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Brennan FH, Swarts EA, Kigerl KA, Mifflin KA, Guan Z, Noble BT, Wang Y, Witcher KG, Godbout JP, Popovich PG. Microglia promote maladaptive plasticity in autonomic circuitry after spinal cord injury in mice. Sci Transl Med 2024; 16:eadi3259. [PMID: 38865485 DOI: 10.1126/scitranslmed.adi3259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 05/16/2024] [Indexed: 06/14/2024]
Abstract
Robust structural remodeling and synaptic plasticity occurs within spinal autonomic circuitry after severe high-level spinal cord injury (SCI). As a result, normally innocuous visceral or somatic stimuli elicit uncontrolled activation of spinal sympathetic reflexes that contribute to systemic disease and organ-specific pathology. How hyperexcitable sympathetic circuitry forms is unknown, but local cues from neighboring glia likely help mold these maladaptive neuronal networks. Here, we used a mouse model of SCI to show that microglia surrounded active glutamatergic interneurons and subsequently coordinated multi-segmental excitatory synaptogenesis and expansion of sympathetic networks that control immune, neuroendocrine, and cardiovascular functions. Depleting microglia during critical periods of circuit remodeling after SCI prevented maladaptive synaptic and structural plasticity in autonomic networks, decreased the frequency and severity of autonomic dysreflexia, and prevented SCI-induced immunosuppression. Forced turnover of microglia in microglia-depleted mice restored structural and functional indices of pathological dysautonomia, providing further evidence that microglia are key effectors of autonomic plasticity. Additional data show that microglia-dependent autonomic plasticity required expression of triggering receptor expressed on myeloid cells 2 (Trem2) and α2δ-1-dependent synaptogenesis. These data suggest that microglia are primary effectors of autonomic neuroplasticity and dysautonomia after SCI in mice. Manipulating microglia may be a strategy to limit autonomic complications after SCI or other forms of neurologic disease.
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Affiliation(s)
- Faith H Brennan
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Department of Biomedical and Molecular Sciences and Center for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Emily A Swarts
- Department of Biomedical and Molecular Sciences and Center for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Kristina A Kigerl
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Katherine A Mifflin
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Zhen Guan
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Benjamin T Noble
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Yan Wang
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Kristina G Witcher
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Institute for Behavioral Medicine Research, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Jonathan P Godbout
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Institute for Behavioral Medicine Research, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Phillip G Popovich
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Belford Center for Spinal Cord Injury, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
- Institute for Behavioral Medicine Research, Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
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Samejima S, Shackleton C, Malik RN, Cao K, Bohorquez A, Nightingale TE, Sachdeva R, Krassioukov AV. Spinal Cord Stimulation Prevents Autonomic Dysreflexia in Individuals with Spinal Cord Injury: A Case Series. J Clin Med 2023; 12:jcm12082897. [PMID: 37109234 PMCID: PMC10146034 DOI: 10.3390/jcm12082897] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 04/04/2023] [Accepted: 04/12/2023] [Indexed: 04/29/2023] Open
Abstract
Spinal cord injury (SCI) results in severe cardiovascular dysfunction due to the disruption of supraspinal control. Autonomic dysreflexia (AD), an uncontrolled rise in blood pressure in response to peripheral stimuli including common bowel routine, digital anorectal stimulation (DARS), reduces the quality of life, and increases morbidity and mortality. Recently, spinal cord stimulation (SCS) has emerged as a potential intervention to mitigate unstable blood pressure following SCI. The objective of this case series was to test the real-time effect of epidural SCS (eSCS) at the lumbosacral spinal cord, the most common implant location, on mitigating AD in individuals with SCI. We recruited three individuals with cervical and upper thoracic motor-complete SCI who have an implanted epidural stimulator. We demonstrated that eSCS can reduce the elevation in blood pressure and prevent DARS-induced AD. The blood pressure variability analysis indicated that eSCS potentially reduced vascular sympathetic nervous system activity during DARS, compared to without eSCS. This case series provides evidence to support the use of eSCS to prevent AD episodes during routine bowel procedures, improving the quality of life for individuals with SCI and potentially reducing cardiovascular risks.
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Affiliation(s)
- Soshi Samejima
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
| | - Claire Shackleton
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
| | - Raza N Malik
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
| | - Kawami Cao
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
| | - Anibal Bohorquez
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
- Spinal Cord Program, GF Strong Rehabilitation Centre, Vancouver Coastal Health, Vancouver, BC V5Z 2G9, Canada
| | - Tom E Nightingale
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
- Centre for Trauma Sciences Research, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Rahul Sachdeva
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
| | - Andrei V Krassioukov
- International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 1M9, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, Vancouver, BC V5Z 2G9, Canada
- Spinal Cord Program, GF Strong Rehabilitation Centre, Vancouver Coastal Health, Vancouver, BC V5Z 2G9, Canada
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Noble BT, Brennan FH, Wang Y, Guan Z, Mo X, Schwab JM, Popovich PG. Thoracic VGluT2 + Spinal Interneurons Regulate Structural and Functional Plasticity of Sympathetic Networks after High-Level Spinal Cord Injury. J Neurosci 2022; 42:3659-3675. [PMID: 35304427 PMCID: PMC9053847 DOI: 10.1523/jneurosci.2134-21.2022] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 02/25/2022] [Accepted: 02/28/2022] [Indexed: 11/21/2022] Open
Abstract
Traumatic spinal cord injury (SCI) above the major spinal sympathetic outflow (T6 level) disinhibits sympathetic neurons from supraspinal control, causing systems-wide "dysautonomia." We recently showed that remarkable structural remodeling and plasticity occurs within spinal sympathetic circuitry, creating abnormal sympathetic reflexes that exacerbate dysautonomia over time. As an example, thoracic VGluT2+ spinal interneurons (SpINs) become structurally and functionally integrated with neurons that comprise the spinal-splenic sympathetic network and immunological dysfunction becomes progressively worse after SCI. To test whether the onset and progression of SCI-induced sympathetic plasticity is neuron activity dependent, we selectively inhibited (or excited) thoracic VGluT2+ interneurons using chemogenetics. New data show that silencing VGluT2+ interneurons in female and male mice with a T3 SCI, using hM4Di designer receptors exclusively activated by designer drugs (Gi DREADDs), blocks structural plasticity and the development of dysautonomia. Specifically, silencing VGluT2+ interneurons prevents the structural remodeling of spinal sympathetic networks that project to lymphoid and endocrine organs, reduces the frequency of spontaneous autonomic dysreflexia (AD), and reduces the severity of experimentally induced AD. Features of SCI-induced structural plasticity can be recapitulated in the intact spinal cord by activating excitatory hM3Dq-DREADDs in VGluT2+ interneurons. Collectively, these data implicate VGluT2+ excitatory SpINs in the onset and propagation of SCI-induced structural plasticity and dysautonomia, and reveal the potential for neuromodulation to block or reduce dysautonomia after severe high-level SCI.SIGNIFICANCE STATEMENT In response to stress or dangerous stimuli, autonomic spinal neurons coordinate a "fight or flight" response marked by increased cardiac output and release of stress hormones. After a spinal cord injury (SCI), normally harmless stimuli like bladder filling can result in a "false" fight or flight response, causing pathological changes throughout the body. We show that progressive hypertension and immune suppression develop after SCI because thoracic excitatory VGluT2+ spinal interneurons (SpINs) provoke structural remodeling in autonomic networks within below-lesion spinal levels. These pathological changes can be prevented in SCI mice or phenocopied in uninjured mice using chemogenetics to selectively manipulate activity in VGluT2+ SpINs. Targeted neuromodulation of SpINs could prevent structural plasticity and subsequent autonomic dysfunction in people with SCI.
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Affiliation(s)
- Benjamin T Noble
- Department of Neuroscience, Center for Brain and Spinal Cord Repair, Belford Center for Spinal Cord Injury, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
| | - Faith H Brennan
- Department of Neuroscience, Center for Brain and Spinal Cord Repair, Belford Center for Spinal Cord Injury, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
| | - Yan Wang
- Department of Neuroscience, Center for Brain and Spinal Cord Repair, Belford Center for Spinal Cord Injury, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
| | - Zhen Guan
- Department of Neuroscience, Center for Brain and Spinal Cord Repair, Belford Center for Spinal Cord Injury, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
| | - Xiaokui Mo
- Center for Biostatistics, The Ohio State University, Columbus, Ohio 43210
| | - Jan M Schwab
- Department of Neurology, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
| | - Phillip G Popovich
- Department of Neuroscience, Center for Brain and Spinal Cord Repair, Belford Center for Spinal Cord Injury, Wexner Medical Center, The Ohio State University, Columbus, Ohio 43210
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Development of a Spinal Cord Injury Model Permissive to Study the Cardiovascular Effects of Rehabilitation Approaches Designed to Induce Neuroplasticity. BIOLOGY 2021; 10:biology10101006. [PMID: 34681105 PMCID: PMC8533334 DOI: 10.3390/biology10101006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 09/23/2021] [Accepted: 09/29/2021] [Indexed: 11/24/2022]
Abstract
Simple Summary People living with high-level spinal cord injury experience worse cardiovascular health than the general population. In most spinal cord injuries, there are some remaining functioning pathways leading from the brain through the spinal cord to the organs and muscles, but not enough to sustain normal levels of function. Recently, therapies that aim to increase the strength of connections in these remaining pathways have shown great potential in restoring walking, hand, and breathing function in the spinal cord injured population. In order to test these therapies for their effects on cardiovascular function, we developed a new type of spinal cord injury rat model that spares enough pathways for these therapies to act upon but still produces measurable reductions in heart and blood vessel function that can be targeted with interventions/treatments. Abstract As primary medical care for spinal cord injury (SCI) has improved over the last decades there are more individuals living with neurologically incomplete (vs. complete) cervical injuries. For these individuals, a number of promising therapies are being actively researched in pre-clinical settings that seek to strengthen the remaining spinal pathways with a view to improve motor function. To date, few, if any, of these interventions have been tested for their effectiveness to improve autonomic and cardiovascular (CV) function. As a first step to testing such therapies, we aimed to develop a model that has sufficient sparing of descending sympathetic pathways for these interventions to target yet induces robust CV impairment. Twenty-six Wistar rats were assigned to SCI (n = 13) or naïve (n = 13) groups. Animals were injured at the T3 spinal segment with 300 kdyn of force. Fourteen days post-SCI, left ventricular (LV) and arterial catheterization was performed to assess in vivo cardiac and hemodynamic function. Spinal cord lesion characteristics along with sparing in catecholaminergic and serotonergic projections were determined via immunohistochemistry. SCI produced a decrease in mean arterial pressure of 17 ± 3 mmHg (p < 0.001) and left ventricular contractility (end-systolic elastance) of 0.7 ± 0.1 mmHg/µL (p < 0.001). Our novel SCI model produced significant decreases in cardiac and hemodynamic function while preserving 33 ± 9% of white matter at the injury epicenter, which we believe makes it a useful pre-clinical model of SCI to study rehabilitation approaches designed to induce neuroplasticity.
