Altered gravity affects ventral root activity during fictive swimming and the static vestibuloocular reflex in young tadpoles (Xenopus laevis)

During early periods of life, modifications of the gravitational environment affect the development of sensory, neuronal and motor systems. The vestibular system exerts significant effects on motor networks that control eye and body posture as well as swimming. The objective of the present study was to study whether altered gravity (AG) affects vestibuloocular and spinal motor systems in a correlated manner. During the French Soyuz taxi flight Andromède to the International Space Station ISS (launch: October 21, 2001; landing: October 31, 2001) Xenopus laevis embryos were exposed for 10 days to microgravity (microg). In addition, a similar experiment with 3g-hypergravity (3g) was performed in the laboratory. At onset of AG, embryos had reached developmental stages 24 to 27. After exposure to AG, each tadpole was tested for its roll-induced vestibuloocular reflex (rVOR) and 3 hours later it was tested for the neuronal activity recorded from the ventral roots (VR) during fictive swimming. During the post-AG recording periods tadpoles had reached developmental stages 45 to 47. It was observed that microgravity affected VR activity during fictive swimming and rVOR. In particular, VR activity changes included a significant decrease of the rostrocaudal delay and a significant increase of episode duration. The rVOR-amplitude was transiently depressed. Hypergravity was less effective on the locomotor pattern; occurring effects on fictive swimming were the opposite of microg effects. As after microgravity, the rVOR was depressed after 3g-exposure. All modifications of the rVOR and VR-activity recovered to normal levels within 4 to 7 days after termination of AG. Significant correlations between the rVOR amplitude and VR activity of respective tadpoles during the recording period have been observed in both tadpoles with or without AG experience. The data are consistent with the assumptions that during this period of life which is characterized by a progressive development of vestibuloocular and vestibulospinal projections (i) microgravity retards the development of VR activity while hypergravity weakly accelerates it; (ii) that microgravity retards the rVOR development while hypergravity caused a sensitization, and that (iii) AG-induced changes of VR activity during fictive swimming have a vestibular origin.     

"Critical periods" in vestibular development or adaptation of gravity sensory systems to altered gravitational conditions?

1. A feature of sensory, neuronal and motor systems is the existence of a critical period during their development. Modification of environmental conditions during this specific period of life affects development in a long-term manner, or even irreversibly. Deprivation is the prefered approach to study the existence and duration of critical periods. For gravity sensory systems, space flights offer the only opportunity for deprivation conditions. 2. Studies in a fish (Oreochromis mossambicus) and an amphibian (Xenopus laevis) revealed a significant sensitivity of their roll-induced static vestibuloocular reflex (rVOR) to a 9- to 10-day gravity deprivation (microgravity) during a spaceflight. In some instances, the rVOR was augmented after the flight as demonstrated in young Oreochromis which were launched when their rVOR had not been developed, and in Xenopus tadpoles launched after their rVOR had developed. Fish which could perform the rVOR at launch were insensitive to microgravity exposure. A similar insensitivity to microgravity was observed in Xenopus tadpoles with normal body shape which had not yet developed their rVOR at launch. Some tadpoles, however, developed an upward bended tail during their space flight; their rVOR was significantly depressed after termination of microgravity independent of the age at onset of the flight. Hypergravity depressed the rVOR for all so far tested developmental stages in both Oreochromis and Xenopus. 3. Both adaptive processes during exposure to altered gravity as well as the existence of a critical period in vestibular development might be responsible for the modulation of the rVOR recorded after exposure to altered gravity. Deprivation studies have to be extended to older developmental stages to test the possibility of a critical period; however, this approach is limited due to the low number of space flights.     

Hypergravity decreases carbonic anhydrase-reactivity in inner ear maculae of fish

Previous investigations revealed that fish inner ear otolith growth depends on the amplitude and the direction of gravity. Both otolith total size, otolith bilateral size-asymmetry and the total and bilateral calcium-incorporation are also affected by gravity. Hypergravity, e.g., slows down otolith growth and diminishes bilateral otolith asymmetry as compared to 1 g control specimens raised in parallel. Since the enzyme carbonic anhydrase (CA) plays a prominent role in otolithic calcification, the reactivity of inner ear CA during otolith growth under hypergravity was investigated. CA-reactivity was demonstrated histochemically and densitometrically on sections of inner ear maculae of larval cichlid fish (Oreochromis mossambicus), that were kept for 6 hrs in a 3 g hypergravity centrifuge. The total unilateral macular CA-reactivity and the bilateral difference in CA between the left and the right maculae were significantly lower in 3 g animals than in 1g controls. The result is in complete agreement with previous studies indicating that a regulatory mechanism, which adjusts otolith size and asymmetry towards the gravity vector, acts via activation/deactivation of macular CA.     

