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Li W, Gong Y, Liu J, Guo Y, Tang H, Qin S, Zhao Y, Wang S, Xu Z, Chen B. Peripheral and Central Pathological Mechanisms of Chronic Low Back Pain: A Narrative Review. J Pain Res 2021; 14:1483-1494. [PMID: 34079363 PMCID: PMC8166276 DOI: 10.2147/jpr.s306280] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 05/01/2021] [Indexed: 12/31/2022] Open
Abstract
Chronic low back pain (CLBP), lasting >3 months, is the end result of multiple pathogenic factors. Unfortunately, little is known about CLBP pathogenesis, which limits its advancements in clinical therapy and disease management. This paper summarizes the known pathological axes of CLBP, involving both peripheral and central systems. In particular, this paper details injurious nerve stimulation, inflammation-induced peripheral pathway, and central sensitization. Lumbar components, such as intervertebral disc (IVD), facet joints, muscles, fascia, ligaments, and joint capsules, contain pain receptors called nociceptors. Degeneration of the aforementioned lumbar components activates inflammatory pathways, which can directly damage nerves, lower nociceptor threshold to fire action potentials (AP), and cause pain. Additionally, damaged lumbar IVDs and endplates can also lead to the pathologic invasion of nerve growth and innervation, followed by the compression of herniated IVDs on nerve roots, thereby causing traumatic neuropathic pain. The central mechanism of CLBP involves alteration of the sensory processing of the brain and malfunction of the descending pain modulatory system, which facilitates pain amplification in the center nervous system (CNS). Lastly, abnormalities in the brain biochemical metabolism, activation of glial cells, and subsequent inflammation also play important roles in CLBP development. Taken together, inflammation plays an important role in both peripheral and central sensitization of CLBP. Due to the heterogeneity of CLBP, its pathological mechanism remains complex and difficult to understand. Therefore, it is a worthy field for future research into the subcomponents of CLBP pathogenesis, in order to distinguish the specific form of the disease, identify its origins, and develop corresponding highly effective comprehensive therapy against CLBP.
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Affiliation(s)
- Wei Li
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Yinan Gong
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Jingyi Liu
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Yongming Guo
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China.,School of Acupuncture & Moxibustion and Tuina, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, People's Republic of China.,National Clinical Research Center for Chinese Medicine Acupuncture and Moxibustion, Tianjin, 300381, People's Republic of China
| | - Huiling Tang
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Siru Qin
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Yadan Zhao
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Songtao Wang
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China
| | - Zhifang Xu
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China.,School of Acupuncture & Moxibustion and Tuina, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, People's Republic of China.,National Clinical Research Center for Chinese Medicine Acupuncture and Moxibustion, Tianjin, 300381, People's Republic of China
| | - Bo Chen
- Research Center of Experimental Acupuncture Science, Tianjin University of Traditional Chinese Medicine, Tianjin, People's Republic of China.,School of Acupuncture & Moxibustion and Tuina, Tianjin University of Traditional Chinese Medicine, Tianjin, 301617, People's Republic of China.,National Clinical Research Center for Chinese Medicine Acupuncture and Moxibustion, Tianjin, 300381, People's Republic of China
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Chan AK, Ballatori A, Nyayapati P, Mummaneni NV, Coughlin D, Liebenberg E, Külling FA, Zhang N, Waldorff EI, Ryaby JT, Lotz JC. Pulsed Electromagnetic Fields Accelerate Sensorimotor Recovery Following Experimental Disc Herniation. Spine (Phila Pa 1976) 2021; 46:E222-E233. [PMID: 33475275 DOI: 10.1097/brs.0000000000003762] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN An experimental animal study. OBJECTIVE The aim of this study was to investigate the effect of pulsed electromagnetic fields (PEMF) on recovery of sensorimotor function in a rodent model of disc herniation (DH). SUMMARY OF BACKGROUND DATA Radiculopathy associated with DH is mediated by proinflammatory cytokines. Although we have demonstrated the anti-inflammatory effects of PEMF on various tissues, we have not investigated the potential therapeutic effect of PEMF on radiculopathy resulting from DH. METHODS Nineteen rats were divided into three groups: positive control (PC; left L4 nerve ligation) (n = 6), DH alone (DH; exposure of left L4 dorsal root ganglion [DRG] to harvested nucleus pulposus and DRG displacement) (n = 6), and DH + PEMF (n = 7). Rodents from the DH + PEMF group were exposed to PEMF immediately postoperatively and for 3 hours/day until the end of the study. Sensory function was assessed via paw withdrawal thresholds to non-noxious stimuli preoperatively and 1 and 3 days postoperatively, and every 7 days thereafter until 7 weeks after surgery. Motor function was assessed via DigiGait treadmill analysis preoperatively and weekly starting 7 days following surgery until 7 weeks following surgery. RESULTS All groups demonstrated marked increases in the left hindlimb response threshold postoperatively. However, 1 week following surgery, there was a significant effect of condition on left hindlimb withdrawal thresholds (one-way analysis of variance: F = 3.82, df = 2, P = 0.044) where a more rapid recovery to baseline threshold was evident for DH + PEMF compared to PC and DH alone. All groups demonstrated gait disturbance postoperatively. However, DH + PEMF rodents were able to regain baseline gait speeds before DH and PC rodents. When comparing gait parameters, DH + PEMF showed consistently less impairment postoperatively suggesting that PEMF treatment was associated with less severe gait disturbance. CONCLUSION These data demonstrate that PEMF accelerates sensorimotor recovery in a rodent model of DH, suggesting that PEMF may be reasonable to evaluate for the clinical management of patients with herniation-associated radiculopathy.Level of Evidence: N/A.