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O'Reilly ML, Tom VJ. Neuroimmune System as a Driving Force for Plasticity Following CNS Injury. Front Cell Neurosci 2020; 14:187. [PMID: 32792908 PMCID: PMC7390932 DOI: 10.3389/fncel.2020.00187] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 05/29/2020] [Indexed: 12/15/2022] Open
Abstract
Following an injury to the central nervous system (CNS), spontaneous plasticity is observed throughout the neuraxis and affects multiple key circuits. Much of this spontaneous plasticity can elicit beneficial and deleterious functional outcomes, depending on the context of plasticity and circuit affected. Injury-induced activation of the neuroimmune system has been proposed to be a major factor in driving this plasticity, as neuroimmune and inflammatory factors have been shown to influence cellular, synaptic, structural, and anatomical plasticity. Here, we will review the mechanisms through which the neuroimmune system mediates plasticity after CNS injury. Understanding the role of specific neuroimmune factors in driving adaptive and maladaptive plasticity may offer valuable therapeutic insight into how to promote adaptive plasticity and/or diminish maladaptive plasticity, respectively.
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Affiliation(s)
- Micaela L O'Reilly
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Veronica J Tom
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
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Thoracic sympathetic nuclei ischemia: Effects on lower heart rates following experimentally induced spinal subarachnoid hemorrhage. Neurochirurgie 2020; 66:155-161. [PMID: 32387429 DOI: 10.1016/j.neuchi.2019.12.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 12/09/2019] [Accepted: 12/26/2019] [Indexed: 11/24/2022]
Abstract
BACKGROUND The neuropathological mechanism of heart rhythm disorders, following spinal cord pathologies, to our knowledge, has not yet been adequately investigated. In this study, the effect of the ischemic neurodegeneration of the thoracic sympathetic nuclei (TSN) on the heart rate (HR) was examined following a spinal subarachnoid hemorrhage (SSAH). METHODS This study was conducted on 22 rabbits. Five rabbits were used as a control group, five as SHAM, and twelve as a study group. The animals' HRs were recorded via monitoring devices on the first day, and those results were accepted as baseline values. The HRs were remeasured after injecting 0.5 cc of isotonic saline for SHAM and 0.5 cc of autolog arterial blood into the thoracic spinal subarachnoid space at T4-T5 for the study group. After a three-week follow-up with continuous monitoring of their HRs, the rabbit's thoracic spinal cords and stellate ganglia were extracted. The specimens were evaluated by histopathological methods. The densities of degenerated neurons in the TSN and stellate ganglia were compared with the HRs. RESULTS The mean HRs and mean degenerated neuron density of the TSN and stellate ganglia in control group were 251±18/min, 5±2/mm3, and 3±1/mm3, respectively. The mean HRs and the mean degenerated neuron density of the TSN and stellate ganglia were detected as 242±13/min, 6±2/mm3, and 4±2/mm3 in SHAM (P>0.05 vs. control); 176±19/min, 94±12/mm3, and 28±6/mm3 in the study group (P<0.0001 vs. control and P<0.005 vs. SHAM), respectively. CONCLUSIONS SAH induced TSN neurodegeneration may have been responsible for low HRs following SSAH. To date this has not been mentioned in the literature.
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7
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Michael FM, Patel SP, Rabchevsky AG. Intraspinal Plasticity Associated With the Development of Autonomic Dysreflexia After Complete Spinal Cord Injury. Front Cell Neurosci 2019; 13:505. [PMID: 31780900 PMCID: PMC6856770 DOI: 10.3389/fncel.2019.00505] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 10/28/2019] [Indexed: 01/02/2023] Open
Abstract
Traumatic spinal cord injury (SCI) leads to disruption of sensory, motor and autonomic function, and triggers structural, physiological and biochemical changes that cause reorganization of existing circuits that affect functional recovery. Propriospinal neurons (PN) appear to be very plastic within the inhibitory microenvironment of the injured spinal cord by forming compensatory circuits that aid in relaying information across the lesion site and, thus, are being investigated for their potential to promote locomotor recovery after experimental SCI. Yet the role of PN plasticity in autonomic dysfunction is not well characterized, notably, the disruption of supraspinal modulatory signals to spinal sympathetic neurons after SCI at the sixth thoracic spinal segment or above resulting in autonomic dysreflexia (AD). This condition is characterized by unmodulated sympathetic reflexes triggering sporadic hypertension associated with baroreflex mediated bradycardia in response to noxious yet unperceived stimuli below the injury to reduce blood pressure. AD is frequently triggered by pelvic visceral distension (bowel and bladder), and there are documented structural relationships between injury-induced sprouting of pelvic visceral afferent C-fibers. Their excitation of lumbosacral PN, in turn, sprout and relay noxious visceral sensory stimuli to rostral disinhibited thoracic sympathetic preganglionic neurons (SPN) that manifest hypertension. Herein, we review evidence for maladaptive plasticity of PN in neural circuits mediating heightened sympathetic reflexes after complete high thoracic SCI that manifest cardiovascular dysfunction, as well as contemporary research methodologies being employed to unveil the precise contribution of PN plasticity to the pathophysiology underlying AD development.
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Affiliation(s)
- Felicia M Michael
- Department of Physiology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY, United States
| | - Samir P Patel
- Department of Physiology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY, United States
| | - Alexander G Rabchevsky
- Department of Physiology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY, United States
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Wiggins JW, Kozyrev N, Sledd JE, Wilson GG, Coolen LM. Chronic Spinal Cord Injury Reduces Gastrin-Releasing Peptide in the Spinal Ejaculation Generator in Male Rats. J Neurotrauma 2019; 36:3378-3393. [PMID: 31111794 DOI: 10.1089/neu.2019.6509] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Spinal cord injury (SCI) causes sexual dysfunction, including anejaculation in men. Likewise, chronic mid-thoracic contusion injury impairs ejaculatory reflexes in male rats. Ejaculation is controlled by a spinal ejaculation generator (SEG) comprised of a population of lumbar spinothalamic (LSt) neurons. LSt neurons co-express four neuropeptides, including gastrin-releasing peptide (GRP) and galanin and control ejaculation via release of these peptides in lumbar and sacral autonomic and motor nuclei. Here, we tested the hypothesis that contusion injury causes a disruption of the neuropeptides that are expressed in LSt cell bodies and axon terminals, thereby causing ejaculatory dysfunction. Male Sprague Dawley rats received contusion or sham surgery at spinal levels T6-7. Five to six weeks later, animals were perfused and spinal cords were immunoprocessed for galanin and GRP. Results showed that numbers of cells immunoreactive for galanin were not altered by SCI, suggesting that LSt cells are not ablated by SCI. In contrast, GRP immunoreactivity was decreased in LSt cells following SCI, evidenced by fewer GRP and galanin/GRP dual labeled cells. However, SCI did not affect efferent connections of LSt, cells as axon terminals containing galanin or GRP in contact with autonomic cells were not reduced following SCI. Finally, no changes in testosterone plasma levels or androgen receptor expression were noted after SCI. In conclusion, chronic contusion injury decreased immunoreactivity for GRP in LSt cell soma, but did not affect LSt neurons per se or LSt connections within the SEG. Since GRP is essential for triggering ejaculation, such loss may contribute to ejaculatory dysfunction following SCI.
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Affiliation(s)
- J Walker Wiggins
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi.,Graduate Program in Neuroscience, University of Mississippi Medical Center, Jackson, Mississippi
| | - Natalie Kozyrev
- Robarts Institute, Western University, London, Ontario, Canada
| | - Jonathan E Sledd
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi
| | - George G Wilson
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi
| | - Lique M Coolen
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi.,Department of Biological Sciences, Kent State University, Kent, Ohio
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Järve A, Todiras M, Lian X, Filippelli-Silva R, Qadri F, Martin RP, Gollasch M, Bader M. Distinct roles of angiotensin receptors in autonomic dysreflexia following high-level spinal cord injury in mice. Exp Neurol 2018; 311:173-181. [PMID: 30315807 DOI: 10.1016/j.expneurol.2018.10.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 09/21/2018] [Accepted: 10/09/2018] [Indexed: 12/16/2022]
Abstract
Autonomic dysreflexia (AD), a syndrome caused by loss of supraspinal control over sympathetic activity and amplified vascular reflex upon sensory stimuli below injury level, is a major health problem in high-level spinal cord injury (SCI). After supraspinal sympathetic control of the vasculature below the lesion is lost, the renin-angiotensin system (RAS) is thought to be involved in AD by regulating blood pressure and vascular reactivity. In this study, we aimed to assess the role of different RAS receptors during AD following SCI. Therefore, we induced AD by colorectal distention (CRD) in wild-type mice and mice deficient in the RAS components angiotensin (Ang) II type 1a receptor (AT1a) (Agtr1a-/-) and Ang-(1-7) receptor Mas (Mas-/-) four weeks after complete transection of spinal cord at thoracic level 4 (T4). Systemic blood pressure measurements and wire myography technique were performed to assess hemodynamics and the reactivity of peripheral arteries, respectively. CRD increased mean arterial blood pressure (MAP) and decreased heart rate (HR) in all three animal groups. However, we found less increases in MAP in Mas-/- mice compared to control mice after CRD, whereas AT1a deficiency did not affect the hemodynamic response. We found that the reactivity of wild-type and Mas-/- mesenteric arteries, which are innervated from ganglia distal but close to thoracic level T4, was diminished in response to Ang II in AD after T4-SCI, but this difference was not observed in the absence of AT1a receptors. CRD did not influence the reactivity of femoral arteries which are innervated from ganglia more distal to thoracic level T4, in response to Ang II in AD. In conclusion, we identified a specific role of the Ang-(1-7) receptor Mas in regulating the systemic blood pressure increase in AD in T4-SCI mice. Furthermore, AT1a signaling is not involved in this hemodynamic response, but underlies increased vascular reactivity in mesenteric arteries in response to Ang II, where it may contribute to adaptive changes in regional blood flow.
