Permeability Of Blood-nerve Barrier Research Articles

Fibroblast-derived PI16 sustains inflammatory pain via regulation of CD206+ myeloid cells

Originally identified in fibroblasts, Protease Inhibitor (PI)16 was recently shown to be crucial for the development of neuropathic pain via effects on blood-nerve barrier permeability and leukocyte infiltration, though its impact on inflammatory pain has not been established. Using the complete Freund’s Adjuvant inflammatory pain model, we show that Pi16-/- mice are protected against sustained inflammatory pain. Accordingly, intrathecal delivery of a PI16 neutralizing antibody in wild-type mice prevented sustained CFA pain. In contrast to neuropathic pain models, we did not observe any changes in blood-nerve barrier permeability due to PI16 deletion. Instead, Pi16-/- mice display reduced macrophage density in the CFA-injected hindpaw. Furthermore, there was a significant bias toward CD206hi (anti-inflammatory) macrophages in the hindpaw and associated dorsal root ganglia. Following CFA, intrathecal depletion of CD206+ macrophages using mannosylated clodronate liposomes promoted sustained pain in Pi16-/- mice. Similarly, an IL-10 neutralizing antibody also promoted sustained CFA pain in the Pi16-/ when administered intrathecally. Collectively, our results point to fibroblast-derived PI16 mediating substantial differences in macrophage phenotype in the pain neuroaxis under conditions of inflammation. The co-expression of PI16 alongside fibroblast markers in human DRG raise the likelihood that a similar mechanism operates in human inflammatory pain states. Collectively, our findings may have implications for targeting fibroblast-immune cell crosstalk for the treatment of chronic pain.

Blood-nerve barrier disruption and coagulation system activation induced by mechanical compression injury participate in the peripheral sensitization of trigeminal neuralgia.

The aim of this study was to investigate the effect and possible mechanisms of the blood-nerve barrier (BNB) and the coagulation-anticoagulation system in modulating the mechanical allodynia in a trigeminal neuralgia (TN) rat model induced by chronic compression of the trigeminal root entry zone (TREZ). Von Frey filaments were applied to determine the orofacial mechanical allodynia threshold. The BNB permeability was evaluated by Evans blue extravasation test. Immunohistochemical staining and laser confocal microscopy were used to measure the length of the depletion zones of the nodes of Ranvier in the TREZ, the diameter of nerve fibers and the length of the nodal gap. The transcriptional levels of prothrombin and endogenous thrombin inhibitor protease nexin-1 (PN-1) in the TREZ of TN rats were assessed by RT-qPCR. A Western blotting assay was performed to detect the expression of paranodal proteins neurofascin-155 (NF155) and neurofascin-125 (NF125) in the TREZ. The spatiotemporal expression pattern of thrombin activated receptor (i.e. protease activated receptor 1, PAR1) in TREZ were defined by immunostaining and immunoblotting assays. PAR1 receptor inhibitors SCH79797 were administrated to TN rats to analyze the effect of thrombin-PAR1 on orofacial hyperalgesia. A compression injury of a rat's TREZ successfully induced TN-like behavior and was accompanied by the destruction of the permeability of the BNB and the promotion of prothrombin and thrombin inhibitor protease nexin-1 (PN-1) expression. The expression of the paranodal proteins neurofascin-155 (NF155) and neurofascin-125 (NF125) was increased, while the nodal gap length of the nodes of Ranvier was widened and the length of node-depleted zones was shortened. Moreover, the expression of PAR1 within the TREZ was upregulated at an early stage of TN, and administration of the PAR1 antagonist SCH79797 effectively ameliorated orofacial mechanical allodynia. A compression injury of the TREZ increased the permeability of the BNB and induced disturbances in the local coagulation-anticoagulation system, concomitant with the structural changes in the nodes of Ranvier, thrombin-PAR1 may play a critical role in modulating orofacial mechanical hyperalgesia in a TN rat model.

