Vesicular disruption of myelin in autoimmune demyelination

A pattern of autoimmune demyelination in EAE and EAN has been described which was encountered consistently and was sometimes more common than the better known phenomenon of active stripping of myelin by macrophages. This pattern involved the rapid dissolution of myelin into a vesicular network which was later degraded by macrophages. It occurred early in the disease, was not accentuated perivascularly, and was usually associated with the presence of macrophases. The underlying mechanisms are not known but several alternatives have been discussed, viz., activity of locally released antibody, cytotoxic factors, or hydrolytic enzymes.

Ultrastructure of nerve plexus in flatworms. II. Sites of synaptic interactions

Synaptic components from the peripheral nervous system of the polyclad flatworm. Notoplana acticola, are described from electron microscopic observations. Quasi-neuropile, defined as clusters of neurites containing synaptic vesicles, occurs as scattered islands among the peripheral nerve cords of the plexus. Some neurite clusters only contain one type of synaptic vesicle but others are mixed. The most usual synaptic configuration consists of a single presynaptic element and a pair of postsynaptic neurites sharing a common synaptic cleft. These synapses are polarized and contain clear, 420 A vesicles. GABA-type synapses are also found. At least two kinds of solid-core vesicles also occur.

Recurrent experimental allergic neuritis. An electron microscope study

Experimental allergic neuritis has been induced in 52 guinea pigs by the inoculation of rabbit peripheral nerve in Freund's adjuvant. The majority of the animals developed an acute monophasic illness after a mean interval of 16 days and, if they survived, recovered fully after an average period of 52 days. Two animals displayed a more chronic course and 1 animal relapsed spontaneously after clinical recovery had occurred. Twenty-three animals that recovered were re-inoculated when recovery was complete and in 4 a relapse was induced. In the remainder, no clinical response was observed, even after repeated reinoculations. The ultrastructural appearances in the animals with a monophasic illness were similar to those previously reported. The appearances differed markedly in those animals that were induced to relapse and were similar to those in the animal that relapsed spontaneously. The findings indicated persistent demyelination and remyelination with striking hypertrophic changes (onion bulb neuropathy). The possible reasons for the differences between the two groups are discussed.

Axon-glia relationships in crab nerves

The nerves of the walking legs in the crab Lebidoclea grammania were studied by electron microscopy. Particular atthetion was directed to the structure of the connective tissue, its arrangement within the axon sheaths and its association with the glial cells. The connective tissue of the neural lamella of the giant axons and the fascicles is formed by collagen fibrils aand bands of mucopolysaccharides. Prolongations of the neural lamella divide the fascicles into bundles of contiguous axons, groups of loosely sheathed axons and nerve fibres wrapped by layers of glial cell processes alternating with layers of connective tissue. The glial cell processes close to the axons contained numerous microtubules whereas glycogen granules predominated in the more peripheral processes. These observations suggest that the connective tissue and glial cell processes forming the envelopes of the axons together participate in the maintenance of the microenvironment around axons.

Degeneration of sensory and motor axons in transplanted segments of a crustacean peripheral nerve

Segments of sensory and motor axons 0.3-0.5 mm in length were taken from crayfish peripheral limb nerves and transplanted into the abdominal cavity of the same animal. Transplanted sensory axons showed relatively few ultra-structural changes after one week, many had undergone complete lysis within two weeks, and almost all degenerated within three weeks. Transplanted motor axons appeared normal after one week, except for some hypertrophy of their surrounding glial sheaths. After two weeks, glial sheaths were grossly hypertrophied around motor axons; axonal mitochondria had increased in number and many had migrated from the periphery to the centre of the axon. The axonal membranes of all motor axons were still intact after three weeks, although most were no longer continuous after four weeks. By five weeks, all axonal material had completely disintegrated. These data suggest that axonal synthetic processes in crayfish sensory (and presumably motor) axons can maintain the axons relatively intact for 7-14 days and that transfer of substances form hypertrophied glial cells to motor axons may account for the longer survival times of transplanted motor axons.

