Ganglioside and neurotrophic growth factor interactions in retinal neuronal and glial cells

Ganglioside (GG) and neurotrophic growth factor (GF) interactions in retinal neuronal and glial cells have been very little studied. Rat retinas were mechanically separated into outer (photoreceptor or PR) and inner (other neurons, IR) halves by planar vibratome sectioning and retinal Müller glial (RMG) cells were isolated and cultured according to previously published methods. The distribution on a percent molar basis of individual GG was different between the two halves: PR were dominated by GD3 (48% total GG) and contained only trace amounts (< 4%) of complex species (GT1b, GQ); IR was more typical of mature brain tissue, exhibiting substantial amounts (approximately 25%) of more complex GG. The GG profile of RMG cells was also simple, dominated by GM3 (60%) and GD1a (20%). A single addition to the medium of 500 pM bFGF or EGF for 48 hr to cultured RMG cells led to significant increases in total GG levels of 30-40%. Such treatments by both growth factors induced increases in GM3, whereas longer exposure (96 hr) of confluent RMG to these factors additionally stimulated synthesis of more complex GG. Incubations of RMG with [3H]-glucosamine showed that GG synthesis was 2-fold stimulated by growth factors. We also tested the effect of GM3 on one of the bFGF receptor transduction pathways, namely PI-3 kinase activation. To our knowledge these data constitute the first demonstration of neurotrophic factor stimulation of GG levels in cells of CNS in vitro. Such complex interactions may have particularly important consequences for neural physiopathology.

Survival and regeneration of adult human and other mammalian photoreceptors in culture

PURPOSE

Fully mature neurons of central nervous system origin generally are considered unable to survive for extended periods of time in simple culture conditions. The authors report that adult and aged human, porcine, and rodent retinal neurons, including rod and cone photoreceptors, constitute an exception to this idea.

METHODS

Cells were dissociated from human postmortem retinas, adult mammalian retinas, and selected brain regions and were seeded into tissue culture plates and left to develop as monolayer cultures for up to 2 months. A battery of antibody markers was used to identify the nature and morphology of the cells in vitro.

RESULTS

Photoreceptor cell survival of rods and cones was observed routinely when the delay between the time of death until culture preparation was 50 hours or less, compatible with current eye bank practice. Two-week-old cultures were formed of rod photoreceptors, representing approximately 50% of neuronal cell types; cone photoreceptors, representing 5% to 30% of neuronal cell types; other retinal neurons (especially amacrine cells approximately 20%); and retinal glial cells, present in variable numbers. Glial cells were essential for long-term photoreceptor survival and neurite outgrowth. Adult mammalian brain neurons isolated under the same conditions did not survive.

CONCLUSIONS

Fully adult human and other mammalian retinal neurons, including photoreceptors, exhibit remarkable plasticity in vitro, and such monolayer models may have applications in physiological, pharmacologic, and toxicologic studies of human and other mammalian retina.

Ganglioside effects on basic fibroblast and epidermal growth factor receptors in retinal glial cells

Gangliosides have long been implicated in cell growth regulation and play an important role as modulators in protein phosphorylation. In order to better understand how glycosphingolipids and growth factors interact, we examined the modulation of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) effects on retinal Müller glial cells (RMG), following modification of their GG composition. Treatment of MG cells with GG (GM1, GT1b) and asialoGM1 resulted in modifications of several aspects of cellular responses to EGF- and FGF-receptor (R) activation: mitogenesis, cell migration, tyrosine phosphorylation of the EGF-R and FGF-R and even their cellular substrates were particularly influenced by GG. Indeed GG caused modifications of EGF-R and FGF-R autophosphorylation kinetics. GG long term effects (mitogenesis and migration) correlate with short term effects (tyrosine phosphorylation) and differences in receptor tyrosine kinase signalling could explain the specificity in growth factor responses.

