Diagnostic value of ultrastructural nerve examination in Charcot-Marie-Tooth disease: two CMT 1B cases with pseudo-recessive inheritance

We report two sporadic patients of CMT disease in different consanguineous families. The electrophysiological examination led to the diagnosis of a severe demyelinating neuropathy. The nerve biopsies exhibited numerous outfoldings of the myelin sheaths and onion-bulb proliferations. The consanguinity and the histological findings pointed to a diagnosis of CMT 4B. However, the detection of abnormal and regular widenings between the major dense lines of the myelin lamellae by electron microscopy led us to search for a P0 gene mutation. Two heterozygous mutations of this gene were identified: S63F and N131Y. Different aspects of uncompacted myelin lamellae have been described in some cases of P0 mutations and a few now appear to be quite specific to it. More than 30 genes are implicated in CMT and as mutation search is time- and money-consuming, we believe that in some selected patients ultrastructural examination of nerves, among other criteria, helps orientate the molecular diagnosis of CMT.

Morphological analysis of human acupuncture points through immunohistochemistry

OBJECTIVE

At present, the functional mechanism of acupuncture is not yet fully understood. Analysis of the subanatomic morphology of acupuncture points (APs) could help compensate for this shortcoming. In immunohistochemistry, the use of specific antibodies enables in situ characterization of the molecular profile of tissue microenvironments. Thus, as proof in principle for the utility of immunohistochemistry, we determined whether the nerve density in biopsies of autopsied skin of a selected standard AP differed from that of a control point (CP).

DESIGN

We analyzed pairs of skin samples from nine autopsy cases and studied the presence and density of soluble protein 100 (S-100), neuron-specific enolase (NSE), and neurofilament (NF) as markers of peripheral nerve structures. Cross-sections of nerves were counted by conventional microscopy and normalized to millimeters squared of subcutaneous fat, followed by statistical analyses for formal comparisons.

RESULTS

Immunohistochemistry could clearly identify myelinated peripheral nerves. The number of nerve structures expressing S-100 protein was significantly reduced in APs compared with CPs (0.020 1 0.005 vs. 0.061 +/- 0.014; P < 0.006). The same pattern was seen in staining of NSE (AP: 0.011 +/- 0.003 vs. CP: 0.045 +/- 0.011) and NF (AP: 0.011 +/- 0.004 vs. CP: 0.054 +/- 0.015; both P < 0.007).

CONCLUSIONS

In this study, we introduce immunohistochemistry as a suitable technology for acupuncture research. In addition, our findings demonstrate that a human AP is not necessarily associated with an increased but, rather, a significantly decreased number and density of subcutaneous nerve structures compared with skin biopsies from locations not recognized as effective for acupuncture. This pilot study, executed on a limited number of individuals and skin samples, justifies the application of immunohistochemistry on a larger collection of biopsy material.

Regeneration of baroafferents after implantation into different vessels

Regeneration of peripheral nerves involves an essential contribution by surrounding tissues. This study focuses on the role of the target tissue on the regeneration of afferent peripheral nerves. We hypothesized that nerves implanted into the appropriate target tissue regain their function, whereas they degenerate when implanted into a different tissue. Therefore, aortic nerves of rabbits were transected and implanted into arteries or veins, and their function and structure was reevaluated after 1.5, 3, and 10 months. In a subset of animals, the nerves were again severed and implanted into the other vessel. Twelve of 18 nerves implanted into arteries regained typical neurophysiological activity, but none of those implanted into veins. Two times even baroreflexes were elicited through the newly built nerve endings. The structure of the nerve endings implanted into arteries resembled baroreceptors, whereas no fiber growth was detected in veins. Morphometrically, the fiber number and diameter increased over the observed time period after implantation into arteries. Nerves implanted into veins, transected after 3 months, and then implanted into arteries also regained neurophysiological activity. Again, they rebuilt baroreceptors and significantly increased their fiber number and diameter. In conclusion, when severed baroafferents are implanted into arteries, they regenerate new baroreceptors and restore the normal myelination and fiber size of the nerve over time, whereas veins seem to inhibit nerve fiber sprouting and regeneration of severed fibers.

Endotoxin-induced Injury of the Central, Autonomic and Enteric Nervous Systems and Intestinal Muscularis in Thoroughbred Horses

To evaluate the effects of endotoxin on the morphology of the equine central, autonomic and enteric nervous system and intestinal muscularis, six Thoroughbred horses with experimentally induced endotoxaemia were examined. The lesions in the central nervous system consisted of perivascular oedema around arterioles, suggesting brain oedema, and ring haemorrhages around veins, similar to those in human patients with septic shock. In the cranial mesenteric ganglia, neuronal cell bodies became pink or red, with shrinkage of cytoplasm indicative of ischaemic changes; intramural and perivascular infiltration by erythrocytes and neutrophils occurred around arterioles in the epineurium (acute focal interstitial inflammation). In addition, transmission electron microscopy revealed oedema of the endoneurium and mesoaxon in the nerve fascicles running inside or outside the ganglia. Myenteric neurons showed shrinkage of the cytoplasm with multiple cytoplasmic vacuoles, suggesting ischaemic changes. Oedematous degeneration and coagulation necrosis of smooth muscle cells, with dissociation of the cells, were prominent in the tunica muscularis. It is suggested that arterionecrosis elicited by endotoxin and frequently observed in the autonomic and enteric nervous system and intestinal muscularis, was the result of vasoconstriction or vasospasm.

Major myelin protein gene (P0) mutation causes a novel form of axonal degeneration

Mutations in the major peripheral nervous system (PNS) myelin protein, myelin protein zero (MPZ), cause Charcot-Marie-Tooth Disease type 1B (CMT1B), typically thought of as a demyelinating peripheral neuropathy. Certain MPZ mutations, however, cause adult onset neuropathy with minimal demyelination but pronounced axonal degeneration. Mechanism(s) for this phenotype are unknown. We performed an autopsy of a 73-year-old woman with a late-onset neuropathy caused by an H10P MPZ mutation whose nerve conduction studies suggested severe axonal loss but no demyelination. The autopsy demonstrated axonal loss and reorganization of the molecular architecture of the axolemma. Segmental demyelination was negligible. In addition, we identified focal nerve enlargements containing MPZ and ubiquitin either in the inner myelin intralaminar and/or periaxonal space that separates axons from myelinating Schwann cells. Taken together, these data confirmed that a mutation in MPZ can cause axonal neuropathy, in the absence of segmental demyelination, thus uncoupling the two pathological processes. More important, it also provided potential molecular mechanisms as to how the axonal degeneration occurred: either by disruption of glial-axon interaction by protein aggregates or by alterations in the molecular architecture of internodes and paranodes. This report represents the first study in which the molecular basis of axonal degeneration in the late-onset CMT1B has been explored in human tissue.