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Affiliation(s)
- Anne Järve
- Max Delbrück Center for Molecular Medicine (MDC) in the Helmholtz Association, Berlin, Germany; Berlin Institute of Health (BIH), Berlin, Germany.
| | - Mihail Todiras
- Max Delbrück Center for Molecular Medicine (MDC) in the Helmholtz Association, Berlin, Germany
| | - Xiaoming Lian
- Experimental and Clinical Research Center (ECRC), Charité Medical Faculty and Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany
| | - Rafael Filippelli-Silva
- Department of Biophysics, UNIFESP Universidade Federal de São Paulo, São Paulo, São Paulo 04039-032, Brazil
| | - Fatimunnisa Qadri
- Max Delbrück Center for Molecular Medicine (MDC) in the Helmholtz Association, Berlin, Germany
| | - Renan P Martin
- Department of Biophysics, UNIFESP Universidade Federal de São Paulo, São Paulo, São Paulo 04039-032, Brazil; Institute of Genetic Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | - Maik Gollasch
- Experimental and Clinical Research Center (ECRC), Charité Medical Faculty and Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany; Nephrology/Intensive Care, Virchow Klinikum, Charité - University Medicine, Berlin, Germany
| | - Michael Bader
- Max Delbrück Center for Molecular Medicine (MDC) in the Helmholtz Association, Berlin, Germany; Berlin Institute of Health (BIH), Berlin, Germany; German Center for Cardiovascular Research (DZHK), Partner Site Berlin, Berlin, Germany; Institute for Biology, University of Lübeck, Lübeck, Germany
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Biering-Sørensen F, Biering-Sørensen T, Liu N, Malmqvist L, Wecht JM, Krassioukov A. Alterations in cardiac autonomic control in spinal cord injury. Auton Neurosci 2018; 209:4-18. [DOI: 10.1016/j.autneu.2017.02.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2016] [Revised: 01/30/2017] [Accepted: 02/14/2017] [Indexed: 01/22/2023]
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11
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Vitores AA, Sloley SS, Martinez C, Carballosa-Gautam MM, Hentall ID. Some Autonomic Deficits of Acute or Chronic Cervical Spinal Contusion Reversed by Interim Brainstem Stimulation. J Neurotrauma 2017; 35:560-572. [PMID: 29160143 DOI: 10.1089/neu.2017.5123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Prolonged electrical stimulation of the hindbrain's nucleus raphe magnus (NRM) or of its major midbrain input region, the periaqueductal gray (PAG), was previously found in rats to promote recovery from sensory-motor and histological deficits of acute thoracic spinal cord injury (SCI). Here, some visceral deficits of acute and chronic midline cervical (C5) contusion are similarly examined. Cranially implanted wireless stimulators delivered intermittent 8 Hz, 30-70 μA cathodal pulse trains to a brainstem microelectrode. Injured controls were given inactive stimulators; rats without injuries or implants were also compared. Rectal distension or squeezing of the forepaws caused an exaggerated rise in mean arterial pressure in injured, untreated rats under anesthesia on post-injury week 6, probably reflecting autonomic dysreflexia (AD). These pressor responses became normal when 7 days of unilateral PAG stimulation was started on the injury day. Older untreated injuries (weeks 18-19) showed normal pressor responses, but unexpectedly had significant resting and nociceptive bradycardia, which was reversed by 3 weeks of PAG stimulation started on weeks 7 or 12. Subsequent chronic studies examined gastric emptying (GE), as indicated by intestinal transit of gavaged dye, and serum chemistry. GE and fasting serum insulin were reduced on injury weeks 14-15, and were both normalized by ∼5 weeks of PAG stimulation begun in weeks 7-8. Increases in calcitonin gene-related peptide, a prominent visceral afferent neurotransmitter, measured near untreated injuries (first thoracic segment) in superficial dorsal laminae were reversed by acutely or chronically initiated PAG stimulation. The NRM, given 2-3 weeks of stimulation beginning 2 days after SCI, prevented abnormalities in both pressor responses and GE on post-injury week 9, consistent with its relaying of repair commands from the PAG. The descending PAG-NRM axis thus exhibits broadly restorative influences on visceral as well as sensory-motor deficits, improving chronic as well as acute signs of injury.
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Affiliation(s)
- Alberto A Vitores
- Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine , Miami, Florida
| | - Stephanie S Sloley
- Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine , Miami, Florida
| | - Catalina Martinez
- Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine , Miami, Florida
| | - Melissa M Carballosa-Gautam
- Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine , Miami, Florida
| | - Ian D Hentall
- Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine , Miami, Florida
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Eldahan KC, Rabchevsky AG. Autonomic dysreflexia after spinal cord injury: Systemic pathophysiology and methods of management. Auton Neurosci 2017; 209:59-70. [PMID: 28506502 DOI: 10.1016/j.autneu.2017.05.002] [Citation(s) in RCA: 126] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 03/30/2017] [Accepted: 05/03/2017] [Indexed: 12/11/2022]
Abstract
Traumatic spinal cord injury (SCI) has widespread physiological effects beyond the disruption of sensory and motor function, notably the loss of normal autonomic and cardiovascular control. Injury at or above the sixth thoracic spinal cord segment segregates critical spinal sympathetic neurons from supraspinal modulation which can result in a syndrome known as autonomic dysreflexia (AD). AD is defined as episodic hypertension and concomitant baroreflex-mediated bradycardia initiated by unmodulated sympathetic reflexes in the decentralized cord. This condition is often triggered by noxious yet unperceived visceral or somatic stimuli below the injury level and if severe enough can require immediate medical attention. Herein, we review the pathophysiological mechanisms germane to the development of AD, including maladaptive plasticity of neural circuits mediating abnormal sympathetic reflexes and hypersensitization of peripheral vasculature that collectively contribute to abnormal hemodynamics after SCI. Further, we discuss the systemic effects of recurrent AD and pharmacological treatments used to manage such episodes. Contemporary research avenues are then presented to better understand the relative contributions of underlying mechanisms and to elucidate the effects of recurring AD on cardiovascular and immune functions for developing more targeted and effective treatments to attenuate the development of this insidious syndrome following high-level SCI.
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Affiliation(s)
- Khalid C Eldahan
- Department of Physiology, University of Kentucky, Lexington, KY 40536, United States; Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536, United States
| | - Alexander G Rabchevsky
- Department of Physiology, University of Kentucky, Lexington, KY 40536, United States; Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536, United States.
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13
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Abstract
Autonomic dysreflexia (AD) is a serious cardiovascular disorder in patients with spinal cord injury (SCI). The primary underlying cause of AD is loss of supraspinal control over sympathetic preganglionic neurons (SPNs) caudal to the injury, which renders the SPNs hyper-responsive to stimulation. Central maladaptive plasticity, including C-fiber sprouting and propriospinal fiber proliferation exaggerates noxious afferent transmission to the SPNs, causing them to release massive sympathetic discharges that result in severe hypertensive episodes. In parallel, upregulated peripheral vascular sensitivity following SCI exacerbates the hypertensive response by augmenting gastric and pelvic vasoconstriction. Currently, the majority of clinically employed treatments for AD involve anti-hypertensive medications and Botox injections to the bladder. Although these approaches mitigate the severity of AD, they only yield transient effects and target the effector organs, rather than addressing the primary issue of central sympathetic dysregulation. As such, strategies that aim to restore supraspinal reinnervation of SPNs to improve cardiovascular sympathetic regulation are likely more effective for AD. Recent pre-clinical investigations show that cell transplantation therapy is efficacious in reestablishing spinal sympathetic connections and improving hemodynamic performance, which holds promise as a potential therapeutic approach.
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Affiliation(s)
- Hisham Sharif
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Shaoping Hou
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
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Transcriptional and Epigenetic Regulation in Injury-Mediated Neuronal Dendritic Plasticity. Neurosci Bull 2016; 33:85-94. [PMID: 27730386 DOI: 10.1007/s12264-016-0071-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/27/2016] [Indexed: 12/26/2022] Open
Abstract
Injury to the nervous system induces localized damage in neural structures and neuronal death through the primary insult, as well as delayed atrophy and impaired plasticity of the delicate dendritic fields necessary for interneuronal communication. Excitotoxicity and other secondary biochemical events contribute to morphological changes in neurons following injury. Evidence suggests that various transcription factors are involved in the dendritic response to injury and potential therapies. Transcription factors play critical roles in the intracellular regulation of neuronal morphological plasticity and dendritic growth and patterning. Mounting evidence supports a crucial role for epigenetic modifications via histone deacetylases, histone acetyltransferases, and DNA methyltransferases that modify gene expression in neuronal injury and repair processes. Gene regulation through epigenetic modification is of great interest in neurotrauma research, and an early picture is beginning to emerge concerning how injury triggers intracellular events that modulate such responses. This review provides an overview of injury-mediated influences on transcriptional regulation through epigenetic modification, the intracellular processes involved in the morphological consequences of such changes, and potential approaches to the therapeutic manipulation of neuronal epigenetics for regulating gene expression to facilitate growth and signaling through dendritic arborization following injury.
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Abstract
Both sensorimotor and autonomic dysfunctions often occur after spinal cord injury (SCI). Particularly, a high thoracic or cervical SCI interrupts supraspinal vasomotor pathways and results in disordered hemodynamics due to deregulated sympathetic outflow. As a result of the reduced sympathetic activity, patients with SCI may experience hypotension, cardiac dysrhythmias, and hypothermia post-injury. In the chronic phase, changes within the CNS and blood vessels lead to orthostatic hypotension and life-threatening autonomic dysreflexia (AD). AD is characterized by an episodic, massive sympathetic discharge that causes severe hypertension associated with bradycardia. The syndrome is often triggered by unpleasant visceral or sensory stimuli below the injury level. Currently the only treatments are palliative - once a stimulus elicits AD, pharmacological vasodilators are administered to help reduce the spike in arterial blood pressure. However, a more effective means would be to mitigate AD development by attenuating contributing mechanisms, such as the reorganization of intraspinal circuits below the level of injury. A better understanding of the neuropathophysiology underlying cardiovascular dysfunction after SCI is essential to better develop novel therapeutic approaches to restore hemodynamic performance.
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Affiliation(s)
- Elizabeth Partida
- Spinal Cord Research Center, Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Eugene Mironets
- Spinal Cord Research Center, Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Shaoping Hou
- Spinal Cord Research Center, Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Veronica J Tom
- Spinal Cord Research Center, Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
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Detloff MR, Quiros-Molina D, Javia AS, Daggubati L, Nehlsen AD, Naqvi A, Ninan V, Vannix KN, McMullen MK, Amin S, Ganzer PD, Houlé JD. Delayed Exercise Is Ineffective at Reversing Aberrant Nociceptive Afferent Plasticity or Neuropathic Pain After Spinal Cord Injury in Rats. Neurorehabil Neural Repair 2015; 30:685-700. [PMID: 26671215 DOI: 10.1177/1545968315619698] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Neuropathic pain is a debilitating consequence of spinal cord injury (SCI) that correlates with sensory fiber sprouting. Recent data indicate that exercise initiated early after SCI prevents the development of allodynia and modulated nociceptive afferent plasticity. This study determined if delaying exercise intervention until pain is detected would similarly ameliorate established SCI-induced pain. Adult, female Sprague-Dawley rats with a C5 unilateral contusion were separated into SCI allodynic and SCI non-allodynic cohorts at 14 or 28 days postinjury when half of each group began exercising on automated running wheels. Allodynia, assessed by von Frey testing, was not ameliorated by exercise. Furthermore, rats that began exercise with no allodynia developed paw hypersensitivity within 2 weeks. At the initiation of exercise, the SCI Allodynia group displayed marked overlap of peptidergic and non-peptidergic nociceptive afferents in the C7 and L5 dorsal horn, while the SCI No Allodynia group had scant overlap. At the end of 5 weeks of exercise both the SCI Allodynia and SCI No Allodynia groups had extensive overlap of the 2 c-fiber types. Our findings show that exercise therapy initiated at early stages of allodynia is ineffective at attenuating neuropathic pain, but rather that it induces allodynia-aberrant afferent plasticity in previously pain-free rats. These data, combined with our previous results, suggest that there is a critical therapeutic window when exercise therapy may be effective at treating SCI-induced allodynia and that there are postinjury periods when exercise can be deleterious.