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Affiliation(s)
- Andrew K Chan
- Department of Neurological Surgery, University of California San Francisco, San Francisco, CA
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Alexander Ballatori
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Priya Nyayapati
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Nikhil V Mummaneni
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Dezba Coughlin
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Ellen Liebenberg
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
| | - Fabrice A Külling
- Department of Orthopaedics and Traumatology, Kantonsspital St. Gallen, St. Gallen, Switzerland
| | | | | | | | - Jeffrey C Lotz
- Department of Orthopaedic Surgery University of California, San Francisco, San Francisco, CA
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Localized Sympathectomy Reduces Mechanical Hypersensitivity by Restoring Normal Immune Homeostasis in Rat Models of Inflammatory Pain. J Neurosci 2017; 36:8712-25. [PMID: 27535916 DOI: 10.1523/jneurosci.4118-15.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 07/09/2016] [Indexed: 12/28/2022] Open
Abstract
UNLABELLED Some forms of chronic pain are maintained or enhanced by activity in the sympathetic nervous system (SNS), but attempts to model this have yielded conflicting findings. The SNS has both pro- and anti-inflammatory effects on immunity, confounding the interpretation of experiments using global sympathectomy methods. We performed a "microsympathectomy" by cutting the ipsilateral gray rami where they entered the spinal nerves near the L4 and L5 DRG. This led to profound sustained reductions in pain behaviors induced by local DRG inflammation (a rat model of low back pain) and by a peripheral paw inflammation model. Effects of microsympathectomy were evident within one day, making it unlikely that blocking sympathetic sprouting in the local DRGs or hindpaw was the sole mechanism. Prior microsympathectomy greatly reduced hyperexcitability of sensory neurons induced by local DRG inflammation observed 4 d later. Microsympathectomy reduced local inflammation and macrophage density in the affected tissues (as indicated by paw swelling and histochemical staining). Cytokine profiling in locally inflamed DRG showed increases in pro-inflammatory Type 1 cytokines and decreases in the Type 2 cytokines present at baseline, changes that were mitigated by microsympathectomy. Microsympathectomy was also effective in reducing established pain behaviors in the local DRG inflammation model. We conclude that the effect of sympathetic fibers in the L4/L5 gray rami in these models is pro-inflammatory. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some chronic inflammatory pain conditions. SIGNIFICANCE STATEMENT Sympathetic blockade is used for many pain conditions, but preclinical studies show both pro- and anti-nociceptive effects. The sympathetic nervous system also has both pro- and anti-inflammatory effects on immune tissues and cells. We examined effects of a very localized sympathectomy. By cutting the gray rami to the spinal nerves near the lumbar sensory ganglia, we avoided widespread sympathetic denervation. This procedure profoundly reduced mechanical pain behaviors induced by a back pain model and a model of peripheral inflammatory pain. One possible mechanism was reduction of inflammation in the sympathetically denervated regions. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some inflammatory conditions.
