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Deng L, Chen Y, Wang Z, Zeng N, Zhang Q, Zhou T, Chen Y, Wu S. Analysis of the influencing factors related to neuropathic pain in patients with spinal cord injuries: a retrospective study. Br J Neurosurg 2023; 37:1588-1593. [PMID: 35200073 DOI: 10.1080/02688697.2022.2043242] [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: 10/08/2021] [Accepted: 02/12/2022] [Indexed: 11/02/2022]
Abstract
BACKGROUND The aim of this study was to investigate the related influencing factors of neuropathic pain (NP) in patients with spinal cord injury (SCI). METHODS Patients diagnosed with SCI between January 2016 and December 2019 in the Department of Rehabilitation Medicine, Affiliated Hospital of Guizhou Medical University, were screened for NP by using the Douleur Neuropathique 4 (DN4) questionnaire. A total of 133 patients diagnosed with SCI with NP were finally included in the study. We collected the patients' basic information, including gender, age, body mass index (BMI), disease course, injury segment, American Spinal Injury Association (ASIA) grade, occupation, educational level, whether painkillers were used, stability of economic support, and pain level. Univariate and multiple ordered logistic regression analyses were used to examine the influencing factors of NP in the patients with SCI. RESULTS The chi-square test revealed that disease course, injury level, severity of SCI (ASIA classification), stable economic support during hospitalization, and the use of painkillers had statistical significance (p < .01). A multivariate logistic regression analysis was performed to analyze the influencing factors of NP. ASIA grade, stable economic support, and use of painkillers were independent influencing factors of NP in patients with SCI, among which injury severity was the independent risk factor (odds ratio [OR] > 1). Stable economic support and painkiller use were protective factors (OR < 1). CONCLUSIONS In this study, we found no significant correlation between NP after SCI and sex, age, BMI, disease course, injury level, and occupation. However, the injury severity was an independent risk factor, and stable economic support and painkiller use were protective factors.
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Affiliation(s)
- Luoyi Deng
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Yuan Chen
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Zhitao Wang
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Ni Zeng
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Qian Zhang
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Tengfei Zhou
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
| | - Yan Chen
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
- School of Clinical Medicine, Guizhou Medical University Guiyang, Guiyang, PR China
| | - Shuang Wu
- Department of Rehabilitation Medicine, The Affiliated Hospital of Guizhou Medical University, Guiyang, PR China
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Kim DH, Sim KB. A Novel Acute Discogenic Myelopathy Model Using Merocel ® Sponge: Comparison With Clip Compression Model in Rats. Korean J Neurotrauma 2023; 19:204-217. [PMID: 37431382 PMCID: PMC10329878 DOI: 10.13004/kjnt.2023.19.e28] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2023] [Revised: 06/02/2023] [Accepted: 06/08/2023] [Indexed: 07/12/2023] Open
Abstract
Objective Animal models of spinal cord injuries (SCIs) use rats to simulate human SCIs. Among the various techniques, clips have been used to reproduce the compression-contusion model. However, the mechanism of injury in discogenic incomplete SCI may differ from that in clip injury; however, a model has yet to be established. Previously, we issued a patent (No. 10-2053770) for a rat SCI model using Merocel®, a water-absorbing self-expanding polymer sponge. The objectives of this study were to compare the locomotor and histopathological changes between the Merocel®-compression model (MC group) and clip compression model (clip group). Methods This study included 4 groups of rats: MC (n=30), MC-sham (n=5), clip (n=30), and clip-sham (n=5). Locomotor function was evaluated in all groups using the Basso, Beattie, and Bresnahan (BBB) scoring system, 4 weeks after injury. Histopathological analyses included morphology, presence of inflammatory cells, microglial activation, and extent of neuronal damage, which were compared among the groups. Results The BBB scores in the MC group were significantly higher than those in the clip group throughout the 4 weeks (p<0.01). Neuropathological changes in the MC group were significantly less severe than those in the clip group. In addition, motor neurons were well preserved in the ventral horn of the MC group but poorly preserved in the ventral horn of the clip group. Conclusion The novel MC group can help elucidate the pathophysiology of acute discogenic incomplete SCIs and may be applied in various SCI therapeutic strategies.
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Affiliation(s)
- Do-Hyung Kim
- Department of Neurosurgery, Seoul National University Hospital, Seoul, Korea
| | - Ki-Bum Sim
- Department of Neurosurgery, College of Medicine, Jeju National University, Jeju, Korea
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Scrambler Therapy for Chronic Pain after Burns and Its Effect on the Cerebral Pain Network: A Prospective, Double-Blinded, Randomized Controlled Trial. J Clin Med 2022; 11:jcm11154255. [PMID: 35893347 PMCID: PMC9332864 DOI: 10.3390/jcm11154255] [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: 05/09/2022] [Revised: 07/16/2022] [Accepted: 07/19/2022] [Indexed: 02/05/2023] Open
Abstract
Chronic pain is common after burn injuries, and post-burn neuropathic pain is the most important complication that is difficult to treat. Scrambler therapy (ST) is a non-invasive modality that uses patient-specific electrocutaneous nerve stimulation and is an effective treatment for many chronic pain disorders. This study used magnetic resonance imaging (MRI) to evaluate the pain network-related mechanisms that underlie the clinical effect of ST in patients with chronic burn-related pain. This prospective, double-blinded, randomized controlled trial (ClinicalTrials.gov: NCT03865693) enrolled 43 patients who were experiencing chronic neuropathic pain after unilateral burn injuries. The patients had moderate or greater chronic pain (a visual analogue scale (VAS) score of ≥5), despite treatment using gabapentin and other physical modalities, and were randomized 1:1 to receive real or sham ST sessions. The ST was performed using the MC5-A Calmare device for ten 45 min sessions (Monday to Friday for 2 weeks). Baseline and post-treatment parameters were evaluated subjectively using the VAS score for pain and the Hamilton Depression Rating Scale; MRI was performed to identify objective central nervous system changes by measuring the cerebral blood volume (CBV). After 10 ST sessions (two weeks), the treatment group exhibited a significant reduction in pain relative to the sham group. Furthermore, relative to the pre-ST findings, the post-ST MRI evaluations revealed significantly decreased CBV in the orbito-frontal gyrus, middle frontal gyrus, superior frontal gyrus, and gyrus rectus. In addition, the CBV was increased in the precentral gyrus and postcentral gyrus of the hemisphere associated with the burned limb in the ST group, as compared with the CBV of the sham group. Thus, a clinical effect from ST on burn pain was observed after 2 weeks, and a potential mechanism for the treatment effect was identified. These findings suggest that ST may be an alternative strategy for managing chronic pain in burn patients.
