Search PubMed⌕ Search

Biomedical subjects

H Rahmann

Publications and source records attributed to H Rahmann.

At least 73 records · Page 4Linked to original sources
PubMed1994

Behavioural and biochemical investigations of the influence of altered gravity on the CNS of aquatic vertebrates during ontogeny.

Quantitative data are presented on the influences of hyper-gravity (3 +/- 1g) and of simulated weightlessness (approximately 0g) during early ontogeny of cichlid fish (Oreochromis mossambicus) and clawed toad (Xenopus laevis, Daudin) demonstrating changes in the swimming behaviour and the brain energy and plasma membrane metabolism. After return to 1g conditions, hyper-g reared fish and toads express the well known "loop-swimming" behaviour. By means of a computer based video analyzing system different types of swimming movements and velocities were quantitatively determined. Analyses of the brain energy and plasma-membrane metabolism of hyper-g fish larvae demonstrated an increase in energy availability (glucose 6Pi dehydrogenase, G-6P-DH), a decrease of cellular energy transformation (creatine kinase activity, CK) but no changes in energy consumptive processes (e.g. ATPases) and cytochrome oxidase activity (Cyt.-Ox). In contrast hypo-g fish larvae showed a slight increase in brain CK activity. In addition, unlike 1g controls, hyper-g fish larvae showed pronounced variations in the composition (=polarity) of sialoglycosphingolipids (=gangliosides), typical constituents of the nerve cell membranes, and a slight increase in the activity of sialidase, the enzyme responsible for ganglioside degradation.

Animals↗
PubMed1994

Activities of five different sialyltransferases in fish and rat brains.

To investigate the role of sialyltransferases in the metabolism of brain gangliosides, we examined activities of five different sialyltransferases (GM3-, GD3-, GT3-, GD1a-, and GT1a-synthase) using total membrane preparations from cichlid fish and Sprague-Dawley rat brains, and analyzed the relationship between the enzyme activities and the ganglioside compositions. The patterns of sialyltransferase activities in fish and rat brains differed from each other. In fish brain, the GM3-synthase activity was lower than GD3-synthase activity, whereas the opposite relationship was observed in rat brain. The GT3-synthase reaction with fish brain membranes produced radiolabeled GM3, GD3, and a ganglioside that was identified as GT3 based on mobility on TLC using two different solvent systems. No GT3-synthase activity was detected in rat brain. The GD1a- and GT1a-synthase activities in fish brain were higher than those in rat brain. Although GT1a was a single radiolabeled ganglioside in fish GT1a-synthase reaction, this ganglioside could not be detected in rat brain. The ratios of GM3-, GD3-, GT3-, GD1a-, and GT1a-synthase activities in fish and rat brain were 23:31:4:28:14 and 61:21:0:18:0, respectively. Ganglioside analysis showed that fish brain was enriched with c-series gangliosides including GT3 and polysialo-species, whereas a- and b-series gangliosides were major components in rat brain. These results suggest that the species-specific expression of gangliosides in brain tissues may be regulated, at least in part, at the level of sialyltransferase activities.

Animals↗
PubMed1993

Effects of development and altered gravity conditions on cytochrome oxidase activity in a vestibular nucleus of the larval teleost brain: a quantitative electronmicroscopical study.

The mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fish Oreochromis mossambicus were analyzed at different developmental stages (4, 10, and 35 days post-hatching) and after long-term exposure (8 days) to increased gravity (2-4 g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper-g-exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity-sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons.

Animals↗
PubMed1993

Brain creatine kinase activity during ontogeny of the cichlid fish oreochromis mossambicus and the clawed toad Xenopus laevis, influence of gravity?

