Lysosomal activity at nodes of Ranvier in dorsal column and dorsal root axons of the cat after injection of horseradish peroxidase in the dorsal column nuclei.

The occurrence of acid phosphatase (AcPase)-positive bodies, i.e. lysosomes, in dorsal column and dorsal root axons of the spinal cord segments C8 and L7 in adult cats was analyzed by light and electron cytochemical methods after injection of horseradish peroxidase (HRP) in the dorsal column nuclei. Axonal lysosomes were, with few exceptions, concentrated at the nodes of Ranvier. We found no changes in nodal occurrence and distribution of lysosomes in axons of the HRP-injected sides, as compared to axons of the uninjected sides or of animals not exposed to HRP. Axonal lysosomes were very rare in the dorsal columns, where the frequency of nodes containing light microscopically detectable AcPase-positive bodies was 0-5% at the HRP-injected sides, 0-6% at the contralateral sides, and 0-3% in control animals. The corresponding values in the cervical and lumbar dorsal roots were 6-23%, 9-20%, 10-12% and 19-37%, 21-40%, 26-43%, respectively. In view of our recent observations in alpha-motor neurons, the results point at a noteworthy difference in local degradative ability between dorsal column axons and alpha-motor axons, the latter being able to accumulate intramuscularly injected and retrogradely transported HRP at their PNS nodes of Ranvier for 48-60 h, during which period the axoplasmic AcPase activity/concentration increases at some nodes. Such a degradative activity, which could protect the motor neurons by restricting axoplasmic transport of exogenous materials imbibed by their axon terminals outside the CNS, may not be of the same significance for neurons, e.g. dorsal root ganglion neurons, the axon terminals of which are located within the CNS.     

Peroxidase activity at CNS nodes of Ranvier and in initial axon segments of lumbosacral alpha-motoneurons after intramuscular administration of horseradish peroxidase

The occurrence of peroxidase activity in central (CNS) and peripheral nervous system (PNS) parts of alpha-motor axons was studied by light and electron microscopy in adult cats after injection of horseradish peroxidase (HRP) into the medial gastrocnemius muscle. The intrafunicular parts of the axons were virtually free of HRP-positive bodies except at a few nodes of Ranvier. Most of these nodes were weakly HRP-positive and contained, irrespective of a survival time between 25 and 48 h, only a few HRP-positive bodies randomly scattered in the nodal axoplasm. In contrast to this and as described elsewhere (J. Neurocytol., 15 [1986] 253-260), the nodal regions of alpha-motor axons at the level of the ventral root showed strong and characteristic accumulations of HRP-activity. The initial axon segments and adjoining axonal parts contained many HRP-positive bodies. We conclude that the CNS and the PNS parts of an alpha-motor axon differ with regard to the way nodal regions interact with retrogradely transported HRP. Possible mechanisms behind this difference are discussed.     

Transfer of horseradish peroxidase from oligodendrocyte to axon in the myelinating neonatal rat optic nerve: Artefact or transcellular exchange?

In this paper we make the surprising observation that intracellular injection of horseradish peroxidase (HRP) into a single myelinating oligodendrocyte also resulted in localised HRP labelling at the nodes of Ranvier of some axons of the unit. It appeared that HRP had been transferred to the nodal axoplasm from the paranodal loops of the HRP-filled oligodendrocyte. Three HRP-filled oligodendrocytes from isolated optic nerves of 14-day-old rats were analysed by serial section electron microscopy, and HRP was observed in the axonal cytoplasm at three of the nodes of Ranvier delineated by one of the cells. At labelled nodes, HRP was of a uniform intensity throughout the nodal axoplasm. Axonal labelling gradually diminished along the paranodal regions and was not evident in the contiguous internodal axoplasm beyond 20 μm from the node. The myelin sheaths, paranodal loops, and axons appeared normal at labelled nodes, and the paranodal loops and astrocyte perinodal processes adjacent to those of the HRP-filled oligodendrocyte unit did not contain HRP. There was no evidence of extracellular HRP or tissue damage in the surrounding neuropil, and axons neighbouring those enwrapped by the HRP-filled oligodendrocyte did not contain HRP. The possibility that axonal labelling was an artefact of either iontophoretic injection or tissue preparation is discussed. This provocative finding is not definite proof of exchange, but the balance of evidence supports the possibility that there was transcellular exchange of HRP at paranodes between the labelled oligodendrocyte and some of the axons in the unit. The rarity of HRP transfer to axons suggests that it may be a transient or labile event. It is not clear whether oligodendrocyte to axon macromolecular exchange has real physiological and/or pathological significance. © Wiley-Liss, Inc.     

