Outflow Pathway Research Articles

Cadaveric Anatomy of Frontal Sinus Outflow Pathway

Cadaveric Anatomy of Frontal Sinus Outflow Pathway

MRP4-mediated regulation of intracellular cAMP and cGMP levels in trabecular meshwork cells and homeostasis of intraocular pressure.

Multidrug, resistance-associated protein-4 (MRP4) is a membrane transporter that regulates the cellular efflux of cyclic nucleotides (cAMP and cGMP) involved in various physiologic responses. This study examined the expression and distribution of MRP4 in the trabecular meshwork (TM) cells and its role in homeostasis of IOP. Expression and distribution of MRP4 in human TM (HTM) cells and aqueous humor (AH) outflow pathway was determined by RT-PCR, immunoblotting, and immunofluorescence. Effects of inhibiting MRP4 activity and suppression of MRP4 expression on cAMP and cGMP levels, myosin light chain (MLC) phosphorylation, actin filament organization and activity of protein kinase G (PKG), protein kinase A (PKA), Rho guanosine triphosphatase (GTPase), and MLC phosphatase was monitored in HTM cells using ELISA, siRNA, biochemical, and immunofluorescence analyses. Topical application of the MRP4 inhibitor MK571 was tested to assess changes in IOP in rabbits. RT-PCR, immunoblot, and immunofluorescence analyses confirmed the expression of MRP4 in HTM cells and distribution in human AH outflow pathway. Inhibition of MRP4 in HTM cells by MK571 or probenecid resulted in cell shape changes and decreases in actin stress fibers and MLC phosphorylation. Levels of intracellular cAMP and cGMP in HTM cells were increased significantly under these conditions. MK571-induced HTM cell relaxation appeared to be mediated predominantly via activation of the cGMP-dependent PKG signaling pathway. Topical application of MK571 significantly decreased IOP in Dutch-Belted rabbits. These observations reveal that cyclic nucleotide efflux controlling transporter-MRP4 plays a significant role in IOP homeostasis potentially by regulating the relaxation characteristics of AH outflow pathway cells.

GPR158, an Orphan Member of G Protein-Coupled Receptor Family C: Glucocorticoid-Stimulated Expression and Novel Nuclear Role

Members of the large G protein-coupled receptor (GPCR) clan are implicated in many physiological and disease processes, making them important therapeutic drug targets. In the present study, we follow up on results of a pilot study suggesting a functional relationship between glucocorticoid (GC)-induced ocular hypertension and GPR158, one of three orphan members of the GPCR Family C. GC treatment increases levels of GPR158 mRNA and protein through transcriptional mechanisms, in cultured trabecular meshwork (TBM) cells derived from the eye's aqueous outflow pathway. Like treatment with GCs, transient overexpression of GPR158 stimulates cell proliferation, while siRNA knockdown of endogenous GPR158 has the opposite effect. Both endogenous and overexpressed GPR158 show an unusual subcellular localization pattern, being found almost entirely in the nucleus. However, when cells are treated with inhibitors of clathrin-mediated endocytosis, GPR158 is shifted to the plasma membrane. Mutation of a bipartite nuclear localization signal (NLS) in the 8th helix also shifts GPR158 out of the nucleus, but in this case the protein is found in vesicles localized in the cytoplasm. These results suggest that newly synthesized GPR158 first traffics to the plasma membrane, where it rapidly undergoes endocytosis and translocation to the nucleus. Significantly, mutation of the NLS abrogates GPR158-mediated enhancement of cell proliferation, indicating a functional requirement for nuclear localization. GPR158 overexpression upregulates levels of the cell cycle regulator cyclin D1, but mutation of the NLS reverses this. Overexpression of GPR158 enhances the barrier function of a TBM cell monolayer, which is associated with an increase in the levels of tight junction proteins ZO-1 and occludin, similar to reported studies on GC treatment. Regulated paracellular permeability controls aqueous outflow facility in vivo. Since GCs stimulate GPR158 expression, the result is consistent with a role for elevation of GPR158 expression in GC-induced ocular hypertension.

