Role of the blood-spinal cord barrier in posttraumatic syringomyelia

Transplantation of miR-145a-5p modified M2 type microglia promotes the tissue repair of spinal cord injury in mice

BACKGROUND

The traumatic spinal cord injury (SCI) can cause immediate multi-faceted function loss or paralysis. Microglia, as one of tissue resident macrophages, has been reported to play a critical role in regulating inflammation response during SCI processes. And transplantation with M2 microglia into SCI mice promotes recovery of motor function. However, the M2 microglia can be easily re-educated and changed their phenotype due to the stimuli of tissue microenvironment. This study aimed to find a way to maintain the function of M2 microglia, which could exert an anti-inflammatory and pro-repair role, and further promote the repair of spinal cord injury.

METHODS

To establish a standard murine spinal cord clip compression model using Dumont tying forceps. Using FACS, to sort microglia from C57BL/6 mice or CX3CR1GFP mice, and further culture them in vitro with different macrophage polarized medium. Also, to isolate primary microglia using density gradient centrifugation with the neonatal mice. To transfect miR-145a-5p into M2 microglia by Lipofectamine2000, and inject miR-145a-5p modified M2 microglia into the lesion sites of spinal cord for cell transplanted therapy. To evaluate the recovery of motor function in SCI mice through behavior analysis, immunofluorescence or histochemistry staining, Western blot and qRT-PCR detection. Application of reporter assay and molecular biology experiments to reveal the mechanism of miR-145a-5p modified M2 microglia therapy on SCI mice.

RESULTS

With in vitro experiments, we found that miR-145a-5p was highly expressed in M2 microglia, and miR-145a-5p overexpression could suppress M1 while promote M2 microglia polarization. And then delivery of miR-145a-5p overexpressed M2 microglia into the injured spinal cord area significantly accelerated locomotive recovery as well as prevented glia scar formation and neuron damage in mice, which was even better than M2 microglia transplantation. Further mechanisms showed that overexpressed miR-145a-5p in microglia inhibited the inflammatory response and maintained M2 macrophage phenotype by targeting TLR4/NF-κB signaling.

CONCLUSIONS

These findings indicate that transplantation of miR-145a-5p modified M2 microglia has more therapeutic potential for SCI than M2 microglia transplantation from epigenetic perspective.

Long-Term Impairment of the Blood-Spinal Cord Barrier in Patients With Post-Traumatic Syringomyelia and its Effect on Prognosis

STUDY DESIGN

Cohort study.

OBJECTIVE

The aim of this study was to explore the association between blood-spinal cord barrier (BSCB) markers and other factors associated with an unfavorable outcome among patients with post-traumatic syringomyelia (PTS) who achieved successful intradural adhesion lysis (IAL).

SUMMARY OF BACKGROUND DATA

Only approximately half of PTS patients receiving IAL have a favorable outcome.

PATIENTS AND METHODS

Forty-six consecutive patients with PTS and 19 controls (CTRL) were enrolled. All PTS patients underwent physical and neurological examinations and spinal magnetic resonance imaging before and 3 to 12 months after IAL. All patients underwent myelography before surgery. BSCB disruption was detected by increased intrathecal and serum concentrations of albumin, immunoglobulin (Ig)G, IgA, and IgM. A multivariable analysis was performed with a logistic regression model to identify factors associated with unfavorable outcomes. Receiver operating characteristic curves were calculated to investigate the diagnostic value of biomarkers.

RESULTS

The ages and general health of the PTS and CTRL groups did not differ significantly. QAlb, IGAQ, IGGQ, and IGMQ was significantly higher in PTS patients than in controls ( P =<0.001). The degree of intradural adhesion was significantly higher in the unfavorable outcome group than in the favorable outcome group ( P <0.0001). QAlb, immunoglobulin (Ig)AQ, IGGQ, and IGMQ was significantly correlated with clinical status ( R =-0.38, P <0.01; R =-0.47, P =0.03; R =-0.56, P =0.01; R =-0.43, P =0.05, respectively). Higher QAlb before surgery (odds ratio=2.66; 95% CI: 1.134-6.248) was significantly associated with an unfavorable outcome. The receiver operating characteristic curve analysis demonstrated a cutoff for QAlb higher than 10.62 with a specificity of 100% and sensitivity of 96.3%.