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Fauss GNK, Hudson KE, Grau JW. Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia. BIOLOGY 2022; 11:234. [PMID: 35205100 PMCID: PMC8869318 DOI: 10.3390/biology11020234] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/27/2022] [Accepted: 01/29/2022] [Indexed: 12/12/2022]
Abstract
As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.
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Affiliation(s)
| | | | - James W. Grau
- Department of Psychological and Brain Sciences, Texas A&M University, College Station, TX 77843, USA; (G.N.K.F.); (K.E.H.)
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Regional Hyperexcitability and Chronic Neuropathic Pain Following Spinal Cord Injury. Cell Mol Neurobiol 2020; 40:861-878. [PMID: 31955281 DOI: 10.1007/s10571-020-00785-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Accepted: 01/02/2020] [Indexed: 12/15/2022]
Abstract
Spinal cord injury (SCI) causes maladaptive changes to nociceptive synaptic circuits within the injured spinal cord. Changes also occur at remote regions including the brain stem, limbic system, cortex, and dorsal root ganglia. These maladaptive nociceptive synaptic circuits frequently cause neuronal hyperexcitability in the entire nervous system and enhance nociceptive transmission, resulting in chronic central neuropathic pain following SCI. The underlying mechanism of chronic neuropathic pain depends on the neuroanatomical structures and electrochemical communication between pre- and postsynaptic neuronal membranes, and propagation of synaptic transmission in the ascending pain pathways. In the nervous system, neurons are the only cell type that transmits nociceptive signals from peripheral receptors to supraspinal systems due to their neuroanatomical and electrophysiological properties. However, the entire range of nociceptive signaling is not mediated by any single neuron. Current literature describes regional studies of electrophysiological or neurochemical mechanisms for enhanced nociceptive transmission post-SCI, but few studies report the electrophysiological, neurochemical, and neuroanatomical changes across the entire nervous system following a regional SCI. We, along with others, have continuously described the enhanced nociceptive transmission in the spinal dorsal horn, brain stem, thalamus, and cortex in SCI-induced chronic central neuropathic pain condition, respectively. Thus, this review summarizes the current understanding of SCI-induced neuronal hyperexcitability and maladaptive nociceptive transmission in the entire nervous system that contributes to chronic central neuropathic pain.
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Central Plasticity of Cutaneous Afferents Is Associated with Nociceptive Hyperreflexia after Spinal Cord Injury in Rats. Neural Plast 2019; 2019:6147878. [PMID: 31827498 PMCID: PMC6885787 DOI: 10.1155/2019/6147878] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 05/30/2019] [Accepted: 09/05/2019] [Indexed: 11/18/2022] Open
Abstract
Electrical stimulations of dorsal cutaneous nerves (DCNs) at each lumbothoracic spinal level produce the bilateral cutaneus trunci muscle (CTM) reflex responses which consist of two temporal components: an early and late responses purportedly mediated by Aδ and C fibers, respectively. We have previously reported central projections of DCN A and C fibers and demonstrated that different projection patterns of those afferent types contributed to the somatotopic organization of CTM reflex responses. Unilateral hemisection spinal cord injury (SCI) was made at T10 spinal segments to investigate the plasticity of early and late CTM responses 6 weeks after injury. Both early and late responses were drastically increased in response to both ipsi- and contralateral DCN stimulations both above (T6 and T8) and below (T12 and L1) the levels of injury demonstrating that nociceptive hyperreflexia developed at 6 weeks following hemisection SCI. We also found that DCN A and C fibers centrally sprouted, expanded their projection areas, and increased synaptic terminations in both T7 and T13, which correlated with the size of hemisection injury. These data demonstrate that central sprouting of cutaneous afferents away from the site of injury is closely associated with enhanced responses of intraspinal signal processing potentially contributing to nociceptive hyperreflexia following SCI.
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Spinal Cord Stimulation for Pain Treatment After Spinal Cord Injury. Neurosci Bull 2018; 35:527-539. [PMID: 30560438 DOI: 10.1007/s12264-018-0320-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 08/11/2018] [Indexed: 12/30/2022] Open
Abstract
In addition to restoration of bladder, bowel, and motor functions, alleviating the accompanying debilitating pain is equally important for improving the quality of life of patients with spinal cord injury (SCI). Currently, however, the treatment of chronic pain after SCI remains a largely unmet need. Electrical spinal cord stimulation (SCS) has been used to manage a variety of chronic pain conditions that are refractory to pharmacotherapy. Yet, its efficacy, benefit profiles, and mechanisms of action in SCI pain remain elusive, due to limited research, methodological weaknesses in previous clinical studies, and a lack of mechanistic exploration of SCS for SCI pain control. We aim to review recent studies and outline the therapeutic potential of different SCS paradigms for traumatic SCI pain. We begin with an overview of its manifestations, classification, potential underlying etiology, and current challenges for its treatment. The clinical evidence for using SCS in SCI pain is then reviewed. Finally, future perspectives of pre-clinical research and clinical study of SCS for SCI pain treatment are discussed.
