Effects of long-term space flights on organization of horizontal gaze fixation reaction

Results of Russian-Austrian space experiment "Monimir" which was a part of international space program "Austromir" are presented in this paper. Characteristics of horizontal gaze fixation reaction (hGFR) to visual targets were analyzed. Seven crewmembers of "Mir" space station expeditions took part in the experiment. Experiments were carried out 4 times before space flight, 5 times in flight and 3-4 times after landing. There were revealed significant alterations in characteristics of gaze fixation reaction during flight and after its accomplishing, namely: an increase of the time of gaze fixation to the target, changes of eye and head movements' velocity and increase of the gain of vestibular-ocular reflex, that pointed out to the disturbances of the control mechanisms of vestibular-ocular reflex in weightlessness caused by changes of vestibular input's activity. There was discovered also the difference in the strategies of adaptation to microgravity conditions among the cosmonauts of flight and non-flight occupation: in the first group exposure to weightlessness was accompanied by gaze hypermetry and inhibition of head movements; in the second one--on the contrary--by increase of head movement velocity and decrease of saccades' velocity.     

Changes in the gaze fixation reaction in rhesus monkeys during the initial stage of water immersion

The gaze fixation reaction was studied in three rhesus monkeys before and during thermoneutral (34.5 degrees C) water immersion to the mid-chest level. The angular vestibulo-ocular reflex gain increased and the head angular velocity decreased significantly in all monkeys in 5 h after the start of immersion. Additionally, one animal was immersed to the neck level. Two hours in the condition of more pronounced support deprivation decreased significantly angular velocity of the head but not increased the angular vestibulo-ocular reflex gain. Therefore, support deprivation act upon the head movement control first.     

Velocity of head movements and sensory-motor adaptation during and after short spaceflight

To investigate to time course of sensory-motor adaptation to microgravity, we tested spatially-directed voluntary head movements before, during and after short spaceflight. We also tested the re-adaptation of postural responses to sensory stimulation after space flight. The cosmonaut performed in microgravity six cycles of voluntary head rotation in pitch, roll and yaw directions. During the first days of weightlessness the angular velocity of head movements increased. Over the next days of microgravity the velocity of head movements gradually decreased. On landing day a significant decrease of head rotation velocity was observed compared to the head movement velocity before spaceflight. Re-adaptation to Earth condition measured by body sway on soft support showed similar time course, but re-adaptation measured by postural responses to vestibular galvanic stimulation was prolonged. These results showed that the angular velocity of aimed head movements of cosmonauts is a good indicator of sensory-motor adaptation in altered gravity conditions.     

Alterations of characteristics of horizontal gaze fixation reaction in long-term space flights

The study was performed to explore effects of long-duration SF on the characteristics of horizontal gaze fixation reaction (hGFR). Changes in GFR observed in long-duration space flight (SF) point out to serious disturbances of the VOR system due to, apparently, altered vestibular activity. Two strategies of reaction adaptation to the microgravity conditions were discovered in cosmonauts of civic occupations and pilots.     

Simulated microgravity‐induced epigenetic changes in human lymphocytes

Real space flight and modeled microgravity conditions result in changes in the expression of genes that control important cellular functions. However, the mechanisms for microgravity‐induced gene expression changes are not clear. The epigenetic changes of DNA methylation and chromatin histones modifications are known to regulate gene expression. The objectives of this study were to investigate whether simulated microgravity alters (a) the DNA methylation and histone acetylation, and (b) the expression of DNMT1, DNMT3a, DNMT3b, and HDAC1 genes that regulate epigenetic events. To achieve these objectives, human T‐lymphocyte cells were grown in a rotary cell culture system (RCCS) that simulates microgravity, and in parallel under normal gravitational conditions as control. The microgravity‐induced DNA methylation changes were detected by methylation sensitive‐random amplified polymorphic DNA (MS‐RAPD) analysis of genomic DNA. The gene expression was measured by Quantitative Real‐time PCR. The expression of DNMT1, DNMT3a, and DNMT3b was found to be increased at 72 h, and decreased at 7 days in microgravity exposed cells. The MS‐RAPD analysis revealed that simulated microgravity exposure results in DNA hypomethylation and mutational changes. Gene expression analysis revealed microgravity exposure time‐dependent decreased expression of HDAC1. Decreased expression of HDAC1 should result in increased level of acetylated histone H3, however a decreased level of acetylated H3 was observed in microgravity condition, indicating thereby that other HDACs may be involved in regulation of H3 deacetylation. The findings of this study suggest that epigenetic events could be one of the mechanistic bases for microgravity‐induced gene expression changes and associated adverse health effects. J. Cell. Biochem. 111: 123–129, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of vestibular and support afferentation upon visual pursuit in microgravity

