Developmental changes of ganglioside expressions in postnatal rat cerebellar cortex

We previously described the differential distribution of gangliosides in adult rat brain as detected by specific antibodies. We report here the distribution of gangliosides during the development of postnatal rat cerebellum by an immunofluorescence technique with mouse monoclonal antibodies (mAbs). Eleven mAbs that specifically recognize each ganglioside were used. Our study revealed that the expression of each ganglioside changed dramatically during the development. GD3 and O-Ac-GD3 were expressed intensely in the external granular layer at 1, 5, and 10 days, whereas GD2 was firstly detected in the internal granular layer at 5 days and GD1b was diffusely detected throughout all layers of the cerebellar cortex at early postnatal days. GD2 and GD1b were more intensely expressed in the granular layer at 20, 30, and 80 days, suggesting that premature granule cells express GD3 and its derivative, O-Ac-GD3, whereas mature granule cells express GD2 and GD1b intensely. On the other hand, GM1 was exclusively detected in the external granular layer and the molecular layer at 1 and 5 days. The staining sites spread gradually from these outer layers into the internal granular layer and the white matter after 10 days. The positive cells in the external granular layer and the molecular layer appeared to be Bergmann glial cells and their radially ascending cytoplasmic processes. The intensity of the staining in these specialized astroglial cells decreased gradually during postnatal days. In contrast, the expression of GQ1b was very faint at birth, but gradually increased during the development and was detected intensely in the internal granular layer, particularly in the cerebellar glomeruli in adulthood, suggesting that GQ1b expression may be associated with synapse-related structures. The developmental changes of the expression of other gangliosides were also recognized in the postnatal rat cerebellum. These results suggest that specific gangliosides may play an important role in regulating the early events responsible for the orderly formation of the cerebellar cortex.     

Effect of colchicine on ganglioside composition of rat primary culture neurons.

Developmental changes in gangliosides in the course of neurite outgrowth were examined in dissociated fetal rat cerebral neurons in culture. About a 2-fold increase in ganglioside levels was seen with the progression of neurite formation for up to 24 h in predominantly neuronal cultures. Ganglioside patterns appeared to be unchanged during the first 24 h, subsequently consisted of higher amounts of GD3 and b-series gangliosides (such as GD1b, GT1b, and GQ1b), and lower amounts of a-series gangliosides (GM1 and GD1a). Although the addition of colchicine to the cell growth medium inhibited neurite outgrowth in developing neurons, little if any differences in ganglioside patterns were found between control and colchicine-treated cells. Ganglioside levels decreased slightly in colchicine-treated cells in agreement with the decrease in cell attachment to culture dishes. Although colchicine treatment 8 h after plating caused complete retraction of formed neurites, the ganglioside level of the cells continued to increase during the following 16-hour incubation. Thus, the data suggest that ganglioside synthesis in differentiating neurons does not primarily accompany the expansion in cell surfaces due to neurite formation, and raises the possibility that a large proportion of gangliosides is retained in intracellular compartments.     

Cerebellar ganglioside abnormalities in pcd mutant mice

The distribution of cerebellar gangliosides was studied in Purkinje cell degeneration (pcd/pcd) mutant mice at postnatal days 25, 30, 50, and 150. These mutants lose the majority of Purkinje cells between 18 and 50 days of age. A reactive gliosis accompanies Purkinje cell loss and a partial loss of granule cells occurs in pcd/pcd mice older than p50. Purkinje cell loss is associated with significant reductions in cerebellar weight and ganglioside concentration. This neuronal loss was also developmentally correlated with reductions of gangliosides (GT1a/LD1 and GT1b and with elevations of GD3. These results agree with previous findings in other cerebellar mutants that GT1a/LD1 and GT1b are concentrated in Purkinje cells and that GD3 is enriched in reactive glial cells. A slight, but significant, reduction in GD1a concentration occurred only in older pcd/pcd mice, consistent with previous findings in weaver and staggerer mice that GD1a is enriched in mature granule cells. The findings with pcd/pcd and other neurological mutants indicate that certain gangliosides can serve as cell-surface markers for monitoring changes in cerebellar cytoarchitecture that accompany development or disease.     

