The differentiation of oligodendrocytes in the rat optic nerve

Phagocytosis of degenerating myelin in transected feline optic nerve: an immunohistochemical study

The phagocytic activity of neuroglial cells in adult feline degenerating optic nerve was investigated by immunocytochemistry at both light and electron microscopy levels. Degeneration was initiated by unilateral eye enucleation and the segment distal to the transection showing true Wallerian degeneration was examined. Following enucleation, twelve adult domestic cats were examined over a period of seven to 215 days. All cases showed slow clearance of myelin debris and absence of proliferating monocytes throughout the post-enucleation period. All phagocytic cells present were neuroglial cells, and many of these cells expressed oligodendroglial antigens. These findings demonstrate the persistence of an active population of oligodendrocytes that might play an additional functional role during Wallerian degeneration of feline optic nerve.

Role of myelination in the development of a uniform olivocerebellar conduction time

Purkinje cells generate simultaneous complex spikes as a result of olivocerebellar activity. This synchronization (to within 1 ms) is thought to result from electrotonic coupling of inferior olivary neurons. However, the distance from the inferior olive (IO) varies across the cerebellar cortex. Thus signals generated simultaneously at the IO should arrive asynchronously across the cerebellar cortex, unless the length differences are compensated for. Previously, it was shown that the conduction time from the IO to the cerebellar cortex remains nearly constant at approximately 4 ms in the rat, implying the existence of such compensatory mechanisms. Here, we examined the role of myelination in generating a constant olivocerebellar conduction time by investigating the latency of complex spikes evoked by IO stimulation during development in normal rats and myelin-deficient mutants. In normal rats, myelination not only reduced overall olivocerebellar conduction time, but also disproportionately reduced the conduction time to vermal lobules, which had the longest response latencies prior to myelination. The net result was a nearly uniform conduction time. In contrast, in myelin-deficient rats, conduction time differences to different parts of the cerebellum remained during the same developmental period. Thus myelination is the primary factor in generating a uniform olivocerebellar conduction time. To test the importance of a uniform conduction time for generating synchronous complex spike activity, multiple electrode recordings were obtained from normal and myelin-deficient rats. Average synchrony levels were higher in normal rats than mutants. Thus the uniform conduction time achieved through myelination of olivocerebellar fibers appears to be essential for the normal expression of complex spike synchrony.

5’-Nucleotidase Activity and Galactolipid Accumulation in Triethyllead-exposed Glial Cell Cultures

The developing nervous system is vulnerable to heavy metal exposure, which can cause alterations in neuronal and glial cells in the brain. Thus, heavy metals such as mercury and lead reduce myelin galactocerebroside (GalC) synthesis, and increase the ratio of non-hydroxylated fatty acids to hydroxylated fatty acids (GalC-N:GalC-OH) in the GalC molecules in newborn rats. This study investigated the effect of lead on the expression of myelin components by the myelin-forming oligodendroglial cells (OG) in vitro. Primary cultures of mixed glial cells from brains of newborn rats were continuously exposed to triethyllead (TEL; 1nM, 10nM, 50nM and 100nM) for 3 weeks, one week after seeding. The first morphological alteration observed was an increased proliferation of OG in cultures exposed to 10nM TEL. Biochemical analyses showed up-regulation of the enzymes, 2'3’-cyclic nucleotide 3’-phosphodiesterase and 5’-nucleotidase. GalC synthesis was also stimulated, and the ratio GalC-N:GalC-OH was reduced. The results indicate that TEL stimulates the differentiation and maturation of OG in cultures, which suggests that the alterations induced by heavy metals in newborn rats are not due to interference with the OG maturation.

Do oligodendrocytes divide?

Remyelination occurs in the adult central nervous system following a wide variety of experimental and naturally occurring demyelinating conditions, including multiple sclerosis. Remyelination is preceded by the appearance of new oligodendrocytes. These new cells may be generated from glial precursor cells, or from pre-existing differentiated oligodendrocytes that re-enter the cell cycle, which may first dedifferentiate, or both processes may occur. The evidence for the source of new oligodendrocytes following toxic or immune-mediated lesions is reviewed. Good evidence exists that fully differentiated oligodendrocytes can incorporate [3H]thymidine but this may be a rare event. Most of the evidence points towards glial precursor cells as the source of new oligodendrocytes in the adult, but definitive experiments have not yet been done. Research strategies, using our current knowledge and techniques, are outlined for solving this problem.