CONCLUSION

This study is the first to detect increased permeability and BSCB disruption in PTS patients. QAlb>10.62 was significantly associated with unfavorable clinical outcomes following intradural decompression.

LEVEL OF EVIDENCE

Level III-prognostic.

Role of Preoperative Albumin Quotient in Surgical Planning for Posttraumatic Syringomyelia: A Comparative Cohort Study

OBJECTIVE

Surgical procedures for patients with posttraumatic syringomyelia (PTS) remain controversial. Until now, there have been no effective quantitative evaluation methods to assist in selecting appropriate surgical plans before surgery.

METHODS

We consecutively enrolled PTS patients (arachnoid lysis group, n = 42; shunting group, n = 14) from 2003 to 2023. Additionally, 19 intrathecal anesthesia patients were included in the control group. All patients with PTS underwent physical and neurological examinations and spinal magnetic resonance imaging preoperatively, 3-12 months postoperatively and during the last follow-up. Preoperative lumbar puncture was performed and blood-spinal cord barrier disruption was detected by quotient of albumin (Qalb, cerebrospinal fluid/serum).

RESULTS

The ages (p = 0.324) and sex (p = 0.065) of the PTS and control groups did not differ significantly. There were also no significant differences in age (p = 0.216), routine blood data and prognosis (p = 0.399) between the arachnoid lysis and shunting groups. But the QAlb level of PTS patients was significantly higher than that of the control group (p < 0.001), and the shunting group had a significantly higher QAlb (p < 0.001) than the arachnoid lysis group. A high preoperative QAlb (odds ratio, 1.091; 95% confidence interval, 1.004-1.187; p = 0.041) was identified as the predictive factor for the shunting procedure, with the receiver operating characteristic curve showing 100% specificity and 80.95% sensitivity for patients with a QAlb > 12.67.

CONCLUSION

Preoperative QAlb is a significant predictive factor for the types of surgery. For PTS patients with a QAlb > 12.67, shunting represents the final recourse, necessitating the exploration and development of novel treatments for these patients.

Pericyte-derived exosomal miR-210 improves mitochondrial function and inhibits lipid peroxidation in vascular endothelial cells after traumatic spinal cord injury by activating JAK1/STAT3 signaling pathway

BACKGROUND

Spinal cord injury (SCI) remains a significant health concern, with limited available treatment options. This condition poses significant medical, economic, and social challenges. SCI is typically categorized into primary and secondary injuries. Inflammation, oxidative stress, scar formation, and the immune microenvironment impede axon regeneration and subsequent functional restoration. Numerous studies have shown that the destruction of the blood-brain barrier (BBB) and microvessels is a crucial factor in severe secondary injury. Additionally, reactive oxygen species (ROS)-induced lipid peroxidation significantly contributes to endothelial cell death. Pericytes are essential constituents of the BBB that share the basement membrane with endothelial cells and astrocytes. They play a significant role in the establishment and maintenance of BBB.

RESULTS

Immunofluorescence staining at different time points revealed a consistent correlation between pericyte coverage and angiogenesis, suggesting that pericytes promote vascular repair via paracrine signaling. Pericytes undergo alterations in cellular morphology and the transcriptome when exposed to hypoxic conditions, potentially promoting angiogenesis. We simulated an early ischemia-hypoxic environment following SCI using glucose and oxygen deprivation and BBB models. Co-culturing pericytes with endothelial cells improved barrier function compared to the control group. However, this enhancement was reduced by the exosome inhibitor, GW4869. In vivo injection of exosomes improved BBB integrity and promoted motor function recovery in mice following SCI. Subsequently, we found that pericyte-derived exosomes exhibited significant miR-210-5p expression based on sequencing analysis. Therefore, we performed a series of gain- and loss-of-function experiments in vitro.