Differential modulation of basic fibroblast and epidermal growth factor receptor activation by ganglioside GM3 in cultured retinal Müller glia

Polypeptide growth factors and membrane-bound gangliosides are involved in cell signaling, including that observed in cells of neural origin. To analyze possible interactions between these two systems, we investigated the modulation of short- and long-term responses to basic fibroblast and epidermal growth factor (bFGF and EGF, respectively) in cultured retinal Müller glial cells following experimental modification of their ganglioside composition. These glial cells readily incorporated exogenously administered GM3 ganglioside, which was not substantially metabolized within 24 h. Such treatments significantly inhibited bFGF-induced DNA replication and cell migration, while having much less effect on analogous EGF-mediated behaviors. To explore GM3/growth factor interactions further, different aspects of glial metabolism in response to bFGF or EGF stimulation were examined: membrane fluidity, growth factor binding, global and individual changes in growth factor-induced phosphotyrosine levels, and growth factor-induced activation of mitogen-activated protein kinase. GM3 reduced the intensity of immunocytochemical labeling of phosphotyrosine-containing proteins within bFGF-stimulated cells and down-regulated FGF receptor activation and tyrosine phosphorylation of its cellular substrates, whereas similar parameters in EGF-stimulated cells were much less affected. Hence the data reveal a complex relationship in normal neural cells between polypeptide growth factors and membrane-bound gangliosides, which may participate in retinal cellular physiology in vivo.

Stimulation of endogenous ganglioside metabolism by neurotrophic growth factors in cultured retinal Müller glia

Neurotrophic factors such as basic fibroblast and epidermal factor (bFGF and EGF respectively) are known to influence many differentiative processes, but their effects on an important group of glycosylated signalling molecules involved in neural differentiation, the gangliosides, are unknown. To study this possibility, we analyzed the effects of exogenously added bFGF and EGF upon the amount and type of endogenous gangliosides extracted from purified cultures of retinal Müller glial cells. A single addition of 500 pM bFGF or EGF for 48 h to such cultures led to significant increases in total ganglioside levels of 30-40%. Analysis of the distribution of specific ganglioside species within control and growth factor treated cells revealed that the precursor form GM3 formed 50-60% of the total ganglioside pool in all cases, the remainder being composed principally of GD1a (20%) with no detectable tri-sialogangliosides. Growth factor treatment for 48 h led to increases mainly in GM3, whereas longer exposure (96 h) of confluent glial cultures to growth factors additionally stimulated synthesis of GT1b. Furthermore, growth factor-induced ganglioside increases were dose-dependent, reaching maximal stimulation at 500 pM for bFGF. Incorporation of radiolabelled [3H]-glucosamine into glial cultures showed that ganglioside synthesis was stimulated 2-fold by the growth factors. To our knowledge these data constitute the first demonstration of neurotrophic factor stimulation of ganglioside levels in cells of central nervous system origin. Such complex interactions between peptide growth factors and gangliosides, if occurring in vivo, could have important consequences for retinal cell behaviour.

[Retinal grafts: biological problems and clinical stakes]

Retinal transplantation, formerly perceived as unrealistic, has become over the past decade a major clinical and biological undertaking in several laboratories and eye clinics. We describe the insights gained through the pioneering experimental works of Del Cerro et al, Turner et al, Gouras et al, Aramant et al, Lund et al e.g. the survival of transplants, the lack of immune response to photoreceptors, their integration and expression of neuronal markers, but also the dysplastic arrangement into rosettes and the lack of a definitive proof for functionality. Our laboratory has undertaken to establish the trophic and synaptic functions of sheets of photoreceptors transplanted, as described by Silverman et al, in the subretinal space of mutant rd mice carrying a retinal degeneration similar to human retinitis pigmentosa. Clinical applications to this condition as well as in cases of end-stage age related macular degeneration are discussed.

Simplified ganglioside composition of photoreceptors compared to other retinal neurons

PURPOSE

The quantitative and qualitative ganglioside composition of retinal photoreceptor cells is unknown. The aim of this study was to analyze the lipid, especially ganglioside, make-up of photoreceptors compared to other retinal cells.

METHODS

Retinas from adult normal rats were mechanically separated into outer (photoreceptors) and inner (other retinal neurons and glia) halves be planar vibratome sectioning. Total lipids were extracted, and each fraction (neural, phospholipids, and glycosphingolipids) was eluted sequentially by column chromatography and quantitated through high-performance thin layer chromatogram analysis. Similar analyses were performed on entire retinas from adult normal rats, adult dystrophic rats lacking photoreceptors (RCS-rdy-p+ strain), and isolated photoreceptor outer segments.

