The blood-nerve barrier in Wallerian degeneration: a sequential long-term study

Engineered bio-functional material-based nerve guide conduits for optic nerve regeneration: a view from the cellular perspective, challenges and the future outlook

Nerve injuries can be tantamount to severe impairment, standard treatment such as the use of autograft or surgery comes with complications and confers a shortened relief. The mechanism relevant to the regeneration of the optic nerve seems yet to be fully uncovered. The prevailing rate of vision loss as a result of direct or indirect insult on the optic nerve is alarming. Currently, the use of nerve guide conduits (NGC) to some extent has proven reliable especially in rodents and among the peripheral nervous system, a promising ground for regeneration and functional recovery, however in the optic nerve, this NGC function seems quite unfamous. The insufficient NGC application and the unabridged regeneration of the optic nerve could be a result of the limited information on cellular and molecular activities. This review seeks to tackle two major factors (i) the cellular and molecular activity involved in traumatic optic neuropathy and (ii) the NGC application for the optic nerve regeneration. The understanding of cellular and molecular concepts encompassed, ocular inflammation, extrinsic signaling and intrinsic signaling for axon growth, mobile zinc role, Ca2+ factor associated with the optic nerve, alternative therapies from nanotechnology based on the molecular information and finally the nanotechnological outlook encompassing applicable biomaterials and the use of NGC for regeneration. The challenges and future outlook regarding optic nerve regenerations are also discussed. Upon the many approaches used, the comprehensive role of the cellular and molecular mechanism may set grounds for the efficient application of the NGC for optic nerve regeneration.

Photosealed Neurorrhaphy Using Autologous Tissue

Photochemical sealing of a nerve wrap over the repair site isolates and optimizes the regenerating nerve microenvironment. To facilitate clinical adoption of the technology, we investigated photosealed autologous tissue in a rodent sciatic nerve transection and repair model. Rats underwent transection of the sciatic nerve with repair performed in three groups: standard microsurgical neurorrhaphy (SN) and photochemical sealing with a crosslinked human amnion (xHAM) or autologous vein. Functional recovery was assessed at four-week intervals using footprint analysis. Gastrocnemius muscle mass preservation, histology, and nerve histomorphometry were evaluated at 120 days. Nerves treated with a PTB-sealed autologous vein improved functional recovery at 120 days although the comparison between groups was not significantly different (SN: -58.4 +/- 10.9; XHAM: -57.9 +/- 8.7; Vein: -52.4 +/- 17.1). Good muscle mass preservation was observed in all groups, with no statistical differences between groups (SN: 69 +/- 7%; XHAM: 70 +/- 7%; Vein: 70 +/- 7%). Histomorphometry showed good axonal regeneration in all repair techniques. These results demonstrate that peripheral nerve repair using photosealed autologous veins produced regeneration at least equivalent to current gold-standard microsurgery. The use of autologous veins removes costs and foreign body concerns and would be readily available during surgery. This study illustrates a new repair method that could restore normal endoneurial homeostasis with minimal trauma following severe nerve injury.

Neuromuscular ultrasound changes in unilateral symptomatic subacute lumbosacral radiculopathy: A prospective simple blinded cohort study

INTRODUCTION/AIMS

Lumbosacral radiculopathy (LR) is a common disorder. Neuromuscular ultrasound (NMU) is a rapidly evolving technique for the investigation of peripheral nerve and muscle disorders, but studies using NMU in LR are lacking. The aim of the present study was to investigate ultrasonographic neuromuscular changes distant from root compression in patients with subacute to chronic compressive LR with motor impairment.

METHODS

Patients with unilateral subacute to chronic L4, L5, or S1 radiculopathy with motor impairment and confirmed by magnetic resonance imaging were included. The sciatic and femoral nerve cross-sectional areas (CSA), the CSA of lower limb muscles, and muscle fasciculation detection rate were assessed using a pre-specified neuromuscular ultrasound evaluation with blinded side-to-side comparison.

RESULTS

Of the 18 included patients, 66% were male and the mean age was 51 years. Overall, 16.7% had L4, 55.5% L5, and 27.8% S1 radiculopathy, mostly due to disc herniation (83%). Sciatic nerve CSA of the symptomatic side was increased (61.4 mm2 vs. 51.3 mm2; p = .001), and the fasciculation detection rate was higher in the affected muscles (delta = 13%, p = .007) compared to unaffected ones. Muscle CSA in affected and nonaffected muscles was decreased on the symptomatic side.

DISCUSSION

NMU evaluation in patients with symptomatic subacute to chronic LR revealed sciatic nerve enlargement distant from nerve root compression and higher fasciculation rates. These structural findings on NMU might be due to an axonal repair mechanism and an inflammatory response with endoneurial edema induced by ongoing nerve damage and potentially reflect progressive axonal loss.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration and regeneration: part 2, non-invasive imaging

Peripheral neuroregenerative research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, novel biomarkers can elucidate regenerative mechanisms and open new avenues for research. Without such measures, clinical decision-making is impaired, and research becomes more costly, time-consuming, and sometimes infeasible. Part 1 of this two-part scoping review focused on neurophysiology. In part 2, we identify and critically examine many current and emerging non-invasive imaging techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Contrast-enhanced ultrasound of a traumatic neuroma of the extrahepatic bile duct: A case report and review of literature

BACKGROUND

Traumatic neuromas result from nerve injury after trauma or surgery but rarely occur in the bile duct. However, it is challenging to diagnose traumatic neuromas correctly preoperatively. Although some previous reports have described the imaging features of traumatic neuroma in the bile duct, no features of traumatic neuromas in the bile duct have been identified by using contrast-enhanced ultrasound (CEUS) imaging before.

CASE SUMMARY

A 55-year-old male patient presented to our hospital with a 3-mo history of abdominal distension and anorexia and history of cholecystectomy 4 years ago. Grayscale ultrasound demonstrated mild to moderate intrahepatic bile duct dilatation. Meanwhile, a hyperechoic nodule was found in the upper extrahepatic bile duct. The lesion approximately 0.8 cm × 0.6 cm with a regular shape and clear margins. The nodule of the bile duct showed slight hyperenhancement in the arterial phase and isoenhancement in the venous phase on CEUS. Laboratory tests showed that alanine aminotransferase and aspartate aminotransferase were increased significantly, while the tumor marker carbohydrate antigen 19-9 was increased slightly. Then, hilar bile duct resection and end-to-end bile ductal anastomosis were performed. The histological examination revealed traumatic neuroma of the extrahepatic bile duct. The patient had an uneventful recovery after surgery.

CONCLUSION

The current report will help enhance the current knowledge regarding identifying traumatic neuromas by CEUS imaging and review the related literature.

