Graviresponses of Paramecium biaurelia during parabolic flights

The thresholds of graviorientation and gravikinesis in Paramecium biaurelia were investigated during the 5th DLR (German Aerospace Center) parabolic-flight campaign at Bordeaux in June 2003. Parabolic flights are a useful tool for the investigation of swimming behaviour in protists at different accelerations. At normal gravity (1 g) and hypergravity (1 g to 1.8 g), precision of orientation and locomotion rates depend linearly on the applied acceleration as seen in earlier centrifuge experiments. After transition from hypergravity to decreased gravity (minimal residual acceleration of <10(-2) g), graviorientation as well as gravikinesis show a full relaxation with different kinetics. The use of twelve independent cell samples per flight guarantees high data numbers and secures the statistical significance of the obtained data. The relatively slow change of acceleration between periods of microgravity and hypergravity (0.4 g/s) enabled us to determine the thresholds of graviorientation at 0.6 g and of gravikinesis at 0.4 g. The gravity-unrelated propulsion rate of the sample was found to be 874 microm/s, exceeding the locomotion rate of horizontally swimming cells (855 microm/s). The measured thresholds of graviresponses were compared with data obtained from earlier centrifuge experiments on the sounding rocket Maxus-2. Measured thresholds of gravireactions indicate that small energies, close to the thermal noise level, are sufficient for the gravitransduction process. Data from earlier hypergravity experiments demonstrate that mechanosensitive ion channels are functioning over a relative wide range of acceleration. From this, we may speculate that gravireceptor channels derive from mechanoreceptor channels.     

Atrial distension in humans during weightlessness induced by parabolic flights

Central venous pressure, esophageal pressure, and left atrial diameter were measured in individuals during each stage of parabolic flight, with emphasis on weightlessness. Results indicated that short periods of weightlessness lead to an increase in transmural central venous pressure and left atrial diameter, although there is a decrease in central venous pressure.     

Atrial distension in humans during microgravity induced by parabolic flights

Videbaek, Regitze, and Peter Norsk. Atrialdistension in humans during microgravity induced by parabolic flights.J. Appl. Physiol. 83(6):1862-1866, 1997.The hypothesis was tested that human cardiacfilling pressures increase and the left atrium is distended during 20-speriods of microgravity (µG) created by parabolic flights, comparedwith values of the 1-G supine position. Left atrial diameter(n = 8, echocardiography) increasedsignificantly during µG from 26.8 ± 1.2 to 30.4 ± 0.7 mm(P < 0.05). Simultaneously, centralvenous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 ± 1.5 to 4.5 ± 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from1.5 ± 1.6 to 4.1 ± 1.7 mmHg (P < 0.05). Thus transmural CVP(TCVP = CVP  EP; n = 4)increased during µG from 6.1 ± 3.2 to 10.4 ± 2.7 mmHg(P < 0.05). It is concluded thatshort periods of µG during parabolic flights induce an increase inTCVP and left atrial diameter in humans, compared with the resultsobtained in the 1-G horizontal supine position, despite a decrease inCVP.

     

Arterial pressure in humans during weightlessness induced by parabolic flights.

Results from our laboratory have indicated that, compared with those of the 1-G supine (Sup) position, left atrial diameter (LAD) and transmural central venous pressure increase in humans during weightlessness (0 G) induced by parabolic flights (R. Videbaek and P. Norsk. J. Appl. Physiol. 83: 1862-1866, 1997). Therefore, because cardiopulmonary low-pressure receptors are stimulated during 0 G, the hypothesis was tested that mean arterial pressure (MAP) in humans decreases during 0 G to values below those of the 1-G Sup condition. When the subjects were Sup, 0 G induced a decrease in MAP from 93 +/- 4 to 88 +/- 4 mmHg (P < 0.001), and LAD increased from 30 +/- 1 to 33 +/- 1 mm (P < 0.001). In the seated position, MAP also decreased from 93 +/- 6 to 87 +/- 5 mmHg (P < 0.01) and LAD increased from 28 +/- 1 to 32 +/- 1 mm (P < 0.001). During 1-G conditions with subjects in the horizontal left lateral position, LAD increased compared with that of Sup (P < 0.001) with no further effects of 0 G. In conclusion, MAP decreases during short-term weightlessness to below that of 1-G Sup simultaneously with an increase in LAD. Therefore, distension of the heart and associated central vessels during 0 G might induce the hypotensive effects through peripheral vasodilatation. Furthermore, the left lateral position in humans could constitute a simulation model of weightlessness.     