RESULTS

Whereas phospholipids were distributed equally between the two halves, inner retina contained significantly more cholesterol (68% total) and gangliosides (74% total) than outer retina on a unit protein basis. The distribution on a percent molar basis of specific gangliosides also was significantly different between the two halves: Outer retina was dominated by GD3 (45% total ganglioside) and contained only trace amounts (<4%) of complex species (GT1b and GQ1b); inner retina was more typical of mature brain tissue exhibiting substantial amounts (approximately 25%) of more complex species. These data were supported by lipid compositional analyses of mutant photoreceptor-less retina. However, isolated outer segments resembled whole retina in containing higher levels of complex gangliosides.

CONCLUSIONS

These data indicate that, compared to other central nervous system-derived neurons, photoreceptor cell body membranes exhibit a highly unusual simplified ganglioside composition. Such an unusual neuronal lipid composition may reflect structural adaptations to their specialized function.

Monosialoganglioside GM1 reduces ischemia--reperfusion-induced injury in the rat retina

PURPOSE

Gangliosides are normal components of cell membranes, contribute to structural rigidity and membrane function, and have been shown to protect against various insults to the brain. This study evaluates the effect of exogenously administered monosialoganglioside GM1 on retinal damage induced by transient retinal ischemia and reperfusion.

METHODS

Retinal ischemia was induced unilaterally in Long Evans rats by increasing intraocular pressure to 160 mm Hg for 60 minutes. GM1 (30 mg/kg, intraperitoneally) or buffer controls were administered at 48 hours, and 15 minutes before ischemia, and survival time after ischemia was either 8 or 15 days. The degree of retinal damage was assessed by histopathologic study according to Hughes' quantification of ischemic damage.

RESULTS

Retinal ischemia led to significant reductions in thickness and cell number, principally in the inner retinal layers (30% to 80%), and to a lesser extent in the outer retinal layers (18% to 42%). Pretreatment with intraperitoneally injected monosialoganglioside GM1 conferred significant protection against retinal ischemic damage either 8 or 15 days after ischemic survival time. After 8 days reperfusion, the ischemic-induced loss in overall retinal thickness was reduced by 70%, and those of the inner nuclear and plexiform layers were reduced by 77% and 44%, respectively. Ischemic-induced ganglion cell, inner nuclear, and outer nuclear layer cell density losses were reduced by 45%, 40%, and 57%, respectively. After 15 days of reperfusion, approximately the same statistically significant differences could be observed in comparison with the 15-day ischemic--reperfusion group.

CONCLUSIONS

Monosialoganglioside GM1 protects the rat retina from pressure-induced ischemic injury when administered intraperitoneally 2 days before insult. This protection afforded by GM1 can be observed even after 8 days or 15 days of reperfusion.

Molecular species analysis of 1,2-diglycerides on phorbol ester stimulation of LA-N-1 neuroblastoma cells during proliferation and differentiation

1,2-Diacyl-sn-glycerol (DAG) is a product of cell activation that has emerged as an important intracellular messenger whose primary function appears to be the activation of protein kinase C. They originate by the activation of phospholipases, which hydrolyze different phospholipids depending on the external stimulus and the nature of the cells, leading to the production of different molecular species. In the present study the quantitative changes in the total mass and the molecular species of DAG formed on phorbol ester (12-O-tetradecanoyl-phorbol 13-acetate) stimulation were investigated in proliferating and retinoic acid (RA)-differentiated human LA-N-1 cells. The TPA treatment of both cell types elicited an increase in the total amount of DAG. The increase was biphasic; i.e., an initial peak at 2-5 min was followed by a sustained increase that persisted for > 30 min. The analysis of the molecular species of DAG and phospholipids showed that in proliferating LA-N-1 cells, the DAG increase corresponds to the production of mainly saturated/monounsaturated (16:0-18:1, 18:0-18:1) and saturated/saturated (16:0-16:0, 16:0-18:0) species, suggesting that they originate essentially from the hydrolysis of phosphatidylcholine. In contrast, RA-differentiated cells responded to TPA treatment by increasing the level of saturated/polyunsaturated (16:1-22:6, 18:0-22:6, 16:0-20:4, 18:0-20:4) and monounsaturated/monounsaturated (18:1-18:1) species, suggesting mainly a phosphatidylethanolamine origin. These findings indicate that the treatment of LA-N-1 cells with TPA generates different molecular species of DAG depending on their physiological state. These observations suggest in turn that different phospholipases are activated by TPA in proliferating and RA-differentiated cells.