Evaluation of the accuracy of eye turns (saccades) to fix a jerky pointed stimulus, and smooth pursuit of slow linear and sinusoidal movements of both pointed and optokinetic stimuli was performed in 31 cosmonauts on flight days 2-3, 5-8, 30, and once in one or two months of mission. An additional investigation of the eye pursuit function involved 10 cosmonauts, who, after testing during free floating, fulfilled stimulus tracking following a cycle of active head rotation, and 14 cosmonauts who received support afferentation. It was found that at the beginning of adaptation and periodically in the course of long mission, the systems of slow pursuit tracking adopted the strategy of saccadic approximation whereby gaze fixation was achieved through a sequence of macro- or microsaccadic movements. It was demonstrated that these disturbances, practically in all investigated cosmonauts, were consequent to the vestibular deprivation developing in microgravity. Vestibular afferentation produced by active head rotation improved characteristics of visual pursuit. Support deprivation also affects pursuit tracking by cosmonauts who form the concept of space orientation based on perception of their head and leg position. With support afferentation, these cosmonauts demonstrated improved visual pursuit characteristics.     

Eye-Head Coordination for Visual Cognitive Processing

We investigated coordinated movements between the eyes and head (“eye-head coordination”) in relation to vision for action. Several studies have measured eye and head movements during a single gaze shift, focusing on the mechanisms of motor control during eye-head coordination. However, in everyday life, gaze shifts occur sequentially and are accompanied by movements of the head and body. Under such conditions, visual cognitive processing influences eye movements and might also influence eye-head coordination because sequential gaze shifts include cycles of visual processing (fixation) and data acquisition (gaze shifts). In the present study, we examined how the eyes and head move in coordination during visual search in a large visual field. Subjects moved their eyes, head, and body without restriction inside a 360° visual display system. We found patterns of eye-head coordination that differed those observed in single gaze-shift studies. First, we frequently observed multiple saccades during one continuous head movement, and the contribution of head movement to gaze shifts increased as the number of saccades increased. This relationship between head movements and sequential gaze shifts suggests eye-head coordination over several saccade-fixation sequences; this could be related to cognitive processing because saccade-fixation cycles are the result of visual cognitive processing. Second, distribution bias of eye position during gaze fixation was highly correlated with head orientation. The distribution peak of eye position was biased in the same direction as head orientation. This influence of head orientation suggests that eye-head coordination is involved in gaze fixation, when the visual system processes retinal information. This further supports the role of eye-head coordination in visual cognitive processing.     

Head Movements Evoked in Alert Rhesus Monkey by Vestibular Prosthesis Stimulation: Implications for Postural and Gaze Stabilization