Pulmonary diffusing capacity and pulmonary capillary blood volume during parabolic flights

Vaïda, Pierre, Christian Kays, Daniel Rivière,Pierre Téchoueyres, and Jean-Luc Lachaud.Pulmonary diffusing capacity and pulmonary capillary blood volumeduring parabolic flights. J. Appl.Physiol. 82(4): 1091-1097, 1997.Data from theSpacelab Life Sciences-1 (SLS-1) mission have shown sustained butmoderate increase in pulmonary diffusing capacity(DL). Because of the occupational constraints of the mission, data were only obtained after24 h of exposure to microgravity. Parabolic flights are often used tostudy some effects of microgravity, and we measured changes inDL occurring at the very onsetof weightlessness. Measurements ofDL, membrane diffusing capacity,and pulmonary capillary blood volume were made in 10 male subjectsduring the 20-s 0-G phases of parabolic flights performed by the"zero-G" Caravelle aircraft. Using the standardized single-breathtechnique, we measuredDL for CO andnitric oxide simultaneously. We found significant increases inDL for CO (62%),in membrane diffusing capacity for CO (47%), inDL for nitric oxide (47%), andin pulmonary capillary blood volume (71%). We conclude that majorchanges in the alveolar membrane gas transfers and in the pulmonarycapillary bed occur at the very onset of microgravity. Because thesechanges are much greater than those reported during sustainedmicrogravity, the effects of rapid transition from hypergravity tomicrogravity during parabolic flights remain questionable.

     

Gravity effects on regional lung ventilation determined by functional EIT during parabolic flights.

Gravity-dependent changes of regional lung function were studied during normogravity, hypergravity, and microgravity induced by parabolic flights. Seven healthy subjects were followed in the right lateral and supine postures during tidal breathing, forced vital capacity, and slow expiratory vital capacity maneuvers. Regional 1) lung ventilation, 2) lung volumes, and 3) lung emptying behavior were studied in a transverse thoracic plane by functional electrical impedance tomography (EIT). The results showed gravity-dependent changes of regional lung ventilation parameters. A significant effect of gravity on regional functional residual capacity with a rapid lung volume redistribution during the gravity transition phases was established. The most homogeneous functional residual capacity distribution was found at microgravity. During vital capacity and forced vital capacity in the right lateral posture, the decrease in lung volume on expiration was larger in the right lung region at all gravity phases. During tidal breathing, the differences in ventilation magnitudes between the right and left lung regions were not significant in either posture or gravity phase. A significant nonlinearity of lung emptying was determined at normogravity and hypergravity. The pattern of lung emptying was homogeneous during microgravity.     

Cerebral cortical blood flow in rabbits during parabolic flights (hypergravity and microgravity)

We studied the effect of gravity on cerebral cortical blood flow (CBF), mean arterial blood pressure () and heart rate in six rabbits exposed to parabolic flights. The CBF was obtained using a laser-Doppler probe fixed on to a cranial window. Before weightlessness, the animals were exposed to chest-to-back directed acceleration (1.8–2.0 g). The CBF values were expressed as a percentage of CBF_o (mean CBF during 60 s before the 1st parabola). Propranolol (1 mg · kg⁻¹ IV) was given after the 11th parabola and pentobarbital (12–15 mg · kg⁻¹ IV) after the 16th parabola. Before the administration of the drugs, CBF increased (P < 0.01) during hypergravity [i.e. maximal CBF 151 (SD 64)% CBF_o. Simultaneously increased [maximal , 119 (SD 11) mmHg (P < 0.01)]. At the onset of weightlessness, CBF and reached maximal values [194 (SD 96)% CBF_o (P < 0.01) and 127 (SD 19) mmHg, (P < 0.01) respectively]. The microgravity-induced increase in CBF was transient since CBF returned to its baseline value after 8 (SD 2) s of microgravity. After propranolol administration, CBF was not statistically different during hypergravity but an elevation of CBF was still observed in weightlessness. The increases in CBF and also persisted during weightlessness after pentobarbital administration. These data would indicate that CBF of nonanesthetized rabbits increases during the first seconds of weightlessness and demonstrate the involvement of rapid active regulatory mechanisms since CBF returned to control values within 8 (SD 2) s. We concluded that this elevation in blood flow was not related to stress because it persisted after the administration of propranolol and pentobarbital. Accepted: 6 November 1997     

Oriented movement of statoliths studied in a reduced gravitational field during parabolic flights of rockets

