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.