Neuroinflammation, Microglia and Implications for Retinal Ganglion Cell Survival and Axon Regeneration in Traumatic Optic Neuropathy

Traumatic optic neuropathy (TON) refers to a pathological condition caused by a direct or indirect insult to the optic nerves, which often leads to a partial or permanent vision deficit due to the massive loss of retinal ganglion cells (RGCs) and their axonal fibers. Retinal microglia are immune-competent cells residing in the retina. In rodent models of optic nerve crush (ONC) injury, resident retinal microglia gradually become activated, form end-to-end alignments in the vicinity of degenerating RGC axons, and actively internalized them. Some activated microglia adopt an amoeboid morphology that engulf dying RGCs after ONC. In the injured optic nerve, the activated microglia contribute to the myelin debris clearance at the lesion site. However, phagocytic capacity of resident retinal microglia is extremely poor and therefore the clearance of cellular and myelin debris is largely ineffective. The presence of growth-inhibitory myelin debris and glial scar formed by reactive astrocytes inhibit the regeneration of RGC axons, which accounts for the poor visual function recovery in patients with TON. In this Review, we summarize the current understanding of resident retinal microglia in RGC survival and axon regeneration after ONC. Resident retinal microglia play a key role in facilitating Wallerian degeneration and the subsequent axon regeneration after ONC. However, they are also responsible for producing pro-inflammatory cytokines, chemokines, and reactive oxygen species that possess neurotoxic effects on RGCs. Intraocular inflammation triggers a massive influx of blood-borne myeloid cells which produce oncomodulin to promote RGC survival and axon regeneration. However, intraocular inflammation induces chronic neuroinflammation which exacerbates secondary tissue damages and limits visual function recovery after ONC. Activated retinal microglia is required for the proliferation of oligodendrocyte precursor cells (OPCs); however, sustained activation of retinal microglia suppress the differentiation of OPCs into mature oligodendrocytes for remyelination after injury. Collectively, controlled activation of retinal microglia and infiltrating myeloid cells facilitate axon regeneration and nerve repair. Recent advance in single-cell RNA-sequencing and identification of microglia-specific markers could improve our understanding on microglial biology and to facilitate the development of novel therapeutic strategies aiming to switch resident retinal microglia’s phenotype to foster neuroprotection.

Ventricular Infusion and Nanoprobes Identify Cerebrospinal Fluid and Glymphatic Circulation in Human Nerves

Growing evidence suggests that cerebrospinal fluid circulates in human nerves. Several conditions encountered by the plastic surgeon may be related to dysregulation of this system, including nerve transection, stretch injuries, and peripheral neuropathy. The purpose of this study was to show how ventricular infusion and nanoprobes identify CSF and glymphatic circulation in neural sheaths of human nerves.

METHODS

The technique of ventricular infusion using buffered saline was developed in 2017. The technique was used in a series of eight fresh cadavers before dissection of the median nerve, and combined with fluorescent imaging and nanoprobe injections in selected specimens.

RESULTS

Eight cadaver specimens underwent ventricular infusion. There were six female and two male specimens, ages 46-97 (mean 76.6). Ventricular cannulation was performed successfully using coordinates 2 cm anterior to coronal suture and 2.5 cm lateral to sagittal suture. Depth of cannulation ranged from 44 to 56 mm (mean 49.7). Ventricular saline infusion complemented by nanoprobe injection suggests CSF flows in neural sheaths, including pia meninges, epineurial channels, perineurium, and myelin sheaths (neurolemma).

CONCLUSIONS

Ventricular infusion and nanoprobes identify CSF flow in neural sheaths of human nerves. CSF flow in nerves is an open circulatory system that occurs via channels, intracellular flow, and cell-to-cell transport associated with glial cells. Neural sheaths, including neurolemma, may participate in glucose and solute transport to axons. These techniques may be used in anatomic dissection and live animal models, and have been extended to the central nervous system to identify direct ventricle-to-pia meninges CSF pathways.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Immune mechanisms, the role of complement, and related therapies in autoimmune neuropathies

INTRODUCTION

Autoimmune neuropathies have diverse presentations and underlying immune mechanisms. Demonstration of efficacy of therapeutic agents that inhibit the complement cascade would confirm the role of complement activation.

AREAS COVERED

A review of the pathophysiology of the autoimmune neuropathies, to identify those that are likely to be complement mediated.

EXPERT OPINION

Complement mediated mechanisms are implicated in the acute and chronic neuropathies associated with IgG or IgM antibodies that target the Myelin Associated Glycoprotein (MAG) or gangliosides in the peripheral nerves. Antibody and complement mechanisms are also suspected in the Guillain-Barré syndrome and chronic inflammatory demyelinating neuropathy, given the therapeutic response to plasmapheresis or intravenous immunoglobulins, even in the absence of an identifiable target antigen. Complement is unlikely to play a role in paraneoplastic sensory neuropathy associated with antibodies to HU/ANNA-1 given its intracellular localization. In chronic demyelinating neuropathy with anti-nodal/paranodal CNTN1, NFS-155, and CASPR1 antibodies, myotonia with anti-VGKC LGI1 or CASPR2 antibodies, or autoimmune autonomic neuropathy with anti-gAChR antibodies, the response to complement inhibitory agents would depend on the extent to which the antibodies exert their effects through complement dependent or independent mechanisms. Complement is also likely to play a role in Sjogren's, vasculitic, and cryoglobulinemic neuropathies.

From the low-density lipoprotein receptor-related protein 1 to neuropathic pain: a potentially novel target

The low-density lipoprotein receptor–related protein 1 plays a major role in the regulation of neuroinflammation, neurodegeneration, neuroregeneration, neuropathic pain, and deficient cognitive functions.

This review describes the roles of the low-density lipoprotein receptor–related protein 1 (LRP-1) in inflammatory pathways, nerve nerve degeneration and -regeneration and in neuropathic pain. Induction of LRP-1 is able to reduce the activation of the proinflammatory NFκB-mediated pathway and the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase and p38 signaling pathways, in turn decreasing the production of inflammatory mediators. Low-density lipoprotein receptor-related protein 1 activation also decreases reactive astrogliosis and polarizes microglial cells and macrophages from a proinflammatory phenotype (M1) to an anti-inflammatory phenotype (M2), attenuating the neuroinflammatory environment. Low-density lipoprotein receptor-related protein 1 can also modulate the permeability of the blood–brain barrier and the blood–nerve barrier, thus regulating the infiltration of systemic insults and cells into the central and the peripheral nervous system, respectively. Furthermore, LRP-1 is involved in the maturation of oligodendrocytes and in the activation, migration, and repair phenotype of Schwann cells, therefore suggesting a major role in restoring the myelin sheaths upon injury. Low-density lipoprotein receptor-related protein 1 activation can indirectly decrease neurodegeneration and neuropathic pain by attenuation of the inflammatory environment. Moreover, LRP-1 agonists can directly promote neural cell survival and neurite sprouting, decrease cell death, and attenuate pain and neurological disorders by the inhibition of MAPK c-Jun N-terminal kinase and p38-pathway and activation of MAPK extracellular signal–regulated kinase pathway. In addition, activation of LRP-1 resulted in better outcomes for neuropathies such as Alzheimer disease, nerve injury, or diabetic peripheral neuropathy, attenuating neuropathic pain and improving cognitive functions. To summarize, LRP-1 plays an important role in the development of different experimental diseases of the nervous system, and it is emerging as a very interesting therapeutic target.

Imaging in the repair of peripheral nerve injury

Surgical intervention followed by physical therapy remains the major way to repair damaged nerves and restore function. Imaging constitutes promising, yet underutilized, approaches to improve surgical and postoperative techniques. Dedicated methods for imaging nerve regeneration will potentially provide surgical guidance, enable recovery monitoring and postrepair intervention, elucidate failure mechanisms and optimize preclinical procedures. Herein, we present an outline of promising innovations in imaging-based tracking of in vivo peripheral nerve regeneration. We emphasize optical imaging because of its cost, versatility, relatively low toxicity and sensitivity. We discuss the use of targeted probes and contrast agents (small molecules and nanoparticles) to facilitate nerve regeneration imaging and the engineering of grafts that could be used to track nerve repair. We also discuss how new imaging methods might overcome the most significant challenges in nerve injury treatment.