Macrophage colony stimulating factor is a crucial factor for the intrinsic macrophage response in mice heterozygously deficient for the myelin protein P0

Mouse mutants heterozygously deficient for the myelin protein P0 (P0+/-) resemble certain forms of human hereditary neuropathies. Endoneurial macrophages of intrinsic origin are intimately involved in the pathogenesis of the demyelinating neuropathy in these mutants. We have previously shown that deficiency for macrophage colony stimulating factor (M-CSF) prevents an increase of the number of endoneurial macrophages and alleviates the mutants' demyelinating phenotype. The aim of this study was to investigate which population of endoneurial macrophages - long-term resident macrophages or recently infiltrated macrophages - is affected by M-CSF deficiency. For this purpose, we generated bone marrow chimeric mice by transplanting GFP+ bone marrow into P0 mutants (P0+/-) and P0 mutants that lack M-CSF (P0+/- mcsf-op). This enabled us to discriminate recently infiltrated short-term resident GFP+ macrophages from long-term resident GFP- macrophages. Three months after bone marrow transplantation, P0+/- mice expressing M-CSF showed a substantial upregulation and activation of both GFP- and GFP+ macrophages in femoral nerves when compared to P0+/+ mice. In contrast, in P0+/- mcsf-op mutants, both GFP- and GFP+ macrophages did not substantially increase. Only small numbers of GFP+ but no GFP- macrophages were activated and phagocytosed myelin in chimeric P0+/- mcsf-op mutants, possibly reflecting recent activation outside the endoneurium before entering the nerve. Our findings demonstrate that M-CSF is crucial for the activation, in situ increase and myelin phagocytosis of both long-term and short-term resident endoneurial macrophages in P0+/- myelin mutants. M-CSF is, therefore, considered as a target candidate for therapeutic strategies to treat human demyelinating neuropathies.

Renaut bodies in nerves of the trunk of the African elephant,Loxodonta africana

Renaut bodies are loosely textured, cell-sparse structures in the subperineurial space of peripheral nerves, frequently found at sites of nerve entrapment. The trunk of the elephant is a mobile, richly innervated organ, which serves for food gathering, object grasping and as a tactile organ. These functions of the trunk lead to distortion and mechanical compression of its nerves, which can therefore be expected to contain numerous Renaut bodies. Samples of the trunk wall of an adult African elephant (Loxodonta africana) were examined histologically using conventional staining methods, immunohistochemistry, and lectin histochemistry. Architecture of nerve plexuses and occurrence of Renaut bodies in the elephant trunk were compared with those in tissues surrounding the nasal vestibule of the pig. Prominent nerve plexuses were found in all layers of the elephant trunk. Almost all (81%) nerve profiles contained Renaut bodies, a basophilic, discrete subperineurial layer resembling cushions around the nerve core. In contrast, Renaut bodies were seen in only 15% of nerve profiles in the porcine nasal vestibule. Within Renaut bodies, fusiform fibroblasts and round, ruff-like cells were placed into a matrix of acidic glycosaminoglycans with delicate collagen and very few reticular fibers. The turgor of this matrix is thought to protect nerves against compression and shearing strain. Renaut bodies are readily stained with alcian blue (pH 2.5) favorably in combination with immunohistochemical markers of nerve fibers. They should be regarded as a physiological response to repeated mechanical insults and are distinct from pathological alterations. alterations.

Survival of long nerve allografts following donor antigen pretreatment: a pilot study

In this study, the authors evaluated whether the pretransplant portal venous administration of UV-B irradiated donor alloantigen would induce tolerance to long peripheral nerve allografts in a swine model. They completed nerve allograft transplantation between four swine of separate lineages. Regeneration across the nerve allografts was followed for 10 months postoperatively. Sequential IN VITRO assays demonstrated the successful and prolonged suppression of the recipient immune response to donor antigen following antigen inoculation. Histomorphometric analysis demonstrated successful regeneration across the long nerve allografts in the pretreated recipients, but not across allografts in unimmunosuppressed recipients. A single pretransplant antigen delivery protocol has the potential to replace chronic medicinal immunosuppressant therapy and its associated morbidities. Furthermore, tolerance to long nerve allografts has immediate applicability to clinical requirements for bridging multiple, complex, long nerve gaps.

Role of N-cadherin in Schwann cell precursors of growing nerves

In the present paper, we determine the localization and developmental regulation of N-cadherin in embryonic rat nerves and examine the role of N-cadherin in this system. We also identify a major transition in the architecture of embryonic nerves and relating it to N-cadherin expression. We find that in early embryonic nerves, N-cadherin is primarily expressed in Schwann cell precursors. Pronounced expression is seen at distal nerve fronts where these cells associate with growth cones, and the proximal nerve ends, in boundary cap cells. Unexpectedly, N-cadherin is downregulated as precursors generate Schwann cells, coinciding with the time at which most axons make target connections. Therefore, glial N-cadherin expression is essentially restricted to the period of axon outgrowth. We also provide evidence that N-cadherin supports the formation of contacts between Schwann cell precursors and show that these cells are a favorable substrate for axon growth, unlike N-cadherin-negative Schwann cells. Induction of N-cadherin expression in Schwann cells by neuregulin-1 restores their ability to form contacts and support axon growth. Finally, we show that the loss of glial N-cadherin during embryonic nerve development is accompanied by a transformation of nerve architecture, involving the appearance of endoneurial connective tissue space, fibroblasts, Schwann cell basal lamina, and blood vessels. Because N-cadherin is likely to promote the extensive glial contacts typical of the compact embryonic nerve, we suggest that N-cadherin loss at the time of Schwann cell generation allows endoneurial space to appear between the glial cells, a development that eventually permits the extensive interactions between connective tissue and individual axon-Schwann cell units necessary for myelination.

Peripheral myelin maintenance is a dynamic process requiring constant Krox20 expression

Onset of myelination in Schwann cells is governed by several transcription factors, including Krox20/Egr2, and mutations affecting Krox20 result in various human hereditary peripheral neuropathies, including congenital hypomyelinating neuropathy (CHN) and Charcot-Marie-Tooth disease (CMT). Similar molecular information is not available on the process of myelin maintenance. We have generated conditional Krox20 mutations in the mouse that allowed us to develop models for CHN and CMT. In the latter case, specific inactivation of Krox20 in adult Schwann cells results in severe demyelination, involving rapid Schwann cell dedifferentiation and increased proliferation, followed by an attempt to remyelinate and a block at the promyelinating stage. These data establish that Krox20 is not only required for the onset of myelination but that it is also crucial for the maintenance of the myelinating state. Furthermore, myelin maintenance appears as a very dynamic process in which Krox20 may constitute a molecular switch between Schwann cell myelination and demyelination programs.

Invariant mantling of growth cones by Schwann cell precursors characterize growing peripheral nerve fronts

Little is known about the cytoarchitecture of growth fronts in developing mammalian nerves. We report here the first quantitative, ultrastructural analysis of growth cones (GCs) and their immediate cellular and tissue environment at tips of growing nerves that are nearing their targets in fore limbs of E14 rat embryos. Schwann cell precursor (SCP) marker, p75 neurotrophin receptor, and growth cone marker, SCG10, were used to identify nerve fronts, respectively. Using confocal 3D reconstructions and immunoelectron microscopy, we found that growth cone and Schwann cell precursor migrate together at the nerve front, where growth cone contact adjacent growth cone and Schwann cell precursor with similar frequency. Schwann cell precursor are extensively connected by adherens junctions and form elaborate scaffolds that enmantle growth cone at nerve fronts, so that 80% of the nerve front surface is covered by Schwann cell precursor. Although they interdigitate in complex ways among growth cone, the total contact area between growth cone and glial membranes is remarkably constant among the 100 growth fronts analyzed. In contrast to this consistency, other growth cone contacts varied markedly from front to front such that the frequencies of GC-GC contacts are increasing proportional to their decreasing contacts with mesenchymal tissue. Thus, at the nerve front, it is the Schwann cell precursor that are most exposed to extracellular environment while forming a surprisingly invariant substrate for advancing growth cone. This study shows for the first time that Schwann cell precursor are close and consistent cellular companions of growth cone in their approach to their final targets in the developing limb and suggests a previously unappreciated role for Schwann cell precursor in growth cone advance through the limb mesenchyme.