Management of breast cancer in the elderly

This paper examines data which has been published on breast cancer in the elderly and concludes that, wherever possible, combined modality treatment should be offered to elderly breast cancer patients. It appears from an examination of the literature that single modality treatment in the form of hormone treatment often results in very high rates of loco-regional recurrence.

Breast cancer in elderly women: a retrospective analysis of combined treatment with tamoxifen and once-weekly irradiation

PURPOSE

To evaluate retrospectively the efficacy of combined modality treatment (hormone therapy and hypofractionated radiotherapy) in a population of very elderly women with breast cancer.

METHODS AND MATERIALS

Records on 70 patients of median age 81 years, treated between January 1988 and February 1994, whose median follow-up is now 36 months, have been evaluated. Information obtained included clinical stage at diagnosis, histology, tumor grading, hormone receptor levels, details of treatment, type of failure, survival data, and status at last follow-up examination. Treatment consisted of Tamoxifen 20 mg daily and a hypofractionated course of high dose-per-fraction once-weekly radiotherapy. In the majority of cases this consisted of seven exposures of 6.5 Gy (five to the involved breast, and two to the tumor bed) given over 6 weeks, on a 60Co unit. Nodes were treated when clinically involved, to a dose of 27.5-30 Gy in five to six fractions.

RESULTS

At median follow-up of 36 months, the overall survival rate is 87% [confidence interval (CI) 78-95%], the disease specific survival rate is 88% (CI 80-96%), and 72% (CI 60-84%) of patients are free of disease. The local control rate at 36 months is 86% (CI 76-95%). When analyzed by T stage, 81% of T1 patients, 96% of T2 patients, 60% of T3 patients and, paradoxically 100% of T4 patients were in local control at 36 months, although at that point there were just four such patients available for consideration in the T4 group. Initial response to hormone therapy does not appear to be a predictive indicator for ultimate loco-regional control. There is a trend towards greater probability of loco-regional failure if total dose delivered to the breast is less than 35 Gy.

CONCLUSIONS

Women of elderly age are often denied combined modality therapy, because of coexistant disease or fears held by the responsible physicians that elderly patients are unable to tolerate surgery or protracted courses of radiotherapy. Consequently, many are treated by tamoxifen alone with poor results. This study demonstrates that very high rates of loco-regional control are achievable using hormonal treatment combined with high dose-per-fraction once-weekly radiotherapy.

Survival and regeneration of adult human photoreceptors in vitro

Adult human retina from enucleated ocular tissue was enzymatically dissociated and plated into plastic dishes for cell culture in serum-supplemented medium. Within a few days following seeding, islands of glial-like cells with rounded neurons growing on top of them were visible. Immunocytochemical labelling of these cultures revealed that virtually all the surviving neurons (> 98%) were rod photoreceptors, and that they extended long neurites across the glial cell surface. Hence, adult human photoreceptors retain a remarkable capacity for survival and regrowth, and such preparations may be of value for physiopathological and retinal grafting studies.

The conversion of ethanolamine and of its metabolites to choline in human neuroblastoma clones: effect of differentiation induced by retinoic acid

The sequential methylation of ethanolamine (Etn) or phosphorylethanolamine to the corresponding choline (Cho) derivatives was studied in both undifferentiated and retinoic acid (RA) differentiated human neuroblastoma clones LA-N-1 and LA-N-2. Conversion of Etn derivatives to the respective Cho metabolites was low in both cell types. However, after treatment of the cultures with ethanol or RA, the methylation of phosphoryl-Etn was stimulated while that of phosphatidyl-Etn was severely reduced in both cholinergic LA-N-2 and catecholaminergic LA-N-1 cells.

