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Tan S, Faull RLM, Curtis MA. The tracts, cytoarchitecture, and neurochemistry of the spinal cord. Anat Rec (Hoboken) 2023; 306:777-819. [PMID: 36099279 DOI: 10.1002/ar.25079] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 08/01/2022] [Accepted: 09/11/2022] [Indexed: 11/06/2022]
Abstract
The human spinal cord can be described using a range of nomenclatures with each providing insight into its structure and function. Here we have comprehensively reviewed the key literature detailing the general structure, configuration of tracts, the cytoarchitecture of Rexed's laminae, and the neurochemistry at the spinal segmental level. The purpose of this review is to detail current anatomical understanding of how the spinal cord is structured and to aid researchers in identifying gaps in the literature that need to be studied to improve our knowledge of the spinal cord which in turn will improve the potential of therapeutic intervention for disorders of the spinal cord.
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Affiliation(s)
- Sheryl Tan
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Richard L M Faull
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
| | - Maurice A Curtis
- Centre for Brain Research and Department of Anatomy and Medical Imaging, University of Auckland, Auckland, New Zealand
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2
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Dhanasobhon D, Medrano MC, Becker LJ, Moreno-Lopez Y, Kavraal S, Bichara C, Schlichter R, Inquimbert P, Yalcin I, Cordero-Erausquin M. Enhanced analgesic cholinergic tone in the spinal cord in a mouse model of neuropathic pain. Neurobiol Dis 2021; 155:105363. [PMID: 33845128 DOI: 10.1016/j.nbd.2021.105363] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 03/12/2021] [Accepted: 03/31/2021] [Indexed: 11/30/2022] Open
Abstract
Endogenous acetylcholine (ACh) is an important modulator of nociceptive sensory processing in the spinal cord. An increased level of spinal ACh induces analgesia both in humans and rodents while interfering with cholinergic signaling is allodynic, demonstrating that a basal tone of spinal ACh modulates nociceptive responses in naïve animals. The plasticity undergone by this cholinergic system in chronic pain situation is unknown, and the mere presence of this tone in neuropathic animals is controversial. We have addressed these issues in mice through behavioral experiments, histology, electrophysiology and molecular biology, in the cuff model of peripheral neuropathy. Our behavior experiments demonstrate the persistence, and even increased impact of the analgesic cholinergic tone acting through nicotinic receptors in cuff animals. The neuropathy does not affect the number or membrane properties of dorsal horn cholinergic neurons, nor specifically the frequency of their synaptic inputs. The alterations thus appear to be in the neurons receiving the cholinergic signaling, which is confirmed by the fact that subthreshold doses of acetylcholinesterase (AChE) inhibitors in sham animals become anti-allodynic in cuff mice and by the altered expression of the β2 nicotinic receptor subunit. Our results demonstrate that endogenous cholinergic signaling can be manipulated to relieve mechanical allodynia in animal models of peripheral neuropathy. Until now, AChE inhibitors have mainly been used in the clinics in situations of acute pain (parturition, post-operative). The fact that lower doses (thus with fewer side effects) could be efficient in chronic pain conditions opens new avenues for the treatment of neuropathic pain. SIGNIFICANCE STATEMENT: Chronic pain continues to be the most common cause of disability that impairs the quality of life, accruing enormous and escalating socio-economic costs. A better understanding of the plasticity of spinal neuronal networks, crucially involved in nociceptive processing, could help designing new therapeutic avenues. We here demonstrate that chronic pain modifies the spinal nociceptive network in such a way that it becomes more sensitive to cholinergic modulations. The spinal cholinergic system is responsible for an analgesic tone that can be exacerbated by acetylcholinesterase inhibitors, a property used in the clinic to relief acute pain (child birth, post-op). Our results suggest that lower doses of acetylcholinesterases, with even fewer side effects, could be efficient to relieve chronic pain.
