased approximately 3-fold in sickle mice as compared to control mice. Thus, the RVM contributes to hyperalgesia in sickle mice via a specific ON cell-dependent descending facilitation of nociceptive transmission.
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Affiliation(s)
- Victoria M Rogness
- Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Joseph Juliette
- Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Iryna A Khasabova
- Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Kalpna Gupta
- Hematology/Oncology, Department of Medicine, University of California, Irvine and Southern California Institute for Research and Education, VA Medical Center, Long Beach, CA, USA
| | - Sergey G Khasabov
- Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA
| | - Donald A Simone
- Department of Diagnostic & Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN 55455, USA.
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4
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Follansbee T, Domocos D, Nguyen E, Nguyen A, Bountouvas A, Velasquez L, Iodi Carstens M, Takanami K, Ross SE, Carstens E. Inhibition of itch by neurokinin 1 receptor (Tacr1) -expressing ON cells in the rostral ventromedial medulla in mice. eLife 2022; 11:69626. [PMID: 35972457 PMCID: PMC9381038 DOI: 10.7554/elife.69626] [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: 04/21/2021] [Accepted: 08/04/2022] [Indexed: 12/03/2022] Open
Abstract
The rostral ventromedial medulla (RVM) is important in descending modulation of spinal nociceptive transmission, but it is unclear if the RVM also modulates spinal pruriceptive transmission. RVM ON cells are activated by noxious algesic and pruritic stimuli and are pronociceptive. Many RVM-spinal projection neurons express the neurokinin-1 receptor (Tacr1), and ON-cells are excited by local administration of substance P (SP). We hypothesized that Tacr1-expressing RVM ON cells exert an inhibitory effect on itch opposite to their pronociceptive action. Intramedullary microinjection of SP significantly potentiated RVM ON cells and reduced pruritogen-evoked scratching while producing mild mechanical sensitization. Chemogenetic activation of RVM Tacr1-expressing RVM neurons also reduced acute pruritogen-evoked scratching. Optotagging experiments confirmed RVM Tacr1-expressing neurons to be ON cells. We conclude that Tacr1-expressing ON cells in RVM play a significant role in the modulation of pruriceptive transmission.
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Affiliation(s)
- Taylor Follansbee
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States.,Department of Neuroscience, Johns Hopkins University, Baltimore, United States
| | - Dan Domocos
- Department of Anatomy, Animal Physiology and Biophysics, University of Bucharest, Bucharest, Romania
| | - Eileen Nguyen
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
| | - Amanda Nguyen
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Aristea Bountouvas
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Lauren Velasquez
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Mirela Iodi Carstens
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
| | - Keiko Takanami
- Department of Environmental Life Science, National Nara Women University, Nara, Japan
| | - Sarah E Ross
- Pittsburgh Center for Pain Research and Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
| | - Earl Carstens
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, United States
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Cooper AH, Hedden NS, Prasoon P, Qi Y, Taylor BK. Postsurgical Latent Pain Sensitization Is Driven by Descending Serotonergic Facilitation and Masked by µ-Opioid Receptor Constitutive Activity in the Rostral Ventromedial Medulla. J Neurosci 2022; 42:5870-5881. [PMID: 35701159 PMCID: PMC9337598 DOI: 10.1523/jneurosci.2038-21.2022] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Revised: 05/22/2022] [Accepted: 05/27/2022] [Indexed: 01/29/2023] Open
Abstract
Following tissue injury, latent sensitization (LS) of nociceptive signaling can persist indefinitely, kept in remission by compensatory µ-opioid receptor constitutive activity (MORCA) in the dorsal horn of the spinal cord. To demonstrate LS, we conducted plantar incision in mice and then waited 3-4 weeks for hypersensitivity to resolve. At this time (remission), systemic administration of the opioid receptor antagonist/inverse agonist naltrexone reinstated mechanical and heat hypersensitivity. We first tested the hypothesis that LS extends to serotonergic neurons in the rostral ventral medulla (RVM) that convey pronociceptive input to the spinal cord. We report that in male and female mice, hypersensitivity was accompanied by increased Fos expression in serotonergic neurons of the RVM, abolished on chemogenetic inhibition of RVM 5-HT neurons, and blocked by intrathecal injection of the 5-HT3R antagonist ondansetron; the 5-HT2AR antagonist MDL-11 