Incorporation of [3H]ethanolamine into acetylcholine by a human cholinergic neuroblastoma clone

Human neuroblastoma cholinergic LA-N-2 cells were used as an experimental model to test the possibility that the methylation of phosphoethanolamine (PEtn) to phosphocholine (PCho) and free choline (Cho) (Andriamampandry et al. 1989) could contribute to acetylcholine (AcCho) synthesis. LA-N-2 cells were incubated with [3H]Cho for 90 min and 22.7% of the radioactivity was present in PCho, 18.5% in free Cho and 4.8% as AcCho. The ratio of Cho/AcCho, however, was of about 1 after 16 hours of incubation. The incorporation of 10 microM [3H]ethanolamine (Etn) into MeEtn, PMeEtn, PMe2Etn and their corresponding phospholipids was reduced in cells incubated in medium containing 7.2 microM choline as compared to cells incubated in medium devoid of choline indicating that the lack of Cho from the incubation medium stimulated the conversion of PEtn to Cho water soluble derivatives. Incubation of LA-N-2 cells with [3H]Etn led to the labelling of [3H]AcCho. Cultures incubated in parallel with [3H]Cho showed that roughly 10% of [3H]AcCho obtained after 16 hrs of incubation with the Cho label derived from [3H]Etn. The synthesis of Cho and AcCho from Etn may be enhanced after cellular differentiation induced by the growth of the cells in the presence of retinoic acid (RA). The results indicate that the methylation of [3H]Etn and/or of [3H]PEtn may be used by cholinergic neurons as precursor for AcCho.

Molecular species of choline and ethanolamine glycerophospholipids in rat brain myelin during development

The composition of the molecular species of various phospholipid subclasses was examined in myelin isolated from brain of 15-, 21- and 90-day-old rats. The molecular species of diacylglycerophosphocholine (PtdCho), diacylglycerophosphoethanolamine (PtdEtn) and plasmenyl-ethanolamine (PlsEtn) were quantified by high-performance liquid chromatography (HPLC) after phospholipase C treatment and dinitrobenzoyl derivatization. In rat brain myelin, each phospholipid subclass showed a specific pattern of molecular species that changed during development. PtdCho contained large amounts of saturated/monounsaturated and disaturated species and low amounts of saturated/polyunsaturated species. During brain development, the levels of saturated/monounsaturated molecular species increased whereas those of the disaturated and saturated/polyunsaturated species decreased. PtdEtn were characterized by their low levels of disaturated species and a high content of saturated/monounsaturated and saturated/polyunsaturated species, of which those containing fatty acids of the n-3 series decreased, whereas those containing fatty acids of the n-6 series did not change during brain development. The levels of saturated/monounsaturated species increased in PtdEtn. No disaturated molecular species could be detected in PlsEtn. This alkenylacyl subclass contained large amounts of saturated/polyunsaturated, saturated/monounsaturated and dimonounsaturated molecular species. During development, the levels of saturated/polyunsaturated molecular species decreased while those of the two others increased. The data indicated that myelin sheaths undergo phospholipid changes during brain development and maturation.

Comparison of different lipid substrates on intestinal adaptation in the rat

The relative effects of medium chain (MCT) and long chain triglycerides (LCT) on intestinal morphology and functions were compared. Adult rats received intragastrically for 10 days an isoenergetic mixture containing either 50% MCT/50% LCT or 100% LCT. The other constituents of the diets were identical, and animals fed a standard diet orally were used as a reference group. Animals who were given the MCT/LCT diet showed a higher mucosal mass and protein content and increased villus length and crypt depth in the proximal part of the small intestine compared with the LCT and control diet groups. Administration of [3H] thymidine 12 hours before death resulted in a significant increase in the incorporation of the precursor into cellular DNA in the jejunum of rats given MCT. In rats given LCT as the only fat, the free fatty acid content of the microvillus membrane showed a 20 fold increase and at the same time there was a significant drop in the cholesterol content and in the cholesterol/protein ratio. Differences in the lipid composition of enterol diet or in the microvillus membrane did not effect adversely membrane bound hydrolase activities. These findings suggest that MCT in the diet confers advantages in addition to the provision of rapidly available energy.

In vitro and in vivo ethanolamine metabolism in rat brain: effect of time and aging

The effect of the time in culture of foetal rat neurons and age on the incorporation of radioactive ethanolamine into methylated derivatives was investigated. Decreased incorporation of [3H]ethanolamine into its various methylated water-soluble and lipidic derivatives was observed in rat neurons cultures at 12 day in vitro (DIV) as compared to the 3rd and the 7th DIV. In vivo studies showed that there was a diminished labeling of methylated products in the older animals as compared to the younger ones. These in vitro and in vivo observations suggest a generalized decrease of N-methyltransferase activities during maturation and aging.