Gadolinium DTPA Enhancement Characteristics of the Rat Sciatic Nerve after Crush Injury at 4.7T

BACKGROUND AND PURPOSE

Traumatic peripheral nerve injury is common and results in loss of function and/or neuropathic pain. MR neurography is a well-established technique for evaluating peripheral nerve anatomy and pathology. However, the Gd-DTPA enhancement characteristics of acutely injured peripheral nerves have not been fully examined. This study was performed to determine whether acutely crushed rat sciatic nerves demonstrate Gd-DTPA enhancement and, if so, to evaluate whether enhancement is affected by crush severity.

MATERIALS AND METHODS

In 26 rats, the sciatic nerve was crushed with either surgical forceps (6- to 20-N compressive force) or a microvascular/microaneurysm clip (0.1-0.6 N). Animals were longitudinally imaged at 4.7T for up to 30 days after injury. T1WI, T2WI, and T1WI with Gd-DTPA were performed.

RESULTS

Forceps crush injury caused robust enhancement between days 3 and 21, while clip crush injury resulted in minimal-to-no enhancement. Enhancement after forceps injury peaked at 7 days and was seen a few millimeters proximal to, in the region of, and several centimeters distal to the site of crush injury. Enhancement after forceps injury was statistically significant compared with clip injury between days 3 and 7 (P < .04).

CONCLUSIONS

Gd-DTPA enhancement of peripheral nerves may only occur above a certain crush-severity threshold. This phenomenon may explain the intermittent observation of Gd-DTPA enhancement of peripheral nerves after traumatic injury. The observation of enhancement may be useful in judging the severity of injury after nerve trauma.

Role of macrophages in Wallerian degeneration and axonal regeneration after peripheral nerve injury

The peripheral nervous system (PNS) has remarkable regenerative abilities after injury. Successful PNS regeneration relies on both injured axons and non-neuronal cells, including Schwann cells and immune cells. Macrophages are the most notable immune cells that play key roles in PNS injury and repair. Upon peripheral nerve injury, a large number of macrophages are accumulated at the injury sites, where they not only contribute to Wallerian degeneration, but also are educated by the local microenvironment and polarized to an anti-inflammatory phenotype (M2), thus contributing to axonal regeneration. Significant progress has been made in understanding how macrophages are educated and polarized in the injured microenvironment as well as how they contribute to axonal regeneration. Following the discussion on the main properties of macrophages and their phenotypes, in this review, we will summarize the current knowledge regarding the mechanisms of macrophage infiltration after PNS injury. Moreover, we will discuss the recent findings elucidating how macrophages are polarized to M2 phenotype in the injured PNS microenvironment, as well as the role and underlying mechanisms of macrophages in peripheral nerve injury, Wallerian degeneration and regeneration. Furthermore, we will highlight the potential application by targeting macrophages in treating peripheral nerve injury and peripheral neuropathies.

Circulatory dynamics of the cauda equina in lumbar canal stenosis using dynamic contrast-enhanced magnetic resonance imaging

BACKGROUND CONTEXT

There has been no study regarding the cauda equina circulation of patients with neurogenic intermittent claudication (NIC) in lumbar spinal canal stenosis (LSCS) using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

PURPOSE

The mechanism responsible for the onset of NIC was investigated using DCE-MRI to examine changes in cauda equina blood flow in patients with LSCS.

STUDY DESIGN

This was a retrospective longitudinal registry and magnetic resonance imaging study.

PATIENT SAMPLE

The subjects consisted of 23 patients who had LSCS associated with NIC (stenosis group). Ten asymptomatic volunteers who did not have NIC served as controls (control group). In the LSCS group, the cross-sectional area of the dural sac was <75 mm2 at the site of most severe stenosis. These patients were further divided into single and double stenosis subgroups.

OUTCOME MEASURES

The main measures we used were the signal intensity (S-I) ratio and the shape and size of the time intensity (T-I) curves. We compared these between the stenosis and control groups.

METHODS

At first, plain T1-weighted MR images were obtained and the lumbar dural sac cross-sectional area was measured using a digitizer. For DCE-MRI, sagittal T1-weighted images of the same slice were acquired continuously for 10 minutes after administration of gadolinium as an intravenous bolus to observe the distribution of contrast medium (gadolinium) in the cauda equina. To objectively evaluate changes in contrast enhancement of the cauda equina at the site of canal stenosis, regions of interest were established. The signal intensity (SI) ratio was calculated to compare the signal intensities before and after contrast enhancement, and time-intensity curves were prepared to investigate changes over time.

RESULTS

The static imaging findings and the changes of gadolinium uptake showed striking differences between the study and control patients. In the stenosis group, abnormal intrathecal enhancement showed around the site of stenosis on enhanced MR imaging. The SI ratio at the site of canal stenosis had a slower increase in the arterial phase when compared with that in the control group and remained high in the venous phase for up to 10 minutes. Finally, abnormal intrathecal enhancement was visible around the site of stenosis on enhanced MR imaging in all patients.

CONCLUSIONS

These clinical data indicate that cauda equina nerve roots in the LSCS patients are pathologic even when symptoms are not elicited in the supine position, suggesting that intraradicular venous congestion and edema themselves do not influence the existence of radicular symptoms.

MRI features of peripheral traumatic neuromas

OBJECTIVES

To describe the MRI appearance of traumatic neuromas on non-contrast and contrast-enhanced MRI sequences.

METHODS

This IRB-approved, HIPAA-compliant study retrospectively reviewed 13 subjects with 20 neuromas. Two observers reviewed pre-operative MRIs for imaging features of neuroma (size, margin, capsule, signal intensity, heterogeneity, enhancement, neurogenic features and denervation) and the nerve segment distal to the traumatic neuroma. Descriptive statistics were reported. Pearson's correlation was used to examine the relationship between size of neuroma and parent nerve.

RESULTS

Of 20 neuromas, 13 were neuromas-in-continuity and seven were end-bulb neuromas. Neuromas had a mean size of 1.5 cm (range 0.6-4.8 cm), 100 % (20/20) had indistinct margins and 0 % (0/20) had a capsule. Eighty-eight percent (7/8) showed enhancement. All 100 % (20/20) had tail sign; 35 % (7/20) demonstrated discontinuity from the parent nerve. None showed a target sign. There was moderate positive correlation (r = 0.68, p = 0.001) with larger neuromas arising from larger parent nerves. MRI evaluation of the nerve segment distal to the neuroma showed increased size (mean size 0.5 cm ± 0.4 cm) compared to the parent nerve (mean size 0.3 cm ± 0.2 cm).

CONCLUSION

Since MRI features of neuromas include enhancement, intravenous contrast medium cannot be used to distinguish neuromas from peripheral nerve sheath tumours. The clinical history of trauma with the lack of a target sign are likely the most useful clues.

KEY POINTS

• MRI features of neuromas include enhancement and lack of a target sign. • Contrast material cannot be used to distinguish traumatic neuromas from PNSTs. • Traumatic neuromas can simulate peripheral nerve neoplasms on imaging.

