An electron microscopic study of normal bovine spinal ganglia and nerves

Summary The ultrastructure of bovine spinal ganglia and intercostal nerves is described. The capsule of the ganglion and the perineurium of the nerve were similar and consisted of an inner zone of four to six layers of perineural epithelial cells and an outer zone of collagen. The ganglionic neuron was entirely surrounded by a layer of satellite cells but in some neurons processes from the neuronal perikaryon penetrated the satellite cell sheath and terminated adjacent to the basement membrane of the satellite cell layer. Similar axonal projections were occasionally observed in nerve fibres at the nodes of Ranvier. Irrespective of size all neurons had a similar morphology. Bifurcation of the nerve fibre was occasionally seen in the ganglion. The nerve was composed of both myelinated and unmylinated fibres and nodes of Ranvier and Schmidt-Lantermann clefts were frequently encountered. Capillaries were surrounded by pericyte cells and in the interstitial tissues mast cells were frequently seen.     

Acute and chronic effects of the neurolytic agent ricin on dorsal root ganglia, spinal cord, and nerves

The short- and long-term effects of ricin injections into nerves have been evaluated with light microscopy in the dorsal root ganglia, spinal cord, and peripheral nerves in rats and cats. Dorsal root ganglion cells initially exhibited chromatolysis, followed by gliosis and cell death. These changes were associated with Fink-Heimer degeneration in the somatotopically appropriate region of the dorsal horn. There were no signs of chromatolysis in dorsal horn neurons in ricin-injected animals, but chromatolytic motoneurons were observed. Ricin produced acute necrosis of injected nerves and dissolution of axoplasm. At long survival times (greater than 4 weeks) some apparently regenerating axons were seen in the injection sites of rats. Cell counts indicated that a substantial percentage of dorsal root ganglion neurons associated with the injected nerves were killed, but the presence of regenerating axons suggested that some cells survived the ricin treatment. Although the lesion may not always be complete, even with maximum sublethal doses, this method appears to be useful for specifically destroying afferent fibers associated with a particular nerve without transynaptic destruction of dorsal horn neurons.     

Alphaherpesvirus saimiri infection in rabbits

Summary A light and electron microscopic study was undertaken to determine pathological changes in cutaneous spinal nerves of rabbits following intradermal inoculation with alphaherpesvirus saimiri (HVS) isolate KM 322. Infected rabbits were killed at 3, 10, 17, 45 days and 2 years after infection. No abnormalities were seen at 3 days postinoculation. In the nerves of the rabbits killed at 10, 17 and 45 days after infection, axonal (Wallerian-type) degeneration was the main pathological feature. Regeneration, manifested by axonal sprouting, was observed in the nerves of the rabbits killed at 45 days post-inoculation. Neural fibrosis and paucity of unmyelinated axons was the final outcome. The severity of the neural damage not only varied according to the progression of the disease but between nerves taken from the same rabbit. This was probably associated with variation in the numbers of virus particles that had reached the dorsal root ganglion of the dermatome served by a particular nerve. Since HVS (isolate KM 322) provides a model system for the study of virus latency in dorsal root ganglia, and consequently for the study of varicellazoster infection in man, these findings give further insight into the pathology of herpetic neuropathy.     

Cell changes in sensory ganglia following proximal and distal nerve section in the monkey

