Reinhard Hilbig

Ground-based facilities for simulation of microgravity: organism-specific recommendations for their use, and recommended terminology.

Research in microgravity is indispensable to disclose the impact of gravity on biological processes and organisms. However, research in the near-Earth orbit is severely constrained by the limited number of flight opportunities. Ground-based simulators of microgravity are valuable tools for preparing spaceflight experiments, but they also facilitate stand-alone studies and thus provide additional and cost-efficient platforms for gravitational research. The various microgravity simulators that are frequently used by gravitational biologists are based on different physical principles. This comparative study gives an overview of the most frequently used microgravity simulators and demonstrates their individual capacities and limitations. The range of applicability of the various ground-based microgravity simulators for biological specimens was carefully evaluated by using organisms that have been studied extensively under the conditions of real microgravity in space. In addition, current heterogeneous terminology is discussed critically, and recommendations are given for appropriate selection of adequate simulators and consistent use of nomenclature.

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.

Variability in Brain Gangliosides of Fishes

Gangliosides are membrane-bound glycosphingolipids containing different residues of sialic acid. In the nervous tissue gangliosides seem t o be involved in the process of synaptic transmission (Rahmann et al., 1976) and adaptive neuronal functions (Rahmann 1978: Rahmann et al., 1976). In the CNS of adult mammals less polar monoand d is ia logangl ios ide f r a c t i o n s d o m i n a t e (68-84%). trisialogangliosides occur at 8-2257, and more polar fractions make up only about 412% (Ledeen and Yu. 1976). In contrast to these findings the brain ganglioside patterns of the few fish species investigated up to now (Tettamanti et al.. 1965; Gielen. 1968; Ishizuka and Wiegandt, 1972: Avrova, 197 I ; McCluer and Agranoff, 1972; Rosner e t al.. 1973: Breer, 1975) show a great variability. In some elasmobranchs partly contradictory results are reported concerning the occurrence of polar ganglioside fractions. With the exception of the elasmobranchs, the fish brain ganglioside pattern in comparison to that of mammals seems to be characterized by the preponderance of more polar fractions. In order to elucidate the question of whether the brain ganglioside pattern of vertebrates might generally be correlated with the phylogenetic position of the different systematic groups-or with any other, probably environmental, factors in the present study-the brain ganglioside composition of 16 different fish species was compared.

Influence of long-term altered gravity on the swimming performance of developing cichlid fish: including results from the 2nd German Spacelab Mission D-2.

This study presents qualitative and quantitative data concerning gravity-dependent changes in the swimming behaviour of developing cichlid fish larvae (Oreochromis mossambicus) after a 9 resp. 10 days exposure to increased acceleration (centrifuge experiments), to reduced gravity (fast-rotating clinostat), changed accelerations (parabolic aircraft flights) and to near weightlessness (2nd German Spacelab Mission D-2). Changes of gravity initially cause disturbances of the swimming performance of the fish larvae. With prolonged stay in orbit a step by step normalisation of the swimming behaviour took place in the fish. After return to 1g earth conditions no somersaulting or looping could be detected concerning the fish, but still slow and disorientated movements as compared to controls occurred. The fish larvae adapted to earth gravity within 3-5 days. Fish seem to be in a distinct early developmental stages extreme sensitive and adaptable to altered gravity; However, elder fish either do not react or show compensatory behaviour e.g. escape reactions.

Brain gangliosides and temperature adaptation in eury- and stenothermic teleost fish (carp and rainbow trout)

1. 1.|The brain ganglioside pattern of eurythermic carp (Cyprinus carpio) and stenothermic rainbow trout (Salmo gairdneri) was investigated by means of biochemical methods under experimentally induced temperature changes (acclimination), and seasonal temperature fluctuations (acclimatization). 2. 2.|In both species during the process of thermal adaptation to lowered environmental temperatures, changes in the brain gangliosides could be registered resulting in a more polar pattern. 3. 3.|While in carp this “polysialization” was indicated by a decrease of all oligosialogangliosides in favour of more polar fractions; in rainbow trout a more differentiated change of the pattern occurred characterized by a significant decrease (∼ 60%) in the concentration of the monosialoganglioside GM3. 4. 4.|The results are discussed with respect to a possible involvement of neuronal gangliosides in the mechanism of thermal adaptation of poikilothermic animals to changes in the environmental temperatures.