Expression of protein 4.1G in Schwann cells of the peripheral nervous system

The membrane-associated cytoskeletal proteins, including protein 4.1 family, play important roles in membrane integrity, protein targeting, and signal transduction. Although protein 4.1G (4.1G) is expressed ubiquitously in mammalian tissues, it can have very discrete distributions within cells. The present study investigated the expression and distributions of 4.1G in rodent sciatic nerve. Northern and Western blot analysis detected abundant 4.1G mRNA and protein in rat sciatic nerve extracts. Immunohistochemical staining with a 4.1G-specific antibody and double immunolabeling with E-cadherin, betaIV spectrin, and connexin 32 detected 4.1G in paranodal loops, Schmidt-Lanterman incisures, and periaxonal, mesaxonal, and abaxonal membranes of rodent sciatic nerve. Immunoelectron microscopy confirmed the immunodistribution of 4.1G in Schwann cells. In developing mouse sciatic nerves, 4.1G was diffusely distributed in immature Schwann cells and gradually localized at paranodes, incisures, and periaxonal and mesaxonal membranes during their maturation. These data support the concept that 4.1G plays an important role in the membrane expansion and specialization that occurs during formation and maintenance of myelin internodes in the peripheral nervous system.

Peripheral nerve morphometry: Comparison between manual and semi-automated methods in the analysis of a small nerve

Manual nerve morphometry has been usually described as tedious, time consuming, difficult to perform correctly and subject to many sources of errors. The above considerations might suggest that fully automated image analysis systems could be ideally programmed to analyze myelinated fibers. However, operator intervention is necessary to manually eliminate dark tissue elements such as pericytes and Schwann cell nuclei. The aims of the present study were to compare the manual and semi-automated techniques in the evaluation of a small nerve, comparing the most commonly used morphometric parameters for nerve descriptions. The aortic depressor nerves (ADN) of male Wistar rats (N = 12) were prepared with conventional techniques for epoxy resin embedding. Manual morphometry was performed on photomicrographs using a digitizing tablet. Semi-automated morphometry was performed with the aid of computer software, on the same negative images used on the photographic procedure, which were scanned and digitized to a microcomputer. Our results show no differences between data obtained with both methods, for any of the evaluated parameters (area, perimeter, diameters, myelin sheath thickness, g ratio, distribution histograms). In conclusion, manual morphometry reproduced data obtained with semi-automated technique in a small nerve, with the advantages of being less-expensive and an affordable method.

Axonal ensheathment and septate junction formation in the peripheral nervous system of Drosophila

Axonal insulation is critical for efficient action potential propagation and normal functioning of the nervous system. In Drosophila, the underlying basis of nerve ensheathment is the axonal insulation by glial cells and the establishment of septate junctions (SJs) between glial cell membranes. However, the details of the cellular and molecular mechanisms underlying axonal insulation and SJ formation are still obscure. Here, we report the characterization of axonal insulation in the Drosophila peripheral nervous system (PNS). Targeted expression of tau-green fluorescent protein in the glial cells and ultrastructural analysis of the peripheral nerves allowed us to visualize the glial ensheathment of axons. We show that individual or a group of axons are ensheathed by inner glial processes, which in turn are ensheathed by the outer perineurial glial cells. SJs are formed between the inner and outer glial membranes. We also show that Neurexin IV, Contactin, and Neuroglian are coexpressed in the peripheral glial membranes and that these proteins exist as a complex in the Drosophila nervous system. Mutations in neurexin IV, contactin, and neuroglian result in the disruption of blood-nerve barrier function in the PNS, and ultrastructural analyses of the mutant embryonic peripheral nerves show loss of glial SJs. Interestingly, the murine homologs of Neurexin IV, Contactin, and Neuroglian are expressed at the paranodal SJs and play a key role in axon-glial interactions of myelinated axons. Together, our data suggest that the molecular machinery underlying axonal insulation and axon-glial interactions may be conserved across species.

Practical nerve morphometry

Histopathological examination of peripheral nerves is often complemented by morphometric analysis in both clinical and research settings. However, existing manual or semi-automated methods are highly tedious, labour intensive and time-consuming, whereas fully automated morphometry is prone to error from the conversion of maldetected particles to spurious data. Both fully and interactive-automated morphometry have significant hardware requirements and may be difficult to implement. A new method for nerve morphometry is described aiming to combine the speed of automated morphometry with the accuracy of manual or semi-automated methods, and requiring only a digital image of the nerve section and two widely available software packages. Comparison with a standard digitizer pen method of nerve morphometry without sampling yielded statistically similar axon counts, mean area assessments and axonal area frequency distribution histograms, with assessment times of the new method between 35% and 45% of those of the standard method. This has widespread potential experimental and clinical applications and offers a means of relieving much of the tedium currently associated with nerve morphometry.

Attenuated demyelination in the absence of the macrophage-restricted adhesion molecule sialoadhesin (Siglec-1) in mice heterozygously deficient in P0

Mouse mutants heterozygously deficient for the myelin component P0 mimic some forms of inherited neuropathies in humans. We have previously shown that both T lymphocytes and macrophages contribute to the demyelinating neuropathy. Both cell types appear to influence each other mutually, i.e., impaired T lymphocyte development in RAG-1-deficient P0 mutants leads to decreased macrophage numbers and retarded macrophage activation causes reduced T lymphocyte numbers in the peripheral nerves of P0(+/-) mice. In the present study, we investigated the possible role of the macrophage-restricted sialic acid-binding Ig-like lectin sialoadhesin (Sn, Siglec-1) in the pathogenesis of inherited demyelination in P0(+/-) mice. We found that most peripheral nerve macrophages express Sn in the mutants. Myelin mutants devoid of Sn show reduced numbers of CD8+ T lymphocytes and macrophages in peripheral nerves and less severe demyelination, resulting in improved nerve conduction properties. Our findings are potentially important in the development of future treatment strategies for inherited demyelinating neuropathies.

Neuro-muscular biopsy in Churg-Strauss syndrome: 24 cases

Churg-Strauss syndrome (CSS) is a distinctive clinical entity in which systemic vasculitis, associated with eosinophilia, occurs almost exclusively in individuals with adult-onset asthma. The major complications of the condition result from damage to the lungs, heart, and peripheral nerves. Necrotizing vasculitis with eosinophils in the cellular infiltrate, vascular or perivascular infiltration by eosinophils in absence of vessel wall necrosis, extra-vascular eosinophil infiltrates, and vascular or extra-vascular granuloma are histopathological features supportive of CSS. As the peripheral nerve disease often dominates the clinical picture, the peripheral nerve biopsy may be decisive in establishing the diagnosis. In this retrospective study of neuro-muscular biopsies in 24 CSS cases, the authors give an extensive description of neuropathological lesions associated with this disorder. Fifteen patients (62.5%) exhibited eosinophils either in extra-vascular infiltrates or in vessel walls, and 6 of them (25%) had an associated necrotizing vasculitis. Granulomas were found in only 3 cases (12.5%). The clinical diagnosis of CSS was supported in 15 out of the 24 patients (62.5%), in the nerve in 2 cases (8.3%), in the muscle in 8 cases (33.3%), and in both nerve and muscle in 5 others (20.8%).

Early paranodal myelin swellings (tomacula) in an avian riboflavin deficiency model of demyelinating neuropathy

INTRODUCTION

Disruption of the complex architectural and molecular organization of the paranodal region of myelinated peripheral nerve fiber may initiate the evolving time dependent process of segmental demyelination. In support of this notion was the finding of focal paranodal myelin swellings (tomacula) due to redundant folding of myelin sheaths, early in the time course of an avian riboflavin deficiency model of demyelinating neuropathy.

