Clinicopathologic analysis of 124 biopsy-proven peripheral nerve diseases

We reviewed dinical, histological and ultrastructural findings of 124 cases of sural nerve biopsy specimens to delineate the trends of peripheral nerve diseases in our institute. Eighty-one were men and 43 were women. We categorized them into five groups: specific diagnosis (66 cases, 53.2%), axonal degeneration type (47 cases, 37.9%), demyelinating type (4 cases, 3.2%), mixed axonal degeneration-demyelinating type (6 cases, 4.8%) and normal (1 case, 0.9%). Cases with specific diagnosis included 21 inflammatory demyelinating polyneuropathy (15 chronic inflammatory demyelinating polyradiculoneuropathy, 6 Guillain-Barre disease), 13 hereditary motor and sensory neuropathy (7 Charcot-Marie-Tooth type I, 6 Charcot-Marie-Tooth type II), 10 vasculitis, 6 toxic neuropathy, 4 leprosy, 3 diabetic neuropathy, 2 alcoholic neuropathy, 1 Fabry's disease and other specific diseases (5 cases). In our cases, the proportion of specific diagnoses was higher, while the proportion of demyelinating peripheral neuropathies and normal were lower than those of Western series. The results of this study indicate that 1) a dose clinicopathologic correlation is important to make a precise diagnosis of peripheral nerve biopsy, 2) Biopsy under strict indication may reduce unnecessary histologic examination, 3) There is no difference in disease pattern of peripheral neuropathy between Western people and Koreans.

Dejerine-sottas disease with a novel de novo dominant mutation, Ser 149 Arg, of the peripheral myelin protein 22

The Ser149Arg mutation of peripheral myelin protein 22 (PMP22) was found in a 19-year-old woman with a sporadic case of Dejerine-Sottas disease. The patient showed delayed motor development. She walked for the first time with support at the age of 2 years. Scoliosis developed at age 4 years. Her walking ability was best at age 11. Thereafter, she showed progressive muscle weakness and sensory disturbances in the distal extremities. At the age of 18 years, the use of a wheelchair became necessary. Motor and sensory nerve conduction studies showed absent motor and sensory responses on electrical stimulation of the limb nerves. A sural nerve biopsy specimen showed marked decreases in the numbers of both large and small myelinated fibers, abundant onion-bulb formation, and hypomyelination. Electron microscopic observation revealed the presence of demyelinated axons and myelin sheaths disproportionately thin relative to axon diameter. That this was a de novo mutation was established by parentage testing and PMP22 gene analysis of the parents. The mutation seems to be novel and dominant.

Expression of dystroglycan and laminin-2 in peripheral nerve under axonal degeneration and regeneration

In Schwann cells, the transmembrane glycoprotein beta-dystroglycan composes the dystroglycan complex, together with the extracellular glycoprotein alpha-dystroglycan which binds laminin-2, a major component of the Schwann cell basal lamina. To provide clues to the biological functions of the interaction of the dystroglycan complex with laminin-2 in peripheral nerve, the expression of beta-dystroglycan and laminin-alpha2 chain was studied in rat sciatic nerves undergoing axonal degeneration and regeneration as well as in normal condition. In normal sciatic nerve, immunoreactivity for the cytoplasmic domain of beta-dystroglycan was consistently and selectively localized in the Schwann cell cytoplasm underlying the outer (abaxonal) membrane apposing the basal lamina. While beta-dystroglycan expression was gradually down-regulated in Schwann cells losing contact with axons during axonal degeneration, it was progressively up-regulated as the regenerating process of ensheathment and myelination proceeded during regeneration. Interestingly, beta-dystroglycan expression, when detectable, was always restricted to the Schwann cell cytoplasm beneath the outer membrane apposing the basal lamina during both axonal degeneration and regeneration. Furthermore, laminin-alpha2 immunoreactivity roughly paralleled that of beta-dystroglycan during both axonal degeneration and regeneration, indicating that the expression of beta-dystroglycan and laminin-alpha2 is induced and maintained by the Schwann cell contact with axons. Our results indicate that the dystroglycan complex is involved in the adhesion of the Schwann cell outer membrane with the basal lamina and suggest that the dystroglycan complex may play a role in the process of Schwann cell ensheathment and myelination through the interaction with laminin-2.

Actin bundles in perineurial cells of rat spinal nerves

The overall distribution of the actin cytoskeleton in perineurial cells of rat spinal nerves was examined by confocal laser and thin-section electron microscopy. Confocal laser microscopy of whole-mount nerves stained with fluorescent-labelled phalloidin revealed two types of actin bundles in perineurial cells; stress fiber-type actin bundles and circumferential actin bundles. The degree of development of the actin cytoskeleton varied in different segments of different nerves. Stress fiber-type actin bundles were also immunostained for myosin and vinculin and were well-developed in the perineurial cells of large-sized nerves and dorsal root ganglia, whereas they were poor in spinal nerve root sheaths within the subarachnoid space. In peripheral nerves, stress fiber-type actin bundles tended to be arranged transverse to the nerve axis. Circumferential actin bundles were localized along intercellular junctions, which were immunostained with several junctional proteins such as alpha-catenin, occludin and ZO-1. Thin-section electron microscopy confirmed the distribution pattern of actin bundles observed by confocal laser microscopy. These findings suggest that actin bundles may play some roles in structurally stabilizing the perineurium by providing mechanical support for the cell layers as well as cell junctions to maintain perineurial integrity and form diffusion barriers in peripheral nerves.

Verification of the two-dimensional disector, a method for the unbiased estimation of density and number of myelinated nerve fibers in peripheral nerves

Quantification of the number of myelinated fibers in peripheral nerves is a common requirement in quantitative morphology. This parameter provides important information on the consequences of various physiological, pathological and experimental conditions on the nerve structure and is one of the main indicators of success of peripheral nerve repair. In this paper, the theoretical rationale for the application of stereological principles to obtain unbiased estimates of the density and total number of myelinated fibers in peripheral nerves is discussed and a simple stereological method is described. The method is applied together with a systematic random sampling scheme, that was optimized for the purposes of the present study, and with sampling scheme analysis by calculating the coefficient of error (CE). The stereological method, which consists of a two-dimensional variation of the classical disector procedure (two-dimensional disector), and the sampling scheme are verified by comparing estimates with the true density and total number of myelinated fibers in peripheral nerve trunks where true values have been accurately determined by extensive counting. The verification of the 2-D disector method, both of normal and regenerated nerves, showed that estimates of density and total number of myelinated nerve fibers are unbiased. The method also proved to be efficient (time-saving): Estimation of density and total number of myelinated fibers in a single nerve takes about 2-3 hours.

Teased-fiber technique for peripheral myelinated nerves: methodology and interpretation

Teased-fiber technique is the best approach for studying peripheral myelinated nerve fibers in their continuity. It enables the assessment of size of myelin segments formed by Schwann cells and characterization of pathologic changes affecting the internodia, the paranodal regions, and the invested axons. Fiber teasing is performed on prestained proximodistally oriented portions of peripheral nerves. Specimens about 10 mm long are stained for 24-48 hours in Sudan black and then transferred to glycerin, where, using a pair of fine forceps and a stereomicroscope, they are separated into smaller fiber bundles from which single fibers are isolated. The work is performed on a glass slide with an adhesive surface (albuminized or "superfrost"), on which the fibers are placed in strict proximodistal orientation. Following drying in an oven, the slides are mounted with glycerin-gelatine (same as used for frozen sections). The changes, when present, can usually be recognized during the preparation, but fibers are reexamined and changes confirmed in mounted slides. Photographic reconstruction of the fibers facilitates their assessment and enables the documentation of findings. The teased-fiber technique is auxiliary to histopathology, and to limit the workload and save costs, it can be performed on only a few specimens selected for better characterization of changes recognized or suspected in tissue sections. In particular, segmental demyelination and early stages of Wallerian or secondary axonal degeneration can be recognized in teased fibers. Segmental demyelination is characterized by loss of fully myelinated segments and their replacement by newly formed short and thin segments, remyelinating the preserved axon. The early stage of secondary axonal degeneration is recognized by formation of ovoidal fiber fragments in the midinternodal region.