The vestibular system detects motion of the head in space and in turn generates reflexes that are vital for our daily activities. The eye movements produced by the vestibulo-ocular reflex (VOR) play an essential role in stabilizing the visual axis (gaze), while vestibulo-spinal reflexes ensure the maintenance of head and body posture. The neuronal pathways from the vestibular periphery to the cervical spinal cord potentially serve a dual role, since they function to stabilize the head relative to inertial space and could thus contribute to gaze (eye-in-head + head-in-space) and posture stabilization. To date, however, the functional significance of vestibular-neck pathways in alert primates remains a matter of debate. Here we used a vestibular prosthesis to 1) quantify vestibularly-driven head movements in primates, and 2) assess whether these evoked head movements make a significant contribution to gaze as well as postural stabilization. We stimulated electrodes implanted in the horizontal semicircular canal of alert rhesus monkeys, and measured the head and eye movements evoked during a 100ms time period for which the contribution of longer latency voluntary inputs to the neck would be minimal. Our results show that prosthetic stimulation evoked significant head movements with latencies consistent with known vestibulo-spinal pathways. Furthermore, while the evoked head movements were substantially smaller than the coincidently evoked eye movements, they made a significant contribution to gaze stabilization, complementing the VOR to ensure that the appropriate gaze response is achieved. We speculate that analogous compensatory head movements will be evoked when implanted prosthetic devices are transitioned to human patients.     

Dynamics of root growth in microgravity

An experiment to study the growth of garden cress roots in microgravity is described. The experiment, denoted RANDOM, was an ESA Biorack experiment in the IML-2 flight in July 1994. In the absence of gravity, it can be anticipated that the roots would show random growth, changing their direction randomly. The hypothesis that such random growth movements occur according to random walk theory, leads to predictions as to the detailed manner in which deviations increase with time. The experiment was designed to test this random walk hypothesis. The paper concentrates on the technological aspects of studying the roots in microgravity. The development of suitable plant chambers, fitting containers developed by ESA, is described as well as the techniques used to grow the seeds between agar slices. hardware was developed to record photographically root movements between the agar slices. Photos were taken once per hour. Some plant chambers were designed to allow fixation of plant material in space. The practical solutions found using glutaraldehyde for prefixation in the Spacelab, within the restrictions given, are described. The experimental results show that the growth pattern in fact followed the prediction from the random walk approach. The average changes in the growth direction stayed constant and equal to zero during the experiment while the squared angular deviations increased proportional to time. Furthermore, plant material prefixed in orbit was permanently fixed after the flight. Light microscopy and electron microscopy pictures are shown as examples of the results achieved. The long prefixation period meant a drawback for the quality of the fixation process. However, sections suitable for study were achieved. The main goals of the RANDOM experiment were therefore achieved.     

Tests of a linear model of visual-vestibular interaction using the technique of parameter estimation

The goal of this study was to test whether a superposition model of smooth-pursuit and vestibulo-ocular reflex (VOR) eye movements could account for the stability of gaze that subjects show as they view a stationary target, during head rotations at frequencies that correspond to natural movements. Horizontal smooth-pursuit and the VOR were tested using sinusoidal stimuli with frequencies in the range 1.0–3.5 Hz. During head rotation, subjects viewed a stationary target either directly or through an optical device that required eye movements to be approximately twice the amplitude of head movements in order to maintain foveal vision of the target. The gain of compensatory eye movements during viewing through the optical device was generally greater than during direct viewing or during attempted fixation of the remembered target location in darkness. This suggests that visual factors influence the response, even at high frequencies of head rotation. During viewing through the optical device, the gain of compensatory eye movements declined as a function of the frequency of head rotation (P < 0.001) but, at any particular frequency, there was no correlation with peak head velocity (P > 0.23), peak head acceleration (P > 0.22) or retinal slip speed (P > 0.22). The optimal values of parameters of smooth-pursuit and VOR components of a simple superposition model were estimated in the frequency domain, using the measured responses during head rotation, as each subject viewed the stationary target through the optical device. We then compared the model's prediction of smooth-pursuit gain and phase, at each frequency, with values obtained experimentally. Each subject's pursuit showed lower gain and greater phase lag than the model predicted. Smooth-pursuit performance did not improve significantly if the moving target was a 10 deg × 10 deg Amsler grid, or if sinusoidal oscillation of the target was superimposed on ramp motion. Further, subjects were still able to modulate the gain of compensatory eye movements during pseudo-random head perturbations, making improved predictor performance during visual-vestibular interactions unlikely. We conclude that the increase in gain of eye movements that compensate for head rotations when subjects view, rather than imagine, a stationary target cannot be adequately explained by superposition of VOR and smooth-pursuit signals. Instead, vision may affect VOR performance by determining the context of the behavior. Received: 16 June 1997 / Accepted: 5 December 1997     

