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.

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.

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).

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.

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]

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.

The function of perineuronal satellite oligodendrocytes: an immunohistochemical study

Perineuronal satellite oligodendrocytes in the mouse have been investigated immunocytochemically using antisera to myelin basic protein and myelin-associated glycoprotein. In the normal animal, during remyelination, and following trauma the staining characteristics of these cells resembled those of other grey and white matter oligodendrocytes. It is concluded that these cells are, in many respects, functionally similar to other oligodendrocytes.

Isolation and transplantation of oligodendrocyte precursor cells

Newborn DBA/1J mouse neopallium was disaggregated and grown in high cell densities in tissue culture. In culture, the oligodendrocyte cell precursors are recognized as small refractile cells which use astrocyte precursor cells as a substratum. Using metrizamide density gradients, the oligodendrocyte precursor cells were separated from the astroblasts after 7 days in culture and then transplanted into the cerebellums of neonatal mice. The differentiation of the cultured oligodendrocyte precursors was analyzed in the transplants by nuclear morphometry, light and electron microscopy and immunocytochemistry. Analysis of the experiments indicated that the oligodendrocyte precursor cells, initially grown in culture, differentiated and myelinated host neuronal processes after transplantation. Moreover, the ultrastructure of the transplanted oligodendrocytes resembled mature oligodendrocytes in situ.

Immunohistochemical study with an anti-myelin serum. A marker for all glial cells except 'dark' oligodendrocytes

The usefulness of an anti-myelin antiserum as a possible marker for glial cells and related structures was investigated using rat brain. As expected, the myelin fibers were heavily stained but the neuronal cells and their processes were unreactive. The oligodendrocytes, identified on electron microscopy, revealed labelling of only the light and medium types, but not the dark cells. These results indicate that the suggested morphological classification of oligodendrocytes may be based on varying amounts of myelin antigen synthesis. Astrocytes from all areas, Golgi epithelial cells, Bergmann fibers and some subependymal cells also reacted with this anti-myelin antiserum but the staining was abolished completely by preabsorption with kidney powder. In contrast, the myelin fibers and the light and medium oligodendrocytes could still be labelled. We conclude that this anti-myelin antiserum should prove useful in studies of oligodendrocytes in the central nervous system.

An in-vitro approach to the study of oligodendrocytes and their involvement in multiple sclerosis

Evidence is presented for and against the participation of oligodendrocytes in the etiology and pathogenesis of MS,. The structure and properties of these cells are described, and the merits of in-vitro studies to learn of the cells' involvement in MS are argued.

Identification of mitotic oligodendrocytes in semithin sections of the developing mouse corpus callosum and hippocampal commissure

Mitotic oligodendrocytes in all phases of mitosis and with processes attached to myelin sheaths were demonstrated in semithin sections of mouse corpus callosum and hippocampal commissure at 17 days postnatum. Mitotic oligodendrocytes make up to one fifth of the mitotic cells present. The majority (54%) of mitotic cells are pale staining glial cell precursors, while the remainder are probably dark glioblasts (23%) and microglial cells (4%). Mitotic oligodendrocytes with both light and medium staining cytoplasm were found in similar stages of mitosis. It is suggested that mitotic oligodendrocytes play only a small part in the large increase in oligodendrocyte number accompanying myelination.

Survival and differentiation of oligodendrocytes from neural tissue transplanted into new-born mouse brain

Fragments of new-born mouse central nervous system have been transplanted into new-born mice host brains, under conditions in which the myelin synthesized by the oligodendrocytes included in the graft, could be distinguished from the host myelin. The work demonstrates that transplanted oligodendrocytes survive in the host brain, migrate out of the graft and synthesize myelin. No sign of rejection was observed during the time of the experiment.