Localization and functional roles of PMP22 in peripheral nerves of P0-deficient mice

Peripheral nerves of P0-deficient (P0(-)) mice show a severe dysmyelination and altered expression of several cell surface molecules. In the present study we investigated the subcellular localization of the peripheral myelin protein (PMP)22 in the abnormal axon-Schwann cell units of the mutants. We show by postembedding immunoelectron microscopy that PMP22 is expressed in both noncompacted and abnormally compacted myelin-like regions of P0(-) mice. By the generation of mice deficient for both P0 and PMP22 (P0(-)/PMP22(-) double mutants) we investigated the functional role(s) of PMP22 in P0(-) mice. In 4-week-old double mutants, some abnormally compacted myelin-like sheaths showed slight alterations in compaction with collapsed intraperiod lines, whereas the totally uncompacted axon-Schwann cell units displayed a more irregular cytoarchitecture owing to the presence of more cytoplasm within the loose Schwann cell loops. These findings show an only subtle impact of PMP22 on the structure of P0-deficient myelin-like sheaths. During early stages of myelin formation, peripheral nerves of P0(-)/PMP22(-) mice resembled those of PMP22(-) mutants in that they were characterized by a strongly retarded spiralling of Schwann cell processes. Thus, P0 appears to be the major determinant of myelin structure, whereas PMP22 is the predominant regulator of the timely correct initiation of myelination.

Light and electron microscopic study of the hindgut of the ant (Formica nigricans, hymenoptera): II. Structure of the rectum

The rectum of the ant Formica nigricans is composed of six ovoid rectal papillae inserted into a rectal pouch. The wall of the rectal pouch is made up of a flat epithelium of simple rectal cells lined by cuticle, and surrounded by a circular muscle layer. Each rectal papilla is comprised by a simple columnar epithelium of principal cells facing the lumen, and a simple cuboid epithelium of secondary cells towards the hemolymph; a group of 20-25 slender junctional cells lies laterally between both epithelia enclosing an intrapapillar sinus. The muscle layer of the rectal wall also surrounds the base of the papillae. Principal cells do not exhibit extensive infoldings at the apical and basal plasma membranes. Lateral membranes, in contrast, develop highly folded mitochondria-scalariform junction complexes enclosing very narrow intercellular canaliculi between adjacent cells. These canaliculi open to wider intercellular sinuses that ultimately drain into the intrapapillar sinus at the sites of entry of tracheal cells. The lateral plasma membranes do not link to the apical or basal plasma membrane, thus originating a syncytium throughout the principal cells. The apical plasma membrane of secondary cells shows invaginations in relation with an apical tubulovacuolar system, bearing portasomes to the cytoplasmic side of the membrane. Secondary cells unite by convoluted septate junctions, and basolateral infoldings are also developed. These ultrastructural traits, some of them different from those found in other insects, are discussed and examined in relation to their role in water and solute absorption. A route for rectal transport in F. nigricans is proposed.

Nerve regeneration through side-to-side neurorrhaphy sites in a rat model: a new concept in peripheral nerve surgery

Despite great improvement and refinements in nerve repair techniques, there were still problems in repair of peripheral nerve injuries for which proximal stumps were not available. In these circumstances for which classic end-to-end neurorrhaphy was impossible, new treatment modalities, benefiting by an adjacent healthy nerve, have been under investigation to overcome this problem. Therefore, end-to-side nerve repair with its modifications came to view and axonal passages through this site were shown. Moreover, the results were unsatisfactory or necessitating sacrifice of another healthy nerve. Three groups, containing 10 rats each, were included in the study. First was the control group, with end-to-end repair of the peroneal nerve. Second was the end-to-side repair group, in which the distal stump of the peroneal nerve trunk was anastomosed to the lateral side of the tibial nerve. The third was the side-to-side repair group. In this technique, 1-mm diameter epineural windows, both from peroneal and tibial nerve trunks facing each other, were removed and side-to-side neurorrhaphy was performed. After 3 weeks, as the second step, the peroneal nerve was sectioned proximally. At 2, 4, 8, 12, 20, and 28 weeks, functional assessment of nerve regeneration was performed by using walking track analysis. The number of myelinated fibers and fiber diameters were measured and an electron microscopic evaluation was carried out. Statistically, both in morphometric and gait analysis, the differences in values between the groups were significant in favor of the control group, followed by the side-to-side group. The study showed that axonal passage was possible with side-to-side technique and the functional results were satisfactory and superior to the end-to-side technique. Continuous supply of neurotrophic factors from their target cells was the probable cause of superior functional return in side-to-side repair, because both joining nerves were intact and healthy during the anastomosis procedure and after 3 weeks. It was concluded that this technique could be indicated in salvage of nerves in cases for which any intermediate segments would be removed, as in tumor ablation surgery, harvesting of nerve grafts, or both.

Immunolocalization of tight junction proteins, occludin and ZO-1, and glucose transporter GLUT1 in the cells of the blood-nerve barrier

Facilitated-diffusion glucose transporter GLUT1 is abundant in the blood-nerve barrier. To observe the relationship between glucose transfer across the barrier and the molecular architecture of the barrier, we examined the localization of GLUT1 and tight junction proteins, occludin and zonula occludens-1 (ZO-1), by immunofluorescence microscopy and immunogold electron microscopy in the rat sciatic nerve. GLUT1 was enriched at the whole aspects of the plasma membranes of the cells of the barrier: perineurial cells, and endothelial cells of the blood vessels in the endoneurium. These GLUT1-positive cells were also positive for occludin and ZO-1, both of which were localized at tight junctions. ZO-1 additionally was present in the GLUT1-negative cells not serving as the blood-nerve barrier. These observations suggest that occludin in the tight junctions and GLUT1 at the plasma membranes in the cells of the barrier may constitute a mechanism for the selective transfer of glucose across the barrier while preventing the non-specific flow of blood constituents.

Inside-out vs. standard vein graft to repair a sensory nerve in rats

Nerve regeneration in a sensory nerve was obtained by the application of different techniques: inside-out vein graft (IOVG group) and standard vein graft (SVG group). These techniques provide a good microenvironment for axon regeneration in motor nerves, but their efficiency for regeneration of sensory nerves is controversial. The saphenous nervtce was sectioned and repaired by the inside-out and standard vein graft techniques in rats. After 4, 12, and 20 weeks the graft and the distal stump were observed under electron microscopy. In each studied period, the pattern, diameters, and thickness of the myelin sheaths of the regenerated axons were measured in the graft and distal stump. A comparative study about the regenerated nerve fibers by these two different techniques was performed. Regenerated nerve fibers were prominent in both vein grafts 4 weeks after the surgical procedures. On the other hand, in the distal stump, regenerated nerve fibers were observed only from 12 weeks. In both inside-out vein graft and standard vein graft statistical difference was not observed about the diameters and thickness of the myelinated fibers after 20 weeks. On the other hand, the inside-out group had greater regenerated axon number when compared to the standard group. There is a capillary invasion in both graft and distal stump, especially in the IOVG group. The regenerated axons follow these capillaries all the time like satellite microfascicles. After 20 weeks, the diameters of regenerated fibers repaired by the standard vein graft technique were closer to the normal fibers compared to the inside-out vein graft. On the other hand, the pattern of these regenerated axons was better in the IOVG group.