Hydroxy- and non-hydroxy-galactolipids in developing rat CNS

Rat spinal cord (1-24 weeks postnatal) was analysed by HPLC for various species of galactolipids that accumulate in mammalian myelin during development. Cerebral tissue of the same animals was taken as reference. The levels of the major galactolipids, galactosylceramide (GalCer) and its sulfated analog (SGalCer), increased linearly during the first 2 months after birth. At 3 months, constant levels were reached that were approx. 4-fold (GalCer) and 2.5-fold (SGalCer) higher than in cerebral tissue of corresponding age. The accumulation of galactoglycerolipids slightly preceded that of galactosphingolipids. Levels of galacto-glycerolipids were much lower (4% of galactosphingolipids in 3-and 2.5% in 6-month-old spinal cord on weight basis) and decreased upon CNS maturation. During the first postnatal month, the ratio of non-hydroxy- over hydroxy-species (NFA/HFA) of cerebral GalCer declined from 2.2 to 0.5 whereas the NFA/HFA ratio for cerebral SGalCer increased from 1.0 to 1.8 in the same period. Through development the hydroxy-species contributed 56-60% to GalCer and 28-41% to SGalCer in spinal cord, whereas in cerebrum of 24-week-old rats 73% of GalCer and 48% of SGalCer was alpha-hydroxylated in the ceramide moiety. These data point to different developmental programs with respect to galactolipid metabolism of oligodendrocytes in high- (spinal cord) as compared to low-myelinated (cerebral) areas of rat CNS.

Axons modulate the expression of proteolipid protein in the CNS

We examined the expression of mRNA encoding proteolipid protein (PLP), the major myelin protein in the CNS, in developing rat cerebrum, and in normal and degenerating optic nerves. PLP transcripts were initiated at two clusters of start sites that were separated by about 30 base pairs. During the peak of PLP mRNA expression in developing cerebrum, a higher proportion of PLP transcripts were initiated from the distal start site, furthest from the open reading frame, than in mature cerebrum. We enucleated one eye of immature rats to cause Wallerian degeneration in the optic nerve. In these degenerating optic nerves, the steady state levels of PLP mRNA fell markedly, and the proportion of distally initiated PLP transcripts declined to the same proportion found in normal adult nerves. Changes in myelin gene expression were not limited to PLP mRNA, as the steady-state levels of myelin basic protein (MBP) mRNA paralleled those of PLP mRNA in the developing cerebrum and in degenerating optic nerves. Thus, oligodendrocytes require axons to maintain their normal levels of PLP and MBP transcripts and the high proportion of distally initiated PLP transcripts that characterize early myelination.

Effects of combined pre- and postnatal ethanol exposure (three trimester equivalency) on glial cell development in rat optic nerve

This study evaluated the effects of a combined gestational and 10 day postnatal alcohol exposure (human three trimester equivalency) on the development of glial cells in the rat optic nerve. Pregnant rats were exposed to alcohol via a liquid diet, then their pups were artificially reared and further exposed to alcohol for 10 postnatal days via a gastrostomy fed liquid diet. Control animals, born of pair fed dams, were artificially reared on pair fed isocaloric diets. Optic nerve tissues were prepared for light and electron microscopic studies from animals on gestational days (G) 15 and 20 and postnatal days (P) 5, 10, 15, 20 and 90. There were fewer glial cells per cross-section on day 15 and the cross-sectional areas of optic nerves were smaller on days G20, P15 and P90 in the ethanol exposed animals. There was an alcohol-induced delay in the appearance of immature cells within the oligodendroglia lineage and a decrease in the number of oligodendroglia present at 15 and 20 days, indicating a delay in the maturation of oligodendroglial cells. These effects were compensated for by 90 days. Maturation of the astrocytic cell lineage was generally unaffected by the alcohol although there was evidence of increased numbers of cells in the lineage. There was no consistent indication of alcohol-induced degeneration of glial cells or their organelles. Thus, alcohol exposure for all of gestation and 10 postnatal days in the rat causes a delay in oligodendrocyte maturation but appears to have no long-term effects on the glial cell population of the optic nerve. Such a delay, by contributing to delays in myelin development, could help to explain some of the neurological dysfunctions associated with developmental alcohol exposures.