The oligodendroglial cell: biology and immunology and relationship to multiple sclerosis

Myelin is elaborated and maintained in the central nervous system by the oligodendrocyte. The interaction between the oligodendrocyte and the neuron which initiates myelin formation is of major importance, and modern immunological technology using monoclonal antibodies and the fluorescence activated cell sorter have provided the means by which purified homogeneous populations of oligodendrocytes and neurons can be studied in vitro. The oligodendrocyte appears to have limited capacity to divide in situ which may contribute to the vulnerability of such cells in disease states; however it has been found that under certain culture conditions oligodendrocytes can proliferate in vitro. Multiple sclerosis (MS) is associated with loss of oligodendrocytes within the lesions and the intractability of the disease compared to other demyelinating conditions, both experimental and clinical, suggests, that the oligodendrocyte is the primary target of this disease. The cause of oligodendrocyte destruction is as yet uncertain although an immunological response may be in part responsible. The possible mechanism of immune recognition and cytolysis are discussed with regard to the unique nature of the nervous system.

Peripheral nervous system of shiverer mutant mice: developmental change of myelin components and immunohistochemical demonstration of the absence of MBP and presence of P2 protein

Peripheral nerves of the shiverer mouse, which are characterized by the absence of major dense lines and myelin basic proteins in CNS myelin, were analyzed. From subcellular fractionation of sciatic nerves, it was found from the SDS-polyacrylamide gel electrophoresis that the Pl and Pr proteins equivalent to myelin basic protein of CNS and PM protein were missing in the shiverer in both P2A and P3A fractions in which PNS myelin is recovered. No extra bands were observed in any other fractions of the shiverer in place of the absence of the proteins. The activities of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) of P2A and P3A fractions were high, but that of the P3X fraction which floated over 0.32 M sucrose was the highest among the fractions examined in both the shiverer and the control. Developmental analysis of the protein profiles revealed that PO, Pl, Pr and PM proteins increased rapidly from the sixth day postnatally up to the twentieth day after birth in the control. No differences were observed between the shiverer and the control as for PO protein, but Pl, Pr and PM proteins were absent in the shiverer throughout the development. The CNPase activity of total homogenate of sciatic nerve fibers at birth in the control showed high activity comparable to that of the adult value, but there was no significant difference in activity between the control and the shiverer at any stage of development. Immunohistochemical reaction using peroxidase anti-peroxidase method showed that the myelin from the shiverer did not react with the MBP antiserum, while that of the control reacted positively. On the contrary, the myelin from both shiverer and the control reacted positively against P2 antibody.

The application of organotypic nerve cultures to problems in neurology with special reference to their potential use in research into neuromuscular diseases

In organotypic nerve cell cultures there is production of central and peripheral myelin as well as synapse formation and long-term survival (months) of neuronal cell types and their associated glia. These cultures can be viewed continuously by light microscopy and are amenable to both electron microscopy and electrophysiology. Organotypic cultures have been used in studies of myelin formation and of demyelination by "toxic" sera, in the search for a neurotoxic factor in motor neurone disease and in studies of neurotrophic viruses. They have also been used to demonstrate the effects of toxins such as cyanide, lead, various industrial chemicals and neurotransmitter analogues (such as kainic acid) on myelin, axons and neurones in culture. They are currently being used in conjunction with small bundles of teased adult mammalian muscle fibres. Such bundles, cultured alone, do not regenerate. However, in the presence of various foetal tissues (neuronal or non-neuronal), the muscle regenerates to form new myotubes. Only in the presence of foetal spinal cord neurones will these myotubes differentiate further to form cross-striated, contracting muscle fibres. If the spinal cord tissue is removed when contractions have just begun, the muscle fibres revert to undifferentiated myotubes.

Developmental changes of glial fibrillary acidic protein in cerebral white matter

Developmental changes were observed in the glial fibrillary acidic protein (GFAP)--positive glia of cerebral white matter (including myelination glia) in the frontal lobes of 38 normal cases. With age, GFAP-positive processes gradually became larger and their location shifted from preponderantly in the deep white matter to mostly in the superficial white matter. This shift in pattern of GFAP-positive glia may be related to the parallel changes in perinatal brains in the localization of leukomalacic lesions. However, the shift is a normal developmental phenomenon on which such lesions are superimposed.