Updating the mild encephalitis hypothesis of schizophrenia

Emerging evidence indicates that low level neuroinflammation (LLNI) may not occur infrequently. Many infectious agents with low overall pathogenicity are risk factors for psychoses including schizophrenia and for autoimmune disorders. According to the mild encephalitis (ME) hypothesis, LLNI represents the core pathogenetic mechanism in a schizophrenia subgroup that has syndromal overlap with other psychiatric disorders. ME may be triggered by infections, autoimmunity, toxicity, or trauma. A ‘late hit’ and gene–environment interaction are required to explain major findings about schizophrenia, and both aspects would be consistent with the ME hypothesis. Preliminary criteria for subgrouping neurodevelopmental, genetic, ME, and other types of schizophrenias were provided. Considering recent investigations of CSF, the ME schizophrenia subgroup may constitute approximately 40% of cases. LLNI may involve dysfunction of the blood–brain barrier, the blood–CSF barrier of CNS-endogenous immunity in part mediated by the volume transmission mode involving CNS-extracellular-fluid and CSF signaling. Both together could represent a common pathogenetic link for the distributed brain dysfunction observed in schizophrenia. However, CSF signaling may even extend along nerves into peripheral tissues via the CSF outflow pathway and explain peripheral topologies of dysfunctions/lesions found (dysautonomia, muscle lesions). In general, CSF signaling including at the PCOP could play an underestimated role in neuroinflammatory disorders.

Abstract WP217: Hemodynamics of the Internal Jugular Vein in Healthy Subjects Using Quantitative magnetic resonance angiography

Objective: To study the hemodynamics of cerebral venous system by evaluation of the internal jugular veins (IJV) using quantitative magnetic resonance angiography (QMRA) in healthy subjects. Methods: 263 healthy subjects (129 females; 134 males; mean age 50 ± 16 years) with no history of cerebrovascular disease were evaluated in supine position with QMRA at 3T. Flow rates of the internal carotid artery (ICA) and vertebral artery (VA) were quantified prospectively with 2D phase contrast MR imaging. IJV flow rates were retrospectively measured from previously acquired 2 D phase contrast imaging of the neck between the C5 and C6 level. Total internal jugular venous flow (TIJVF=LIJV + RIJV) was compared to total cerebral flow (TCBF=ICAs + VAs). Regression analysis was used to examine the effects of age, mean blood pressure (MBP), and other variables on TIJVF. Results: LIJV flow rates (229 ± 141 ml/min) was significantly less than RIJV (362 ± 165 ml/min) (P< 0.0001). TIJVF (592 ± 177 ml/min) was 84% of TCBF (703 ± 115). As expected, TIJVF was significantly dependent on TCBF (p<0.0001). Unlike TCBF, TIJVF did not depend on age (p= 0.3), nor on MBP (p=0.5), or on gender (p=0.6). Conclusions: IJVs are the principle outflow pathway of intracranial blood. Reference values for flows in IJVs and TIJVF may help in the evaluation of conditions characterized by venous outflow obstruction (e.g. venous sinus thrombosis or pseudotumor) or excessive venous output (e.g. arterio-venous fistulae or malformations), as well as investigation of conditions hypothesized to be associated cerebral venous insufficiency, such as multiple sclerosis.