Studies of glial lineage and proliferation in vitro using an early marker for committed oligodendrocytes

The potential of immature glial cells to differentiate into astrocytes (ASs) or oligodendrocytes (OLs) has been examined using a monoclonal antibody (007) that is specific for OLs in vivo. Cells were dissociated from 2-day postnatal mouse cortex and labeled with the 007 antibody 2 hr after plating. The cells which were labeled during this single, brief exposure to the antibody retained the antibody on their surfaces over the course of the experiments. Cells were double stained at various timepoints for residual 007 antibody and either galactocerebroside (GC) or glial fibrillary acidic protein (GFAP). Shortly after plating, most 007+ cells were GC- and none expressed GFAP. These cells were round, although some had begun to extend very short processes. After 96 hr, greater than 95% of cells with residual 007 on their surfaces also expressed GC. By this time, all the 007+ cells had several processes of varying lengths extending from their cell bodies. Cells expressing both 007 and GFAP were never seen. The 007+/GC+ OLs were not induced to differentiate from 007+ bipotential progenitors since they were grown in fetal calf serum. These results show that under our culture conditions the 007 antibody is OL specific. Immunostaining for bromodeoxyuridine, a marker for dividing cells, revealed that some 007+ cells were proliferating. The majority of these proliferating cells had already extended three or more processes. We therefore conclude that immature, process-bearing cells can be committed to the OL lineage at times before they express detectable amounts of GC. Since these young 007+ OLs are actively proliferating, committed cells can serve as an important source of new OLs.

Division of astroblasts and oligodendroblasts in postnatal rodent brain: evidence for separate astrocyte and oligodendrocyte lineages

What precursor cells are the source of the macroglia generated during postnatal development? In order to answer this question, we studied the expression of glial specific antigens in proliferating neuroglia in postnatal rodent brain and optic nerve. Immunocytochemistry using antibodies to oligodendrocyte (OL) specific markers (sulfatide and galactocerebroside) and an astrocyte (AS) specific marker (glial fibrillary acidic protein) was combined with thymidine autoradiography. During the first week of postnatal development when most ASs are being generated, one third to one half of the proliferating cells in the optic system are positive for glial fibrillary acidic protein after a 1 h injection of thymidine (Skoff, Dev. Biol., 139:149-168, 1990). During the second postnatal week when OLs are being generated, 30 to 100% of the proliferating cells in presumptive white matter tracts are sulfatide positive and at least 10% are galactocerebroside positive. This finding demonstrates that ASs and OLs divide during postnatal development. These results confirm previous electron microscopic autoradiographic studies showing that the vast majority of proliferating cells in postnatal rat optic nerve have the morphologic characteristics of differentiating ASs or OLs (Skoff, J. Comp. Neurol., 169:291-312, 1976). Since proliferating ASs (astroblasts) and OLs (oligodendroblasts) constitute the majority of the dividing cells at the time that ASs and OLs are being generated, these glioblasts must be the major source for the macroglia generated postnatally. The findings strongly suggest that separate lineages exist for ASs and OLs during postnatal development. There is no compelling in vivo evidence for a bipotential progenitor cell that generates the majority of OLs and certain ASs in postnatal rodent brain. There may, of course, be distinct lineages for the subtypes of ASs and possibly even for subtypes of OLs. We review the concepts of commitment and plasticity and apply these terms to glial differentiation. In situ, the presence of oligodendroblasts and astroblasts demonstrates the COMMITMENT of proliferating cells to a specific glial lineage during normal development. Culture conditions may provide an environment that permits proliferating glial cells to vacillate in their selection of a specific lineage. This situation demonstrates developmental PLASTICITY and the ability of glia to adapt to an altered environment. Whether committed glial cells in situ can be induced to switch their lineage when normal CNS conditions are altered is an intriguing question that remains to be answered.