Ganglion cell changes were studied in 25 monkeys following systematic section of spinal and cranial sensory nerves proximal or distal to the ganglion. Ganglion cells were studied in Nissl preparations while central degeneration was studied in Nauta-Gygax stained sections. Morphological characteristics of normal ganglia were studied in unoperated controls. In normal ganglia three categories of cells were identified: (1) A predominant largecelled group (ranging from 20 to 100 μ), (2) small dark cells, and (3) a small number of “atypical” cells. Division of nerves proximal to ganglia produced no cellular changes in most cases; changes attributed to relative ischemia occurred in a few ganglia. Centrally projecting fibers of sectioned nerves were degenerated. Division of sensory nerves distal to ganglia produced profuse chromatolytic changes in cells of all sizes and types within ganglia but no central degeneration. Cervical section of the vagus produced chromatolytic cell changes in the inferior ganglion and a small portion of the superior ganglion unrelated to the auricular nerve. Section of the facial nerve distal to the geniculate ganglion produced chromatolysis in approximately half of the ganglion cells. An accessory trigeminal ganglion, composed of cells of autonomic type, was found distal to the trigeminal ganglion in association with the third division of the nerve. Severance of nerve fibers distal to sensory ganglia eliminates peripheral neurotrophic influences necessary for the growth and maintenance of the ganglion cell. It is postulated that the integrity of this influence is sufficient to sustain sensory ganglion cells after their central processes have been sectioned.     

PERIPHERAL NEUROPATHY IN MOUSE HEREDITARY DIABETES MELLITUS. II. ULTRASTRUCTURAL CORRELATES OF DEGENERATIVE AND REGENERATIVE CHANGES

Carson K.A., Bossen E.H. & Hanker J.S. (1980) Neuropathology and Applied Neurobiology 6,361–374
Peripheral neuropathy in mouse hereditary diabetes mellitus. II. Ultrastructural correlates of degenerative and regenerative changes
The fine structural changes in some peripheral nerves and sensory ganglia from mice (C57BL/K & J, db/db) with an hereditary diabetic syndrome, similar to human maturity-onset diabetes mellitus, were studied during development of the mild peripheral neuropathy. The abnormalities observed included axonal degeneration, disruption of myelin, accumulation of electron-dense material in axons, satellite cells and Schwann cells, increased frequency of it granules of Reich in Schwann cells, enlarged mitochondria, and proliferated and thickened Schwann cell basal laminae. Distal hind limb nerves were most affected. Sensory ganglion neurons were normal except for occasional chro-matolytic cells, so that nerve cell loss was not present in this peripheral neuropathy. Morphological indications of Schwann cell hyperplasia, hypertrophy, and axonal sprouting supported the contention that a continuous cycle of axonal degeneration and regeneration was occurring. The ultrastructural changes and accumulation of electron-opaque, lipid material suggested that a defect in lipid metabolism, secondary to the diabetic condition, could be an important factor in the peripheral neuropathy in the diabetic mouse.     

Ultrastructure of herpes simplex virus infection of the nervous system of mice

Summary The nervous system and small intestine of mice infected with herpes simplex virus were examined by electron microscopy from the viewpoint of virus-host interaction.The host cells examined included the neuron, astrocyte, oligodendrocyte, and Schwann cell. The susceptibility of the latter was not less than that of the neuron. The endothelial cell, perineural fibrocyte and smooth muscle cell were also host cells. Replication of herpes virus in the nervous system was proven to be identical to that occurringin vitro; initial reproduction of nucleocapsids in the nucleus and subsequent maturation at the nuclear membrane with envelope formation, followed by discharge into the cytoplasmic reticular cavities and finally release from the host cell. Inconsistency in the distribution of virus particles and viral antigen was chiefly concerned with the host cell nucleus and the glial cytoplasm.Herpes virions, though few, were identified in the axons of peripheral nerves, and in the periaxonal space of myelinated fibres in the brain and the nerve ganglia. Virions were present in tiny vesicles in the perikarya or as naked particles. In the distal parts of peripheral nerve, there was marked dissociation in the amount of virions between Schwann cells and the axon. The significance of the endoneural space and the axon in the neural speread of infection is discussed briefly.     