939 had no effect. Second, to test for MORCA, we microinjected the MOR inverse agonist d-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) and/or neutral opioid receptor antagonist 6β-naltrexol. Intra-RVM CTAP produced mechanical hypersensitivity at both hindpaws; 6β-naltrexol had no effect by itself, but blocked CTAP-induced hypersensitivity. This indicates that MORCA, rather than an opioid ligand-dependent mechanism, maintains LS in remission. We conclude that incision establishes LS in descending RVM 5-HT neurons that drives pronociceptive 5-HT3R signaling in the dorsal horn, and this LS is tonically opposed by MORCA in the RVM. The 5-HT3 receptor is a promising therapeutic target for the development of drugs to prevent the transition from acute to chronic postsurgical pain.SIGNIFICANCE STATEMENT Surgery leads to latent pain sensitization and a compensatory state of endogenous pain control that is maintained long after tissue healing. Here, we show that either chemogenetic inhibition of serotonergic neuron activity in the RVM or pharmacological inhibition of 5-HT3 receptor signaling at the spinal cord blocks behavioral signs of postsurgical latent sensitization. We conclude that MORCA in the RVM opposes descending serotonergic facilitation of LS and that the 5-HT3 receptor is a promising therapeutic target for the development of drugs to prevent the transition from acute to chronic postsurgical pain.
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Affiliation(s)
- Andrew H Cooper
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Naomi S Hedden
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Pranav Prasoon
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Yanmei Qi
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Bradley K Taylor
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
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Mo 莫思怡 SY, Xu 徐啸翔 XX, Bai 白珊珊 SS, Liu 刘云 Y, Fu 傅开元 KY, Sessle BJ, Cao 曹烨 Y, Xie 谢秋菲 QF. Neuronal Activities in the Rostral Ventromedial Medulla Associated with Experimental Occlusal Interference-Induced Orofacial Hyperalgesia. J Neurosci 2022; 42:5314-5329. [PMID: 35667852 PMCID: PMC9270923 DOI: 10.1523/jneurosci.0008-22.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 04/14/2022] [Accepted: 05/24/2022] [Indexed: 01/09/2023] Open
Abstract
The imbalanced conditions of pronociceptive ON-cells and antinociceptive OFF-cells in the rostral ventromedial medulla (RVM) alter nociceptive transmission and play an important role in the development of chronic pain. This study aimed to explore the neuroplastic mechanisms of the RVM ON-cells and OFF-cells in a male rat model of experimental occlusal interference (EOI)-induced nociceptive behavior reflecting orofacial hyperalgesia and in modified models involving EOI removal at early and later stages. We recorded the mechanical head withdrawal thresholds, orofacial operant behaviors, and the activity of identified RVM ON-cells and OFF-cells in these rats. EOI-induced orofacial hyperalgesia could be relieved by EOI removal around postoperative day 3; this effect could be inhibited by intra-RVM microinjection of the κ-opioid receptor agonist U-69593. EOI removal around postoperative day 8 did not relieve the orofacial hyperalgesia, which could, however, be reversed by intra-RVM microinjection of the NK-1 (neurokinin-1) receptor antagonist L-733060. The activity of ON-cells and OFF-cells did not change during both the initial 3 and 6 d of EOI. When EOI was removed on postoperative day 3, OFF-cell responses decreased, contributing to the reversal of hyperalgesia. When EOI lasted for 8 d or was removed on postoperative day 8, spontaneous activity and stimulus-evoked responses of ON-cell increased, contributing to the maintained hyperalgesia. In contrast, when the EOI lasted for 14 d, OFF-cell responses decreased, possibly participating in the maintenance of hyperalgesia with persistent EOI. Our results reveal that adaptive changes in the RVM were associated with orofacial pain following EOI placement and removal.SIGNIFICANCE STATEMENT A considerable proportion of patients experience chronic orofacial pain throughout life despite the therapies given or removal of potential etiologic factors. However, current therapies lack effectiveness because of limited knowledge of the chronicity mechanisms. Using electrophysiological recording, combined with a behavioral test, we found that the prevailing descending facilitation in the rostral ventromedial medulla (RVM) participates in the maintenance of orofacial hyperalgesia following late removal of nociceptive stimuli, while the prevailing descending inhibition from the RVM may contribute to the reversal of orofacial hyperalgesia following early removal of nociceptive stimuli. Thus, variable clinical outcomes of orofacial pain may be associated with descending modulation, and an optimal window of time may exist in the management of chronic orofacial pain.
