Hinrich Rahmann

A functional model of sialo-glyco-macromolecules in synaptic transmission and memory formation.

A concept is presented of the molecular involvement of sialo-glyco-macromolecules in the processes of synaptic transmission and memory formation. The main point of the concept is the assumption that by complexation between lipid-bound negative charged sialic acid and Ca 2+ -ions the synaptic membrane is “closed”, while dissociation of these complexes will cause an “opening” of presynaptic regions. The synaptic zones of contact are assumed to become functionable during ontogenesis, only after the incorporation of sialyl residues into the carbohydrate coat of neuronal membrane. Additional accretion of sialo-glyco-macromolecules at the contact zones, could be the molecular basis for a facilitation of defined neural pathways, which might be the morphological correlate of an engram. Published experimental data are used as evidence for the validity of this concept.

Heterogeneous Expression of the Polysialyltransferases ST8Sia II and ST8Sia IV During Postnatal Rat Brain Development

Abstract: Polysialic acid on the neural cell adhesion molecule is developmentally regulated and has been implicated in the plasticity of cell‐cell interactions. The sialyltransferases ST8Sia II and ST8Sia IV are able to catalyze the synthesis of polysialic acid. This study compares the expression of ST8Sia II and ST8Sia IV mRNA during postnatal rat brain development. Northern blot analysis indicated a substantial down‐regulation of ST8Sia II from high expression at postnatal day 2 to almost undetectable levels at the age of 6 months. In contrast, the decline of ST8Sia IV content was moderate. In the mature brain, ST8Sia IV is the predominant polysialyltransferase. In situ hybridization of selected brain regions at postnatal days 2, 11, and 21 confirmed the decline of ST8Sia II level in isocortex, hippocampus, and cerebellum. ST8Sia II was not detectable at any time point in the subependymal layer and the layers of the olfactory bulb. Persistent ST8Sia IV expression was localized in the subependymal layer, the glomerular layer of the olfactory bulb, and the granule cell layer of the dentate gyrus and in some widely dispersed cells of the isocortex. The distinct expression patterns of ST8Sia II and ST8Sia IV suggest their differential regulation. As discussed with regard to the persistent polysialic acid expression, ST8Sia IV should receive particular attention in the mature brain.

Gangliosides and Modulation of Neuronal Functions

Gangliosides (= amphiphilic sialic acid containing glycosphingolipids) are components of all plasma membranes and as such ubiquitous in vertebrate tissues. They are especially abundant and complex in neuronal membranes, where they are anchored in the outer leaflet of the membrane bilayer by their hydrophobic ceramide moiety, while exposing their negatively charged hydrophilic and spacious sialo-oligosaccharide residue into the extracellular space (Fig. 1). Together with neutral glycolipids, glycoproteins and glycosaminoglycans, gangliosides comprise the glycocalix of the cell surface.

Morphometry of fish inner ear otoliths after development at 3g hypergravity

Size and asymmetry (size difference between the left and right sides) of inner ear otoliths of larval cichlid fish were determined after a long-term stay in moderate hypergravity conditions (3g; centrifuge), in the course of which the animals completed their ontogenetic development from hatch to freely swimming. Neither the normal morphogenetic development nor the timely onset and gain of performance of swimming behaviour were impaired by the experimental conditions. However, both utricular and saccular otoliths (lapilli and sagittae, respectively) were significantly smaller after hyper-g exposure compared to 1g control specimens raised in parallel. The asymmetry of sagittae was significantly increased in the experimental animals, whereas the respective asymmetry of lapilli was pronouncedly decreased compared with the 1g controls. These findings suggest that growth and development of bilateral asymmetry of otoliths are guided by the environmental gravity vector. Some of the hyper-g animals revealed a kinetotic behaviour on transfer to normal 1g earth conditions, which was similar to the behaviour observed in previous experiments on the transfer from 1g to microgravity (parabolic aircraft flights). The lapillar asymmetry of kinetotic samples was found to be significantly higher than that of normally behaving experimental specimens. No differences in asymmetry of sagittae were obtained between the two groups. This supports an earlier theoretical concept, according to which human static space sickness might be based on asymmetric utricular otoliths.

Surface potentials and electric dipole moments of ganglioside and phospholipid monolayers: contribution of the polar headgroup at the water/lipid interface