The effects of canine distempr virus on explant tissue cultures of canine cerebellum

Summary Canine cerebellar explant cultures were employed as a model for studying the effects of the virus associated with demyelinating canine distemper encephalomyelitis. Cultures which were inoculated after four to seven days of growth with distemper virus (Lederle strain) had beginning cytopathic effect (CPE) in the peripheral outgrowth on the eighth post-inoculation day. The cells predominantly affected were astroglia and mesenchymal cells. The cellular lesions consisted of inclusion body development (intracytoplasmic and intranuclear), syncytial giant cell formation, and production of a reticular pattern in the outgrowth. Astrocytes subsequently became affected in the inner outgrowth and explant. Cellular degeneration was common, but a high degree of apparent coexistence of virus (inclusion bodies) and cells was a characteristic feature.Neuronal degeneration followed either a lack of myelin development or demyelination in infected cultures. Three to four weeks post-inoculation, infected cultures had few or no large neurons (Purkinje cells or neurons of the cerebellar nuclei), whereas these cells were numerous in the controls. Smaller neurons (granule and stellate cells) also became degenerated (three weeks post-inoculation) and frequently contained intranuclear inclusions following staining and/or silver impregnation.Immunofluorescent studies established that cytoplasmic, as well as nuclear, inclusion material of astrocytes and mesenchymal cells contained viral antigen. The areas of antigen concentration were comparable in shape, size and time of occurrence with inclusions demonstrated in stained preparations. Intranuclear viral antigen was also occasionally detected in granule cells.Supported in part by Grants NBO3423 and CAO8502 from the National Institutes of Health.     

Mechanism of nerve destruction in tuberculoid-borderline leprosy. An electron-microscopic study

The ultrastructural changes in radial cutaneous nerve biopsies from 3 tuberculoid and 14 tuberculoid-borderline patients were studied. In tuberculoid leprosy the nerve parenchyma was almost entirely replaced by tuberculoid granuloma. In nerves from borderline-tuberculoid leprosy many axons showed segmental demyelination and Wallerian degeneration. The nerve tissue was gradually replaced by proliferating collagen fibrils and inflammatory granulomata. M. leprae were rare and when present they were found in phagolysosomes of Schwann cells and macrophages. Schwann cells were surrounded and occasionally infiltrated by lymphocytes and macrophages. It was suggested that “sensitized Schwann cells” were the target of a hypersensitivity reaction resulting in their degeneration or death which in turn produced segmental demyelination or Wallerian degeneration.     

CHRONOLOGICAL STUDY OF ULTRASTRUCTURAL CHANGES IN THE PERIPHERAL NERVES IN MAREK'S DISEASE

Chronological study of ultrastructural changes in the peripheral nerves in Marek's disease
A chronological study was made of the ultrastructural changes in peripheral nerves following inoculation of 1-day-old chicks with a neurogenic strain of Marek Disease virus. No virus particles were found in nerves. Cellular infiltration of nerves was detected as early as 5 days after inoculation and by 3 weeks some nerves contained proliferative lesions which possessed many of the ultrastructural features characteristic of normal, reactive lymphoid tissue. About 4 weeks after inoculation, coinciding with the onset of neurological signs, areas of widespread demyelination appeared within these lesions; lymphocytes and macrophages penetrated and destroyed the myelin sheath, but spared Schwann cells and most axons. Later oedematous, sparsely infiltrated B type lesions were observed, some of which contained demyelin-ated nerve fibres undergoing repair; these were therefore a stage in the regression of the proliferative lesions. Our observations do not favour the hypothesis that cellular infiltration of nerves in Marek's disease is the direct result of auto-sensiti-zation to normal myelin. They are consistent with the hypothesis that demyelination is a secondary feature and that the primary lesions are preferential sites for immune demyelination.     

Abnormalities of peripheral nerve in patients with human immunodeficiency virus infection

The purpose of this study was to assess systematically morphology of peripheral nerves from patients with human immunodeficiency virus infection (acquired immunodeficiency syndrome [AIDS] and AIDS-related complex) examined at autopsy. Sural nerve specimens were taken from 25 patients (mean age 44 years) and evaluated by routine procedures used in our laboratory. In 13 cases no detectable abnormality was seen. Twelve patients (48%) showed loss of myelinated fibers with disproportionately greater loss of large myelinated fibers. Three of these patients showed severe myelinated fiber loss; 2 had no documented symptoms and no other known predisposing factors for a peripheral neuropathy. Changes suggestive of wallerian degeneration were occasionally seen, as were epineurial and endoneurial inflammatory infiltrates. Segmental demyelination was not identified in any nerve examined. Electron microscopy revealed thickened basement membranes around small blood vessels, Schwann cells, and fibroblasts. Peripheral nerve abnormalities in patients with AIDS or ARC are frequent and their pathogenesis remains unclear.     