The organization of the nervous system in the crayfish Procambarus clarkii, with emphasis on the blood-brain interface

Central neural connectives and peripheral nerves of the crayfish Procambarus clarkii are surrounded by an acellular neural lamella, beneath which lies a layer of specialised glia, the perineurium. Cell process of the connective perineurium interdigitate extensively, and are frequently closely associated with each other by gap junctions. Occasional zonulae occludentes are encountered. Nerve perineurium, however, is much less elaborate, and may be reduced to a single or incomplete cell layer. In both connective and nerve, the perineurium appears involved in the formation of the collagen-like fibrils of the neural lamella. The comparative fine structure of connective and peripheral nerve correlates well with recent experimental studies in crayfish, where it was concluded that the perineurium in connective but not nerve offers some restriction to diffusion of small ions and molecules. Within the connective, deeper glia re either closely associated with axons (Schwann cells) or lie relatively free in the extracellular space. Cytoplasmic process of both cell types possess "tubular lattice" systems, which are especially elaborate in the Schwann cells. The extracellular space contains a flocculent material and bundles of collagen, together with layers of basal lamina-like material. The physiological implications of the observations are discussed.

Electron microscopy of trypsin-digested peripheral nerve myelin

Sciatic nerves from mice were removed and soaked in either PBS (phosphate buffered saline) or PBS plus I% trypsin (Sigma Type III) for various periods of time. Specimens were soaked at either room temperature or 37-degrees C at pH's ranging from 7.5 to 8.0. The epineural and perineural sheaths were split to allow the trypsin to penetrate the nerve. Tissue was prepared for electron microscopy by fixation in cacodylate buffered formaldehyde-glutaraldehyde solutions, post-fixed in OSO4 and embedded in Epon 812 or in glutaraldehyde-urea resin without osmication. After four h incubation at 37-degrees C or eight h at room temperature, the basement membranes of the Schwann cells became fragmented and detached and the myelin intraperiod band lost some density. After 18 h, myelin with swollen intraperiod bands displaying a loss of electron density and split main period bands was noted adjacent to normal myelin. Other areas had been transformed into vesicles indicating that the membranes of these vesicles appeared to have been derived from the detachment of both the intraperiod and main period bands within the myelin. Evidence is presented for the presence of trypsin digestable proteins in both the main period and intraperiod bands of peripheral nervouse system myelin.

Polyglycolic acid suture in peripheral nerve: an electron microscopic study

The aim of this experiment was to investigate the reaction of peripheral nerve tissue to a synthetic absorbable suture material. Polyglycolic acid suture material was investigated by means of electron photomicrographs. It was concluded that placement of polyglycolic acid into the peculiar environment of endoneurial tissues results in minimal scarring and in minimal disturbance of the surrounding nerve fibers. The material was progressively absorbed with minimal disturbance of intrafascicular structures.

[Pathology of peripheral nerves (elementary lesions, their development and different types of neuropathies) (1st part)]

The ultrastructural features of the normal components of the endoneurium are described. The sequence of events of axonal (wallerian) and segmental demyelination are enumerated. The process of ageing in the peripheral nervous system is analysed.

Ultrastructural aspects of muscle and nerve in Werdnig-Hoffmann disease

The authors describe in biopsies from 6 cases of Werdnig-Hoffmann disease, including 2 of the more benign type, the ultrastructural typical aspects of denervation. They compare their findings with those of other workers. The striking points are the great variation in the diameter of the muscle fibres and the myofibrils, the disorganisation of the myofibrils, the sarcomeres and the filaments, with persistance of the relations between thick and thin filaments at various levels, the modifications of the Z-band and the triads in chains. The folds and the basement membrane are examined. Centrioles are present in a muscle fibre and in a satellite. Glycogen is very abundant. The nerves seem normal but some Schwann cells contain pi granules which are not observed usually at the age of the patient. The end plates and a muscle spindle are normal.

Nerves and nerve endings in pigmented nevi. Part I

Electron microscopic investigations revealed numerous unmyelinated nerve fibres in different types of pigmented nevi. The structure of these fibres was similar to the cutaneous unmyelinated fibres. Axon terminals were observed between nevus cells and smooth muscle cells, the former proved to be efferent-type free endings. Pure receptor-type endings were rarely seen. The contradiction between the receptor-like construction ov nevic corpuscles and the abundance of the effector-type endings is discussed.