Removal of retrogradely transported material from rat lumbosacral alpha-motor axons by paranodal axon-schwann cell networks

The aim of this study was to investigate the potential ability of Schwann cells to sequester axonally transported material via so called axon-Schwann cell networks (ASNs). These are entities consisting of sheets of Schwann cell adaxonal plasma membrane that invade the axon and segregate portions of axoplasm in paranodes of large myelinated mammalian nerve fibres. Rat hindlimb alpha-motor axons were examined in the L4–S1 ventral roots using light/fluorescence, confocal laser, and electron microscopy for detection of retrogradely transported red-fluorescent latex nanospheres taken up at a sciatic nerve crush, and intramuscularly injected horseradish peroxidase endocytosed by intact synaptic terminals. Survival times after tracer administration ranged from 27 hours to 4 weeks. During their retrograde transport toward the motor neuron perikarya, organelles carrying nanospheres/peroxidase accumulated at nodes of Ranvier, where they often appeared in close association with the paranodal myelin sheath. Serial section electron microscopy showed that many of the tracer-containing bodies were situated within ASN complexes, thereby being segregated from the main axon. Four weeks after nanosphere administration, several node-paranode regions still showed ASN-associated aggregations of spheres, some of which were situated in the adaxonal Schwann cell cytoplasm. The data establish the ability of Schwann cells to segregate material from motor axons with intact myelin sheaths, using the ASN as mediator. Taken together with our earlier observations that ASNs in alpha-motor axons are also rich in lysosomes, this process would allow a local elimination and secluded degradation of retrogradely transported foreign substances and degenerate organelles before reaching the motor neuron perikarya. In addition, ASNs may serve as sites for disposal of indigestable material. GLIA 20:115–126, 1997. © 1997 Wiley-Liss Inc.     

Caspr reveals an aggregation of nodes and flanking node free zones at the rat trigeminal sensory root and dorsal root entry zones

The sensory root entry zone demarcates the transition from the peripheral nervous system (PNS) to the central nervous system (CNS). In this study, we describe the organization of nodes of Ranvier at the trigeminal sensory and dorsal root entry zones of the rat. Caspr immunoreactivity (IR) was used to identify the paranodal region of nodes of Ranvier, while L-MAG-IR was used to identify CNS oligodendrocytes. Immunofluorescence confocal microscopy revealed a dense aggregation of nodes precisely at the PNS to CNS transition with prominent node-depleted zones on either side, while L-MAG-IR was confined to ensheathing fibers on the central side of nodes located in this dense band and identified these as transitional nodes. Morphometric analysis of the PNS and CNS sides of the trigeminal and the PNS side of the dorsal root entry zones confirmed the presence of virtually node-free domains flanking the transitional zone. Further, the reappearance of nodes on the far side of the node-free zones strongly correlated with nodal diameter, with small nodes reappearing first. These findings suggest that the PNS/CNS transition may represent the initial site of myelination of the primary afferent axon within this area.     