The development of creatine kinase (CK) activity was studied in the brain of cichlid fish and clawed toads. The activity of CK in the whole brain of the fish decreases immediately after hatching (stage 6) from values of about 135 nmol substrate cleaved/mg protein/min to a value of about 105 at stage 8 (5 days post hatch at 20 degrees C). With the exception of a significant peak (125 nmol) between stages 9 and 10 (7 and 9 days respectively, post hatch at 20 degrees C) and a small intermediate peak at stages 12 and 13 (about 10 days post hatch at 20 degrees C) a constant level of about 100 nmol cleaved substrate is maintained until maturity. In contrast, CK activity was determined to be 3-fold higher in the whole brain of the clawed toad. With the exception of two significant peaks at stages 47 and 49 (5 and 12 days respectively, post fertilization at 23 degrees C) a value of about 360 nmol was found during larval development and metamorphosis, as well as in the adult brain. In investigating the possible influence of gravity on CK activity during early ontogeny of the brain both animal species were exposed to hyper-gravity (3 +/- 1 g) for 7 days. A significant decrease of total CK activity of 20% was found in the fish brain and of about 5% in the toad.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Variability in brain ganglioside content and composition of endothermic mammals, heterothermic hibernators and ectothermic fishes.

Content and composition of brain gangliosides were compared among endothermic mammals, heterothermic hibernators and ectothermic fishes from habitats with extreme ambient temperatures (tropic vs. antarctic waters). In general the content of brain gangliosides in fishes is significantly lower and exhibits a greater variability than in mammals. The composition of brain gangliosides was investigated using both one- and two-dimensional High Performance Thin Layer Chromatography (HPTLC). Both techniques showed a remarkable increase in the number of individual ganglioside fractions and an additional increase of higher polar fractions in fishes as compared with mammals. The 2D-HPTLC revealed a significant decrease in the relative proportion of alkali-labile gangliosides in the course of evolution from fish to mammals. Moreover this decrease in alkali-lability is correlated with the state of thermal adaptation (antarctic fishes, 53-66%; tropical cichlid fish, 35%). These results provide additional evidence for the notion that the extremely high polarity of brain gangliosides, especially of cold-blooded vertebrates, reflects a very efficient mechanism on the molecular level to keep the neuronal membrane functional under low temperature conditions.

Acclimatization↗
PubMed1993

Influence of seasonal adaptation on the distribution of cytochemically detectable endogenous calcium in synaptic terminals of the optic tectum of crucian carp (Carassius carassius L.).

Crucian carps were seasonally adapted to high (23 degrees C) or low (4 degrees C) temperatures and synaptic regions in the optic tectum were analyzed by means of energy-filtering transmission electron microscopy (EFTEM). The amount of cytochemically detectable endogenous calcium in synaptic clefts was quantified by means of image analysis and the amount of glycogen granules in synaptic regions was assessed. In cold-adapted fish, glycogen is increased, especially in glial cells, while the calcium-containing precipitates are reduced. This is interpreted as a characteristic feature of inactive synapses, in which glycogen accumulates and in which the calcium turnover is slowed down. Short-term thermal stress did not influence the amount of calcium or glycogen.

Acclimatization↗
PubMed1993

Morphogenetic differentiation of the brain of the cichlid fish, Oreochromis mossambicus.

In the present study, the morphogenetic brain differentiation of the cichlid fish, Oreochromis mossambicus, is described using conventional histological methods. Cross sections through the developing brain of fish larvae aged 2, 8, 10, 12 and 20 days post hatch, and of adults, were investigated in order to characterize individual brain regions and nuclei, especially parts of the diencephalon, brainstem and cerebellum during critical phases of early larval development. The above age stages conform to the following developmental (larval) stages: 2 days = stage 7, 8 days = stage 10, 10 days = stage 11, 12 days = stage 12 and 20 days = stage 15. An increasing number of nuclei and a volumetric increase in size of individual brain parts in older fish larvae and in adult fish were registered. In the optic tectum, an extreme lateral extension was found in contrast to an insignificant increase in stratification at this developmental time. In one part of the brainstem, the Area octavolateralis (AOL) of 2-day-old larvae, only a few undifferentiated perikarya were found and in the AOL of 20-day-old animals up to 5 nuclei, versus 7 AOL-nuclei in adult fish brain, could be discriminated. Variations in the position of the Mauthner cell versus the surrounding and corresponding brain nuclei were shown during the ontogenetic development. The results were presented by cartoon portrayals of the relationships between characteristic nuclei and by drawings of specific brain cross sections in different aged larval stages.

