Microgravity effects on "postural" muscle activity patterns.

Changes in neuromuscular activation patterns associated with movements made in microgravity can contribute to muscular atrophy. Using EMG to monitor "postural" muscles, it was found that free floating arm flexions made in microgravity were not always preceded by neuromuscular activation patterns normally observed during movements made in unit gravity. Additionally, manipulation of foot sensory input during microgravity arm flexion impacted upon anticipatory postural muscle activation.     

Clover development during spaceflight: a model system.

The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed.     

Balloon altitude studies of southern hemisphere hard X-ray sources by the Imperial College-University of Tasmania-INPE collaboration

Hard X-ray balloon altitude measurements with a 1600 cm² phoswich array are described. Data from observations on Sco X-1, GX1+4, GX5−1, Nova Oph. 1977, SMC X-1, SS433, IC 4329A and MR 2251-178 are presented. The role of Comptonisation in X-ray production for Sco X-1 and GX1+4 is discussed.     

Performance of a blood chemistry analyzer during parabolic flight

We have tested the performance of the VISION System Blood Analyzer, produced by Abbott Laboratories, during parabolic flight on a KC-135 aircraft (NASA 930). This fully automated instrument performed flawlessly in these trials, demonstrating its potential for efficient, reliable use in a microgravity environment. In addition to instrument capability, we demonstrated that investigators could readily fill specially modified test packs with fluid during zero gravity, and that filled test packs could be easily loaded into VISION during an episode of microgravity.     

Embryogenesis, hatching and larval development of Artemia during orbital spaceflight.

Developmental biology studies, using gastrula-arrested cysts of the brine shrimp Artemia franciscana, were conducted during two flights of the space shuttle Atlantis (missions STS-37 and STS-43) in 1991. Dehydrated cysts were activated, on orbit, by addition of salt water to the cysts, and then development was terminated by the addition of fixative. Development took place in 5 ml syringes, connected by tubing to activation syringes, containing salt water, and termination syringes, containing fixative. Comparison of space results with simultaneous ground control experiments showed that equivalent percentages of naupliar larvae hatched in the syringes (40%). Thus, reactivation of development, completion of embryogenesis, emergence and hatching took place, during spaceflight, without recognizable alteration in numbers of larvae produced. Post-hatching larval development was studied in experiments where development was terminated, by introduction of fixative, 2 days, 4 days, and 8 days after reinitiation of development. During spaceflight, successive larval instars or stages, interrupted by molts, occurred, generating brine shrimp at appropriate larval instars. Naupliar larvae possessed the single naupliar eye, and development of the lateral pair of adult eyes also took place in space. Transmission electron microscopy revealed extensive differentiation, including skeletal muscle and gut endoderm, as well as the eye tissues. These studies demonstrate the potential value of Artemia for developmental biology studies during spaceflight, and show that extensive degrees of development can take place in this microgravity environment.     

Liposome formation in microgravity.

Liposomes are artificial vesicles with a phospholipid bilayer membrane. The formation of liposomes is a self-assembly process that is driven by the amphipathic nature of phospholipid molecules and can be observed during the removal of detergent from phospholipids dissolved in detergent micelles. As detergent concentration in the mixed micelles decreases, the non-polar tail regions of phospholipids produce a hydrophobic effect that drives the micelles to fuse and form planar bilayers in which phospholipids orient with tail regions to the center of the bilayer and polar head regions to the external surface. Remaining detergent molecules shield exposed edges of the bilayer sheet from the aqueous environment. Further removal of detergent leads to intramembrane folding and membrane folding and membrane vesiculation, forming liposomes. We have observed that the formation of liposomes is altered in microgravity. Liposomes that were formed at 1-g did not exceed 150 nm in diameter, whereas liposomes that were formed during spaceflight exhibited diameters up to 2000 nm. Using detergent-stabilized planar bilayers, we determined that the stage of liposome formation most influenced by gravity is membrane vesiculation. In addition, we found that small, equipment-induced fluid disturbances increased vesiculation and negated the size-enhancing effects of microgravity. However, these small disturbances had no effect on liposome size at 1-g, likely due to the presence of gravity-induced buoyancy-driven fluid flows (e.g., convection currents). Our results indicate that fluid disturbances, induced by gravity, influence the vesiculation of membranes and limit the diameter of forming liposomes.     

Production and action of cytokines in space.

B6MP102 cells, a continuously cultured murine bone marrow macrophage cell line, were tested for secretion of tumor necrosis factor-alpha and Interleukin-1 during space flight. We found that B6MP102 cells secreted more tumor necrosis factor-alpha and interleukin-1 when stimulated in space with lipopolysaccharide than controls similarly stimulated on earth. This compared to increased secretion of interferon-beta and -gamma by lymphocytes that was measured on the same shuttle flights. Although space flight enhanced B6MP102 secretion of tumor necrosis factor-alpha, an experiment on a subsequent space flight (STS-50) found that cellular cytotoxicity, mediated by tumor necrosis factor-alpha, was inhibited.     

Educational opportunities within the NASA Specialized Center of Research and Training in Gravitational Biology.

The NASA Specialized Center of Research and Training (NSCORT) in Gravitational Biology was established at Kansas State University, supported through NASA's Life Science Division, Office of Space Science and Applications. Educational opportunities, associated with each of the research projects which form the nucleus of the Center, are complemented by program enrichments such as scholar exchanges and linkages to other NASA and commercial programs. The focus of this training program, and a preliminary assessment of its successes, are described.     

Formation and vesiculation of biomembranes during spaceflight.

Shuttle flight, sounding rocket flight, and parabolic flight experiments demonstrate the formation of bilayer membrane vesicles (liposomes) in reduced gravity, following the dilution of detergent from detergent-phospholipid mixed micelles. The reduction in detergent concentration initiates assembly of bilayer membrane sheets, which are sensitive to solution disturbances. An increase in disturbances by forced dilution results in small diameter liposomes (< 150 nm), in both ground and flight samples. In the absence of forced dilution, liposomes remain small at 1-g, but exhibit much larger diameters at 0-g (1000-2000 nm). Our spaceflight data reveal that membrane assembly and vesiculation are strongly influenced by gravity-induced solution disturbances (e.g., convection currents), which limit vesicle diameter.