Volume 1 (2013): Issue 1 (July 2013)

During spaceflight, mice are housed in specially designed cages called the Animal Enclosure Module (AEM). Utilization of this flight hardware may affect the skeletal properties of housed animals, independent of microgravity considerations. To address this issue, we studied the effect of 13 days of AEM housing versus standard vivarium enclosure on female C57BL/6J mice (n=12/group). The effects of AEM housing were most pronounced in the trabecular compartment. AEM mice had 44% and 144% greater trabecular bone volume fraction and connectivity density, respectively, versus vivarium. A similar response was seen at the proximal humerus. We noted a decrease in proximal tibia osteoclast surface (-65%) and eroded surface (-73%) for AEM versus vivarium, while tibia trabecular mineralizing surface (MS/BS) was nearly three-fold greater. Surprisingly, there was also decreased osteoblast surface, as well as lower osteoid volume, surface, and thickness at this site. The effects of AEM housing on femur cortical bone were modest: there was greater periosteal MS/BS, with no effect at the endocortical surface, and lower femur stiffness. Taken together, we have demonstrated significant effects of AEM housing on ground control mice, particularly in the trabecular bone compartment. These findings suggest that an early increase in bone formation, perhaps due to altered behavior and loading in this unique housing environment, was followed by decreased bone formation and resorption as the animals adapted to their new environment. Characterization of spaceflight animal housing is critical to elucidating the true effects of microgravity on skeletal parameters and for the proper selection of ground-based controls.

The effects of microgravity on biological tissues are relatively unexplored, especially in regard to the mammalian female reproductive system. To begin to address this issue, the uterine tissue of female mice flown on NASA shuttle mission STS-118 was studied. Three sets of female mice, each consisting of 12 animals, were utilized in this study: flight animals, ground control animals, and baseline animals. The flight animals were housed in the Animal Enclosure Module (AEM) of the Commercial Biomedical Testing Module-2 (CBMT-2), which was a part of the payload of the shuttle’s mid-deck locker. Ground control animals were housed in ground-based AEMs, which were kept in a room specifically designed to mimic the environmental conditions of the flight units with regard to temperature, humidity, and light/dark cycles on a 48 hour delay. Baseline animals were housed in standard rodent cages at ambient temperature and humidity and a 12/12 light/dark cycle. The uterine tissue was stained using an Alcian Blue Periodic Acid Schiff staining procedure and the apical mucin layer thickness was subsequently analyzed. Analysis of the mucin layer in the uterus revealed that the thickness of the mucin layer in the flight tissue was significantly thicker that the mucin layers of the ground control and baseline tissue.

Spaceflight exploration presents environmental stressors including microgravity-induced cephalad fluid shift and radiation exposure. Ocular changes leading to visual impairment in astronauts are of occupational health relevance. The effect of this complex environment on ocular morphology and function is poorly understood. Female 10-12 week-old BALB/cJ mice were assigned to a flight (FLT) group flown on shuttle mission STS-133, Animal Enclosure Module ground control group (AEM), or vivarium-housed (VIV) ground controls. Eyes were collected at 1, 5, and 7 days after landing and were fixed for histological sectioning. The contralateral eye was used for gene expression profiling by RT-qPCR. Sections were visualized by hematoxylin/eosin stain and processed for 8-hydroxy-2’-deoxyguanosine (8-OHdG), caspase-3, and glial fibrillary acidic protein (GFAP) and β-amyloid double-staining. 8-OHdG and caspase-3 immunoreactivity was increased in the retina in FLT samples at return from flight (R+1) compared to ground controls, and decreased at day 7 (R+7). β-amyloid was seen in the nerve fibers at the post-laminar region of the optic nerve in the flight samples (R+7). Expression of oxidative and cellular stress response genes was upregulated in the retina of FLT samples upon landing, followed by lower levels by R+7. These results suggest that reversible molecular damage occurs in the retina of mice exposed to spaceflight and that protective cellular pathways are induced in the retina and optic nerve in response to these changes.

The purpose of this study was to clarify the beneficial effect of an underwater environment on heart rate (HR) and cardiac autonomic nervous activity (HF) during arm-cranking exercise. Ten healthy young men participated in this study. The arm-cranking exercise (40% peakV̇O₂) was performed for 10 minutes under two conditions: in water and in air. After the exercise, a recovery phase for 30 seconds followed. Changes in HR, V̇O₂, and HF did not differ between the conditions. The time constant of the heart rate decay for the first 30 seconds after exercise in the water was less than in air. The results suggest that cardiac parasympathetic nervous activity influences earlier recovery of HR after exercise in water. The results of our study suggest underwater exercise may be applied to wider areas of health management for individuals returning from space travel or sedentary patients in simulated microgravity environments.