Aging↗
PubMed1993

Characteristic and differential calcium signals from cell structures of the root cap detected by energy-filtering electron microscopy (EELS/ESI).

Characteristic calcium signals were analyzed in structures of three cell types of the root cap of cress: statocytes, meristematic cells and secretion cells. Twenty-four hour-old roots were fixed with glutaraldehyde (postfixed with osmiate/potassium bichromate) or with potassium permanganate. No visible precipitates were formed, but calcium signals typical for different cell structures could be detected by means of energy-filtering transmission electron microscopy (EELS/ESI). In statocytes, calcium signals were recorded from the plasma membrane, the membranes of the endoplasmic reticulum, the amyloplast envelope and the mitochondrial membranes. In contrast to the excitable statocytes, the two other, non-excitable cell types, meristematic and secretion cells, exhibited much lower intensities of the calcium signals recorded from the same membrane systems. The revealed characteristic calcium-related properties of the different membrane systems may be related to the special function of statocytes, namely transduction of the gravity stimulus. In all three cell types, additional calcium signals were recorded from cell structures with well known calcium contents, i.e., mitochondrial granules, starch grains and cell walls. For the first time, clear calcium signals were detected from the lipid bodies which are mobilized during the developmental stage of the examined roots. It is supposed that free fatty acids and lipases are the binding sites for calcium. The reliability of the applied method is especially proven by comparison of the electron microscopic images from lipid bodies according to the two different fixation methods. After glutaraldehyde fixation followed by osmiate/potassium bichromate postfixation, the lipid bodies were well fixed and appeared homogeneously grey with homogeneous calcium signals. However, due to potassium permanganate fixation the lipid bodies were only partly fixed; they had an electron-lucid core, from which the lipids are lost during the dehydration procedure, without calcium signals and an electron-dense border zone, which is a reaction product of potassium permanganate with triacylglycerols, with calcium signals.

Calcium↗
PubMed1992

Influence of exogenous gangliosides on the three-dimensional sprouting of goldfish retinal explants in vitro.

To investigate the 3-dimensional outgrowth of ganglion cells of normal and regenerating goldfish retina, retinal explants were cultured in a serum free 3-D fibrin matrix. Daily applications of exogenous gangliosides (GM1), injected either intraocularly (i.o.) or intraperitoneally (i.p.) had no significant effect on the sprouting activity of retinal explants prepared from lesion-activated goldfish whose corresponding optic nerve had been transected. However, in normal, unlesioned animals, a local i.o. injection of GM1 or mixed gangliosides led to a significant enhancement of the basal retinal sprouting activity as compared to controls, which were injected with a 0.9% NaCl solution. This ganglioside related stimulation was maximal after i.o. injection of low concentrations (3 micrograms/eye), didn't occur at high concentrations (30 micrograms/eye) and was similar to the response obtained after i.o. injection of NGF or insulin. I.o. injected phospholipids had no or a slightly inhibitory effect on the sprouting activity as compared to NaCl controls. Daily in vivo i.o. injections of the monoclonal antibody Q211, specifically recognizing c-pathway polysialogangliosides, led to a dose dependent inhibition of the in vitro sprouting of goldfish retina explants. In summary, these data suggest an involvement of gangliosides in the complex process of induction of neuronal sprouting.

Animals↗
PubMed1992

Calcium-ganglioside interactions and synaptic plasticity: effect of calcium on specific ganglioside/peptide (valinomycin, gramicidin A)-complexes in mixed mono- and bilayers.