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Affiliation(s)
- Si-Yi Mo 莫思怡
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
| | - Xiao-Xiang Xu 徐啸翔
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
| | - Shan-Shan Bai 白珊珊
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
| | - Yun Liu 刘云
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
| | - Kai-Yuan Fu 傅开元
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
- Center for Temporomandibular Disorders and Orofacial Pain, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
| | - Barry J Sessle
- Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada
- Centre for the Study of Pain, University of Toronto, Toronto, Ontario M5T 1P8, Canada
| | - Ye Cao 曹烨
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
| | - Qiu-Fei Xie 谢秋菲
- Department of Prosthodontics, Center for Oral and Jaw Functional Diagnosis, Treatment and Research, School and Hospital of Stomatology, Peking University, Beijing 100081, People's Republic of China
- National Engineering Research Center for Oral Biomaterials and Digital Medical Devices, Beijing 100081, People's Republic of China
- National Clinical Research Center for Oral Diseases, Beijing 100081, People's Republic of China
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Chen Q, Heinricher MM. Shifting the Balance: How Top-Down and Bottom-Up Input Modulate Pain via the Rostral Ventromedial Medulla. FRONTIERS IN PAIN RESEARCH 2022; 3:932476. [PMID: 35836737 PMCID: PMC9274196 DOI: 10.3389/fpain.2022.932476] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 05/23/2022] [Indexed: 11/17/2022] Open
Abstract
The sensory experience of pain depends not only on the transmission of noxious information (nociception), but on the state of the body in a biological, psychological, and social milieu. A brainstem pain-modulating system with its output node in the rostral ventromedial medulla (RVM) can regulate the threshold and gain for nociceptive transmission. This review considers the current understanding of how RVM pain-modulating neurons, namely ON-cells and OFF-cells, are engaged by “top-down” cognitive and emotional factors, as well as by “bottom-up” sensory inputs, to enhance or suppress pain.
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Affiliation(s)
- Qiliang Chen
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Stanford, CA, United States
| | - Mary M. Heinricher
- Department of Neurological Surgery and Behavioral Neuroscience, Oregon Health & Science University, Portland, OR, United States
- *Correspondence: Mary M. Heinricher
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Ng SY, Ariffin MZ, Khanna S. Neurokinin receptor mechanisms in forebrain medial septum modulate nociception in the formalin model of inflammatory pain. Sci Rep 2021; 11:24358. [PMID: 34934106 PMCID: PMC8692436 DOI: 10.1038/s41598-021-03661-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 12/07/2021] [Indexed: 12/03/2022] Open
Abstract
The present study has explored the hypothesis that neurokinin1 receptors (NK1Rs) in medial septum (MS) modulate nociception evoked on hind paw injection of formalin. Indeed, the NK1Rs in MS are localized on cholinergic neurons which have been implicated in nociception. In anaesthetized rat, microinjection of L-733,060, an antagonist at NK1Rs, into MS antagonized the suppression of CA1 population spike (PS) evoked on peripheral injection of formalin or on intraseptal microinjection of substance P (SP), an agonist at NK1Rs. The CA1 PS reflects the synaptic excitability of pyramidal cells in the region. Furthermore, microinjection of L-733,060 into MS, but not LS, attenuated formalin-induced theta activation in both anaesthetized and awake rat, where theta reflects an oscillatory information processing by hippocampal neurons. The effects of L-733,060 on microinjection into MS were nociceptive selective as the antagonist did not block septo-hippocampal response to direct MS stimulation by the cholinergic receptor agonist, carbachol, in anaesthetized animal or on exploration in awake animal. Interestingly, microinjection of L-733,060 into both MS and LS attenuated formalin-induced nociceptive flinches. Collectively, the foregoing novel findings highlight that transmission at NK1R provide an affective valence to septo-hippocampal information processing and that peptidergic transmission in the septum modulates nociceptive behaviours.