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Affiliation(s)
- Dhanasak Dhanasobhon
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Maria-Carmen Medrano
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Léa J Becker
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Yunuen Moreno-Lopez
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Sehrazat Kavraal
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Charlotte Bichara
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Rémy Schlichter
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Perrine Inquimbert
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Ipek Yalcin
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France
| | - Matilde Cordero-Erausquin
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, 67000 Strasbourg, France; University of Strasbourg Institute for Advanced Study (USIAS), 67000 Strasbourg, France.
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Liu P, Zhang X, He X, Jiang Z, Wang Q, Lu Y. Spinal GABAergic neurons are under feed-forward inhibitory control driven by A δ and C fibers in Gad2 td-Tomato mice. Mol Pain 2021; 17:1744806921992620. [PMID: 33586515 PMCID: PMC7890716 DOI: 10.1177/1744806921992620] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 01/10/2020] [Accepted: 01/13/2020] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Spinal GABAergic neurons act as a critical modulator in sensory transmission like pain or itch. The monosynaptic or polysynaptic primary afferent inputs onto GABAergic neurons, along with other interneurons or projection neurons make up the direct and feed-forward inhibitory neural circuits. Previous research indicates that spinal GABAergic neurons mainly receive excitatory inputs from Aδ and C fibers. However, whether they are controlled by other inhibitory sending signals is not well understood. METHODS We applied a transgenic mouse line in which neurons co-expressed the GABA-synthesizing enzyme Gad65 and the enhanced red fluorescence (td-Tomato) to characterize the features of morphology and electrophysiology of GABAergic neurons. Patch-clamp whole cell recordings were used to record the evoked postsynaptic potentials of fluorescent neurons in spinal slices in response to dorsal root stimulation. RESULTS We demonstrated that GABAergic neurons not only received excitatory drive from peripheral Aβ, Aδ and C fibers, but also received inhibitory inputs driven by Aδ and C fibers. The evoked inhibitory postsynaptic potentials (eIPSPs) mediated by C fibers were mainly Glycinergic (66.7%) as well as GABAergic mixed with Glycinergic (33.3%), whereas the inhibition mediated by Aδ fibers was predominately both GABA and Glycine-dominant (57.1%), and the rest of which was purely Glycine-dominant (42.9%). CONCLUSION These results indicated that spinal GABAergic inhibitory neurons are under feedforward inhibitory control driven by primary C and Aδ fibers, suggesting that this feed-forward inhibitory pathway may play an important role in balancing the excitability of GABAergic neurons in spinal dorsal horn.
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Affiliation(s)
- Peng Liu
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Xiao Zhang
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Xiaolan He
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Zhenhua Jiang
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Qun Wang
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Yan Lu
- Department of Pain Medicine, Department of Anesthesiology & Perioprative Medicine, Xijing Hospital, Fourth Military Medical University, Xi’an, China
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Boyle KA, Gradwell MA, Yasaka T, Dickie AC, Polgár E, Ganley RP, Orr DPH, Watanabe M, Abraira VE, Kuehn ED, Zimmerman AL, Ginty DD, Callister RJ, Graham BA, Hughes DI. Defining a Spinal Microcircuit that Gates Myelinated Afferent Input: Implications for Tactile Allodynia. Cell Rep 2020; 28:526-540.e6. [PMID: 31291586 PMCID: PMC6635381 DOI: 10.1016/j.celrep.2019.06.040] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 03/29/2019] [Accepted: 06/10/2019] [Indexed: 12/16/2022] Open
Abstract
Chronic pain presents a major unmet clinical problem. The development of more effective treatments is hindered by our limited understanding of the neuronal circuits underlying sensory perception. Here, we show that parvalbumin (PV)-expressing dorsal horn interneurons modulate the passage of sensory information conveyed by low-threshold mechanoreceptors (LTMRs) directly via presynaptic inhibition and also gate the polysynaptic relay of LTMR input to pain circuits by inhibiting lamina II excitatory interneurons whose axons project into lamina I. We show changes in the functional properties of these PV interneurons following peripheral nerve injury and that silencing these cells unmasks a circuit that allows innocuous touch inputs to activate pain circuits by increasing network activity in laminae I-IV. Such changes are likely to result in the development of tactile allodynia and could be targeted for more effective treatment of mechanical pain.