Effect of hypergravity stimulus on XTH gene expression in Arabidopsis thaliana.

There are several reports indicating that hypergravity and microgravity influence the mechanical properties of cell walls in shoots, resulting in changes in the growth rate. The mechanical properties of cell walls in dicots are mainly determined by the physicochemical properties of xyloglucan, a matrix polysaccharide. An increase in the molecular mass of xyloglucan correlated with a decrease in cell wall extensibility. Hypergravity is known to increase the molecular mass of xyloglucan. The cell wall enzyme, xyloglucan endotransglucosylase/hydrolase (XTH) is involved in xyloglucan metabolism. Using Arabidopsis, it was examined whether or not the expression of XTH genes in the floral stem and rosette leaf is influenced by hypergravity. RT-PCR analysis revealed that the expression of XTH genes changes in response to hypergravity of 300 g.     

Responses to hypergravity in proliferation of Paramecium tetraurelia

It has been reported that Paramecium proliferates faster when cultured under microgravity in orbit, and slower when cultured under hypergravity. This shows that the proliferation rate of Paramecium affected by gravity. The effect of gravity on Paramecium proliferation has been argued to be direct in a paper with an axenic culture under hypergravity. To clear up uncertainties with regard to the effect of gravity, Paramecium tetraurelia was cultured axenically under hypergravity (20 x g) and the time course of the proliferation was investigated quantitatively by a new non-invasive method, laser-beam optical slice, for measuring the cell density. This method includes optical slicing a part of the culture and computer-aided counting of cells in the sliced volume. The effects of hypergravity were assessed by comparing the kinetic parameters of proliferation that were obtained through a numerical analysis based on the logistic growth equation. Cells grown under 20 x g conditions had a significantly lower proliferation rate, and had a lower population density at the stationary phase. The lowered proliferation rate continued as long as cells were exposed to hypergravity (> one month). Hypergravity reduced the cell size of Paramecium. The long and short axes of the cell became shorter at 20 x g than those of control cells, which indicates a decrease in volume of the cell grown under hypergravity and is consistent with the reported increase in cell volume under microgravity. The reduced proliferation rate implies changes in biological time defined by fission age. In fact the length of autogamy immaturity decreased by measure of clock time, whereas it remained unchanged by measure of fission age.     

BIOPACK: the ground controlled late access biological research facility

Future Space Shuttle flights shall be characterized by activities necessary to further build the International Space Station, ISS. During these missions limited resources are available to conduct biological experiments in space. The Shuttles' Middeck is a very suitable place to conduct science during the ISS assembly missions or dedicated science missions. The BIOPACK, which flew its first mission during the STS-107, provides a versatile Middeck Locker based research tool for gravitational biology studies. The core facility occupies the space of only two Middeck Lockers. Experiment temperatures are controlled for bacteria, plant, invertebrate and mammalian cultures. Gravity levels and profiles can be set ranging from 0 to 2.0 x g on three independent centrifuges. This provides the experimenter with a 1.0 x g on-board reference and intermediate hypogravity and hypergravity data points to investigate e.g. threshold levels in biological responses. Temperature sensitive items can be stored in the facilities' -10 degrees C and +4 degrees C stowage areas. During STS-107 the facility also included a small glovebox (GBX) and passive temperature controlled units (PTCU). The GBX provides the experimenter with two extra levels of containment for safe sample handling. This biological research facility is a late access (L-10 hrs) laboratory, which, when reaching orbit, could automatically be starting up reducing important experiment lag-time and valuable crew time. The system is completely telecommanded when needed. During flight system parameters like temperatures, centrifuge speeds, experiment commanding or sensor readouts can be monitored and changed when needed. Although ISS provides a wide range of research facilities there is still need for an STS-based late access facility such as the BIOPACK providing experimenters with a very versatile research cabinet for biological experiments under microgravity and in-flight control conditions.     