CONCLUSION

Our findings suggest that miR-210-5p regulates endothelial barrier function by inhibiting JAK1/STAT3 signaling. This process is achieved by regulating lipid peroxidation levels and improving mitochondrial function, suggesting a potential mechanism for restoration of the blood-spinal cord barrier (BSCB) after SCI.

Blood-spinal cord barrier disruption in degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) is the most prevalent cause of spinal cord dysfunction in the aging population. Significant neurological deficits may result from a delayed diagnosis as well as inadequate neurological recovery following surgical decompression. Here, we review the pathophysiology of DCM with an emphasis on how blood-spinal cord barrier (BSCB) disruption is a critical yet neglected pathological feature affecting prognosis. In patients suffering from DCM, compromise of the BSCB is evidenced by elevated cerebrospinal fluid (CSF) to serum protein ratios and abnormal contrast-enhancement upon magnetic resonance imaging (MRI). In animal model correlates, there is histological evidence of increased extravasation of tissue dyes and serum contents, and pathological changes to the neurovascular unit. BSCB dysfunction is the likely culprit for ischemia-reperfusion injury following surgical decompression, which can result in devastating neurological sequelae. As there are currently no therapeutic approaches specifically targeting BSCB reconstitution, we conclude the review by discussing potential interventions harnessed for this purpose.

Aquaporin-4 expression and modulation in a rat model of post-traumatic syringomyelia

Aquaporin-4 (AQP4) has been implicated in post-traumatic syringomyelia (PTS), a disease characterised by the formation of fluid-filled cysts in the spinal cord. This study investigated the expression of AQP4 around a mature cyst (syrinx) and the effect of pharmacomodulation of AQP4 on syrinx size. PTS was induced in male Sprague-Dawley rats by computerized spinal cord impact and subarachnoid kaolin injection. Immunofluorescence of AQP4 was carried out on mature syrinx tissue 12 weeks post-surgery. Increased AQP4 expression corresponded to larger, multiloculated cysts (R2 = 0.94), yet no localized changes to AQP4 expression in perivascular regions or the glia limitans were present. In a separate cohort of animals, at 6 weeks post-surgery, an AQP4 agonist (AqF026), antagonist (AqB050), or vehicle was administered daily over 4 days, with MRIs performed before and after the completion of treatment. Histological analysis was performed at 12 weeks post-surgery. Syrinx volume and length were not altered with AQP4 modulation. The correlation between increased AQP4 expression with syrinx area suggests that AQP4 or the glia expressing AQP4 are recruited to regulate water movement. Given this, further investigation should examine AQP4 modulation with dose regimens at earlier time-points after PTS induction, as these may alter the course of syrinx development.

Spinal Obstruction-Related vs. Craniocervical Junction-Related Syringomyelia: A Comparative Study

Background

No prior reports have focused on spinal cord injury (SCI) characteristics or inflammation after destruction of the blood–spinal cord barrier by syringomyelia. This study aimed to determine the differences in syringomyelia-related central SCI between craniocervical junction (CCJ) syringomyelia and post-traumatic syringomyelia (PTS) before and after decompression.

Methods

In all, 106 CCJ, 26 CCJ revision and 15 PTS patients (mean history of symptoms, 71.5 ± 94.3, 88.9 ± 85.5, and 32.3 ± 48.9 months) between 2015 and 2019 were included. The symptom course was analyzed with the American Spinal Injury Association ASIA and Klekamp–Samii scoring systems, and neurological changes were analyzed by the Kaplan–Meier statistics. The mean follow-up was 20.7 ± 6.2, 21.7 ± 8.8, and 34.8 ± 19.4 months.

Results

The interval after injury was longer in the PTS group, but the natural history of syringomyelia was shorter (p = 0.0004 and 0.0173, respectively). The initial symptom was usually paraesthesia (p = 0.258), and the other main symptoms were hypoesthesia (p = 0.006) and abnormal muscle strength (p = 0.004), gait (p < 0.0001), and urination (p < 0.0001). SCI associated with PTS was more severe than that associated with the CCJ (p = 0.003). The cavities in the PTS group were primarily located at the thoracolumbar level, while those in the CCJ group were located at the cervical-thoracic segment at the CCJ. The syrinx/cord ratio of the PTS group was more than 75% (p = 0.009), and the intradural adhesions tended to be more severe (p < 0.0001). However, there were no significant differences in long-term clinical efficacy or peripheral blood inflammation markers (PBIMs) except for the red blood cell (RBC) count (p = 0.042).