A controlled exchange of calcium between the extracellular space (mM Ca2+) and the neuroplasm (microM Ca2+) is considered to be an essential prerequisite for almost every stage of neuronal activity. Our research interest is focused on those compounds, which due to their physico-chemical properties and localization within the synaptic membrane might fulfill the task as neuromodulators for functional synaptic proteins. Because of this specific binding properties towards calcium and their peculiar interactions with calcium in model systems gangliosides (amphiphilic sialic acid containing glycosphingolipids) are favorite candidates for a functional involvement in synaptic transmission of information. In this study we used monolayers to investigate the molecular packing and surface potential at the air/water interface, the interaction of gangliosides with the depsipeptide valinomycin (= monovalent ion carrier), and its influenceability by calcium. Furthermore we looked at calcium effects on the single channel conductance and mean channel life-time of the monovalent ion channel gramicidin A in mixed PC/ganglioside bilayers. In pure ganglioside monolayers the addition of 0.01 mM Ca2+ induces monolayer condensation, a rise in collapse pressure (= higher film stability), a shift of phase transition (= change of conformation), and a more negative head group potential (change of electric properties). In mixed ganglioside-valinomycin monolayers the addition of Ca2+ causes phase separation and/or aggregate formation between the ganglioside and the peptide. Single channel conductance fluctuations as well as mean channel life-time were analyzed for gramicidin A incorporated into binary mixed black lipid membranes of negatively charged gangliosides (GM1, GD1a, GT1b, GMix) and neutral lecithin (DOPC) in different molar ratios. At monovalent electrolyte concentrations up to < 250 mM CsCl the single channel conductance was significantly larger in the negatively charged mixed DOPC/ganglioside membranes than in the neutral DOPC membrane. Additionally, in the presence of gangliosides the mean channel life-time is increased. The addition of calcium (0.05 mM) induced a reduction of single channel conductance of gramicidin A in DOPC- and mixed DOPC/ganglioside membranes. These physico-chemical data in connection with new electromicroscopical evidences for a precise localization of calcium, a calcium pump (Ca(2+)-ATPase), a clustered arrangement of gangliosides in synaptic terminals, and biochemical results with regard to activatory nature of exogenous gangliosides for neuronal protein phosphorylation and ATPases, support the hypothesis of a modulatory function of gangliosides in synaptic transmission.

Animals↗
PubMed1992

Gangliosides and neuronal differentiation.

Using the GD3-specific mAb R24 we demonstrate by immunohistochemistry that the first embryonic cells of chicken expressing GD3 represent heavily proliferating cells of mesodermal origin (mesenchymal stem and endothelial cells). At this developmental stage (E1-1.5) neuroectodermal cells of the forming neural tube are not stained by R24 or any other available anti-ganglioside antibodies. These cells of the neural tube start to express GD3 at around E1.5 in parallel with increasing proliferative activity. Likewise proliferating and migrating neuronal crest derivates as well as undifferentiated retinal cells, the forming lens and otic placodes increasingly express GD3 in an organ-specific pattern following the spatiotemporal increase in mitotic activity. Immunostaining of GD1b (mAb D21b) or c-pathway polysialogangliosides (mAb Q211) is not obtained before E2.5, is nervous tissue specific and restricted to "new-born" neurons, which start to migrate and form first neurites. This striking change in ganglioside synthesis and expression also occurs in primary cell cultures (after or without previous Q211-mediated complement kill of neurons) during differentiation of mitotic progenitor cells to neurons (neurogenesis). In cell culture, the fluorescence staining is evenly distributed over the whole neuronal surface including filopodia at the growth cones. Monensin (10(-8) M) prevents expression of GD1b and c-polysialogangliosides and simultaneously differentiation of neuronal morphology (neurogenesis). The presence of exogenous gangliosides from bovine brain leads to a decrease of the monensin effect or even abolishes it.

Animals↗
PubMed1992

Gangliosides and regeneration of the goldfish optic nerve in vivo and in vitro.