Pro-inflammatory cytokines and leukocyte integrins associated with chronic neuropathic pain in traumatic and inflammatory neuropathies: Initial observations and hypotheses.

Leukocyte infiltration and persistence within peripheral nerves have been implicated in chronic nociception pathogenesis in murine peripheral neuropathy models. Endoneurial cytokine and chemokine expression contribute to leukocyte infiltration and maintenance of a pro-inflammatory state that delays peripheral nerve recovery and promotes chronic pain behaviors in these mice. However, there has been a failure to translate murine model data into safe and effective treatments for chronic neuropathic pain in peripheral neuropathy patients, or develop reliable biomarkers that may help diagnose or determine treatment responses in affected patients. Initial work showed that persistent sciatic nerve CD11b+ CD45+ leukocyte infiltration was associated with disease severity in three mouse models of inflammatory and traumatic peripheral neuropathies, implying a direct contributing role in disease pathogenesis. In support of this, CD11b+ leukocytes were also seen in the sural nerve biopsies of chronic neuropathic pain patients with three different peripheral neuropathies. Systemic CD11b antagonism using a validated function-neutralizing monoclonal antibody effectively treated chronic nociception following unilateral sciatic nerve crush injury (a representative traumatic neuropathy model associated with axonal degeneration and increased blood-nerve barrier permeability) and does not cause drug addiction behaviors in adult mice. These data suggest that CD11b could be an effective molecular target for chronic neuropathic pain treatment in inflammatory and traumatic peripheral neuropathies. Despite known murine peripheral neuropathy model limitations, our initial work suggests that early expression of pro-inflammatory cytokines, such as tissue inhibitor of metalloproteinases-1 may predict subsequent chronic nociception development following unilateral sciatic nerve crush injury. Studies aligning animal model investigation with observational data from well-characterized human peripheral neuropathies, including transcriptomics and proteomics, as well as animal model studies using a human clinical trial design should foster the identification of clinically relevant biomarkers and effective targeted treatments with limited addiction potential for chronic neuropathic pain in peripheral neuropathy patients.

GPR40 Activation Abolishes Diabetes-Induced Painful Neuropathy by Suppressing VEGF-A Expression.

G-protein-coupled receptor 40 (GPR40) is a promising target to support glucose-induced insulin release in patients with type 2 diabetes. We studied the role of GPR40 in the regulation of blood-nerve barrier integrity and its involvement in diabetes-induced neuropathies. Because GPR40 modulates insulin release, we used the streptozotocin model for type 1 diabetes, in which GPR40 functions can be investigated independently of its effects on insulin release. Diabetic wild-type mice exhibited increased vascular endothelial permeability and showed epineural microlesions in sciatic nerves, which were also observed in naïve GPR40-/- mice. Fittingly, expression of vascular endothelial growth factor-A (VEGF-A), an inducer of vascular permeability, was increased in diabetic wild-type and naïve GPR40-/- mice. GPR40 antagonists increased VEGF-A expression in murine and human endothelial cells as well as permeability of transendothelial barriers. In contrast, GPR40 agonists suppressed VEGF-A release and mRNA expression. The VEGF receptor inhibitor axitinib prevented diabetes-induced hypersensitivities and reduced endothelial and epineural permeability. Importantly, the GPR40 agonist GW9508 reverted established diabetes-induced hypersensitivity, an effect that was blocked by VEGF-A administration. Thus, GPR40 activation suppresses VEGF-A expression, thereby reducing diabetes-induced blood-nerve barrier permeability and reverting diabetes-induced hypersensitivities.

Jmjd3 Mediates Neuropathic Pain by Inducing Macrophage Infiltration and Activation in Lumbar Spinal Stenosis Animal Model.