Monolayers of different gangliosides (GM1, GD1a, GT1b, GMix), ceramide (Cer), sulfatide (Sulf), phospholipids (DOPC, DPPE, DPPS, DOPA), a quaternary ammonium salt (DOMA) and fatty acids (C16, C18, C20) were investigated at the air/water interface on pure water as well as on buffered subphases. Monolayers at the air/water interface consist of two interfaces: the water/lipid and the lipid/air interfaces. The normal components of the effective total dipole moments (Δμ), the effective local dipole moments (Δμα) and effective local surface potentials (ΔVα) of polar headgroups at the water/lipid interface have been calculated from surface potential (ΔV) and mean molecular area (A) measurements of close-packed monolayers. The contribution of the lipid/air interface was previously determined experimentally by partial dipole compensation approach (Vogel, V. and Mobius, D. (1988) Thin Solid Films 159, 73–81). The surface potentials (ΔV) of ganglioside monolayers are quite similar (e.g., GMI = −17 mV, GTib = −39 mV; at surface pressure π = 30 mN/m triethanolamine (TEA)/HCl buffer, pH 7.4, as subphase); this indicates that variations in molecular structure of gangliosides like the influence of the number of negative charges per ganglioside which lead to appreciate changes in the average molecular packing do not cause large changes in surface potential. The local surface potentials (ΔVα) reach to minus several hundred millivolts for nearly all compounds, but clear differences are shown between negatively charged phospholipids (e.g., DPPS = −296 mV at π = 30 mN/m) and glycolipids (e.g., GM1 = −413 mV), and within glycolipids at different surface pressures (e.g., GD1n: − 342 mV at π = 20 mN/m versus −453 mV at π = 30mN/m nly in gangliosides (except for GD1b) the total dipole moments (Δμ) are negative (−0.029 up to − 0.078 D) and directed to the water. Unlike DOPC (+0.069 D) and DOMA (+0.421 D), the local dipole moments (Δμα of all hydrated polar headgroups are negative (e.g., DPPS = −0.331 D; GM1 = −0.729 D) and directed from the monolayer (−) to the water (+). Under well-defined conditions investigated such data are helpful for a better understanding of the large functional role of gangliosides especially in determining the surface potential of biological membranes.

SIALIC ACID INCORPORATION INTO GANGLIOSIDES AND GLYCOPROTEINS OF THE FISH BRAIN

—The concentration of lipid‐ and non‐lipid‐bound sialic acid in the optic nerve tract and tectum and in whole brain of fish was estimated. The incorporation of sialic acid into gangliosides and non‐lipid components was studied in fish by intracranial or intraocular application of N‐[3H]acetylmannosamine or N‐[3H]acetylglucosamine. After intracranial injection of N‐[3H]acetylmannosamine autoradiography showed lipid‐ and non‐lipid‐bound radioactivity in the tectum opticum evenly distributed over regions of nerve fibres or perikarya indicating an ubiquitous incorporation of label. Sialic acid incorporation into glycoproteins after intracranial injection of N‐acetylmannosamine always exceeded that into gangliosides. TCA‐precipitable non‐lipid material is labelled from intracranially applied N‐acetylmannosamine in the sialic acid portion and also in nonsialic acid components, whereby the percentage of label in sialic acid increases reaching 90 per cent of the total radioactivity after 90 min. After intraocular application of N‐[3H]acetylmannosamine, sialic acid in gangliosides was generally found to be more highly labelled than in glycoproteins. The ratio of radioactivity in gangliosides and glycoproteins increased with time of incubation and the distance from the eye. TCA‐soluble radioactivity was translocated by fast axonal transport. Cycloheximide inhibited incorporation of N‐acetylmannosamine‐derived radioactivity into gangliosides and proteins but not the transport of TCA‐soluble material, which accumulates in the tectum. After intraocular application of N‐[3H]acetylglucosamine, TCA‐soluble label arrives later in the optic tectum than radioactivity of high molecular weight components. The ratio of lipid to non‐lipid‐bound radioactivity does not change considerably with the time after injection or the distance from the eye. There was no accumulation of TCA‐soluble radioactivity after the inhibition of incorporation into high molecular weight components.

Modulatory effects of different temperatures and Ca2+ concentrations on gangliosides and phospholipids in monolayers at air/water interfaces and their possible functional role

Summary1.Gangliosides are neuraminic acid-containing glycolipids preferently localized in nervous membranes and showing physicochemical peculiarities, e.g., drastically changing amphiphilic properties by Ca2+ binding. On account of this they are favorite compounds to act as modulators of membraneous organization and functions during synaptic transmission. Lipid monolayers are suitable experimental systems for the study of the surface behavior of amphipatic molecules and therefore are useful to interpret membraneous organization.2.The surface pressure/area isotherms of monolayers of different individual gangliosides (GM1, GD1a, GD1b, GT1b) of an artificial reconstituted and a natural ganglioside mixture from bovine brain and of ganglioside mixtures from different brain parts of summer- and winter-adapted dsungarian hamsters were compared at three temperatures (11, 20, and 37°C) with egg phosphatidylcholine (PC) and phosphatidylserine (PS) monolayers. The monolayers were formed in a Teflon trough on a triethanolamine/HCl-buffered (pH 7.4) subphase, in some cases containing different amounts of CaCl2.3.The surface pressure/area isotherms of ganglioside monolayers, in contrast to phospholipids, generally showed slowly rising slopes, with transitions from the liquidexpanded to the liquid-condensed state at a surface pressure of 20–30 mN/m. Ganglioside monolayers, in particular from GD1a or GT1b versus GD1b or from mixtures from summer- versus winter-adapted hamster brain, were differently affected by temperature and/or by Ca2+. PS monolayers were slightly condensed only by Ca2+. PC monolayers, however, were influenced neither by temperature nor by Ca2+. In mixed monolayers of the unpolar natural lipid cholesterol (Ch) and the disialoganglioside GD1a, intermolecular interactions were indicated.4.Ganglioside monolayers, in contrast to phospholipids, were shown to be easily modulated by temperature and/or Ca2+ ions, thus enabling gangliosides to act as possible membrane modulators, e.g., during synaptic transmission. In particular, the differences concerning the influences of temperature and/or Ca2+ on the surface behavior of ganglioside mixtures from the brain of summer- compared with winteradapted hamsters are correlated with other physiologically relevant data.