A new combined bodian-luxol technique for staining unmyelinated axons in semithin, resin-embedded peripheral nerves: a comparison with electron microscopy

Quantitation of unmyelinated fibers (UF) in peripheral nerves has classically relied upon ultrastructural morphometry. Because this method is time-consuming, it is not typically performed in routine analysis of nerve biopsies. We applied the Bodian-Luxol technique to detect unmyelinated axons by light microscopy on semithin sections from resin-embedded nerve tissue. Estimates were compared to ultrastructural counts. The staining appeared highly specific for axons. Excellent correlation was found between optic densities and the population of UF larger than 0.5 microm. The smallest profiles detected by light microscopy had a diameter close to 0.6 microm. This new technique is not a substitute for ultrastructural quantitative morphometry of UF, as very small unmyelinated axons, especially regenerating ones, can not be reliably visualized. However, it provides a valuable light microscopic method for evaluating axonal loss among UF.

Morphology of aortic depressor nerve myelinated fibers in normotensive Wistar-Kyoto and spontaneously hypertensive rats

Reports on the morphology of the baroreceptor terminal of spontaneously hypertensive rats (SHR) did not demonstrate any difference when compared to the axonal terminal of normotensive rats. Although several studies reporting baroreceptor terminal and blood vessel wall morphology have been carried out to better understand the baroreceptor function and resetting to hypertensive levels, there are no reports examining the morphology of the fibers of the aortic depressor nerve (ADN) in hypertensive models. Therefore, the objective of the present study was to investigate the morphological aspects of SHR ADN compared to Wistar-Kyoto (WKY) rats. Before the morphologic study, the nerves were isolated and the pressure-nerve activity curve was determined for each ADN. SHR exhibited an increase in the threshold pressure for baroreceptor activation, a rightward shift in the pressure-nerve activity curve with decreases in slope and maximum activity. Semithin (0.3 to 0.5 microm thick) sections of the proximal (close to the nodose ganglion) and distal (close to the aortic arch) segments of the ADN were analyzed by light microscopy. A morphometric study of the nerve fascicles and myelinated fibers was performed. Comparison between proximal and distal segments of the two strains revealed that the ADN of WKY rats were consistently larger. All morphometric parameters studied in myelinated fibers and their respective axons were smaller in SHR. The area of the myelin sheath was comparatively larger in WKY rats. These data show morphologic differences between the ADN of SHR and WKY rats, which may explain, at least in part, the decreased slope and maximum activity of the pressure-nerve activity curve observed with the baroreceptor resetting in SHR.

Peripheral neuropathy caused by proteolipid protein gene mutations

Pelizaeus-Merzbacher disease (PMD) is a dysmyelinating disorder of the central nervous system typically caused by duplications or missense mutations of the proteolipid protein (PLP) gene. Most investigators have found that peripheral nerve function and structure is normal in PMD patients. We have found that null mutations of the PLP gene cause demyelinating peripheral neuropathy, whereas duplications and a proline 14 to leucine mutation do not affect nerve function. A family with a nonsense mutation at position 144, which affects only PLP but not the alternatively spliced gene product DM20, has a very mild syndrome, including normal peripheral nerve function. Our findings suggest that DM20 alone is sufficient to maintain normal nerve function and that there may be domains of PLP/DM20 that have a relatively more active role in the peripheral nervous system compared with that in the central nervous system.

Schwann cell-derived Desert hedgehog controls the development of peripheral nerve sheaths

We show that Schwann cell-derived Desert hedgehog (Dhh) signals the formation of the connective tissue sheath around peripheral nerves. mRNAs for dhh and its receptor patched (ptc) are expressed in Schwann cells and perineural mesenchyme, respectively. In dhh-/- mice, epineurial collagen is reduced, while the perineurium is thin and disorganized, has patchy basal lamina, and fails to express connexin 43. Perineurial tight junctions are abnormal and allow the passage of proteins and neutrophils. In nerve fibroblasts, Dhh upregulates ptc and hedgehog-interacting protein (hip). These experiments reveal a novel developmental signaling pathway between glia and mesenchymal connective tissue and demonstrate its molecular identity in peripheral nerve. They also show that Schwann cell-derived signals can act as important regulators of nerve development.

Ultrastructural changes in peripheral nerve in hereditary motor and sensory neuropathy-Lom

Ultrastructural observations have been made on nerve biopsy specimens from five cases of hereditary motor and sensory neuropathy-Lom (HMSNL). A number of features that distinguish it from other hereditary demyelinating neuropathies were identified. Teased fibre studies were not feasible but examination of longitudinal sections by electron microscopy demonstrated demyelination/remyelination. Severe progressive axonal loss was a conspicuous feature. There was no indication of axonal atrophy. Hypertrophic onion bulb changes were present in the younger patients which later regressed, probably secondary to axonal loss. Myelin thickness was generally reduced in relation to axon diameter, indicating hypomyelination, and partial ensheathment of axons by Schwann cells was observed. The Schmidt-Lanterman incisures were atypical in extending for long lengths along the internode. Uncompacted myelin with a periodicity greater than that observed in other neuropathies in which it occurs was a feature, as was the accumulation of pleomorphic material in the adaxonal Schwann cell cytoplasm. An unusual finding was the presence of intra-axonal accumulations of irregularly arranged curvilinear profiles. These resemble those that have been described in experimental vitamin E deficiency. The amount of endoneurial collagen was markedly increased and some endoneurial blood vessels showed a non-specific basal laminal reduplication.

Fibre composition in the interosseous nerve of the pigeon

The interosseous nerve of birds innervates a string of Herbst corpuscles located near the interosseous membrane between the tibia and fibula. Fibre composition of this nerve was assessed including both myelinated and unmyelinated axons. The diameter of the whole nerve is approximately 100 microm. Complete data were obtained for 3 nerves. The mean total number of myelinated fibres and unmyelinated axons was 2872 +/- 53. The mean number of myelinated fibres was 280 +/- 20 and that for unmyelinated axons was 2600 +/- 47. There was a broad distribution of diameters for myelinated fibres ranging from approximately 2 microm to 10 microm with a distinct peak at approximately 3-5 microm and a less prominent second peak at 6-8 microm. Similarly, myelin sheath thickness distribution showed 2 peaks, one at 0.6-0.8 microm and another at 1.4-1.6 microm. It is suggested that the group represented by the second peak innervates the Herbst corpuscles. The group of smaller myelinated fibres and the unmyelinated axons are assumed to innervate other types of receptors, some of which may be nociceptors.

Motor neuropathy in porphobilinogen deaminase-deficient mice imitates the peripheral neuropathy of human acute porphyria

Acute porphyrias are inherited disorders caused by partial deficiency of specific heme biosynthesis enzymes. Clinically, porphyrias are manifested by a neuropsychiatric syndrome that includes peripheral neuropathy. Although much is known about the porphyrias' enzyme defects and their biochemical consequences, the cause of the neurological manifestations remains unresolved. We have studied porphyric neuropathy in mice with a partial deficiency of porphobilinogen deaminase (PBGD). PBGD-deficient mice (PBGD-/-) imitate acute porphyria through massive induction of hepatic delta-aminolevulinic acid synthase by drugs such as phenobarbital. Here we show that PBGD-/- mice develop impairment of motor coordination and muscle weakness. Histologically femoral nerves of PBGD-/- mice exhibit a marked decrease in large-caliber (>8 microm) axons and ultrastructural changes consistent with primary motor axon degeneration, secondary Schwann cell reactions, and axonal regeneration. These findings resemble those found in studies of affected nerves of patients with acute porphyria and thus provide strong evidence that PBGD deficiency causes degeneration of motor axons without signs of primary demyelination, thereby resolving a long-standing controversy. Interestingly, the neuropathy in PBGD-/- mice developed chronically and progressively and in the presence of normal or only slightly (twofold) increased plasma and urinary levels of the putative neurotoxic heme precursor delta-aminolevulinic acid. These data suggest that heme deficiency and consequent dysfunction of hemeproteins can cause porphyric neuropathy.