Lumbar spinal stenosis (LSS) is a major cause of chronic neuropathic back and/or leg pain. Recently, we demonstrated that a significant number of macrophages infiltrated into the cauda equina after compression injury, causing neuroinflammation, and consequently mediating neuropathic pain development and/or maintenance. However, the molecular mechanisms underlying macrophage infiltration and activation have not been elucidated. Here, we demonstrated the critical role of histone H3K27 demethylase Jmjd3 in blood-nerve barrier dysfunction following macrophage infiltration and activation in LSS rats. The LSS rat model was induced by cauda equina compression using a silicone block within the epidural spaces of the L5-L6 vertebrae with neuropathic pain developing 4 weeks after compression. We found that Jmjd3 was induced in the blood vessels and infiltrated macrophages in a rat model of neuropathic pain. The blood-nerve barrier permeability in the cauda equina was increased after compression and significantly attenuated by the Jmjd3 demethylase inhibitor, GSK-J4. GSK-J4 also inhibited the expression and activation of MMP-2 and MMP-9 and significantly alleviated the loss of tight junction proteins and macrophage infiltration. Furthermore, the activation of a macrophage cell line, RAW 264.7, by LPS was significantly alleviated by GSK-J4. Finally, GSK-J4 and a potential Jmjd3 inhibitor, gallic acid, significantly inhibited mechanical allodynia in LSS rats. Thus, our findings suggest that Jmjd3 mediates neuropathic pain development and maintenance by inducing macrophage infiltration and activation after cauda equina compression and thus may serve as a potential therapeutic target for LSS-induced neuropathic pain.

Prostaglandin D2 synthase modulates macrophage activity and accumulation in injured peripheral nerves.

We have previously reported that prostaglandin D2 Synthase (L-PGDS) participates in peripheral nervous system (PNS) myelination during development. We now describe the role of L-PGDS in the resolution of PNS injury, similarly to other members of the prostaglandin synthase family, which are important for Wallerian degeneration (WD) and axonal regeneration. Our analyses show that L-PGDS expression is modulated after injury in both sciatic nerves and dorsal root ganglia neurons, indicating that it might play a role in the WD process. Accordingly, our data reveals that L-PGDS regulates macrophages phagocytic activity through a non-cell autonomous mechanism, allowing myelin debris clearance and favoring axonal regeneration and remyelination. In addition, L-PGDS also appear to control macrophages accumulation in injured nerves, possibly by regulating the blood-nerve barrier permeability and SOX2 expression levels in Schwann cells. Collectively, our results suggest that L-PGDS has multiple functions during nerve regeneration and remyelination. Based on the results of this study, we posit that L-PGDS acts as an anti-inflammatory agent in the late phases of WD, and cooperates in the resolution of the inflammatory response. Thus, pharmacological activation of the L-PGDS pathway might prove beneficial in resolving peripheral nerve injury.

Peripheral nerve pathology in sickle cell disease mice.

Introduction:Many patients with sickle cell disease (SCD) suffer from chronic pain, which is often described as neuropathic in nature. Although vascular and inflammatory pathology undoubtedly contribute to the SCD pain experience, the nociceptive signals that ultimately drive symptoms are detected and transmitted by peripheral sensory neurons. To date, no systematic histological examination of peripheral nerves has been completed in patients or mouse models of SCD to diagnose disease-related neuropathy.Objectives:In this brief report, we compared peripheral nerve morphology in tissues obtained from Berkeley transgenic SCD mice and control animals.Methods:Sciatic nerves were visualized using light and transmission electron microscopy. Myelin basic protein expression was assessed through Western blot. Blood–nerve barrier permeability was measured using Evan's blue plasma extravasation.Results:Peripheral fibers from SCD mice have thinner myelin sheaths than control mice and widespread myelin instability as evidenced by myelin sheath infolding and unwrapping. Deficits are also observed in nonmyelinating Schwann cell structures; Remak bundles from SCD nerves contain fewer C fibers, some of which are not fully ensheathed by the corresponding Schwann cell. Increased blood–nerve barrier permeability and expression of myelin basic protein are noted in SCD tissue.Conclusions:These data are the first to characterize Berkeley SCD mice as a naturally occurring model of peripheral neuropathy. Widespread myelin instability is observed in nerves from SCD mice. This pathology may be explained by increased permeability of the blood–nerve barrier and, thus, increased access to circulating demyelinating agents at the level of primary sensory afferents.