[Micromorphology of the intraorganic nerves of the hand muscles in human fetuses of the 2d half of the prenatal development and in children up to 1 year of age]

The intraorganic nerves of the fetus hand muscles in the second half of the prenatal development (beginning from the 4.5th month of the intrauterine development) have a conductive part in the nerve system with certain signs of immaturity: weak branching of the neural trunks, abundant perineural cells, great amount of the intratrunkal plexuses, various forms of the neural fibre transversal section. By the time of birth, in the fetal neural trunclets fine fibres predominate, percent of the middle one increases. After birth, general architectonics of the intraorganic nerves remain the same. During the first year of life, the amount of the intramuscular nerves and their branchings increases, the neural fibres acquire a more regulated course, the intratruncal plexuses become less pronounced. In the neural faciculi, percent of the middle fibres increases essentially, the thick ones appear. By the first year of life, a considerable difference in the intratruncal structure of the intraorganic nerves in the eminence muscle of the thumb and the little finger becomes evident.

Increased proliferation of oligodendrocytes in the hypomyelinated mouse mutant-jimpy

Previous studies of the hypomyelinated mouse mutant jimpy have shown that the number of oligodendrocytes are reduced about 50%. To determine the cause of the cellular reduction, light and electron microscopy were combined with thymidine autoradiographic techniques. The number of neuroglial cells which incorporate radioactive thymidine in the mutants is increased severalfold over control values. Electron microscopic autoradiograms indicate the majority of the labeled cells are oligodendroblasts. However, the total number of glia in the white matter of jimpy and control animals is the same during development and even up to the time of the animal's death. The presence of mitotic cells suggest that the oligodendrocytes undergo division but the abundance of dying cells suggests that they die sometime afterwards. The results of the quantitative autoradiographic studies in combination with our other data strongly suggest that the immediate failure of these cells to form myelin sheaths is due to a shortened life span and/or continued cell proliferation.

Neuritogenic determinant of bovine P2 protein in peripheral nerve myelin

Experimental allergic neuritis (EAN) is an experimentally produced demyelinating disease of peripheral nervous system. Several peptides of bovine P2 protein were tested for neuritogenic activity in Lewis rats. The hexacosapeptide CiT4 (residues 53--78 of bovine P2 protein) showed the highest neuritogenic activity among the peptides tested. The nonapeptide (residues 70--78) and the tridecapeptide (residues 66--78) were synthesized using the liquid phase peptide synthesis technique. The tridecapeptide showed mild, but definite activity in inducing EAN in the rats, while the nonapeptide was inactive. The localization of the neuritogenic determinant of bovine P2 protein in Lewis rats is discussed.

The ultrastructure of sheath cells in developing rat vomeronasal nerve

Maturation of the vomeronasal nerve was studied in fetal, newborn and 3 months old rats. Early in development, each nerve consists of large numbers of bare axons with clusters of polygonal sheath cells lying at the periphery. The latter insinuate themselves between the axons which they segregate into bundles. The sheath cells and their processes which first delineate axon bundles from one another form a network in the interstices of which lie the emergent axon bundles. Each sheath cell is not confined to the sleeve around a single bundle. Its perikaryon and processes commonly contribute to the septa between several adjacent bundles. Eventually, each bundle comes to be surrounded by its own proper sheath which consists of processes of more than one Schwann cell. These developmental trends, of a progressive increase in the number both of axons per bundle and of Schwann cells associated with each bundle, are the reverse of those found in the PNS generally, where bundle size decreases and axon size increases with maturation. As individual bundles separate from one another, interfascicular collagen appears between them and each comes to be surrounded by a basal lamina. Separation is rarely complete, however; even at the mature stage, processes are exchanged between adjacent sheaths at one or more points on their circumferences. Schwann cell processes surrounding individual bundles become increasingly complex with maturation. Where adjoining processes meet, they commonly branch profusely and interdigitate intricately, forming stacks of closely apposed layered processes. In other areas, the branches are covered by basal lamina and bound intricate labyrinths which commonly extend deeply into the bundle and contain collagen fibrils.