Cellular and extracellular components at nodes of Ranvier in rat white matter

Rat CNS nodes of Ranvier were investigated by electron microscopy and immunohistochemistry. Nodes along thin callosal axons possess tiny node gaps containing few or no astrocytic processes. Nodes along thick spinal axons exhibit spatious node gaps containing relatively few irregularly arranged astrocytic processes. Antibodies against HNK-1, chondroitin sulfate, tenascin or NSP-4 do not label small nodes but stain large nodes. We conclude that rat CNS fibers do not exhibit a strict relation between nodal complexity and fiber size comparable to that found in rat PNS fibers.     

Features associated with paranodal demyelination at a specialized site in the non-pathological nervous system

Experimental demyelination in the CNS and PNS have been shown in some cases to exhibit a paranodal distribution. The electric organ of the gymnotid Sternarchus is composed of specialized axons which generate external electric fields. The structure of the nodes of Ranvier changes characteristically along the course of these specialized non-pathological axons. The nodes of Ranvier in two locations along the fibers are markedly enlarged. At the enlarged nodes, but not at normal nodes from the same fibers, the paranodal myelin exhibits morphological features associated with paranodal demyelination. These features include termination of the innermost myelin lamellae at distances of up to 200 μm from the nodal gap. The results indicate that these morphological findings are not necessarily associated with pathological demyelination, and suggest that remodeling of the myelin sheath, including programmed demyelination, may play a role in the development of certain specialized neural systems.     

Retrograde transport of horseradish peroxidase in transected axons. 3. Entry into injured axons and subsequent localization in perikaryon.

Horseradish peroxidase (HRP) applied to crushed mouse sciatic nerves diffused through the damaged perineurium into the endoneurium. In the injured area, HRP passed into damaged myelinated and unmyelinated axons forming columns of reaction product, which extended for several millimeters proximally to the lesion. Ultrastructurally, HRP adhered to the inner surface of the axoplasm and to the surfaces of neurotubules and neurofilaments in such columns. At more proximal levels axons contained HRP in vesicular and tubular organelles and, later, nerve cell bodies of the corresponding spinal ganglia showed HRP, accumulation in cytoplasmic vesicles, cup-shaped bodies, multivesicular bodies and tubules of agranular endoplasmic reticulum. Markedly less HRP reached neurons in the spinal ganglia when applied to the nerve 30 or 60 min after the crush. After such time intervals solid HRP containing axons were also less frequently observed. Conceivably, HRP enters crushed axons momentarily after a crush as an injured cell reaction. Subsequently it is incorporated into organelles higher up in the axons, from where retrograde transport to the perikaryon will fellow. This phenomenon of a sudden non-specific influx of exogenous macromolecules into axotomized neurons and their subsequent transport to the perikaryon might be relevant for development of certain biochemical and morphological responses, e.g. lysosomal alterations, of the neuron to an axonal injury.     

Remyelination following viral-induced demyelination: ferric ion-ferrocyanide staining of nodes of Ranvier within the CNS

Ferric ion-ferrocyanide (Fe-FeCN) staining was used to stain nodes of Ranvier in remyelinating central nervous system (CNS) axons following viral-induced demyelination. As at normal nodes, Fe-FeCN staining was observed on the cytoplasmic surface of the nodal axolemma of remyelinated fibers. These fibers were identified on the basis of inappropriately short internode lengths and thin myelin sheaths. Thus, newly formed nodes along remyelinated CNS axons recapitulate at least one normal nodal membrane property.     

Early onset of degenerative changes at nodes of Ranvier in alpha-motor axons of Cntf null (-/-) mutant mice