Intrathecal antibody responses to GalC in Guillain-Barré syndrome triggered by Mycoplasma pneumoniae

Mycoplasma pneumoniae (Mp) triggers Guillain-Barré syndrome (GBS) and elicits anti-galactocerebroside (GalC) antibodies. Specifically anti-GalC IgG is associated with Mp-GBS, possibly because of its better ability to cross the blood-nerve barrier (BNB). We here investigated CSF for the presence of anti-GalC in GBS. Intrathecal anti-GalC was found in 46% of Mp-GBS patients (n=6/13), in contrast to 16% of GBS controls (n=4/25) and 0% of non-GBS controls (n=0/7). The antibodies most likely originated from increased BNB permeability and/or intrathecal synthesis. Intrathecal anti-GalC IgG was specifically associated with Mp-GBS, further supporting that anti-GalC IgG contributes to the pathogenesis of GBS.

Early alterations of Hedgehog signaling pathway in vascular endothelial cells after peripheral nerve injury elicit blood-nerve barrier disruption, nerve inflammation, and neuropathic pain development.

Changes in the nerve's microenvironment and local inflammation resulting from peripheral nerve injury participate in nerve sensitization and neuropathic pain development. Taking part in these early changes, disruption of the blood-nerve barrier (BNB) allows for infiltration of immunocytes and promotes the neuroinflammation. However, molecular mechanisms engaged in vascular endothelial cells (VEC) dysfunction and BNB alterations remain unclear. In vivo, BNB permeability was assessed following chronic constriction injury (CCI) of the rat sciatic nerve (ScN) and differential expression of markers of VEC functional state, inflammation, and intracellular signaling was followed from 3 hours to 2 months postinjury. Several mechanisms potentially involved in functional alterations of VEC were evaluated in vitro using human VEC (hCMEC/D3), then confronted to in vivo physiopathological conditions. CCI of the ScN led to a rapid disruption of endoneurial vascular barrier that was correlated to a decreased production of endothelial tight-junction proteins and an early and sustained alteration of Hedgehog (Hh) signaling pathway. In vitro, activation of Toll-like receptor 4 in VEC downregulated the components of Hh pathway and altered the endothelial functional state. Inhibition of Hh signaling in the ScN of naive rats mimicked the biochemical and functional alterations observed after CCI and was, on its own, sufficient to evoke local neuroinflammation and sustained mechanical allodynia. Alteration of the Hh signaling pathway in VEC associated with peripheral nerve injury, is involved in BNB disruption and local inflammation, and could thus participate in the early changes leading to the peripheral nerve sensitization and, ultimately, neuropathic pain development.

Topical tranexamic Acid does not affect electrophysiologic or neurovascular sciatic nerve markers in an animal model.