Wirkmechanismen, klinisches Profil und Stellenwert von Prostaglandin- und Prostamid-Analoga in der antiglaukomatösen Therapie

Prostaglandin and prostamide analogues belong to a new substance group which came into the market in the 1990s. They have revolutionised antiglaucomatous therapy by their once-daily dosing regimen and fewer side effects. Today, prostaglandin and prostamide analogues are approved as first-line therapy for patients with primary open-angle glaucoma and ocular hypertension. They lower the intraocular pressure primarily by increasing the uveoscleral outflow. Recent investigations have shown that they also improve the trabecular outflow facility and thus the conventional outflow pathways. Prostaglandin and prostamide analogues are highly efficient in lowering the intraocular pressure, for which they are superior to other antiglaucomatous substance groups. In particular, they appear to have a good control of 24-hour intraocular pressure fluctuations by primarily improving the outflow pathways. Furthermore, they have less systemic side effects than β-blockers. However, their use is often associated with higher costs. In case of undesirable events, they mostly present with ocular symptoms. Based on their good clinical profile, prostaglandin and prostamide analogues play an important role in the primary and additive therapy for glaucoma.

The Juxtacanalicular Region of Ocular Trabecular Meshwork: A Tissue with a Unique Extracellular Matrix and Specialized Function

The trabecular meshwork (TM) is a filter-like tissue located in the anterior segment of the eye. It is composed of a series of fenestrated beams through which aqueous humor flows to exit the anterior chamber via Schlemm's canal. The primary function of the TM is to regulate the flow of aqueous humor in order to establish intraocular pressure (IOP). Dysregulated aqueous humor outflow causes elevated IOP, which is a primary risk factor for glaucoma. The region of the TM implicated in establishing IOP lies adjacent to Schlemm's canal and is called the juxtacanalicular tissue (JCT) or cribriform region. Recent advanced light microscopy studies suggest that the JCT can be subdivided into inner and outer zones based on the localization of certain extracellular matrix (ECM) molecules. By comparing the ECM of the JCT to other connectives tissues and disease processes, this review outlines the evidence for two new concepts in TM biology: (1) continuous maintenance ECM remodeling, which may be critical in order to preserve open aqueous humor flow channels by releasing trapped debris and associated ECM fragments from the outflow pathways; (2) the JCT ECM as a barrier to functionally isolate the aqueous outflow channels. The ECM surrounding the outflow channels in the JCT may function to sequester small active regulatory molecules and prevent them from aberrantly modulating outflow resistance. These adaptations point to a distinctive tissue that has evolved transient ECM remodeling processes in order to regulate aqueous humor outflow and maintain rigorous control of IOP.

Integrins in Trabecular Meshwork and Optic Nerve Head: Possible Association with the Pathogenesis of Glaucoma

Integrins are a family of membrane-spanning proteins that are important receptors for cell adhesion to extracellular matrix proteins. They also provide connections between the extracellular environment and intracellular cytoskeletons and are responsible for activation of many intracellular signaling pathways. In vitro and in vivo data strongly indicate that integrin-mediated signaling events can modulate the organization of the actin cytoskeleton in trabecular meshwork (TM) cells and are associated with astrocyte migration and microglia activation of the optic nerve head in patients with primary open angle glaucoma. Consequently, increase in resistance in the TM outflow pathways and remodeling of the optic nerve head occur, which in turn increases intraocular pressure (IOP), adds additional mechanical stress and strain to optic nerve axons, and accelerates damage of axons initially caused by optic nerve head remodeling. Integrins appear to be ideal candidates for translating physical stress and strain into cellular responses known to occur in glaucomatous optic neuropathy.

Glaucoma associated with the management of rhegmatogenous retinal detachment

Transient or permanent elevation of intraocular pressure (IOP) is a common complication following vitreoretinal surgery. Usually secondary glaucoma, which develops after scleral buckling procedures, or pars plana vitrectomy for repair of rhegmatogenous retinal detachment, is of multifactorial origin. It is essential, for appropriate management, to detect the cause of outflow obstruction. An exacerbation of preexisting open-angle glaucoma or a steroid-induced elevation of IOP should also be considered. Scleral buckling may be complicated by congestion and anterior rotation of the ciliary body resulting in secondary angle closure, which can usually resolve with medical therapy. The use of intravitreal gases may also induce secondary angle-closure with or without pupillary block. Aspiration of a quantity of the intraocular gas may be indicated. Secondary glaucoma can also develop after intravitreal injection of silicone oil due to pupillary block, inflammation, synechial angle closure, or migration of emulsified silicone oil in the anterior chamber and obstruction of the aqueous outflow pathway. In most eyes medical therapy is successful in controlling IOP; however, silicone oil removal with or without concurrent glaucoma surgery may also be required. Diode laser transscleral cyclophotocoagulation and glaucoma drainage devices constitute useful treatment modalities for long-term IOP control. Cooperation between vitreoretinal and glaucoma specialists is necessary to achieve successful management.

