The origin of remyelinating oligodendrocytes in antiserum-mediated demyelinative optic neuropathy.

The origin of the remyelinating oligodendrocyte in a focal antigalactocerebroside-induced demyelinating lesion of the cat optic nerve was studied with detailed correlative electron microscopy and immunocytochemistry using a panel of antigenic markers. Within 10 days of the destruction of all endogenous oligodendrocytes and demyelination of all axons in the lesion, a new population of small glial cells appeared coincident with division of the residual astrocytes and developed a process-bearing axon-embracing morphology. The processes of these small glial cells (SGCs) contained intermediate filaments composed not of glial fibrillary acidic protein but of vimentin and over the ensuing 14 days these cells confirmed their oligodendrocyte destiny by differentiating to lose the intermediate filaments, form myelin and acquire the acquire the typical oligodendrocyte antigenic phenotype. It is suggested that the extensive remyelination of this lesion is sponsored by the new population of SGCs which in turn are generated either by dedifferentiated reactive astrocytes or by as yet unidentified precursor cells.

Defective ensheathment of motoric nerves in the Splotch mutant mouse.

Mouse embryos, homozygous for mutations at the Splotch locus, are afflicted with spina bifida and disturbances of neural-crest-derived tissues, e.g. spinal ganglia and pigment cells. The development of Schwann cells is affected in homozygotes to a varying degree along the rostrocaudal axis. In cervical motoric roots, nerves are associated with apparently normal Schwann cells. At the thoracic level, nerve-associated cells become more scarce and resemble the surrounding mesenchymal cells. They are not enveloped by a basal lamina and frequently show wide gaps between neighbouring cells. Lumbar motoric roots are mostly devoid of any associated cells. The Splotch mutant embryo is proposed to be a new animal model for the study of peripheral nerve ensheathment. The implications for Schwann-cell-mediated axon guidance are discussed.

Differentiation-regulated loss of the polysialylated embryonic form and expression of the different polypeptides of the neural cell adhesion molecule by cultured oligodendrocytes and myelin.

The expression of the neural cell adhesion molecule (N-CAM) on cultured murine oligodendrocytes, their precursors, and myelin was examined by indirect immunofluorescence, biosynthetic radiolabeling followed by immunoprecipitation and Western blot analysis, using antibodies specific for various forms of the molecule. In all culture systems studied, whether the oligodendrocytes were cultured as an enriched fraction containing precursor cells or in the presence of astrocytes and neurons, a similar differentiation-stage-related expression of N-CAM was seen. At early developmental stages many tetanus toxin receptor- and A2B5 antigen-positive putative oligodendrocyte precursors with bipolar morphology were seen and found to express N-CAM in its embryonic form. Of the 04 antigen-positive immature oligodendrocytes with few slender processes most expressed N-CAM, but few the embryonic form of N-CAM. The more mature 01 or 010 antigen-positive oligodendrocytes were found to express exclusively the adult form of N-CAM. Oligodendrocytes synthesized the 120 and 140 kD forms of N-CAM (N-CAM 120 and N-CAM 140), but not N-CAM 180, although with differentiation, N-CAM 120 predominated in oligodendrocytes and also in pure myelin. N-CAM 120 could be released from oligodendrocytes and myelin by phosphatidylinositol-specific phospholipase C, suggesting that in both oligodendrocytes and myelin N-CAM 120 is inserted into the membrane by covalent linkage to phosphatidylinositol.

The lateral giant fibers of the tubificid worm, Branchiura sowerbyi: structural and functional asymmetry in a paired interneuronal system.

Neuroanatomical and ultrastructural studies of the paired lateral giant nerve fibers (LGFs) in posterior segments of the tubificid worm, Branchiura sowerbyi, demonstrate that the fibers are 1) segmental in origin (two cell bodies per segment), 2) joined longitudinally and transversely to form an intersegmental syncytial network, and 3) surrounded by a myelinlike sheath. The LGFs are unique among paired giant fiber systems because of their extreme asymmetry, the diameter of the left fiber being several times greater than that of the right. Electrophysiological studies demonstrate that the small, right fiber has a high input resistance and, during mechanosensory stimulation, functions as the locus for LGF spike initiation. The larger, left fiber contributes by enhancing the speed of LGF spike conduction along the animal. One physiological benefit of this asymmetric arrangement may be optimization of escape reflex sensitivity to mechanosensory inputs.

Can oligodendrocytes attached to myelin proliferate?