[Fluorescence anisotropy and myelin structure. IV. An analysis of the effect of temperature changes on the membrane structure]

The temperature dependence of birefringence and fluorescent polarization of stained nerve fibers has been studied. Theoretical aspects of the determination of the orientation of chromophores from polarized emission experiments are aslo considered. The experiments with changing temperature permits a conclusion that the organization of polar groups of the membrane becomes random with the decline of temperature from 20 degrees to 0 degree C, while the order of organization of hydrophobic groups increases.

A marker for oligodendrocytes and its relation to myelinogenesis: an immunocytochemical study with experimental allergic encephalomyelitis serum and C.N.S. cultures

To investigate a possible marker for oligodendrocytes and its relation to myelinogenesis, experimental allergic encephalomyelitis (EAE) serum has been used to study C.N.S. cultures from the time of explantation to maturity at 26 days in vitro (DIV). Cultures of foetal mouse spinal cord were exposed for 1 h to heated (complement-inactivated), rabbit anti-bovine white matter (WM-EAE) or control serum, fixed and processed by an immunoperoxidase technique for demonstrating bound immunoglobulin (Ig) by light and electron microscopy. From 5 to 26 DIV, cells morphologically identical to oligodendrocytes displayed binding of Ig to the plasmalemma of the cell body and its processes. At 5 DIV, immunoreactive oligodendrocytes had a large nucleus and nucleolus, prominent Golgi apparatus, and microtubules but no filaments. Occasionally a centriole was present, suggesting an early stage of differentiation. In myelinated cultures (from 11-12 DIV onwards), reaction product was present on the oligodendroglial outer plasmalemma apposed to myelin and along the outer loop. Sometimes it extended into the external mesaxon, outer layer of myelin, inner mesaxon and periaxonal space. No other structures were reactive, and oligodendroglia did not bind control Ig. These findings indicate that WM-EAE serum can be used as a marker for oligodendrocytes in cultures from 5 DIV onwards. The findings that oligodendrocytes acquire the antigen(s) prior to myelination and that the antigen(s) is localized on the plasmalemma of the inner and outer loops of actively myelinating oligodendroglial processes suggest that the antigen(s) may have a role in oligodendrocyte maturation and myelinogenesis. The antigen(s) involved is not yet established, but it is probably not myelin basic protein. This marker should prove useful in studies of C.N.S. development and the demyelinating diseases.

Study of myelin purity in relation to axonal contaminants

Axonal remnants are considered a probable source of contamination of isolated myelin in view of the relatively tight axon-glial intercellular junction. Using the rabbit optic system to label specifically axonal components, we have found the levels of such contaminants to depend on the myelin isolation procedure, the tissue source, and the nature of the contaminant. A procedure employing repetitive treatments with EGTA was found to be highly effective in removing proline-labeled axonal proteins, the estimated upper limit of such contamination being approximately 0.6-1.2% of the myelin protein. The standard isolation procedure of Norton and Poduslo, supplemented with an additional discontinuous gradient step, proved equally effective in removing rapidly transported proteins from myelin isolated from the superior colliculus or lateral geniculate body. When the optic tract was the source, however, the EGTA procedure proved more effective in removing both rapidly and slowly transported proteins. Axonal gangliosides labeled with N-[3H] acetylmannosamine were efficiently removed by both procedures, adding support to the proposition that gangliosides detected in isolated myelin are intrinsic to that membrane.