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Affiliation(s)
- Si Yun Ng
- grid.4280.e0000 0001 2180 6431Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, MD9, 2 Medical Drive, Singapore, 117593 Singapore ,grid.4280.e0000 0001 2180 6431Neurobiology Programme, Life Sciences Institute, National University of Singapore, Singapore, Singapore
| | - Mohammed Zacky Ariffin
- grid.4280.e0000 0001 2180 6431Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, MD9, 2 Medical Drive, Singapore, 117593 Singapore ,grid.4280.e0000 0001 2180 6431Neurobiology Programme, Life Sciences Institute, National University of Singapore, Singapore, Singapore
| | - Sanjay Khanna
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, MD9, 2 Medical Drive, Singapore, 117593, Singapore. .,Neurobiology Programme, Life Sciences Institute, National University of Singapore, Singapore, Singapore. .,Healthy Longevity Translational Research Programme, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
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Mo SY, Bai SS, Xu XX, Liu Y, Fu KY, Sessle BJ, Cao Y, Xie QF. Astrocytes in the rostral ventromedial medulla contribute to the maintenance of oro-facial hyperalgesia induced by late removal of dental occlusal interference. J Oral Rehabil 2021; 49:207-218. [PMID: 34042200 DOI: 10.1111/joor.13211] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 04/29/2021] [Accepted: 05/18/2021] [Indexed: 11/27/2022]
Abstract
BACKGROUND Astrocytes in the rostral ventromedial medulla (RVM) contribute to descending pain modulation, but their role in oro-facial pain induced by persistent experimental dental occlusal interference (PEOI) or following EOI removal (REOI) is unknown. OBJECTIVE To explore the involvement of RVM astrocytes in PEOI-induced oro-facial hyperalgesia or its maintenance following REOI. METHODS Male rats were randomly assigned into five groups: sham-EOI, postoperative day 6 and 14 of PEOI (PEOI 6 d and PEOI 14 d), postoperative day 6 following REOI on day 3 (REOI 3 d) and postoperative day 14 following REOI on day 8 (REOI 8 d). The nociceptive head withdrawal threshold (HWT) and activities of RVM ON- or OFF-cells were recorded before and after intra-RVM astrocyte gap junction blocker carbenoxolone (CBX) microinjection. RVM astrocytes were labelled immunohistochemically with glial fibrillary acidic protein (GFAP) and analysed semi-quantitatively. RESULTS Persistent experimental dental occlusal interference-induced oro-facial hyperalgesia, as reflected in decreased HWTs, was partially inhibited by REOI at day 3 but not at day 8 after EOI placement. Increased GFAP-staining area occurred only in REOI 8 d group in which CBX could inhibit the maintained hyperalgesia; CBX was ineffective in inhibiting hyperalgesia in PEOI 14 d group. OFF-cell activities showed no change, but the spontaneous activity and responses of ON-cells were significantly enhanced that could be suppressed by CBX in REOI 8 d group. CONCLUSION Rostral ventromedial medulla astrocytes may not participate in PEOI-induced oro-facial hyperalgesia or hyperalgesia inhibition by early REOI but are involved in the maintenance of oro-facial hyperalgesia by late REOI.