Conclusion

PTS tends to progress faster than CCJ-related syringomyelia. Except for the RBC count, PBIMs showed no value in distinguishing the two forms of syringomyelia. The predictive value of the neutrophil-to-lymphocyte ratio for syringomyelia-related inflammation was negative except in the acute phase.

Slosh Simulation in a Computer Model of Canine Syringomyelia

The exact pathogenesis of syringomyelia is unknown. Epidural venous distention during raised intrathoracic pressure (Valsalva) may cause impulsive movement of fluid ("slosh") within the syrinx. Such a slosh mechanism is a proposed cause of syrinx dissection into spinal cord parenchyma resulting in craniocaudal propagation of the cavity. We sought to test the "slosh" hypothesis by epidural excitation of CSF pulse in a computer model of canine syringomyelia. Our previously developed canine syringomyelia computer model was modified to include an epidural pressure pulse. Simulations were run for: cord free of cavities; cord with small syringes at different locations; and cord with a syrinx that was progressively expanding caudally. If small syringes are present, there are peaks of stress at those locations. This effect is most pronounced at the locations at which syringes initially form. When a syrinx is expanding caudally, the peak stress is typically at the caudal end of the syrinx. However, when the syrinx reaches the lumbar region; the stress becomes moderate. The findings support the "slosh" hypothesis, suggesting that small cervical syringes may propagate caudally. However, when the syrinx is large, there is less focal stress, which may explain why a syrinx can rapidly expand but then remain unchanged in shape over years.

Blood-Spinal Cord Barrier in Spinal Cord Injury: A Review

The blood-spinal cord barrier (BSCB), a physical barrier between the blood and spinal cord parenchyma, prevents the toxins, blood cells, and pathogens from entering the spinal cord and maintains a tightly controlled chemical balance in the spinal environment, which is necessary for proper neural function. A BSCB disruption, however, plays an important role in primary and secondary injury processes related to spinal cord injury (SCI). After SCI, the structure of the BSCB is broken down, which leads directly to leakage of blood components. At the same time, the permeability of the BSCB is also increased. Repairing the disruption of the BSCB could alleviate the SCI pathology. We review the morphology and pathology of the BSCB and progression of therapeutic methods targeting BSCB in SCI.

Micro-computed tomography utility for estimation of intraparenchymal spinal cord cystic lesions in small animals

Precise assessment of spinal cord cystic lesions is crucial to formulate effective therapeutic strategies, yet histological assessment of the lesion remains the primary method despite numerous studies showing inconsistent results regarding estimation of lesion size via histology. On the other hand, despite numerous advances in micro-computed tomography (micro-CT) imaging and analysis that have allowed precise measurements of lesion size, there is not enough published data on its application to estimate intraspinal lesion size in laboratory animal models. This work attempts to show that micro-CT can be valuable for spinal cord injury research by demonstrating accurate estimation of syrinx size and compares between micro-CT and traditional histological analysis. We used a post-traumatic syringomyelia rat model to compare micro-CT analysis to conventional histological analysis. The study showed that micro-CT can detect lesions within the spinal cord very similar to histology. Importantly, micro-CT appears to provide more accurate estimates of the lesions with more measures (e.g., surface area), can detect compounds within the cord, and can be done with the tissue of interest (spinal cord) intact. In summary, the experimental work presented here provides one of the first investigations of the use of micro-CT for estimating the size of intraparenchymal cysts and detecting materials within the spinal cord. All animal procedures were approved by the University of Akron Institutional Animal Care and Use Committee (IACUC) (protocol # LRE 16-05-09 approved on May 14, 2016).