Growth of nerve-cell body and myelinogenesis in mouse trigemnal ganglion and root: a combined cytofluorometric and morphometric study

Postnatal growth of mouse trigeminal ganglion cells and myelinogenesis in the central and peripheral portions of the trigeminal root were studied in animals aged 0-120 days. The trigeminal ganglion cells were dispersed into single cell suspensions. The growth of individual nerve cells was quantitated by measuring total protein content with a new cytofluorometric method based on o-phthaldialdehyde binding to cells fixed in a mixture of ethanol and acetic acid. White matter from the C.N.S. protrudes from the brainstem into the trigeminal root, comes into direct contact with the P.N.S. in a transitional region. C.N.S. and P.N.S. and myelinogenesis were studied in the same population of trigeminal sensory nerve fibres. Myelinogenesis was quantitated at the ultrastuctural level by morphometric techniques. A prominent peak in nerve cell body growth occurred between 3 and 6 days. Myelinogenesis in terms of established contacts between axons and their myelinating cells started at the same time in C.N.S. and P.N.S. and the transformation from nonmyelinated to promyelinated and myelinated fibres occurred concurrently in the central and peripheral parts of the trigeminal root. The growth of the myelin sheath, that is, the addition of myelin lamellae, was faster and more intense in P.N.S. than in C.N.S. This could reflect the fact that a Schwann cell myelinates only one internode, whereas an oligodendrocyte provides myelin for several internodes in different axons. These results support the concept of a common 'signal' for myelinogenesis in C.N.S. and P.N.S.

Chronological study of oligodendroglial alterations and myelination in quaking mice

Chronological morphological investigation was carried out in the spinal cord of quaking mice from day 3 to day 130. Numbers of myelinated fibres were far fewer in quaking mice at day 3 compared to controls. However, when the animals became older, myelination progressed and numbers of myelinated fibres increased although myelin sheaths remained far thinner than the size of axons. Many oligodendroglia during day 5 to 15 in quaking mice revealed prominent dilation and proliferation of smooth walled vesicles and cisterns but after 20 days, such changes were no longer observed. Tortuous bizarre oligodendroglial processes, aberrant myelination and myelin figures were very prominent around day 5--15, but such changes also gradually subsided. Density of glial cells during pre-myelination gliosis was similar in both quaking and control mice. However, glial cell population decreased far slower pace than controls when myelination progressed. Thus, glial cell density remained proportionally higher in quaking than controls although the density declined with age in both.

A morphological and biochemical study of myelinogenesis in fish brain

Myelinogenesis in different brain parts of trout was studied comparatively by means of histochemistry and biochemistry. A more detailed approach, including ultrastructural analysis, to characterize this important differentiation process, particularly in the optic tectum, revealed a good correlation between the structural development of myelinated axons and the lipid composition of membranes. The molar ratio of cholesterol to phospholipids and galactolipids proved to be most suitable for monitoring myelination in fish CNS.

Histology of the peripheral nerve trunks

The anatomic structure of the peripheral nerve trunks is briefly reviewed. The nerve fibers are divided into myelinated and non-myelinated fibers and in the limbs they are composed of motor, sensory, and sympathetic fibers. On functional grounds the fibers are considered either efferent or afferent. The general scheme of vascular supply to the nerve fibers is described.

Mitotic division of oligodendrocytes which have begun myelination

Examination of spinal cords of 5 days old mice showed a number of examples of oligodendrocytes, in various phases of mitosis, which remained in contact with the axons which they were myelinating. Cells in prophases had thick processes between the perikaryon and the myelinating axons but as mitosis proceeded the oligodendrocyte processes became thin and spider-like, probably due to the extrusion of cytoplasm from the processes into the perikaryon. Mitotic astrocytes were also present.

The use of networks of dissociated rat dorsal root ganglion neurons to induce myelination by oligodencrocytes in culture

A neuronal culture system has been developed that has the demonstrated ability to induce myelin formation by added oligodendrocytes. Networks of dissociated dorsal root ganglion neurons were prepared by suppressing non-neuronal cells (i.e. fibroblasts and Schwann cells) with a continuous 2 week exposure to 10(-5)M fluorodeoxyuridine in the culture medium. After drug withdrawal, neuroglial cells were introduced in optic nerve implants from 1-2 week-old rats. These added glial cells migrated extensively over the unensheathed neurites and central myelin was formed by 2 weeks after the implant addition.