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Affiliation(s)
- Si-Yi Mo
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
| | - Shan-Shan Bai
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
| | - Xiao-Xiang Xu
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
| | - Yun Liu
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
| | - Kai-Yuan Fu
- Center for TMD & Orofacial Pain, Peking University School & Hospital of Stomatology, Beijing, China
| | - Barry J Sessle
- Faculty of Dentistry, and Department of Physiology, Faculty of Medicine, and Centre for the Study of Pain, University of Toronto, Toronto, ON, Canada
| | - Ye Cao
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
| | - Qiu-Fei Xie
- Center for Oral and Jaw Functional Diagnosis, Treatment and Research, Department of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing, China
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10
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The nAChR Chaperone TMEM35a (NACHO) Contributes to the Development of Hyperalgesia in Mice. Neuroscience 2021; 457:74-87. [PMID: 33422618 PMCID: PMC7897319 DOI: 10.1016/j.neuroscience.2020.12.027] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 12/17/2020] [Accepted: 12/21/2020] [Indexed: 01/21/2023]
Abstract
Pain is a major health problem, affecting over fifty million adults in the US alone, with significant economic cost in medical care and lost productivity. Despite evidence implicating nicotinic acetylcholine receptors (nAChRs) in pathological pain, their specific contribution to pain processing in the spinal cord remains unclear given their presence in both neuronal and non-neuronal cell types. Here we investigated if loss of neuronal-specific TMEM35a (NACHO), a novel chaperone for functional expression of the homomeric α7 and assembly of the heteromeric α3, α4, and α6-containing nAChRs, modulates pain in mice. Mice with tmem35a deletion exhibited thermal hyperalgesia and mechanical allodynia. Intrathecal administration of nicotine and the α7-specific agonist, PHA543613, produced analgesic responses to noxious heat and mechanical stimuli in tmem35a KO mice, respectively, suggesting residual expression of these receptors or off-target effects. Since NACHO is expressed only in neurons, these findings indicate that neuronal α7 nAChR in the spinal cord contributes to heat nociception. To further determine the molecular basis underlying the pain phenotype, we analyzed the spinal cord transcriptome. Compared to WT control, the spinal cord of tmem35a KO mice exhibited 72 differentially-expressed genes (DEGs). These DEGs were mapped onto functional gene networks using the knowledge-based database, Ingenuity Pathway Analysis, and suggests increased neuroinflammation as a potential contributing factor for the hyperalgesia in tmem35a KO mice. Collectively, these findings implicate a heightened inflammatory response in the absence of neuronal NACHO activity. Additional studies are needed to determine the precise mechanism by which NACHO in the spinal cord modulates pain.
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Liu X, Wang G, Ai G, Xu X, Niu X, Zhang M. Selective Ablation of Descending Serotonin from the Rostral Ventromedial Medulla Unmasks Its Pro-Nociceptive Role in Chemotherapy-Induced Painful Neuropathy. J Pain Res 2020; 13:3081-3094. [PMID: 33262643 PMCID: PMC7700091 DOI: 10.2147/jpr.s275254] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Accepted: 10/22/2020] [Indexed: 12/22/2022] Open
Abstract
Purpose Chemotherapy-induced painful neuropathy (CIPN) is a severe adverse effect of many anti-neoplastic drugs that is difficult to manage. Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter in the rostral ventromedial medulla (RVM), which modulates descending spinal nociceptive transmission. However, the influence of the descending 5-HT from the RVM on CIPN is poorly understood. We investigated the role of 5-HT released from descending RVM neurons in a paclitaxel-induced CIPN rat model. Methods CIPN rat model was produced by intraperitoneally injecting of paclitaxel. Pain behavioral assessments included mechanical allodynia and heat hyperalgesia. 5-HT content was analyzed by high-performance liquid chromatography (HPLC). Western blot and immunohistochemistry were used to determine tryptophan hydroxylase (Tph) and c-Fos expression. The inhibitors p-chlorophenylalanine (PCPA) and SB203580 were administrated by stereotaxical RVM microinjection. Ondansetron was injected through intrathecal catheterization. Results The results demonstrated that Tph, the rate-limiting enzyme in 5-HT synthesis, was significantly upregulated in the RVM, and that spinal 5-HT release was increased in CIPN rats. Intra-RVM microinjection of Tph inhibitor PCPA significantly attenuated mechanical and thermal pain behavior through Tph downregulation and decreased spinal 5-HT. Intra-RVM administration of p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580 alleviated paclitaxel-induced pain in a similar manner to PCPA. Intrathecal injection of ondansetron, a 5-HT3 receptor antagonist, partially reversed paclitaxel-induced pain, indicating that 5-HT3 receptors were involved in descending serotoninergic modulation of spinal pain processing. Conclusion The results suggest that activation of the p38 MAPK pathway in the RVM leads to increased RVM Tph expression and descending serotoninergic projection to the spinal dorsal horn and contributes to the persistence of CIPN via spinal 5-HT3 receptors.