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Affiliation(s)
- Kieran A Boyle
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Mark A Gradwell
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle NSW 2308, Australia
| | - Toshiharu Yasaka
- Department of Anatomy and Physiology, Saga University, Saga 849-8501, Japan
| | - Allen C Dickie
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Erika Polgár
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Robert P Ganley
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Desmond P H Orr
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK
| | - Masahiko Watanabe
- Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan
| | - Victoria E Abraira
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Emily D Kuehn
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Amanda L Zimmerman
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
| | - David D Ginty
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Robert J Callister
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle NSW 2308, Australia
| | - Brett A Graham
- School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle NSW 2308, Australia.
| | - David I Hughes
- Spinal Cord Research Group, Institute of Neuroscience and Psychology, University of Glasgow, Glasgow G12 8QQ, UK.
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Gradwell MA, Callister RJ, Graham BA. Reviewing the case for compromised spinal inhibition in neuropathic pain. J Neural Transm (Vienna) 2019; 127:481-503. [PMID: 31641856 DOI: 10.1007/s00702-019-02090-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Accepted: 09/30/2019] [Indexed: 12/20/2022]
Abstract
A striking and debilitating property of the nervous system is that damage to this tissue can cause chronic intractable pain, which persists long after resolution of the initial insult. This neuropathic form of pain can arise from trauma to peripheral nerves, the spinal cord, or brain. It can also result from neuropathies associated with disease states such as diabetes, human immunodeficiency virus/AIDS, herpes, multiple sclerosis, cancer, and chemotherapy. Regardless of the origin, treatments for neuropathic pain remain inadequate. This continues to drive research into the underlying mechanisms. While the literature shows that dysfunction in numerous loci throughout the CNS can contribute to chronic pain, the spinal cord and in particular inhibitory signalling in this region have remained major research areas. This review focuses on local spinal inhibition provided by dorsal horn interneurons, and how such inhibition is disrupted during the development and maintenance of neuropathic pain.
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Affiliation(s)
- M A Gradwell
- School of Biomedical Sciences and Pharmacy, Faculty of Health, University of Newcastle, Callaghan, NSW, 2308, Australia
- Hunter Medical Research Institute (HMRI), New Lambton Heights, NSW, Australia
| | - R J Callister
- School of Biomedical Sciences and Pharmacy, Faculty of Health, University of Newcastle, Callaghan, NSW, 2308, Australia
- Hunter Medical Research Institute (HMRI), New Lambton Heights, NSW, Australia
| | - B A Graham
- School of Biomedical Sciences and Pharmacy, Faculty of Health, University of Newcastle, Callaghan, NSW, 2308, Australia.
- Hunter Medical Research Institute (HMRI), New Lambton Heights, NSW, Australia.