Effect of Purkinje cell loss on cerebellar gangliosides in nervous mutant mice

The distribution of cerebellar gangliosides was studied in adult (73 ± 2 days) nervous (nr/nr) mutant mice which lose 50–90% of their Purkinje cells. This neuronal loss is associated with significant reductions in cerebellar weight and ganglioside concentration. The cerebellar dry weights (mg) and the ganglioside concentrations (μg N-acetylneuraminic acid per 100 mg dry weight) in nr/nr mice and age-matched normal littermates (+/?) are 7.4 ± 0.3 mg and 13.2 ± 0.4 mg; and 411.7 ± 4.8 μg and 438.5 ± 2.1 μg, respectively. Abnormalities were also observed for the concentration of certain ganglioside species. Most notably, GT1a is significantly reduced by 42%, and GD3 is significantly increased by 29% in the nr/nr mice compared to the +/? mice. The nr/nr mice also express a slight but significant reduction in GT1b. No ganglioside abnormalities were observed between the nr/nr and +/? mice in cerebral cortex. We previously found reduced cerebellar GT1a content in other mutants that also lose Purkinje cells, i.e., sg/sg, pcd/pcd, and Lc/+. GT1a is not reduced, however, in wv/wv mice that lose mostly granule cells. The findings in nr/nr mice are therefore consistent with our hypothesis that GT1a is enriched in Purkinje cells. GD1a, which is enriched in mature granule cells, is not reduced in the nr/nr mice. Since we previously found that GD3 is a good marker for reactive glia in neurological disease, the elevated GD3 concentration in the nr/nr mice indicates a mild gliosis. Our findings with nr/nr and the other neurological mutants indicate that gangliosides can be useful as cell-surface markers for monitoring changes in the cytoarchitecture of the mouse cerebellum.     

Immunostaining of ganglioside GD1b, GD3 and GM1 in rat cerebellum: cellular layer and cell type specific associations

We have studied the cellular distribution of gangliosides GD1b, GD3 and GM1 in rat cerebellum by immunostaining, using monoclonal antibodies and confocal microscopy. Antibodies against astroglial, neuronal and synaptic vesicle associated molecules were used for colocalization analyses. In the gray matter, the anti-GD1b antibody stained thin strands in the molecular layer (ML), interpreted as Bergman glia fibers based on colocalized staining with anti-glial fibrillary acidic protein (GFAP). The neuropil in the granule (GL) and Purkinje (PL) cell layers was also anti-GD1b positive. The anti-GD3 antibody stained the ML, the neuropil in the GL and PL and also the granule and Purkinje cell bodies, appearing intracytoplasmically and vesicle associated. Anti-GD1b and anti-GD3 staining in the GL glomeruli were colocalized with anti-synaptophysin staining. The anti-GM1 antibody stained cell bodies in the ML but they could not be characterized in colocalization experiments. The GL and PL were not stained with the anti-GM1 antibody. In the white matter, different staining patterns were seen for the gangliosides, the anti-GM1 staining being the most intense. This study shows cellular layer and cell type specific associations of the investigated gangliosides and localization of GD1b and GD3 at synaptic sites, warranting further studies on their role in synaptic mechanisms.     