Peripheral nerve structure and function in long-term galactosemic dogs: morphometric and electron microscopic analyses

Experimental galactosemia for activating the polyol pathway is used extensively to explore the pathogenesis of diabetic complications. However, despite the presence of severe neuropathy in galactosemic rats, changes in the peripheral nerve have not been well established in galactosemic dogs. We therefore conducted biochemical, electrophysiological, and morphometric studies on peripheral nervous systems (PNS) in dogs given a 30% galactose diet for 44 months. Age- and sex-matched dogs given a 30% cellulose diet were used as control. Chronic galactosemia resulted in accumulation of galactitol and decrease in myo-inositol in the sciatic nerve. Electrophysiological and teased fiber analyses demonstrated no significant abnormalities in the ulnar and peroneal nerves in galactosemic dogs. Morphometric analyses revealed a tendency of myelinated fiber atrophy (24% reduction of average fiber size) associated with 20% decrease (P < 0.05 vs control) in mean myelinated fiber occupancy rate in the peroneal nerve in galactosemic dogs. In the anterior mesenteric ganglion, there was a slight but significant increase (8%) in mean neuronal cell size in galactosemic dogs (P < 0.05 vs control). Electron microscopy revealed that galactosemia did not produce dystrophic and degenerative changes in the autonomic ganglion in dogs. We conclude that structural and functional changes in the PNS of galactosemic dogs are mild and different from those of the rat model. These findings suggest that the severity of peripheral neuropathy induced by chronic galactosemia may be species dependent.

Characterization of the transmembrane molecular architecture of the dystroglycan complex in schwann cells

We have demonstrated previously 1) that the dystroglycan complex, but not the sarcoglycan complex, is expressed in peripheral nerve, and 2) that alpha-dystroglycan is an extracellular laminin-2-binding protein anchored to beta-dystroglycan in the Schwann cell membrane. In the present study, we investigated the transmembrane molecular architecture of the dystroglycan complex in Schwann cells. The cytoplasmic domain of beta-dystroglycan was co-localized with Dp116, the Schwann cell-specific isoform of dystrophin, in the abaxonal Schwann cell cytoplasm adjacent to the outer membrane. beta-dystroglycan bound to Dp116 mainly via the 15 C-terminal amino acids of its cytoplasmic domain, but these amino acids were not solely responsible for the interaction of these two proteins. Interestingly, the beta-dystroglycan-precipitating antibody precipitated only a small fraction of alpha-dystroglycan and did not precipitate laminin and Dp116 from the peripheral nerve extracts. Our results indicate 1) that Dp116 is a component of the submembranous cytoskeletal system that anchors the dystroglycan complex in Schwann cells, and 2) that the dystroglycan complex in Schwann cells is fragile compared with that in striated muscle cells. We propose that this fragility may be attributable to the absence of the sarcoglycan complex in Schwann cells.

Ultrastructural changes in the central and peripheral nervous system in the rat with experimental allergic encephalomyelitis

The aim of the study was the evaluation of ultrastructural changes in rats central and peripheral nervous system after the introduction of experimental allergic encephalomyelitis (EAE) and after the treatment with spinal cord protein hydrolysate. Reduced structural disturbances in myelin were found after oral treatment with hydrolysate. In addition, the indications of remyelinization processes have been observed.

The distribution of ganglioside-like moieties in peripheral nerves

GM1 ganglioside has been implicated as a target of immune attack in some diseases of the peripheral nervous system. Anti-GM1 ganglioside antibodies are associated with certain acquired immune-mediated neuropathies. It is not clear how anti-GM1 antibodies cause nerve dysfunction and injury; however, sodium and/or potassium ion channel dysfunction at the node of Ranvier has been implicated. To gain insight into the pathogenesis of these neuropathies, we examined the distribution of GM1 ganglioside and Gal(beta1-3)GalNAc moieties in nerve fibres and their relationship to voltage-gated sodium and potassium (Kv1.1, 1.5) channels at the nodes of Ranvier in peripheral nerves from human, rat and dystrophic mice. Gal(beta1-3)GalNAc moieties were localized via the binding of cholera toxin and peanut agglutinin. As a control for the specificity of these findings, we compared the distribution of GM1 moieties to that of the ganglioside GT1b. Our study provides definitive evidence for the presence of Gal(beta1-3)GalNAc bearing moieties on the axolemmal surface of mature myelinated fibres and on Schwann cells. Gal(beta1-3)GalNAc binding sites did not have an obligatory co-localization with voltage-gated sodium channels or the potassium ion channels Kv1.1 and Kv1.5 and are thus not likely carried by these ion channels. In contrast with Gal(beta1-3)GalNAc, GT1b-like moieties are restricted to the axolemma.

Selective impairment of fast anterograde axonal transport in the peripheral nerves of asymptomatic transgenic mice with a G93A mutant SOD1 gene

Transgenic mice that express a mutant Cu/Zn superoxide dismutase (SOD1) gene have been provided a valuable model for human amyotrophic lateral sclerosis (ALS). We studied a possible impairment of fast axonal transport in transgenic mice carrying a Gly93-->Ala (G93A) mutant SOD1 gene found in human familial ALS (FALS). Left sciatic nerve was ligated for 6 h in transgenic (Tg) and age-matched wild-type (WT) mice. Immunohistochemical analyses were performed for accumulations of kinesin and cytoplasmic dynein on both sides of the ligation site. Clinical function and histology in the spinal cords, sciatic nerves and gastrocnemius muscles were also assessed. The mice were examined at an early asymptomatic stage (aged 19 weeks) and a late stage (30 weeks) just before the development of the symptoms. WT mice showed an apparent increase in immunoreactivities for kinesin and cytoplasmic dynein at proximal and distal of the ligation, respectively. In contrast, the young Tg mice showed a selective decrease of kinesin accumulation in the proximal of the ligation. The mice were asymptomatic with a mild histological change only in muscles. The old Tg mice showed a marked reduction of the immunoreactivity for kinesin and cytoplasmic dynein on both sides of the ligation. They had a significant loss of spinal motor neurons, relatively small myelinated fiber densities of sciatic nerves, and severe muscular changes. These results provide direct evidence that the SOD1 mutation leads to impaired fast axonal transport, particularly in the anterograde direction at an early, asymptomatic stage preceding loss of spinal motor neurons and peripheral axons. This impairment may contribute to subsequent selective motor neuron death in the present model implicated for human FALS.

Histologic analysis of needle biopsy of urethral sphincter from women with normal and stress incontinence with comparison of electromyographic findings

OBJECTIVE

Our goal was to compare urethral sphincter biopsy and needle electromyography between women who had genuine stress incontinence and those who did not.

STUDY DESIGN

Seventeen continent women and 10 women with stress incontinence had urethral sphincter needle electromyography and urethral biopsy specimens blindly processed for light and electron microscopy.

RESULTS

The continent group had greater skeletal muscle content and percentage in each muscle fascicle and each urethral sphincter. The group with genuine stress incontinence had higher connective tissue content. All urethral skeletal muscle was type 1. The smooth muscle was "multiunit" type and was morphologically indistinguishable between the 2 groups. On electromyography, patients with genuine stress incontinence had significantly more fibrillation potentials, fewer motor unit action potentials, a higher percentage of polyphasia, and less maximum voluntary electrical activity than control subjects.

CONCLUSIONS

Women with stress incontinence differ from continent women in skeletal muscle volume, amount of fibrosis, and electromyographic parameters; these differences support a neurogenic contribution to genuine stress incontinence. Urethral sphincter has only type 1 skeletal muscle and "multiunit" type smooth muscle.