Tranexamic acid is a safe and effective antifibrinolytic agent used systemically and topically to reduce blood loss and transfusion rate in patients having TKA or THA. As the hip does not have a defined capsule, topical application of tranexamic acid may entirely envelop the sciatic nerve during THA. Accidental application of tranexamic acid onto the spinal cord in spinal anesthesia has been shown to produce seizures; therefore, we sought to investigate if topical application of tranexamic acid on the sciatic nerve has a deleterious effect. We explored whether there were any short- or long-term alterations in (1) electrophysiologic measures, (2) macrophage recruitment, or (3) blood-nerve barrier permeability. Our hypothesis was that local application of tranexamic acid would have a transient effect or no effect on histologic features and function of the sciatic nerve. We used a rat protocol to model sciatic nerve exposure in THA to determine the effects of tranexamic acid on neural histologic features and function. We evaluated 35 rats by the dorsal gluteal splitting approach to expose the sciatic nerve for topical use of control and tranexamic acid. We evaluated EMG changes (distal latency, amplitude, nerve conduction velocity), histologic signs of nerve injury via macrophage recruitment, and changes in blood-nerve barrier permeability at early (4 days) and late (1 month) times after surgery, after application of subtherapeutic (1 mg/kg body weight [1.6 mg]), therapeutic (10 mg/kg [16 mg]), and supratherapeutic (100 mg/kg [160 mg]) concentrations of tranexamic acid. Differences in blood-nerve barrier permeability, macrophage recruitment, and EMG between normal and tranexamic acid-treated nerves were calculated using one-way ANOVA, with Newman-Keuls post hoc analyses, at each time. A post hoc power calculation showed that with the numbers available, we had 16% power to detect a 50% difference in EMG changes between the control, 1 mg/kg group, 10 mg/kg group, and 100 mg/kg group. At the early and late times, with the numbers available, there were no differences in EMG except for distal latency at 4 days, macrophage recruitment, or changes in blood-nerve barrier between control rats and those with tranexamic acid-treated nerves. The distal latency in the 1 mg tranexamic acid-treated animals at 4 days was 1.06 ± 0.15 ms (p = 0.0036 versus all other groups, 95% CI, 0.89-1.25), whereas the distal latencies in the control, the 10 mg/kg, and 100 mg/kg tranexamic acid-treated animals were 0.83 ± 0.11, 0.89 ± 0.05, and 0.87 ± 0.13, respectively. Distal latencies were not increased in any of the groups at 1 month with the numbers available (0.81 ± 0.10, 0.89 ± 0.03, 0.81 ± 0.06, and 0.83 ± 0.08 ms, respectively, for controls; 1 mg/kg, 10 mg/kg, and 100 mg/kg for the tranexamic acid-treated groups). In our in vivo rat model study, tranexamic acid did not appear to have any clinically relevant effect on the sciatic nerve resulting from topical administration up to 1 month. However, because our statistical power was low, these data should be considered hypothesis-generating pilot data for larger, more-definitive studies. Topical tranexamic acid is effective in decreasing patient blood loss during THA, and results from our in vivo rat model study suggest there may be no electrophysiologic and histologic effects on the sciatic nerve, with the numbers available, up to 1 month.

Safety, efficacy, and molecular mechanism of claudin-1-specific peptides to enhance blood–nerve–barrier permeability

The blood–nerve barrier consists of the perineurium and endoneurial vessels. The perineurial barrier is composed of a basal membrane and a layer of perineurial cells sealed by tight junction proteins preventing e.g. application of analgesics for selective regional pain control. One of the barrier-sealing proteins in the blood–nerve barrier is claudin-1. Therefore, the claudin-1-peptidomimetics (C1C2), derived from the first extracellular loop (ECL1) on claudin-1 was developed. In this study, we further evaluated the expression of tight junction proteins in the perineurium in Wistar rats and characterized the specificity, in vivo applicability, mechanism of action as well as the biocompatibility of C1C2. In the perineurium, claudin-19, tricellulin and ZO-1, but no claudin-2, 3, 8 and -11 were expressed. C1C2 specifically bound to the ECL1 of claudin-1 and fluorescent 5,6-carboxytetramethylrhodamine-C1C2 was rapidly internalized. Opening the perineurium with C1C2 reduced the mRNA and protein expression of claudin-1 and increased small and macromolecule permeability into the peripheral nerve. Application of C1C2 facilitated regional analgesia using μ-opioid receptor agonists like DAMGO or morphine without motor impairment in naïve rats as well as rats with hind paw inflammation. In contrast the control peptide C2C2 derived from ECL1 on claudin-2 did neither open the barrier nor facilitated opioid-mediated regional analgesia. C1C2 delivery was well tolerated and caused no morphological and functional nerve damage. C1C2 effects could be reversed by interference with the wnt-signal-transduction pathway, specifically the homeobox transcription factor cdx2, using a glycogen-synthase-kinase-3 inhibitor. In summary, we describe the composition of and a pathway to open the perineurial barrier employing a peptide to deliver hydrophilic substances to the peripheral nerve.