Abnormalities in spinal cord ultrastructure in a rat model of post-traumatic syringomyelia

BACKGROUND

Syringomyelia is a serious complication of spinal cord trauma, occurring in approximately 28% of spinal cord injuries. Treatment options are limited and often produce unsatisfactory results. Post-traumatic syringomyelia (PTS) is presumably related to abnormalities of cerebrospinal fluid (CSF) and interstitial fluid hydrodynamics, but the exact mechanisms are unknown.

METHODS

Transmission electron microscopy (TEM) was used to investigate in detail the interfaces between fluid and tissue in the spinal cords of healthy Sprague-Dawley rats (n = 3) and in a rat model of PTS (n = 3). PTS was induced by computer-controlled impact (75 kDyn) to the spinal cord between C6 and C8, followed by a subarachnoid injection of kaolin to produce focal arachnoiditis. Control animals received a laminectomy only to C6 and C7 vertebrae. Animals were sacrificed 12 weeks post-surgery, and spinal cords were prepared for TEM. Ultra-thin spinal cord sections at the level of the injury were counterstained for structural anatomy.

RESULTS

Spinal cords from animals with PTS displayed several abnormalities including enlarged perivascular spaces, extracellular edema, cell death and loss of tissue integrity. Additionally, alterations to endothelial tight junctions and an abundance of pinocytotic vesicles, in tissue adjacent to syrinx, suggested perturbations to blood-spinal cord barrier (BSCB) function.

CONCLUSIONS

These findings support the hypothesis that perivascular spaces are important pathways for CSF flow into and out of the spinal cord, but also suggest that fluid may enter the cord through vesicular transport and an altered BSCB.

Computer simulation of syringomyelia in dogs

Background

Syringomyelia is a pathological condition in which fluid-filled cavities (syringes) form and expand in the spinal cord. Syringomyelia is often linked with obstruction of the craniocervical junction and a Chiari malformation, which is similar in both humans and animals. Some brachycephalic toy breed dogs such as Cavalier King Charles Spaniels (CKCS) are particularly predisposed. The exact mechanism of the formation of syringomyelia is undetermined and consequently with the lack of clinical explanation, engineers and mathematicians have resorted to computer models to identify possible physical mechanisms that can lead to syringes. We developed a computer model of the spinal cavity of a CKCS suffering from a large syrinx. The model was excited at the cranial end to simulate the movement of the cerebrospinal fluid (CSF) and the spinal cord due to the shift of blood volume in the cranium related to the cardiac cycle. To simulate the normal condition, the movement was prescribed to the CSF. To simulate the pathological condition, the movement of CSF was blocked.

Results

For normal conditions the pressure in the SAS was approximately 400 Pa and the same applied to all stress components in the spinal cord. The stress was uniformly distributed along the length of the spinal cord. When the blockage between the cranial and spinal CSF spaces forced the cord to move with the cardiac cycle, shear and axial normal stresses in the cord increased significantly. The sites where the elevated stress was most pronounced coincided with the axial locations where the syringes typically form, but they were at the perimeter rather than in the central portion of the cord. This elevated stress originated from the bending of the cord at the locations where its curvature was high.

Conclusions

The results suggest that it is possible that repetitive stressing of the spinal cord caused by its exaggerated movement could be a cause for the formation of initial syringes. Further consideration of factors such as cord tethering and the difference in mechanical properties of white and grey matter is needed to fully explore this possibility.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1410-7) contains supplementary material, which is available to authorized users.

Characteristics of CSF Velocity-Time Profile in Posttraumatic Syringomyelia

BACKGROUND AND PURPOSE

The development of syringomyelia has been associated with changes in CSF flow dynamics in the spinal subarachnoid space. However, differences in CSF flow velocity between patients with posttraumatic syringomyelia and healthy participants remains unclear. The aim of this work was to define differences in CSF flow above and below a syrinx in participants with posttraumatic syringomyelia and compare the CSF flow with that in healthy controls.

MATERIALS AND METHODS

Six participants with posttraumatic syringomyelia were recruited for this study. Phase-contrast MR imaging was used to measure CSF flow velocity at the base of the skull and above and below the syrinx. Velocity magnitudes and temporal features of the CSF velocity profile were compared with those in healthy controls.