Axonal modulation of myelin gene expression in the peripheral nerve

Myelin gene expression (P0, MBP, P2, and MAG) was investigated during Wallerian degeneration and in the presence or absence of subsequent axonal regeneration and remyelination. The steady state levels of mRNA and protein were assessed in the crushed or permanently transected rat sciatic nerve at 0, 1, 4, 7, 10, 12, 14, 21, and 35 days after injury. The mRNA and protein steady state levels of the myelin specific genes, P0 and the MBPs, decreased to low yet detectable levels during Wallerian degeneration and returned to normal levels with subsequent axonal regeneration. The steady state level of P2 protein also followed a similar pattern of expression. The steady state level of MAG mRNA decreased to undetectable levels by 4 days of injury in the permanently transected nerve. After crush injury, re-expression of MAG to levels comparable to those of normal nerves preceded that of P2 by 2 days and that of P0 and the MBPs by 3 weeks during axonal regeneration and remyelination. These results support the proposed roles for MAG in the formation of initial Schwann cell-axonal contact required for myelin assembly, for P2 in fatty acid transport during myelination, and for P0 and the MBPs in the maintenance of the integrity and compactness of the myelin sheath. In addition, these results indicate that the expression of the myelin specific genes, P0 and MBP, is constitutive and that the level of myelin specific mRNAs is modulated by axonal contact and myelin assembly.

Evidence that secondary rat Schwann cells in culture maintain their differentiated phenotype

Schwann cells, on receiving the correct signal, will encircle an axon and wrap it with a myelin sheath. To begin examining some of the mechanisms underlying the process of myelination in vitro, we isolated Schwann cells from the sciatic nerves of neonatal rats and generated large cell populations with cholera toxin. The immunological and biochemical properties of these secondary Schwann cells were characterized after five to seven passages in the absence of axonal contact. These cells continued to express antigens found in both myelinating (P0 and 2',3'-cyclic nucleotide phosphohydrolase) and nonmyelinating cells in vivo (A5E3 and glial fibrillary acidic protein) in addition to the markers common to both types of cells (Ran-1, 217c, S-100, and laminin). Biochemical analyses showed that these cells synthesize the very-long-chain fatty acids (22-26 carbon atoms) found in myelin membranes. Moreover, the enzymes required for the synthesis of myelin glycolipids (including sphingosine acyltransferase, UDP-galactose:ceramide galactosyltransferase, and cerebroside sulfotransferase) were still active, and metabolic labeling studies showed that galactocerebroside and sulfatide were synthesized even though the galactocerebroside pool was insufficient to be detected by immunostaining. Secondary Schwann cells also synthesized four species of myelin basic protein and the major structural glycoprotein in myelin, P0. The pathway necessary for glycosylation of P0 protein remained active, and an analysis of the oligosaccharide chain revealed that approximately 70% was processed to a complex form. In summary, we found that secondary Schwann cells still express most of the immunological markers of differentiated cells and continue to synthesize low levels of myelin components. Therefore, Schwann cells do not dedifferentiate in culture, as previously believed.

Myelin basic protein immunohistochemistry: a study of the early stages of myelination in the brainstem of the rat

An immunohistochemical study of MBP distribution in the brainstem of neonate till 16 d old rats based on the peroxidase-antiperoxidase method is described. Axons already invested with immunoreactive sheaths were found in neonate rats in the ventral funiculus of the cervical spinal cord and in the medial longitudinal fascicle of the medulla oblongata. Fibres commencing with myelination showed a closely spaced array of varicosities in longitudinal sections which diminished gradually. A caudo-rostral decrease in density of myelinated fibres in the brainstem was found in the medial and dorsal longitudinal fascicles. In contrast to other pathways, myelination in the fibres of the corticospinal tract in the brainstem occurred in a strictly synchronized pattern. The same temporal pattern of myelination was also observed in the cervical corticospinal tract, except that a few myelinated fibres had been visible much earlier within the area of the tract. At the exit of cranial nerves, the transitorial zone from central to peripheral myelin was outlined by a decrease in immunostaining.

Effects of postnatal ethanol exposure on glial cell development in rat optic nerve

This study morphologically evaluated the effects of limited postnatal alcohol exposure on the development of glial cells in the rat optic nerve. Rat pups were artificially reared on Days 5-18 with a supplemented milk diet fed via a chronic gastrostomy tube. Experimental animals received 4% ethanol in their diet on Days 5-9, otherwise the experimental and control animals received identical diets. Optic nerve tissues were prepared for electron microscopy on Days 10, 16, 22, 29, and 90. There were fewer glial cells per cross section and the cross-sectional areas of optic nerves were smaller on Days 10 and 16 in the ethanol-exposed animals. The alcohol caused a delay in the maturation of oligodendroglial cells at 10 days as evidenced by decreases in the total number of oligodendroglia present and by a delay in the appearance of immature cells within the oligodendroglial lineage. All of these effects were compensated for at later ages. There was no evidence of alcohol-induced degeneration of glial cells or their organelles. Thus, postnatal alcohol exposure causes a delay in oligodendrocyte maturation but appears to have no long-term effects on the glial cell population of rat optic nerve.