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Grava ALDS, Ferrari LF, Parada CA, Defino HLA. EVALUATION OF HYPERALGESIA AND HISTOLOGICAL CHANGES OF DORSAL ROOT GANGLION INDUCED BY NUCLEUS PULPOSUS. Rev Bras Ortop 2015; 45:460-7. [PMID: 27022595 PMCID: PMC4799083 DOI: 10.1016/s2255-4971(15)30436-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
To evaluate the hyperalgesia and histological abnormalities induced by contact between the dorsal root ganglion and the nucleus pulposus. Methods: Twenty Wistar rats were used, divided into two experimental groups. In one of the groups, a fragment of autologous nucleus pulposus was removed from the sacrococcygeal region and deposited on the L5 dorsal root ganglia. In the other group (control), a fragment of adipose tissue was deposited on the L5 dorsal root ganglia. Mechanical and thermal hyperalgesia was evaluated on the third day and the first, third, fifth and seventh weeks after the operation. A L5 dorsal root ganglion was removed in the first, third, fifth and seventh weeks after the operation for histological study using HE staining and histochemical study using specific labeling for iNOS. Results: Higher intensity of mechanical and thermal hyperalgesia was observed in the group of animals in which the nucleus pulposus was placed in contact with the dorsal root ganglion. In this group, the histological study showed abnormalities of the dorsal root ganglion tissue, characterized by an inflammatory process and axonal degeneration. The histopathological abnormalities of the dorsal root ganglion tissue presented increasing intensity with increasing length of observation, and there was a correlation with maintenance of the hyperalgesia observed in the behavioral assessment. Immunohistochemistry using specific labeling for iNOS in the group of animals in which the nucleus pulposus was placed in contact with the dorsal root ganglion showed higher expression of this enzyme in the nuclei of the inflammatory cells (glial cells) surrounding the neurons. Conclusion: Contact between the nucleus pulposus and the dorsal root ganglion induced mechanical and thermal hyperalgesia and caused histological abnormalities in the dorsal root ganglion components. These abnormalities were characterized by an inflammatory and degenerative process in the structures of the dorsal root ganglion, and they presented increasing intensity with longer periods of observation.
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Affiliation(s)
- André Luiz de Souza Grava
- Postgraduate student in the Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, Ribeirão Preto School of Medicine, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Luiz Fernando Ferrari
- Postgraduate student in the Department of Pharmacology, Ribeirão Preto School of Medicine, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Carlos Amílcar Parada
- Supervising Professor in the Department of Pharmacology, Ribeirão Preto School of Medicine, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Helton Luiz Aparecido Defino
- Titular Professor of the Department of Biomechanics, Medicine and Rehabilitation of the Locomotor Apparatus, Ribeirão Preto School of Medicine, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
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Sympathectomy and Sympathetic Blockade Reduce Pain Behavior Via Alpha-2 Adrenoceptor of the Dorsal Root Ganglion Neurons in a Lumbar Radiculopathy Model. Spine (Phila Pa 1976) 2015; 40:E1269-75. [PMID: 26165214 DOI: 10.1097/brs.0000000000001050] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN Animal experimental study with intervention. OBJECTIVE We investigated whether sympathectomy and pharmacological sympathetic blockade reduced pain behavior and reversed adrenoceptor mRNA expression of the dorsal root ganglion (DRG) in a lumbar radiculopathy model. SUMMARY OF BACKGROUND DATA The abnormal sympathetic-somatosensory interaction may underlie some forms of neuropathic pain. There are several reports that sympathectomy and pharmacological sympathetic blockades are often effective to treat neuropathic pain. However, its pathophysiological mechanisms remain obscure. METHODS We used 91 male Sprague-Dawley rats. Just after root constriction (RC), the rats underwent sympathectomy or received 3 local injections of subtype-specific α-adrenergic receptor antagonists around the DRG. We evaluated the analgesic effects of sympathectomy and sympathetic blockade using behaviors indicative mechanical allodynia and thermal hyperalgesia. We estimated the mRNA expression levels of the DRG adrenoceptor subtypes using real time reverse transcription polymerase chain reaction. RESULTS Sympathectomy and α2-antagonist significantly reduced the mechanical allodynia and thermal hyperalgesia after RC. Real time reverse transcription polymerase chain reaction analysis indicated that sympathectomy possibly reversed α2A- and α2B-adrenoceptors mRNA overexpression in the DRG after RC. CONCLUSION We considered that pain behaviors of neuropathic pain are due, at least in part, to enhanced sympathetic noradrenergic transmission within the DRG. Suppression of sympathetic activity by reducing adrenergic release, α2-adrenoceptor stimulation, and/or α2-adrenoceptor upregulation in the DRG may relieve neuropathic pain. LEVEL OF EVIDENCE 3.