Body mass change during altered gravity: spaceflight, centrifugation, and return to 1 G

To assess the effect of gravity on growth, immature rats (130-200 g) were studied during chronic altered gravity exposure and while transitioning between gravity fields. Body mass gain of rats (n = 12) exposed to 14 days of microgravity (spaceflight) was evaluated and compared to mass gain of 1 G controls. Spaceflight did not affect mass gain. Six rats exposed to 1 G following spaceflight, when compared to controls, experienced a significant (0 < 0.05) post-flight mass loss over 48 h of 13 g. Over subsequent days, however, this loss was compensated for, and no difference from 1 G controls was noted after 5 days. Exposure to hypergravity (2 G) for 16 days was evaluated [(n = 6/group): Centrifuge (C); On Center Control (OCC); Centrifuge Control (CC)]. Body mass of centrifuged and OCC rats was reduced within 24 h, with OCCs regaining control mass within 13 days. The mass difference (44 g) in centrifuged animals persisted, however, with no subsequent difference in rate of mass gain between centrifuged animals and controls over Days 3-16 (3.7 +/- 0.1 vs. 3.9 +/- 0.1 g/day, respectively). Transitioning from 2 G to 1 G resulted in a mass increase within 48 hours for centrifuged animals. Over Days 3-16 at 1 G, the rate of gain for centrifuged animals continued to increase (3.1 +/- 0.1 g/day compared to 2.1 +/- 0.1 g/day for controls); differences from control, however, were still noted on Day 16. Transitioning to an increase in a gravity field causes acute losses in body mass. In hypergravity, the acute reduction in body mass persists but the rate of mass gain is normal. Animals returning to 1 G, after acute changes, adjust to attain control mass.     

Ontogenesis of mammals and gravity

The results of the experiments with Wistar rats in microgravity and 2G hypergravity are summarized. Their analysis allows to conclude that adaptive potentials of adult animals in space flights lasting up to 1/50 of their life span are enough for maintenance of adequate reactions to acute and chronic stressors in the postflight period, rapid elimination of space-induced metabolic and structural alterations on return to Earth, maintenance of normal reproductive function after space flight. In embryological experiments it was demonstrated that during space flight it is possible not only to maintain physiological functions of an adult organism, but to form functions of a developing fetus. The animals that spent the portion of their prenatal development in space flight were capable to go through the entire cycle of postnatal development, up to sexual maturity and reproduction. In ground based centrifuge experiments with 2G it was demonstrated the possibility of realizing, under hypergravity, of all the main stages of prenatal and early postnatal development of rats: fertilization, embryon implantation, fetal development, birth and lactation of progeny. Exposure of rats to microgravity did not reduce their life span post flight. Alterations in biological age of animals were small.     

Dome formation and tubule morphogenesis by Xenopus kidney A6 cell cultures exposed to microgravity simulated with a 3D-clinostat and to hypergravity

Confluent high-density cell cultures of A6 cells derived from adult male Xenopus kidney exhibit spontaneous dome-formation at 1 g. To determine whether this morphogenetic property is altered by gravity, we used a three-dimensional (3D) clinostat to subject the cells to simulated microgravity, and a centrifuge to subject them to hypergravity. We used the generation orbit control method as the new rotation control system of the 3D-clinostat, not the random method. The growth of A6 cells was significantly enhanced by hypergravity, but significantly reduced by simulated microgravity. Dome formation by A6 cells at high confluence was inhibited under simulated microgravity conditions, whereas hypergravity promoted dome formation and induced tubule morphogenesis, compared to the control at 1 g. These results indicated that changes in gravity influence the morphogenetic properties of A6 cells, such as dome formation and tubule morphogenesis. When dome formation by A6 cells at high confluence was induced spontaneously in the control 1 g culture, the gene expression of the HGF family of pleiotropic factors, such as HGF-like protein (HLP) and growth factor-Livertine (GF-l.ivertine), an epithelial serine protease of channel activating protease 1 (CAP1), and Na+, K+-adenosine triphosphatase (ATPase), increased. Simulated microgravity increased the gene expression of activin A and reduced the gene expression of HLP, GF-Livertine, CAP1, and Na+, K+-ATPase. Hypergravity, on the other hand, decreased the gene expression of activin A and increased the gene expression of HLP, GF-Livertine, CAP1, and Na+, K+-ATPase. These results suggest that the effects of gravitational changes on expression of the HGF family member gene, CAP1, and Na+, K+-ATPase gene may be important for the cell growth, tubule morphogenesis, and dome formation of A6 cells in altered     