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Affiliation(s)
| | | | - Amy S Javia
- Drexel University College of Medicine, Philadelphia, PA, USA
| | | | | | - Ali Naqvi
- Drexel University College of Medicine, Philadelphia, PA, USA
| | - Vinu Ninan
- Drexel University College of Medicine, Philadelphia, PA, USA
| | | | | | - Sheena Amin
- Drexel University College of Medicine, Philadelphia, PA, USA
| | | | - John D Houlé
- Drexel University College of Medicine, Philadelphia, PA, USA
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Warren PM, Awad BI, Alilain WJ. Reprint of "Drawing breath without the command of effectors: the control of respiration following spinal cord injury". Respir Physiol Neurobiol 2014; 204:120-30. [PMID: 25266395 DOI: 10.1016/j.resp.2014.09.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The maintenance of blood gas and pH homeostasis is essential to life. As such breathing, and the mechanisms which control ventilation, must be tightly regulated yet highly plastic and dynamic. However, injury to the spinal cord prevents the medullary areas which control respiration from connecting to respiratory effectors and feedback mechanisms below the level of the lesion. This trauma typically leads to severe and permanent functional deficits in the respiratory motor system. However, endogenous mechanisms of plasticity occur following spinal cord injury to facilitate respiration and help recover pulmonary ventilation. These mechanisms include the activation of spared or latent pathways, endogenous sprouting or synaptogenesis, and the possible formation of new respiratory control centres. Acting in combination, these processes provide a means to facilitate respiratory support following spinal cord trauma. However, they are by no means sufficient to return pulmonary function to pre-injury levels. A major challenge in the study of spinal cord injury is to understand and enhance the systems of endogenous plasticity which arise to facilitate respiration to mediate effective treatments for pulmonary dysfunction.
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Affiliation(s)
- Philippa M Warren
- Department of Neurosciences, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH 44109, USA
| | - Basem I Awad
- Department of Neurosciences, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH 44109, USA; Department of Neurological Surgery, Mansoura University School of Medicine, Mansoura, Egypt
| | - Warren J Alilain
- Department of Neurosciences, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH 44109, USA.
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Kim H, Jones KE, Heckman CJ. Asymmetry in signal propagation between the soma and dendrites plays a key role in determining dendritic excitability in motoneurons. PLoS One 2014; 9:e95454. [PMID: 25083794 PMCID: PMC4118843 DOI: 10.1371/journal.pone.0095454] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2013] [Accepted: 03/27/2014] [Indexed: 12/31/2022] Open
Abstract
It is widely recognized that propagation of electrophysiological signals between the soma and dendrites of neurons differs depending on direction, i.e. it is asymmetric. How this asymmetry influences the activation of voltage-gated dendritic channels, and consequent neuronal behavior, remains unclear. Based on the analysis of asymmetry in several types of motoneurons, we extended our previous methodology for reducing a fully reconstructed motoneuron model to a two-compartment representation that preserved asymmetric signal propagation. The reduced models accurately replicated the dendritic excitability and the dynamics of the anatomical model involving a persistent inward current (PIC) dispersed over the dendrites. The relationship between asymmetric signal propagation and dendritic excitability was investigated using the reduced models while varying the asymmetry in signal propagation between the soma and the dendrite with PIC density constant. We found that increases in signal attenuation from soma to dendrites increased the activation threshold of a PIC (hypo-excitability), whereas increases in signal attenuation from dendrites to soma decreased the activation threshold of a PIC (hyper-excitability). These effects were so strong that reversing the asymmetry in the soma-to-dendrite vs. dendrite-to-soma attenuation, reversed the correlation between PIC threshold and distance of this current source from the soma. We propose the tight relation of the asymmetric signal propagation to the input resistance in the dendrites as a mechanism underlying the influence of the asymmetric signal propagation on the dendritic excitability. All these results emphasize the importance of maintaining the physiological asymmetry in dendritic signaling not only for normal function of the cells but also for biophysically realistic simulations of dendritic excitability.
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Affiliation(s)
- Hojeong Kim
- Division of Robotics Research, Daegu Gyeongbuk Institute of Science & Technology, Daegu, Korea
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, United States of America
- * E-mail:
| | - Kelvin E. Jones
- Centre for Neuroscience and Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Canada
| | - C. J. Heckman
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, United States of America
- Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, Chicago, United States of America
- Department of Physical Therapy and Human Movement Science, Northwestern University Feinberg School of Medicine, Chicago, United States of America
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19
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Detloff MR, Smith EJ, Quiros Molina D, Ganzer PD, Houlé JD. Acute exercise prevents the development of neuropathic pain and the sprouting of non-peptidergic (GDNF- and artemin-responsive) c-fibers after spinal cord injury. Exp Neurol 2014; 255:38-48. [PMID: 24560714 PMCID: PMC4036591 DOI: 10.1016/j.expneurol.2014.02.013] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 01/29/2014] [Accepted: 02/14/2014] [Indexed: 11/18/2022]
Abstract
Spinal cord injury (SCI) impaired sensory fiber transmission leads to chronic, debilitating neuropathic pain. Sensory afferents are responsive to neurotrophic factors, molecules that are known to promote survival and maintenance of neurons, and regulate sensory neuron transduction of peripheral stimuli. A subset of primary afferent fibers responds only to the glial cell-line derived neurotrophic factor (GDNF) family of ligands (GFLs) and is non-peptidergic. In peripheral nerve injury models, restoration of GDNF or artemin (another GFL) to pre-injury levels within the spinal cord attenuates neuropathic pain. One non-invasive approach to increase the levels of GFLs in the spinal cord is through exercise (Ex), and to date exercise training is the only ameliorative, non-pharmacological treatment for SCI-induced neuropathic pain. The purpose of this study was 3-fold: 1) to determine whether exercise affects the onset of SCI-induced neuropathic pain; 2) to examine the temporal profile of GDNF and artemin in the dorsal root ganglia and spinal cord dorsal horn regions associated with forepaw dermatomes after SCI and Ex; and 3) to characterize GFL-responsive sensory fiber plasticity after SCI and Ex. Adult, female, Sprague-Dawley rats received a moderate, unilateral spinal cord contusion at C5. A subset of rats was exercised (SCI+Ex) on automated running wheels for 20min, 5days/week starting at 5days post-injury (dpi), continuing until 9 or 37dpi. Hargreaves' and von Frey testing was performed preoperatively and weekly post-SCI. Forty-two percent of rats in the unexercised group exhibited tactile allodynia of the forepaws while the other 58% retained normal sensation. The development of SCI-induced neuropathic pain correlated with a marked decrease in the levels of GDNF and artemin in the spinal cord and DRGs. Additionally, a dramatic increase in the density and the distribution throughout the dorsal horn of GFL-responsive afferents was observed in rats with SCI-induced allodynia. Importantly, in SCI rats that received Ex, the incidence of tactile allodynia decreased to 7% (1/17) and there was maintenance of GDNF and artemin at normal levels, with a normal distribution of GFL-responsive fibers. These data suggest that GFLs and/or their downstream effectors may be important modulators of pain fiber plasticity, representing effective targets for anti-allodynic therapeutics. Furthermore, we highlight the potent beneficial effects of acute exercise after SCI.
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Affiliation(s)
- Megan Ryan Detloff
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA 19129, USA.
| | - Evan J Smith
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA 19129, USA
| | - Daniel Quiros Molina
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA 19129, USA
| | - Patrick D Ganzer
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA 19129, USA
| | - John D Houlé
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA 19129, USA
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20
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Detloff MR, Wade RE, Houlé JD. Chronic at- and below-level pain after moderate unilateral cervical spinal cord contusion in rats. J Neurotrauma 2013; 30:884-90. [PMID: 23216008 DOI: 10.1089/neu.2012.2632] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Chronic neuropathic pain is a significant consequence of spinal cord injury (SCI) that is associated with evoked pain, including allodynia and/or hyperalgesia. Allodynia is defined as a painful response to normally innocuous stimuli, and hyperalgesia occurs when there is an amplified pain response to normally noxious stimuli. We describe a model of a unilateral cervical level (C5) contusion injury where sensory recovery was assessed weekly for 6 weeks in 32 adult, female, Sprague-Dawley rats. Bilateral thermal hyperalgesia and tactile allodynia are detectable in the fore- and hindpaws as early as 7 days post-injury (dpi) and persist for at least 42 days. Paw withdrawal latency in response to a noxious thermal stimulus significantly intra-animal pre-operative values. Change in paw withdrawal latency plateaued at 21 dpi. Interestingly, bilateral forepaw allodynia develops in fewer than 40% of rats as measured by von Frey monofilament testing. Similar results occur in the hindpaws, where bilateral allodynia occurs in 46% of rats with SCI. The contralesional forepaw and both hindpaws of rats showed a slight increase in paw withdrawal threshold to tactile stimuli acutely after SCI, corresponding to ipsilesional forelimb motor deficits that resolve over time. That there is no difference among allodynic and non-allodynic groups in overall spared tissue or specifically of the dorsal column or ventrolateral white matter where ascending sensory tracts reside suggests that SCI-induced pain does not depend solely on the size or extent of the lesion, but that other mechanisms are in play. These observations provide a valid model system for future testing of therapeutic interventions to prevent the onset or to reduce the debilitating effects of chronic neuropathic pain after SCI.