The nodes of Ranvier are sites of specific interaction between Schwann cells and axons. Besides their crucial role in transmission of action potentials, the nodes of Ranvier and in particular the paranodal axon-Schwann cell networks (ASNs) are thought to function as local centers in large motor axons for removal, degradation, and disposal of organelles. In order to test whether ciliary neurotrophic factor (CNTF), which is present at high levels in the Schwann cell cytoplasm, is involved in the maintenance of these structures, we have examined lumbar ventral root nerve fibers of alpha-motor neurons by electron microscopy in 3- and 9-month-old Cntf null ((-/-)) mutant mice. Nerve fibers and nodes of Ranvier in 3-month-old Cntf(-/-) mutants appeared morphologically normal, except that ASNs were more voluminous in the mutants than in wild-type control animals at this age. In 9-month-old Cntf(-/-) animals, morphological changes, such as reduction in nerve fiber and axon diameter, myelin sheath disruption, and loss of ASNs at nodes of Ranvier, were observed. These findings suggest that endogenous CNTF, in addition to its role in promoting motor neuron survival and regeneration, is needed for long-term maintenance of alpha-motor nerve fibers. The premature loss of paranodal ASNs in animals lacking CNTF, which seems to be a defect related to a disturbed interaction in the nodal region between the axon and its myelinating Schwann cells, could impede the maintenance of a normal milieu in the motor axon, preceding more general neuronal damage.     

Differential expression of proteoglycans at central and peripheral nodes of Ranvier

The nodes of Ranvier are regularly spaced gaps between myelin sheaths that are markedly enriched in voltage-gated sodium channels and associated proteins. Myelinating glia play a key role in promoting node formation, although the requisite glial signals remain poorly understood. In this study, we have examined the expression of glial proteoglycans in the peripheral and central nodes. We report that the heparan sulfate proteoglycan, syndecan-3, becomes highly enriched with PNS node formation; its ligand, collagen V, is also concentrated at the PNS nodes and at lower levels along the abaxonal membrane. The V1 isoform of versican, a chondroitin sulfate proteoglycan, is also present in the nodal gap. By contrast, CNS nodes are enriched in versican isoform V2, but not syndecan-3. We have examined the molecular composition of the PNS nodes in syndecan-3 knockout mice. Nodal components are normally expressed in mice deficient in syndecan-3, suggesting that it has a nonessential role in the organization of nodes in the adult. These results indicate that the molecular composition and extracellular environment of the PNS and CNS nodes of Ranvier are significantly distinct.     

Disruption of paranodal axo–glial interaction and/or absence of sulfatide causes irregular type I inositol 1,4,5‐trisphosphate receptor deposition in cerebellar Purkinje neuron axons

Paranodal axo–glial junctions (PNJs) play an essential role in the organization and maintenance of molecular domains in myelinated axons. To understand the importance of PNJs better, we investigated cerebroside sulfotransferase (CST; a sulfatide synthetic enzyme)‐deficient mice, which partially lack PNJs in both the central nervous system (CNS) and the peripheral nervous system (PNS). Previously, we reported that axonal mitochondria at the nodes of Ranvier in the PNS were large and swollen in CST‐deficient mice. Although we did not observed significant defects in the nodal regions in several areas of the CNS, myelinated internodal regions showed many focal swellings in Purkinje cell axons in the cerebellum, and the number and the size of swellings increased with age. In the present analysis of various stages of the swellings in 4–12‐week‐old mutant mice, calbindin‐positive axoplasm swellings started to appear at an early stage. After that, accumulation of neurofilament and mitochondria gradually increased, whereas deposition of amyloid precursor protein became prominent later. Ultrastructural analysis showed accumulations of tubular structures closely resembling smooth endoplasmic reticulum (ER). Staining of cerebellar sections of the mutant mice for type I inositol 1,4,5‐trisphosphate receptor (IP₃R1) revealed high immunoreactivity within the swellings. This IP₃R1 deposition was the initial change and was not observed in development prior to the onset of myelination. This suggests that local calcium regulation through ER was involved in these axonal swellings. Therefore, in addition to the biochemical composition of the internodal myelin sheath, PNJs might also affect maintenance of axonal homeostasis in Purkinje cells. © 2014 Wiley Periodicals, Inc.     