RESULTS

CSF flow velocity in the spinal subarachnoid space of participants with syringomyelia was similar at different locations despite differences in syrinx size and locations. Peak cranial and caudal velocities above and below the syrinx were not significantly different (peak cranial velocity, P = .9; peak caudal velocity, P = 1.0), but the peak velocities were significantly lower (P < .001, P = .007) in the participants with syringomyelia compared with matched controls. Most notably, the duration of caudal flow was significantly shorter (P = .003) in the participants with syringomyelia.

CONCLUSIONS

CSF flow within the posttraumatic syringomyelia group was relatively uniform along the spinal canal, but there are differences in the timing of CSF flow compared with that in matched healthy controls. This finding supports the hypothesis that syrinx development may be associated with temporal changes in spinal CSF flow.

Role of hypoxia-induced VEGF in blood-spinal cord barrier disruption in chronic spinal cord injury

Chronic spinal cord lesions (CSCL) which result in irreversible neurologic deficits remain one of the most devastating clinical problems. Its pathophysiological mechanism has not been fully clarified. As a crucial factor in the outcomes following traumatic spinal cord injury (SCI), the blood-spinal cord barrier (BSCB) disruption is considered as an important pathogenic factor contributing to the neurologic impairment in SCI. Vascular endothelial growth factor (VEGF) is a multirole element in the spinal cord vascular event. On one hand, VEGF administrations can result in rise of BSCB permeability in acute or sub-acute periods and even last for chronic process. On the other hand, VEGF is regarded to be correlated with angiogenesis, neurogenesis and improvement of locomotor ability. Hypoxia inducible factor-1 (HIF-1) is a primary regulator of VEGF during hypoxic conditions. Therefore, hypoxia-mediated up-regulation of VEGF may play multiple roles in the BSCB disruption and react on functional restoration of CSCL. The purpose of this article is to further explore the relationship among HIF-1, hypoxia-mediated VEGF and BSCB dysfunction, and investigate the roles of these elements on CSCL.

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

Direct-trauma model of posttraumatic syringomyelia with a computer-controlled motorized spinal cord impactor

OBJECTIVE The pathogenesis of posttraumatic syringomyelia remains enigmatic and is not adequately explained by current theories. Experimental investigations require a reproducible animal model that replicates the human condition. Current animal models are imperfect because of their low reliability, severe neurological deficits, or dissimilar mechanism of injury. The objective of this study was to develop a reproducible rodent model of posttraumatic syringomyelia using a spinal cord impactor that produces an injury that more closely mimics the human condition and does not produce severe neurological deficits. METHODS The study consisted of 2 parts. Seventy animals were studied overall: 20 in Experiment 1 and 48 in Experiment 2 after two rats with severe deficits were killed early. Experiment 1 aimed to determine the optimal force setting for inducing a cystic cavity without neurological deficits using a computer-controlled motorized spinal cord impactor. Twenty animals received an impact that ranged from 50 to 150 kDyn. Using the optimal force for producing an initial cyst determined from Experiment 1, Experiment 2 aimed to compare the progression of cavities in animals with and those without arachnoiditis induced by kaolin. Forty-eight animals were killed at 1, 3, 6, or 12 weeks after syrinx induction. Measurements of cavity size and maximum anteroposterior and lateral diameters were evaluated using light microscopy. RESULTS In Experiment 1, cavities were present in 95% of the animals. The duration of limb weakness and spinal cord cavity size correlated with the delivered force. The optimal force chosen for Experiment 2 was 75 kDyn. In Experiment 2, cavities occurred in 92% of the animals. Animals in the kaolin groups developed larger cavities and more vacuolations and enlarged perivascular spaces than those in the nonkaolin groups. CONCLUSIONS This impact model reliably produces cavities that resemble human posttraumatic syringomyelia and is suitable for further study of posttraumatic syringomyelia pathophysiology.