LONGTERM INFECTION OF CULTURED HAMSTER DORSAL ROOT GANGLIA WITH HALLÉ SSPE VIRUS

Longterm infection of cultured hamster dorsal root ganglia with Hallé SSPE virus The morphogenesis of Hallé SSPE virus in cultures of hamster dorsal root ganglia (DRG) over a period of 60 days was followed by light and electron microscopy and by immunoperoxidase techniques. The Hallé virus was originally isolated from the lymph node of a patient with SSPE, and had been passaged only in non-neural cell lines. In organotypic cultures of hamster DRG, all cells except the neurons became infected. Large intracytoplasmic and intranuclear inclusions were commonly found in fibroblasts, but never in Schwann cells. The latter cells rounded up and were lost from the culture by 20 days post-infection (PI). Cell-free virus was detected by 7 days PI, reached a maximum at 30–40 days PI, and even at 60 days PI, substantial amounts of virus were still recorded. Budding virus particles were seen throughout the course of the infection. The formation of syncytia was rare. The present results are compared with previous data on the growth of measles virus in hamster DRG, and the growth of measles and SSPE viruses in cultures of hamster cerebellum. It was concluded that among the available strains of SSPE and measles virus, the Hallé strain is unique in its failure to infect nerve cells.     

Detection of herpes simplex virus mRNA in latently infected trigeminal ganglion neurons by in situ hybridization

Latent infection of the trigeminal ganglion with herpes simplex virus type 2 (HSV-2) was studied in guinea pigs by in situ DNA hybridization. Frozen ganglion sections from animals killed during the period of latent virus infection were studied under nondenaturing conditions. Some sections were treated with deoxyribonuclease (DNase) or ribonuclease (RNase) before incubation with HSV DNA probes. HSV probes consisted of viral DNA nick translated and labeled in vitro with tritiated nucleotides. Bacteriophage lambda DNA, similarly prepared, was used as a control probe. The lambda probe was negative in all situations, including HSV-2-infected monolayer cells in cell culture. HSV-2 probes produced heavy label and, therefore, evidence of hybridization with HSV-2-infected monolayer cells. When HSV-2 probes were incubated with latently infected ganglion sections, hybridization was detected in 71% of guinea pigs and 46% of ganglia. Label was seen only in neurons, and in positive ganglia 0.3 to 5% of neurons were labeled. The amount of label was markedly decreased by pretreatment of ganglion sections with RNase but not DNase, indicating that the DNA probes hybridized to HSV messenger RNA in the latently infected ganglia.     

DEMYELINATION INDUCED IN MICE BY AVIRULENT SEMLIKI FOREST VIRUS. I. VIROLOGY AND EFFECTS ON OPTIC NERVE

Illavia S.J., Webb H.E. & Pathak S. (1982) Neuropathology and Applied Neurobiology 8, 35–42
Demyelination induced in mice by avirulent Semliki Forest virus. I. Virology and effects on optic nerve
wiss A₂G mice were infected intraperitoneally with an avirulent strain of Semliki Forest virus. The virus titres in the optic nerves, retina and brain were estimated on post-inoculation days 3 to 8. High titres of virus were obtained in the optic nerve, retina and brain. The optic nerves, retina and brain were studied by light microscopy up to post-inoculation day 67. Electron microscope studies were carried out on the optic nerve on post-inoculation days 11 and 14. Inflammatory, microcystic changes and demyelination seen in the optic nerve were similar to those found in the central nervous system.     