Axonal bifurcation in the dorsal root ganglion of the cat: a light and electron microscopic study

Bifurcation of the axon of unipolar neurons in the dorsal root ganglion of the cat has been studied by light and electron microscopy. Osmic acid, Golgi and silver preparations have revealed two types of bifurcation: (1) of myelinated fibers characterized by constriction at the nodal region with peripheral and central branches of equal diameter; (2) of small fibers characterized by a broad triangular expansion at the junctional region with a much thicker peripheral as compared to the central branch. These differences in bifurcation of unmyelinated and myelinated axons can be related to the velocity of conduction in the peripheral nerve and dorsal roots. The ultrastructure of the nodal region at the bifurcation resembles the node of Ranvier of a peripheral nerve fiber. The node of Ranvier at the bifurcation consists of three cells of Schwann and adjacent cells are closely apposed and interdigitated. Neurofilaments and microtubules are prominent structures within the axoplasm at the nodal regions. They group into two streams as the unipolar process bifurcates, entering the peripheral and central branch respectively. At the junctional region within the axoplasm, numerous mitochondria and scattered multivesicular bodies are always observed.     

Distribution of retrogradely transported fluorescent latex microspheres in rat lumbosacral ventral root axons following peripheral crush injury: a light and electron microscopic study

The retrograde axonal tranport of fluorescent latex microspheres, which are tracers extensively used for studying the neuronal connectivity in the CNS, was investigated in large myelinated lumbosacral ventral root nerve fibres of adult rats following peripheral crush injury. After crushing the sciatic nerve, a suspension of 30 nm red-fluorescent latex beads was injected in the crush region. Following postoperative survival times of 24, 48, 72 and 120 h, the animals were fixed by vascular perfusion using different types of paraformaldehyde-based fixatives. At shorter survival times, red-fluorescent granules were seen distributed mainly internodally in several axons, while at longer times ( >; 48 h) an accumulation at nodes of Ranvier, close to the paranodal myelin sheath, predominated. Photoconversion of to the fluorescent labelling into a stable, highly electron dense reaction product was performed using diaminobenzidine, permitting ultrastructural observations. The electron dense material that formed over the fluorescent granules appeared in association with membrane-diliminated bodies. In some bodies the electron dense material formed well-defined, solitary spheres of sizes corresponding to those of the latex beads. When located close to the paranodal myelin sheath, the bodies were often situated within larger membranous structures, which sometimes were partly engulfed by protrusions of the so called axon-Schwann cell cell network. At longer survival times, some bodies containing photoconversion reaction product appeared within the axon-Schwann cell network, thereby being segregated from the main axoplasm. The study introduces a new application for fluorescent latex microspheres. The used approach, combining light/fluorescence and electron microscopy, should be suitable for long term investigations of the fate of axonally transported non-neuronal substances.     

Postnatal differentiation of rat optic nerve fibers: Electron microscopic observations on the development of nodes of Ranvier and axoglial relations

The postnatal differentiation of rat optic nerve fibres was examined by transmission electron microscopy. The results show that many early developing axons contain clusters of vesiculotubular profiles prior to Myelination. At places vesicular elements appear to fuse with the axolemma, and, in addition, some axons exhibit deep axolemmal invaginations and axoplasmic lamellated bodies. It is suggested that these feature might reflect axolemmal remodeling, possibly involving axoglial signalling and/or functional differentiation of the axolemma. The size distribution of unmyelinated optic nerve axons changes little during development. Ensheathment of larger axons commences 6 days postnatally. The subsequent formation of compact sheaths are a few microns long and separated by long bare axon segments. In optic nerves from 10–12-day-old rat pups, a few sheaths consisting of about five layers border primitive asymmetric nodes with a patchy axolemmal undercoating. Extensions from one of the terminating sheaths are often associated with undercoated patches of axolemma. Relatively differentiated nodes of Ranvier first appear 14–16 days after birth. The continued nodal maturation involves establishment of a regular nodal geometry, increasing distinctness of the axolemmal undercoating, and formation of perinodal astrocytic processes embedded in an extracellular node gap substance. The results are compared with available data on the conduction properties of rat optic nerve fibres during development.     