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Affiliation(s)
- Xijiang Liu
- Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
| | - Gongming Wang
- Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
| | - Geyi Ai
- Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
| | - Xiqiang Xu
- Department of Orthopedics, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
| | - Xinhuan Niu
- Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
| | - Mengyuan Zhang
- Department of Anesthesiology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, People's Republic of China
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Immediate inhibition of spinal secretory phospholipase A2 prevents the pain and elevated spinal neuronal hyperexcitability and neuroimmune regulatory genes that develop with nerve root compression. Neuroreport 2020; 31:1084-1089. [PMID: 32881777 DOI: 10.1097/wnr.0000000000001520] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cervical nerve root injury induces a host of inflammatory mediators in the spinal cord that initiate and maintain neuronal hyperexcitability and pain. Secretory phospholipase A2 (sPLA2) is an enzyme that has been implicated as a mediator of pain onset and maintenance in inflammation and neural injury. Although sPLA2 modulates nociception and excitatory neuronal signaling in vitro, its effects on neuronal activity and central sensitization early after painful nerve root injury are unknown. This study investigated whether inhibiting spinal sPLA2 at the time of nerve root compression (NRC) modulates the pain, dorsal horn hyperexcitability, and spinal genes involved in glutamate signaling, nociception, and inflammation that are seen early after injury. Rats underwent a painful C7 NRC injury with immediate intrathecal administration of the sPLA2 inhibitor thioetheramide-phosphorlycholine. Additional groups underwent either injury alone or sham surgery. One day after injury, behavioral sensitivity, spinal neuronal excitability, and spinal cord gene expression for glutamate receptors (mGluR5 and NR1) and transporters (GLT1 and EAAC1), the neuropeptide substance P, and pro-inflammatory cytokines (TNFα, IL1α, and IL1β) were assessed. Treatment with the sPLA2 inhibitor prevented mechanical allodynia, attenuated neuronal hyperexcitability in the spinal dorsal horn, restored the proportion of spinal neurons classified as wide dynamic range, and reduced genes for mGluR5, substance P, IL1α, and IL1β to sham levels. These findings indicate spinal regulation of central sensitization after painful neuropathy and suggest that spinal sPLA2 is implicated in those early spinal mechanisms of neuronal excitability, perhaps via glutamate signaling, neurotransmitters, or inflammatory cascades.
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Evaluation of the Antinociceptive Effect of Maropitant, a Neurokinin-1 Receptor Antagonist, in Cats Undergoing Ovariohysterectomy. Vet Med Int 2019; 2019:9352528. [PMID: 31093325 PMCID: PMC6476118 DOI: 10.1155/2019/9352528] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Revised: 01/24/2019] [Accepted: 02/20/2019] [Indexed: 12/14/2022] Open
Abstract
Maropitant is a neurokinin-1 (NK1) receptor antagonist that can be used for pain management. The objective of this study was to evaluate the effect of continuous infusion of two doses of maropitant on cardiorespiratory parameters and its postoperative analgesic effect in cats undergoing ovariohysterectomy. Thirty cats were randomly assigned to one of three groups (10 cats each group): the control group (CG) received a continuous infusion of 10 ml/kg/h Ringer's lactate; GM30 and GM100 first received an intravenous (IV) bolus of 1 mg/kg maropitant; GM30 then received continuous infusion of 30 μg/kg/h maropitant; and GM100 then received continuous infusion of 100 μg/kg/h maropitant. The maropitant was diluted into Ringer's lactate and the GM30 and GM100 also received fluids intraoperatively. In all groups, premedication included intramuscular injections of morphine and acepromazine, followed by induction with propofol and maintenance with isoflurane. Temperature, heart rate (HR), Doppler blood pressure (DBP), respiratory rate, oxygen saturation, and measuring the end-tidal carbon dioxide and isoflurane were monitored. Postoperative pain was evaluated using a visual analog scale and the UNESP-Botucatu multidimensional composite pain scale in cats; morphine was used for analgesic rescue. During the surgical procedure, cats in GM100 demonstrated lower HR and DBP than those in CG. With regard to the evaluation of postoperative pain, GM100 required the least frequent morphine rescue and less rescue analgesia compared with CG. In conclusion, cats in GM100 maintained lower DBP and HR and required lower analgesic rescue during the postoperative period. The results suggested that animals receiving maropitant bolus (1 mg/kg) plus (100 μg/kg/h) experienced greater postoperative comfort, reflected by the lesser need for analgesic rescue. The use of maropitant in surgical procedures in cats contributes to postoperative comfort.