Role of Dopaminergic Receptors in Glaucomatous Disease Modulation

Both studies on animals and humans suggest the presence of dopamine (DA) receptors in the anterior segment of the eye. Their role in the dynamics of intraocular pressure (IOP) is not yet clear. DA2 and DA3 receptors are mainly located on postganglionic sympathetic nerve endings. Their stimulation reduces the release of norepinephrine and suppresses the production of aqueous humor. DA1 receptors seem to be more expressed by the ciliary body and the outflow pathway of aqueous humor. The administration of DA1-selective agonists stimulates the production of aqueous humor, increasing IOP, whereas DA2- and DA3-selective agonists could reduce IOP and, therefore, the risk to develop a glaucoma (GL). GL is a broad spectrum of eye diseases which have in common the damage to the optic nerve and the progressive loss of the visual field. Further studies are desirable to clarify the role of the dopaminergic system and the usefulness of DA2 and DA3 agonists in reducing IOP.

Regulation of Adherens Junctions in Trabecular Meshwork Cells by Rac GTPase and their influence on Intraocular Pressure.

Intercellular adherens junctions and cell-extracellular matrix interactions are presumed to influence aqueous humor (AH) drainage via the conventional route, however, their direct role in modulation of intraocular pressure (IOP) is not well understood. Here, we investigated the role of Rac GTPase signaling in basal and growth factor-induced formation of adherens junctions in human trabecular meshwork (HTM) cells as compared to human umbilical vascular endothelial cells, and evaluated the effects of inhibition of Rac GTPase activity on IOP in rabbits. Expression of a constitutively active Rac1 GTPase or treatment with platelet derived growth factor (PDGF), a known activator of Rac GTPase, induced formation of β-catenin-based adherens junctions, actin cytoskeletal reorganization and membrane ruffle in HTM cells. In contrast, treatment of HTM cells with inhibitors of Rac GTPase caused cell-cell separation, a decrease in adherens junctions, and reorganization of actin stress fibers to the cell cortical regions and focal adhesion to the cell leading edges. Both, constitutively active Rac1 and PDGF stimulated generation of Reactive Oxygen Species (ROS) in HTM cells, and ROS were found to increase adherens junction formation and transendothelial electrical resistance (TEER) in HTM cells. Topical application of Rac GTPase inhibitors (EHT1864 and NSC23766), however, only marginally influenced IOP in rabbit eyes. Taken together, these data reveal that while Rac GTPase signaling plays a significant role in regulation of adherens junctions, ROS production and TEER in cells of the AH outflow pathway, Rac inhibitors showed only a marginal influence on IOP in live rabbits.

Gastric Varices: Is There a Role for Endoscopic Cyanoacrylates, or Are We Entering the BRTO Era?

Bleeding from portal hypertension-related gastric varices arising in the cardiofundal region of the stomach presents a challenge due to the unique underlying vascular anatomy which is sometimes underappreciated in endoscopic classification schemes. They often have dominant tributaries from the splenic vein or splenic hilum and terminate in the left renal vein (spontaneous splenorenal or gastrorenal shunts). This may limit the applicability of a transjugular intrahepatic portosystemic shunt (TIPS), because of the shunt's distance from the hilum of the liver. Endoscopically, the presence of a large systemic outflow track also may influence the performance of different cyanoacrylates. However, this anatomy allows an alternative approach, balloon-occluded retrograde transvenous obliteration (BRTO), which accesses the varix via the outflow pathway. Definitive comparisons between TIPS, endoscopic cyanoacrylate, and BRTO will be challenging because the incidence of this type of varix is insufficient for large trials. Here, I provide a perspective based on existing literature, 15 years of experience with various cyanoacrylates, and 4 years of experience with BRTO.