Exogenous gangliosides modulate calcium fluxes in cultured neuronal cells

Previous work from this and other laboratories has shown that the neuritogenic effect due to exogenous gangliosides on primary neurons in culture is accompanied by several morphological and biochemical modifications. The present results indicate that the treatment of these neurons with gangliosides, under the experimental conditions which are known to produce a sprouting effect, inhibited the influx of 45Ca2+ and increased the release of 45Ca2+ from the cells. No significant differences were noted using concentrations of gangliosides (10(-8)-10(-5) M) either below or above the critical micellar concentrations. No apparent specificity was observed among various species of individual sialocompounds (GM1, GD1a). Moreover the presence or absence of fetal calf serum in the culture medium influenced the levels of 45Ca2+ fluxes. This study confirms the hypothesis that gangliosides may be considered as Ca2+ flux modulators in neuronal cells.

Stimulation of mono- and diacylglycerol lipase activities by gangliosides in chicken neuronal cultures

Chicken neurons in culture display measurable activities of mono- and diacylglycerol lipases. Treatment of chicken neuronal cultures with gangliosides (10(-8)M to 10(-5)M) resulted in a time and dose dependent increase in monoacylglycerol lipase activity. The diacylglycerol lipase showed significant increase in specific activity before that of monoacylglycerol lipase. The increase was observed only up to 24 hours and no differences between diacylglycerol lipase activity of control and ganglioside treated cells were observed after 48 hours. The data indicate that the treatment of neurons with exogenous gangliosides affect the diglyceride metabolism in stimulating not only the enzymes catalyzing their production but also those involved in their catabolism.

Effect of monomethylethanolamine, dimethylethanolamine, gangliosides, isoproterenol, and 2-hydroxyethylhydrazine on the conversion of ethanolamine to methylated products by cultured chick brain neurons

The sequential methylation of ethanolamine and its phosphorylated derivatives has been studied with chick neurons in culture in the presence of several pharmacological agents. Incubation with [3H]ethanolamine in the presence of monomethylethanolamine and dimethylethanolamine indicated that in these neurons the preferential conversion to choline-containing compounds is via the methylation of phosphorylethanolamine. The possibility that there are two separate enzymes, i.e., one responsible for the methylation of water-soluble ethanolamine-containing compounds and another for the ethanolamine phospholipids, was examined with agents believed to influence these conversions. Incubation of neurons in the presence of a mixture of exogenous gangliosides at 10(-8) M and 10(-5) M concentrations showed that these neuritogenic compounds stimulate the methylation of phosphatidylethanolamine and decrease that of phosphorylethanolamine. The inhibitor of phosphatidylethanolamine methyltransferase (EC 2.1.1.17), 2-hydroxyethylhydrazine, decreased the conversion of phosphatidylethanolamine to phosphatidylcholine and increased that of phosphorylethanolamine to phosphorylcholine. The possible effects of adrenergic stimulation were studied by the incubation of neurons with isoproterenol at 10(-6) M and 10(-5) M concentrations. There was a reduction of phosphorylethanolamine methylation and a stimulation of that of phosphatidylethanolamine, and these effects were counteracted by the presence of 5 x 10(-5) M propranolol.

Exogenous gangliosides may affect methylation mechanisms in neuronal cell cultures

Primary neurons in culture from chick embryo cerebral hemispheres were treated with a mixture of gangliosides added to the growth medium (final concentration: 10(-5)M and 10(-8)M) from the 3rd to the 6th day in vitro. Under these conditions methylation processes measured with [3H] and [35S] methionine and [3H]ethanolamine as precursors showed an increased methylation of [3H]ethanolamine containing phospholipids, a correspondent increased conversion of these compounds to [3H]choline containing phospholipids, and a general increased methylation of trichloroacetic acid precipitable macromolecules containing labeled methionine. A small increase in protein synthesis was observed after incubation of neurons with [3H]- and [35S]methionine. This was confirmed after electrophoretic separation of a protein extract with increased 3H- and 35S-labeling in protein bands with moecular weights between 50 and 60 KDaltons. A protein band of about 55 KDaltons appeared to be preferentially labelled when [3H] methionine was the precursor. The treatment with gangliosides increased the incorporation of [methyl-3H] label after incubation of neurons with [3H] methionine, into total DNA and decreased that of total RNA. The treatment of neurons in culture with exogenous gangliosides hence affects differently methylation processes, a finding which may confirm the involvement of gangliosides on the intracellular mediation of neuronal information mechanisms.