Expression and function of ganglioside 9-O-acetyl GD3 in postmitotic granule cell development

We have shown previously that the Jones monoclonal antibody (Jones mAb) recognizes 9-O-acetyl GD3 expressed during periods of neuronal migration and neurite outgrowth in the developing rat nervous system. In the present study we investigated the expression of this ganglioside in the developing cerebellum and correlated this expression with granule cell migration. Electron microscopic immunocytochemistry revealed that around the peak of cerebellar neuronal migration (7-day-old rat), 9-O-acetyl GD3 was localized at the contact sites between migrating granule cells and radial glia in the external granular layer and prospective molecular layer. In addition, using microexplant and slice cultures of the postnatal rat cerebellum, we tested whether the ganglioside detected by our antibody contribute to the regulation of neuronal migration in the cerebellar cortex. We have shown that the Jones mAb blocks the migration of neurons in a dose-dependent manner. These findings suggest strongly that 9-O-acetyl GD3 is involved in granule cell migration in the developing cerebellum.     

Restricted occurrence of an unusual ganglioside GD1α in rat brain and its possible involvement in dendritic growth of cerebellar Purkinje neurons

The spatial pattern of expression of a minor disialosyl ganglioside GD1α in the rat brain was investigated immunohistochemically using a specific murine monoclonal antibody KA-17. The antibody shows noticeable immunoreactivity in the proximal dendrites and neuronal cell bodies of restricted populations of neurons including cerebral pyramidal neurons and cerebellar Purkinje neurons. Immunocytochemical analysis revealed that Purkinje neurons maintained in a dissociate culture condition also express GD1α in the dendrites and cell bodies. We have examined the functional involvement of this ganglioside in the growth of brain neurons using KA-17 antibody. Addition of the antibody to cerebellar primary cultures caused perturbation of the dendritic development of Purkinje neurons in a dose-dependent manner. The length and branching of the dendrites were severely decreased by the antibody treatment. When other anti-glycoconjugate or sphingolipid monoclonal antibodies were tested, only HNK-1 monoclonal antibody that recognizes sulfoglucuronic residues in glycolipids and glycoproteins had similar but moderate inhibitory actions on the dendritic development of these neurons. In contrast to the morphological alterations observed in Purkinje cells, other cerebellar cells including granule neurons appear to be almost normal following the antibody treatment. These observations lead to the possibility that GD1α ganglioside has a role in the development of Purkinje cell dendrites. © 1996 Wiley-Liss, Inc.     

Ethanol-induced increase of sphingosine recycling for ganglioside biosynthesis: a study performed on cerebellar granule cells in culture

The effect of ethanol on ganglioside metabolism was assessed in cultured rat cerebellar granule cells. Cells were incubated in the presence of tritiated serine or galactose, and the synthesis of radioactive gangliosides was followed. The rate of de novo biosynthesis of gangliosides labeled in the oligosaccharide moiety (deriving from tritiated galactose) was not affected by the presence of ethanol. On the contrary, the biosynthesis of gangliosides labeled in the ceramide long chain base moiety (deriving from tritiated serine), dramatically decreased in the presence of alcohol. These results suggest that the gap between the extent of the biosynthesis of lipid and polar portions observed in the presence of ethanol, is filled by an increased recycling of sphingosine produced from ganglioside degradation. This hypothesis was confirmed by pulse-chase experiments with GM1 ganglioside, tritiated in the sphingosine moiety, and following radiolabeled gangliosides deriving from its metabolic processing. In fact, the radioactivity carried by gangliosides whose labeling could derive exclusively (GD1b + GT1b) or partially (GD1a) from the recycling of catabolic radiolabeled sphingosine, dramatically increased in ethanol-treated cells during the chase period. Taken together, these results suggest that ethanol increases ceramide sphingosine recycling for ganglioside biosynthesis.     

Ganglioside alterations in guinea pig brains at end stages of experimental Creutzfeldt-Jakob disease.

Gangliosides were isolated from guinea pig brains at the end stages of experimental Creutzfeldt-Jakob disease. Quantitative analyses revealed marked decreases of ganglioside levels in pathologically devastated tissues such as cerebral cortex (-21%), basal ganglia and thalamus (-18%), and brain stem (-23%). The cerebellum revealed only minor pathological abnormalities and its ganglioside level remained unchanged. Thin-layer chromatography of the Creutzfeldt-Jakob brain gangliosides showed aberrant ganglioside patterns in all regions studied, including the cerebellum. With some exceptions, a trend in ganglioside pattern changes was detected which consisted of proliferation of GM3, GD3, GD2 and loss of GM1, GD1a, GD1b and GT1b.     