Conjunctival modifications induced by medical and surgical therapies in patients with glaucoma

Lowering intra-ocular pressure, either medically or surgically, is the proven strategy to control glaucoma, though profound changes to the ocular surface and conjunctiva are caused. Toxicity and allergy initiated by medical therapy induce modifications, which progressively worsen with the length of treatment and number of drugs. Conjunctival changes lead to symptoms of ocular surface disease, reduced quality of life, reduced therapeutic compliance and increased risk of surgical failure. Surgery modifies conjunctiva by inducing bleb formation in fistulizing techniques, and by activating secondary aqueous humour outflow pathways, such as trans-scleral routes, in both filtration and bleb-less approaches. The use of unpreserved medications, limitation of intra-operative conjunctival damage and development of bleb-less surgery are advisable.

Characterization of a spontaneously immortalized bovine trabecular meshwork cell line

Trabecular meshwork (TM) cells have widely been used as an in vitro model for glaucoma research. However, primary TM cells suffer the disadvantages of limited cell numbers and slow rates of proliferation. We discovered a spontaneously transformed bovine TM (BTM) cell line, BTM-28T. This cell line proliferated rapidly in low-glucose culture medium but also demonstrated contact inhibition in high-glucose culture medium. BTM-28T cells expressed key TM cell markers including α-smooth muscle actin (α-SMA), laminin and collagen IV (col IV). Also, 100 nM dexamethasone (DEX) enhanced the formation of cross-linked actin networks (CLANs) in confluent BTM-28T cell cultures. Transforming growth factor beta 2 (TGFβ2) induced the expression of fibronectin (FN), plasminogen activator inhibitor-1 (PAI-1), and connective tissue growth factor (CTGF) in our cell cultures. This cell line will be helpful to better understand the aqueous humor outflow pathway as related to the pathophysiology of glaucoma.

Elevated Levels of RhoA in the Optic Nerve Head of Human Eyes With Glaucoma

To determine changes in the expression profile of RhoA and Rho kinase (ROCK-1 and ROCK-2) in the aqueous humor outflow pathway and optic nerve head (ONH) of human eyes with or without glaucoma to explore their potential involvement in glaucoma pathophysiology. Age-matched paraffin-embedded postmortem eyes from patients with or without glaucoma were stained immunohistochemically using polyclonal antibodies raised against RhoA, ROCK-1, and ROCK-2. The intensity of the immunostaining in the aqueous humor outflow pathway and the ONH was graded by 4 individuals who were masked concerning whether the eyes were from normal individuals or those with glaucoma. Both normal eyes and those with glaucoma showed a positive staining for RhoA, ROCK-1, and ROCK-2 in the trabecular meshwork, ciliary muscle, and ONH. There was a significant increase in the RhoA protein levels in the glaucomatous ONH compared with the age-matched controls. Elevated levels of RhoA in the ONH of glaucomatous eyes suggest possible involvement of RhoA in the pathophysiology of glaucoma.