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Gu Y, Qiu Z, Cheng N, Chen C, Hei Z, Li X. Identification of potential mechanism and hub genes for neuropathic pain by expression-based genome-wide association study. J Cell Biochem 2018; 120:4912-4923. [PMID: 30269359 DOI: 10.1002/jcb.27766] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 09/06/2018] [Indexed: 01/07/2023]
Abstract
Neuropathic pain (NP) is a common pathological pain state with limited effective treatments. This study was designed to identify potential mechanisms and candidate genes using gene expression-based genome-wide association study (eGWAS). All NP-related microarray experiments were obtained from Gene Expression Omnibus and ArrayExpress. Significantly dysregulated genes were identified between experimental and untreated groups, and the number of microarray experiments in which each gene was dysregulated was calculated. Significantly dysregulated genes were ranked according to P values of the chi-square test. Using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes database, we performed functional and pathway enrichment analysis. Protein-protein interaction (PPI) network and module analysis was performed using Cytoscape software. A total of 115 candidate genes were identified from 19 independent microarray experiments by eGWAS based on the Bonferroni threshold ( P < 2.97 × 10 -6 ). Immune and inflammatory responses, and complement and coagulation cascades, were respectively the most enriched biological process and pathways for candidate genes. The hub genes with highest connectivity in PPI network and two modules Ccl2 and Jun, and Ctss application of the eGWAS methodology can identify mechanisms and candidate genes associated with NP. Our results support the validity and prevalence of inflammatory and immune mechanisms across different NP models, and Ccl2, Jun, and Ctss may be the hub genes for NP.
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Affiliation(s)
- Yu Gu
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Zhuolin Qiu
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Nan Cheng
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Chaojin Chen
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Ziqing Hei
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
| | - Xiang Li
- Department of Anesthesiology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China
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Sidorova YA, Bespalov MM, Wong AW, Kambur O, Jokinen V, Lilius TO, Suleymanova I, Karelson G, Rauhala PV, Karelson M, Osborne PB, Keast JR, Kalso EA, Saarma M. A Novel Small Molecule GDNF Receptor RET Agonist, BT13, Promotes Neurite Growth from Sensory Neurons in Vitro and Attenuates Experimental Neuropathy in the Rat. Front Pharmacol 2017; 8:365. [PMID: 28680400 PMCID: PMC5478727 DOI: 10.3389/fphar.2017.00365] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2017] [Accepted: 05/26/2017] [Indexed: 12/25/2022] Open
Abstract
Neuropathic pain caused by nerve damage is a common and severe class of chronic pain. Disease-modifying clinical therapies are needed as current treatments typically provide only symptomatic relief; show varying clinical efficacy; and most have significant adverse effects. One approach is targeting either neurotrophic factors or their receptors that normalize sensory neuron function and stimulate regeneration after nerve damage. Two candidate targets are glial cell line-derived neurotrophic factor (GDNF) and artemin (ARTN), as these GDNF family ligands (GFLs) show efficacy in animal models of neuropathic pain (Boucher et al., 2000; Gardell et al., 2003; Wang et al., 2008, 2014). As these protein ligands have poor drug-like properties and are expensive to produce for clinical use, we screened 18,400 drug-like compounds to develop small molecules that act similarly to GFLs (GDNF mimetics). This screening identified BT13 as a compound that selectively targeted GFL receptor RET to activate downstream signaling cascades. BT13 was similar to NGF and ARTN in selectively promoting neurite outgrowth from the peptidergic class of adult sensory neurons in culture, but was opposite to ARTN in causing neurite elongation without affecting initiation. When administered after spinal nerve ligation in a rat model of neuropathic pain, 20 and 25 mg/kg of BT13 decreased mechanical hypersensitivity and normalized expression of sensory neuron markers in dorsal root ganglia. In control rats, BT13 had no effect on baseline mechanical or thermal sensitivity, motor coordination, or weight gain. Thus, small molecule BT13 selectively activates RET and offers opportunities for developing novel disease-modifying medications to treat neuropathic pain.
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Affiliation(s)
- Yulia A Sidorova
- Laboratory of Molecular Neuroscience, Institute of Biotechnology, University of HelsinkiHelsinki, Finland
| | - Maxim M Bespalov
- Laboratory of Molecular Neuroscience, Institute of Biotechnology, University of HelsinkiHelsinki, Finland
| | - Agnes W Wong
- Department of Anatomy and Neuroscience, The University of MelbourneMelbourne, VIC, Australia
| | - Oleg Kambur
- Department of Pharmacology, Faculty of Medicine, University of HelsinkiHelsinki, Finland
| | - Viljami Jokinen
- Department of Pharmacology, Faculty of Medicine, University of HelsinkiHelsinki, Finland
| | - Tuomas O Lilius
- Department of Pharmacology, Faculty of Medicine, University of HelsinkiHelsinki, Finland
| | - Ilida Suleymanova
- Laboratory of Molecular Neuroscience, Institute of Biotechnology, University of HelsinkiHelsinki, Finland
| | | | - Pekka V Rauhala
- Department of Pharmacology, Faculty of Medicine, University of HelsinkiHelsinki, Finland
| | - Mati Karelson
- Department of Molecular Technology, Institute of Chemistry, University of TartuTartu, Estonia
| | - Peregrine B Osborne
- Department of Anatomy and Neuroscience, The University of MelbourneMelbourne, VIC, Australia
| | - Janet R Keast
- Department of Anatomy and Neuroscience, The University of MelbourneMelbourne, VIC, Australia
| | - Eija A Kalso
- Department of Pharmacology, Faculty of Medicine, University of HelsinkiHelsinki, Finland.,Pain Clinic, Department of Anesthesiology, Intensive Care and Pain Medicine, University of Helsinki and Helsinki University HospitalHelsinki, Finland
| | - Mart Saarma
- Laboratory of Molecular Neuroscience, Institute of Biotechnology, University of HelsinkiHelsinki, Finland
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Shu B, Yang F, Guan Y. Intra-spinal microstimulation may alleviate chronic pain after spinal cord injury. Med Hypotheses 2017; 104:73-77. [PMID: 28673596 DOI: 10.1016/j.mehy.2017.05.028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2016] [Accepted: 05/25/2017] [Indexed: 12/30/2022]
Abstract