Inwardly rectifying potassium channel 4.1 expression in post-traumatic syringomyelia

Post-traumatic syringomyelia (PTS) is a serious neurological disorder characterized by fluid filled cavities that develop in the spinal cord. PTS is thought to be caused by an imbalance between fluid inflow and outflow in the spinal cord, but the underlying mechanisms are unknown. The ion channel Kir4.1 plays an important role in the uptake of K(+) ions from the extracellular space and release of K(+) ions into the microvasculature, generating an osmotic gradient that drives water movement. Changes in Kir4.1 expression may contribute to disturbances in K(+) homeostasis and subsequently fluid imbalance. Here we investigated whether changes in Kir4.1 protein expression occur in PTS. Western blotting and immunohistochemistry were used to evaluate Kir4.1 and glial fibrillary acidic protein (GFAP) expression in a rodent model of PTS at 3 days, 1, 6 or 12 weeks post-surgery. In Western blotting experiments, Kir4.1 expression increased 1 week post-surgery at the level of the cavity. Immunohistochemical analysis examined changes in the spinal parenchyma directly in contact with the syrinx cavity. In these experiments, there was a significant decrease in Kir4.1 expression in PTS animals compared to controls at 3 days and 6 weeks post-surgery, while an up-regulation of GFAP in PTS animals was observed at 1 and 12 weeks. This suggests that while overall Kir4.1 expression is unchanged at these time-points, there are many astrocytes surrounding the syrinx cavity that are not expressing Kir4.1. The results demonstrate a disturbance in the removal of K(+) ions in tissue surrounding a post-traumatic syrinx cavity. It is possible this contributes to water accumulation in the injured spinal cord leading to syrinx formation or exacerbation of the underlying pathology.

Pulse wave myelopathy: An update of an hypothesis highlighting the similarities between syringomyelia and normal pressure hydrocephalus

Most hypotheses trying to explain the pathophysiology of idiopathic syringomyelia involve mechanisms whereby CSF is pumped against a pressure gradient, from the subarachnoid space into the cord parenchyma. On review, these theories have universally failed to explain the disease process. A few papers have suggested that the syrinx fluid may originate from the cord capillary bed itself. However, in these papers, the fluid is said to accumulate due to impaired fluid drainage out of the cord. Again, there is little evidence to substantiate this. This proffered hypothesis looks at the problem from the perspective that syringomyelia and normal pressure hydrocephalus are almost identical in their manifestations but only differ in their site of effect within the neuraxis. It is suggested that the primary trigger for syringomyelia is a reduction in the compliance of the veins draining the spinal cord. This reduces the efficiency of the pulse wave dampening, occurring within the cord parenchyma, increasing arteriolar and capillary pulse pressure. The increased capillary pulse pressure opens the blood-spinal cord barrier due to a direct effect upon the wall integrity and interstitial fluid accumulates due to an increased secretion rate. An increase in arteriolar pulse pressure increases the kinetic energy within the cord parenchyma and this disrupts the cytoarchitecture allowing the fluid to accumulate into small cystic regions in the cord. With time the cystic regions coalesce to form one large cavity which continues to increase in size due to the ongoing interstitial fluid secretion and the hyperdynamic cord vasculature.

Aquaporin-4 expression in post-traumatic syringomyelia

Aquaporin-4 (AQP4) is an astroglial water channel protein that plays an important role in the transmembrane movement of water within the central nervous system. AQP4 has been implicated in numerous pathological conditions involving abnormal fluid accumulation, including spinal cord edema following traumatic injury. AQP4 has not been studied in post-traumatic syringomyelia, a condition that cannot be completely explained by current theories of cerebrospinal fluid dynamics. Alterations of AQP4 expression or function may contribute to the fluid imbalance leading to syrinx formation or enlargement. The aim of this study was to examine AQP4 expression levels and distribution in an animal model of post-traumatic syringomyelia. Immunofluorescence and western blotting were used to assess AQP4 and glial fibrillary acidic protein (GFAP) expression in an excitotoxic amino acid/arachnoiditis model of post-traumatic syringomyelia in Sprague-Dawley rats. At all time-points, GFAP-positive astrocytes were observed in tissue surrounding syrinx cavities, although western blot analysis demonstrated an overall decrease in GFAP expression, except at the latest stage investigated. AQP4 expression was significantly higher at the level of syrinx at three and six weeks following the initial syrinx induction surgery. Significant increases in AQP4 expression also were observed in the upper cervical cord, rostral to the syrinx except in the acute stage of the condition at the three-day time-point. Immunostaining showed that AQP4 was expressed around all syrinx cavities, most notably adjacent to a mature syrinx (six- and 12-week time-point). This suggests a relationship between AQP4 and fluid accumulation in post-traumatic syringomyelia. However, whether this is a causal relationship or occurs in response to an increase in fluid needs to be established.