Germline ablation of VGF increases lipolysis in white adipose tissue

Targeted deletion of VGF, a neuronal and endocrine secreted protein and neuropeptide precursor, produces a lean, hypermetabolic mouse that is resistant to diet-, lesion-, and genetically induced obesity and diabetes. We hypothesized that increased sympathetic nervous system activity in Vgf-/Vgf- knockout mice is responsible for increased energy expenditure and decreased fat storage and that increased β-adrenergic receptor stimulation induces lipolysis in white adipose tissue (WAT) of Vgf-/Vgf- mice. We found that fat mass was markedly reduced in Vgf-/Vgf- mice. Within knockout WAT, phosphorylation of protein kinase A substrate increased in males and females, phosphorylation of hormone-sensitive lipase (HSL) (ser563) increased in females, and levels of adipose triglyceride lipase, comparative gene identification-58, and phospho-perilipin were higher in male Vgf-/Vgf- WAT compared with wild-type, consistent with increased lipolysis. The phosphorylation of AMP-activated protein kinase (AMPK) (Thr172) and levels of the AMPK kinase, transforming growth factor β-activated kinase 1, were decreased. This was associated with a decrease in HSL ser565 phosphorylation, the site phosphorylated by AMPK, in both male and female Vgf-/Vgf- WAT. No significant differences in phosphorylation of CREB or the p42/44 MAPK were noted. Despite this evidence supporting increased cAMP signaling and lipolysis, lipogenesis as assessed by fatty acid synthase protein expression and phosphorylated acetyl-CoA carboxylase was not decreased. Our data suggest that the VGF precursor or selected VGF-derived peptides dampen sympathetic outflow pathway activity to WAT to regulate fat storage and lipolysis.

Pharmacologic Manipulation of Conventional Outflow Facility in Ex Vivo Mouse Eyes

Mouse models are useful for glaucoma research, but it is unclear whether intraocular pressure (IOP) regulation in mice operates through mechanisms similar to those in humans. Our goal was to determine whether pharmacologic compounds that affect conventional outflow facility in human eyes exert similar effects in C57BL/6 mice. A computerized perfusion system was used to measure conventional outflow facility in enucleated mouse eyes ex vivo. Paired eyes were perfused sequentially, either immediately after enucleation or after 3 hours storage at 4°C. Three groups of experiments examined sphingosine 1-phosphate (S1P), S1P with antagonists to S1P(1) and S1P(2) receptors, and the prostanoid EP(4) receptor agonist 3,7-dithia PGE(1). We also examined whether a 24-hour postmortem delay affected the response to 3,7-dithia prostaglandin E(1) (PGE(1)). S1P decreased facility by 39%, and was blocked almost completely by an S1P(2), but not S1P(1), receptor antagonist. The S1P(2) receptor antagonist alone increased facility nearly 2-fold. 3,7-dithia PGE(1) increased facility by 106% within 3 hours postmortem. By 24 hours postmortem, the facility increase caused by 3,7-dithia PGE(1) was reduced 3-fold, yet remained statistically detectable. C57BL/6 mice showed opposing effects of S1P(2) and EP(4) receptor activation on conventional outflow facility, as observed in human eyes. Pharmacologic effects on facility were detectable up to 24 hours postmortem in enucleated mouse eyes. Mice are suitable models to examine the pharmacology of S1P and EP(4) receptor stimulation on IOP regulation as occurs within the conventional outflow pathway of human eyes, and are promising for studying other aspects of aqueous outflow dynamics.

Morphometric analysis of aqueous humor outflow structures with spectral-domain optical coherence tomography.

To describe morphometric details of the human aqueous humor (AH) outflow microvasculature visualized with 360-degree virtual castings during active AH outflow in cadaver eyes and to compare these structures with corrosion casting studies. The conventional AH outflow pathways of donor eyes (n = 7) and eyes in vivo (n = 3) were imaged with spectral-domain optical coherence tomography (SD-OCT) and wide-bandwidth superluminescent diode array during active AH outflow. Digital image contrast was adjusted to isolate AH microvasculature, and images were viewed in a 3D viewer. Additional eyes (n = 3) were perfused with mock AH containing fluorescent tracer microspheres to compare microvasculature patterns. Observations revealed components of the conventional outflow pathway from Schlemm's canal (SC) to the superficial intrascleral venous plexus (ISVP). The superficial ISVP in both our study and corrosion casts were composed of interconnected venules (10-50 μm) forming a hexagonal meshwork. Larger radial arcades (50-100 μm) drained the region nearest SC and converged with larger tortuous vessels (>100 μm). A 360-degree virtual casting closely approximated corrosion casting studies. Tracer studies corroborated our findings. Tracer decorated several larger vessels (50-100 μm) extending posteriorly from the limbus in both raw and contrast-enhanced fluorescence images. Smaller tracer-labeled vessels (30-40 μm) were seen branching between larger vessels and exhibited a similar hexagonal network pattern. SD-OCT is capable of detailed morphometric analysis of the conventional outflow pathway in vivo or ex vivo with details comparable to corrosion casting techniques.