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Abstract
PURPOSE OF REVIEW The goal of the review was to highlight recent advances in our understanding of descending pain-modulating systems and how these contribute to persistent pain states, with an emphasis on the current state of knowledge around "bottom-up" (sensory) and "top-down" (higher structures mediating cognitive and emotional processing) influences on pain-modulating circuits. RECENT FINDINGS The connectivity, physiology, and function of these systems have been characterized extensively over the last 30 years. The field is now beginning to ask how and when these systems are engaged to modulate pain. A recent focus is on the parabrachial complex, now recognized as the major relay of nociceptive information to pain-modulating circuits, and plasticity in this circuit and its connections to the RVM is marked in persistent inflammatory pain. Top-down influences from higher structures, including hypothalamus, amygdala, and medial prefrontal areas, are also considered. The challenge will be to tease out mechanisms through which a particular behavioral context engages distinct circuits to enhance or suppress pain, and to understand how these mechanisms contribute to chronic pain.
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Abstract
Substance P (SP) is a highly conserved member of the tachykinin peptide family that is widely expressed throughout the animal kingdom. The numerous members of the tachykinin peptide family are involved in a multitude of neuronal signaling pathways, mediating sensations and emotional responses (Steinhoff et al. in Physiol Rev 94:265–301, 2014). In contrast to receptors for classical transmitters, such as glutamate (Parsons et al. in Handb Exp Pharmacol 249–303, 2005), only a minority of neurons in certain brain areas express neurokinin receptors (NKRs) (Mantyh in J Clin Psychiatry 63:6–10, 2002). SP is also expressed by a variety of non-neuronal cell types such as microglia, as well as immune cells (Mashaghi et al. in Cell Mol Life Sci 73:4249–4264, 2016). SP is an 11-amino acid neuropeptide that preferentially activates the neurokinin-1 receptor (NK1R). It transmits nociceptive signals via primary afferent fibers to spinal and brainstem second-order neurons (Cao et al. in Nature 392:390–394, 1998). Compounds that inhibit SP’s action are being investigated as potential drugs to relieve pain. More recently, SP and NKR have gained attention for their role in complex psychiatric processes. It is a key goal in the field of pain research to understand mechanisms involved in the transition between acute pain and chronic pain. The influence of emotional and cognitive inputs and feedbacks from different brain areas makes pain not only a perception but an experience (Zieglgänsberger et al. in CNS Spectr 10:298–308, 2005; Trenkwaldner et al. Sleep Med 31:78–85, 2017). This review focuses on functional neuronal plasticity in spinal dorsal horn neurons as a major relay for nociceptive information.
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Forebrain medial septum sustains experimental neuropathic pain. Sci Rep 2018; 8:11892. [PMID: 30089875 PMCID: PMC6082830 DOI: 10.1038/s41598-018-30177-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 07/25/2018] [Indexed: 12/14/2022] Open
Abstract
The present study explored the role of the medial septal region (MS) in experimental neuropathic pain. For the first time, we found that the MS sustains nociceptive behaviors in rodent models of neuropathic pain, especially in the chronic constriction injury (CCI) model and the paclitaxel model of chemotherapy-induced neuropathic pain. For example, inactivation of the MS with intraseptal muscimol (2 μg/μl, 0.5 μl), a GABA mimetic, reversed peripheral hypersensitivity (PH) in the CCI model and induced place preference in a conditioned place preference task, a surrogate measure of spontaneous nociception. The effect of intraseptal muscimol on PH was comparable to that seen with microinjection of the local anesthetic, lidocaine, into rostral ventromedial medulla which is implicated in facilitating experimental chronic nociception. Cellular analysis in the CCI model showed that the MS region sustains nociceptive gain with CCI by facilitating basal nociceptive processing and the amplification of stimulus-evoked neural processing. Indeed, consistent with the idea that excitatory transmission through MS facilitates chronic experimental pain, intraseptal microinjection of antagonists acting at AMPA and NMDA glutamate receptors attenuated CCI-induced PH. We propose that the MS is a central monitor of bodily nociception which sustains molecular plasticity triggered by persistent noxious insult.