Ultrastructural abnormalities in the skin nerves of a patient with scleredema adultorum (Buschke) and diabetes mellitus

In an electron-microscopic study of the skin of a patient with scleredema adultorum (Buschke) and diabetes mellitus, the unmyelinated nerve fibres showed accumulations of glycogen. On morphological grounds, these accumulations appeared to be located in the axons.

Effect of zinc ions on structure and distribution of neurotubules (author's transl)

Being interested in factors stabilizing neurotubules (NTs) in situ, we decided to immerse short segments of fresh rat peripheral nerves in buffered solutions containing ZnCl2 in final concentrations up to 10-2 m prior to fixation with buffered osmium or glutaraldehyde, both containing ZnCl2. Zinc treatment resulted in a remarkable structural preservation of NTs after fixation with osmium, though they are not preserved by osmium fixation alone. Cross sections of myelinated nerve fibres show NTs arranged predominantly in compact groups. Within the groups NTs are surrounded or embedded in an electron dense fine granular material. The occurrence of incomplete C-shaped NTs and NT-like densities can be seen. NTs exhibit relatively constant distances and sometimes geometric patterns of arrangement. A lot of intertubule cross bridges and NTs with arms could be observed. In longitudinal section the bridge and arm spacing is seen to be periodic along the tubule axis at about 500 A. Zinc treatment of nerves fixed in glutaraldehyde resulted in the same ultrastructural alterations described above. The resistance of zinc-stabilized NTs to degradation by osmium and the ultrastructural changes induced by zinc are discussed. The results suggest that in the presence of zinc ions osmium-labile NTs are transformed--by disassembly and reassembly--to osmium-stabile microtubules that are not identical with preexisting ones.

[Globoid cell leucodystrophy (Krabbe's disease). Peripheral nerve lesion (author's transl)]

Morphological study of peripheral nerves in two patients with globoid cell leucodystrophy (Krabbe's disease) demonstrates: 1degree segmentary demyelination; 2degrees marked loss of large (8-10 micra) myelinated fibres; 3degrees significant increase of the mean transverse fascicular area by proliferating collagen fibres; 4degrees electron-microscopic signs of remyelination with small onion-bulb formations. These findings can explain clinical features such as the disappearance of the deep tendon reflexes, the gradual transition of hypertonia into combined hypertonia-hypotonia and the concomitant slowing of nerve conduction velocity. The ultrastructural study reveals the presence of large and small inclusions which are either located within lysosomes or free in the cytoplasm of Schwann cells and fibroblasts. The inclusions are probably consequences of the disturbed metabolism of cerebrosides. Their appearance is sufficiently specific in order to allow a diagnosis of Krabbe's disease.

Early street rabies virus infection in striated muscle and later progression to the central nervous system

Twelve isolates of street rabies virus were inoculated intramuscularly into young hamsters and the course of infection was followed by frozen section immunofluorescence. Animals infected with 10 of the 12 viruses had antigen in striated muscle at day 3, but involvement of other tissues was absent or extremely sparse. Muscle infection was still most pronounced at day 6, but neuromuscular spindle, nerve, and brain infections were also detected in a majority of animals. Progression of infection was continuous, with striking terminal accumulations of antigen. The early myotropism of rabies virus may yield the virus which invades the peripheral nervous system, and may represent a phase of infection vulnerable to postexposure intervention.

Mast cell invasion of peripheral nerve in skin lesions of atopic dermatitis

To ascertain whether or not a spatial relationship between mast cells and peripheral nerves is present in skin lesions of atopic dermatitis, 10 biopsy specimens of the skin lesions were examined with both semi-thin and ultrathin serial sections. Mast cell invasion of peripheral nerves was observed in 9 out of the 10 biopsy specimens (4 subacute lesions, 3 lichenified lesions, and 3 prurigo lesions). The mast cells within peripheral nerves often showed degranulation, and the nerve fiber bundle showed conspicuous edema. The degranulation of mast cells within peripheral nerve bundles and edema of the nerve bundle may pay a role in provoking or aggravating itchiness of atopic dermatitis.