Cyclic AMP regulates the rate of differentiation of oligodendrocytes without changing the lineage commitment of their progenitors

Oligodendrocytes differentiate in primary cultures of rat brain cells on a specific schedule similar to that observed in vivo. We show that the pace of this developmental schedule is accelerated by the addition of the cyclic AMP analogs dibutyryl cAMP (dbcAMP) or 8-bromo cAMP. Dibutyryl cAMP also inhibits DNA synthesis in A2B5-positive oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells, consistent with the relationship between cessation of proliferation and onset of differentiation observed in vivo and in vitro. Treatment of cultures with dbcAMP has no effect on the proportion of O-2A progenitors that become oligodendrocytes rather than type 2 astrocytes and thus does not affect progenitor lineage decisions. Thus, cyclic AMP analogs accelerate the differentiation of cells apparently already determined to become oligodendrocytes.

Myelin composition and activities of CNPase and Na+,K+-ATPase in hypomyelinated "pt" mutant rabbit

A disorder of CNS myelination was found in paralytic tremor ("pt") rabbits. The condition is inherited in a sex-linked recessive mode. Ultrastructurally, an obvious myelin deficiency with aberration of myelin sheath formation is observed. The yield of myelin isolation was reduced to 20-30% of control. Myelin isolated from 4-week-old "pt" rabbits contained reduced amounts of galactosphingolipids and of several myelin protein markers. Moreover, myelin basic protein, analyzed by two-dimensional gel electrophoresis, showed a deficit in its more basic components. All these facts suggest a delay in myelin maturation. Ganglioside content was increased as well as Na+,K+-ATPase specific activity. 2',3'-Cyclic nucleotide phosphodiesterase (CNPase) specific activity was the same in "pt" as in control myelin but differed by having greater sensitivity to detergent activation.

The sequence of myelination in the brainstem of the rat monitored by myelin basic protein immunohistochemistry

The temporal order which is observed by nervous pathways in their myelination was investigated in the brainstem of neonatal to 16-day-old albino rats. The immunohistochemical detection of myelin basic protein in newly forming myelin sheaths provided a highly sensitive and specific criterion to judge the time of onset and the progress of myelination in its initial stages. Immunohistochemistry was performed on paraffin-embedded tissue according to the unlabeled peroxidase-antiperoxidase method. A small number of immunoreactive fibers was already present in neonate rats in the ventral funiculus of the cervical spinal cord and in the medial longitudinal fascicle of the medulla oblongata. By the 4th postnatal day myelination had commenced in many sensory tracts and in the trigeminal root, in the tectospinal tract, in the inferior cerebellar peduncle and in the roots of most cranial motor nerves. The auditory pathway up to the inferior colliculus, the gracile, spinocerebellar and rubrospinal tracts and the superior cerebellar peduncle had acquired some myelin on the 7th day. Phylogenetic late fiber systems also appeared to myelinate comparatively late: the transverse pontine fibers and the medial cerebellar peduncle started on the 10th day, and in the corticospinal tract a conspicuously synchronized myelination appeared on the 13th day. All pathways of the brainstem possessed myelinated fibers on the 16th day and some tracts had approached their relative maturity.

Brain lipids of a myelin-deficient rabbit mutant during development

The paralytic tremor (pt) rabbit, a neurological mutant, exhibits hypomyelination transmitted in X-linked recessive fashion. This rabbit mutant was used for regional lipid analyses of different brain structures during development. There was a significant decrease of myelin-specific lipids, particularly in the cerebroside and sulfatide in pt rabbits. The decrease of phospholipid and cholesterol was relevant to the total lipids depletion. The molar ratio of galactolipid to phospholipid decreased in the pt rabbit brain in each age group examined. The other lipids typical for myelin, such as ethanolamine glycerophospholipids, sphingomyelin, and GM1 ganglioside, were also diminished in the myelin-rich structures, but were not changed in the cortical gray matter of pt rabbits. In contrast, the total amount of gangliosides was near control levels and, therefore, in the mutant rabbits, the white matter and brain stem contained a higher proportion of lipid, as ganglioside, relative to the control animals. This result suggests that neuronal membranes were not involved in this pathology. The characteristic biochemical abnormalities exhibited in the pt rabbit suggest that a defect of oligodendroglial cell function is primarily responsible for the myelin abnormality.