Artificial control of blood-nerve barrier: a novel therapeutic approach to peripheral neuropathies

Blood-nerve barrier (BNB) is a "Janus-faced" structure for the peripheral nerve parenchyma. Healthy BNB may contribute to stabilize the internal milleu of peripheral nervous system (PNS) and to stop the entrance of toxic substances and harmful leukocytes into nerve parenchyma. On the other hand, healthy BNB may sometimes be a drawback because the peripheral nerve parenchyma cannot receive enough amount of nutrients and growth factors and cannot excrete toxic substances into systemic circulation because of its presence. Here we present a future therapeutic strategy to control BNB function, based on the basic knowledge acquired from recently developed human immortalized cell lines of BNB origin. If we can artificially regulate the BNB permeability and the expression of adhesion molecules on the surface of BNB-forming endothelial cells, and stop the entrance of toxic substances as well as pathogenic leukocytes into PNS parenchyma, the treatment of inflammatory neuropathies may make great progresses. For hereditary, metabolic and ischemic neuropathies, the promotion of the entrance of growth factors into PNS parenchyma and of the excretion of toxic substances should powerfully encourage the regeneration of axons.

The effect of 2,5-hexanedione on permeability of blood-nerve barrier in rats

To explore the effect of 2,5-hexanedione on permeability of blood-nerve barrier, adult Wistar rats were administered with 400 mg x kg(-1) x d(- 1) 2,5-hexanedione to establish animal model of 2,5-hexnedione neuropathy. Evans blue was injected through left femoral vein of the rats after the model had been established. The distribution of fluorescence in sciatic-tibial nerve was observed and assessed. For the transverse sections of sciatic-tibial nerves, the average fluorescence intensity of proximal section was stronger (p < .01) than those of intermediate and distal sections and the average fluorescence intensity of intermediate section was stronger (p < .01) than that of distal section in the intoxicated group. In the control, the weak fluorescence was shown, and average fluorescence intensity of distal section was stronger (p < .05) than that of proximal section. The average fluorescence intensity of proximal, intermediate and distal sections in the intoxicated group was stronger (p < .01) than those of the corresponding sections in the control. For the longitudinal sections of sciatic-tibial nerves, fluorescence was observed in both proximal and distal sections in the intoxicated group. The fluorescence intensity of distal section in the control was weak and almost no fluorescence was shown in the proximal section. The permeability of blood-nerve barrier could be increased by 2,5-hexanedione.

Development of the blood-nerve barrier in neonatal rats.

The blood-nerve barrier (BNB) is constituted by the perineurium and the endothelium of endoneurial microvessels. We investigated the age at which the vascular component of BNB function is established in the rat and the ultrastructural modifications accompanying changes in permeability. BNB permeability was assessed with injections of Evans blue albumin (EBA) and horseradish peroxidase (HRP) in rats of different ages. Sciatic nerve sections were studied using fluorescence and electron microscopy. Nerves from animals injected with EBA indicated that the BNB is not functional before 13 days of life but that its function is established by 16 days. These results were confirmed by electron microscope examination of nerve sections from animals injected with HRP, which showed clefts between the endothelial cells of endoneurial vessels in young rats. In rats over 18 days, these clefts were occluded by tight junctions, which prevented HRP from leaving the vessel lumen and conferred BNB function. Systematic morphometric analysis of nerves from different age groups allowed the establishment of baseline normal histologic neural development with age.

Activated T cells of nonneural specificity open the blood-nerve barrier to circulating antibody.