Brain Gangliosides during the Life Span (Embryogenesis to Senescence) of the Rat

The concentration of gangliosides, sialoglycoproteins and proteins was studied in the whole brains and single brain structures (cortex, olfactory bulb, corpora quadrigemina region equals midbrain, cerebellum, thalamic region and oblongated medulla) of female rats from 14 developmental stages ranging from day 8 of gestation to more than 3 years of age. The content of protein- and ganglioside-bound neuraminic acid showed a peak at 3 weeks of age and then decreased with aging, whereas that of proteins increased until senescence. All over the life span the developmental profiles of 12 individual gangliosides in the different brain structures (cortex, corpora quadrigemina region approximately midbrain, cerebellum, thalamic region, medulla) and in whole brain samples were followed. There are distinct differences between the brain structures. Additionally each brain region is characterized by specific developmental ganglioside profiles. However, some ganglioside changes are common to all regions: GD3 in general is a marker for cell division and migration, whereas the polar ganglioside fractions GQ1b and GP1 are characteristic for nerve cell sprouting and arborization. Especially in the cortex GD1a seems to be the marker for synaptogenesis and GM1 and GM4 for myelination. The results were discussed in view of the main morphological patterns of differentiation.

Phylogenetical aspects of brain gangliosides in vertebrates

SummaryThe concentration and composition of brain gangliosides in 78 vertebrate species belonging to the classes of Agnathes, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia were investigated.1.An increase in the concentration of gangliosides takes place with anagenetic progress of nervous organization during phylogeny which is accompanied by a simultaneous decrease in the content of neuronal sialo-glycoproteins. This tendency can be observed in the main classes from cartilaginous fishes to mammals and also in smaller taxonomic units such as Elasmobranchia, Salmoniformes, Gadiformes, Percoidea, Notothenoidea, Rodentia. This indicates that gangliosides were more frequently selected than sialo-glycoproteins during vertebrate evolution.2.Over a phylogenetic series the complexity of brain ganglioside composition is strikingly reduced. Among cold-blooded vertebrates a large number of complex and highly sialylated ganglioside fractions is present in the CNS, whereas in the warm-blooded birds and mammals only few fractions constitute the brain pattern, and these have less polarity.3.The anagenetic change in the complexity of the brain ganglioside character is correlated to changes in the use of the three biosynthesis pathways of gangliosides (‘b’-pathway in Agnatha, ‘b’ and ‘c’ in cartilaginous and lower bony fishes, ‘a, b, c’ in ancient sturgeons and lungfish, ‘c’ in higher evolved bony fish, ‘b’, ‘c’ in amphibians, ‘b’ and ‘a’ in reptiles and birds and mainly the ‘a’-pathway in highly evolved mammals).4.The data support the hypothesis that the great variations in concentration and composition of vertebrate brain gangliosides are not only dependent on the phylogenetic level of nervous organisation, but that they may also originate from the state of thermal adaptation. By these variations, vertebrates may be to maintain optimum rates of neuronal transmission while being adapted to different temperature habitats.

Developmental profiles of gangliosides in mouse and rat cerebral cortex

SummaryDevelopmental profiles of 11 gangliosides, concentration of lipid- and glycoprotein-bound sialic acid, and activity of AChE of the rat and mouse cerebral cortex were followed from the 7th day of gestation to the 21st postnatal day.There are three main changes in ganglioside concentration, which are similar in both species. The first occurs from gestation day 10 until birth: parallel to decreased proliferation, cell migration, and neuroblast differentiation, GM3 and GD3 in mouse cortex and GD3 in the rats decreases in favor of GQ1b, GT1b, and GD1a.The second occurs from birth until the first postnatal week: Parallel to increased growth and arborization of dendrites and axons as well as synaptogenesis in rats and mice, there is a two-fold rise of GD1a, whereas GQ1b and GT1b remain on a nearly constant level. Concomitantly, GM3 and GD3 decreases. The third period of ganglioside changes starts in the second postnatal week, parallel to onset of myelination, and is characterized by an increase of GM1 in parallel with a decrease of the polysialogangliosides GT1b and GQ1b.