One to forty days after optic nerve transection, goldfish received an i.p. injection of [3H]proline (proteins), 3HNAcGluc (gangliosides) or [3H]thymidine (DNA). After 1 or 2 days of incorporation, both optic systems were analyzed by biochemical and autoradiographical procedures. In the regenerating retina an enhanced retinal mitotic activity, protein synthesis (up to 2-fold) and ganglioside synthesis (up to 1.5-fold) was found. Simultaneously, a transiently enhanced accumulation (up to 4.5-fold) of axonally transported protein- and ganglioside-bound radioactivity in the regenerating optic nerve stump occurred. These regeneration-related proliferative and metabolic changes were found to be maximal at 6-8 days post lesion, but still measurable after 40 days. Concerning the endogenous ganglioside metabolism, in the regenerating retina no obvious change in ganglioside synthesis and composition could be observed, while in the regenerating optic nerve there was an enhanced accumulation of the ganglioside GP1c. Daily i.p. application of a ganglioside mixture from bovine brain (GMix) or of the monosialoganglioside GM1, did not alter significantly the degree and time course of the above regeneration induced metabolic changes or the regain of visual acuity. Sprouting activity of goldfish retinal explants was found to strongly depend upon a conditioning lesion of the optic nerve, reaching a maximum 8 days after nerve transection. This result strictly coincided with the profile of metabolic changes observed in vivo. Again, daily i.p. or i.o. injection of exogenous gangliosides did not influence the lesion induced increase of retinal sprouting activity. However, in normal, not regenerating animals, a local i.o. injection of GMix or GM1 led to a significant enhancement of the "basal" sprouting activity, normally occurring after lesion of the retina after injection of 0.9% NaCl. This ganglioside related stimulation was maximal at low concentrations (3 micrograms/eye) and did not occur at high concentrations (> 30 micrograms/eye). Injection of the phospholipid phosphatidylcholine or phosphatidylserine had no or a slightly inhibitory effect, when compared to NaCl controls. These data suggest an involvement of gangliosides in the complex process of induction of axonal sprouting.

Acetylglucosamine↗
PubMed1992

Cell surface distribution of endogenous and effects of exogenous gangliosides on neuronal survival, cell shape and growth in vitro.

In vitro immunostaining of neurons from spinal cord or brain of embryonic chicken by means of monoclonal anti-ganglioside antibodies (Q211, D21b) revealed a fluorescence-labeling of c-polysialogangliosides and GD1b evenly distributed over the entire neuronal surface including filopodia at the growth cones. On electronmicroscopical level the gold-stained ganglioside-antigens were found more or less densely packed in small adjacent areas suggesting a concentration in local "domains". Survival in serum-free or serum-containing medium of embryonic spinal cord motoneurons, which normally died if not cultivated in muscle conditioned medium or in contact to myotubes, was remarkably improved in the presence of a ganglioside mixture (10 microM) from bovine brain. If embryonic neurons from optic lobes were cultivated at low Ca(2+)-concentration (< 20 microM) they developed flat, broad cell bodies with many filopodia and only a few flat-shaped short processes. A very weak cytoskeleton-staining by means of rhodamine-linked phalloidine indicated that polymerization of actin was impaired in these neurons. At the same low Ca(2+)-concentration of < 20 microM but in the presence of ganglioside GM1 (up to 100 microM) most of the neurons developed a "normal" cell shape with rounded perikarya and thin neurites with "normal" shaped growth cones. In this case rhodamine-linked phalloidine revealed a much more intense staining mainly concentrated within the growing tips. The morphology and growth of the ganglioside-treated neurons resembled that of neurons cultivated at a higher Ca(2+)-concentration of at least 600 microM.

Animals↗
PubMed1992

Synaptic plasticity and gravity: ultrastructural, biochemical and physico-chemical fundamentals.

On the basis of quantitative disturbances of the swimming behaviour of aquatic vertebrates ("loop-swimming" in fish and frog larvae) following long-term hyper-g-exposure the question was raised whether or not and to what extent changes in the gravitational vector might influence the CNS at the cellular level. Therefore, by means of histological, histochemical and biochemical analyses the effect of 2-4 x g for 9 days on the gross morphology of the fish brain, and on different neuronal enzymes was investigated. In order to enable a more precise analysis in future-microgravity-experiments of any gravity-related effects on the neuronal synapses within the gravity-perceptive integration centers differentiated electron-microscopical and electronspectroscopical techniques have been developed to accomplish an ultrastructural localization of calcium, a high-affinity Ca2(+)-ATPase, creatine kinase and cytochrome oxidase. In hyper-g animals vs. 1-g controls, a reduction of total brain volume (15%), a decrease in creatine kinase activity (20%), a local increase in cytochrome oxidase activity, but no differences in Ca2+/Mg(2+)-ATPase activities were observed. Ultrastructural peculiarities of synaptic contact formation in gravity-related integration centers (Nucleus magnocellularis) were found. These results are discussed on the basis of a direct effect of hyper-gravity not only on the gravity-sensitive neuronal integration centers but possibly also on the physico-chemical properties of the lipid bilayer of neuronal membranes in general.