Responses of collicular fixation neurons to gaze shift perturbations in head-unrestrained monkey reveal gaze feedback control

A prominent hypothesis in motor control is that endpoint errors are minimized because motor commands are updated in real time via internal feedback loops. We investigated in monkey whether orienting saccadic gaze shifts made in the dark with coordinated eye-head movements are controlled by feedback. We recorded from superior colliculus fixation neurons (SCFNs) that fired tonically during fixation and were silent during gaze shifts. When we briefly (相似文献   

Lymphocyte movements and interactions in microgravity

Cell-cell contacts and the formation of aggregates play an important role in the mitogen induced in-vitro activation of lymphocytes. The fact that the formation of cell aggregates is only slightly reduced in microgravity suggests that cells are moving and interacting also in space. Direct evidence was obtained for the first time in an experiment performed on a sounding rocket flight, where the movements and interactions of free-floating, non activated cells could be observed in real time in microgravity. In an experiment performed on the IML-2 mission in July 1994, the movements and interactions of human lymphocytes during activation with the mitogen Con A were studied in real time in microgravity.     

Ethylene Is Responsible for a Disturbed Development of Plant Reproductive System under Conditions of Space Flight

The development of reproductive organs was studied on three dwarf cultivars of wheat Triticum aestivum and the fast-cycling Brassica rapa plants, grown under earth control conditions, during the space flight in the Mir orbital station, and in a earth experiment that simulated growth conditions during the space flight, including an elevated content of ethylene in the air (1 mg/m³ on average). We found that the embryological characteristics of the plants were not affected by space flight conditions. The elevated ethylene content in air resulted in some changes in the morphometric characteristics of inflorescences and a greater frequency of sterility similar under conditions of space flight and control earth experiment. We conclude that the abnormalities and modifications in the development of reproductive organs, induced by space flight conditions, were caused by a secondary factor, an elevated ethylene content in the cabin air, rather than by microgravity.     

Gravity-related critical periods in vestibular and tail development of Xenopus laevis

Sensory systems are characterized by developmental periods during which they are susceptible to environmental modifications, in particular to sensory deprivation. The experiment, XENOPUS, on Soyuz in 2008 was the fourth space flight experiment since 1993 to explore whether tail and vestibular development of Xenopus laevis has a gravity-related critical period. During this flight, tadpoles were used that had developed either the early hindlimb (stage 47) or forelimb bud (stage 50) at launch of the spacecraft. The results revealed (1) no impact of microgravity on the development of the roll-induced vestibuloocular reflex (rVOR) in both stages and (2) a stage-related sensitivity of tail development to microgravity exposure. These results were combined and compared with observations from space flights on other orbital platforms. The combined data revealed (1) a narrow gravity-related critical period for rVOR development close to the period of the first appearance of the reflex and (2) a longer one for tail development lasting from the early tail bud to the early forelimb bud stage.     

Survival of micro-organisms in space

Dried suspensions ofPenicillium roqueforti Thom, Coliphage T-1,Bacillus subtilis and tobacco mosaic virus were exposed to space on board the Gemini-IX-A and XII earth satellites and the Agena-VIII space rocket. All micro-organisms tested survived the direct exposure during the Gemini-IX-A experiment. In the Gemini-XII experiment only the T-1 phage survived the direct exposure. The survival was influenced by the suspending medium and depended on the species of the microorganism. After four months of space flight on the Agena-VIII space rocket surviving fractions between 2×10^–3 and 1.0 were found in the unopened flight container. However, micro-organisms exposed on the cover of the container during this period were completely inactivated. Shielding against solar ultraviolet radiation during flight resulted in survival of micro-organisms exceeding to that of the transport controls, and the survival was considered complete.Sterile methylcellulose collection surfaces were exposed to space on board the Gemini-IX-A and XII satellites in an attempt to collect viable micro-organisms in space. None of the collection surfaces yielded viable micro-organisms.     