Therapeutic targets in glaucoma

AbstractGlaucoma leads to irreversible blindness and is characterized by changes in the optic disc and the visual field. The elevated intraocular pressure is considered the most important factor responsible for the glaucomatous optic neuropathy. There are multiple factors involved in the development of retinal ganglion cell death. The goal of glaucoma treatment is to preserve the visual field of patients and prevent the loss of visual function that is associated with the disease (European Guidelines). We should focus at least on three separate targets of glaucoma treatment (Brubaker RF. Survey of Ophthalmology 2003: Three targets for glaucoma management): Intraocular pressure (IOP), outflow facility, and the retinal ganglion cell (RGC). Elevated IOP is still the primary risk factor for the development and progression of glaucoma, and many studies have shown that IOP reduction can limit the progression of glaucoma and slow the loss of visual function. IOP lowering can be beneficial for normal‐tension as well as high‐tension glaucoma patients, and it may also prevent or delay the onset of visual field loss and optic disk damage in individuals with ocular hypertension. The second target of glaucoma treatment is outflow facility. In a healthy eye, aqueous production (flow) equals aqueous outflow through the trabecular and uveoscleral outflow pathways. Any imbalance between flow and outflow results in a change in IOP, yet even a transient elevation of IOP may cause significant glaucomatous damage. The third target of glaucoma treatment is the RGC itself. RGC death in glaucoma might have many causes, including vascular insufficiency, blockage of axonal transport, diffusion of toxic agents into the nerve cell, or initiation of apoptosis. Treatment that aims to directly protect the RGC from every possible insult might be the ultimate treatment for glaucoma because a strategy of neuroprotection could preserve the visual function of patients regardless of the etiology of their glaucoma.

Fluid Outflow in a Large-Animal Model of Posttraumatic Syringomyelia

Posttraumatic syringomyelia affects approximately 28% of spinal cord injury patients, and current treatments are often ineffective. The pathogenesis of this condition remains poorly understood. Previous reports have focused on pathways and mechanisms of fluid inflow; however, disturbances of fluid outflow mechanisms and pathways may be important in syrinx formation and enlargement. To determine the route of fluid outflow from a syrinx in an animal model of posttraumatic syringomyelia. A model of posttraumatic syringomyelia using excitotoxic amino acid and kaolin-induced arachnoiditis was created in 12 Merino wethers. Six weeks after syrinx induction, the cavities were localized and a cerebrospinal fluid tracer, horseradish peroxidase (HRP), was injected into the syrinx under ultrasonic guidance. After 10 minutes, the animals were killed and the spinal cords harvested for microscopy. An extracanalicular syrinx developed in 6 of the 12 sheep. HRP was successfully injected into 5 of the 6 syrinx cavities. HRP reaction product was observed in gray and white matter adjacent to the syrinx in a diffuse pattern. There were moderate amounts of HRP around the central canal and perivascular spaces and minimal amounts in the dorsal subarachnoid space. In this model of posttraumatic syringomyelia, fluid outflow occurred in a diffuse manner into the surrounding extracellular space and toward the central canal and perivascular spaces. Fluid outflow may be an important consideration in the pathogenesis of syringomyelia and the development of new therapies.