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Affiliation(s)
- Megan Ryan Detloff
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
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21
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Weaver LC, Fleming JC, Mathias CJ, Krassioukov AV. Disordered cardiovascular control after spinal cord injury. HANDBOOK OF CLINICAL NEUROLOGY 2013; 109:213-33. [PMID: 23098715 DOI: 10.1016/b978-0-444-52137-8.00013-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Damage to the spinal cord disrupts autonomic pathways, perturbing cardiovascular homeostasis. Cardiovascular dysfunction increases with higher levels of injury and greater severity. Disordered blood pressure control after spinal cord injury (SCI) has significant ramifications as cord-injured people have an increased risk of developing heart disease and stroke; cardiovascular dysfunction is currently a leading cause of death among those with SCI. Despite the clinical significance of abnormal cardiovascular control following SCI, this problem has been generally neglected by both the clinical and research community. Both autonomic dysreflexia and orthostatic hypotension are known to prevent and delay rehabilitation, and significantly impair the overall quality of life after SCI. Starting with neurogenic shock immediately after a higher SCI, ensuing cardiovascular dysfunctions include orthostatic hypotension, autonomic dysreflexia and cardiac arrhythmias. Disordered temperature regulation accompanies these autonomic dysfunctions. This chapter reviews the human and animal studies that have furthered our understanding of the pathophysiology and mechanisms of orthostatic hypotension, autonomic dysreflexia and cardiac arrhythmias. The cardiovascular dysfunction that occurs during sexual function and exercise is elaborated. New awareness of cardiovascular dysfunction after SCI has led to progress toward inclusion of this important autonomic problem in the overall assessment of the neurological condition of cord-injured people.
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22
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Profice P, Renna R, Pilato F, Sestito A, Infusino F, Bruno I, Pravatà E, Di Lazzaro V. Cardiovascular impairment in a patient with acute myelitis. Spinal Cord 2013; 51:511-3. [DOI: 10.1038/sc.2013.30] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Bose PK, Hou J, Parmer R, Reier PJ, Thompson FJ. Altered patterns of reflex excitability, balance, and locomotion following spinal cord injury and locomotor training. Front Physiol 2012; 3:258. [PMID: 22934014 PMCID: PMC3429034 DOI: 10.3389/fphys.2012.00258] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 06/20/2012] [Indexed: 11/13/2022] Open
Abstract
Spasticity is an important problem that complicates daily living in many individuals with spinal cord injury (SCI). While previous studies in human and animals revealed significant improvements in locomotor ability with treadmill locomotor training, it is not known to what extent locomotor training influences spasticity. In addition, it would be of considerable practical interest to know how the more ergonomically feasible cycle training compares with treadmill training as therapy to manage SCI-induced spasticity and to improve locomotor function. Thus the main objective of our present studies was to evaluate the influence of different types of locomotor training on measures of limb spasticity, gait, and reflex components that contribute to locomotion. For these studies, 30 animals received midthoracic SCI using the standard Multicenter Animal Spinal cord Injury Studies (MASCIS) protocol (10 g 2.5 cm weight drop). They were divided randomly into three equal groups: control (contused untrained), contused treadmill trained, and contused cycle trained. Treadmill and cycle training were started on post-injury day 8. Velocity-dependent ankle torque was tested across a wide range of velocities (612-49°/s) to permit quantitation of tonic (low velocity) and dynamic (high velocity) contributions to lower limb spasticity. By post-injury weeks 4 and 6, the untrained group revealed significant velocity-dependent ankle extensor spasticity, compared to pre-surgical control values. At these post-injury time points, spasticity was not observed in either of the two training groups. Instead, a significantly milder form of velocity-dependent spasticity was detected at postcontusion weeks 8-12 in both treadmill and bicycle training groups at the four fastest ankle rotation velocities (350-612°/s). Locomotor training using treadmill or bicycle also produced significant increase in the rate of recovery of limb placement measures (limb axis, base of support, and open field locomotor ability) and reflex rate-depression, a quantitative assessment of neurophysiological processes that regulate segmental reflex excitability, compared with those of untrained injured controls. Light microscopic qualitative studies of spared tissue revealed better preservation of myelin, axons, and collagen morphology in both locomotor trained animals. Both locomotor trained groups revealed decreased lesion volume (rostro-caudal extension) and more spared tissue at the lesion site. These improvements were accompanied by marked upregulation of BDNF, GABA/GABA(b), and monoamines (e.g., norepinephrine and serotonin) which might account for these improved functions. These data are the first to indicate that the therapeutic efficacy of ergonomically practical cycle training is equal to that of the more labor-intensive treadmill training in reducing spasticity and improving locomotion following SCI in an animal model.
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Affiliation(s)
- Prodip K Bose
- Brain Rehabilitation Research Center, North Florida/South Georgia VA Medical Center Gainesville, FL, USA
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24
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Zahner MR, Kulikowicz E, Schramm LP. Recovery of baroreflex control of renal sympathetic nerve activity after spinal lesions in the rat. Am J Physiol Regul Integr Comp Physiol 2011; 301:R1584-90. [PMID: 21900643 PMCID: PMC3213932 DOI: 10.1152/ajpregu.00295.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Accepted: 09/03/2011] [Indexed: 02/07/2023]
Abstract
Spinal cord injury (SCI) has serious long-term consequences on sympathetic cardiovascular regulation. Orthostatic intolerance results from insufficient baroreflex regulation (BR) of sympathetic outflow to maintain proper blood pressure upon postural changes. Autonomic dysreflexia occurs due to insufficient inhibition of spinal sources of sympathetic activity. Both of these conditions result from the inability to control sympathetic activity caudal to SCI. It is well established that limited motor ability recovers after incomplete SCI. Therefore, the goal of this study was to determine whether recovery of BR occurs after chronic, left thoracic spinal cord hemisection at either T(3) or T(8). Baroreflex tests were performed in rats by measuring the reflex response of left (ipsilateral) renal sympathetic nerve activity to decreases and increases in arterial pressure produced by ramped infusions of sodium nitroprusside and phenylephrine, respectively. One week after a T(3) left hemisection, BR function was modestly impaired. However, 8 wk after a T(3) left hemisection, BR function was normal. One week after a T(8) left hemisection, BR function was significantly impaired, and 8 wk after a T(8) left hemisection, BR function was significantly improved. These results indicate that BR of renal sympathetic nerve activity in rats may partially recover after spinal cord hemisections, becoming normal by 8 wk after a T(3) lesion, but not after a T(8) lesion. The nature of the spinal cord and/or brain stem reorganization that mediates this recovery remains to be determined.
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Affiliation(s)
- Matthew R Zahner
- Dept. of Biomedical Engineering, The Johns Hopkins Univ. School of Medicine, 605 Traylor Bldg., 720 Rutland Ave., Baltimore, MD 21205, USA.
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25
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Rabchevsky AG, Kitzman PH. Latest approaches for the treatment of spasticity and autonomic dysreflexia in chronic spinal cord injury. Neurotherapeutics 2011; 8:274-82. [PMID: 21384222 PMCID: PMC3101828 DOI: 10.1007/s13311-011-0025-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Two of the most prevalent secondary complications following spinal cord injury (SCI), besides loss of function and/or sensation below the level of injury, are uncontrolled muscle spasticity and hypertensive autonomic dysreflexia. Despite the desires of the SCI community, there have been few advances in the treatment and/or management of these fundamental impediments to the quality of life associated with chronic SCI. Therefore, the purpose of this review is to focus on current drug treatment strategies that alleviate symptoms of spasticity and autonomic dysfunction. Subsequently, looking ahead, we discuss whether individuals suffering from autonomic dysreflexia and/or muscle spasms can take certain compounds that specifically and rapidly block the neurotransmission of pain into the injured spinal cord to get rapid relief for both aberrant reflexes for which painful stimuli below the level of SCI are common precipitants.
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Affiliation(s)
- Alexander G Rabchevsky
- Spinal Cord & Brain Injury Research Center, University of Kentucky, Lexington, KY 40536-0509, USA.
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Zahner MR, Schramm LP. Spinal regions involved in baroreflex control of renal sympathetic nerve activity in the rat. Am J Physiol Regul Integr Comp Physiol 2011; 300:R910-6. [PMID: 21228341 PMCID: PMC3075085 DOI: 10.1152/ajpregu.00646.2010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Accepted: 01/10/2011] [Indexed: 01/23/2023]
Abstract
Spinal cord injury causes debilitating cardiovascular disturbances. The etiology of these disturbances remains obscure, partly because the locations of spinal cord pathways important for sympathetic control of cardiovascular function have not been thoroughly studied. To elucidate these pathways, we examined regions of the thoracic spinal cord important for reflex sympathetic control of arterial pressure (AP). In anesthetized rats, baroreceptor relationships between pharmacologically induced changes in AP and changes in left renal sympathetic nerve activity (RSNA) were generated in spinally intact rats and after acute surgical hemisection of either the dorsal, left, or right T8 spinal cord. None of these individual spinal lesions prevented the baroreceptor-mediated increases in RSNA caused by decreases in AP. Thus, baroreceptor-mediated increases in RSNA in rats are mediated by relatively diffuse, bilateral, descending, excitatory projections. The ability to reduce RSNA at increased AP was impaired after both dorsal and left hemisections, and baroreceptor gain was significantly decreased. Baroreceptor-induced maximum decreases in RSNA were not affected by right hemisections. However, baroreflex gain was impaired. Because both dorsal and left hemisections, but not right hemisections, attenuated the decrease in RSNA at elevated AP, we conclude that pathways involved in the tonic inhibition of spinal sources of sympathetic activity descend ipsilaterally in the dorsal spinal cord. Our results show that many lesions that do not fully transect the spinal cord spare portions of both descending excitatory pathways that may prevent orthostatic hypotension and descending inhibitory pathways that reduce the incidence of autonomic dysreflexia.
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Affiliation(s)
- Matthew R Zahner
- Dept. of Biomedical Engineering, The Johns Hopkins Univ. School of Medicine, 605 Traylor Bldg., 720 Rutland Ave., Baltimore, MD 21205, USA.
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Nesic O, Guest JD, Zivadinovic D, Narayana PA, Herrera JJ, Grill RJ, Mokkapati VUL, Gelman BB, Lee J. Aquaporins in spinal cord injury: the janus face of aquaporin 4. Neuroscience 2010; 168:1019-35. [PMID: 20109536 PMCID: PMC2885549 DOI: 10.1016/j.neuroscience.2010.01.037] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 01/16/2010] [Accepted: 01/19/2010] [Indexed: 02/07/2023]
Abstract
Although malfunction of spinal cord water channels (aquaporins, AQP) likely contributes to severe disturbances in ion/water homeostasis after spinal cord injury (SCI), their roles are still poorly understood. Here we report and discuss the potential significance of changes in the AQP4 expression in human SCI that generates glial fibrillary acidic protein (GFAP)-labeled astrocytes devoid of AQP4, and GFAP-labeled astroglia that overexpress AQP4. We used a rat model of contusion SCI to study observed changes in human SCI. AQP4-negative astrocytes are likely generated during the process of SCI-induced replacement of lost astrocytes, but their origin and role in SCI remains to be investigated. We found that AQP4-overexpression is likely triggered by hypoxia. Our transcriptional profiling of injured rat cords suggests that elevated AQP4-mediated water influx accompanies increased uptake of chloride and potassium ions which represents a protective astrocytic reaction to hypoxia. However, unbalanced water intake also results in astrocytic swelling that can contribute to motor impairment, but likely only in milder injuries. In severe rat SCI, a low abundance of AQP4-overexpressing astrocytes was found during the motor recovery phase. Our results suggest that severe rat contusion SCI is a better model to analyze AQP4 functions after SCI. We found that AQP4 increases in the chronic post-injury phase are associated with the development of pain-like behavior in SCI rats, while possible mechanisms underlying pain development may involve astrocytic swelling-induced glutamate release. In contrast, the formation and size of fluid-filled cavities occurring later after SCI does not appear to be affected by the extent of increased AQP4 levels. Therefore, the effect of therapeutic interventions targeting AQP4 will depend not only on the time interval after SCI or animal models, but also on the balance between protective role of increased AQP4 in hypoxia and deleterious effects of ongoing astrocytic swelling.