We investigated the effects of altered gravity on the life cycle of Dictyostelium discoideum after and during life-long exposure to one of three altered gravity (g) environments: (1) substrate inverted, parallel to and facing the surface of the Earth; (2) hyper-g; (3) reduced-g. To this end, we measured the height of the final stage of the life cycle, the mature spore-bearing sorocarp. Typically, the sorocarp stands erect and perpendicular to the substrate. In the case of each altered g environment, the control cultures were produced and treated identically to the experimental cultures except for the conditions of their exposure to altered g. Inverted cultures developing and growing in the same direction as the gravity vector had a mean height of 1.84 mm. Their counterpart control cultures had a mean height of 1.64 mm being therefore statistically significantly shorter. Cultures chronically exposed to a hyper (10) g environment produced sorocarps with a mean height of 1.13 mm. These were statistically significantly shorter than their 1 g controls whose mean height was 2.06 mm. Clinorotated (simulated reduced g) sorocarp heights (mean equal to 2.12 mm) were statistically significantly taller compared to their 1 g controls (mean equal to 1.79 mm). The significance level for all the statistical analyses is p < 0.05. Therefore, measurements of the mature stage after life-long exposure to simulated altered gravity show that the final height of the sorocarp is ultimately determined, at least partially, by the gravity environment in which development occurs.

In this paper we use Nace’s previous work in order to model the effects of gravity in cells and similar objects. In the presence of the gravitational field of a primary body, the gravity vector can result in numerous effects, some of which are tension, shear, and finally torque. To model the torque effect we use a complete expression for the gravitational acceleration, as this is given on the surface of a planetary body as well as in orbit around it. In particular, on the surface of the Earth the acceleration is corrected for the effect of oblateness and rotation. In the gravitational acceleration the effect of oblateness can be modeled with the inclusion of a term that contains the J₂ harmonic coefficient, as well as a term that depends on the square of angular velocity of the Earth. In orbit the acceleration of gravity at the point of the spacecraft is a function of the orbital elements and includes, only in our case, the J₂ harmonic since no Coriolis force is felt by the spacecraft. We derive analytical expressions and calculate the resulting torque effects for various geocentric latitudes, as well as circular and elliptical orbits of various eccentricities and inclinations. We find that elliptical polar orbits result in higher torques, and that higher eccentricities result in higher the torque effects. To any measurable extent, our results do not drastically impact any existing biophysical conclusions.

Exposure to total-body radiation induces hematological changes, which can detriment one’s immune response to wounds and infection. Here, the decreases in blood cell counts after acute radiation doses of γ-ray or proton radiation exposure, at the doses and dose-rates expected during a solar particle event (SPE), are reported in the ferret model system. Following the exposure to γ-ray or proton radiation, the ferret peripheral total white blood cell (WBC) and lymphocyte counts decreased whereas neutrophil count increased within 3 hours. At 48 hours after irradiation, the WBC, neutrophil, and lymphocyte counts decreased in a dose-dependent manner but were not significantly affected by the radiation type (γ-rays verses protons) or dose rate (0.5 Gy/minute verses 0.5 Gy/hour). The loss of these blood cells could accompany and contribute to the physiological symptoms of the acute radiation syndrome (ARS).

Plants will be an important component of off-Earth life support systems for food production and atmosphere recycling. “Veggie” is a small vegetable production unit designed for space flight, with a passive water delivery system. Plants can be grown in Veggie using small bags with a wicking surface containing media and fertilizer, i.e., pillows. Pillows planted with seeds can be placed on the wicking surface of the Veggie reservoir and water will wick throughout the media. Multiple small salad and herb species were grown in Veggie analog conditions using both commercial peat-based media and arcillite. Biometric measurements and microbial loads were assessed. Some species grew better in a particular media, but no general trends were apparent. Lettuce plants grew best in the blends of the peat-based and arcillite media. Microbial counts were lower on plants grown in arcillite. Four media types (peat-based mix, arcillite, and blends of the two) were tested in the rooting pillows; tests included Chinese cabbage, Swiss chard, lettuce, snow pea, and radish. Most species grew best in blends of the commercial mix and arcillite. Edible biomass production varied from 3.5-8 grams dry mass/m²/day with lettuce having the lowest biomass and Chinese cabbage highest. Radish plants showed an increasing percentage of partitioning to edible roots with increasing arcillite in the media. Pillows appear to offer a simple, effective strategy for containing rooting media and avoiding free water while growing plants in the Veggie hardware.

The Mark III Rodent Habitat Workshop was held at NASA Ames Research Center on March 21-22, 2013 to prepare top-level science requirements for developing a habitat to support studies of mammalian reproduction and development on the International Space Station (ISS). This timely workshop assembled a diverse team with expertise in reproductive and developmental biology, behavior, space biosciences, habitat development, physiology, mouse genetics, veterinary medicine, rodent husbandry, flight hardware development (rodent), and spaceflight operations. Participants received overview presentations from each discipline, discussed concerns, potential risks, and risk mitigations corresponding to distinctive reproductive and developmental phases, and reviewed specific examples of research within the major space bioscience disciplines requiring a Mark III habitat¹ to achieve their objectives. In this review, we present the workshop materials and products, and summarize major recommendations for defining the requirements envelope for the NASA Rodent Habitat (RH) Mark III. Development of this habitat will permit the first long duration studies of mammalian reproduction and development in space, within and across generations.