Levels of sulfatide synthesis distinguish oligodendroglia in different stages of maturation

In the central nervous system, oligodendroglia elaborate extensive quantities of membranes to form the multilamellar myelin sheath. Whether the production of extensive networks of processes by oligodendroglia in culture is a similar type of phenomenon as the formation of myelin is an unanswered question. Rat oligodendroglia, prepared by a modification of a differential shaking and plating method, elaborate extensive processes in culture. In contrast, bovine oligodendroglia, obtained by a bulk-isolation method, produce whorls of membrane lamellae, adjacent to the cell soma. The incorporation of various radiolabeled substrates into specific lipids was compared with the two cell types. It was found that rat oligodendroglia do produce myelin specific lipids, but at a lower level than bovine oligodendroglia which are actively synthesizing myelin lipids, especially cerebrosides, from a variety of substrates. Interestingly sulfatides are produced at a higher level in the cells not producing myelin, rat oligodendroglia. Other lipids that are associated with myelination (cerebrosides with alpha-hydroxy fatty acids and phosphatidylinositides) are produced at higher levels in bovine oligodendroglia. Thus it appears that the extension of processes by oligodendroglia in culture is a different phenomenon than the production of myelin membranes and requires lower levels of myelin lipids.

Myelin basic protein in the optic nerve of the developing albino rat: an immunoperoxidase study of paraffin embedded tissue

The distribution of myelin basic protein (MBP) was determined by application of the unlabeled peroxidase-anti-peroxidase method to sections of paraffin embedded optic nerve taken from the developing albino rat. MBP was not detected in optic nerves from animals younger than 90 hours postnatum. MBP staining presented first as faint, diffuse deposits of chromagen which were found in approximately one-third of the 90 hour subjects. The number of MBP positive regions and the intensity of staining of these regions increased rapidly with age. There was no obvious radial gradient in the distribution of MBP in cross sections of developing optic nerves, nor were smooth central/peripheral gradients apparent in longitudinal sections.

Bulk separation and long-term culture of oligodendrocytes from adult pig brain. II. Some biochemical data

Oligodendroglial proteins labeled with radioactive amino acids were subjected to one- and two-dimensional polyacrylamide electrophoresis. Bands comigrating with myelin proteins, the basic protein (MBP), the proteolipid protein (PLP), and the Wolfgram protein (WP) doublet, were detected by Coomassie Blue staining and by autoradiography. The identity of the MBP and WP in the cellular material is evidenced by immunoblotting with specific antibodies. A comparative study of myelin samples from rat and pig CNS reveals that WP can be detected immunochemically in both species. Different protein patterns, however, are observed. Three protein bands are found with antibodies against the myelin-associated glycoprotein (MAG). The high-molecular-weight component prevails in pig myelin, whereas the medium-molecular-weight component is predominant in rat myelin. Moreover, two protein bands, of molecular weights 35,000 and 33,000 (Ol 1 and Ol 2), are present in high amounts in oligodendroglial particulate material but are not detectable in myelin. These oligodendroglial characteristic proteins are not species-specific, since they are found in preparations of cat oligodendrocytes as well. Activities of cerebroside sulfotransferase (EC 2.8.2.11) are low in freshly isolated cells and increase during the first week of culture. A reverse course of enzyme activities is observed with 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37). Values reach a minimum about day 5 in culture and recover their initial values. At day 10 they remain stable until the end of the third week of the culture period.