Ganglioside a/b ratio in different rat brain regions following chronic diazepam treatment

Gangliosides are sialic acid-containing glycosphingolipids that play a variety of important functions in neurons. The main purpose of this study was to determine the a/b ratio of gangliosides in different rat brain regions (cerebral cortex, hypothalamus, caudate nucleus, hippocampus, thalamus and cerebellum) after prolonged diazepam treatment. Male Wistar rats were maintained on a nutritionally adequate diet and diazepam was administered in a dose of 10 mg/kg day for 180 days. Total gangliosides were extracted according to Harth and the total ganglioside-NeuAc content was determined by Svennerholm's resorcinol method, modified by Miettinen and Takki-Luukkainen. The a/b ratio remained unchanged in rat hypothalamus, thalamus and cerebellum. It was slightly decreased in the caudate nucleus and hippocampus, but this was not statistically significant. A drastic decrease (p<0.01) in ganglioside content, compared to control animals, was found in rat cerebral cortex. Ganglioside a/b profile did not change significantly in most of the brain regions (except in cerebral cortex), which suggests that adaptive changes occurred upon prolonged exposure to diazepam, in order to maintain the physiological ratio of ganglioside a- and b-series in distinct brain areas. Received: 10 October 2001 / Accepted in revised form: 15 April 2002     

Lack of cell density-dependent changes in gangliosides of rat primary culture neurons.

Cell density-dependent changes in neuronal gangliosides, primarily relating to neurite outgrowth under dense to sparse conditions, were examined at cell seeding densities over an 8-fold range. During the first 24 h of incubation, the dissociated fetal rat neurons showed characteristic protrusion of neurites as a function of cell density. Ganglioside and protein contents per the same cell numbers were higher in dense cultures than sparse ones. However, the ganglioside pattern was essentially unchanged from dense to sparse culture, showing a predominance of GD3 and GT1b. The biosynthetic activity of gangliosides, as estimated by the incorporation of 3H-labeled N-acetyl-D-mannosamine, a precursor of sialic acid, was similar at various cell densities, with the labeling of b-series gangliosides predominating. The expression of neuronal gangliosides was monitored by indirect immunofluorescence using anti-GM1 antibody, but was found to be poor. A2B5 antigen, which was mainly identified as GT1b, appeared to be readily expressed on cell surfaces in sparse cultures. In contrast, the highly polysialylated form of the neural cell adhesion molecule (NCAM-H) was fully expressed on both the neurites and cell soma at various cell densities. The results suggest that the polysialic acids in NCAM have more important roles in neurite outgrowth than gangliosides, since the composition and synthesis of gangliosides are not affected by cell seeding density.     

GD3 ganglioside is prevalent in fully differentiated neurons from rat retina

Adult mammalian retinas contain unusually high amounts of GD3, a ganglioside of the lactosylceramide series. In this respect, they differ from adult avian retina and other regions of the adult avian and mammalian brain, where GD3 is a minor ganglioside and gangliosides of the gangliotetraosylceramide series (GM1, GD1a, GD1b, GT1b) are the predominant ones. We compare here the ganglioside patterns of rat, human, horse, and guinea pig retinas, which are known to differ in the degree of vascularization and astrocytic cell content. All these retinas showed a prevalence of pathway "b" gangliosides over pathway "a" gangliosides but showed no correlation between GD3 content and the degree of vascularization and astrocytic cell content. Immunostaining of rat retina sections showed the presence of GD3 in the inner and outer plexiform layers and also in the ganglion cell and inner nuclear layers. About 60% of the cells dissociated from rat retina showed immuno-colocalization of GD3 and the neuronal marker class III beta tubulin isotype or cholera toxin binding. All morphologically identifiable glial Muller cells coexpress GD3 and gangliotetraosylgangliosides. GD3 was a minor ganglioside among these axonally transported by ganglion cells in rats and guinea pigs, suggesting that it is either not synthesized by ganglion cells or, if so, it is restricted to the cell soma and/or dendritic tree. Our results demonstrate that, unlike neurons from avian retina and other regions of avian and mammalian brain, neurons from mammalian retina not only contain gangliosides of the gangliotetraosylceramide series but also keep a prevalence of gangliosides of the lactosylceramide series (GD3) when they are fully differentiated.     