Chronic pain after spinal cord injury (SCI) is a form of central neuropathic pain that is debilitating and often refractory to current pharmacological treatments. Neurostimulation pain therapies, such as epidural spinal cord stimulation, have only moderate success in reducing SCI pain. The pathogenesis of SCI pain may involve a state of central neuronal hyperexcitability, especially in the spinal cord dorsal horn, that develops after injury. We hypothesize that the neuronal structures near the spinal cord injury site may be an important pain generator, and intraspinal microstimulation (ISMS) may normalize dorsal horn neuronal hyperexcitability and hence alleviate SCI pain. Specifically, ISMS may induce frequency-dependent conduction block on axons of afferent sensory neurons, in the spinothalamic tract and Lissauer's tract. ISMS may also facilitate primary afferent depolarization that elicits presynaptic inhibition of incoming afferent inputs. Together, these actions will reduce abnormal afferent inputs and ascending pain signals before they can reach the brain. Furthermore, ISMS may directly induce inhibitory postsynaptic potentials in dorsal horn neurons, and trigger the release of endogenous inhibitory neurotransmitters, opioids and serotonin to inhibit postsynaptic neurons and restore the compromised segmental pain inhibition after SCI. Finally, ISMS may alter the frequency and pattern of discharge such that the rostrally conducted impulses no longer code pain or activate brain areas concerned with pain signaling. Based on recent progress in understanding spinal learning and plasticity, we also postulate that repetitive or long-term ISMS may help the dorsal horn "reset" neuronal excitability and regain normal pain processing for a prolonged period. By finely tuning the stimulation parameters (e.g., intensity, pulse width, frequency), position, and geometry of ISMS electrode, multiple spinal structures (e.g., dorsal horn, dorsal column, spinothalamic tract) may be modulated to induce synergistic pain inhibition. Our hypothesis can be readily tested in preclinical models of SCI pain by using a combination of in vivo electrophysiological (neuronal activity) and animal behavioral (pain response) approaches. Since ISMS electrodes stimulate the spinal structures directly, we expect that the effective stimulus intensity and energy consumption can be lower than that for epidural spinal cord stimulation. The proposed hypothesis may provide insights and rationales for developing a novel neurostimulation pain therapy by directly inhibiting the pain generators in the spinal cord, and ISMS may be an alternative strategy to treat SCI pain.
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Affiliation(s)
- Bin Shu
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA; Department of Anesthesiology and Pain Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
| | - Fei Yang
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA
| | - Yun Guan
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, Baltimore, MD 21205, USA.
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Kramer JLK, Minhas NK, Jutzeler CR, Erskine ELKS, Liu LJW, Ramer MS. Neuropathic pain following traumatic spinal cord injury: Models, measurement, and mechanisms. J Neurosci Res 2016; 95:1295-1306. [PMID: 27617844 DOI: 10.1002/jnr.23881] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 07/19/2016] [Accepted: 07/19/2016] [Indexed: 02/06/2023]
Abstract
Neuropathic pain following spinal cord injury (SCI) is notoriously difficult to treat and is a high priority for many in the SCI population. Resolving this issue requires animal models fidelic to the clinical situation in terms of injury mechanism and pain phenotype. This Review discusses the means by which neuropathic pain has been induced and measured in experimental SCI and compares these with human outcomes, showing that there is a substantial disconnection between experimental investigations and clinical findings in a number of features. Clinical injury level is predominantly cervical, whereas injury in the laboratory is modeled mainly at the thoracic cord. Neuropathic pain is primarily spontaneous or tonic in people with SCI (with a relatively smaller incidence of allodynia), but measures of evoked responses (to thermal and mechanical stimuli) are almost exclusively used in animals. There is even the question of whether pain per se has been under investigation in most experimental SCI studies rather than simply enhanced reflex activity with no affective component. This Review also summarizes some of the problems related to clinical assessment of neuropathic pain and how advanced imaging techniques may circumvent a lack of patient/clinician objectivity and discusses possible etiologies of neuropathic pain following SCI based on evidence from both clinical studies and animal models, with examples of cellular and molecular changes drawn from the entire neuraxis from primary afferent terminals to cortical sensory and affective centers. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- John L K Kramer
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Nikita K Minhas
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Catherine R Jutzeler
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Erin L K S Erskine
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Lisa J W Liu
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Matt S Ramer
- International Collaboration on Repair Discoveries, The University of British Columbia, Vancouver, British Columbia, Canada
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Merighi A. Targeting the glial-derived neurotrophic factor and related molecules for controlling normal and pathologic pain. Expert Opin Ther Targets 2015; 20:193-208. [PMID: 26863504 DOI: 10.1517/14728222.2016.1085972] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
INTRODUCTION Glial-derived neurotrophic factor (GDNF) and its family of ligands (GFLs) have several functions in the nervous system. As a survival factor for dopaminergic neurons, GDNF was used in clinical trials for Parkinson's disease. GFLs and their receptors are also potential targets for new pain-controlling drugs. Although molecules with analgesic activities in rodents mostly failed to be effective in translational studies, this potential should not be underestimated. AREAS COVERED The circuitry, molecular, and cellular mechanisms by which GFLs control nociception and their intervention in inflammatory and neuropathic pain are considered first. The problems related to effective GDNF delivery to the brain and the possibility to target the GFL receptor complex rather than its ligands are then discussed, also considering the use of non-peptidyl agonists. EXPERT OPINION In nociceptive pathways, an ideal drug should either: i) target the release of endogenous GFLs from large dense-cored vesicles (LGVs) by acting, for example, onto the phosphatidylinositol-3-phosphate [PtdIns(3)P] pool, which is sensitive to Ca(2+) modulation, or ii) target the GFL receptor complex. Besides XIB403, a tiol molecule that enhances GFRα family receptor signaling, existing drugs such as retinoic acid and amitriptyline should be considered for effective targeting of GDNF, at least in neuropathic pain. The approach of pain modeling in experimental animals is discussed.