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Affiliation(s)
- O Nesic
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA.
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Kalincik T, Jozefcikova K, Sutharsan R, Mackay-Sim A, Carrive P, Waite PME. Selected changes in spinal cord morphology after T4 transection and olfactory ensheathing cell transplantation. Auton Neurosci 2010; 158:31-8. [PMID: 20594923 DOI: 10.1016/j.autneu.2010.05.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Accepted: 05/28/2010] [Indexed: 01/17/2023]
Abstract
Spinal cord transection at T4 results in severe damage of the nervous tissue, with impairment of motor, sensory and autonomic functions. Transplantation of olfactory ensheathing cells (OECs) has the potential to improve these functions through a number of mechanisms, which include facilitation of regeneration and neuroprotection. For cardiovascular functions, we have previously shown that OECs reduce the duration of autonomic dysreflexia, without evidence of regeneration. To further understand the mechanisms underpinning this improvement, we have studied changes in selected morphological features (cavitation, non-cavity tissue loss, morphology of sympathetic preganglionic neurons and primary afferent fibre density) in the T4-transected rat spinal cord over 9 weeks, both in control and OEC-transplanted animals. T4 transection led to a number of structural changes: gradual formation of cavities, non-cavity tissue loss, a long-term increase in soma size of sympathetic preganglionic neurons and a temporary increase in the extent of their dendritic arbours, and an increase in the density of primary afferent fibres caudal to the lesion. OECs decreased the cavitation and normalised soma size of the sympathetic preganglionic neurons below the lesion, while increasing the extent of dendritic arbours in the preganglionic neurons above the lesion. Thus the OECs may contribute to the normalisation of the dysreflexic hypertension through tissue preservation and normalisation of the morphology of the preganglionic neurons caudal to the lesion, while enhancing the input on the rostral preganglionic neurons, whose vasomotor control remains intact. We hypothesise that these changes are mediated through secretion of soluble trophic factors by the transplanted OECs.
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Affiliation(s)
- Tomas Kalincik
- School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
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Llewellyn-Smith IJ. Anatomy of synaptic circuits controlling the activity of sympathetic preganglionic neurons. J Chem Neuroanat 2009; 38:231-9. [DOI: 10.1016/j.jchemneu.2009.06.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Revised: 06/01/2009] [Accepted: 06/02/2009] [Indexed: 01/17/2023]
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Hou S, Duale H, Rabchevsky AG. Intraspinal sprouting of unmyelinated pelvic afferents after complete spinal cord injury is correlated with autonomic dysreflexia induced by visceral pain. Neuroscience 2008; 159:369-79. [PMID: 19146928 DOI: 10.1016/j.neuroscience.2008.12.022] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2008] [Revised: 12/05/2008] [Accepted: 12/05/2008] [Indexed: 10/21/2022]
Abstract
Autonomic dysreflexia is a potentially life-threatening hypertensive syndrome following high thoracic (T) spinal cord injury (SCI). It is commonly triggered by noxious pelvic stimuli below the injury site that correlates with increased sprouting of primary afferent C-fibers into the lumbosacral (L/S) spinal cord. We have recently demonstrated that injury-induced plasticity of (L/S) propriospinal neurons, which relay pelvic visceral sensations to thoracolumbar sympathetic preganglionic neurons, is also correlated with the development of this syndrome. To determine the phenotype of pelvic afferent fiber sprouts after SCI, cholera toxin subunit beta (CTb) was injected into the distal colon 2 weeks post-T4 transection/sham to label colonic visceral afferents. After 1 week of transport, the (L/S) spinal cords were cryosectioned and immunohistochemically stained for CTb, the nociceptive-specific marker calcitonin gene-related peptide (CGRP), and the myelinated fiber marker RT97. Quantitative analysis showed that the density of CGRP(+) afferent fibers was significantly increased in the L/S dorsal horns of T4-transected versus sham rats, whereas RT97(+) afferent fiber density showed no change. Importantly, CTb-labeled pelvic afferent fibers were co-localized with CGRP(+) fibers, but not with RT97(+) fibers. These results suggest that the sprouting of unmyelinated nociceptive pelvic afferents following high thoracic SCI, but not myelinated fibers, contributes to hypertensive autonomic dysreflexia induced by pelvic visceral pain.
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Affiliation(s)
- S Hou
- Spinal Cord and Brain Injury Research Center, Department of Physiology, B471, Biomedical and Biological Sciences Research Building, University of Kentucky, 741 South Limestone Street, Lexington, KY 40536-0509, USA
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Hou S, Duale H, Cameron AA, Abshire SM, Lyttle TS, Rabchevsky AG. Plasticity of lumbosacral propriospinal neurons is associated with the development of autonomic dysreflexia after thoracic spinal cord transection. J Comp Neurol 2008; 509:382-99. [PMID: 18512692 PMCID: PMC2536612 DOI: 10.1002/cne.21771] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Complete thoracic (T) spinal cord injury (SCI) above the T6 level typically results in autonomic dysreflexia, an abnormal hypertensive condition commonly triggered by nociceptive stimuli below the level of SCI. Overexpression of nerve growth factor in the lumbosacral spinal cord induces profuse sprouting of nociceptive pelvic visceral afferent fibers that correlates with increased hypertension in response to noxious colorectal distension. After complete T4 SCI, we evaluated the plasticity of propriospinal neurons conveying visceral input rostrally to thoracic sympathetic preganglionic neurons. The anterograde tracer biotinylated dextran amine (BDA) was injected into the lumbosacral dorsal gray commissure (DGC) of injured/nontransected rats immediately after injury (acute) or 2 weeks later (delayed). At 1 or 2 weeks after delayed or acute injections, respectively, a higher density (P < 0.05) of BDA(+) fibers was found in thoracic dorsal gray matter of injured vs. nontransected spinal cords. For corroboration, fast blue (FB) or cholera toxin subunit beta (CTb) was injected into the T9 dorsal horns 2 weeks postinjury/nontransection. After 1 week transport, more retrogradely labeled (P < 0.05) DGC propriospinal neurons (T13-S1) were quantified in injured vs. nontransected cords. We also monitored immediate early gene c-fos expression following colorectal distension and found increased (P < 0.01) c-Fos(+) cell numbers throughout the DGC after injury. Collectively, these results imply that, in conjunction with local primary afferent fiber plasticity, injury-induced sprouting of DGC neurons may be a key constituent in relaying visceral sensory input to sympathetic preganglionic neurons that elicit autonomic dysreflexia after high thoracic SCI.
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Affiliation(s)
- Shaoping Hou
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
- Department of Physiology, University of Kentucky, Lexington, KY 40536−0509
| | - Hanad Duale
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
- Department of Physiology, University of Kentucky, Lexington, KY 40536−0509
| | - Adrian A. Cameron
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
| | - Sarah M. Abshire
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
| | - Travis S. Lyttle
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
| | - Alexander G. Rabchevsky
- Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40536−0509
- Department of Physiology, University of Kentucky, Lexington, KY 40536−0509
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Laird AS, Finch AM, Waite PME, Carrive P. Peripheral changes above and below injury level lead to prolonged vascular responses following high spinal cord injury. Am J Physiol Heart Circ Physiol 2007; 294:H785-92. [PMID: 18055525 DOI: 10.1152/ajpheart.01002.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Autonomic dysreflexia (AD) is a debilitating disorder producing episodes of extreme hypertension in patients with high-level spinal cord injury (SCI). Factors leading to AD include loss of vasomotor baroreflex control to regions below injury level, changes in spinal circuitry, and peripheral changes. The present study tested for peripheral changes below and above injury level 6 wk after a transection at the fourth thoracic spinal level. Changes in vascular conductance were recorded in the femoral, renal, brachial, and carotid arteries in response to intravenous injections of two alpha-adrenergic agonists, phenylephrine (PE; 0.03-100 microg/kg) and methoxamine (Meth; 1-300 microg/kg). Unlike PE, Meth is not subject to neuronal reuptake. Ganglionic blockade (0.6 mg/kg chlorisondamine) was used to eliminate the central component of the cardiovascular response. After ganglionic blockade, SCI animals exhibited prolonged vasoconstriction in response to PE in all blood vessels measured compared with those in intact animals (all, P < 0.035). However, the PE dose-response curves obtained after ganglionic blockade revealed no significant difference in the potency between the two groups (all, P > 0.06), indicating that the prolonged vasoconstriction was not due to supersensitivity to PE. In contrast to PE, vascular responses to Meth did not vary between intact and SCI groups (all P > 0.108). These results show the development of a widespread peripheral change producing prolonged vasoconstriction in response to PE, but not Meth, possibly due to reduced neuronal reuptake of PE after SCI. This is the first study to report such a change in blood vessels not only below but also above injury level. Interventions to correct this reduced reuptake may help limit the development of AD.
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Affiliation(s)
- A S Laird
- Department of Anatomy, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia
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Zimmer MB, Nantwi K, Goshgarian HG. Effect of spinal cord injury on the respiratory system: basic research and current clinical treatment options. J Spinal Cord Med 2007; 203:98-108. [PMID: 17853653 DOI: 10.1016/j.resp.2014.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 08/11/2014] [Accepted: 08/12/2014] [Indexed: 02/09/2023] Open
Abstract
Spinal cord injury (SCI) often leads to an impairment of the respiratory system. The more rostral the level of injury, the more likely the injury will affect ventilation. In fact, respiratory insufficiency is the number one cause of mortality and morbidity after SCI. This review highlights the progress that has been made in basic and clinical research, while noting the gaps in our knowledge. Basic research has focused on a hemisection injury model to examine methods aimed at improving respiratory function after SCI, but contusion injury models have also been used. Increasing synaptic plasticity, strengthening spared axonal pathways, and the disinhibition of phrenic motor neurons all result in the activation of a latent respiratory motor pathway that restores function to a previously paralyzed hemidiaphragm in animal models. Human clinical studies have revealed that respiratory function is negatively impacted by SCI. Respiratory muscle training regimens may improve inspiratory function after SCI, but more thorough and carefully designed studies are needed to adequately address this issue. Phrenic nerve and diaphragm pacing are options available to wean patients from standard mechanical ventilation. The techniques aimed at improving respiratory function in humans with SCI have both pros and cons, but having more options available to the clinician allows for more individualized treatment, resulting in better patient care. Despite significant progress in both basic and clinical research, there is still a significant gap in our understanding of the effect of SCI on the respiratory system.