Expression of GD3 ganglioside by developing rat cerebellar Purkinje cells in situ

GD3 is a major ganglioside of the immature vertebrate CNS, and its expression is suggested to be characteristic of immature neuroectodermal cells. Using immunocytochemistry on cryostat sections of developing rat cerebellum with a monoclonal antibody specific for GD3, we have found that GD3 begins to be expressed on the plasma membrane of Purkinje cell bodies and dendrites beginning at postnatal day 7. Staining became brighter as the dendritic tree of the cells enlarged. As the Purkinje cells began to mature in different folia, they became GD3+, until by 15 days postnatal all Purkinje cells were GD3+. Positive staining of the dendritic tree was still present in the adult cerebellum. Using a monoclonal antibody 7-8D2, which recognizes cerebellar granule cells and their axons (the parallel fibres), and polyclonal antibodies against a synaptic vesicle component synaptophysin, double-immunofluorescence staining together with anti-GD3 antibodies suggested that the appearance of GD3 immunoreactivity did not correlate either with the ingrowth of parallel fibres or the presence of their synapses on Purkinje cell dendrites. However, comparison with earlier morphological studies showed that the appearance of GD3 immunoreactivity correlated well with the formation of climbing fibre synapses on Purkinje cell dendrites and the onset of the rapid expansion of the dendritic tree. These results are in keeping with the idea that elevated GD3 concentrations are found in certain cell types during periods of rapid growth or high metabolic activity but also show that this is not only restricted to immature cells.     

Changes in ganglioside profile in chick embryo retina: Studies on tissue and cell cultures

The developmental profile of gangliosides in the neural retina of the chick embryo is characterized by a progressive decrease in the concentration of GD3 complex from a high level on day 6; by a continuous increase in GD1a concentration; and by less striking increases in GD1b and GT1b concentrations during the growth phase; GM1 increases in the post-mitotic retina. Gangliosides were analyzed by thin layer chromatography and by densitometry of the TLC plates. (Ganglioside nomenclature is according to Svennerholm.³⁷)We have examined comparatively ganglioside changes in organ cultures of retina tissue from 6 day embryos (R³⁶), in cell aggregates and in primary monolayer cultures of R²⁶ cells, all maintained for 6 days in vitro. In all cases, the pattern of ganglioside changes was qualitatively similar to that in the retina in vivo. These results suggest that, unlike some other aspects of retina differentiation, the progression of ganglioside changes in the 6–12 day embryonic retina is not critically dependent on histotypic cell organization or on specific contact-dependent cell interactions; these changes appear to be largely preprogrammed in the cells at some earlier phase of development.     

Chronic sensory ataxic neuropathy associated with IgM antibody against b-series gangliosides including GD1b]

We described a 62-year-old man with a 10 years history of chronic sensory ataxic neuropathy. His laboratory investigations revealed elevated serum IgM with IgM kappa paraproteinemia, IgM antibody against b-series gangliosides including GD3, GD2, GD1b, GT1b, GQ1b, GQ1b alpha, and high titer of cold agglutinin. The clinical and serological features in our patient were compatible with the diagnosis of CANOMAD (chronic ataxic neuropathy with ophthalmoplegia, M-protein, agglutination, and disialosyl antibodies), proposed by Willison et al. IgM antibody against b-series gangliosides including GD1b appeared to play an essential role in developing autoimmune sensory ataxic neuropathy.     