Recent studies from our laboratory and by other investigators have shown that autoreactive CD4+ cells specific for peripheral nerve P2 protein have a powerful effect on blood-nerve barrier permeability. In this study we injected CD4+ T cells reactive to a nonneural antigen (ovalbumin) systemically and achieved their accumulation in the tibial nerve of Lewis rats by previous intraneural injection of ovalbumin. Selected rats were given systemic demyelinating antibody (antigalactocerebroside) to provide an indicator of changes in the permeability of the blood-nerve barrier, and the animals were monitored by sequential neurophysiological studies and histology. Circulating ovalbumin-specific T cells accumulated at sites of intraneural ovalbumin injection without inducing demyelination in control animals. In rats with circulating galactocerebroside antibodies, local conduction block and demyelination were seen in the region of T-cell accumulation. Electron microscopy demonstrated dissolution of some tight junctions between endothelial cells in areas of T-cell accumulation, and T cells traversing the endothelium between endothelial cells and through their cytoplasm. Endothelial cell damage was evident in these areas. This study demonstrates breakdown of the blood-nerve barrier by activated T cells, even of nonneural specificity, allowing the development of focal conduction block and demyelination in the presence of circulating antimyelin antibodies.

Mast cell degranulation and blood-nerve barrier permeability in rat sciatic nerve after 7 days of hyperglycemia

The association between hyperglycemia and altered blood-nerve barrier permeability was examined after 7 days of experimental diabetes. In nerves of rats fed a diet of 40% galactose, permeability to [14C]mannitol [13.43 +/- 2.47 x 10(-5) (SD) ml.s-1.g dry wt-1] and water content [3.43 +/- 0.24 (SD) mg/mg dry wt] were significantly increased compared with control (9.24 +/- 2.09 x 10(-5) ml.s-1.g dry wt-1 and 2.15 +/- 0.28 mg/mg dry wt) and streptozotocin-diabetic animals (8.43 +/- 2.94 x 10(-5) ml.s.-1.g dry wt-1 and 2.35 +/- 0.56 mg/mg dry wt). Electron microscopy revealed significant increases in the number of degranulating perivascular mast cells and in an index of vasoconstriction in galactose-treated rats (3.8 +/- 1.6 and 0.160 +/- 0.062, respectively) compared with control (0.5 +/- 0.8 and 0.072 +/- 0.017, respectively) and diabetic animals (1.4 +/- 1.7 and 0.083 +/- 0.033, respectively). The data are consistent with a role for mast cells in permeability changes occurring after only 7 days of galactose intoxication.

Non-neural-specific T lymphocytes can orchestrate inflammatory peripheral neuropathy.

Neural-specific T lymphocytes are held to play a pathological role in inflammatory peripheral nerve disorders such as the Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP). Here, non-neural-specific T-cell-mediated inflammation was studied in peripheral nerves in Lewis rats by systemic transfer of ovalbumin-specific activated T cells followed by intraneural injection of ovalbumin. Rapid endoneurial perivenular infiltration of alpha beta T cells and ED1+ macrophages occurred with ovalbumin injection following transfer of 2 x 10(6) T cells. This cellular infiltration and accumulation produced marked increases in blood-nerve barrier (BNB) permeability. In contrast, control casein injections produced neither significant cell accumulation nor BNB permeability changes. Transfer of a higher number of T cells (5 x 10(6)) induced severe Wallerian degeneration and nerve conduction failure in ovalbumin injected nerves. Fewer T cells (5 x 10(5)) induced conduction block and mild demyelination which were markedly augmented by systemic cotransfer of anti-myelin immunoglobulin. This study demonstrates that activated T cells of non-neural specificity can accumulate in peripheral nerve, produce dramatic changes in BNB permeability and with intravenous anti-myelin antibody orchestrate primary demyelination or axonal degeneration in a dose-dependent fashion.