The uptake of thymidine by oligodendrocytes in the brains of adult mice was examined after the induction of cortical traumatic lesions in an attempt to determine whether mature oligodendrocytes actively attached to myelin sheaths were capable of proliferating. In view of the great difficulty in visualizing the connection between a given oligodendrocyte and a myelin sheath even in the normal adult animal, the neuropil was made edematous in the traumatized animals in order to separate out the components and to study the oligodendrocyte processes. Uptake of tritiated thymidine was found in oligodendrocytes, as well as in endothelial cells, astrocytes, and microglia. The percentage of labeled oligodendrocytes appeared low in relation to the total number of the oligodendrocytes. In addition, in a few labeled cells, cytoplasmic processes could be seen extending to and apparently forming the myelin sheath. The possibility that a differentiated cell still attached to myelin may at the same time be able to proliferate is of great significance in understanding the potential for remyelination and recovery, in the adult, because it would imply that any oligodendrocyte is a candidate for proliferation, rather than only uncommitted or immature glial cells, which may be limited in the mature brain.

[Silver impregnation of the myelin sheath. II]. / Silberimprägnation der Markscheiden. II.

A modified method is described based on the following steps: 1. simultaneous mordanting, using an alcoholic solution of phosphotungstic acid and tannic acid, 2. treatment with pH = 10.4 silver nitrate solution, 3. physical development (one or two phases).

Leu-7 immunoreactivity in human, monkey, and pig bronchopulmonary neuroepithelial bodies and neuroendocrine cells.

Anti-Leu 7 is a monoclonal antibody recognizing a surface antigen on human natural killer cells. By applying the indirect immunoperoxidase method, we demonstrated Leu-7 immunoreactivity in the cytoplasm of neuroepithelial bodies (NEB) and neuroendocrine cells (NEC) of human, monkey, and pig respiratory mucosa. In addition, the anti-Leu-7 monoclonal antibody stained the myelin sheaths of nerve fibers in all tissues investigated. Our findings support the hypothesis that shared antigens exist between the nervous, endocrine, and immune systems.

Specific asparagine-linked oligosaccharides are not required for certain neuron-neuron and neuron-Schwann cell interactions.

To determine whether specific asparagine-linked (N-linked) oligosaccharides present in cell surface glycoproteins are required for cell-cell interactions within the peripheral nervous system, we have used castanospermine to inhibit maturation of N-linked sugars in cell cultures of neurons or neurons plus Schwann cells. Maximally 10-15% of the N-linked oligosaccharides on neuronal proteins have normal structure when cells are cultured in the presence of 250 micrograms/ml castanospermine; the remaining oligosaccharides are present as immature carbohydrate chains not normally found in these glycoproteins. Although cultures were treated for 2 wk with castanospermine, cells always remained viable and appeared healthy. We have analyzed several biological responses of embryonic dorsal root ganglion neurons, with or without added purified populations of Schwann cells, in the presence of castanospermine. We have observed that a normal complement of mature, N-linked sugars are not required for neurite outgrowth, neuron-Schwann cell adhesion, neuron-induced Schwann cell proliferation, or ensheathment of neurites by Schwann cells. Treatment of neuronal cultures with castanospermine increases the propensity of neurites to fasciculate. Extracellular matrix deposition by Schwann cells and myelination of neurons by Schwann cells are greatly diminished in the presence of castanospermine as assayed by electron microscopy and immunocytochemistry, suggesting that specific N-linked oligosaccharides are required for the expression of these cellular functions.

Central pontine myelinolysis. A case report with typical neuropathological findings.

A case of central pontine myelinolysis (CPM) in an alcoholic patient with severe electrolyte changes is presented. Data in the literature suggest that it is safe to correct severe symptomatic hyponatremia to a value of 125-130 mEq/1 in 24 h. At the present time acute severe hyponatremia carries a bad prognosis if not treated with hypertonic NaCl solution. Electrolyte abnormalities are not the sole cause of CPM.

Intermediate glial cells and reactive astrocytes revisited. A study in organotypic tissue culture.

The existence of cells sharing features of oligodendrocytes and astrocytes has been repeatedly proposed. We have studied this problem ultrastructurally in organotypic tissue culture together with light-microscopic immunocytochemistry for the astrocyte marker glial fibrillary acidic protein (GFAP) and for 2 oligodendrocyte markers, myelin basic protein (MBP) and myelin-associated glycoprotein (MAG). Large numbers of GFAP+ cells (astrocytes) were seen, invariably giving rise to a wealth of tapering processes. In contrast, oligodendrocytes were found far less frequently either immunocytochemically or ultrastructurally, and showed smooth contours and scarcity of processes. Ultrastructurally, the cells corresponding to the intermediate glial cells in the literature which were far more numerous in culture than MBP-stained cells, were identified as reactive astrocytes by their numbers, location and morphological similarity with the GFAP-stained cells. Other characteristics were the presence of bundles of intermediate filaments and the covering of the plasmalemma adjacent to the collagen substrate by a basal lamina, in spite of the content of microtubules and the density of the cells. It was possible to demonstrate the difference between the wrapping of axons by astrocytic digitiform processes, and true myelination by processes identifiable as oligodendrocytes. We conclude that in this model the astrocytic and oligodendrocytic cell lines appear separate from the time of initial differentiation; in other systems such as dissociated cell culture, this may not be so. The cells with 'intermediate' features are in fact a reactive form of astrocyte.