Pathways regulating modality-specific axonal regeneration in peripheral nerve

Following peripheral nerve injury, the distal nerve is primed for regenerating axons by generating a permissive environment replete with glial cells, cytokines, and neurotrophic factors to encourage axonal growth. However, increasing evidence demonstrates that regenerating axons within peripheral nerves still encounter axonal-growth inhibitors, such as chondroitin sulfate proteoglycans. Given the generally poor clinical outcomes following peripheral nerve injury and reconstruction, the use of pharmacological therapies to augment axonal regeneration and overcome inhibitory signals has gained considerable interest. Joshi et al. (2014) have provided evidence for preferential or modality-specific (motor versus sensory) axonal growth and regeneration due to inhibitory signaling from Rho-associated kinase (ROCK) pathway regulation. By providing inhibition to the ROCK signaling pathway through Y-27632, they demonstrate that motor neurons regenerating their axons are impacted to a greater extent compared to sensory neurons. In light of this evidence, we briefly review the literature regarding modality-specific axonal regeneration to provide context to their findings. We also describe potential and novel barriers, such as senescent Schwann cells, which provide additional axonal-growth inhibitory factors for future consideration following peripheral nerve injury.

Assessment of diabetic peripheral neuropathy in streptozotocin-induced diabetic rats with magnetic resonance imaging

OBJECTIVE

To determine the role of magnetic resonance (MR) imaging and quantitative T2 value measurements in the assessment of diabetic peripheral neuropathy (DPN).

METHODS

Sequential MR imaging, T2 measurement, and quantitative sensory testing of sciatic nerves were performed in streptozotocin-induced diabetic rats (n = 6) and normal control rats (n = 6) over a 7-week follow-up period. Histological assessment was obtained from 48 diabetic rats and 48 control rats once weekly for 7 weeks (n = 6 for each group at each time point). Nerve signal abnormalities were observed, and the T2 values, mechanical withdrawal threshold (MWT), and histological changes were measured and compared between diabetic and control animals.

RESULTS

Sciatic nerves in the diabetic rats showed a gradual increase in T2 values beginning at 2 weeks after the induction (P = 0.014), while a decrease in MWT started at 3 weeks after the induction (P = 0.001). Nerve T2 values had a similar time course to sensory functional deficit in diabetic rats. Histologically, sciatic nerves of diabetic rats demonstrated obvious endoneural oedema from 2 to 3 weeks after the induction, followed by progressive axonal degeneration, Schwann cell proliferation, and coexistent disarranged nerve regeneration.

CONCLUSION

Nerve T2 measurement is potentially useful in detecting and monitoring diabetic neuropathy.

KEY POINTS

• Sciatic nerves in diabetic rats showed a gradual increase in T2 values • Nerve T2 values were negatively correlated with sensory function impairment • Longitudinal T2 values can be used to monitor the disease progress • Nerve degeneration contributed mainly to progressive prolongation of nerve T2 values.

Imaging of the peripheral nervous system

This chapter summarizes progress in the evaluation of peripheral nerve (PN) lesions and disorders by imaging techniques encompassing magnetic resonance imaging (MRI) and nerve ultrasound (US). Due to the radiation exposure and limited sensitivity in soft tissue contrast, computed-tomography (CT) plays no significant role in the diagnostic work-up of PN disorders. MRI and US are complementary techniques for the evaluation of peripheral nerves, each having particular advantages and disadvantages. Nerve injury induces intrinsic MRI signal alterations on T2-weighted sequences in degenerating or demyelinating nerve segments as well as in corresponding muscle groups exhibiting denervation which can be exploited diagnostically. Nerve US is based on changes in the nerve echotexture due to tumor formation or focal enlargement caused by entrapment or inflammation. Both MRI and US provide morphological information on the precise site and extent of nerve injury. While US has the advantage of easy accessibility, providing images with superior spatial resolution at low cost, MRI shows better soft tissue contrast and better image quality for deep-lying nerve structures since imaging is not hindered by bone. Recent advances have remarkably increased spatial resolution of both MRI and US making imaging indispensible for the elucidation of causes of nerve compression, peripheral nerve tumors, and focal inflammatory conditions. Both MRI and US further guide neurosurgical exploration and can simplify treatment. Importantly, imaging can reveal treatable conditions even in the absence of gross electrophysiological alterations, illustrating its increasing role in clinical practice. In experimental settings, novel molecular and cellular MRI contrast agents allow in-vivo assessment of nerve regeneration as well as monitoring of neuroinflammation. Depending on further clinical development, contrast-enhanced MRI has the potential to follow cellular responses over time in vivo and to overcome the current limitations of histological assessment of nerve afflictions. Further advances in contrast-enhanced US has the potential for developing into a tool for the assessment of nerve blood perfusion, paving the way for better assessments of ischemic neuropathies.

Magnetic resonance imaging of blood brain/nerve barrier dysfunction and leukocyte infiltration: closely related or discordant?

Unlike other organs the nervous system is secluded from the rest of the organism by the blood brain barrier (BBB) or blood nerve barrier (BNB) preventing passive influx of fluids from the circulation. Similarly, leukocyte entry to the nervous system is tightly controlled. Breakdown of these barriers and cellular inflammation are hallmarks of inflammatory as well as ischemic neurological diseases and thus represent potential therapeutic targets. The spatiotemporal relationship between BBB/BNB disruption and leukocyte infiltration has been a matter of debate. We here review contrast-enhanced magnetic resonance imaging (MRI) as a non-invasive tool to depict barrier dysfunction and its relation to macrophage infiltration in the central and peripheral nervous system under pathological conditions. Novel experimental contrast agents like Gadofluorine M (Gf) allow more sensitive assessment of BBB dysfunction than conventional Gadolinium (Gd)-DTPA enhanced MRI. In addition, Gf facilitates visualization of functional and transient alterations of the BBB remote from lesions. Cellular contrast agents such as superparamagnetic iron oxide particles (SPIO) and perfluorocarbons enable assessment of leukocyte (mainly macrophage) infiltration by MR technology. Combined use of these MR contrast agents disclosed that leukocytes can enter the nervous system independent from a disturbance of the BBB, and vice versa, a dysfunctional BBB/BNB by itself is not sufficient to attract inflammatory cells from the circulation. We will illustrate these basic imaging findings in animal models of multiple sclerosis, cerebral ischemia, and traumatic nerve injury and review corresponding findings in patients.

Detection of blood-nerve barrier permeability by magnetic resonance imaging

The blood-nerve barrier (BNB) separates the endoneurium from the endovascular space and the epineurial connective tissue. An intact BNB is very important for integrity and functions of the nerve fibers within the endoneurial space. Disruption of the BNB which leads to functional and structural impairment of the peripheral nerve plays an important role in many disorders of the peripheral nerve like Wallerian degeneration, inflammatory nerve disorders, and demyelination. So far, this increased BNB permeability can only be assessed ex vivo. Assessing BNB disruption in vivo would be of great value for studying disorders of the peripheral nervous system. Gadofluorine M (Gf), a new amphiphilic contrast agent for MRI, accumulates in rat nerves with increased permeability of the BNB. After application of Gf, T1-weighted MR images show contrast enhancement of nerves with a disrupted BNB. This new tool of assessing BNB permeability in vivo is described.