Effects of mast cell degranulation on blood-nerve barrier permeability and nerve conduction in vivo

Changes in blood-nerve barrier (BNB) integrity and nerve conduction were assessed in rat tibial nerves in which mast cell degranulation was induced by intraneural injection of Compound 48 80 ( C 48 80 ) . BNB permeability changes were quantitated by the endoneurial accumulation of Evan's blue-labelled albumin (EBA). Over 24 h following intraneural injections, nerves receiving saline showed a 6-fold increase in endoneurial extravasated EBA compared to non-injected nerves. Injection of 250 ng C 48 80 produced a similar level of EBA accumulation as saline injections. Increasing the C 48 80 dose to 1 μg produced twice the EBA accumulation as control saline injections and a 12-fold increase over non-injected nerves. Tibial nerves injected with these C 48 80 doses showed completely normal nerve conduction. In contrast, increasing the dose to 5 μg C 48 80 induced, again, increased EBA accumulation over lower doses, but also significant axonal degeneration indicated by profound decreases in compound muscle action potential amplitudes measured with nerve stimulation distal to the injection site. Co-injection of Leupeptin and neutralizing anti-TNF-alpha antibodies with C 48 80 failed to mitigate conduction abnormalities suggesting a direct toxic effect of C 48 80 on nerve fibres. Time-kinetic studies showed rapid restoration of BNB integrity 24–48 h after injections in all nerves, but at these timepoints C 48 80 injected nerves still showed significantly increased BNB permeability compared to nerves injected with saline. Neural mast cell stimulation in the absence of a primed immune response can produce profound temporary changes in blood-nerve barrier permeability and endoneurial fluid composition without affecting nerve conduction.

Restoration of Blood-Nerve Barrier in Neuropathy is Associated with Axonal Regeneration and Remyelination

We investigated the temporal course of blood-nerve barrier (BNB) breakdown during the evolution of tellurium neuropathy, ricin neuropathy, and Wallerian degeneration following nerve transection or nerve crush. Blood-nerve barrier permeability was assessed with a 4,000-molecular weight fluoresceinated dextran from three days to 19 weeks after onset of neuropathy. Blood-nerve barrier breakdown was present during the first two weeks in all four models of neuropathy. Restoration of the BNB to the dextran began within four weeks and was complete by 14 weeks in tellurium neuropathy, a model of demyelinating neuropathy characterized by rapid remyelination, and after nerve crush, a model of Wallerian degeneration characterized by rapid axonal regeneration into distal stump. In contrast, there was persistence of BNB breakdown beyond 14 weeks in ricin neuropathy, a model of neuropathy with no axonal regeneration or remyelination, and after nerve transection, a model of Wallerian degeneration characterized by minimal axonal regeneration into distal stump. We conclude from these data that alterations in the BNB over the course of neuropathy differ among various types of neuropathy, and that these alterations are dependent on the form of nerve fiber injury. The lack of regenerating or remyelinating axons in ricin neuropathy and after nerve transection may be responsible for the persistent BNB breakdown found in these neuropathies.

Prevention of Nerve Edema and Increased Blood-Nerve Barrier Permeability–Surface Area Product in Galactosemic Rats by Aldose Reductase or Thromboxane Synthetase Inhibitors

Nerve water content and the permeability-surface area product (PA) to [3H]-or [14C]sucrose at the blood-nerve barrier were determined in unanesthetized control rats fed a normal diet and in rats fed galactose with or without an aldose reductase inhibitor (Statil or AL 1576) or a thromboxane synthetase inhibitor (CGS 12970). Nerve water content was determined by taking the difference between dry and wet weights of whole tibial nerves. PA was determined by an intravenous bolus injection of radiotracer with multiple-time-point graphic and quantitative autoradiographic methods. The mean nerve water content in galactosemic rats was 15% higher than in control rats after 7-11 mo on the diet. Statil and AL 1576 prevented nerve edema, but CGS 12970 was only partially effective in preventing an increase in nerve water content in galactose-fed rats. In galactosemic rats, the mean PA to sucrose at the blood-nerve barrier, calculated from nerve dry weight, was twofold higher than in control rats. Treatment with Statil, AL 1576, or CGS 12970 prevented increased PA. Our results suggest that nerve edema and increased blood-nerve barrier PA are secondary to polyol production and can be prevented by inhibiting aldose reductase.