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Affiliation(s)
- M Beth Zimmer
- Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan 48201, USA.
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Laird AS, Carrive P, Waite PME. Cardiovascular and temperature changes in spinal cord injured rats at rest and during autonomic dysreflexia. J Physiol 2006; 577:539-48. [PMID: 16973703 PMCID: PMC1890430 DOI: 10.1113/jphysiol.2006.116301] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In patients with high spinal cord injuries autonomic dysfunction can be dangerous, leading to medical complications such as postural hypotension, autonomic dysreflexia and temperature disturbance. While animal models have been developed to study autonomic dysreflexia, associated temperature changes have not been documented. Our aim here was to use radiotelemetry and infrared thermography in rodents to record the development of cardiovascular and skin temperature changes following complete T4 transection. In adult male Wistar rats (n=5), responses were assessed prior to spinal cord injury (intact) and for 6 weeks following injury. Statistical analysis by a repeated-measure ANOVA revealed that following spinal cord injury (SCI), rats exhibited decreased mean arterial pressure (MAP, average decrease of 26 mmHg; P<0.035) and elevated heart rate (HR, average increase of 65 bpm, P<0.035) at rest. The basal core body temperature following SCI was also significantly lower than intact levels (-0.9 degrees C; P<0.0035). Associated with this decreased basal core temperature following SCI was an increased skin temperature of the mid-tail and hindpaw (+5.6 and +4.0 degrees C, respectively; P<0.0003) consistent with decreased cutaneous vasoconstrictor tone. Autonomic dysreflexia, in response to a 1 min colorectal distension (25 mmHg), was fully developed by 4 weeks after spinal cord transection, producing increases in MAP greater than 25 mmHg (P<0.0003). In contrast to the tachycardia seen in intact animals in response to colorectal distension, SCI animals exhibited bradycardia (P<0.0023). During episodes of autonomic dysreflexia mid-tail surface temperature decreased (approximately -1.7 degrees C, P<0.012), consistent with cutaneous vasoconstriction. This is the first study to compare cardiovascular dysfunction with temperature changes following spinal cord transection in rats.
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Affiliation(s)
- A S Laird
- Department of Anatomy, School of Medical Sciences, University of New South Wales, NSW 2052, Sydney, Australia
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Llewellyn-Smith IJ, Weaver LC, Keast JR. Effects of spinal cord injury on synaptic inputs to sympathetic preganglionic neurons. PROGRESS IN BRAIN RESEARCH 2006; 152:11-26. [PMID: 16198690 DOI: 10.1016/s0079-6123(05)52001-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Spinal cord injuries often lead to disorders in the control of autonomic function, including problems with blood pressure regulation, voiding, defecation and reproduction. The root cause of all these problems is the destruction of brain pathways that control spinal autonomic neurons lying caudal to the lesion. Changes induced by spinal cord injuries have been most extensively studied in sympathetic preganglionic neurons, cholinergic autonomic neurons with cell bodies in the lateral horn of thoracic and upper lumbar spinal cord that are the sources of sympathetic outflow. After an injury, sympathetic preganglionic neurons in mid-thoracic cord show plastic changes in their morphology. There is also extensive loss of synaptic input from the brain, leaving these neurons profoundly denervated in the acute phase of injury. Our recent studies on sympathetic preganglionic neurons in lower thoracic and upper lumbar cord that regulate the pelvic viscera suggest that these neurons are not so severely affected by spinal cord injury. Spinal interneurons appear to contribute most of the synaptic input to these neurons so that injury does not result in extensive denervation. Since intraspinal circuitry remains intact after injury, drug treatments targeting these neurons should help to normalize sympathetically mediated pelvic visceral reflexes. Furthermore, sympathetic pelvic visceral control may be more easily restored after an injury because it is less dependent on the re-establishment of direct synaptic input from regrowing brain axons.
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Affiliation(s)
- Ida J Llewellyn-Smith
- Cardiovascular Medicine and Centre for Neuroscience, Flinders University, Bedford Park, SA 5042, Australia.
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36
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Rabchevsky AG. Segmental organization of spinal reflexes mediating autonomic dysreflexia after spinal cord injury. PROGRESS IN BRAIN RESEARCH 2006; 152:265-74. [PMID: 16198706 PMCID: PMC3529572 DOI: 10.1016/s0079-6123(05)52017-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Spinal cord injuries above mid-thoracic levels can lead to a potentially life-threatening hypertensive condition termed autonomic dysreflexia that is often triggered by distension of pelvic viscera (bladder or bowel). This syndrome is characterized by episodic hypertension due to sudden, massive discharge of sympathetic preganglionic neurons in the thoracolumbar spinal cord. This hypertension is usually accompanied by bradycardia, particularly if the injury is caudal to the 2nd to 4th thoracic spinal segments. The development of autonomic dysreflexia is correlated with aberrant sprouting of peptidergic afferent fibers into the spinal cord below the injury. In particular, sprouting of nerve growth factor-responsive afferent fibers has been shown to have a major influence on dysreflexia, perhaps by amplifying the activation of disinhibited sympathetic neurons. Using a model of noxious bowel distension after complete thoracic spinal transection at the 4th thoracic segment in rats, we selectively altered C-fiber sprouting, at specified spinal levels caudal to the injury, with microinjections of adenovirus encoding the growth-promoting nerve growth factor or the growth-inhibitory semaphorin 3A. This was followed by assessment of physiological responses to colorectal distension and subsequent histology. Additionally, anterograde tract tracers were injected into the lumbosacral region to compare the extent of labeled propriospinal rostral projections in uninjured cords to those in cords after complete 4th thoracic transection. In summary, overexpression of chemorepulsive semaphorin 3A impeded C-fiber sprouting in lumbosacral segments and mitigated hypertensive autonomic dysreflexia, whereas the opposite results were obtained with nerve growth factor overexpression. Furthermore, compared to naïve rats, there were significantly more labeled lumbosacral propriospinal projections rostrally after thoracic injury. Collectively, our findings suggest that distension of pelvic viscera increases the excitation of expanded afferent terminals in the disinhibited lumbosacral spinal cord. This, in turn, triggers excitation and sprouting of local propriospinal neurons to relay visceral sensory stimuli and amplify the activation of sympathetic preganglionic neurons in the thoracolumbar cord, to enhance transmission in the spinal viscero-sympathetic reflex pathway. These responses are manifested as autonomic dysreflexia.
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Affiliation(s)
- Alexander G Rabchevsky
- University of Kentucky, Spinal Cord & Brain Injury Research Center and Department of Physiology, 741 South Limestone Street, B371 BBSRB, Lexington, KY 40536-0509, USA.
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Weaver LC, Marsh DR, Gris D, Brown A, Dekaban GA. Autonomic dysreflexia after spinal cord injury: central mechanisms and strategies for prevention. PROGRESS IN BRAIN RESEARCH 2006; 152:245-63. [PMID: 16198705 DOI: 10.1016/s0079-6123(05)52016-8] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Spinal reflexes dominate cardiovascular control after spinal cord injury (SCI). These reflexes are no longer restrained by descending control and they can be impacted by degenerative and plastic changes within the injured cord. Autonomic dysreflexia is a condition of episodic hypertension that stems from spinal reflexes initiated by sensory input entering the spinal cord caudal to the site of injury. This hypertension greatly detracts from the quality of life for people with cord injury and can be life-threatening. Changes in the spinal cord contribute substantially to the development of this condition. Rodent models are ideal for investigating these changes. Within the spinal cord, injury-induced plasticity leads to nerve growth factor (NGF)-dependent enlargement of the central arbor of a sub-population of sensory neurons. This enlarged arbor can provide increased afferent input to the spinal reflex, intensifying autonomic dysreflexia. Treatments such as antibodies against NGF can limit this afferent sprouting, and diminish the magnitude of dysreflexia. To assess treatments, a compression model of SCI that leads to progressive secondary damage, and also to some white matter sparing, is very useful. The types of spinal reflexes that likely mediate autonomic dysreflexia are highly susceptible to inhibitory influences of bulbospinal pathways traversing the white matter. Compression models of cord injury reveal that treatments that spare white matter axons also markedly reduce autonomic dysreflexia. One such treatment is an antibody to the integrin CD11d expressed by inflammatory leukocytes that enter the cord acutely after injury and cause significant secondary damage. This antibody blocks integrin-mediated leukocyte entry, resulting in greatly reduced white-matter damage and decreased autonomic dysreflexia after cord injury. Understanding the mechanisms for autonomic dysreflexia will provide us with strategies for treatments that, if given early after cord injury, can prevent this serious disorder from developing.
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Affiliation(s)
- Lynne C Weaver
- Spinal Cord Injury Team, BioTherapeutics Research Group, Robarts Research Institute, 100 Perth Drive, P.O. Box 5015, London, ON N6A 5K8, Canada.
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Abstract
Autonomic dysreflexia is a potentially life-threatening condition in which episodic hypertension occurs after injuries above the mid-thoracic segments of the spinal cord. Despite the seriousness of this condition, little is known of the molecular mechanisms that lead to its development. The completed sequencing of the mouse genome, its dense genetic map, and the large repository of engineered and spontaneous mouse mutants, make the mouse an ideal model organism in which to study the molecular mechanisms underlying autonomic dysreflexia. We subjected two wild-type strains of mice, 129Sv and C57BL/6, and one spontaneous mouse mutant, Wallerian degeneration slow (Wld s), to spinal cord transection and clip-compression injury. We found that the incidence of autonomic dysreflexia is greatly reduced, compared to spinal cord-transected wild-type mice, in Wld s mice after both injury paradigms and in 129Sv and C57BL/6 that have undergone the clip-compression injury. We also found that the amplitude of the dysreflexic response was greater in cord-compressed 129Sv than in C57BL/6 mice. These results implicate axonal degeneration as an important source of signals that trigger the development of autonomic dysreflexia and are discussed in the context of mouse genetics, interstrain differences and possible molecular mechanisms underlying autonomic dysreflexia after spinal cord injury.
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Affiliation(s)
- A Brown
- Biotherapeutics Research Group, The Spinal Cord Injury Team, Robarts Research Institute and The Graduate Program in Neuroscience, The University of Western Ontario, P.O. Box 5015, 100 Perth Drive, London, ON N6A 5K8, Canada.