During five rocket flights (TEXUS 18, 19, 21, 23 and 25), experiments were performed to investigate the behaviour of statoliths in rhizoids of the green alga Chara globularia Thuill. and in statocytes of cress (Lepidium sativum L.) roots, when the gravitational field changed to approx. 10^–4 · g (i.e. microgravity) during the parabolic flight (lasting for 301–390 s) of the rockets. The position of statoliths was only slightly influenced by the conditions during launch, e.g. vibration, acceleration and rotation of the rocket. Within approx. 6 min of microgravity conditions the shape of the statolith complex in the rhizoids changed from a transversely oriented lens into a longitudinally oriented spindle. The center of the statolith complex moved approx. 14 m and 3.6 m in rhizoids and root statocytes, respectively, in the opposite direction to the originally acting gravity vector. The kinetics of statolith displacement in rhizoids demonstrate that the velocity was nearly constant under microgravity whereas it decreased remarkably after inversion of rhizoids on Earth. It can be concluded that on Earth the position of statoliths in both rhizoids and root statocytes depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by microfilaments.Abbreviations ER endoplasmic reticulum - g 9.806 m · s^–2 - MF microfilament - TEXUS Technologische Experimente unter Schwerelosigkeit (technological experiments under reduced gravity) Dedicated to Professor Wolfgang Haupt on the occasion of his 70th birthday     

Gravity-induced absorption changes in Phycomyces blakesleeanus during parabolic flights: first spectral approach in the visible

Gravity-induced absorption changes as experienced during a series of parabolas on the Airbus 300 Zero-G have been measured previously pointwise on the basis of dual-wavelength spectroscopy. Only the two wavelengths of 460 and 665 nm as generated by light-emitting diodes have been utilised during our first two parabolic-flight campaigns. In order to gain complete spectral information throughout the wavelength range from 400 to 900 nm, a miniaturized rapid scan spectrophotometer was designed. The difference of spectra taken at 0 g and 1.8 g presents the first gravity-induced absorption change spectrum measured on wild-type Phycomyces blakesleeanus sporangiophores, exhibiting a broad positive hump in the visible range and negative values in the near infrared with an isosbestic point near 735 nm. The control experiment performed with the stiff mutant A909 of Phycomyces blakesleeanus does not show this structure. These results are in agreement with those obtained with an array spectrophotometer. In analogy to the more thoroughly understood so-called light-induced absorption changes, we assume that gravity-induced absorption changes reflect redox changes of electron transport components such as flavins and cytochromes localised within the plasma membrane.     

Lipoxygenase activity of intact human platelets

The oxygenation by lipoxygenase of different icosaenoic and docosaenoic acids by intact human platelets was studied. The HPLC analysis of the hydroxy compound (s) derived from icosaenoic acids showed that the 12-derivatives predominate. The increase of the fatty acid concentration markedly enhanced their oxygenation except for icosapentaenoic acid. The conversion of this acid into its hydroxy derivative rose in the presence of arachidonic acid, probably through both its cyclo-oxygeuase and lipoxygenase product formation. Since 12-hydroxy-icosaenoic acids are modulators of PGH₂-induced platelet aggregation, we conclude that the interactions between polyunsaturated fatty acids during their oxygenation by platelet lipoxygenase could be relevant to the regulating activity of dietary fatty acids.     

The behavioral responses of amphibians and reptiles to microgravity on parabolic flights

In the present study, we exposed 53 animals from 23 different species of amphibians and reptiles to microgravity (mug). This nearly doubles the number of amphibians and reptiles observed so far in mug. The animals were flown on a parabolic flight, which provided 20-25s of mug, to better characterize behavioral reactions to abrupt exposure to mug. Highly fossorial limbless caecilians and amphisbaenians showed relatively limited movement in mug. Limbed quadrupedal reptiles that were non-arboreal in the genera Leiocephalus, Anolis, and Scincella showed the typical righting response and enormous amounts of body motion and tail rotation, which we interpreted as both righting responses and futile actions to grasp the substrate. Both arboreal and non-arboreal geckos in the genera Uroplatus, Palmatogecko, Stenodactylus, Tarentola, and Eublepharis instead showed a skydiving posture previously reported for highly arboreal anurans. Some snakes, in the genera Thamnophis and Elaphe, which typically thrashed and rolled in mug, managed to knot their own bodies with their tails and immediately became quiescent. This suggests that these reptiles gave stable physical contact, which would indicate that they were not falling, primacy over vestibular input that indicated that they were in freefall. The fact that they became quiet upon self-embrace further suggests a failure to distinguish self from non-self. The patterns of behavior seen in amphibians and reptiles in mug can be explained in light of their normal ecology and taxonomic relations.     

How to activate a plant gravireceptor. Early mechanisms of gravity sensing studied in characean rhizoids during parabolic flights

Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14 g, but not of 0.05 g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 x 10(-14) n act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths.     