Morphometric investigations of sensory vestibular structures in tadpoles (Xenopus laevis) after a spaceflight: implications for microgravity-induced alterations of the vestibuloocular reflex

In lower vertebrates, gravity deprivation by orbital flights modifies the vestibuloocular reflex. Using the amphibian Xenopus laevis, the experiments should clarify to which extent macular structures of the labyrinth are responsible for these modifications. In particular, the shape of otoconia and number and size of sensory macular cells expressing CalBindin were considered. CalBindin is common in mature sensory cells including vestibular hair cells and is probably involved in otoconia formation. Two developmental stages were used for this study: stage 26/27 embryos, which were unable to perform the roll-induced vestibuloocular reflex (rVOR) at onset of microgravity, and stage 45 tadpoles, which had already developed the reflex. The main observations were that the developmental progress of the animals was not affected by microgravity; that in the young tadpole group with normal body shape the rVOR was not modified by microgravity, while in the older group with microgravity experience, the rVOR was augmented; and that significant effects on the shape of otoconia and on the number and size of CalBindin-expressing cells of the labyrinthine maculae cells were absent. In addition, behavioural data were never significantly correlated with morphological features of macular structures such as size and number of CalBindin-expressing cells. It is postulated that mechanisms of vestibular adaptation to microgravity during early development are probably based on mechanisms located in central structures of the vestibular system.     

Effects of spaceflight on human calf hemodynamics.

Chronic microgravity may modify adaptations of the leg circulation to gravitational pressures. We measured resting calf compliance and blood flow with venous occlusion plethysmography, and arterial blood pressure with sphygmomanometry, in seven subjects before, during, and after spaceflight. Calf vascular resistance equaled mean arterial pressure divided by calf flow. Compliance equaled the slope of the calf volume change and venous occlusion pressure relationship for thigh cuff pressures of 20, 40, 60, and 80 mmHg held for 1, 2, 3, and 4 min, respectively, with 1-min breaks between occlusions. Calf blood flow decreased 41% in microgravity (to 1.15 +/- 0.16 ml x 100 ml(-1) x min(-1)) relative to 1-G supine conditions (1.94 +/- 0.19 ml x 100 ml(-1) x min(-1), P = 0.01), and arterial pressure tended to increase (P = 0.05), such that calf vascular resistance doubled in microgravity (preflight: 43 +/- 4 units; in-flight: 83 +/- 13 units; P < 0.001) yet returned to preflight levels after flight. Calf compliance remained unchanged in microgravity but tended to increase during the first week postflight (P > 0.2). Calf vasoconstriction in microgravity qualitatively agrees with the "upright set-point" hypothesis: the circulation seeks conditions approximating upright posture on Earth. No calf hemodynamic result exhibited obvious mechanistic implications for postflight orthostatic intolerance.     

Neuronal regulation of otolith growth and kinetotic behaviour

Inner ear stones (otoliths) of larval cichlid fish were labelled with the calcium-tracer alizarin-complexone (AC) before animals were subjected to hypergravity (hg; 3 g). After the experiment, the otoliths' area between the two AC-labellings was measured. Growth of hg-otoliths was significantly slowed down as compared to 1 g-control specimens. In the course of a second experiment, the vestibular nerve was unilaterally transacted in neonate swordtail fish which were subsequently incubated in AC. Incorporation of AC was considerably lower in the otoliths of the transacted side. The results strongly suggest that otolith growth is continuously regulated in dependence of the environmental gravity vector. Since the otolithic calcium incorporation ceased on the transected head sides, it is concluded that the regulation of otolith growth is based on the central nervous efferent vestibular system.     

Microgravity alters respiratory sinus arrhythmia and short-term heart rate variability in humans

We studied heart rate (HR), heart rate variability (HRV), and respiratory sinus arrhythmia (RSA) in four male subjects before, during, and after 16 days of spaceflight. The electrocardiogram and respiration were recorded during two periods of 4 min controlled breathing at 7.5 and 15 breaths/min in standing and supine postures on the ground and in microgravity. Low (LF)- and high (HF)-frequency components of the short-term HRV (< or =3 min) were computed through Fourier spectral analysis of the R-R intervals. Early in microgravity, HR was decreased compared with both standing and supine positions and had returned to the supine value by the end of the flight. In microgravity, overall variability, the LF-to-HF ratio, and RSA amplitude and phase were similar to preflight supine values. Immediately postflight, HR increased by approximately 15% and remained elevated 15 days after landing. LF/HF was increased, suggesting an increased sympathetic control of HR standing. The overall variability and RSA amplitude in supine decreased postflight, suggesting that vagal tone decreased, which coupled with the decrease in RSA phase shift suggests that this was the result of an adaptation of autonomic control of HR to microgravity. In addition, these alterations persisted for at least 15 days after return to normal gravity (1G).     