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Affiliation(s)
- Adalberto Merighi
- a University of Turin, Department of Veterinary Sciences , Grugliasco, TO, Italy ;
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PI3K mediated activation of GSK-3β reduces at-level primary afferent growth responses associated with excitotoxic spinal cord injury dysesthesias. Mol Pain 2015; 11:35. [PMID: 26093674 PMCID: PMC4475622 DOI: 10.1186/s12990-015-0041-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Accepted: 06/11/2015] [Indexed: 02/08/2023] Open
Abstract
Background Neuropathic pain and sensory abnormalities are a debilitating secondary consequence of spinal cord injury (SCI). Maladaptive structural plasticity is gaining recognition for its role in contributing to the development of post SCI pain syndromes. We previously demonstrated that excitotoxic induced SCI dysesthesias are associated with enhanced dorsal root ganglia (DRG) neuronal outgrowth. Although glycogen synthase kinase-3β (GSK-3β) is a known intracellular regulator neuronal growth, the potential contribution to primary afferent growth responses following SCI are undefined. We hypothesized that SCI triggers inhibition of GSK-3β signaling resulting in enhanced DRG growth responses, and that PI3K mediated activation of GSK-3β can prevent this growth and the development of at-level pain syndromes. Results Excitotoxic SCI using intraspinal quisqualic acid (QUIS) resulted in inhibition of GSK-3β in the superficial spinal cord dorsal horn and adjacent DRG. Double immunofluorescent staining showed that GSK-3βP was expressed in DRG neurons, especially small nociceptive, CGRP and IB4-positive neurons. Intrathecal administration of a potent PI3-kinase inhibitor (LY294002), a known GSK-3β activator, significantly decreased GSK-3βP expression levels in the dorsal horn. QUIS injection resulted in early (3 days) and sustained (14 days) DRG neurite outgrowth of small and subsequently large fibers that was reduced with short term (3 days) administration of LY294002. Furthermore, LY294002 treatment initiated on the date of injury, prevented the development of overgrooming, a spontaneous at-level pain related dysesthesia. Conclusions QUIS induced SCI resulted in inhibition of GSK-3β in primary afferents and enhanced at-level DRG intrinsic growth (neurite elongation and initiation). Early PI3K mediated activation of GSK-3β attenuated QUIS-induced DRG neurite outgrowth and prevented the development of at-level dysesthesias.
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Forrest SL, Payne SC, Keast JR, Osborne PB. Peripheral injury of pelvic visceral sensory nerves alters GFRα (GDNF family receptor alpha) localization in sensory and autonomic pathways of the sacral spinal cord. Front Neuroanat 2015; 9:43. [PMID: 25914629 PMCID: PMC4392586 DOI: 10.3389/fnana.2015.00043] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Accepted: 03/19/2015] [Indexed: 02/04/2023] Open
Abstract
GDNF (glial cell line-derived neurotrophic factor), neurturin and artemin use their co-receptors (GFRα1, GFRα2 and GFRα3, respectively) and the tyrosine kinase Ret for downstream signaling. In rodent dorsal root ganglia (DRG) most of the unmyelinated and some myelinated sensory afferents express at least one GFRα. The adult function of these receptors is not completely elucidated but their activity after peripheral nerve injury can facilitate peripheral and central axonal regeneration, recovery of sensation, and sensory hypersensitivity that contributes to pain. Our previous immunohistochemical studies of spinal cord and sciatic nerve injuries in adult rodents have identified characteristic changes in GFRα1, GFRα2 or GFRα3 in central spinal cord axons of sensory neurons located in DRG. Here we extend and contrast this analysis by studying injuries of the pelvic and hypogastric nerves that contain the majority of sensory axons projecting to the pelvic viscera (e.g., bladder and lower bowel). At 7 d, we detected some effects of pelvic but not hypogastric nerve transection on the ipsilateral spinal cord. In sacral (L6-S1) cord ipsilateral to nerve injury, GFRα1-immunoreactivity (IR) was increased in medial dorsal horn and CGRP-IR was decreased in lateral dorsal horn. Pelvic nerve injury also upregulated GFRα1- and GFRα3-IR terminals and GFRα1-IR neuronal cell bodies in the sacral parasympathetic nucleus that provides the spinal parasympathetic preganglionic output to the pelvic nerve. This evidence suggests peripheral axotomy has different effects on somatic and visceral sensory input to the spinal cord, and identifies sensory-autonomic interactions as a possible site of post-injury regulation.