METHODS

Newborn broiler meat chickens were maintained either on a routine diet containing 5.0 mg/kg riboflavin (control group) or a riboflavin-deficient diet containing 1.8 mg/kg riboflavin. Riboflavin concentrations in the liver were measured at postnatal day 11. Peripheral nerves were morphologically examined at days 6, 11, 16 and 21 using light and electron microscopy and teased nerve fiber techniques.

RESULTS

Riboflavin-deficient chickens showed signs of a neuropathy from days 8 and pathological examination of peripheral nerves revealed a demyelinating neuropathy with paranodal tomacula formation starting on day 11. Paranodal tomacula consisted of redundant myelin infoldings or outfoldings, increased in size and frequency after day 11. After day 16, the paranodal swellings showed prominent degenerative changes accompanied by an increased frequency of myelinated fibers showing demyelination.

CONCLUSION

Tomacula due to redundant myelin folds are generally considered a remyelination phenomenon, yet in this avian riboflavin deficiency model of demyelination, the paranodal tomacula occurred early in the course of demyelination.

Therapeutic strategies for the inherited neuropathies

More than 30 genetic causes have been identified for the inherited neuropathies collectively referred to as Charcot-Marie-Tooth (CMT) disease. Previous therapies for CMT were limited to traditional approaches such as rehabilitation medicine, ambulation aids, and pain management. Identification of the genes causing CMT has led to improved genetic counseling and assistance in family planning. Identification of these genes is beginning to delineate common molecular pathways in multiple forms of CMT that can be exploited in future molecular therapies. Scientifically based clinical trials for CMT are currently being implemented. Techniques of gene therapy are advancing to the point that they may become feasible options for patients with CMT and other neurodegenerative diseases.

Synaptic ultrastructure of Drosophila Johnston's organ axon terminals as revealed by an enhancer trap

The role of auditory circuitry is to decipher relevant information from acoustic signals. Acoustic parameters used by different insect species vary widely. All these auditory systems, however, share a common transducer: tympanal organs as well as the Drosophila flagellar ears use chordotonal organs as the auditory mechanoreceptors. We here describe the central neural projections of the Drosophila Johnston's organ (JO). These neurons, which represent the antennal auditory organ, terminate in the antennomechanosensory center. To ensure correct identification of these terminals we made use of a beta-galactosidase-expressing transgene that labels JO neurons specifically. Analysis of these projection pathways shows that parallel JO fibers display extensive contacts, including putative gap junctions. We find that the synaptic boutons show both chemical synaptic structures as well as putative gap junctions, indicating mixed synapses, and belong largely to the divergent type, with multiple small postsynaptic processes. The ultrastructure of JO fibers and synapses may indicate an ability to process temporally discretized acoustic information.

Immunohistochemical labelling of components of the endoneurial extracellular matrix of intact and rhizotomized dorsal and ventral spinal roots of the rat--a quantitative evaluation using image analysis

The endoneurial extracellular matrix (ECM) molecules are involved in cell signalling during nervous system development and regeneration. Quantitative differences of immunofluorescence labelling for chondroitin sulfate proteoglycan (CSPG), fibronectin (FN), tenascin-C (TN-C), and thrombospondin (TSP) were evaluated in intact rat dorsal and ventral roots and dorsal and ventral roots 2 and 4 weeks after rhizotomy using image analysis. The distal stumps of spinal roots displayed increased immunolabelling for the molecules with higher immunofluorescence in dorsal than in ventral roots up to 2 weeks from transection. Four weeks after rhizotomy, the immunoreactivity for CSPG, TN-C and TSP decreased in dorsal and increased in ventral root stumps, although a higher level of immunofluorescence for FN remained in both dorsal and ventral root stumps 4 weeks after injury in comparison to 2 weeks after injury. We suggest that the amount of some ECM molecules changed differentially 2 and 4 weeks after rhizotomy to create an appropriate environment in the endoneurium for early and later regrowth of sensory and motor axons. The results presented here are the first report of differences between the endoneurial ECM content of damaged afferent and motor nerve fibers. In addition, the immunohistochemical detection of individual ECM molecules indicated that final extrinsic conditions stimulating the regrowth of regenerating axons probably arise from a balance of both growth-promoting and -inhibiting molecules in the endoneurium.

Peripheral nerve and skeletal muscle involvement in CADASIL

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is characterized by degeneration of vascular smooth muscle cells (VSMC) of nearly all tissues studied so far. The clinical phenotype of CADASIL shows great variability. The disease is caused by mutations of the Notch3 gene encoding the transmembrane receptor Notch3, which is expressed predominantly in VSMC. In some patients, neuromuscular symptoms have been described. To investigate the fine structural features of peripheral nerve and muscle biopsy specimens in more cases and greater detail, seven electron microscopically confirmed CADASIL patients showing a variable amount of granular osmiophilic material on the surface of VSMC were included in this study. Pathogenic mutations within the cluster region (exon 3 and 4) of the Notch3 gene were identified in six cases. Degeneration and regeneration of nerve fibers in the sural nerves, studied in four cases, was present, although moderate, in all nerve biopsy specimens, whereas an intramuscular nerve fascicle showed more severe changes. Enlarged mitochondria with needle-like calcium precipitates were repeatedly seen. In muscle biopsy specimens, some degree of neurogenic atrophy was apparent in addition to myopathic changes, including occasional ragged red fibers with abnormally large mitochondria, focal tubular aggregates, abnormal terminal cisternae, and myofibrillary abnormalities. Automated sequence analysis of the whole mitochondrial DNA performed in one patient revealed several nucleotide polymorphisms, which were not considered pathogenic. The findings suggest that in CADASIL degeneration of small blood vessels is initiated by defects of the surface membrane of VSMC. Dysfunction of these blood vessels may cause low-grade chronic ischemia with secondary hypoxidosis and a large variety of structural changes noted in skeletal muscle and peripheral nerves, although a primary influence of the underlying genetic defect can not be excluded.

Disrupted Schwann cell-axon interactions in peripheral nerves of mice with altered L1-integrin interactions

The cell adhesion molecule L1 is important for peripheral nerve development. Mice lacking the 6th Ig domain of L1 (L1-6D mice) lose L1 homophilic binding and RGD dependent LI-integrin binding [Itoh,K., Cheng, L., Kamei, Y., Fushiki, S., Kamiguchi, H., Gutwein, P.,Stoeck, A., Arnold, B., Altevogt, P., Lemmon, V., 2004. Brain development in mice lacking Li-L homophilic adhesion. J. Cell Biol.165, 145-154]. We examined the ultrastructure of sciatic nerves from L1-6D at postnatal day 7 and 8 weeks. Unmyelinated axons frequently detached at the edge of Schwann cells, and naked axons were observed. Myelin was thinner in L1-6D and abnormal, multiple axons wrapped in a single myelin sheath were routinely observed. Previous work has shown that L1 on axons interacts with a heterophilic binding partner on Schwann cells to facilitate normal peripheral nerve formation. Taken together, it is likely that L1 on axons binds integrins on Schwann cells, resulting in interactions between axons and Schwann cells that are essential for ensheathment and myelination.