Malignant peripheral nerve sheath tumor with perineurial cell differentiation (malignant perineurioma)

A unique case of malignant peripheral nerve sheath tumor (MPNST) with perineurial cell differentiation occurring in a 63-year-old woman in a subcutis of the forearm is described. The tumor contained cellular and myxoid areas. The neoplastic cells were fusiform with distinct cell borders. They were arranged in storiform pattern and in wavy parallel cell cords in the cellular areas. Focally, a pleomorphism and mitotic activity (including atypical mitoses) similar to those of malignant fibrous histiocytoma were seen. The myxoid parts contained haphazardly oriented cells and scarce lipoblast-like multivacuolated cells mimicking a liposarcoma. In the differential diagnosis, myxoid liposarcoma, dermatofibrosarcoma protuberans, malignant fibrous histiocytoma and low-grade fibromyxoid sarcoma were considered. Immunohistochemically, perineurial differentiation was indicated by the diffuse expression of epithelial membrane antigen and focal reactivity for CD34. The tumor was negative with antibodies to S-100 protein, Leu-7, CD68 (KP1), vimentin and cytokeratin AE1/AE3. Ultrastructure of tumor cells revealed features of MPNST. No recurrence occurred in the patient during 2 years follow up.

Perineurial abnormalities in the spontaneously diabetic dog

Structural abnormalities of the perineurium from six spontaneously diabetic dogs (diabetes duration 4-8 years and six control animals were quantified using detailed electron microscopic morphometric methods on superficial peroneal nerve biopsy specimens. Total perineurial sheath thickness (microm) was significantly increased in diabetic (8.8+/-0.6) compared to control animals (6.2+/-0.3) (P < 0.02). This was attributed to a significant increase in the mean perineurial lamellar width in diabetic (0.49+/-0.03) compared to control (0.40+/-0.01) (P < 0.04) animals. The number of lamellae also showed a non-significant increase in diabetic animals (7.8+/-0.4) compared to controls (6.9+/-0.13) (P < 0.06). There was no change in the mean interlamellar space in diabetic (0.7+/-0.05) compared to control (0.6+/-0.06) (P = 0.15) animals. The total interlamellar space was increased in diabetic (5.7+/-0.5) compared to control (4.1+/-0.36) (P < 0.04) animals. The perineurial cell basement membrane thickness (nm) was significantly increased in diabetic (126.9+/-9.8) compared to control (62.8+/-6.1) (P < 0.005) animals. The current study has demonstrated significant abnormalities of the perineurium in the spontaneously diabetic dog, which may have relevance to the pathogenesis of diabetic neuropathy.

Prominent expression of glial cell line-derived neurotrophic factor in human skeletal muscle

Glial cell line-derived neurotrophic factor (GDNF) has been shown to exert neurotrophic effects on motor neurons as well as mesencephalic dopaminergic neurons. Because GDNF promotes survival of motor neurons in vivo and in vitro and rescues motor neurons from naturally occurring cell death, the potential use of GDNF for treatment of motor neuron diseases has been a major focus of recent research. The expression of GDNF in humans, however, has not been fully examined. In the present study, we examined the expression of GDNF in adult human muscle by Northern blot, reverse transcriptase polymerase chain reaction (RT-PCR), and immunohistochemical analyses to address physiological roles of GDNF in humans. Northern blot analysis demonstrated high expression of GDNF mRNA in human skeletal muscle when compared to that of mouse. Intense GDNF immunoreactivity was observed in the vicinity of plasma membranes of skeletal muscle, particularly at neuromuscular junctions. GDNF immunoreactivity was also observed within the axons and surrounding Schwann cells of peripheral nerves. However, RT-PCR detected expression of GDNF mRNA only in skeletal muscle, and not within the anterior horn cells of human spinal cord. These results suggest that GDNF is produced by skeletal muscle and taken up at the nerve terminals for retrograde transport by axons. Thus, GDNF in human skeletal muscle may be involved in promoting motor neuron survival as a target-derived neurotrophic factor.

Peripheral axons of Wlds mice, which regenerate after a delay of several weeks, do so readily when transcription is inhibited in the distal stump

We have raised the hypothesis that differentiated Schwann cells repress regrowth of axons but become permissive upon dedifferentiation. WId(S) mouse is a strain in which severed peripheral nerves do not degenerate for several weeks, and axonal regeneration does not occur either [5,11]. In this strain, we studied the role of resident cells upon axonal regeneration by inhibiting transcription. Regeneration was assessed with the pinch test, electron microscopy and Dil (a fluorescent lipid soluble dye). After a crush, WId(S) axons did not regenerate but they did so when the crush was made through a nerve segment treated with actinomycin D (ActD), an inhibitor of transcription. In contrast, when the crush was made distal to the treated segment no regeneration ensued. Our results support the notion that normal resident cells of peripheral nerves repress axonal growth.

Postnatally induced inactivation of gp130 in mice results in neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects

The pleiotrophic but overlapping functions of the cytokine family that includes interleukin (IL)-6, IL-11, leukemia inhibitory factor, oncostatin M, ciliary neurotrophic factor, and cardiotrophin 1 are mediated by the cytokine receptor subunit gp130 as the common signal transducer. Although mice lacking individual members of this family display only mild phenotypes, animals lacking gp130 are not viable. To assess the collective role of this cytokine family, we inducibly inactivated gp130 via Cre-loxP-mediated recombination in vivo. Such conditional mutant mice exhibited neurological, cardiac, hematopoietic, immunological, hepatic, and pulmonary defects, demonstrating the widespread importance of gp130-dependent cytokines.

Anterior-posterior subdivision of the somite in embryonic zebrafish: implications for motor axon guidance

The ventral branches of the segmental peripheral nerves in the zebrafish embryo are pioneered by the caudal primary (CaP) motor axons, which extend midsegmentally at the interface of the somite and the notochord. The signals that define the CaP pathway are not well understood. To gain insight into the nature of the guidance cues, we have examined the environment of the CaP motor axons by using electron microscopy and histochemistry. Specifically, we have mapped the distribution of the transcription factor engrailed, of a chondrotin sulfate epitope, and of the recognition molecules zebrafish semaphorin z1b and zebrafish tenascin C. Ultrastructural examination of dye-labeled CaP motor axons revealed a close association with the medial surface of the somite but not with the notochord. The CaP axons were always accompanied by cells that appeared to migrate at the interface of somite and notochord. These cells were confined to the posterior half of the somite. Some of the cells may be neural crest derived, many others are probably of sclerotomal origin. The putative migratory cells expressed a chondroitin sulfate epitope that is a marker of sclerotome in the chick. The pathway of the CaP axon and the distribution of the putative neural crest and sclerotome cells correlated with a subdivision of the myotome into an anterior and posterior components, which were evident at the histological level and by the expression of the markers engrailed, semaphorin z1b, chondroitin sulfate, and tenascin C. We suggest that both the pathway choice of the CaP axon and the route of migratory cells reflect this anterior-posterior bipartition of the myotome.