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Affiliation(s)
- Shelley L Forrest
- Pain Management Research Institute (Kolling Institute), University of Sydney at the Royal North Shore Hospital Sydney, NSW, Australia
| | - Sophie C Payne
- Department of Anatomy and Neuroscience, The University of Melbourne Melbourne, VIC, Australia
| | - Janet R Keast
- Pain Management Research Institute (Kolling Institute), University of Sydney at the Royal North Shore Hospital Sydney, NSW, Australia ; Department of Anatomy and Neuroscience, The University of Melbourne Melbourne, VIC, Australia
| | - Peregrine B Osborne
- Pain Management Research Institute (Kolling Institute), University of Sydney at the Royal North Shore Hospital Sydney, NSW, Australia ; Department of Anatomy and Neuroscience, The University of Melbourne Melbourne, VIC, Australia
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15
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Wong AW, K P Yeung J, Payne SC, Keast JR, Osborne PB. Neurite outgrowth in normal and injured primary sensory neurons reveals different regulation by nerve growth factor (NGF) and artemin. Mol Cell Neurosci 2015; 65:125-34. [PMID: 25752731 DOI: 10.1016/j.mcn.2015.03.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 02/19/2015] [Accepted: 03/05/2015] [Indexed: 12/11/2022] Open
Abstract
Neurotrophic factors have been intensively studied as potential therapeutic agents for promoting neural regeneration and functional recovery after nerve injury. Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) that forms a signalling complex with GFRα3 and the tyrosine kinase Ret. Systemic administration of artemin in rodents is reported to facilitate regeneration of primary sensory neurons following axotomy, improve recovery of sensory function, and reduce sensory hypersensitivity that is a cause of pain. However, the biological mechanisms that underlie these effects are mostly unknown. This study has investigated the biological significance of the colocalisation of GFRα3 with TrkA (neurotrophin receptor for nerve growth factor [NGF]) in the peptidergic type of unmyelinated (C-fibre) sensory neurons in rat dorsal root ganglia (DRG). In vitro neurite outgrowth assays were used to study the effects of artemin and NGF by comparing DRG neurons that were previously uninjured, or were axotomised in vivo by transecting a visceral or somatic peripheral nerve. We found that artemin could facilitate neurite initiation but in comparison to NGF had low efficacy for facilitating neurite elongation and branching. This low efficacy was not increased when a preconditioning in vivo nerve injury was used to induce a pro-regenerative state. Neurite initiation was unaffected by artemin when PI3 kinase and Src family kinase signalling were blocked, but NGF had a reduced effect.
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Affiliation(s)
- Agnes W Wong
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia
| | - James K P Yeung
- School of Medical Sciences, UNSW, Randwick, NSW 2052, Australia; Pain Management Research Institute (Kolling Institute), Sydney Medical School - Northern, The University of Sydney NSW 2010, Australia
| | - Sophie C Payne
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Janet R Keast
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia; Pain Management Research Institute (Kolling Institute), Sydney Medical School - Northern, The University of Sydney NSW 2010, Australia
| | - Peregrine B Osborne
- Department of Anatomy and Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia; Pain Management Research Institute (Kolling Institute), Sydney Medical School - Northern, The University of Sydney NSW 2010, Australia.
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16
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Bergner AJ, Stamp LA, Gonsalvez DG, Allison MB, Olson DP, Myers MG, Anderson CR, Young HM. Birthdating of myenteric neuron subtypes in the small intestine of the mouse. J Comp Neurol 2014; 522:514-27. [PMID: 23861145 DOI: 10.1002/cne.23423] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 06/26/2013] [Accepted: 07/03/2013] [Indexed: 12/31/2022]
Abstract
There are many different types of enteric neurons. Previous studies have identified the time at which some enteric neuron subtypes are born (exit the cell cycle) in the mouse, but the birthdates of some major enteric neuron subtypes are still incompletely characterized or unknown. We combined 5-ethynynl-2'-deoxyuridine (EdU) labeling with antibody markers that identify myenteric neuron subtypes to determine when neuron subtypes are born in the mouse small intestine. We found that different neurochemical classes of enteric neuron differed in their birthdates; serotonin neurons were born first with peak cell cycle exit at E11.5, followed by neurofilament-M neurons, calcitonin gene-related peptide neurons (peak cell cycle exit for both at embryonic day [E]12.5-E13.5), tyrosine hydroxylase neurons (E15.5), nitric oxide synthase 1 (NOS1) neurons (E15.5), and calretinin neurons (postnatal day [P]0). The vast majority of myenteric neurons had exited the cell cycle by P10. We did not observe any EdU+/NOS1+ myenteric neurons in the small intestine of adult mice following EdU injection at E10.5 or E11.5, which was unexpected, as previous studies have shown that NOS1 neurons are present in E11.5 mice. Studies using the proliferation marker Ki67 revealed that very few NOS1 neurons in the E11.5 and E12.5 gut were proliferating. However, Cre-lox-based genetic fate-mapping revealed a small subpopulation of myenteric neurons that appears to express NOS1 only transiently. Together, our results confirm a relationship between enteric neuron subtype and birthdate, and suggest that some enteric neurons exhibit neurochemical phenotypes during development that are different from their mature phenotype.
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Affiliation(s)
- Annette J Bergner
- Department of Anatomy & Neuroscience, University of Melbourne, Victoria, Australia
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17
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Forrest SL, Osborne PB, Keast JR. Characterization of axons expressing the artemin receptor in the female rat urinary bladder: a comparison with other major neuronal populations. J Comp Neurol 2014; 522:3900-27. [PMID: 25043933 DOI: 10.1002/cne.23648] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Revised: 07/01/2014] [Accepted: 07/02/2014] [Indexed: 12/12/2022]
Abstract
Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family that has been strongly implicated in development and regeneration of autonomic nerves and modulation of nociception. Whereas other members of this family (GDNF and neurturin) primarily target parasympathetic and nonpeptidergic sensory neurons, the artemin receptor (GFRα3) is expressed by sympathetic and peptidergic sensory neurons that are also the primary sites of action of nerve growth factor, a powerful modulator of bladder nerves. Many bladder sensory neurons express GFRα3 but it is not known if they represent a specific functional subclass. Therefore, our initial aim was to map the distribution of GFRα3-immunoreactive (-IR) axons in the female rat bladder, using cryostat sections and whole wall thickness preparations. We found that GFRα3-IR axons innervated the detrusor, vasculature, and urothelium, but only part of this innervation was sensory. Many noradrenergic sympathetic axons innervating the vasculature were GFRα3-IR, but the noradrenergic innervation of the detrusor was GFRα3-negative. We also identified a prominent source of nonneuronal GFRα3-IR that is likely to be glial. Further characterization of bladder nerves revealed specific structural features of chemically distinct classes of axon terminals, and a major autonomic source of axons labeled with neurofilament-200, which is commonly used to identify myelinated sensory axons within organs. Intramural neurons were also characterized and quantified. Together, these studies reveal a diverse range of potential targets by which artemin could influence bladder function, nerve regeneration, and pain, and provide a strong microanatomical framework for understanding bladder physiology and pathophysiology.