Intraneural blood flow analysis during an intraoperative Phalen's test in carpal tunnel syndrome

Phalen's test has been one of the most significant of clinical signs when making a clinical diagnosis of idiopathic carpal tunnel syndrome (CTS). However, it is unknown whether intraneural blood flow changes during Phalen's test in patients with CTS. In this study, an intraoperative Phalen's test was conducted in patients with CTS to observe the changes in intraneural blood flow using a laser Doppler flow meter. During Phalen's test, intraneural blood flow showed a sharp decrease, which lasted for 1 min. Intraneural blood flow decreased by 56.7%-100% (average, 78.0%) in the median nerve relative to the blood flow before the test. At 1 min after completing the test, intraneural blood flow returned to the baseline value. After carpal tunnel release, there was no marked decrease in intraneural blood flow. This study demonstrated that the blood flow in the median nerve is reduced when Phalen's test is performed in vivo.

Magnetic resonance imaging of the peripheral nervous system

The diagnostic work up of patients with peripheral neuropathy largely depends on clinical and electrophysiological investigations. In contrast to disorders of the CNS, magnetic resonance imaging (MRI) has not been widely used as a diagnostic tool in the PNS except for detection of nerve compressing mass lesions. Normal nerves appear isointense to the surrounding tissue on T1- and T2-weighted (w) MRIs, but upon injury the nerves become hyperintense and thus visible on T2-w MRI. These signal alterations can be exploited to diagnose nerve damage in vivo and to follow regeneration. In patients with peripheral nerve disorders, MRI has been especially useful in detecting focal intrinsic and extrinsic nerve lesions and may reveal treatable conditions even in the absence of gross electrophysiological alterations. This clinical review provides practical guidelines on the performance of nerve imaging by MRI and will focus on focal lesions exemplified by case presentations.

Visualization of intraneural edema using gadolinium-enhanced magnetic resonance imaging of carpal tunnel syndrome

BACKGROUND

In general, carpal tunnel syndrome (CTS) is diagnosed based mainly on clinical findings and electrophysiology. However, the pathological state of the compressed median nerve could not be shown on imaging. Gadolinium-enhanced magnetic resonance (MR) imaging may give us an idea about the status of the blood-nerve barrier of peripheral nerves. Therefore, detecting intraneural edema may be a way of diagnosing entrapment neuropathy. The present study investigated the diagnostic role of gadolinium-enhanced MR imaging of CTS.

METHODS

The subjects were 23 patients (34 hands) with idiopathic CTS. To serve as control subjects, 12 wrists of asymptomatic volunteers were studied. Using the spin-echo method, T1- and T2-weighted axial MR images were obtained. Intravenously injected gadolinium was used to obtain enhanced images. We studied the relation between nerve enhancement and the symptomatology.

RESULTS

After intravenous injection of gadolinium, there was no enhancement of the unaffected nerves in the carpal tunnels of the control group. Gadolinium enhancement was found in only 87% of patients with CTS who visited the hospital at an early stage and therefore had no nerve deficiency on electrophysiological studies (39%). Based on this finding, during the early stages when the nerve is in a state of neuropraxia, gadolinium-enhanced MR imaging of the median nerve might prove to be the most sensitive modality for detecting early nerve dysfunction. MR imaging also revealed a higher frequency of enhancement in the advanced stage of CTS with muscle atrophy.

CONCLUSIONS

We conclude that gadolinium-enhanced MR imaging can detect not only morphological changes but also pathological changes of the median nerve in patients with CTS. Currently, gadolinium-enhanced-MR imaging is probably most commonly used to image patients who have ambiguous electrodiagnostic studies and clinical examination in an early stage of CTS.

Photochemical sealing improves outcome following peripheral neurorrhaphy

INTRODUCTION

Peripheral nerve transection initiates a complex molecular response in the severed nerve endings, resulting in the release of neurotrophic and neurotropic factors that are central to axonal survival and regeneration. In this study we tested the hypothesis that sealing the neurorrhaphy site from the surrounding environment using a photochemically bonded nerve wrap would optimize the endoneural environment and enhance regeneration and nerve function recovery.

MATERIALS AND METHODS

Adult rats underwent unilateral sciatic nerve transection and standard epineural nerve repair. The repair site was wrapped with amniotic membrane or autologous vein and then was either sealed using photochemical tissue bonding (PTB) or secured with sutures. Photochemical sealing without a wrap was also carried out. Functional recovery was assessed at 2-wk intervals using walking track analysis and nerve histomorphometry was assessed at 12 wk.

RESULTS

Treating nerves with PTB-sealed amnion significantly improved functional recovery and increased distal axon and fiber diameters and myelin thickness compared to nerves treated with standard neurorrhaphy alone. Direct PTB sealing of the repair site also improved function. Neither amnion secured with sutures nor vein wraps exhibited improved functional or histological recovery compared to standard neurorrhaphy.

CONCLUSIONS

These results suggest that sealing the peripheral nerve repair site with amnion using a photochemical technique may lead to earlier restoration of neural homeostasis and consequent enhanced repair of nerve injury.

Macrophage depletion alters the blood-nerve barrier without affecting Schwann cell function after neural injury

Previous work has shown that, during the early phases of chronic nerve compression (CNC) injury, axonal pathology is absent while Schwann cells undergo a dramatic process of cellular turnover with marked proliferation. It is known that macrophages may release Schwann cell mitogens, so we sought to explore the role of macrophages in CNC injury by selectively depleting the population of hematogenously derived macrophages in nerves undergoing CNC injury by injecting clodronate liposomes at days 1, 3, and 6 postinjury and evaluating both the integrity of the blood-nerve barrier (BNB) and Schwann cell function. Integrity of the BNB was evaluated by intravenously injecting Evans blue albumin (EBA), and Schwann cell number was determined via stereologic techniques. The BNB was clearly altered by 2 weeks postinjury and continued to disintegrate at later time points. Macrophage depletion attenuated this response at all observed time points. Quantification of Schwann cell nuclei in CNC nerves showed no differences between compressed sections of macrophage-depleted and nondepleted animals. Although macrophages are largely responsible for the increased vascular permeability associated with CNC injury, it is likely that the Schwann cell response to CNC injury is not influenced by macrophage-derived mitogenic signals but rather must be mediated via alternative mechanisms.

Passive immunization with anti-ganglioside antibodies directly inhibits axon regeneration in an animal model

Recent studies have proposed that neurite outgrowth is influenced by specific nerve cell surface gangliosides, which are sialic acid-containing glycosphingolipids highly enriched in the mammalian nervous system. For example, the endogenous lectin, myelin-associated glycoprotein (MAG), is reported to bind to axonal gangliosides (GD1a and GT1b) to inhibit neurite outgrowth. Clustering of gangliosides in the absence of inhibitors such as MAG is also shown to inhibit neurite outgrowth in culture. In some human autoimmune PNS and CNS disorders, autoantibodies against GD1a or other gangliosides are implicated in pathophysiology. Because of neurobiological and clinical relevance, we asked whether anti-GD1a antibodies inhibit regeneration of injured axons in vivo. Passive transfer of anti-GD1a antibody severely inhibited axon regeneration after PNS injury in mice. In mutant mice with altered ganglioside or complement expression, inhibition by antibodies was mediated directly through GD1a and was independent of complement-induced cytolytic injury. The impaired regenerative responses and ultrastructure of injured peripheral axons mimicked the abortive regeneration typically seen after CNS injury. These data demonstrate that inhibition of axon regeneration is induced directly by engaging cell surface gangliosides in vivo and imply that circulating autoimmune antibodies can inhibit axon regeneration through neuronal gangliosides independent of endogenous regeneration inhibitors such as MAG.