The sodium channel isoform transition at developing nodes of ranvier in the peripheral nervous system: Dependence on a Genetic program and myelination‐induced cluster formation

Among sodium channel isoforms, Na_v1.6 is selectively expressed at nodes of Ranvier in both the CNS and the PNS. However, non‐Na_v1.6 isoforms such as Na_v1.2 are also present at the CNS nodes in early development but gradually diminish later. It has been proposed that myelination is part of a glia‐neuron signaling mechanism that produces this change in nodal isoform expression. The present study used isoform‐specific antibodies to demonstrate that, in the PNS, four other neuronal sodium channel isoforms were also clustered at nodes in early development but eventually disappeared during maturation. To study possible roles of myelination in such transitions, we investigated the nodal expression of selected isoforms in the sciatic nerve of the transgenic mouse Oct6^ΔSCE/βgeo, whose PNS myelination is delayed in the first postnatal week but eventually resumes. We found that delayed myelination retarded the formation of nodal channel clusters and altered the expression‐elimination patterns of sodium channel isoforms, resulting in significantly reduced expression levels of non‐Na_v1.6 isoforms in such delayed nodes. However, delayed myelination did not significantly affect the gene expression, protein synthesis, or axonal trafficking of any isoform studied. Rather, we found evidence for a developmentally programmed increase in neuronal Na_v1.6 expression with constant or decreasing neuronal expression of other isoforms that were unaffected by delayed myelination. Thus our results suggest that, in the developmental isoform switch of the PNS, myelination does not play a signaling role as that proposed for the CNS but rather serves only to form nodal clusters from existing isoform pools. J. Comp. Neurol. 522:4057–4073, 2014. © 2014 Wiley Periodicals, Inc.     

Axoplasmic transport of thioredoxin and thioredoxin reductase in rat sciatic nerve

Thioredoxin and thioredoxin reductase were localized immunohistochemically in the rat sciatic nerve by immunofluorescence using specific rabbit antisera. Both proteins showed strong immunoreactivity in the cytoplasm of Schwann cells and at the nodes of Ranvier. The axoplasm of myelinated axons also showed a low, evenly distributed immunoreactivity for both proteins. A single or double crush of the nerve caused accumulation of immunoreactivity in dilatated axons both proximally and distally to the crush for up to 8 h. Local cooling of the nerve or subepineural injection of either colchicine or vinblastine prevented the accumulation indicating a role of microtubules. The results showed that thioredoxin and thioredoxin reductase are synthesized in nerve cell bodies and rapidly transported in axons both in anterograde and retrograde directions.     

Spatiotemporal distribution of spectrin breakdown products induced by anoxia in adult rat optic nerve in vitro.

Hypoxic/ischemic and traumatic injury to central nervous system myelinated axons is heavily dependent on accumulation of Ca ions in the axoplasm, itself promoted by Na influx from the extracellular space. Given the high density of nodal Na channels, we hypothesized that nodes of Ranvier might be particularly vulnerable to Ca overload and subsequent damage, as this is the expected locus of maximal Na influx. Adult rat optic nerves were exposed to in vitro anoxia and analyzed immunohistochemically for the presence of spectrin breakdown. Cleavage of spectrin became detectable between 15 and 30 mins of anoxia, and increased homogeneously along the lengths of fibers; localized breakdown was not observed at nodes of Ranvier at any time point analyzed. Spectrin breakdown was also found in glial processes surrounding axons. Confocal imaging of axoplasmic Ca also revealed a gradual and nonlocalized increase as anoxia progressed, without evidence of Ca 'hot-spots' anywhere along the axons at any time between 0 and 30 mins of anoxic exposure in vitro. Calculations of Ca diffusion rates indicated that even if Ca entered or was released focally in axons, this ion would diffuse rapidly into the internodes and likely produce diffuse injury by activating Ca-dependent proteases. Western blot analysis for voltage-gated Na channel protein revealed that key functional proteins such as these are also degraded by anoxia/ischemia. Thus, proteolysis of structural and functional proteins will conspire to irreversibly injure central axons and render them nonfunctional, eventually leading to transection, degradation, and Wallerian degeneration.     