On the mechanism of Verhoeff's elastica stain: a convenient stain for myelin sheaths

Verhoeff (1908) recommended an iron-hematein formula containing Lugol's solution for demonstration of elastic tissue; sections are differentiated until desired staining patterns are obtained. Verhoeff's stain colored a variety of tissue structures and showed higher substantivity for myelin sheaths than for elastin. Addition of HCL or omission of Lugol's solution decreased or abolished coloration of pseudo-elastica and thus enhanced selectivity for elastin. Substitution of Fe++ for Fe+++ abolished dye binding by elastin. A review of chemical data indicated interaction of components of Lugol's solution with the dye. Hematein and Fe+++ form a variety of cationic, anionic and non-ionic chelates; the ratio of these compounds changes with time. Dye binding apparently occurs mainly via van der Waals forces and hydrogen bonds. Verhoeff's elastica stain is definitely not specific for elastin and is inferior to orcein and resorcin-fuchsin because of the required differentiation with its inherent bias to produce patterns which conform to expectations. However, Verhoeff's elastica stain is far superior to other metal-hematein technics for myelin sheaths. The combined Verhoeff-picro-Sirius Red F3BA stain can be performed in 30 min and does not require differentiation. It is therefore suggested to reclassify Verhoeff's elastica stain as a method for myelin sheaths.

An autoradiographic study of cellular proliferation in remyelination of the central nervous system

The proliferation and origin remyelinating oligodendrocytes was studied by light and electron miscrosopic autoradiography in the superior cerebellar peduncles of mice demyelinated by Cuprizone. In the early phases of demyelination, the cells undergoing mitotic activity were macrophages and astrocytes. In the later phases of demyelination, immature proliferating oligodendrocytes appeared; these differentiated into mature (dark) oligodendrocytes which were responsible for the remyelination of axons seen when animals were again placed on normal diets. The pattern of differentiation recapitulated that seen in developing oligodendrocytes in normal animals. Dark oligodendrocytes did not show mitotic activity. There was no mitotic activity in the subependymal cells around the fourth ventricle adjacent to the superior cerebellar peduncles. This study demonstrates the regenerative capacity of oligodendrocytes and their ability to carry out remeylination in the central nervous system.

Histochemical study of the myelin-associated carbohydrates

Myelin-associated carbohydrates were studied by means of histochemical techniques in the central nervous system of birds and mammals. Polianions in the surface of myelin and in interfascicular oligodendroglia were detected using histochemical techniques. Glycoproteins were studied by means of concanavalin A. The Con-A-PO-DAB sequence was used. Concanavalin-A-binding sites were detected in oligodendroglia and on the myelin surface. Similar results were observed in both birds and mammals. The processes of the interfascicular oligodendroglia also contain carbohydrates. A close association between the carbohydrates of these glial processes and the myelin surface carbohydrates was demonstrated, and their probable identity is assumed.

Disorganization of myelinogenesis in tissue culture by anti-CNS antiserum

The presence of decomplemented anti-CNS antiserum profoundly affects myelinogenesis in cultured mouse embryo spinal cord. Light and electron microscope study has shown that oligodendroglia differentiate and produce an abundance of cell processes which surround the oligodendrocytes in a chaotic, disorganized array. Where the cell processes chance to meet, they form a kind of aberrant swollen myelin. Rarely, the oligodendroglial processes ensheath axons. For the most part, the available axons remain unmyelinated. On removal of the decomplemented antiserum, oligodendroglia differentiate and form normal myelin around the available axons. Myelination of peripheral nervous system (dorsal root ganglion) axons in the same preparations is unaffected by the presence of the antiserum. Thus, under these circumstances, the message from the neuron to the oligodendrocyte to make myelin is apparently intact, yet there is interference with the ability of the oligodendroglial cell process to find, attach to and encircle CNS axons with a normal myelin sheath.