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Dougherty PM, Chen J. Relationship of membrane properties, spike burst responses, laminar location, and functional class of dorsal horn neurons recorded in vitro. J Neurophysiol 2016; 116:1137-51. [PMID: 27334950 PMCID: PMC5013171 DOI: 10.1152/jn.00187.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 06/19/2016] [Indexed: 01/08/2023] Open
Abstract
The input-output and discharge properties of neurons are shaped by both passive and active electrophysiological membrane properties. Whole cell patch-clamp recordings in lamina I-III neurons in an isolated preparation of the whole spinal cord of juvenile rats with attached dorsal roots and dorsal root ganglia were used to further define which of these properties provides the most impactful classification strategy. A total of 95 neurons were recorded in segment L5 and were classified based on the responses to L4 dorsal root stimulation. The results showed that high-threshold and silent neurons had higher membrane resistance and more negative resting membrane potential than low-threshold or wide-dynamic-range neurons. Rheobase in low-threshold and wide-dynamic-range neurons was significantly lower than that of high-threshold or silent neurons. Four types of firing patterns were identified in response to depolarizing current injections. Low-threshold cells most frequently showed a phasic firing pattern characterized by a short initial burst of action potentials, single spiking or irregular firing bursts at the onset of a depolarizing pulse. High-threshold and wide-dynamic-range neurons were characterized by tonic firing with trains of spikes occurring at regular intervals throughout the current pulse. The majority of silent neurons displayed a delayed onset of firing in response to current injection. These results indicate that the passive membrane properties of spinal neurons are tuned to optimize the responses to particular subsets of afferent stimuli.
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Affiliation(s)
- Patrick M Dougherty
- Division of Anesthesiology and Critical Care Medicine, Department of Pain Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas; and
| | - Jinghong Chen
- Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai, China
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Schmidtko A. Nitric oxide-mediated pain processing in the spinal cord. Handb Exp Pharmacol 2015; 227:103-17. [PMID: 25846616 DOI: 10.1007/978-3-662-46450-2_6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
A large body of evidence indicates that nitric oxide (NO) plays an important role in the processing of persistent inflammatory and neuropathic pain in the spinal cord. Several animal studies revealed that inhibition or knockout of NO synthesis ameliorates persistent pain. However, spinal delivery of NO donors caused dual pronociceptive and antinociceptive effects, pointing to multiple downstream signaling mechanisms of NO. This review summarizes the localization and function of NO-dependent signaling mechanisms in the spinal cord, taking account of the recent progress made in this field.
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Affiliation(s)
- Achim Schmidtko
- Institut für Pharmakologie und Toxikologie, Universität Witten/Herdecke, ZBAF, Stockumer Str. 10, 58453, Witten, Germany,
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Lu Y, Dong H, Gao Y, Gong Y, Ren Y, Gu N, Zhou S, Xia N, Sun YY, Ji RR, Xiong L. A feed-forward spinal cord glycinergic neural circuit gates mechanical allodynia. J Clin Invest 2013; 123:4050-62. [PMID: 23979158 DOI: 10.1172/jci70026] [Citation(s) in RCA: 202] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/27/2013] [Indexed: 01/02/2023] Open
Abstract
Neuropathic pain is characterized by mechanical allodynia induced by low-threshold myelinated Aβ-fiber activation. The original gate theory of pain proposes that inhibitory interneurons in the lamina II of the spinal dorsal horn (DH) act as "gate control" units for preventing the interaction between innocuous and nociceptive signals. However, our understanding of the neuronal circuits underlying pain signaling and modulation in the spinal DH is incomplete. Using a rat model, we have shown that the convergence of glycinergic inhibitory and excitatory Aβ-fiber inputs onto PKCγ+ neurons in the superficial DH forms a feed-forward inhibitory circuit that prevents Aβ input from activating the nociceptive pathway. This feed-forward inhibition was suppressed following peripheral nerve injury or glycine blockage, leading to inappropriate induction of action potential outputs in the nociceptive pathway by Aβ-fiber stimulation. Furthermore, spinal blockage of glycinergic synaptic transmission in vivo induced marked mechanical allodynia. Our findings identify a glycinergic feed-forward inhibitory circuit that functions as a gate control to separate the innocuous mechanoreceptive pathway and the nociceptive pathway in the spinal DH. Disruption of this glycinergic inhibitory circuit after peripheral nerve injury has the potential to elicit mechanical allodynia, a cardinal symptom of neuropathic pain.
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Affiliation(s)
- Yan Lu
- Department of Anesthesiology and Pain Management, Xijing Hospital, Fourth Military Medical University, Xian, People's Republic of China.
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