Neuroimmunology of gangliosides in human neurons and glial cells in culture

Gangliosides (sialic-acid-bearing glycolipids) have received attention in recent years because of their role in cell recognition phenomena, synaptic transmission, memory generation, and nerve regeneration in the fields of neurosciences. It is suggested that each brain region or each neural cell type may contain a specific and characteristic set of gangliosides. We have investigated the immunocytochemical localization of several classes of gangliosides that include GM1, GM4, GD3, and GQ gangliosides on the cell surface of various cell types found in human neural cell cultures with antibodies specific for these gangliosides. Cell cultures were obtained from adult human brains and fetal human dorsal root ganglia and spinal cord and cultured in vitro for the period up to 6 months and utilized for the ganglioside immunocytochemistry. It was demonstrated that GM1 ganglioside was present in all galactocerebroside-positive oligodendrocytes and most of glial fibrillary acid protein (GFAP)-positive astrocytes (80%), most of neurofilament-positive neurons (80%), 50-70% of Schwann cells, and 5-10% of fibronectin-positive fibroblasts; GM4 ganglioside could be detected in all oligodendrocytes, 80% of astrocytes, and 50% of Schwann cells, while no staining was found in neurons or fibroblasts; GD3 ganglioside was present in all oligodendrocytes and 5-10% of astrocytes but not in neurons, Schwann cells, or fibroblasts; and all of fetal CNS neurons and approximately 80-90% of fetal dorsal root ganglia (DRG) neurons and a small percentage of astrocytes (10-20% in fetal and less than 1% in adult astrocytes) was labeled by A2B5 antibody which is specific for GQ ganglioside, while this antibody did not stain cell surface of oligodendrocytes, Schwann cells, or fibroblasts. Three classes of gangliosides, GM1, GM4, and GD3 were found to be definite components of fetal and adult human oligodendroglial plasma membrane, while GM1 and GM4 gangliosides were detected on the surface of most astrocytes. Only a minor population of astrocytes from both fetal and adult human CNS contained GD3 and GQ gangliosides. Two classes of gangliosides, GM1 and GQ, were detected on the surface of fetal human neurons. More than half of fetal Schwann cells reacted to GM1 and GM4 antibodies but did not to GD3 or GQ antibodies. We recognized the presence of a specific and characteristic set of gangliosides on the cell surface of different human neural cell types and these findings should facilitate further investigation of the precise biological activity of these gangliosides.     

Neuritogenic and metabolic effects of individual gangliosides and their interaction with nerve growth factor in cultures of neuroblastoma and pheochromocytoma

The 4 major ganglioside species, GM1, GD1a, GD1b and GT1b (200 micrograms/ml), were tested individually for the ability to stimulate neuronal trophic responses. The growth parameters measured were: morphologic changes, quantitated by computer-assisted morphometry of neurite length and number per soma, and metabolic changes, indicated by alterations in ornithine decarboxylase activity (ODC). In addition, the interaction of each ganglioside with nerve growth factor (NGF) was investigated with an NGF-responsive pheochromocytoma PC12 cell line and NGF-insensitive neuroblastoma Neuro-2a cultures. PC12 cells responded to gangliosides only in the presence of NGF (20 micrograms/ml): GM1 produced the greatest morphologic response, but did not alter metabolic levels; GT1b increased both parameters. The presence (5 micrograms/ml) or absence of NGF did not have an effect on the ganglioside-mediated morphologic responses of Neuro-2a cells to each species: GD1b elicited the greatest increase in neurite length, while GD1a and GT1b stimulated both length and number. In contrast, while GT1b alone was able to elevate ODC activity independently of NGF, the simultaneous exposure of Neuro-2a cultures to NGF and GM1 or GD1a resulted in a stimulation of cellular metabolism. These results indicate that each ganglioside species has a specific target action in the stimulation of different trophic responses and that performance in one category is not a predictor of the result in another. In addition, it is possible to confer a sensitivity to NGF by simultaneous treatment with specific gangliosides. This indicates that membrane gangliosides may modulate the actions of neurotrophic factors.     