Hypergravity increases the molecular mass of xyloglucans by decreasing xyloglucan-degrading activity in azuki bean epicotyls.

Elongation growth of dark-grown azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) epicotyls was suppressed by hypergravity at 30 x g and above. Acceleration at 300 x g significantly decreased the mechanical extensibility of cell walls. The amounts of cell wall polysaccharides (pectin, hemicellulose-II and cellulose) per unit length of epicotyls increased under the hypergravity condition. Hypergravity also increased the amounts and the weight-average molecular mass of xyloglucans in the hemicellulose-II fraction, while decreasing the activity of xyloglucan-degrading enzymes extracted from epicotyl cell walls. These results suggest that hypergravity increases the amounts and the molecular mass of xyloglucans by decreasing xyloglucan-degrading activity. Modification of xyloglucan metabolism as well as the thickening of cell walls under hypergravity conditions seems to be involved in making the cell wall mechanically rigid, thereby inhibiting elongation growth of azuki bean epicotyls.     

Hypergravity stimulates collagen synthesis in human osteoblast-like cells: evidence for the involvement of p44/42 MAP-kinases (ERK 1/2).

The formation and organization of skeletal tissue is strongly influenced by mechanical stimulation. There is increasing evidence that gravitational stress has an impact on the expression of early response genes in mammalian cells and may play a role in the formation of extracellular matrix. In particular, osteoblasts may be unique in their response to gravitational stimuli since in these cells microgravity has been reported to reduce collagen synthesis, while in fibroblasts the opposite effect was observed. Here, we have investigated the influence of hypergravity induced by centrifugation on the collagen synthesis of human osteoblast-like cells (hOB) and studied the possible involvement of the mitogen-activated protein (MAP) kinase signaling cascade. Collagen synthesis was significantly increased by 42+/-16% under hypergravity at 13 x g, an effect paralleled by the enhanced expression of the collagen I alpha 2 (COL1A2) mRNA. No difference was seen in the proportion of collagen types I, III, and V synthesized by hOB. Hypergravity induced a markedly elevated phosphorylation of the p44/42 MAP kinases (ERK 1/2). The inhibition of this pathway suppressed the hypergravity-induced stimulation of both collagen synthesis as well as COL1A2 mRNA expression by about 50%. Our results show that the collagen synthesis of non-transformed hOB is stimulated under hypergravitational conditions. This response appears to be partially mediated by the MAP kinase pathway.     

Stimulation of cyclic GMP efflux in human melanocytes by hypergravity generated by centrifugal acceleration

Gravity alteration (micro- and hypergravity) is known to influence cell functions. As guanosine 3',5'-cyclic monophosphate (cGMP) plays an important role in human melanocyte functions and different guanylyl cyclase isoforms are responsible for cGMP synthesis in human non-metastatic and metastatic melanoma cells, we investigated the effects of hypergravity on the regulation of cGMP levels in cultured human melanocytes and in melanoma cell lines with different metastatic potentials. Hypergravity was produced by horizontal centrifugal acceleration. Here we report that long-term application of hypergravity (up to 5 g for 24 h) stimulated cGMP efflux in cultured melanocytes and in non-metastatic melanoma cells in the presence of 0.1 mM 3-isobutyl-1-methylxanthine (IBMX), a non-selective phosphodiesterase (PDE) inhibitor. Under these conditions, cAMP synthesis and melanin production were up-regulated in pigmented melanocytes and non-metastatic melanoma cells. Hypergravity also stimulated cGMP transport in the presence of 1 microM trequinsin, an inhibitor of cGMP-binding PDE (PDE5) and of transport by multidrug resistance proteins MRP4/5, whereas 50 microM trequinsin partially inhibited cGMP transport. Transport was further inhibited by probenecid, an inhibitor of endogenous non-selective transporters as well as of MRP4/5 and by cycloheximide as an inhibitor of de novo protein synthesis. In contrast, hypergravity did not affect cGMP efflux in metastatic melanoma cells, which might be related to an up-regulated cGMP efflux at 1 g. The results of the present study indicate that hypergravity may stimulate cGMP efflux in melanocytes and in non-metastatic melanoma cells most probably by an enhanced expression of endogenous transporters and/or MRP4/5. Thus, an altered acceleration vector may induce signaling events in melanocytic cells.     