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Affiliation(s)
- Shelley L Forrest
- Pain Management Research Institute and Kolling Institute, University of Sydney at Royal North Shore Hospital, Sydney, NSW, Australia
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18
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Forrest SL, Osborne PB, Keast JR. Characterization of bladder sensory neurons in the context of myelination, receptors for pain modulators, and acute responses to bladder inflammation. Front Neurosci 2013; 7:206. [PMID: 24223534 PMCID: PMC3819567 DOI: 10.3389/fnins.2013.00206] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 10/16/2013] [Indexed: 01/23/2023] Open
Abstract
Bladder sensation is mediated by lumbosacral dorsal root ganglion neurons and is essential for normal voiding and nociception. Numerous electrophysiological, structural, and molecular changes occur in these neurons following inflammation. Defining which neurons undergo these changes is critical for understanding the mechanism underlying bladder pain and dysfunction. Our first aim was to define the chemical classes of bladder sensory neurons that express receptors for the endogenous modulators of nociceptor sensitivity, glial cell line-derived neurotrophic factor (GDNF), the related neurotrophic factor, artemin, and estrogens. Bladder sensory neurons of adult female Sprague-Dawley rats were identified with retrograde tracer. Diverse groups of neurons express these receptors, and some neurons express receptors for both neurotrophic factors and estrogens. Lumbar and sacral sensory neurons showed some distinct differences in their expression profile. We also distinguished the chemical profile of myelinated and unmyelinated bladder sensory neurons. Our second aim was to identify bladder sensory neurons likely to be undergoing structural remodeling during inflammation. Following systemic administration of cyclophosphamide (CYP), its renal metabolite acrolein causes transient urothelial loss, exposing local afferent terminals to a toxic environment. CYP induced expression of the injury-related immediate-early gene product, activating transcription factor-3 (ATF-3), in a small population of sacral nitrergic bladder sensory neurons. In conclusion, we have defined the bladder sensory neurons that express receptors for GDNF, artemin and estrogens. Our study has also identified a sub-population of sacral sensory neurons that are likely to be undergoing structural remodeling during acute inflammation of the bladder. Together these results contribute to increased understanding of the neurons that are known to be involved in pain modulation and hyperreflexia during inflammation.
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Affiliation(s)
- Shelley L Forrest
- Pain Management Research Institute and Kolling Institute, University of Sydney at Royal North Shore Hospital Sydney, NSW, Australia
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Ansorena E, De Berdt P, Ucakar B, Simón-Yarza T, Jacobs D, Schakman O, Jankovski A, Deumens R, Blanco-Prieto MJ, Préat V, des Rieux A. Injectable alginate hydrogel loaded with GDNF promotes functional recovery in a hemisection model of spinal cord injury. Int J Pharm 2013; 455:148-58. [PMID: 23916821 DOI: 10.1016/j.ijpharm.2013.07.045] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 07/15/2013] [Accepted: 07/17/2013] [Indexed: 11/29/2022]
Abstract
We hypothesized that local delivery of GDNF in spinal cord lesion via an injectable alginate hydrogel gelifying in situ would support spinal cord plasticity and functional recovery. The GDNF release from the hydrogel was slowed by GDNF encapsulation in microspheres compared to non-formulated GDNF (free GDNF). When injected in a rat spinal cord hemisection model, more neurofilaments were observed in the lesion when the rats were treated with free GDNF-loaded hydrogels. More growing neurites were detected in the tissues surrounding the lesion when the animals were treated with GDNF microsphere-loaded hydrogels. Intense GFAP (astrocytes), low βIII tubulin (neural cells) and RECA-1 (endothelial cells) stainings were observed for non-treated lesions while GDNF-treated spinal cords presented less GFAP staining and more endothelial and nerve fiber infiltration in the lesion site. The animals treated with free GDNF-loaded hydrogel presented superior functional recovery compared with the animals treated with the GDNF microsphere-loaded hydrogels and non-treated animals.
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Affiliation(s)
- Eduardo Ansorena
- Université Catholique de Louvain, Louvain Drug Research Institute, Pharmaceutics and Drug delivery Unit, 1200 Brussels, Belgium
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Bareiss SK, Gwaltney M, Hernandez K, Lee T, Brewer KL. Excitotoxic spinal cord injury induced dysesthesias are associated with enhanced intrinsic growth of sensory neurons. Neurosci Lett 2013; 542:113-7. [DOI: 10.1016/j.neulet.2013.03.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 03/02/2013] [Accepted: 03/07/2013] [Indexed: 11/25/2022]
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Walters ET. Nociceptors as chronic drivers of pain and hyperreflexia after spinal cord injury: an adaptive-maladaptive hyperfunctional state hypothesis. Front Physiol 2012; 3:309. [PMID: 22934060 PMCID: PMC3429080 DOI: 10.3389/fphys.2012.00309] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2012] [Accepted: 07/13/2012] [Indexed: 11/13/2022] Open
Abstract
Spinal cord injury (SCI) causes chronic peripheral sensitization of nociceptors and persistent generation of spontaneous action potentials (SA) in peripheral branches and the somata of hyperexcitable nociceptors within dorsal root ganglia (DRG). Here it is proposed that SCI triggers in numerous nociceptors a persistent hyperfunctional state (peripheral, synaptic, and somal) that originally evolved as an adaptive response to compensate for loss of sensory terminals after severe but survivable peripheral injury. In this hypothesis, nociceptor somata monitor the status of their own receptive field and the rest of the body by integrating signals received by their peripheral and central branches and the soma itself. A nociceptor switches into a potentially permanent hyperfunctional state when central neural, glial, and inflammatory signal combinations are detected that indicate extensive peripheral injury. Similar signal combinations are produced by SCI and disseminated widely to uninjured as well as injured nociceptors. This paper focuses on the uninjured nociceptors that are altered by SCI. Enhanced activity generated in below-level nociceptors promotes below-level central sensitization, somatic and autonomic hyperreflexia, and visceral dysfunction. If sufficient ascending fibers survive, enhanced activity in below-level nociceptors contributes to below-level pain. Nociceptor activity generated above the injury level contributes to at- and above-level sensitization and pain (evoked and spontaneous). Thus, SCI triggers a potent nociceptor state that may have been adaptive (from an evolutionary perspective) after severe peripheral injury but is maladaptive after SCI. Evidence that hyperfunctional nociceptors make large contributions to behavioral hypersensitivity after SCI suggests that nociceptor-specific ion channels required for nociceptor SA and hypersensitivity offer promising targets for treating chronic pain and hyperreflexia after SCI.