Lack of excitability in the internodal membrane of myelinated nerve fiber in frog.

Monophasic action potentials of about 70 and 10 mV were recorded by inserting a microelectrode into the axon and the myelin sheath of an intact myelinated fiber, respectively. When the intra-axonal or the intra-myelinic microelectrode was used for both stimulation and recording, only the anodal current was effective in inducing action potentials. The inter-nodal membrane was, therefore, intrinsically inexitable.

Relapsing experimental allergic encephalomyelitis. An autoimmune model of multiple sclerosis.

R-EAE is a valuable model for human MS. Table 2 outlines the similarities between R-EAE and MS. The clinical course and pathologic changes seen in this model accurately reflect the pattern of MS. The immunologic changes seen in animals with R-EAE also are similar to those seen in MS. Therefore, the clinicopathologic features of MS can be duplicated with a purely autoimmune model. Although this is of considerable pathogenic significance in understanding MS, we do not know what the inciting event is in MS that would be the equivalent of immunizing an animal with neural antigen. Despite this, R-EAE has and should continue to provide experimental data of considerable importance to an understanding of the mechanisms involved in the evolution of inflammatory demyelination. Other important models of MS utilize viral-induced demyelination. Although the clinical picture of most of the chronic demyelinating viral infections does not show as clear a relapsing or remitting pattern as seen in R-EAE, viral etiologies better fit the epidemiology of MS [16]. Several studies have demonstrated development of an acute EAE-like disease with sensitization to neural antigens following viral infection [12, 30, 56]. Thus, one can hypothesize an initial viral illness causing sensitization of the host to a neural antigen (?MBP) with a subsequent immunopathogenic course similar to that seen in R-EAE. Whether this will in fact be the case remains unproven as yet. Our understanding of the immunopathogenic mechanisms underlying inflammatory demyelination has been enlarged through studies of R-EAE. It is now clear that the minimal myelin antigen necessary for production of the disease is MBP, although this may differ in some species. The relapsing nature of this disorder is mediated in part through lymphocytes, as demonstrated in transfer studies, and thus does not require persistent antigenic depots. There is a genetic susceptibility to development of the CNS autoimmune state, and we speculate that an as yet unidentified perturbation of the host immune system allows for the occurrence of relapsing disease (Table 3).

Mature oligodendrocytes. Division following experimental demyelination in adult animals.

Primary demyelination can be caused by injury to oligodendrocytes or to the myelin sheaths that these cells maintain. Although remyelination does take place in multiple sclerosis (MS), its possible role in the recovery from MS attacks has been inadequately considered, partly because of the belief that oligodendrocytes, once destroyed, cannot be replaced in the adult. The injection of lysolecithin into the mouse spinal cord causes primary demyelination, followed by the generation of new oligodendrocytes and remyelination. By using a pulse label of tritiated thymidine, this electron-microscopic autoradiographic study demonstrated a source of these regenerated oligodendrocytes. The replacement of oligodendrocytes can occur through the division of preexisting oligodendrocytes. This is the first demonstration that mature oligodendrocytes are capable of dividing in older animals. These results lend support to recent observations of an apparent proliferation of these cells in an active MS lesion. We believe that the ability of mature oligodendrocytes to divide and to remyelinate axons in the adult may play an important role in the recovery from MS attacks.

[Structural changes in the myelin sheath membranes detectable by using the nonpolar probe perylene. A fluorescence polarization study]. / Strukturnye izmeneniia membran mielinovoi obolochki, vyiavlieamye s pomoshch'iu nepoliarnogo zonda perilena. Poliarizatsionno-fliuorestsentnoe issledovanie.

Perylene as a fluorescent probe has been used to investigate membranes of the myelin sheath of surviving nerve fibres. Fluorescence polarization (P) of perylene was measured in stained nerve fibres, and their dependence on the angle (AD) between the geometrical axis of the fibre and electrical vector of exciting light was studied. The dependence of AD on the temperature showed that P (90 degrees) decreased gradually when the temperature increased at heating within the range of 0-32 degrees. A model of the prove movement in the lipid matrix is described. This model considers the rotation around the axis perpendicular to the plane of the perylene molecule only. Comparison of the results of model calculations and the experimental data allows to estimate the value of energy of viscosity activation. It proved to be 20-25 kcal/mol. Possible causes of such a high value of the kinetic barrier are discussed.