Multifocal motor sensory demyelinating neuropathy: Inflammatory demyelinating polyradiculoneuropathy

The authors present two cases that provide the first autopsy findings in multifocal acquired demyelinating sensory and motor neuropathy (MADSAMN). Both cases documented multifocal but asymmetric demyelinating neuropathy with rare axonal degeneration. One case clearly documented an inflammatory polyradiculoplexoneuropathy, confirming the inflammatory nature of this neuropathy. This study showed that MADSAMN is an inflammatory demyelinating polyradiculoneuropathy that shares histologic features observed in chronic inflammatory demyelinating polyradiculoneuropathy and multifocal motor neuropathy (MMN), suggesting a similar immunopathogenesis for these entities.

Dietary Copper Enhances the Peripheral Myelinopathy Produced by Oral Pyrrolidine Dithiocarbamate

The neurotoxic hazard of a dithiocarbamate is influenced by route of exposure and acid stability of the dithiocarbamate. As an example, oral administration of the acid labile dithiocarbamate N,N-diethyldithiocarbamate (DEDC) causes a central-peripheral axonopathy thought to result from acid-promoted decomposition to CS2 in the stomach. In contrast, parenteral administration of DEDC, which bypasses the acidic environment of the stomach, causes a primary demyelination that is thought to be mediated through the intact parent dithiocarbamate. The relative acid stability of pyrrolidine dithiocarbamate (PDTC) suggests that a significant portion of a dose can be absorbed intact following oral exposure with the potential to produce a primary myelin injury. The present study was performed to characterize the neurotoxicity of PDTC and evaluate the possible role of copper in dithiocarbamate-mediated demyelination. Male Sprague Dawley rats were administered PDTC in drinking water and given either a normal- or high-copper diet for 18, 47, or 58 weeks. Examination of peripheral nerve by light microscopy and electron microscopy at the end of exposures revealed primary myelin lesions and axonal degeneration in the PDTC groups, with a significant increase in the severity of several lesions observed for the PDTC, high-copper group relative to the PDTC normal-copper diet. ICP-AES metal analysis determined that the PDTC groups had significantly increased brain copper, and at 58 weeks a significant increase in copper was seen in the sciatic nerve of PDTC high-copper animals relative to PDTC normal-copper diet animals. Although RP-HPLC analysis could not detect globin alkylaminocarbonyl cysteine modifications analogous to those seen with parenteral DEDC, LC/MS/MS identified (pyrrolidin-1-yl carbonyl)cysteine adducts on PDTC-exposed rat globin. These findings are consistent with previous studies supporting the ability of acid-stable dithiocarbamates to mediate myelin injury following oral exposure. The greater severity of lesions associated with dietary copper supplementation and elevated copper levels in nerve also suggests that perturbation of copper homeostasis may contribute to the development of myelin lesions.

Integration of engrafted Schwann cells into injured peripheral nerve: axonal association and nodal formation on regenerated axons

Transplantation of myelin-forming cells can remyelinate axons, but little is known of the sodium channel organization of axons myelinated by donor cells. Sciatic nerve axons of female wild type mice were transected by a crush injury and Schwann cells (SCs) from green fluorescence protein (GFP)-expressing male mice were transplanted adjacent to the crush site. The male donor cells were identified by GFP fluorescence and fluorescence in situ hybridization (FISH) for Y chromosome. In nerves of GFP-expressing mice, GFP was observed in the axoplasm and in the cytoplasmic compartments of the Schwann cells, but not in the myelin. Following transplantation of GFP-SCs into crushed nerve of wild type mice, immuno-electron microscopic analysis indicated that GFP was observed in the cytoplasmic compartments of engrafted Schwann cells which formed myelin. Nodal and paranodal regions of the axons myelinated by the GFP-SCs were identified by Na(v)1.6 sodium channel and Caspr immunostaining, respectively. Nuclear identification of the Y chromosome by FISH confirmed the donor origin of the myelin-forming cells. These results indicate that engrafted GFP-SCs participate in myelination of regenerated peripheral nerve fibers and that Na(v)1.6 sodium channel, which is the dominant sodium channel at normal nodes, is reconstituted on the regenerated axons.

The immunobiology of Guillain-Barré syndromes

This presentation highlights aspects of the immunobiology of the Guillain-Barré syndromes (GBS), the world's leading cause of acute autoimmune neuromuscular paralysis. Understanding the key pathophysiological pathways of GBS and developing rational, specific immunotherapies are essential steps towards improving the clinical outcome of this devastating disorder. Much of the research into GBS over the last decade has focused on the forms mediated by anti-ganglioside antibodies, and we have made substantial progress in our understanding in several related areas. Particular highlights include (a) the emerging correlations between anti-ganglioside antibodies and specific clinical phenotypes, notably between anti-GM1/anti-GD1a antibodies and the acute motor axonal variant and anti-GQ1b/anti-GT1a antibodies and the Miller Fisher syndrome; (b) the identification of molecular mimicry between GBS-associated Campylobacter jejuni oligosaccharides and GM1, GD1a, and GT1a gangliosides as a mechanism for anti-ganglioside antibody induction; (c) the development of rodent models of GBS with sensory ataxic or motor phenotypes induced by immunisation with GD1b or GM1 gangliosides, respectively. Our work has particularly studied the motor nerve terminal as a model site of injury, and through combined active and passive immunisation paradigms, we have developed murine neuropathy phenotypes mediated by anti-ganglioside antibodies. This has been achieved through use of glycosyltransferase and complement regulator knock-out mice, both for cloning anti-ganglioside antibodies and inducing disease. Through such studies, we have proven a neuropathogenic role for murine anti-ganglioside antibodies and human GBS-associated antisera and identified several determinants that influence disease expression including (a) the level of immunological tolerance to microbial glycans that mimic self-gangliosides; (b) the ganglioside density in target tissue; (c) the level of complement activation and the neuroprotective effects of endogenous complement regulators; and (d) the role of calcium influx through complement pores in mediating axonal injury. Such studies provide us with clear information on an antibody-mediated pathogenesis model for GBS and should lead to rational therapeutic testing of agents that are potentially suitable for use in humans.

Impaired peripheral nerve regeneration in diabetes mellitus

Diabetes mellitus impairs peripheral nerve regeneration. Regenerative failure likely exacerbates deficits from polyneuropathy or focal neuropathies in patients who might otherwise exhibit spontaneous improvement. Some focal neuropathies, like carpal tunnel syndrome, are common, yet render ongoing disability because of their delayed recovery. Why diabetic nerves fail to regenerate is an interesting question to consider because several mechanisms likely contribute. In this review, we examine a number of these causes. These causes include microangiopathy or disease of small blood vessels, failure to provide proper metabolic support for repair, defects in the entry and actions of inflammatory cells within the injury milieu, less robust support of axons by their Schwann cells, and lack of a full repertoire of trophic factors. A number of the mechanisms that generate neuropathy in the first place also likely contribute to failed regenerative programs, but how they do so is not clear.

The ultrastructure of peripheral nerve, motor end-plate and skeletal muscle in patients suffering from spinal muscular atrophy with respiratory distress type 1 (SMARD1)

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is genetically and clinically distinct from classic spinal muscular atrophy (SMA1). It results from mutations in the gene encoding immunoglobulin mu-binding protein 2 (IGHMBP2) on chromosome 11q13. Patients develop distally pronounced muscular weakness and early involvement of the diaphragm, resulting in respiratory failure. Sensory and autonomic nerves are also affected at later stages of the disease. We investigated peripheral nerves, skeletal muscles and neuromuscular junctions (NMJ) ultrastructurally in five unrelated patients and three siblings with genetically confirmed SMARD1. In mixed motor and sensory nerves we detected Wallerian degeneration and axonal atrophy similar to the ultrastructural findings described in SMA1. Isolated axonal atrophy was evident in purely sensory nerves. All investigated NMJ of patients with SMARD1 were dysmorphic and lacked a terminal axon. Moreover, we also observed characteristics of neuropathies, such as abnormalities in myelination, that have not been described in spinal muscular atrophies so far. Based on these findings we conclude that impairment of IGHMBP2 function leads to axonal degeneration, abnormal myelin formation, and motor end-plate degeneration.