Peripheral nervous system demyelination with herpes simplex virus

Inoculation of the cornea or footpad with herpes simplex virus Type I (HSV) has been shown to produce subsequent encephalitis or myelitis respectively. Although Schwann cells become infected, there is no destruction or demyelination in the peripheral nervous system (PNS). Demyelination only occurs in the central nervous system. Previous studies have shown that the Schwann cells infected with HSV do not produce enveloped viral particles. The studies presented here demonstrate that microinjection of HSV into the sciatic nerve of mice causes focal mononuclear cell infiltration and demyelination seven days after injection. The Schwann cells in this model produced enveloped virus. These studies demonstrate that when HSV is introduced into the extracellular space of the PNS, demyelination occurs.     

Peripheral nerve involvement in Werdnig-Hoffmann disease

The number of large myelinated axons was markedly decreased in almost all the intramuscular nerve bundles included in 32 muscle biopsies from patients with Werdnig-Hoffmann disease compared to that in normals. The morphometric analysis of peripheral nerves in 5 epon-embedded sections also showed a selective loss of larger myelinated fibers. The ultrastructural findings of the nerves were similar to those seen in Wallerian degeneration including axonal degeneration, myelin breakdown with phagocytosis, Schwann cell proliferation forming Schwann cell columns, axonal sprouting and probable remyelination. The earlier and more striking peripheral nerve involvement than that previously believed was not different from that seen in amyotrophic lateral sclerosis (ALS). The earlier damage to the peripheral nerves probably resulted from a degeneration of the anterior horn cells or anterior spinal roots as in ALS rather than from a dying-back process.     

Schwann cell-derived CXCL1 contributes to human immunodeficiency virus type 1 gp120-induced neuropathic pain by modulating macrophage infiltration in mice

The neuroinflammatory responses to human immunodeficiency virus type 1 (HIV-1) coat proteins, such as glycoprotein 120 (gp120), are considered to be responsible for the HIV-associated distal sensory neuropathy. Accumulating evidences suggest that T-cell line tropic X4 gp120 increases macrophage infiltration into the peripheral nerves, and thereby induces neuroinflammation leading to pain. However, the mechanisms underlying X4 gp120-induced macrophage recruitment to the peripheral nervous systems remain unclear. Here, we demonstrated that perineural application of X4 gp120 from HIV-1 strains IIIB and MN elicited mechanical hypersensitivity and spontaneous pain-like behaviors in mice. Furthermore, flow cytometry and immunohistochemical studies revealed increased infiltration of bone marrow-derived macrophages into the parenchyma of sciatic nerves and dorsal root ganglia (DRG) 7 days after gp120 IIIB or MN application. Chemical deletion of circulating macrophages using clodronate liposomes markedly suppressed gp120 IIIB-induced pain-like behaviors. In in vitro cell infiltration analysis, RAW 264.7 cell (a murine macrophage cell line) was chemoattracted to conditioned medium from gp120 IIIB- or MN-treated cultured Schwann cells, but not to conditioned medium from these gp120-treated DRG neurons, suggesting possible involvement of Schwann cell-derived soluble factors in macrophage infiltration. We identified using a gene expression array that CXCL1, a chemoattractant of macrophages and neutrophils, was increased in gp120 IIIB-treated cultured Schwann cells. Similar to gp120 IIIB or MN, perineural application of recombinant CXCL1 elicited pain-like behaviors accompanied by macrophage infiltration to the peripheral nerves. Furthermore, the repeated injection of CXCR2 (receptor for CXCL1) antagonist or CXCL1 neutralizing antibody prevented both pain-like behaviors and macrophage infiltration in gp120 IIIB-treated mice. Thus, the present study newly defines that Schwann cell-derived CXCL1, secreted in response to X4 gp120 exposure, is responsible for macrophage infiltration into peripheral nerves, and is thereby associated with pain-like behaviors in mice. We propose herein that communication between Schwann cells and macrophages may play a prominent role in the induction of X4 HIV-1-associated pain.     