Visual gaze control during peering flight manoeuvres in honeybees

As animals travel through the environment, powerful reflexes help stabilize their gaze by actively maintaining head and eyes in a level orientation. Gaze stabilization reduces motion blur and prevents image rotations. It also assists in depth perception based on translational optic flow. Here we describe side-to-side flight manoeuvres in honeybees and investigate how the bees’ gaze is stabilized against rotations during these movements. We used high-speed video equipment to record flight paths and head movements in honeybees visiting a feeder. We show that during their approach, bees generate lateral movements with a median amplitude of about 20 mm. These movements occur with a frequency of up to 7 Hz and are generated by periodic roll movements of the thorax with amplitudes of up to ±60°. During such thorax roll oscillations, the head is held close to horizontal, thereby minimizing rotational optic flow. By having bees fly through an oscillating, patterned drum, we show that head stabilization is based mainly on visual motion cues. Bees exposed to a continuously rotating drum, however, hold their head fixed at an oblique angle. This result shows that although gaze stabilization is driven by visual motion cues, it is limited by other mechanisms, such as the dorsal light response or gravity reception.     

Synergy between stresses: an interaction between spaceflight‐associated conditions and the microgravity response

Gravity is the one constant, ubiquitous force that has shaped life on Earth over its 4.8 billion years of evolution. But the sheer inescapability of Earth’s gravitational pull has meant that its influence on Earth’s organisms is difficult to study. Neutralization of the gravity vector (so‐called simulated microgravity) by random movement in three‐dimensional space is the best option for Earth‐based experiments, with spaceflight alone offering the possibility to assess the effects of an extremely reduced gravitational field (microgravity). However, the technical constraints associated with spaceflight introduce complications that can compromise the interpretation of microgravity experiments. It can be unclear whether changes detected in these experiments reflect additional spaceflight‐related stresses (temperature shifts, vibrational effects, radiation exposure, and so on) as opposed to the loss of gravitational force per se. In this issue, Herranz et al. (2010) report a careful study in which the effects of simulated and actual microgravity on gene expression in Drosophila melanogaster were compared and the effects of the flight‐associated stresses on the microgravity responses were investigated. A striking finding emerged. The additional stresses associated with the spaceflight experiment altered the response to microgravity. Despite controlling for the effects of these stresses/constraints, the group found that responses to microgravity are much stronger in the stressed/constrained background than in its absence. This interaction of gravity with other environmental influences is a novel finding with important implications for microgravity research and other situations where multiple stress factors are combined.     

Circumnutational movement in rice coleoptiles involves the gravitropic response: analysis of an agravitropic mutant and space‐grown seedlings

Plants exhibit helical growth movements known as circumnutation in growing organs. Some studies indicate that circumnutation involves the gravitropic response, but this notion is a matter of debate. Here, using the agravitropic rice mutant lazy1 and space‐grown rice seedlings, we found that circumnutation was reduced or lost during agravitropic growth in coleoptiles. Coleoptiles of wild‐type rice exhibited circumnutation in the dark, with vigorous oscillatory movements during their growth. The gravitropic responses in lazy1 coleoptiles differed depending on the growth stage, with gravitropic responses detected during early growth and agravitropism during later growth. The nutation‐like movements observed in lazy1 coleoptiles at the early stage of growth were no longer detected with the disappearance of the gravitropic response. To verify the relationship between circumnutation and gravitropic responses in rice coleoptiles, we conducted spaceflight experiments in plants under microgravity conditions on the International Space Station. Wild‐type rice seeds were germinated, and the resulting seedlings were grown under microgravity or a centrifuge‐generated 1 g environment in space. We began filming the seedlings 2 days after seed imbibition and obtained images of seedling growth every 15 min. The seed germination rate in space was 92–100% under both microgravity and 1 g conditions. LED‐synchronized flashlight photography induced an attenuation of coleoptile growth and circumnutational movement due to cumulative light exposure. Nevertheless, wild‐type rice coleoptiles still showed circumnutational oscillations under 1 g but not microgravity conditions. These results support the idea that the gravitropic response is involved in plant circumnutation.     