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Ved N, Da Vitoria Lobo ME, Bestall SM, L Vidueira C, Beazley-Long N, Ballmer-Hofer K, Hirashima M, Bates DO, Donaldson LF, Hulse RP. Diabetes-induced microvascular complications at the level of the spinal cord: a contributing factor in diabetic neuropathic pain. J Physiol 2018; 596:3675-3693. [PMID: 29774557 PMCID: PMC6092307 DOI: 10.1113/jp275067] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 05/08/2018] [Indexed: 02/06/2023] Open
Abstract
KEY POINTS Diabetes is thought to induce neuropathic pain through activation of dorsal horn sensory neurons in the spinal cord. Here we explore the impact of hyperglycaemia on the blood supply supporting the spinal cord and chronic pain development. In streptozotocin-induced diabetic rats, neuropathic pain is accompanied by a decline in microvascular integrity in the dorsal horn. Hyperglycaemia-induced degeneration of the endothelium in the dorsal horn was associated with a loss in vascular endothelial growth factor (VEGF)-A165 b expression. VEGF-A165 b treatment prevented diabetic neuropathic pain and degeneration of the endothelium in the spinal cord. Using an endothelial-specific VEGFR2 knockout transgenic mouse model, the loss of endothelial VEGFR2 signalling led to a decline in vascular integrity in the dorsal horn and the development of hyperalgesia in VEGFR2 knockout mice. This highlights that vascular degeneration in the spinal cord could be a previously unidentified factor in the development of diabetic neuropathic pain. ABSTRACT Abnormalities of neurovascular interactions within the CNS of diabetic patients is associated with the onset of many neurological disease states. However, to date, the link between the neurovascular network within the spinal cord and regulation of nociception has not been investigated despite neuropathic pain being common in diabetes. We hypothesised that hyperglycaemia-induced endothelial degeneration in the spinal cord, due to suppression of vascular endothelial growth factor (VEGF)-A/VEGFR2 signalling, induces diabetic neuropathic pain. Nociceptive pain behaviour was investigated in a chemically induced model of type 1 diabetes (streptozotocin induced, insulin supplemented; either vehicle or VEGF-A165 b treated) and an inducible endothelial knockdown of VEGFR2 (tamoxifen induced). Diabetic animals developed mechanical allodynia and heat hyperalgesia. This was associated with a reduction in the number of blood vessels and reduction in Evans blue extravasation in the lumbar spinal cord of diabetic animals versus age-matched controls. Endothelial markers occludin, CD31 and VE-cadherin were downregulated in the spinal cord of the diabetic group versus controls, and there was a concurrent reduction of VEGF-A165 b expression. In diabetic animals, VEGF-A165 b treatment (biweekly i.p., 20 ng g-1 ) restored normal Evans blue extravasation and prevented vascular degeneration, diabetes-induced central neuron activation and neuropathic pain. Inducible knockdown of VEGFR2 (tamoxifen treated Tie2CreERT2 -vegfr2flfl mice) led to a reduction in blood vessel network volume in the lumbar spinal cord and development of heat hyperalgesia. These findings indicate that hyperglycaemia leads to a reduction in the VEGF-A/VEGFR2 signalling cascade, resulting in endothelial dysfunction in the spinal cord, which could be an undiscovered contributing factor to diabetic neuropathic pain.
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Affiliation(s)
- N Ved
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine University of Nottingham, Nottingham, NG7 2UH, UK.,Institute of Ophthalmology, 11-43 Bath St, London, EC1V 9EL, UK.,Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - M E Da Vitoria Lobo
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine University of Nottingham, Nottingham, NG7 2UH, UK
| | - S M Bestall
- Arthritis Research UK Pain Centre and School of Life Sciences, The Medical School QMC, University of Nottingham, Nottingham, NG7 2UH, UK
| | - C L Vidueira
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine University of Nottingham, Nottingham, NG7 2UH, UK
| | - N Beazley-Long
- Arthritis Research UK Pain Centre and School of Life Sciences, The Medical School QMC, University of Nottingham, Nottingham, NG7 2UH, UK
| | | | - M Hirashima
- Division of Vascular Biology, Kobe University, Japan
| | - D O Bates
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine University of Nottingham, Nottingham, NG7 2UH, UK.,Centre of Membrane and Protein and Receptors (COMPARE), University of Birmingham, Birmingham and University of Nottingham, Nottingham, UK
| | - L F Donaldson
- Institute of Ophthalmology, 11-43 Bath St, London, EC1V 9EL, UK
| | - R P Hulse
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine University of Nottingham, Nottingham, NG7 2UH, UK.,School of Science and Technology, Nottingham Trent University, Nottingham, NG11 8NS, UK
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