Animals↗
PubMed1991

Brain Ca2+/Mg(2+)-ATPase activity and seasonal adaptation of the Djungarian dwarf hamster Phodopus sungorus.

1. Of three sets of Djungarian dwarf hamster, two groups were raised during winter under greatly differing circumstances. One winter group was raised within a climate controlled cage in which the ambient temperature was maintained at 22 degrees C and whereby conditions of light vs darkness were maintained in a constant 12 hr cycle. The second winter group was raised out of doors whereby the hamsters were subjected to prevailing seasonal environmental conditions. A third group was studied under summer conditions, as well. Ca(2+)-, Mg(2+)- and (Ca2+/Mg2+)-ATPase activity was analysed in cellular (= total homogenate) and subcellular fractions (P1-, synaptosomal fraction, synaptic membranes) from cortex, cerebellum and basal brain. 2. The data obtained indicate similar ATPase activity in the cortical homogenates of the winter indoor and summer hamsters. 3. Winter outdoor animals experiencing normal torpidity, however, exhibited reduced ATPase activity by about 50%. 4. Cortical subcellular fractions yielded different results: both the winter and the summer groups showed high ATPase activity in the synaptosomal and synaptic membrane fractions. 5. In the total cerebellar homogenate, the hamsters raised under summer and winter conditions showed the greatest enzyme activity, although less activity was seen in the subcellular fractions. 6. The ATPase activity in the basal brain was found to be nearly identical in all three hamster groups.

Adaptation, Physiological↗
PubMed1991

Evidence for the presence of a specific ganglioside GM1/valinomycin complex in mixed monolayers.

The effect of a negatively charged mono-sialoglyco-sphingolipid (GM1-ganglioside) on the molecular organization and on physiochemical properties of lipid/peptide (valinomycin) systems was investigated in monolayers at the air/water interface. At a high molar fraction of GM1, the surface pressure/area isotherms of the two-component films of the system GM1/valinomycin and the isotherm of the pure ganglioside monolayer are identical concerning the space requirement of the molecules and thereby the packing of the monolayer. Using space-filling molecular models, a simple calculation gives the theoretical amount of 4.5 ganglioside molecules associated with one molecule of the depsipeptide valinomycin. The average surface potential indicates, that valinomycin, interacting with the polar head group of GM1, becomes partly embedded within the lipid interface. For GM1/eicosanol and valinomycin/eicosanol mixtures, the agreement between theory and experimental data strongly supports the model of ideal mixing without any molecular interactions between the different components. The results suggest the formation of a ganglioside/valinomycin complex with simultaneous alteration of the surface potential and molecular structure of the single components.

Air↗
PubMed1991

The application of energy-filtering electron microscopy for the cytochemical localization of Ca(2+)-ATPase activity in synaptic terminals.

The energy-filtering electron microscopical modes of electron energy-loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) have been applied to the cytochemical detection of Ca(2+)-ATPase activity in synaptic terminals in the brain of a cichlid fish. Using a recently developed modification of an enzyme-histochemical method, cerium phosphate was precipitated as a marker of high-affinity Ca(2+)-ATPase activity. This is considered to be a marker for the plasmalemma-bound calcium pump, an enzyme which plays a crucial role in the regulation of the cytoplasmic calcium concentrations and therefore of the reactivity of nerve cells. High-affinity Ca(2+)-ATPase activity is located preferentially at the inner side of synaptic plasma membranes and enables a discrimination of different types of synapse. It is only by using EELS and ESI that the very small amounts of high-affinity Ca(2+)-ATPase reaction product can be analysed reliably and located precisely. These new electron microscopical techniques offer powerful tools for cytochemical studies.

Animals↗