Peripheral neuropathy in the twitcher mouse: accumulation of extracellular matrix in the endoneurium and aberrant expression of ion channels

Globoid cell leukodystrophy (GLD; Krabbe’s disease), caused by a genetic galactosylceramidase deficiency, affects both the central and peripheral nervous systems (CNS and PNS). Allogenic hematopoietic stem-cell transplantation (HSCT) has been beneficial for clinical improvement of this disease. However, recent reports by Siddiqi et al. suggested that none of their transplanted patients achieved complete normalization of their peripheral nerve function, despite the well-documented remyelination of the CNS and PNS in the treated patients. We hypothesized that the PNS dysfunction in GLD is due to altered Schwann cell–axon interactions, resulting in structural abnormalities of the node of Ranvier and aberrant expression of ion channels caused by demyelination and that the persistence of this altered interaction is responsible for the dysfunction of the PNS after HSCT. Since there has not been any investigation of the Schwann cell–axonal relationship in twitcher mice, an authentic model of GLD, we first investigated structural abnormalities, focusing on the node of Ranvier in untreated twitcher mice, and compared the results with those obtained after receiving bone marrow transplantation (BMT). As expected, we found numerous supernumerary Schwann cells that formed structurally abnormal nodes of Ranvier. Similar findings, though at somewhat variable extent, were detected in mice treated with BMT. Activated supernumerary Schwann cells expressed GFAP immunoreactivity and generated Alcian blue-positive extracellular matrix (ECM) in the endoneurial space. The processes of these supernumerary Schwann cells often covered and obliterated the nodal regions. Furthermore, the distribution of Na⁺ channel immunoreactivity was diffuse without the concentration at the nodes of Ranvier as seen in wild-type mice. Neither K⁺ channels nor Neurexin IV/ Caspr/ Paranoidin (NCP-1) were detected in the twi/twi sciatic nerve. The results of our study suggest the importance of normalization of the Schwann cell–axon relationship for the functional recovery of peripheral nerves, when one considers therapeutic strategies for PNS pathology in GLD.     

Experimental neuropathy due to acrilamide. Histological and ultrastructural studies (author's transl)]

The effects of acrylamide intoxication were studied both in peripheral (PNS) and central (CNS) nervous system of rats. The animals were sacrified at different time intervals from the beginning of the intoxication. Histological and ultrastructural studies of peripheral nerves and long tracts of the spinal cord revealed a severe axonopathy, characterized by swelling of axons, particularly in the paranodal regions due to accumulation of neurofilaments with almost complete disappearance of neurotubules. There was also aggregation of dense bodies, swollen mitochondria and multivescicolar bodies in subaxolemmal regions. Presynaptic endings in the anterior horns of the spinal cord and in the cuneate nuclei were swollen and filled with packed filaments. Fiber degeneration at different stages was seen both in PNS and in CNS. These changes are not specific for acrylamide intoxication, having been observed in other experimentally induced neuropathies (n-hexane, Mn-BK, CS2, ...), as well as in a variety of diseases both genetically determined and due to exposure to toxic substances (glue-sniffing, leather cement poisoning, antiblastic therapy, ...). Accumulation of filaments in peripheral and central axons is the pattern of fiber degeneration characterizing the dying-back neuropathies. These axonal changes are particularly marked in the pacinian bodies as well as in the distal segments of the fibres. These data support the hypothesis that a dying-back neuropathy might depend on the direct effect of the toxic substance on the most vulnerable segments of the fibres, rather than on the perikaryon of the nerve cell, as previously supposed.