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Affiliation(s)
- Edgar T Walters
- Department of Integrative Biology and Pharmacology, University of Texas Medical School at Houston Houston, TX, USA
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Bedi SS, Lago MT, Masha LI, Crook RJ, Grill RJ, Walters ET. Spinal cord injury triggers an intrinsic growth-promoting state in nociceptors. J Neurotrauma 2011; 29:925-35. [PMID: 21939395 DOI: 10.1089/neu.2011.2007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022] Open
Abstract
Although most investigations of the mechanisms underlying chronic pain after spinal cord injury (SCI) have examined the central nervous system (CNS), recent studies have shown that nociceptive primary afferent neurons display persistent hyperexcitability and spontaneous activity in their peripheral branches and somata in dorsal root ganglia (DRG) after SCI. This suggests that SCI-induced alterations of primary nociceptors contribute to central sensitization and chronic pain after SCI. Does SCI also promote growth of these neurons' fibers, as has been suggested in some reports? The present study tests the hypothesis that SCI induces an intrinsic growth-promoting state in DRG neurons. This was tested by dissociating DRG neurons 3 days or 1 month after spinal contusion injury at thoracic level T10 and measuring neuritic growth 1 day later. Neurons cultured 3 days after SCI exhibited longer neurites without increases in branching ("elongating growth"), compared to neurons from sham-treated or untreated (naïve) rats. Robust promotion of elongating growth was found in small and medium-sized neurons (but not large neurons) from lumbar (L3-L5) and thoracic ganglia immediately above (T9) and below (T10-T11) the contusion site, but not from cervical DRG. Elongating growth was also found in neurons immunoreactive to calcitonin gene-related peptide (CGRP), suggesting that some of the neurons exhibiting enhanced neuritic growth were nociceptors. The same measurements made on neurons dissociated 1 month after SCI revealed no evidence of elongating growth, although evidence for accelerated initiation of neurite outgrowth was found. Under certain conditions this transient growth-promoting state in nociceptors might be important for the development of chronic pain and hyperreflexia after SCI.
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Affiliation(s)
- Supinder S Bedi
- Department of Pediatric Surgery, University of Texas Medical School at Houston, Houston, Texas 77030, USA.
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23
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Changes in cutaneous innervation in patients with chronic pain after burns. Burns 2011; 37:631-7. [DOI: 10.1016/j.burns.2010.11.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 10/25/2010] [Accepted: 11/06/2010] [Indexed: 12/14/2022]
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Densmore VS, Kalous A, Keast JR, Osborne PB. Above-level mechanical hyperalgesia in rats develops after incomplete spinal cord injury but not after cord transection, and is reversed by amitriptyline, morphine and gabapentin. Pain 2010; 151:184-193. [DOI: 10.1016/j.pain.2010.07.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Revised: 05/23/2010] [Accepted: 07/10/2010] [Indexed: 12/22/2022]
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Keast JR, Forrest SL, Osborne PB. Sciatic nerve injury in adult rats causes distinct changes in the central projections of sensory neurons expressing different glial cell line-derived neurotrophic factor family receptors. J Comp Neurol 2010; 518:3024-45. [PMID: 20533358 DOI: 10.1002/cne.22378] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Most small unmyelinated neurons in adult rat dorsal root ganglia (DRG) express one or more of the coreceptors targeted by glial cell line-derived neurotrophic factor (GDNF), neurturin, and artemin (GFRalpha1, GFRalpha2, and GFRalpha3, respectively). The function of these GDNF family ligands (GFLs) is not fully elucidated but recent evidence suggests GFLs could function in sensory neuron regeneration after nerve injury and peripheral nociceptor sensitization. In this study we used immunohistochemistry to determine if the DRG neurons targeted by each GFL change after sciatic nerve injury. We compared complete sciatic nerve transection and the chronic constriction model and found that the pattern of changes incurred by each injury was broadly similar. In lumbar spinal cord there was a widespread increase in neuronal GFRalpha1 immunoreactivity (IR) in the L1-6 dorsal horn. GFRalpha3-IR also increased but in a more restricted area. In contrast, GFRalpha2-IR decreased in patches of superficial dorsal horn and this loss was more extensive after transection injury. No change in calcitonin gene-related peptide-IR was detected after either injury. Analysis of double-immunolabeled L5 DRG sections suggested the main effect of injury on GFRalpha1- and GFRalpha3-IR was to increase expression in both myelinated and unmyelinated neurons. In contrast, no change in basal expression of GFRalpha2-IR was detected in DRG by analysis of fluorescence intensity and there was a small but significant reduction in GFRalpha2-IR neurons. Our results suggest that the DRG neuronal populations targeted by GDNF, neurturin, or artemin and the effect of exogenous GFLs could change significantly after a peripheral nerve injury.
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Affiliation(s)
- Janet R Keast
- Pain Management Research Institute, Kolling Institute of Medical Research, University of Sydney at Royal North Shore Hospital, St Leonards NSW 2065, Australia.
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Finnerup NB, Baastrup C, Jensen TS. Neuropathic pain following spinal cord injury pain: mechanisms and treatment. Scand J Pain 2009. [DOI: 10.1016/s1877-8860(09)70003-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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