Magnetosensation in zebrafish

Abstract Many species, from bacteria to vertebrates, have been reported to use the geomagnetic field as a major cue for oriented short and long range migration [1–10], but the molecular nature of the underlying receptor has remained elusive. One of the main reasons may be that past attempts to train animals to respond to magnetic stimuli proved surprisingly difficult [11]. We present a novel approach to magnetic conditioning, using a fast, fully automated assay system relying on negative reinforcement. Weak electric impulses were applied to punish fish that failed to escape upon magnetic field alterations (avoidance behaviour). Using this assay we first demonstrate magnetosensation in Mozambique tilapia, a fish migrating regularly between freshwater and the sea. Next we wondered whether non-migratory fish have a magnetic sense, such as zebrafish, the genetic fish model organism. Zebrafish were trained in groups of 4 individuals, and statistically highly significant reactions to magnetic field changes were recorded. The demonstration of magnetosensation in zebrafish opens a possibility to genetically identify the magnetoreceptor and its downstream signalling cascade.

Hibernation-induced changes in the ganglioside composition of dormice (Glis glis)

Abstract 1. 1. The brain ganglioside pattern and the concentration of proteins, sialoglycoproteins and gangliosides in the whole brain and seven different brain parts of normothermic and hibernating dormice ( Glis glis ) were investigated and compared with corresponding data of laboratory rats. 2. 2. The concentration of brain proteins (about 100 mg/g fresh wt), sialoglycoproteins (about 230 μg NeuAc/g fresh wt) of normothermic as well as hibernating dormice is very similar to that of laboratory rats. The concentration of gangliosides however is slightly higher in rats as compared to dormice and reaches values between 500 and 1000 μg NeuAc/g fresh wt, depending on the brain-structure. 3. 3. The ganglioside pattern of normothermic dormice in comparison to that of laboratory rats is characterized by a higher content of the polar trisialoganglioside GT1b (+ 8.5% in the cerebellum) and the tetrasialoganglioside GQ1b (+ 4.5% in the cerebellum). 4. 4. In hibernating dormice in contrast to their normothermic counterparts the brain gangliosides are even more polar resulting in an increase of the polar ganglioside fractions (GT1b, GQ1b, GP) from 30.5 to 35.8% of ganglioside-bound NeuAc. 5. 5. There is not change in the ganglioside pattern with length of torpor. The polysialylation takes place during the first three weeks of hibernation. 6. 6. The results are discussed with regard to the hypothesis, that neuronal membranes provided with more polar gangliosides at lower environmental temperatures might be more efficient with respect to the high complexation ability of gangliosides to Ca 2+ ions.

Sensitivity Differences in Fish Offer Near-Infrared Vision as an Adaptable Evolutionary Trait

Near-infrared (NIR) light constitutes an integrated part of solar radiation. The principal ability to sense NIR under laboratory conditions has previously been demonstrated in fish. The availability of NIR in aquatic habitats, and thus its potential use as a cue for distinct behaviors such as orientation and detection of prey, however, depends on physical and environmental parameters. In clear water, blue and green light represents the dominating part of the illumination. In turbid waters, in contrast, the relative content of red and NIR radiation is enhanced, due to increased scattering and absorption of short and middle range wavelengths by suspended particles and dissolved colored materials. We have studied NIR detection thresholds using a phototactic swimming assay in five fish species, which are exposed to different NIR conditions in their natural habitats. Nile and Mozambique tilapia, which inhabit waters with increased turbidity, displayed the highest spectral sensitivity, with thresholds at wavelengths above 930 nm. Zebrafish, guppy and green swordtail, which prefer clearer waters, revealed significantly lower thresholds of spectral sensitivity with 825–845 nm for green swordtail and 845–910 nm for zebrafish and guppy. The present study revealed a clear correlation between NIR sensation thresholds and availability of NIR in the natural habitats, suggesting that NIR vision, as an integral part of the whole spectrum of visual abilities, can serve as an evolutionarily adaptable trait in fish.

Effects of altered gravity on the swimming behaviour of fish

Humans taking part in parabolic aircraft flights (PAFs) may suffer from space motion sickness-phenomena (SMS, a kinetosis). It has been argued that SMS during PAFs might not be based on microgravity alone but rather on changing accelerations from 0 g to 2 g. We test here the hypothesis that PAF-induced kinetosis is based on asymmetric statoliths (i.e., differently weighed statoliths on the right and the left side of the head), with asymmetric inputs to the brain being disclosed at microgravity. Since fish frequently reveal kinetotic behaviour during PAFs (especially so-called spinning movements and looping responses), we investigated (1) whether or not kinetotically swimming fish at microgravity would have a pronounced inner ear otolith asymmetry and (2) whether or not slow translational and continuously changing linear (vertical) acceleration on ground induced kinetosis. These latter accelerations were applied using a specially developed parabel-animal-container (PAC) to stimulate the cupular organs. The results suggest that the fish tested on ground can counter changing accelerations successfully without revealing kinetotic swimming patterns. Kinetosis could only be induced by PAFs. This finding suggests that it is indeed microgravity rather than changing accelerations, which induces kinetosis. Moreover, we demonstrate that fish swimming kinetotically during PAFs correlates with a higher otolith asymmetry in comparison to normally behaving animals in PAFs.