Aquaporin-4 expression and blood–spinal cord barrier permeability in canalicular syringomyelia

Object

Noncommunicating canalicular syringomyelia occurs in up to 65% of patients with Chiari malformation Type I. The pathogenesis of this type of syringomyelia is poorly understood and treatment is not always effective. Although it is generally thought that syringomyelia is simply an accumulation of CSF from the subarachnoid space, the pathogenesis is likely to be more complex and may involve cellular and molecular processes. Aquaporin-4 (AQP4) has been implicated in numerous CNS pathological conditions involving fluid accumulation, including spinal cord edema. There is evidence that AQP4 facilitates the removal of extracellular water following vasogenic edema. The aim of this study was to investigate AQP4 expression and the structural and functional integrity of the blood–spinal cord barrier (BSCB) in a model of noncommunicating canalicular syringomyelia.

Methods

A kaolin-induced model of canalicular syringomyelia was used to investigate BSCB permeability and AQP4 expression in 27 adult male Sprague-Dawley rats. Control groups consisted of nonoperated, laminectomy-only, and saline-injected animals. The structural integrity of the BSCB was assessed using immunoreactivity to endothelial barrier antigen. Functional integrity of the BSCB was assessed by extravasation of systemically injected horseradish peroxidase (HRP) at 1, 3, 6, or 12 weeks after surgery. Immunofluorescence was used to assess AQP4 and glial fibrillary acidic protein (GFAP) expression at 12 weeks following syrinx induction.

Results

Extravasation of HRP was evident surrounding the central canal in 11 of 15 animals injected with kaolin, and in 2 of the 5 sham-injected animals. No disruption of the BSCB was observed in laminectomy-only controls. At 12 weeks the tracer leakage was widespread, occurring at every level rostral to the kaolin injection. At this time point there was a decrease in EBA expression in the gray matter surrounding the central canal from C-5 to C-7. Aquaporin-4 was expressed in gray- and white-matter astrocytes, predominantly at the glia limitans interna and externa, and to a lesser extent around neurons and blood vessels, in both control and syrinx animals. Expression of GFAP and APQ4 directly surrounding the central canal in kaolin-injected animals was variable and not significantly different from expression in controls.

Conclusions

This study demonstrated a prolonged disruption of the BSCB directly surrounding the central canal in the experimental model of noncommunicating canalicular syringomyelia. The disruption was widespread at 12 weeks, when central canal dilation was most marked. Loss of integrity of the barrier with fluid entering the interstitial space of the spinal parenchyma may contribute to enlargement of the canal and progression of syringomyelia. Significant changes in AQP4 expression were not observed in this model of canalicular syringomyelia. Further investigation is needed to elucidate whether subtle changes in AQP4 expression occur in canalicular syringomyelia.

Interactions between the immune and nervous systems in pain

Immune cells and glia interact with neurons to alter pain sensitivity and to mediate the transition from acute to chronic pain. In response to injury, resident immune cells are activated and blood-borne immune cells are recruited to the site of injury. Immune cells not only contribute to immune protection but also initiate the sensitization of peripheral nociceptors. Through the synthesis and release of inflammatory mediators and interactions with neurotransmitters and their receptors, the immune cells, glia and neurons form an integrated network that coordinates immune responses and modulates the excitability of pain pathways. The immune system also reduces sensitization by producing immune-derived analgesic and anti-inflammatory or proresolution agents. A greater understanding of the role of the immune system in pain processing and modulation reveals potential targets for analgesic drug development and new therapeutic opportunities for managing chronic pain.