Perineurial malignant peripheral nerve sheath tumor (MPNST): a clinicopathologic, immunohistochemical, and ultrastructural study of seven cases

Most malignant peripheral nerve sheath tumors (MPNST) are schwannian in nature. The pathologic features of MPNST with perineurial cell differentiation remain to be characterized. To determine the clinicopathologic, immunohistochemical, and ultrastructural characteristics of perineurial MPNST, 121 MPNST from the Mayo Clinic Tissue Registry were examined. Of these 23 spindle cell tumors with long processes disposed in whorls or storiform patterns, features typical of perineurioma, were studied. On the basis of immunohistochemistry (epithelial membrane antigen+/S-100-), 5 perineurial MPNST were identified among 23 tumors selected. These and two previously characterized perineurial MPNST are the subject of this study. None of seven tumors was associated with NF-1. Patients included five males and two females ranging in age from 11 to 83 years (mean, 45.7 years). The tumors measured 1.5 to 30 cm (mean, 9.1 cm) and arose in the extremities (two), trunk (two), face (one), mediastinum (one), and retroperitoneum (one). Only one tumor was nerve associated (phrenic nerve). All tumors were surgically removed. No encapsulation or neurofibroma components were noted. Necrosis was seen in three lesions. Four tumors were classified as high-grade malignant and three as low grade. Mitotic indices varied from 1 to 85/10 high-power fields (median, 16). Immunoreactivities included epithelial membrane antigen (100%), vimentin (100%), Leu-7 (57%), and CD34 (14%). Stains for S-100 protein, muscle markers, and cytokeratin were nonreactive. Ultrastructurally, perineurial-like cells were noted in three tumors and cells intermediate between perineurial and Schwann cells in one. Four tumors recurred and two metastasized; no deaths of disease were noted at follow-ups of 28 to 98 months (mean, 66.9). In conclusion, 4% of MPNST show perineurial cell differentiation. An NF-1 association has yet to be described. Nerve involvement is infrequent. Their immunophenotype (epithelial membrane antigen+/S-100-) frequently indicates ultrastructural perineurial differentiation. The prognosis of perineural MPNST appears to be more favorable than that of conventional MPNST.

Expression of insulin-like growth factors and corresponding binding proteins (IGFBP 1-6) in rat spinal cord and peripheral nerve after axonal injuries

Insulin-like growth factors (IGFs) exert trophic effects on several different cell types in the nervous system, including spinal motoneurons. After peripheral nerve injury, the increased expression of IGFs in the damaged nerve has been suggested to facilitate axonal regeneration. Here we have examined the expression pattern of mRNAs encoding IGF-1 and and -2, IGF binding proteins (IGFBPs) 1-6 in the rat spinal cord and peripheral nerve in three lesion models affecting lumbar motoneurons, i.e., sciatic nerve transection, ventral root avulsion, and a cut lesion in the ventral funiculus of the spinal cord. The expression was also studied in enriched Schwann cell and astrocyte cultures. The injured sciatic nerve expressed IGF-1 and IGF-2 as well as IGFBP-4 and IGFBP-5, whereas central nervous system (CNS) scar tissue expressed IGF-1, IGFBP-2, and IGFBP-5. IGFBP-6 mRNA was strongly upregulated in spinal motoneurons after all three types of lesions. IGFBP-6-like immunoreactivity was present in motoneuron cell bodies, dendrites in the ventral horn, and axons in the sciatic nerve. In line with the in vivo findings, cultured Schwann cells expressed IGF-1, IGF-2, IGFBP-4, and IGFBP-5 mRNAs, whereas cultured astrocytes expressed IGF-1, IGFBP-2, and IGFBP-5 mRNAs. These findings show that IGF-1 is available for lesioned motoneurons both after peripheral and central axonal lesions, whereas there are clear differences in the expression patterns for IGF-2 and some of the binding proteins in CNS and peripheral nervous system (PNS) scar tissue. The robust upregulation of IGFBP-6 mRNA in lesioned motoneurons suggests that this binding protein may be of special relevance for the severed cells.

Inherited demyelinating neuropathies: from gene to disease

Hereditary peripheral neuropathies have traditionally been classified by the clinical disease pattern and mode of inheritance. It only recently became possible to provide a more precise subdivision of the diseases by the discovery of distinct genetic defects. Most inherited peripheral neuropathies are caused by distinct mutations in the genes of three well known myelin components, peripheral myelin protein 22, P0 and the gap junction protein connexin 32. The present review addresses the expression and functional roles of these myelin components, as well as the putative pathomechanisms caused by distinct mutations in the corresponding genes. Moreover, the suitability of mutant animals, such as knock-out mice and transgenic rodents, as artificial models for these diseases and their use in the study of possible treatment strategies are discussed.

Degeneration and regeneration in rabbit peripheral nerve with long-term nerve cuff electrode implant: a stereological study of myelinated and unmyelinated axons

Selective and dynamically co-ordinated functional electrical stimulation (FES) of paralysed/paretic limbs in upper motor neuron lesioned people depends on optimal contact at the neural interface. Implanted nerve cuff electrodes may form a stable electrical neural interface, but may also inflict nerve damage. In this study the immediate and long-term effects of cuff implantation on the number and sizes of myelinated and unmyelinated axons have been evaluated with unbiased stereological techniques. Cuff electrodes were implanted in rabbit tibial nerves just below the knee joint, and the stereological analyses were carried out 2 weeks and 16 months after implantation. Myelinated axons were analysed at standardised levels proximal to, underneath, and distal to the cuff; unmyelinated axons underneath the cuff. A 27% loss of myelinated axons was found underneath and distal to the nerve cuff 2 weeks post surgery. All axonal sizes were equally lost except for the very smallest. At 16 months post surgery the number of myelinated axons was restored to control values at both levels. Except for the presence of regenerative sprouts at 2 weeks post surgery, no changes in the number or sizes of unmyelinated axons were revealed at either 2 weeks or 16 months post surgery. Our study demonstrates that implanted cuff electrodes may cause an initial loss of myelinated axons but with subsequent regeneration.

Acquired idiopathic generalized anhidrosis with isolated sudomotor neuropathy

The pathogenesis and underlying lesion of acquired idiopathic generalized anhidrosis (AIGA) are apparently heterogeneous. We report a patient with AIGA in whom the eccrine glands were histologically normal. However, electron microscopic examination showed markedly low numbers of nerve terminals and unmyelinated axons associated with the eccrine glands. Our laboratory investigations suggest that degeneration of postganglionic sympathetic cholinergic nerve may be the underlying pathogenetic mechanism of anhidrosis in this patient.

Accelerated demyelination of peripheral nerves in mice deficient in connexin 32 and protein zero

Mutant mice that lack either protein zero (P0) or connexin 32 (Cx32) were generated previously to investigate the function of these myelin proteins in peripheral nerves and to assess the value of these mice as animal models for hereditary human peripheral neuropathies. Mice that are completely devoid of P0 expression (P0(+/0)) show a complex phenotype that is characterized by hypomyelination, compromised myelin compaction, and degeneration of myelin and axons early in life. In contrast, young mouse mutants that have retained one wild-type allele of the P0 gene (P0(+/0)) reveal morphologically normal myelin but start to develop signs of demyelination and remyelination at 4 months of age. A similar late-onset myelin deficiency was observed in Cx32-deficient mice (Cx32(0/0)). We have now generated mice deficient for Cx32 and P0. In animals that lack both proteins (Cx32(0/0)/P0(0/0), the phenotype is morphologically identical to mice that solely lack P0. Animals that lack Cx32 and carry one functional P0 allele (Cx32(0/0/P0(+/0)) revealed demyelination and remyelination as evidenced by thin myelin and Schwann cell onion bulb formation already at the age of 4 weeks, a time point when no pathology was observed in the single mutants. These morphological deficits were also more prominent in 4-month-old Cx32(0/0)/P0(+/0)animals compared to the single mutants. Our data support the view that Cx32 and P0 are crucial molecules for the maintenance of myelin. Furthermore, the function of Cx32 in the peripheral nervous system appears to be largely dispensable when myelin compaction is impaired.

Subacute inflammatory polyneuropathy: two cases with plasmacytoid histiocytes in the endoneurium

Inflammatory polyneuropathies are mainly known by their acute form, Guillain-Barré syndrome, but there are also chronic cases and all are considered as having an autoimmune mechanism. In each form, peripheral nerve biopsies show scattered macrophages in the endoneurium and in certain cases macrophages invade the Schwann cell cytoplasm and destroy the myelin sheath. In rarer cases there is a primary axonal degeneration. The authors studied two chronic cases, which both exhibited mixed primitive axonal and demyelinating lesions, with peculiar histiocytes in the endoneurium. These rounded cells were characteristically well marked by KP1 but showed well-developed rough endoplasmic reticulum cysternae at ultrastructural examination. Such plasmacytoid histiocytes have mainly been studied in subacute lymphadenopathies and have been only briefly illustrated in a few cases of peripheral neuropathies due to Lyme disease or HIV infection. The two cases reported here had no associated diseases and probably correspond to a peculiar subacute autoimmune reaction.