Differential recruitment of CD8+ macrophages during Wallerian degeneration in the peripheral and central nervous system

The strong macrophage response occurring during Wallerian degeneration in the peripheral but not central nervous system has been implicated in tissue remodeling and growth factor production as key requirements for successful axonal regeneration. We have previously identified a population of CD8+ phagocytes in ischemic brain lesions that differed in its recruitment pattern from CD4+ macrophages/microglia found in other lesion paradigms. In the present study we show that crush injury to the sciatic nerve induced strong infiltration by CD8+ macrophages both at the crush site and into the degenerating distal nerve stump. At the crush site, CD8+ macrophages appeared within 24 hours whereas infiltration of the distal nerve parenchyma was delayed to the second week. CD8+ macrophages were ED1+ and CD11b+ but always MHC class II-. Most CD8+ macrophages coexpressed CD4 while a significant number of CD4+/CD8-macrophages was also present. Expression of the resident tissue macrophage marker ED2 was largely restricted to the CD4+/CD8- population. Following intraorbital crush injury to the optic nerve, infiltration of CD8+ macrophages was strictly confined to the crush site. Taken together, our study demonstrates considerable spatiotemporal diversity of CD8+ macrophage responses to axotomy in the peripheral and central nervous system that may have implications for the different extent of axonal regeneration observed in both systems.

Localization and changes of intraneural inflammatory cytokines and inducible-nitric oxide induced by mechanical compression

STUDY DESIGN

Investigation of intraneural inflammation induced by mechanical compression.

OBJECTIVES

In order to investigate the mechanism of neuropathy, this study used a median nerve compression model in dogs. Immunohistochemistry was used to examine the localization and changes of inflammatory cytokines and nitric oxide (NO).

SUMMARY OF BACKGROUND DATA

The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages such as interleulin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), as well as with NO. However, the mediators involved in inflammation of nerve due to mechanical compression remain almost unknown.

METHODS

In this study, the median nerve of dogs was compressed with a clip for three weeks to observe the changes caused by compression. Immunohistochemistry was done by the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against IL-1beta, TNF-alpha, and inducible nitric oxide synthesis (i-NOS) were used to examine the localization and changes of these mediators caused by nerve compression.

RESULTS

In control animals, resident T cells were detected, but there were no macrophages. IL-1beta was positive in the Schwann cells and vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1beta, TNF-alpha and i-NOS.

CONCLUSION

Inflammatory cytokines and NO may be involved in intraneural inflammatory changes arising from mechanical compression. Such mediators may be of importance in the manifestation of neuropathy.

Assessment of nerve degeneration by gadofluorine M-enhanced magnetic resonance imaging

Nerve injury represents a major cause of disability. In the peripheral nervous system, nerves have the capacity to regrow but within weeks after injury, it is impossible to clarify whether proper regeneration is under way or is failing. In this experimental study, we report on a novel tool to assess nerve outgrowth in vivo. After systemic application, the novel gadolinium-based magnetic resonance (MR) contrast agent Gadofluorine M (Gf) selectively accumulated and persisted in nerve fibers undergoing Wallerian degeneration causing bright contrast on T1-weighted MR images. Gf enhancement on MR imaging was present already at 48 hours within the entire nerve segments undergoing Wallerian degeneration, and subsequently disappeared from proximal to distal parts in parallel to regrowth of nerve fibers. Most importantly, Gf enhancement persisted in nonregenerating, permanently transected nerves. Our novel Gf-based MR imaging methodology holds promise for clinical use to bridge the diagnostic gap between nerve injury and completed nerve regeneration, and to determine the necessity for neurolysis and engraftment if spontaneous regeneration is not successful.

[Gadolinium enhancement of the cauda equina following ischemia of the lumbar cord]

Enhancement of the cauda equina is a well-recognized finding, in particular in patients with inflammatory diseases of the peripheral nervous system. However, we report an unusual case of a woman with an ischemic lesion in the lumbar intumescence who developed enhancement of the cauda equina 18 days after disease onset. Seventy-six days after the onset of illness, contrast uptake was no longer detectable. Severe injury to the motor neurons in the lumbar intumescence was evident clinically and electromyographically. We propose that the enhancement of the cauda equina was due to blood-nerve barrier disruption during Wallerian degeneration following ischemic injury to the motor neurons of the lumbar cord.

The recovery of blood-nerve barrier in crush nerve injury--a quantitative analysis utilizing immunohistochemistry

The purpose of this study is to reveal whether the application of immunohistochemical examinations to the peripheral nervous system (PNS) can be a reliable method for the quantitative analysis of the blood-nerve barrier (BNB) and the relationship between restoration of BNB and nerve regeneration. Sciatic nerves in rats were examined after nerve crush. Immunohistochemical staining with anti-rat endothelial cell antigen-1 (anti-RECA-1) that recognizes endothelial cells and anti-endothelial barrier antigen (anti-EBA) for the detection of barrier-type endothelial cells were used. Neurofilament for staining axons was also performed. A quantitative analysis of the BNB was assessed using the ratio of EBA positive cells and RECA-1 positive cells. The ratio of EBA/RECA-1 decreased significantly 3 days postoperatively and reached its lowest level at day 7 in the segment 5 mm proximal and the entire distal stump. The ratio gradually recovered from the proximal and the regeneration of axons started a week earlier than BNB. The ratio of EBA/RECA-1 applied to the PNS can be a reliable method for the quantitative analysis of BNB. In crush injuries, the breakdown of BNB occurred simultaneously in the segment 5 mm proximal and the entire distal stump; restoration began from the proximal to distal and followed a week later to nerve regeneration.

Pathology of lumbar nerve root compression. Part 1: Intraradicular inflammatory changes induced by mechanical compression

STUDY DESIGN

This study is to investigate the intraradicular inflammation induced by mechanical compression using in vivo model.

OBJECTIVES

The relationship between the intraradicular edema and nerve fiber degeneration induced by mechanical compression was determined in the nerve root.

SUMMARY OF BACKGROUND DATA

Recently some studies reported that mechanical compression increased microvascular permeability of the endoneurial capillaries and resulted in an intraradicular inflammation. These changes may be an important factor of the pathogenesis of radiculopathy. However, the natural courses of the intraradicular inflammation after mechanical compression are still poorly understood.

METHODS

In dogs, laminectomy was performed at L7 and the seventh nerve root was exposed to compression at 7.5 gram force (gf) clipping power. The animals were evaluated at 1 and 3 weeks after clipping. After the appropriate period of nerve root compression, Evans blue albumin (EBA) was injected intravenously. The nerve root sections were divided into two groups. The sections were used to investigate the status of the blood-nerve barrier function under the fluorescence microscope. The other sections were used for light and transmission electron microscopic study.

RESULTS

After 1 and 3 weeks, intraradicular edema was observed not only at the site of compression but also in the peripheral zone of a compressed anterior root and in the central zone of a compressed posterior root. The evidence of active Wallerian degeneration was also seen in the area of intraradicular edema. In addition, the nerve roots showing Wallerian degeneration were infiltrated by inflammatory cells, such as macrophages and mast cells.

CONCLUSIONS

Inflammatory reaction, such as Wallerian degeneration, breakdown of blood-nerve barrier and appearance of macrophage, may be deeply involved in radiculitis arising from mechanical compression, and these factors seem to be important in the manifestation of radiculopathy.