An improved procedure for the quantitative determination and characterization of sulfatides in rat kidney and brain by high-performance liquid chromatography

A significant improvement has been made in the desulfation step of our previously published HPLC determination of cerebrosides, sulfatides, and monogalactosyl diacylglycerols (Nonaka, G. and Kishimoto, Y., Biochim. Biophys. Acta 572 (1978) 423-431). Instead of the original two-phase reaction, a solution of trifluoroacetic acid in ethyl acetate is used for the solvolysis in the new method. The revised method was used to determine the levels of cerebrosides and sulfatides in rat kidney. Among four individual glycosphingolipids studied, hydroxysulfatide was present at the highest level (0.7-1.3 nmol/mg of dry tissue), followed by nonhydroxysulfatide (0.3-0.8 nmol/mg of dry tissue). Hydroxycerebroside (0.09-0.16 nmol/mg of dry tissue) and nonhydroxycerebroside (0.03-0.09 nmol/mg of dry tissue) were present in smaller quantities. There appear to be no significant differences between male and female animals of different ages (30-120 days), although the amounts decreased slightly in older animals and there was a higher concentration in female than in male kidney. Tissue size was significantly smaller in females. The homolog composition of rat kidney sulfatide was studied by reverse-phase HPLC, and was found to be significantly different from that reported in human kidney. Rat sulfatides contained fatty acids with a higher degree of saturation and longer chain length. Preliminary studies indicated that rat kidney contained unusually large quantities of C25:1 and C27:1 fatty acids and also that there was more C26:1 than C24:1 acid. In brain of the same animals the ratio of nonhydroxy to hydroxysulfatide decreased with age (1.5:1 in 30-day-old brain; 1:1 at 90 days).

Changing relation between onset of myelination and axon diameter range in developing feline white matter

The size spectra of unmyelinated, ensheathed and initially myelinating CNS axons were examined by electron microscopy in the spinal cord ventral funiculus and the corpus callosum of the cat during development. The first myelin sheaths appeared 4 weeks before and 3 weeks after birth in the spinal and callosal areas, respectively. De novo myelination had largely ceased by 4 months in the ventral funiculus and by 7 months in the corpus callosum. The result show that the diameter ranges, within which spinal and callosal axons undergo primary ensheathment and initial myelination, are markedly different if similar levels of myelination are compared. In both areas, these diameter ranges shift towards smaller sizes with development. However, spinal and callosal axons, which undergo primary ensheathment and initial myelination simultaneously, present comparable diameter ranges. The findings support the view that other factors than the absolute physical size of the axon trigger initiation of CNS myelination. In this respect the developmental stage of the animal appears to play an important role.

Development of oligodendrocytes and Schwann cells studied with a monoclonal antibody against galactocerebroside

We have generated a hybridoma cell line secreting a monoclonal antibody that specifically binds to the surfaces of oligodendrocytes and Schwann cells, the cells involved in myelin formation in the central and peripheral nervous systems, respectively. Binding studies using purified sphingolipids showed that this antibody reacts strongly with galactocerebroside (GalC), the major galactosphingolipid of myelin. The antibody was used in conjunction with rabbit antisera against sulfatide, the sulfated form of GalC, to examine the developmental appearance of these lipids on the surfaces of oligodendrocytes and Schwann cells. In addition, the loss of GalC and sulfatide from freshly dissociated Schwann cells was compared. These studied showed that GalC is expressed on the cell surface prior to sulfatide on both of these cell types in vivo and in vitro. Conversely, dissociated Schwann cells lose their cell surface sulfatide more rapidly than they lose their surface GalC under nonmyelinating conditions.

Immuno-electron-microscopic identification of O-antigen-bearing oligodendroglial cells in vitro

Monoclonal antibodies to cell-surface antigens of oligodendrocytes (Sommer and Schachner 1980; Schachner et al. 1980) were used to identify this cell type by immuno-electron microscopy in monolayer cultures of fetal and early postnatal mouse cerebellum. The ultrastructural features of antigen-positive cells confirm that they are immature and mature oligodendrocytes, but not neurons, astrocytes or fibroblasts or fibroblast-like cells. Type I oligodendrocytes are the immature ones with a relatively large amount of moderately electron-lucent cytoplasm, clusters of ribosomes and complex networks of rough endoplasmic reticulum. Large numbers of mitochondria and microtubules, but not intermediate-sized filaments are seen in these cells. They comprise more than 90% of all 0-antigen-positive cells. Type II cells comprise only approximately 5% of all 0-antigen-positive cells. They are characterized by a limited amount of electron-dense cytoplasm, which appears more compact and granular than in type I cells. The rough endoplasmic reticulum is distributed evenly throughout the cytoplasm. Microtubules and mitochondria are present, but more difficult to distinguish due to the compactness of the cytoplasm. Type II cells display the more mature ultrastructural features of oligodendrocytes.