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Iwase T, Takebayashi T, Tanimoto K, Terashima Y, Miyakawa T, Kobayashi T, Tohse N, Yamashita T. Sympathectomy attenuates excitability of dorsal root ganglion neurons and pain behaviour in a lumbar radiculopathy model. Bone Joint Res 2012; 1:198-204. [PMID: 23610691 PMCID: PMC3626214 DOI: 10.1302/2046-3758.19.2000073] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 07/03/2012] [Indexed: 01/19/2023] Open
Abstract
Objectives In order to elucidate the influence of sympathetic nerves on
lumbar radiculopathy, we investigated whether sympathectomy attenuated
pain behaviour and altered the electrical properties of the dorsal
root ganglion (DRG) neurons in a rat model of lumbar root constriction. Methods Sprague-Dawley rats were divided into three experimental groups.
In the root constriction group, the left L5 spinal nerve root was
ligated proximal to the DRG as a lumbar radiculopathy model. In
the root constriction + sympathectomy group, sympathectomy was performed
after the root constriction procedure. In the control group, no
procedures were performed. In order to evaluate the pain relief
effect of sympathectomy, behavioural analysis using mechanical and
thermal stimulation was performed. In order to evaluate the excitability
of the DRG neurons, we recorded action potentials of the isolated
single DRG neuron by the whole-cell patch-clamp method. Results In behavioural analysis, sympathectomy attenuated the mechanical
allodynia and thermal hyperalgesia caused by lumbar root constriction.
In electrophysiological analysis, single isolated DRG neurons with
root constriction exhibited lower threshold current, more depolarised
resting membrane potential, prolonged action potential duration,
and more depolarisation frequency. These hyperexcitable alterations
caused by root constriction were significantly attenuated in rats
treated with surgical sympathectomy. Conclusion The present results suggest that sympathectomy attenuates lumbar
radicular pain resulting from root constriction by altering the
electrical property of the DRG neuron itself. Thus, the sympathetic
nervous system was closely associated with lumbar radicular pain,
and suppressing the activity of the sympathetic nervous system may therefore
lead to pain relief.
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Affiliation(s)
- T Iwase
- Sapporo Medical University School of Medicine, Department of Orthopaedic Surgery, South 1, West 16, Chuo-ku, Sapporo 060-8543, Japan
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Does norepinephrine influence pain behavior mediated by dorsal root ganglia?: a pilot study. Clin Orthop Relat Res 2011; 469:2568-76. [PMID: 21312078 PMCID: PMC3148377 DOI: 10.1007/s11999-011-1798-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Accepted: 01/20/2011] [Indexed: 01/31/2023]
Abstract
BACKGROUND Postganglionic neurons in the sympathetic nervous system reportedly are involved in lumbar radicular pain and release norepinephrine (NE), a neurotransmitter. Increased numbers of sympathetic nerve fibers have been found in dorsal root ganglion (DRG) neurons in a root constriction model. Whether this is a reasonable model for pain, however, is unclear QUESTIONS/PURPOSES We asked whether: (1) painful behaviors occurred in the root constriction model; (2) NE enhanced the excitability of DRG neurons in the root constriction model; and (3) which adrenoceptors were related to the mediation of the NE effects. METHODS The L5 root was sutured proximal to the DRG as the root constriction model. Behavioral tests were performed until 28 days after surgery. At 10 to 14 days after the root constriction, DRG neurons were quickly excised and digested with collagenase for electrophysiologic studies. Action potentials were recorded from single DRG neurons using a whole-cell patch clamp technique. NE (10 μmol/L) was directly applied to the DRG neurons. The adrenergic sensitivity was examined in combination with antagonists. RESULTS The rats with root constriction exhibited painful behavior. NE increased the excitability of DRG neurons in the root constriction model. The effects of NE were inhibited by pretreatment with an α-antagonist and α(2)-antagonist but not an α(1)-antagonist. CONCLUSIONS Our observations suggest NE plays an important role in generating lumbar radicular pain mainly via α(2)-adrenoceptors. CLINICAL RELEVANCE An α(2)-antagonist may be an appropriate agent for trials to treat lumbar radicular pain.
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Amaya F, Samad TA, Barrett L, Broom DC, Woolf CJ. Periganglionic inflammation elicits a distally radiating pain hypersensitivity by promoting COX-2 induction in the dorsal root ganglion. Pain 2009; 142:59-67. [PMID: 19135800 PMCID: PMC2755568 DOI: 10.1016/j.pain.2008.11.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Revised: 11/20/2008] [Accepted: 11/21/2008] [Indexed: 12/19/2022]
Abstract
We have developed a model in which inflammation contiguous to and within a dorsal root ganglion (DRG) was generated by local application of complete Freund's adjuvant (CFA) to the L4 lumbar spinal nerve as it exits from the intervertebral foramen. The periganglionic inflammation (PGI) elicited a marked reduction in withdrawal threshold to mechanical stimuli and an increase in heat pain sensitivity in the ipsilateral hindpaw in the absence of any hindpaw inflammation. The pain sensitivity appeared within hours and lasted for a week. The PGI also induced a prominent increase in IL-1beta and TNF-alpha levels in the DRG and of cyclooxygenase-2 (COX-2) expression in neurons and satellite cells. A selective COX-2 inhibitor reduced the PGI-induced hyperalgesia. We also show that IL-1beta induces COX-2 expression and prostaglandin release in DRG neurons in vitro in a MAP kinase-dependent fashion. The COX-2 induction was prevented by ERK and p38 inhibitors. We conclude that periganglionic inflammation increases cytokine levels, including IL-1beta, leading to the transcription of COX-2 and prostaglandin production in the affected DRG, and thereby to the development of a dermatomally distributed pain hypersensitivity.