Caught in the act: in vivo mapping of macrophage infiltration in nerve injury by magnetic resonance imaging

In vivo tracking of hematogenous macrophages has been a major challenge because these cells are key players in nerve injury and repair. We visualized the spatiotemporal course of macrophage infiltration after acute peripheral nerve injury in living rats by using superparamagnetic iron oxide (SPIO) particles and magnetic resonance imaging (MRI). A signal loss on MR images indicating iron accumulation was present in degenerating sciatic nerves between days 1 and 8 after a crush lesion, ceased thereafter, and corresponded to the transient presence of iron-labeled ED1-positive macrophages in tissue sections. In contrast, no SPIO accumulation was seen after optic nerve crush, which revealed microglial activation but lacked macrophage infiltration. SPIO-enhanced MRI provides a new tool to selectively visualize active periods of macrophage transmigration into the nervous system, thus enabling dynamic views on a fundamental process in a multitude of nerve disorders.

High-resolution magnetic resonance imaging is a noninvasive method of observing injury and recovery in the peripheral nervous system

OBJECTIVE

Noninvasive observation of degenerating and regenerating peripheral nerves could improve the diagnosis and treatment of nerve injuries. We constructed a novel phased-array radiofrequency coil to permit magnetic resonance imaging (MRI) observation of the sciatic nerve and its target muscles in rats after injury.

METHODS

Adult male Lewis rats underwent either crushing (n = 18) or cutting and capping (n = 17) of their right sciatic nerves and then underwent serial MRI. Serial gait track analysis was performed to assess behavioral recovery. Animals from both groups were killed at several time points for histological evaluation of the nerves, with axon counting.

RESULTS

Crushed sciatic nerves demonstrated increased T2-weighted signals, followed by signal normalization as axonal regeneration and behavioral recovery occurred. Cut sciatic nerves prevented from regenerating displayed a prolonged phase of increased signal intensity. Acutely denervated muscles exhibited hyperintense T2-weighted signals, which normalized with reinnervation and behavioral recovery. Chronically denervated muscles demonstrated persistently increased T2-weighted signals and atrophy.

CONCLUSION

In this study, we demonstrated the ability of MRI to noninvasively monitor injury and recovery in the peripheral nervous system, by demonstrating changes in nerve and muscle that correlated with histological and behavioral evidence of axonal degeneration and regeneration. This study demonstrates the potential of MRI to distinguish traumatic peripheral nerve injuries that recover through axonal regeneration (i.e., axonotmetic grade) from those that do not and therefore require surgical repair (i.e., neurotmetic grade). This diagnostic modality could improve treatment by providing earlier and more accurate diagnoses of nerve damage, as well as reducing the need for exploratory surgery.

Loss and recovery of the blood-nerve barrier in the rat sciatic nerve after crush injury are associated with expression of intercellular junctional proteins

The blood-nerve barrier in peripheral nerves is important for maintaining the environment for axons. Breakdown of the barrier by nerve injury causes various pathologies. We hypothesized that the breakdown and recovery of the blood-nerve barrier after injury are associated with the changes in the expression of intercellular junctional proteins. To test this hypothesis, we induced crush injuries in the rat sciatic nerve by ligation and analyzed spatiotemporal changes of claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 by immunoconfocal microscopy and morphometry and compared them with changes in the permeability of the blood-nerve barrier by intravenous and local administration of Evans blue-albumin (EBA). On day 1 after removal of the ligature EBA leaked into the connective tissue in the endoneurium and then the leakage gradually decreased and disappeared on day 7. On day 1 claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 had totally disappeared from the perineurium and endoneurium. Thereafter, claudin-1, claudin-5, occludin, and VE-cadherin recovered from day 2, whereas connexin43 was redetected on day 5. These results indicate that the breakdown and following recovery of the blood-nerve barrier are closely associated with changes in the expression of claudins, occludin, VE-cadherin, and connexin43 and that the recovery time course is similar but nonidentical.

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.

Cryopreservation of peripheral nerve grafts

The utilization of viable biological nerve graft substitutes and nerve allografts raises the problem of nerve storage. To clarify this, rat sciatic nerve segments were harvested and stored in Dulbecco's modified eagle medium. The segments were divided into three groups. In the first group, no cryoprotectant was added, whereas the second had 10% dimethyl sulfoxide (DMSO) added as cryoprotectant. These two groups of nerve segments were subjected to controlled freezing. In a third group, segments were frozen uncontrolled in liquid nitrogen (-196 degrees C). All nerves were replanted orthotopically. Fresh conventional autografts (fourth group) served as control group. Histologically, freezing did not affect the structural elements such as basal lamina tubes and perineurial tissue. Morphometrically, all cryopreserved grafts had significantly reduced axon counts and less myelinization than did controls. Cryoprotected nerves (group 2) showed no different morphometric parameters compared with the group without DMSO (group 1). Controlled freezing was superior to uncontrolled freezing (group 3). Impaired regeneration was attributed mainly to delayed Wallerian degeneration and slower revascularization. Moreover, decreased survival of resident Schwann cells in the graft may impair regeneration due to the lack of neurotrophic, neurotropic, and attachment factors in early regeneration. Grafts subjected to controlled freezing support axonal regeneration to a certain extent, but further studies are required to assess various cooling patterns, cryoprotectants, and graft revascularization.

MRI of the cauda equina in CIDP: clinical correlations

Isolated reports have documented enhancement and/or enlargement of spinal nerve roots on magnetic resonance imaging (MRI) in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). This work examines those findings in a consecutive series of 16 patients with CIDP, with blinded comparison to MRI in 13 disease controls, including five patients with Charcot-Marie-Tooth disease type 1A. MRI sequences consisted of T1 weighted sagittal and axial views, before and after administration of gadolinium. Blinded MRI interpretation was performed independently by two neuroradiologists. MRI results were correlated with data collected from chart review. Enhancement of the cauda equina was seen in 11 of 16 CIDP patients (69%), and in none of 13 control subjects. Nerve roots were enlarged, most significantly in the extraforaminal region, in three CIDP patients, and in one patient with Charcot-Marie-Tooth type 1A. MRI findings did not correlate with disease activity and severity, nor with any clinical or laboratory features in patients with CIDP.

Regulation of hemopexin synthesis in degenerating and regenerating rat sciatic nerve

In injured peripheral nerves, hemopexin mRNA is expressed by fibroblasts, Schwann cells, and invading blood macrophages, and the protein accumulates in the extracellular matrix. This and its absence of regulation in injured central optic nerve suggest that hemopexin could play a positive role in peripheral nerve repair. Here, we studied the regulation of hemopexin expression in degenerating and regenerating nerves. After a sciatic nerve injury, both the synthesis of hemopexin and the level of its mRNA increase sharply during the first 2 days, leading to an accumulation of hemopexin in the nerve. Afterward, hemopexin expression decreases progressively in regenerating nerves. In permanently degenerated nerves, it is again transiently increased and then strongly decreased, whereas hemopexin from blood origin is accumulating. As part of the elucidation of the complex regulation of hemopexin expression in injured nerves, we demonstrate that interleukin-6 increases hemopexin synthesis in intact nerves, whereas adult rat serum, but not purified hemopexin, inhibits it in degenerated nerves. Hemopexin, known as acute-phase protein, is therefore one of the molecules rapidly and specifically up-regulated in injured peripheral nerves. More generally, our findings suggest that the acute phase could be not only a systemic liver-specific response but also a reaction of injured tissues themselves.