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39
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Schramm LP. Spinal sympathetic interneurons: Their identification and roles after spinal cord injury. PROGRESS IN BRAIN RESEARCH 2006; 152:27-37. [PMID: 16198691 DOI: 10.1016/s0079-6123(05)52002-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Primary afferent neurons rarely, if ever, synapse on the sympathetic preganglionic neurons that regulate the cardiovascular system, nor do sympathetic preganglionic neurons normally exhibit spontaneous activity in the absence of excitatory inputs. Therefore, after serious spinal cord injury "spinal sympathetic interneurons" provide the sole excitatory and inhibitory inputs to sympathetic preganglionic neurons. Few studies have addressed the anatomy and physiology of spinal sympathetic interneurons, to a great extent because they are difficult to identify. Therefore, this chapter begins with descriptions of both neurophysiological and neuroanatomical criteria for identifying spinal sympathetic interneurons, and it discusses the advantages and disadvantages of each. Spinal sympathetic interneurons also have been little studied because their importance in intact animals has been unknown, whereas the roles of direct projections from the brain to sympathetic preganglionic neurons are better known. This chapter presents evidence that spinal sympathetic interneurons play only a minor role in sympathetic regulation when the spinal cord is intact. However, they play an important role after spinal cord injury, both in generating ongoing activity in sympathetic nerves and in mediating segmental and intersegmental sympathetic reflexes. The spinal sympathetic interneurons that most directly influence the activity of sympathetic preganglionic neurons after spinal cord injury are located close to their associated sympathetic preganglionic neurons, and the inputs from distant segments that mediate multisegmental reflexes are relayed to sympathetic preganglionic neurons multisynaptically via spinal sympathetic interneurons. Finally, spinal sympathetic interneurons are more likely to be excited and less likely to be inhibited by both noxious and innocuous somatic stimuli after chronic spinal transection. The onset of this hyperexcitability corresponds to morphological changes in both sympathetic preganglionic neurons and primary afferents, and it may reflect the pathophysiological processes that lead to autonomic dysreflexia and the hypertensive crises that may occur with it in people after chronic spinal injury.
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Affiliation(s)
- Lawrence P Schramm
- Department of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Guízar-Sahagún G, Grijalva I, Salgado-Ceballos H, Espitia A, Orozco S, Ibarra A, Martínez A, Franco-Bourland RE, Madrazo I. Spontaneous and induced aberrant sprouting at the site of injury is irrelevant to motor function outcome in rats with spinal cord injury. Brain Res 2004; 1013:143-51. [PMID: 15193522 DOI: 10.1016/j.brainres.2004.03.062] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/02/2004] [Indexed: 11/24/2022]
Abstract
In the absence of effective regeneration following spinal cord (SC) injury, sprouting from undamaged axons has been regarded as an underlying factor for functional improvement after incomplete SC injury. The influence of spontaneous and induced axonal sprouting at the injury site on motor function was tested using rats subjected to moderate SC contusion at T9 level, using megadoses of methylprednisolone (MP) and intralesion implantation of cells from sciatic nerve (PNI). Groups using MP and PNI combined, implant vehicle, and injury with no treatment were also included. Amount of sprouting at the injury sites was significantly different depending on treatment. It was abundant in PNI-treated rats, moderate in rats treated with vehicle or nontreated, and limited in rats given MP with or without PNI (chi2, p=0.0084). This sprouting showed an aberrant course and was located in proliferating tissue at the site of injury, characterized by the presence of ependymal cells, macrophages, and myelinating and nonmyelinating Schwann cells. Functional scores and amount of spared white matter were not significantly different among groups. Correlation of the amount of sprouting vs. functional outcome or vs. amount of spared tissue was not significant, while correlation of functional outcome vs. amount of spared tissue was significant (p<0.0001). In conclusion, PNI increase aberrant sprouting at the injury site, while MP limits such sprouting, in either case without impact on motor function outcome. Missing guiding channels for sprouting axons could explain the absence of any functional improvement.
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Abstract
Most experimental studies of spinal cord injury have centered on the rat as an experimental model. A shift toward a mouse model has occurred in recent years because of its usefulness as a genetic tool. While many studies have concentrated on motor function and the inflammatory response following spinal cord injury in the mouse, the development of autonomic dysreflexia after injury has yet to be described. Autonomic dysreflexia is a condition in which episodic hypertension develops after injuries above the mid-thoracic segment of the spinal cord. In this study 129Sv mice received a spinal cord transection at the second thoracic segment. The presence of autonomic dysreflexia was assessed 2 weeks later. Blood pressure responses to stimulation were as follows: moderate cutaneous pinch caudal to the injury (35+/-6 mm Hg), tail pinch (25+/-7 mm Hg), and a 0.3 ml balloon distension of the colon (37+/-4 mm Hg). Previous reports have suggested that small diameter primary afferent fiber sprouting after spinal cord injury may be responsible for the development of autonomic dysreflexia. In order to determine whether autonomic dysreflexia in the mouse may be caused by a similar mechanism, the size of the small diameter primary afferent arbor in spinal cord-injured and sham-operated animals was assessed by measuring the area occupied by calcitonin gene-related peptide-immunoreactive fibers. The percentage increase in the area of the small diameter primary afferent arbor in transected over sham-operated spinal cords was 46%, 45% and 80% at spinal segments thoracic T5-8, thoracic T9-12 and thoracic T13-lumbar L2 respectively. This study demonstrates the development of autonomic dysfunction in a mouse model of spinal cord injury that is associated with sprouting of calcitonin gene-related peptide fibers. These results provide strong support for the use of this mouse model of spinal cord injury in the study of autonomic dysreflexia.
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Affiliation(s)
- J E Jacob
- Neurodegeneration Research Group, The John Robarts Research Institute, London, Canada
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Llewellyn-Smith IJ, Weaver LC. Changes in synaptic inputs to sympathetic preganglionic neurons after spinal cord injury. J Comp Neurol 2001; 435:226-40. [PMID: 11391643 DOI: 10.1002/cne.1204] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Spinal cord injury (SCI) leads to plastic changes in organization that impact significantly on central nervous control of arterial pressure. SCI causes hypotension and autonomic dysreflexia, an episodic hypertension induced by spinal reflexes. Sympathetic preganglionic neurons (SPNs) respond to SCI by retracting and then regrowing their dendrites within 2 weeks of injury. We examined changes in synaptic input to SPNs during this time by comparing the density and amino acid content of synaptic input to choline acetyltransferase (ChAT)-immunoreactive SPNs in the eighth thoracic spinal cord segment (T8) in unoperated rats and in rats at 3 days or at 14 days after spinal cord transection at T4. Postembedding immunogold labeling demonstrated immunoreactivity for glutamate or gamma-aminobutyric acid (GABA) within presynaptic profiles. We counted the number of presynaptic inputs to measured lengths of SPN somatic and dendritic membrane and identified the amino acid in each input. We also assessed gross changes in the morphology of SPNs using retrograde labeling with cholera toxin B and light microscopy to determine the structural changes that were present at the time of evaluation of synaptic density and amino acid content. At 3 days after SCI, we found that retrogradely labeled SPNs had shrunken somata and greatly shortened dendrites. Synaptic density (inputs per 10-microm membrane) decreased on ChAT-immunoreactive somata by 34% but increased on dendrites by 66%. Almost half of the inputs to SPNs lacked amino acids. By 14 days, the density of synaptic inputs to dendrites and somata decreased by 50% and 70%, respectively, concurrent with dendrite regrowth. The proportion of glutamatergic inputs to SPNs in spinal cord-transected rats ( approximately 40%) was less than that in unoperated rats, whereas the GABAergic proportion (60-68%) increased. In summary, SPNs participate in vasomotor control after SCI despite profound denervation. An altered balance of excitatory and inhibitory inputs may explain injury-induced hypotension.
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Affiliation(s)
- I J Llewellyn-Smith
- Cardiovascular Neuroscience Group, Cardiovascular Medicine and Centre for Neuroscience, Flinders University, Bedford Park, South Australia 5042, Australia.
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Abstract
Many studies failed to identify a hypercoagulable imbalance in the blood factors or decreased anticoagulant activity. On the other hand, fibrinolysis, a process unrelated to hypercoagulability but closely related to endothelial cell integrity, is predictably altered and contributes to the persistence of venous occlusion by thrombosis. There is considerable evidence that interruption of neurologic impulses and the ensuing paralysis cause metabolic changes in blood vessels and that blood vessel changes are accountable for venous thrombosis. Altered venous competence with complete spinal cord injury manifests by a decrease in venous distensibility and capacity and an increase in venous flow resistance. Vascular adaptations to inactivity and muscle atrophy, rather than the effect of a nonworking leg-muscle pump and sympathetic denervation, seem to lead to the thrombosis; indicating that thrombosis resulting from venous incompetence cannot be reversed by anticoagulation alone.
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Affiliation(s)
- A R Miranda
- Department of Medicine, Michigan State University, East Lansing, USA
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Abstract
After spinal cord injury, hyper-reflexia can lead to episodic hypertension, muscle spasticity and urinary bladder dyssynergia. This condition may be caused by primary afferent fiber sprouting providing new input to partially denervated spinal interneurons, autonomic neurons and motor neurons. However, conflicting reports concerning afferent neurite sprouting after cord injury do not provide adequate information to associate sprouting with hyper-reflexia. Therefore, we studied the effect of mid-thoracic spinal cord transection on central projections of sensory neurons, quantified by area measurements. The area of myelinated afferent arbors, immunolabeled by cholera toxin B, was greater in laminae I-V in lumbar, but not thoracic cord, by one week after cord transection. Changes in small sensory neurons and their unmyelinated fibers, immunolabeled for calcitonin gene-related peptide, were assessed in the cord and in dorsal root ganglia. The area of calcitonin gene-related peptide-immunoreactive fibers in laminae III-V increased in all cord segments at two weeks after cord transection, but not at one week. Numbers of sensory neurons immunoreactive for calcitonin gene-related peptide were unchanged, suggesting that the increased area of immunoreactivity reflected sprouting rather than peptide up-regulation. Immunoreactive fibers in the lateral horn increased only above the lesion and in lumbar segments at two weeks after cord transection. They were not continuous with dorsal horn fibers, suggesting that they were not primary afferent fibers. Using the fluorescent tracer DiI to label afferent fibers, an increase in area could be seen in Clarke's nucleus caudal to the injury two weeks after transection. In conclusion, site- and time-dependent sprouting of myelinated and unmyelinated primary afferent fibers, and possibly interneurons, occurred after spinal cord transection. Afferent fiber sprouting did not reach autonomic or motor neurons directly, but may cause hyper-reflexia by increasing inputs to interneurons.
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Affiliation(s)
- N R Krenz
- The John P. Robarts Research Institute and The Neuroscience Program, University of Western Ontario, London, Canada
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