Protection of neuro-2a cells against calcium ionophore cytotoxicity by gangliosides.

Gangliosides are known to assert both neuritogenic and neuroprotective effects when applied to a variety of neuroblastoma and primary neuronal cultures. We have developed a model employing Neuro-2a neuroblastoma cells with Ca2+ ionophore A23187 as neurotoxic agent causing neurite retraction and eventual cell death. Gangliosides attenuated the toxicity of this substance, increasing both cell survival and neurite stability. In one series of experiments, cells were exposed to A23187 for 24 hr and then incubated in fresh medium (washout) for 18 hr; gangliosides were present at varying times. The paradigm in which cells were only preincubated (2 hr) with ganglioside provided no benefit, nor did incubation of the cells in both ionophore and ganglioside during the 24-hr exposure period. Significant protection was achieved by exposing the cells to ganglioside after washout of A23187, or continuously throughout the whole period. Bovine brain ganglioside mixture and the four major components (GM1, GD1a, GD1b, GT1b) applied individually were all effective. By contrast, GM3 and GM1-alcohol, a neutral derivative of GM1, provided little or no protection. Dichlorobenzamil, an inhibitor of the Na(+)-Ca2+ exchanger, tended to block the neurite stabilizing effect of gangliosides, suggesting that the mechanism might involve potentiation of this antiporter.     

Influence of monensin on ganglioside anabolism and neurite stability in cultured chick neurons

We have examined the effects of monensin, a monovalent cationophore that disrupts exo- and endocytosis of membrane vesicles and diminishes Golgi anabolic function, on the incorporation of [3H]-galactose into glycosphingolipids in neurited primary cultures of chick embryo central nervous system neurons. A linear rate of incorporation into all ganglioside species from extracellular-labeled galactose was observed. Specific activity of anabolic labeling was markedly lower in GT1b and GQ1b than in the other major gangliosides of the embryonic neuron (GM3, GD3; GM2, GD2; GM1, GD1a, GD1b). With 100 nM monensin in the extracellular medium, the rate of labeling of GT1b diminished markedly to 20% of control; GD1a, GD1b, and GD2, to 35%; GQ1B to 48%; GD3 to 60%. Vigorous incorporation of label into GM3 was entirely undiminished by monensin. From these findings, it is suggested that ganglioside biosynthesis is compartmentalized in the cytodifferentiating embryonic neuron, with GM3 entirely, and GD3 and GQ1b partially, an extra-Golgi product. Extensive loss of neurites that occurred after several hours of exposure of the neurons to monensin could not be correlated directly with decreased ganglioside anabolism.     

Ganglioside metabolism in the hippocampus after septal lesion in rats

The changes in ganglioside composition and metabolism of deafferentiated rat hippocampus were estimated after septal lesion. A significant decrease in total ganglioside concentration was found 7 days after the lesion. The reduced level of total gangliosides persisted at 17 and 25 days. Relative increase in the proportion of GD1b and GX (O-acetylated GT1b) and decrease in GM1 were found in hippocampus only at 25 days post-lesion. The incorporation of 3H-N-acetylmannoseamine into gangliosides was examined in rats whose hippocampi were lesioned 25 days prior to radioprecursor injection. Differences in the labeling pattern of total and individual gangliosides were found. Increases in the label in GM1, GD3, and GD1a and decreases in GT1b and GQ1b were found 10 hr after isotope injection. However, decreases in the specific activity of all gangliosides except GT1b and GQ1b were observed 24 hr after 3H-N-acetylomannosamine injection, suggesting the activated turnover of gangliosides in postlesioned hippocampus. The significance of these changes has been discussed in terms of cellular damage and repair in the hippocampal tissue.