Quantitative analysis of edema in the dorsal nerve roots induced by acute mechanical compression

STUDY DESIGN

Edema in the dorsal nerve roots caused by acute compression was assessed quantitatively in the lumbar spine of the adult dog.

OBJECTIVE

To establish quantitative evaluation of edema in the dorsal nerve roots and to observe changes after acute compression with time.

SUMMARY OF BACKGROUND DATA

Mechanical compression induces an increase in microvascular permeability of the endoneurial capillaries and results in intraneural edema. However, there are no quantitative studies on edema in the nerve roots.

METHODS

The seventh lumbar nerve root was compressed with a 60-g force clip for 10 minutes. The nerve roots were removed immediately and at 24 hours, 1 week, and 3 weeks after compression. Nerve roots from the control and the sham groups were also obtained. Before removing the nerve roots, Evans blue albumin was injected intravenously. Changes in edema were examined using fluorescence microscopy. Evans blue albumin emits a bright red fluorescence. The relative red fluorescent area was calculated using computer image analysis, and the data were used to indicate the degree of edema.

RESULTS

In the compressed segment, edema was most pronounced just after decompression and reduced in nerves removed at 24 hours. In nerves removed at 1 week, edema was pronounced but was reduced at 3 weeks. In the segments closest to the spinal cord, edema was seen after 1 week and was significant after 3 weeks. In the segments closest to the dorsal root ganglion, edema was not detected at any time.

CONCLUSION

In the dorsal nerve roots the degree and the area of edema changed with time elapsed after acute compression. The degree of edema 24 hours after decompression was one third the degree immediately after decompression. These results show that edema induced by mechanical compression can recover after decompression.

Human autoimmune neuropathies

Peripheral nerve diseases are among the most prevalent disorders of the nervous system. Because of the accessibility of the peripheral nervous system (PNS) to direct physiological and pathological study, neuropathies have traditionally played a unique role in developing our understanding of basic mechanism of nervous system injury and repair. At present they are providing new insight into the mechanisms of immune injury to the nervous system. A rapidly growing catalogue of PNS disorders are now suspected to be immune-mediated, and in the best understood of these disorders, the molecular and cellular targets of immune attack are known, and the pathophysiology follows directly from the specific immune injury. This review summarizes the immunologically relevant features of the PNS, then considers selected immune-mediated neuropathies, focusing on pathogenetic mechanisms. Finally, the PNS is providing a testing ground for new immunotherapies and approaches to protection and regeneration, including the use of trophic factors. The current status of treatment and implications for future approaches is reviewed.

NGF-dependent and NGF-independent recovery of sympathetic function after chemical sympathectomy with 6-hydroxydopamine

To help clarify the distinction between the nerve growth factor (NGF)-dependent collateral sprouting of sympathetic nerves and their NGF-independent regeneration after crush, we used 6-hydroxydopamine (OHDA) to destroy the sympathetic terminals in adult rats; this leaves the axons damage-free. Would recovery occur by regeneration and/or collateral sprouting? A single 6-OHDA injection abolished the sympathetic pilomotor field revealed by electrical stimulation of a cutaneous nerve. Recovery began within 2 days, and by 20 days the field was reestablished. If the field was "isolated" by adjacent denervations at the time of 6-OHDA treatment, the recovering pilomotor field expanded extensively into the surrounding territory. In the presence of anti-NGF, however, the pilomotor field expansion ceased at about 60% of its former size; if anti-NGF treatment was discontinued, expansion recommended and extended into the surrounding skin. We suggest that the latter, NGF-dependent, growth phase corresponds to collateral sprouting, and the initial NGF-independent one to regeneration. After simple nerve crush, however, such regeneration can triple the normal sympathetic field size. This difference between crush- and 6-OHDA-induced regeneration might relate to the "cell body reaction" (CBR); the CBR is reduced with increasing distance of the lesion and is undetectable after a 6-OHDA lesion. Since the CBR and the vigor of regeneration are both increased by repeated axonal injury, we tested the effects of multiple 6-OHDA treatments; this significantly increased the initial NGF-independent expansion. We hypothesize that regeneration is regulated largely by mechanisms associated with the CBR, and that neurotrophin-dependent collateral sprouting occurs independently of these.

Neuromuscular disease: rehabilitation and electrodiagnosis. 1. Anatomy and physiology of nerve and muscle

This article of the Self-Directed Physiatric Education Program to assist practitioners and trainees in physical medicine and rehabilitation identifies the anatomy and physiology of nerve, neuromuscular junction, and muscle as they relate to rehabilitation of diseases affecting these structures. Structural relationships of the spinal roots, peripheral nerves, motor units, and muscle fibers are outlined, with structural, functional, and electrodiagnostic correlations. Features of nerve and muscle biochemistry and physiology are reviewed as they relate to common neurological diseases, age, and sex. The spontaneous potentials, motor unit activities, and nerve conduction abnormalities found in diseases of nerve and muscle also are described.

Correlation between NGF levels in wound chamber fluid and cytological localization of NGF and NGF receptor in axotomized rat sciatic nerve

When a silicone tube is implanted in transected rat sciatic nerve, there is plasma accumulation and formation of a fibrin cable followed by proliferation and migration of neural and nonneural cells from the nerve stumps into the cable. The wound fluid exhibited neurotrophic activity of unknown origin and nature. In this study, we analyzed the NGF level in wound fluid by a sensitive enzyme immunoassay and correlated the NGF level with the cytological localization of NGF, low affinity NGF receptor (p75NGFR), and Trk receptor in the axotomized nerve by immunohistochemistry. We demonstrated a rising NGF level in wound fluid from 490 pg/ml on Day 1 to 950 pg/ml on Day 7; the serum NGF level was 1/20 of that in the wound fluid. The infiltrating leukocytes expressed strong NGF but no p75NGFR. The proliferative fibroblasts and vascular cells exhibited a short period of NGF but no p75NGFR staining. Schwann cells in the distal segment showed a prolonged period of NGF and p75NGFR expression. No Trk receptor was demonstrated on leukocytes or non-neural cells. These findings suggest that locally synthesized NGF is mainly responsible for the neurotrophic activity in the wound chamber fluid. The NGF produced by the nonneural cells may be bound and stored in the p75NGFR in Schwann cells in the distal segment prior to the arrival of the regenerating axons.

Prolonged survival of transected nerve fibres in C57BL/Ola mice is an intrinsic characteristic of the axon

Transected axons in C57BL/Ola mice survive for extraordinary lengths of time as compared to those of normal rodents. The biological difference in the substrain that confers the phenotype of prolonged axonal survival is unknown. Previous studies suggest that 'defect' to be a property of the nervous system itself, rather than one of haematogenous cells. Neuronal or non-neuronal elements could be responsible for this phenotype. This study was undertaken to determine whether Schwann cells, the most numerous of the non-neuronal cells intrinsic to the peripheral nerve, are responsible for delayed degeneration of transected axons. We created sciatic nerve chimeras by transplanting nerve segments between standard C57BL/6 and C57BL/Ola mice, allowing regeneration of host axons through the grafts containing donor Schwann cells. These nerves were then transected and the time course of axonal degeneration was observed. The results show that fast or slow degeneration is a property conferred by the host, and therefore cannot be ascribed to the Schwann cells. Similarly, transected C57BL/Ola axons in explanted dorsal root ganglia cultures survived longer than transected axons from standard mice. Taken together these results indicate that the responsible abnormality is intrinsic to the C57BL/Ola axon.