Neuropathy in diabetic BB/Wor rats treated with insulin implants

To elucidate the pathophysiology of diabetic neuropathy many workers have examined nerve specimens from diabetic rats. While most workers found that animals with high blood glucose levels develop neuropathy, some researchers report that the peripheral nerves are normal in hyperglycaemic rats. Hypoglycaemia may also cause neuropathy. Some workers suggest that neuropathy is linked to fluctuations of the blood glucose level. In the present study we examine plantar nerves of diabetic BB/Wor rats maintained on an eu-/hyperglycaemic or an eu-/hypoglycaemic regime with insulin implants. Treatment with implants worked well. Light microscopic examination of nerve fibres in non-diabetic control rats and in eu-/hyperglycaemic diabetic rats showed a normal picture. Preparations from eu-/hypoglycemic rats showed irregular myelin sheaths and signs of Wallerian degeneration. The lengths and diameters of the largest internodes were significantly subnormal. We conclude, that periodic moderate hypoglycaemia, but not periodic moderate hyperglycaemia, elicits neuropathy in diabetic BB/Wor rats treated with insulin implants.

Pathological study of mice with total deficiency of sphingolipid activator proteins (SAP knockout mice)

Sphingolipid activator proteins (SAPs) A to D are lysosomal factors required in degradation of sphingolipids with short hydrophilic head groups and are derived from a precursor protein. Sap-B deficiency causes a variant of metachromatic leukodystrophy and sap-C deficiency causes a variant of Gaucher disease. Human total SAP deficiency has been reported in two patients in a single family. In these cases, various inclusions were described in the liver, skin, muscle and peripheral nerves ultrastructurally, but there was no report on the pathological study of the central nervous system (CNS). With targeted disruption of the precursor protein gene, we have generated mice with total SAP deficiency. These mice developed progressive neurological symptoms around day 20 and could not survive beyond day 40. Their cardinal pathology is extensive neurovisceral storage. Neuronal storage was already detected in the dorsal root ganglia as early as postnatal day 1 and diffuse neuronal storage was detected in the CNS after day 10. This storage was immunoreactive with anti-ubiquitin antibody and ultrastructurally appeared as inclusions consisting of numerous concentric lamellar and dense granular structures in the perikarya as well as in dendrites and axons. Axonal spheroids containing electron-dense concentric lamellar bodies and neurofilaments were also conspicuous. The extent of neuronal storage, numbers of storage neurons and axonal spheroids increased with age, accompanied with hypomyelination, astrogliosis and increase of macrophages. After day 30, argyrophilic tangle-like structures, which were immunoreactive with an antibody to phosphorylated neurofilaments, were found in the perikarya of many spinal and some neocortical neurons. Inclusions with various ultrastructural features were also noted in the glial cells, choroid plexus epithelial cells, vascular endothelial cells, Schwann cells, macrophages, fibroblasts, hepatocytes, and renal tubular epithelial cells. Some inclusions in the visceral organs were closely similar to those described in human cases of total SAP deficiency. The ultrastructural features of these inclusions in SAP knockout mice appeared unique and were different from those of other known sphingolipidoses.

Microtubule disorientation and axonal swelling in unmyelinated sensory axons during vincristine-induced painful neuropathy in rat

Neuropathic pain accompanies peripheral nerve injury following a variety of insults including metabolic disorders, traumatic injury, and exposure to neurotoxins such as vincristine and taxol. Vincristine, a microtubule depolymerizing drug, produces a peripheral neuropathy in humans that is accompanied by painful paresthesias and dysesthesias (Sandler et al., [1969] Neurology 19:367-374; Holland et al. [1973] Cancer Res. 33:1258-1264). The recent development of an animal model of vincristine-induced neuropathy provides an opportunity to investigate mechanisms underlying this form of neuropathic pain. Systemic vincristine (100 microg/kg) produces hyperalgesia to mechanical stimuli during the second week of administration, which persists for more than a week (Aley et al. [1996] Neuroscience 73:259-265). To test the hypothesis that changes in microtubule structure in nociceptive sensory neurons accompany vincristine-induced hyperalgesia, we analyzed unmyelinated axons in saphenous nerves of vincristine-treated rats. This study constitutes the first quantitative ultrastructural analysis of the cytoskeleton of unmyelinated axons in peripheral nerve during neuropathic hyperalgesia. There was no evidence of unmyelinated fiber loss or a decrease in the number of microtubules per axons. There was, however, a significant decrease in microtubule density in unmyelinated axons from vincristine-treated rats. This decrease in microtubule density was due to a significant increase in the cross-sectional area of unmyelinated axons, suggesting swelling of axons. In addition, vincristine-treated axons had significantly fewer microtubules cut in cross-section and significantly more tangentially oriented microtubules per axon compared to controls. These results suggest that vincristine causes disorganization of the axonal microtubule cytoskeleton, as well as an increase in the caliber of unmyelinated sensory axons.

Distribution of a murine protein tyrosine phosphatase BL-beta-galactosidase fusion protein suggests a role in neurite outgrowth

We have generated a gene trap insertion into the protein tyrosine phosphatase-BL (PTP-BL) locus, which produces a fusion of the N-terminal half of PTP-BL with beta-galactosidase. During development, beta-galactosidase activity was seen in all epithelial cells: strong staining was observed in the stomach and kidney epithelium, the ependymal layer of the central nervous system, and the surface ectoderm. Particularly prominent beta-galactosidase activity was seen in the peripheral nervous system, which correlated with neurite outgrowth. In epithelial cells, staining was seen in the apical portion of the cells. In nerves, beta-galactosidase activity was associated with growth cones as well as with Schwann cells. This suggests that the amino-terminal portion of PTP-BL contains sequences sufficient to target the fusion protein to specific subcellular compartments. In situ hybridization with a PTP-BL probe demonstrated that all tissues in which beta-galactosidase activity was seen were genuine sites of expression of the PTP-BL gene, although differences in the stability of the PTP-BL protein and the PTP-BL-beta-galactosidase fusion protein may exist. The distribution of beta-galactosidase activity in the peripheral nervous system, together with the structure of the wild-type protein, suggests that this phosphatase may have a role in regulation of the cytoskeleton during the development of the peripheral nervous system.

Formation and maintenance of the myelin sheath in the peripheral nerve: roles of cell adhesion molecules and the gap junction protein connexin 32

Based on previous in vitro studies, the cell adhesion molecules L1, N-CAM, MAG, and P0, which all belong to the immunoglobulin (Ig)-superfamily, have been suggested to mediate myelin formation in the peripheral nervous system. Unexpectedly, studies in mice deficient for the corresponding molecules revealed that only P0 plays pivotal roles during the formation of peripheral nerve myelin in vivo, while L1-, N-CAM-, and MAG-deficient mice develop myelin of normal ultrastructure. However, MAG turned out to be important for the maintenance of myelin, as reflected by degeneration of myelin and axons in MAG-deficient mice older than 6 months. The MAG-mediated maintenance of myelin is backed up by N-CAM, since mice deficient in both MAG and N-CAM show an earlier and more prominent myelin degeneration than MAG single mutants. Another peripheral nerve component involved in the maintenance of myelinated fibers is connexin 32 (Cx32), a gap junction channel protein that does not belong to the Ig-superfamily. Mice deficient in Cx32 initially form normal myelin, which then develops blown-up periaxonal collars and abnormally shaped non-compacted regions followed by myelin and axonal degeneration. Our findings strongly support the view that very few myelin components are necessary for myelin formation whereas the maintenance of myelin is much more sensitive to molecular alterations. In addition, it became evident that myelin molecules can fulfill functionally overlapping roles that ensure that myelination takes place even under conditions in which there is a deficiency in the normal molecular components of myelin.