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Affiliation(s)
- Fumimasa Amaya
- Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, USA
- Department of Anesthesiology, Kyoto Prefectural University of Medicine, Japan
| | - Tarek A. Samad
- Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, USA
| | - Lee Barrett
- Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, USA
| | - Daniel C. Broom
- Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, USA
| | - Clifford J. Woolf
- Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, USA
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Sympathectomy reduces mechanical allodynia, tumor necrosis factor-alpha expression, and dorsal root ganglion apoptosis following nerve root crush injury. Spine (Phila Pa 1976) 2008; 33:1163-9. [PMID: 18469688 DOI: 10.1097/brs.0b013e31817144fc] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN An analysis of pain behavior and neuronal apoptosis in the dorsal root ganglion (DRG) following crush injury to the L5 nerve root, with or without surgical sympathectomy. OBJECTIVES To determine whether sympathectomy prevents pain behavior and to compare pain behavior with expression of tumor necrosis factor (TNF)-alpha and apoptosis in the DRG. SUMMARY OF BACKGROUND DATA Sympathetic block is used to relieve symptoms in radiculopathy patients. One effect of the block is improvement of blood flow to the nerve. However, this beneficial effect continues longer than the expected duration of local anesthesia, suggesting an unknown neuroprotective effect involving interference with sympathetic activity. METHODS Sprague-Dawley rats (n = 102) were used and divided into 4 experimental groups. In the crush group, animals received a crush injury to the L5 nerve root. In the sympathectomy group, animals received sympathectomy (Syx) on the left side. In the Syx + crush group, both sympathectomy and crush injury were performed. In the sham group, the surgical procedure was the same, but neither sympathectomy nor crush injury took place. Mechanical allodynia was determined in 4 groups. Expression of TNF-alpha was compared in rats with crush injury, with and without sympathectomy. Using immunostaining for caspase 3, NeuN, and GFAP, localization of apoptotic cells was observed. In addition, we compared the percentage of neurons undergoing apoptosis in the DRG. RESULTS Sympathectomy prevented mechanical allodynia throughout the 14-day experimental period. TNF-alpha expression was increased in the DRG following crush-only injury, whereas it was decreased in animals undergoing sympathectomy after the crush injury. DRG apoptosis in the crush group was significantly higher than in the sympathectomy group at day 7 (P < 0.05). CONCLUSION Surgical sympathectomy reduced mechanical allodynia for 14 days after nerve root crush injury, and that DRG apoptosis was decreased in injured animals that underwent sympathectomy. Sympathetic block may not only cause an increase in nerve blood flow, but may also prevent the development of significant TNF-alpha elevation, DRG apoptosis, and neuropathic pain.
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Abstract
The anatomical studies, basic to our understanding of lumbar spine innervation through the sinu-vertebral nerves, are reviewed. Research in the 1980s suggested that pain sensation was conducted in part via the sympathetic system. These sensory pathways have now been clarified using sophisticated experimental and histochemical techniques confirming a dual pattern. One route enters the adjacent dorsal root segmentally, whereas the other supply is non-segmental ascending through the paravertebral sympathetic chain with re-entry through the thoracolumbar white rami communicantes. Sensory nerve endings in the degenerative lumbar disc penetrate deep into the disrupted nucleus pulposus, insensitive in the normal lumbar spine. Complex as well as free nerve endings would appear to contribute to pain transmission. The nature and mechanism of discogenic pain is still speculative but there is growing evidence to support a 'visceral pain' hypothesis, unique in the muscloskeletal system. This mechanism is open to 'peripheral sensitisation' and possibly 'central sensitisation' as a potential cause of chronic back pain.
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Affiliation(s)
- M A Edgar
- Surgery UCL, UCLH, Emmanuel Kaye House, 37a Devonshire Street, London W1G 6QA, UK.
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