Tight junctions in Schwann cells of peripheral myelinated axons: a lesson from claudin-19-deficient mice

Tight junction (TJ)-like structures have been reported in Schwann cells, but their molecular composition and physiological function remain elusive. We found that claudin-19, a novel member of the claudin family (TJ adhesion molecules in epithelia), constituted these structures. Claudin-19-deficient mice were generated, and they exhibited behavioral abnormalities that could be attributed to peripheral nervous system deficits. Electrophysiological analyses showed that the claudin-19 deficiency affected the nerve conduction of peripheral myelinated fibers. Interestingly, the overall morphology of Schwann cells lacking claudin-19 expression appeared to be normal not only in the internodal region but also at the node of Ranvier, except that TJs completely disappeared, at least from the outer/inner mesaxons. These findings have indicated that, similar to epithelial cells, Schwann cells also bear claudin-based TJs, and they have also suggested that these TJs are not involved in the polarized morphogenesis but are involved in the electrophysiological "sealing" function of Schwann cells.

Effect of low-power pulsed laser on peripheral nerve regeneration in rats

The purpose of this study was to determine whether low-power pulsed laser irradiation could affect the regeneration of a 10-mm gap of rat sciatic nerve created between the proximal and distal nerve stumps, which were sutured into silicone rubber tubes. After 8 weeks of recovery, pulsed laser-irradiated groups at frequencies of 5 kHz and 20 kHz both had significantly lower success percentages of regeneration (50% and 44%, respectively) compared to sham-irradiated controls (100%). In addition, qualitative and quantitative histology of the regenerated nerves revealed a less mature ultrastructural organization with a smaller cross-sectional area and a lower number of myelinated axons in both pulsed laser-irradiated groups than in controls. These results suggest that pulsed laser irradiation could elicit suppressing effects on regenerating nerves.

Neuroprotective effect of the immune system in a mouse model of severe dysmyelinating hereditary neuropathy: enhanced axonal degeneration following disruption of the RAG-1 gene

In mouse models of later onset forms of human hereditary demyelinating neuropathies, the immune system plays a crucial pathogenic role. Here, we investigated the influence of immune cells on early onset dysmyelination in mice homozygously deficient of the myelin component P0. In peripheral nerves of P0(-/-) mice, CD8+ T-lymphocytes increased with age. Macrophages peaked at 3 months followed by a substantial decline. They were mainly of hematogenous origin. To evaluate the functional role of immune cells, we cross-bred P0(-/-) mutants with RAG-1-deficient mice. At 3 months, the number of endoneurial macrophages did not differ from the macrophage number of immunocompetent myelin mutants, but the later decline of macrophages was not observed. Quantitative electron microscopy revealed that in plantar nerves of 6-month-old double mutants, significantly more axons had degenerated than in immunocompetent littermates. These data suggest a neuroprotective net effect of T-lymphocytes on axon survival in inherited, early onset dysmyelination.

Canine and feline models of human inherited muscle diseases

Animal models are of immense importance for studying mechanisms of disease and testing new therapies, and rodents have been used extensively in the field of neuromuscular disorders. Mice and rats can be genetically manipulated to over-express or not express genes that are important to muscle function, and these animals can be available in large numbers for analysis. Other species, such as cats and dogs, cannot be manipulated in the same ways or be used in large numbers, but they have spontaneously occurring muscle diseases with clinical presentations more closely resembling those of the human disorders. Therefore, cats and dogs may become valuable as intermediate disease models. This review focuses on canine and feline models of human inherited muscle diseases with comparisons to rodent models and an emphasis on the muscular dystrophies.

Role for the epidermal growth factor receptor in neurofibromatosis-related peripheral nerve tumorigenesis

Benign neurofibromas and malignant peripheral nerve sheath tumors are serious complications of neurofibromatosis type 1. The epidermal growth factor receptor is not expressed by normal Schwann cells, yet is overexpressed in subpopulations of Nf1 mutant Schwann cells. We evaluated the role of EGFR in Schwann cell tumorigenesis. Expression of EGFR in transgenic mouse Schwann cells elicited features of neurofibromas: Schwann cell hyperplasia, excess collagen, mast cell accumulation, and progressive dissociation of non-myelin-forming Schwann cells from axons. Mating EGFR transgenic mice to Nf1 hemizygotes did not enhance this phenotype. Genetic reduction of EGFR in Nf1(+/-);p53(+/-) mice that develop sarcomas significantly improved survival. Thus, gain- and loss-of-function experiments support the relevance of EGFR to peripheral nerve tumor formation.

Peripheral nerve endoneurial microangiopathy and necrosis in rats with insulinoma

Peripheral nerve pathology related to chronic hyperinsulinemia and hypoglycemia has yet to be fully explored. Here we conducted a systematic quantitative analysis of morphological alterations in peripheral sensory and motor nerve fibers and endoneurial microvasculature in longstanding insulinoma-carrying rats (I-rats; n=12). Age-matched normal rats (n=6) served as controls. Over the 15-month observation period, two of I-rats developed paresis of the hind limbs when their blood glucose level fell below 1.7 mmol/l. These animals showed a massive myelinated fiber loss associated with active degeneration of residual myelinated fibers and multiple endoneurial microvascular occlusions at the sciatic nerve level. The rest of the non-paretic I-rats showed a decreased density of large myelinated fibers with axonal degeneration in the peroneal nerve and an increased density of small myelinated fibers with preserved morphology in the sural nerve. This was associated with endoneurial microangiopathic changes indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and an increase in endoneurial microvascular density in the sciatic and sural nerves. In conjunction with previous data, these findings suggest that the observed increase in endoneurial microvascular density may be a compensatory response to endoneurial ischemia/hypoxia induced by chronic hyperinsulinemia in I-rats without paresis. In conclusion, the present study showed characteristic morphological alterations in peripheral sensory and motor nerve fibers associated with microangiopathy indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and provides the first evidence for the occurrence of endoneurial necrosis in the sciatic nerve, to which the hind limb paresis can be ascribed in I-rats.

Determination of functional and morphologic changes in palmar digital nerves after nonfocused extracorporeal shock wave treatment in horses

OBJECTIVE

To determine functional and morphologic changes in palmar digital nerves after nonfocused extracorporeal shock wave (ESW) treatment in horses.

ANIMALS

6 horses.

PROCEDURES

The medial and lateral palmar digital nerves of the left forelimb were treated with nonfocused ESWs. The medial palmar digital nerve of the right forelimb served as a nontreated control nerve. At 3, 7, and 35 days after treatment, respectively, 2 horses each were anesthetized and nerves were surgically exposed. Sensory nerve conduction velocities (SNCVs) of treated and control nerves were recorded, after which palmar digital neurectomies were performed. Morphologic changes in nerves were assessed via transmission electron microscopy.

RESULTS

Significantly lower SNCV in treated medial and lateral nerves, compared with control nerves, was found 3 and 7 days after treatment. A significantly lower SNCV was detected in treated medial but not lateral nerves 35 days after treatment. Transmission electron microscopy of treated nerves revealed disruption of the myelin sheath with no evidence of damage to Schwann cell bodies or axons, 3, 7, and 35 days after treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Nonfocused ESW treatment of the metacarpophalangeal area resulted in lower SNCV in palmar digital nerves. This effect likely contributes to the post-treatment analgesia observed in horses and may result in altered peripheral pain perception. Horses with preexisting lesions may be at greater risk of sustaining catastrophic injuries when exercised after treatment.