Experimental viral infections of the facial nerve and geniculate ganglion

Although the cause of Bell's palsy is in most cases unknown, a number of viral infections have been associated with the disease. To determine if human viruses could experimentally infect the facial nerve or ganglion, six different viruses were inoculated into newborn hamsters by intracerebral, intralabyrinthine, or intraperitoneal routes. The facial nerve within the temporal bone and the geniculate ganglion were studied by light and immunofluorescent microscopy for the presence of viral infection. Herpes simplex, rubeola, mumps, and reovirus infected the neurons in the geniculate ganglia, while vaccinia virus infected the stroma cells of the facial nerve and ganglia. Influenza virus did not infect either the nerve or ganglia. These studies indicate that several human viruses can experimentally infect the facial nerve and geniculate ganglia, lending support to the hypothesis that Bell's palsy is caused by a virus.     

Influence of laminin-2 on Schwann cell-axon interactions

The dy/dy mouse suffers from a form of muscular dystrophy caused by a substantial reduction in laminin alpha2-chain protein, a major component of both muscle and Schwann cell basal laminae. This article examines the effect of laminin alpha2 deficiency on Schwann cell-axon interactions both in vivo at varying intervals after nerve crush, and in vitro, in cocultures of neurons and Schwann cells. The morphological spectrum of aberrant Schwann cell-axon associations seen in uncrushed dy/dy sciatic nerves was recapitulated during regeneration: myelination of regenerating axons was delayed compared with the process in unaffected mice and the relatively few myelin sheaths which were formed in dy/dy distal nerve stumps were often uncompacted. In vitro, Schwann cells dissociated from adult dy/dy sciatic nerves predictably failed to express detectable laminin alpha2-chain and displayed an unusual multipolar morphology. Branching of neurites, in terms both of numbers of terminal branches and of complexity of branching, from dorsal root ganglia neurons grown on dy/dy Schwann cells, was significantly less extensive than that seen when neurons were cocultured with Schwann cells from unaffected littermates, but this effect was reversed by exogenous laminin-2. Our results lend strong support to the view that laminin-2 is essential for establishing and/or maintaining Schwann cell-axon interactions, in normal and in regenerating nerves.     

THE GROWTH OF TWO SSPE VIRUSES IN ORGANOTYPIC CULTURES OF HAMSTER DORSAL ROOT GANGLIA

Two isolates of subacute sclerosing panencephalitis virus (LEC and HallB) were used to infect organotypic cultures of hamster dorsal root ganglia. Virus replication was assessed using indirect immunofluorescence, histological staining, and virus production. Using these criteria, the LEC isolate did not infect the cultures, but the Hallé virus establihed a productive infection. Schwann cells appeared to be the initial site of infection from where virus spread to every cell in the culture by 11 days post-inoculation (p.i.), except the neurons and their associated satellite cells, both of which contained no antigen and appeared histologically to be the same as controls even at 15 days p.i. The results are discussed with reference to the growth of measles virus in hamster dorsal root ganglia and the usefulness of this system as a model for subacute sclerosing panencephalitis.     

Autonomic neuropathy in the streptozotocin diabetic rat

An ultrastructural study of the sympathetic ganglia, dorsal sympathetic chain, and Auerbach's plexus is described in the streptozotocin diabetic rat. The observations cover the first six weeks following induction of diabetes. Degenerative changes began to appear in the axonal plasma membranes and axoplasm of unmyelinated fibers at 24 hours and were widespread by two weeks. Axonal sprouting and regenerating axons began to appear and increase in number through the 6th week. Chromatolysis in ganglion cells in sympathetic ganglia became apparent by two weeks as did degenerative changes in axons of Auerbach's plexus. This somewhat later appearance of changes in ganglion cells and Auerbach's plexus suggested the primary changes occurred in the postganglionic fibers. The cycle of change from degeneration to regeneration in the areas examined suggests either a possible toxic effect of streptozotocin or a combination of metabolic disturbances as a cause of this neuropathy.