Modification of growth anisotropy and cortical microtubule dynamics in Arabidopsis hypocotyls grown under microgravity conditions in space

We carried out a space experiment, denoted as Aniso Tubule, to examine the effects of microgravity on the growth anisotropy and cortical microtubule dynamics in Arabidopsis hypocotyls, using lines in which microtubules are visualized by labeling tubulin or microtubule‐associated proteins (MAPs) with green fluorescent protein (GFP). In all lines, GFP‐tubulin6 (TUB6)‐, basic proline‐rich protein1 (BPP1)‐GFP‐ and spira1‐like3 (SP1L3)‐GFP‐expressing using a constitutive promoter, and spiral2 (SPR2)‐GFP‐ and GFP‐65 kDa MAP‐1 (MAP65‐1)‐expressing using a native promoter, the length of hypocotyls grown under microgravity conditions in space was longer than that grown at 1 g conditions on the ground. In contrast, the diameter of hypocotyls grown under microgravity conditions was smaller than that of the hypocotyls grown at 1 g. The percentage of cells with transverse microtubules was increased under microgravity conditions, irrespective of the lines. Also, the average angle of the microtubules with respect to the transverse cell axis was decreased in hypocotyls grown under microgravity conditions. When GFP fluorescence was quantified in hypocotyls of GFP‐MAP65‐1 and SPR2‐GFP lines, microgravity increased the levels of MAP65‐1, which appears to be involved in the maintenance of transverse microtubule orientation. However, the levels of SPR2 under microgravity conditions were comparable to those at 1 g. These results suggest that the microgravity‐induced increase in the levels of MAP65‐1 is involved in increase in the transverse microtubules, which may lead to modification of growth anisotropy, thereby developing longer and thinner hypocotyls under microgravity conditions in space.     

Scanning Behavior in Echolocating Common Pipistrelle Bats (Pipistrellus pipistrellus)

Echolocating bats construct an auditory world sequentially by analyzing successive pulse-echo pairs. Many other mammals rely upon a visual world, acquired by sequential foveal fixations connected by visual gaze saccades. We investigated the scanning behavior of bats and compared it to visual scanning. We assumed that each pulse-echo pair evaluation corresponds to a foveal fixation and that sonar beam movements between pulses can be seen as acoustic gaze saccades. We used a two-dimensional 16 microphone array to determine the sonar beam direction of succeeding pulses and to characterize the three dimensional scanning behavior in the common pipistrelle bat (Pipistrellus pipistrellus) flying in the field. We also used variations of signal amplitude of single microphone recordings as indicator for scanning behavior in open space. We analyzed 33 flight sequences containing more than 700 echolocation calls to determine bat positions, source levels, and beam aiming. When searching for prey and orienting in space, bats moved their sonar beam in all directions, often alternately back and forth. They also produced sequences with irregular or no scanning movements. When approaching the array, the scanning movements were much smaller and the beam was moved over the array in small steps. Differences in the scanning pattern at various recording sites indicated that the scanning behavior depended on the echolocation task that was being performed. The scanning angles varied over a wide range and were often larger than the maximum angle measurable by our array. We found that echolocating bats use a “saccade and fixate” strategy similar to vision. Through the use of scanning movements, bats are capable of finding and exploring targets in a wide search cone centered along flight direction.