Pro-nociceptive role of peripheral galanin in inflammatory pain

We investigated the peripheral function of galanin (GAL) in capsaicin (CAP)-induced inflammatory pain. Intraplantar GAL (0.1 ng/microl) alone does not produce nociceptive behaviors. However, ipsilateral but not contralateral GAL at low doses (0.1 ng/microl) significantly increases CAP-evoked nociceptive behaviors approximately twofold. This effect is attributed to activation of peripheral GAL receptor 2 (GalR2) because a selective GalR2 agonist (AR-M1896) mimics the pro-nociceptive actions of GAL. Recording from nociceptors confirms that GAL does not modify activity of nociceptors but markedly enhances CAP-induced excitation of these fibers. CAP produces a discharge rate of 0.15+/-0.05 impulses/s which increases to 0.54+/-0.17 impulses/s following CAP+GAL. Immunohistochemical studies indicate GalR2 are highly expressed (65.8%) in L5 dorsal root ganglion (DRG) cells. Also, 44.5% GalR2-positive DRG neurons label for the capsaicin receptor (vanilloid receptor 1, VR1) while 61.7% of VR1-positive DRG neurons label for GalR2; 28.1% of total DRG neurons are double-labeled supporting the hypothesis that GAL-induced effects are mediated by GalR2 on capsaicin-sensitive primary afferents. Furthermore, 68.0% unmyelinated and 23.1% myelinated digital nerve axons label for GalR2, indicating the receptor is transported out to the periphery. Immunostaining for GAL peptide in digital nerves labels 46.4% unmyelinated and 27.1% myelinated axons, suggesting that afferents are a major source of ligand for peripheral GalR2. These results suggest that peripheral GAL has an excitatory role in inflammatory pain, likely mediated by peripheral GalR2 and that GAL can modulate VR1 function.

The perineurium modifies the effects of phenol and glycerol in rat sciatic nerve

Endoneurial cell response and type of nerve fibre damage were studied after perineural injections of 7% phenol-aqua and pure glycerol. Our previous studies have shown that phenol and glycerol induce different types of nerve fibre degeneration after intraneural injections: phenol dissolves axons and Schwann cells inside the basal lamina tubes but glycerol breaks them down into cellular flakes. The current study investigated whether the difference in type of endoneurial damage also appears after perineural application and how the perineurium affects the effect of these neurolytic agents. Rat sciatic nerves were treated with perineural injections of 7% phenol-aqua or pure glycerol and were followed up to 6 months. The results support the previous findings that perineural phenol injection induces damage that covers almost the whole endoneurium, but glycerol injection results in minor subperineurial damage. An ultrastructural study showed that the endoneurial effects are much milder after perineural injection than after intraneural injections. Phenol-induced nerve fibre dissolving was only rarely seen and the nerve fibre damage appeared similar to that after regular Wallerian degeneration in both groups. Axonal regeneration began within 2 weeks of the injections. Endoneurial macrophages were numerous in the damaged area in many individual nerves even at 3-6 months in both groups, which may indicate impaired phagocytotic activity. Regenerating axonal sprouts were seen first at 1 week post injection and Schwann cells proliferated within 2 weeks in both groups. However, the number of axonal sprouts was higher (P=0.002) and the size of the sprouts appeared larger after glycerol injection at 4 weeks post injection. The present study shows that the effects of extraneurally applied neurolytic agents phenol and glycerol are modified by the perineurium. Phenol readily penetrates the perineurium, but glycerol causes only subperineurial damage. The type of damage is rather similar to regular Wallerian degeneration in both groups and the endoneurial effects differ from those seen after intraneural injections.

An anti-ganglioside antibody-secreting hybridoma induces neuropathy in mice

Immune responses against gangliosides are strongly implicated in the pathogenesis of some variants of Guillain-Barré syndrome (GBS). For example, IgG antibodies against GM1, GD1a, and related gangliosides are frequently present in patients with post-Campylobacter acute motor axonal neuropathy (AMAN) variant of GBS, and immunization of rabbits with GM1 has produced a model of AMAN. However, the role of anti-ganglioside antibodies in GBS continues to be debated because of lack of a passive transfer model. We recently have raised several monoclonal IgG anti-ganglioside antibodies. We passively transfer these antibodies by intraperitoneal hybridoma implantation and by systemic administration of purified anti-ganglioside antibodies in mice. Approximately half the animals implanted with an intraperitoneal clone of anti-ganglioside antibody-secreting hybridoma developed a patchy, predominantly axonal neuropathy affecting a small proportion of nerve fibers. In contrast to hybridoma implantation, passive transfer with systemically administered anti-ganglioside antibodies did not cause nerve fiber degeneration despite high titre circulating antibodies. Blood-nerve barrier studies indicate that animals implanted with hybridoma had leaky blood-nerve barrier compared to mice that received systemically administered anti-ganglioside antibodies. Our findings suggest that in addition to circulating antibodies, factors such as antibody accessibility and nerve fiber resistance to antibody-mediated injury play a role in the development of neuropathy.

Noncontact measurement of nerve displacement during action potential with a dual-beam low-coherence interferometer

We have used a novel phase-referenced heterodyne dual-beam low-coherence interferometer to perform what we believe are the first noncontact measurements of surface motion in a nerve bundle during the action potential. Nerve displacements of approximately 5-nm amplitude and approximately 10-ms duration are measured without signal averaging. This interferometer may find general application in measurement of small motion in cells and other weakly scattering samples.

Axonal spherical bodies in the peripheral nerves of leprosy patients

Spherical bodies, roughly 10 micro m in diameter, which have not been reported before, were found in the peripheral nerve axons of specimens collected during post-mortem examination of leprosy patients. These bodies were found in the fascicles of all peripheral nerves of the extremities examined (median, radial, ulnar, peroneal and sciatic nerves). Their incidence was not related to the type of leprosy. The area immediately below the thickened perineurium, a feature associated with leprosy, often showed a large number of spherical bodies. When observed under a transmission electron microscope, the spherical lesions often showed a lamellar structure, although some of them were amorphous. No structure resembling organelles was seen within the bodies. Observation with the merge technique showed a clearly lamellar structure in most of the spherical bodies. These bodies and the surrounding myelin sheaths were partially polarized. The axonal spherical bodies observed in our study seem to represent lesions gradually formed due to glycoprotein denaturation over long periods of time and to be associated with leprosy-caused thickening of the perineurium of peripheral nerves.

NG2 proteoglycan expression in the peripheral nervous system: upregulation following injury and comparison with CNS lesions

The chondroitin sulphate proteoglycan NG2 blocks neurite outgrowth in vitro and thus may be able to inhibit axonal regeneration in the CNS. We have used immunohistochemistry to compare the expression of NG2 in the PNS, where axons regenerate, and the spinal cord, where regeneration fails. NG2 is expressed by satellite cells in dorsal root ganglia (DRG) and in the perineurium and endoneurium of intact sciatic nerves of adult rats. Endoneurial NG2-positive cells were S100-negative. Injury to dorsal roots, ventral rami or sciatic nerves had no effect on NG2 expression in DRG but sciatic nerve section or crush caused an upregulation of NG2 in the damaged nerve. Strongly NG2-positive cells in damaged nerves were S100-negative. The proximal stump of severed nerves was capped by dense NG2, which surrounded bundles of regenerating axons. The distal stump, into which axons regenerated, also contained many NG2-positive/S100-negative cells. Immunoelectron microscopy revealed that most NG2-positive cells in distal stumps had perineurial or fibroblast-like morphologies, with NG2 being concentrated at the poles of the cells in regions exhibiting microvillus-like protrusions or caveolae. Compression and partial transection injuries to the spinal cord also caused an upregulation of NG2, and NG2-positive cells and processes invaded the lesion sites. Transganglionically labelled ascending dorsal column fibres, stimulated to sprout by a conditioning sciatic nerve injury, ended in the borders of lesions among many NG2-positive processes. Thus, NG2 upregulation is a feature of the response to injury in peripheral nerves and in the spinal cord, but it does not appear to limit regeneration in the sciatic nerve.