Effect of hypergravity stimulus on XTH gene expression in Arabidopsis thaliana.

Hypergravity stimulus suppresses plant shoot growth by making the cell wall rigid. Xyloglucan endotransglucosylase/hydrolase (XTH) is involved in determining the rigidity of cell walls. We demonstrated that hypergravity influenced the expression of some XTH genes in shoots of Arabidopsis thaliana L.; in response to hypergravity stimulus of 300 g, the expression of AtXTH22 was up-regulated, while that of AtXTH15 was down-regulated. The effect of hypergravity on the expression of these genes was nullified by lanthanum chloride at 0.1 mM, suggesting that the expression of these XTH genes in Arabidopsis is under the control of the mechanoreceptor.     

Optospectroscopic detection of primary reactions associated with the graviperception of Phycomyces. Effects of micro- and hypergravity

The graviperception of sporangiophores of the fungus Phycomyces blakesleeanus involves gravity-induced absorbance changes (GIACs) that represent primary responses of gravitropism (Schmidt and Galland, 2000). GIACs (DeltaA(460-665)) of sporangiophores were measured in vivo with a micro-dual wavelength spectrometer at 460 and 665 nm. Sporangiophores that were placed horizontally displayed an instant increase of the GIACs while the return to the vertical position elicited an instant decrease. The GIACs are specific for graviperception, because they were absent in a gravitropism mutant with a defective madJ gene. During parabola flights hypergravity (1.8 g) elicited a decrease of the GIACs, while microgravity (0 +/- 3 x 10 (-2) g) elicited an instant increase. Hypergravity that was generated in a centrifuge (1.5-6.5 g) elicited also a decrease of the GIACs that saturated at about 5 g. The GIACs have a latency of about 20 ms or shorter and are thus the fastest graviresponses ever measured for fungi, protists, and plants. The threshold for eliciting the GIACs is near 3 x 10 (-2) g, which coincides numerically with the threshold for gravitropic bending. In contrast to gravitropic bending, which requires long-term stimulation, GIACs can be elicited by stimuli as short as 20 to 100 ms, leading to an extremely low threshold dose (acceleration x time) of about 3 x 10 (-3) g s, a value, which is four orders of magnitude below the ones described for other organisms and which makes the GIACs of Phycomyces blakesleeanus the most sensitive gravi-response in literature.     

The behavioral response of zebrafish to hypergravity conditions

Previous reports of the behavior of aquatic organisms in the microgravity environment of space (~10(-6) g) or during the brief weightless period of parabolic flight indicate that most species display a dramatic "looping" or "circling" response (De Jong et al. 1996, Anken, Ibsch and Rahmann 1998). However, the behavior of aquatic species under hypergravity conditions is less clear. Our objectives in the present study were to examine the behavioral response of adult zebrafish (Danio rerio) to hypergravity conditions (2-g), quantify changes in adult swimbladder volume, and to determine if the larvae of zebrafish are capable of accessing the air-water interface for initial swimbladder inflation under hypergravity conditions.     

Behavioral reactions of the bat Carollia perspicillata to abrupt changes in gravity.

As part of an ongoing survey of the behavioral responses of vertebrates to abrupt changes in gravity, we report here on the reactions of bats (Carollia perspicillata) exposed to altered gravity during parabolic aircraft flight. In microgravity, mammals typically behave as if they were upside-down and exhibit repetitive righting reflexes, which often lead to long axis rolling. Since bats, however, normally rest upside-down, we hypothesized that they would not roll in microgravity. Only one of three specimens attempted to fly during microgravity. None rolled or performed any righting maneuvers. During periods of microgravity the bats partially extended their forearms but kept their wings folded and parallel to the body. Between parabolas and occasionally during microgravity the bats groomed themselves. Both the extended limbs and autogrooming may be stress responses to the novel stimulus of altered gravity. This is the first behavioral record of Chiroptera in microgravity.