The cytoplasmic domain of the large myelin-associated glycoprotein isoform is needed for proper CNS but not peripheral nervous system myelination

The myelin-associated glycoprotein (MAG) is a member of the immunoglobulin gene superfamily and is thought to play a critical role in the interaction of myelinating glial cells with the axon. Myelin from mutant mice incapable of expressing MAG displays various subtle abnormalities in the CNS and degenerates with age in the peripheral nervous system (PNS). Two distinct isoforms, large MAG (L-MAG) and small MAG (S-MAG), are produced through the alternative splicing of the primary MAG transcript. The cytoplasmic domain of L-MAG contains a unique phosphorylation site and has been shown to associate with the fyn tyrosine kinase. Moreover, L-MAG is expressed abundantly early in the myelination process, possibly indicating an important role in the initial stages of myelination. We have adapted the gene-targeting approach in embryonic stem cells to generate mutant mice that express a truncated form of the L-MAG isoform, eliminating the unique portion of its cytoplasmic domain, but that continue to express S-MAG. Similar to the total MAG knockouts, these animals do not express an overt clinical phenotype. CNS myelin of the L-MAG mutant mice displays most of the pathological abnormalities reported for the total MAG knockouts. In contrast to the null MAG mutants, however, PNS axons and myelin of older L-MAG mutant animals do not degenerate, indicating that S-MAG is sufficient to maintain PNS integrity. These observations demonstrate a differential role of the L-MAG isoform in CNS and PNS myelin.

Human dorsal root ganglion neurons from embryonic donors extend axons into the host rat spinal cord along laminin-rich peripheral surroundings of the dorsal root transitional zone

Following dorsal root crush, the lesioned axons regenerate in the peripheral compartment of the dorsal root, but stop at the boundary between the peripheral and the central nervous system, the dorsal root transitional zone. We have previously shown that fibres from human fetal dorsal root ganglia grafted to adult rat hosts are able to grow into the spinal cord, but were not able to specify the route taken by the ingrowing fibres. In this study we have challenged the dorsal root transitional zone astrocyte boundary with human dorsal root ganglion transplants from 5-8-week-old embryos. By tracing immunolabelled human fibres in serial sections, we found that fibres consistently grow around the dorsal root transitional zone astrocytes in laminin-rich peripheral surroundings, and extend into the host rat spinal cord along blood vessels, either into deep or superficial laminae of the dorsal horn, or into the dorsal funiculus. Human fibres that did not have access to blood vessels grew on the spinal cord surface. These findings indicate, that in spite of a substantial growth capacity by axons from human embryonic dorsal root ganglion cells as well as their tolerance to non-permissive factors in the mature mammalian CNS, these axons are still sensitive to the repellent effects of astrocytes of the mature dorsal root transitional zone. Furthermore, this axonal ingrowth is consistently associated with laminin-expressing structures until the axons reach the host spinal cord.

Morphological characteristics and clinical significance of nerve distribution in pancreatic cancers

Macroscopic and immunohistochemical observations were made to clarify the innervation of normal pancreatic tissues, and the clinicopathological and electron-microscopic findings of 33 cases of pancreatic cancer were obtained. The results showed that the innervation of both the head and the body of the pancreas mainly consisted of nerve fibers separated from the right celiac neuroganglion and the right half of the superior mesenteric arterial plexus. The pancreas was full of nerve fibers ending at acinar lobules, among which the adrenergic nerves commonly control the walls of blood vessels. Pancreatic cancer tends to be accompanied by invasion and metastasis along intra or extra-pancreatic nerves, and we found that the positive rates for invasion and metastasis were 73.33% and 60.00%, respectively. The follow-up study revealed that the nerve-invasion group had worse prognosis than the non-invasion group (P < 0.05). The approaches of the invasions of the nerves were as follows: (1) through the vessels of the perineurium; (2) through the perineurium; and (3) through the synaptic membrane of nerve endings. The invasion were a continuous process, often resulting in the destruction or even the disappearance of the normal structure of the nerve fibers. The above results suggest that there are plentiful vegetative nerves inside or outside the pancreas and that pancreatic cancers have a tendency of invading and metastasizing along or around nerves.

Abnormal nerve conduction studies in mice expressing a mutant form of the POU transcription factor SCIP

We have previously described transgenic mice that harbor a dominant-negative antagonist of the POU protein SCIP (termed deltaSCIP). Native SCIP is expressed in promyelinating Schwann cells, where it represses expression of the myelin structural genes. The deltaSCIP mice display morphologic and behavioral abnormalities, including decreased axonal diameter, increased myelin thickness, developmentally early myelination, and clinical features of neuropathy. To assess the neurophysiologic correlates of these abnormalities, a series of electrophysiologic tests was performed. Despite having smaller diameter axons, mice expressing the deltaSCIP transgene had similar maximum conduction velocities in caudal, sural, and tibial nerves compared to wild-type controls. Therefore, conduction in deltaSCIP animals was faster than predicted by axon diameter alone. Compound amplitude responses were 38% higher in the deltaSCIP caudal nerve. DeltaSCIP tibial F-wave responses showed less difference between minimum and maximum latencies than controls, suggesting less variance between fastest and slowest conducting fibers. These data further characterize the functional components of the deltaSCIP phenotype. In addition, these studies address the physiologic sequelae of altering the g-ratio in the absence of demyelination or axonal degeneration.

Discrimination between the different compartments in sciatic nerve by 2H double-quantum-filtered NMR

The 2H double-quantum-filtered (DQF) NMR spectrum of isolated rat sciatic nerve, equilibrated with deuterated saline, is composed of three quadrupolar-split water signals. On the basis of the time course of their shift by Co-EDTA2- and CoCl2, the signals with quadrupolar splittings of about 120, 470, and 9 Hz were assigned to water in the epineurium, endoneurium, and intra-axonal compartments, respectively. The signal of the bulk water, which experiences isotropic motion, was eliminated by the DQF pulse sequence. As the maximum intensities of the water signals in the three anisotropic compartments occur at different creation times, in the DQF pulse sequence, it is possible to resolve the signals and measure their properties, such as relaxation times, independently, without perturbing the system with shift reagents.

Peripheral nerve regeneration through nerve guides seeded with adult Schwann cells

This study tested the usefulness of Schwann cells in the repair of a severed nerve with a biosynthetic bridge or guide. Reinforced collagen nerve guides were used to bridge an 18 mm gap in the sciatic nerve of 21 young adult rats. The animals were divided into three groups and the guides were filled with: (i) more than 0.5 x 10(6) cultured syngeneic adult Schwann cells (group L, n = 12); (ii) less than 0.5 x 10(6) Schwann cells (Group S, n = 6); and (iii) phosphate buffered saline (control, n = 3). Schwann cells were pre-labelled with Hoechst dye. Regeneration was assessed functionally and histologically at 1, 2, 3 and 6 + months after surgery. Group L animals showed numerous regenerated axons surrounded by implanted Schwann cells within the first month. The total number of myelinated fibers (12.5 x 10(3)) remained above normal unoperated values (7 x 10(3)) in long-term animals. Regenerated axons were found in Group S in the third month, but no Hoechst labelled cells were found. The number of myelinated fibers (3.9 x 10(3)) remained below normal values in long-term animals. Control guides failed to support axonal regeneration. Functional recovery was evident at week 20 (Group L) and week 30 (Group S) after surgery, with no difference in function between the two groups by the end of the study. Supplementing guides with Schwann cells enhances regeneration of peripheral axons over a distance normally prohibitive. This effect is greatest in the early stages of regeneration (1-3 months) and is dependent on the number of cells implanted.