Implantation of neural stem cells via cerebrospinal fluid into the injured root

In avulsion injury of the dorsal root, regenerating axons cannot extend through the entry zone, i.e. the transition zone between peripheral and central nervous systems, due to the discontinuity between Schwann cells and astrocytes. We infused neural stem cells through the 4th ventricle in an attempt to enhance axonal growth in injured dorsal roots. Infused stem cells were attached to, and integrated into, the lesion of the root and became associated with axons in the same manner as Schwann cells or perineurial sheath cells in the peripheral nerve, and as astrocytes in the central nerve area. These findings suggest that neural stem cells integrated by infusion through CSF might have a beneficial effect on nerve regeneration by inducing a continuity of Schwann cells and astrocytes at the transition zone.

On sampling and sampling errors in histomorphometry of peripheral nerve fibers

Histomorphometrical assessment of regenerated peripheral nerves is a very common goal of many studies in experimental microsurgery. In this paper, the main critical issues in nerve fiber sampling for quantitative morphological assessment are addressed. The equal opportunity rule, i.e., the basic paradigm of random sampling, is described, together with an explanation of how sampling errors, in the selection of histologic fields and of the nerve fibers inside them, can produce a bias in quantitative estimates. Finally, some practical suggestions on how to cope with the most common sampling errors are provided, in order to help researchers obtain reliable histomorphometrical data on peripheral nerve fibers.

Novel technique for peripheral nerve reconstruction in the absence of an artificial conduit

The purpose of this study is to promote nerve regeneration across a peripheral nerve gap, using a biologic, tissue-engineered nerve (TEN), containing a high density of viable Schwann cells (SCs) in the absence of supportive foreign materials and a tubular system. Isolated SCs from adult rat sciatic nerve were seeded onto biodegradable constructs and implanted into the backs of nude mice to create TENs. Six weeks later, the constructs were harvested, implanted into surgically created sciatic nerve gaps in rats without supportive artificial conduits and compared with both an autograft group and a silicone conduit group using SCs. Two months later, functional assessment was evaluated by walking track analysis and the implanted lesions were imaged by transmission electron microscopy. The axonal number and sciatic function index of the TEN were significantly higher than those of the silicone group and achieved a comparable level to the autograft group. The results indicate that the large number of SCs within their own extracellular matrix appeared sufficient to enable neuronal growth across a nerve gap in the absence of an artificial conduit and that these circumstances may have a positive effect on the supplement of growth factors from the surrounding tissues of implanted TEN.

Pathology of a mouse mutation in peripheral myelin protein P0 is characteristic of a severe and early onset form of human Charcot-Marie-Tooth type 1B disorder

Mutations in the gene of the peripheral myelin protein zero (P0) give rise to the peripheral neuropathies Charcot-Marie-Tooth type 1B disease (CMT1B), Déjérine-Sottas syndrome, and congenital hypomyelinating neuropathy. To investigate the pathomechanisms of a specific point mutation in the P0 gene, we generated two independent transgenic mouse lines expressing the pathogenic CMT1B missense mutation Ile106Leu (P0sub) under the control of the P0 promoter on a wild-type background. Both P0sub-transgenic mouse lines showed shivering and ultrastructural abnormalities including retarded myelination, onion bulb formation, and dysmyelination seen as aberrantly folded myelin sheaths and tomacula in all nerve fibers. Functionally, the mutation leads to dispersed compound muscle action potentials and severely reduced conduction velocities. Our observations support the view that the Ile106Leu mutation acts by a dominant-negative gain of function and that the P0sub-transgenic mouse represents an animal model for a severe, tomaculous form of CMT1B.

5-HT2a receptors in rat sciatic nerves and Schwann cell cultures

Pharmacological approaches and optical recordings have shown that Schwann cells of a myelinating phenotype are activated by 5-HT upon its interaction with the 5-HT(2A) receptor (5-HT(2A)R). In order to further characterize the expression and distribution of this receptor in Schwann cells, we examined rat sciatic nerve and cultured rat Schwann cells using probes specific to 5-HT(2A)R protein mRNA. We also examined the endogenous sources of 5-HT in rat sciatic nerve by employing both histochemical stains and an antibody that specifically recognizes 5-HT. Rat Schwann cells of a myelinating phenotype contained both 5-HT(2A)R protein and mRNA. In the healthy adult rat sciatic nerve, 5-HT(2A)Rs were evenly distributed along the outermost portion of the Schwann cell plasma membrane and within the cytoplasm. The most prominent source of 5-HT was within granules of the endoneurial mast cells, closely juxtaposed to Schwann cells within myelinating sciatic nerves. These results support the hypothesis that the 5-HT receptors expressed by rat Schwann cells in vivo are activated by the release of 5-HT from neighboring mast cells.

Early structural effects of oestrogen on pudendal nerve regeneration in the rat

OBJECTIVE

To determine the early effects of oestrogen on the ultrastructure of the pudendal nerve and distal nerve fascicles near the external urethra sphincter (EUS) after a pudendal nerve crush injury. The pudendal nerve is one of the pelvic floor tissues injured during vaginal delivery, possibly contributing to the development of stress urinary incontinence (SUI) in women, the symptoms of which often do not appear until menopause, implicating hormonal factors.

MATERIALS AND METHODS

Twenty-seven virgin female Sprague-Dawley rats were anaesthetized and underwent ovariectomy. Three days later, they had one of four procedures: bilateral pudendal nerve crush plus implant of a subcutaneous oestrogen-containing capsule (NC+E); nerve crush plus implant of a sham saline-containing capsule (NC+S); no nerve crush with an oestrogen capsule; or no nerve crush with a sham capsule. After 2 weeks the pudendal nerves and urethral tissues were prepared for light and electron microscopy. The number of axons, myelin figures and endoneurial nuclei in the pudendal nerve segment distal to the lesion were counted. Nerve fascicles near the EUS were also counted and categorized as normal or showing signs of degeneration and/or regeneration. The location of each nerve fascicle was specified as either ventral or dorsal.

RESULTS

As there were no significant differences between the two control groups they were combined to form a single control group. In the distal pudendal nerve there were significantly fewer myelinated axons and large myelinated axons in the NC+E and NC+S groups than in the control group. There were three times as many large unmyelinated axons in the NC+E group than in either the NC+S or control groups (P < 0.05). There were only half as many nerve fascicles near the ventral side of the EUS in the NC+S group than in both the control and NC+E groups (P < 0.05).

CONCLUSION

Oestrogen appears to affect large unmyelinated axons in both the injured pudendal nerve and at the denervated EUS target. After pudendal nerve crush, nerve fascicles with evidence of degeneration or regeneration near the EUS appear to be spared with oestrogen treatment, particularly in the ventral region. These observations may reflect the early stages of a neuroregenerative effect of oestrogen. Additional studies are needed to confirm these results at later periods and with functional methods.