Molecular species of choline and ethanolamine phospholipids in rat cerebellum during development

The molecular species composition of rat cerebellar phospholipid subclasses has been studied by HPLC after phospholipase C treatment and dinitrophenyl derivatization. During rat cerebellum development (3-90 days postpartum), cholinephosphoglycerides and ethanolamine phosphoglycerides represented approximately 80% of all phospholipids, with their relative amount changing after 1 month. Among ethanolamine phosphoglycerides, the molar ratio of diacylglycerophosphoethanolamine (diacylGPE) to alkenylacylGPE decreased from approximately 1.4 at 3 days to approximately 0.5 after 10 days. The phospholipids investigated contained up to 12 different molecular species. The rate of accumulation of the various molecular species of diacylglycerophosphocholine (diacylGPC), diacylGPE, and alkenylacylGPE during cerebellar development allowed a classification into three main groups. The overall increase of the molecular species of the first group (6-diacylGPC, 5-diacylGPE, and 4-alkenylacylGPE) was approximately 18-fold between 3 and 90 days, with a faster rate of accumulation between 3 and 30 days. Those of the second group (3-diacylGPC, 5-diacylGPE, and 5-akenylacylGPE) increased by approximately 45-fold during the same developmental period, at a slow rate before day 15 and a faster one thereafter. The molecular species of the third group (3-alkenylacylGPE) increased by greater than 250-fold between 3 and 90 days, at a very slow rate before day 21 and more quickly thereafter. The different rates of accumulation of the components of the three groups during cerebellar development suggest a preferential location of the first group in membranes of neuronal perikaryons, glial cells, and synaptosomal structures. Those of the second group appear to be located in both synaptosomal membranes and myelin sheets, and those of the third group can be considered as myelin markers.

Effects of phospholipases, proteases and neuraminidase on gamma-hydroxybutyrate binding sites

gamma-Hydroxybutyric acid (GHB) is a natural compound of mammalian brain synthesized from GABA. The characteristics of its synthesis, transport, release, distribution and turnover, in addition to the presence of a high affinity binding site for this substance in brain are in favor of a modulator role for GHB. The effects of hydrolytic enzymes on the specific binding capacity of GHB have been studied in the present work. Phospholipases A2 and C, neuraminidase and Pronase markedly decrease GHB binding to crude synaptosomal membranes from rat brain. This effect is time and enzyme concentration dependent. Trypsin, under the conditions employed, is less active. The inhibitory effects of phospholipases is correlated with phospholipid hydrolysis. Lysophospholipids, in the absence of bovine fatty acid free serum albumin partially inhibit GHB binding. The action of neuraminidase has been followed by sialic acid release and modifications of the ganglioside profile. The effects of phospholipase C and of neuraminidase are completely different to those on GABA binding sites. These results represent further data concerning the molecular existence of specific GHB binding sites on rat brain membranes.

In vitro synthesis and transbilayer movement of phosphatidylethanolamine molecules labelled with different fatty acids in chick brain microsomes

The transbilayer fatty acid distribution of diacylglycerophosphoethanolamine and the translocation of newly synthesized phosphatidylethanolamine molecules labelled with different fatty acids has been investigated in chick brain microsomes using trinitrobenzensulfonic acid. The determination of the fatty acid composition of diacylglycerophosphoethanolamine in both the outer and the inner leaflet of the microsomal vesicles revealed a similar distribution indicating that both leaflets share the same molecular species. The in vitro incorporation of radioactive fatty acids (16:0, 18:1 and 20:4(n-6] into ethanolamine phospholipids, known to be catalyzed by the lyosphosphatidylethanolamine acyl transferase, showed that the radioactive diacylglycerophosphoethanolamine molecules appeared first in the outer leaflet and were thereafter transferred to the inner leaflet. The apparent rate of translocation of the newly synthesized ethanolamine phospholipid molecules was the highest for those labelled with 16:0 and the lowest for those labelled with 20:4(n-6). The results indicate that the active site of the acyl-CoA:lysophosphatidylethanolamine acyltransferases is located on the outer leaflet of the microsomal vesicles and that the different newly synthesized molecular species of diacylglycerophosphoethanolamine may be translocated from the outer to the inner leaflet at different rates.