The control of optic flow during learning flights

Hymenopteran insects perform systematic learning flights on departure from their nest, during which they acquire a visual representation of the nest environment. They back away from and pivot around the nest in a series of arcs while turning to view it in their fronto-lateral visual field. During the initial stages of the flights, turning rate and arc velocity relative to the nest are roughly constant at 100–200° s⁻¹ and are independent of distance, since the insects increase their flight speed as they back away from the pivoting centre. In this paper I analyse how solitary wasps control their flight by having them perform learning flights inside a rotating striped drum. The wasps' turning velocity is under visual control. When the insects fly inside a drum that rotates around the nest as a centre, their average turning rate is faster than normal when they fly an arc into the direction of drum rotation and slower when they fly in the opposite direction. The average slip speed they experience lies within 100–200° s⁻¹. The wasps also adjust their flight speed depending on the rotation of the drum. They modulate their distance from the pivoting centre accordingly and presumably also their height above ground, so that maximal ground slip is on average 200°␣s⁻¹. The insects move along arcs by short pulses of translation, followed by rapid body turns to correct for the change in retinal position of the nest entrance. Saccadic body turns follow pulses of translation with a delay of 80–120 ms. The optomotor response is active during these turns. The control of pivoting flight most likely involves three position servos, to control the retinal position of both the azimuth and the altitude of nest and the direction of flight relative to it, and two velocity servos, one constituting the optomotor reflex and the other one serving to clamp ground slip at about 200° s⁻¹. The control of ground slip is the prime source of the dynamic constancy of learning flights, which may help wasps to scale the pivoting parallax field they produce during these flights. Constant pivoting rate may in addition be important for the acquisition of a regular sequence of snapshots and in scanning for compass cues. Accepted : 31 July 1996     

Lipoxygenase activity in soybean is modulated by enzyme-substrate ratio

The off-flavour development in soybean based food and oil industry is considered as a serious problem. In soybean three lipoxygenase isozymes namely LOX-1, LOX-2 and LOX-3 which contribute to about 1 % of storage protein have been reported and are the major culprits for the generation of volatile compounds causing the off-flavour. The present study showed that the 3 lipoxygenase isozymes isolated from defatted soybean flour exhibited inhibition potential by modulating the enzyme to substrate ratio. LOX-2 was the most inhibition prone enzyme. Defatting the flour may help in reducing off-flavour generation.     

Problems of ensuring human radiation safety during interplanetary flights

The work contains the analyses and discussion of the main sources of space radiation specified for interplanetary flights, the dosimetric functionals used for describing the processes of radiation lesions and reparation of the organism in the conditions of the complex radiation impact with a broad charge composition of cosmic rays and a peculiar spatial and temporal dose behavior. It represents the results of calculations of the radiation risks during the flight and the total lifelong radiation risk with taking into account all the delayed unfavorable biological consequences. The main uncertainties in the calculated values of radiation risk leading to its undervaluation are analyzed. In addition, also provided is the range of theoretical and experimental investigations necessary for the adjustment of coefficient values used in the algorithm of radiation risk calculations, as well as in the nomenclature of experiments for estimating the individual resistance of man to the extreme influence and investigations aimed at estimating and increasing the reliability of the operator activity of cosmonauts.     

Eye movements and target fixation during dragonfly prey-interception flights

The capture of flying insects by foraging dragonflies is a highly accurate, visually guided behavior. Rather than simply aiming at the prey’s position, the dragonfly aims at a point in front of the prey, so that the prey is intercepted with a relatively straight flight trajectory. To better understand the neural mechanisms underlying this behavior, we used high-speed video to quantify the head and body orientation of dragonflies (female Erythemis simplicicollis flying in an outdoor flight cage) relative to an artificial prey object before and during pursuit. The results of our frame-by-frame analysis showed that during prey pursuit, the dragonfly adjusts its head orientation to maintain the image of the prey centered on the “crosshairs” formed by the visual midline and the dorsal fovea, a high acuity streak that crosses midline at right angles about 60° above the horizon. The visual response latencies to drifting of the prey image are remarkably short, ca. 25 ms for the head and 30 ms for the wing responses. Our results imply that the control of the prey-interception flight must include a neural pathway that takes head position into account.     

Modification of urinary secretion of 8-hydroxy-2'-deoxyguanosine and serum ACTH concentration following repetitive parabolic flights

It is important to clarify the molecular mechanisms of physiological responses of the human body to changes in gravity. Previous reports demonstrated that gravity-changing stress increases the human urinary concentration of 8-hydroxy-2'-deoxyguanosine (8-OHdG). However, it has yet to be clarified whether repetitive parabolic flight modulates the urinary concentration of 8-OHdG after exposure to gravity-changing stress. In the present study, the effects of the number of previous experiences with parabolic flight on urinary excretion of 8-OHdG and concentration of serum ACTH were examined in 12 healthy volunteers.