Avian Development Facility - Development and Function of the Avian Otolith System in Normal Altered Gravity Environments (ADF-Otolith) - 07.15.14
ISS Science for Everyone
Science Objectives for Everyone The avian (bird) experimental model offers opportunities to observe microgravity induced changes in many systems, including the otolith, cardiovascular, musculoskeletal, immunological and neurological. The ADF-Otolith investigation will study the formation of inner ear bones and neurons (involved in the otolith system) under the influence of microgravity.
Science Results for Everyone
My, what big ears you have! In this investigation, the inner ear bones of bird embryos developing onboard ISS appear to grow larger than those in embryos developing on Earth, and the fan-shaped arrangement of receptor cells in the inner ear also seems to change when developing in microgravity. Exposure to space flight is known to produce changes in the human inner ear, which contains sensors that respond to movement and gives us our sense of balance. Disturbances in the inner ear can cause motion sickness and vertigo, the sensation that one’s head is spinning.
NASA Ames Research Center, Moffett Field, CA, United States
Space Hardware Optimization Technology Incoporated, Greenville, IN, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
December 2001 - June 2002
Previous ISS Missions
An earlier version of this experiment, CHIX, flew on Mir and EuroMir.
- ADF-Otolith will determine the effects of gravity upon development of the peripheral vestibular system (inner ear). Exposure to spaceflight can produce changes in the anatomy, physiology, and neuromotor responses related to the vestibular system.
- The otolith organs comprise the inertial sensors that respond to linear acceleration or tilts of the head relative to gravity. These organs are what give animals their sense of balance; disturbances in the vestibular system can give rise to problems for humans such as motion sickness and a malady known as benign positional vertigo.
- During its flight on STS-108, ADF housed two peer-reviewed experiments: Development and Function of the Avian Otolith System in Normal and Altered Gravity Environments and Skeletal Development in Embryonic Quail on the ISS.
The avian development biology experiment, which is a tool for the study of embryogenesis in space, provides the support hardware needed for researchers to better understand and mitigate or nullify the forces of altered gravity on embryo development. Avian eggs are ideal for studying embryo development since they are self-contained and self-sustaining and can be nurtured without a maternal host. The Avian Development Facility (ADF) allows incubation of avian eggs under controlled conditions (humidity, temperature, and gas environment) on orbit and the fixation of the eggs for study while minimizing the effects of launch and landing. Up to 36 eggs in centrifuge carousels can be exposed to simulated gravity of zero-g to one-g in 0.1-g increments.
During its flight on space shuttle mission STS-108 to the ISS, the ADF housed two investigations: the Development and Function of the Avian Otolith System in Normal and Altered Gravity Environments (ADF-Otolith) and the Skeletal Development in Embryonic Quail on the ISS (ADF Skeletal) investigations.
The otolith system (small bones of the inner ear) in all vertebrates functions to detect head position and movement relative to gravity depending on neuromotor responses. The avian otolith system offers an excellent model with which to study the effects of gravity upon development due to the short maturation period following fertilization and due to the extensive knowledge of otolith system structure and function in birds.
Otoliths are part of the vestibular system (balance system) in vertebrates and are an essential component in the production of movement-related responses that are critical for daily function and survival. During space flight, vestibular disturbances are frequently reported by astronauts, with approximately 80 - 90 percent of current astronauts experiencing some symptoms of space motion sickness (disorientation and nausea) during the first 48 - 72 hours of weightlessness.
Many scientists have suggested that lack of gravity as a constant stimulus during space flight produces significant changes in vestibular system function. Preliminary studies indicate that the structure and function of the vestibular system is affected by exposure to microgravity. For example, changes in size of otoconia in the receptor-afferent morphology, hair cell conductance, vestibular afferent responsiveness, vestibular central pathways, and vestibular-related neuromotor responses have all been observed in both adult and developing animals that are exposed for brief periods to either microgravity or hypergravity.
ADF-Otolith studied how the absence of gravity during the body's formative stage affects basic neural function in an effort to isolate the major influences on the neurovestibular system, the system that allows us to control our eye movement, balance, and coordination.
During embryonic development on Earth, the visual system, if deprived of light during the early critical period, normal sight is impaired or eliminated during maturation. In the vestibular system which controls normal postural, eye and head movement responses during motion, no effort to study the effects of gravity upon development have been extensively performed. Thus, it is currently unknown whether altered gravity environments affect vestibular system development and subsequent reflex motor behavior. The research should provide basic answers into questions related to vestibular receptor pathology that is known to occur with aging humans and in some disease cases.
ADF has 36 egg holders, which isolate and cushion the eggs from ambient vibrations that could disturb development. The holders fit into one of the two centrifuge carousels. Each carousel can be independently programmed to simulate different gravity levels, from 0 up to 1 g (in 0.1-g increments). The holders also rotate on their longitudinal axis in either/both carousels. ADF required continuous power from the time that the eggs were loaded into the holders until the experiment was completed and turned over to the research team.
The surrounding hardware provides other critical support. ADF can maintain temperature between 26 degrees C and 40 degrees C, control relative humidity, and adjust the oxygen (pressure level greater than or equal to 21percent during incubation) and carbon dioxide (pressure level less than 1 percent during incubation) levels to provide the optimal incubation environment. When the desired growth period has been reached, ADF will inject the eggs with a fixative (4 percent formaldehyde) to preserve the embryo's state until the specimen is returned to its principle investigator.
Japanese quail eggs, due to their short incubation time of 15 days were exposed to different levels of gravity during embryogenesis and their vestibular receptor systems examined using a number of different quantitative anatomical measures. Quail raised from fertilization in either normal gravity, hypergravity (2 - 3g), or microgravity (spaceflight) conditions will be compared. The anatomical development of the receptor cell organization and the afferent innervation patterns of day 4, 7 and 12 quail embryos were collected for comparison across the different gravity conditions and developmental stages.
Once incubation began, the temperature inside ADF gradually increased over the next few hours from 13 degrees C to 37.5 degrees C. One carousel, set to rotate at 1g simulating Earth's gravity, acted as an inflight experiment control. For this flight, the other carousel was kept at 0g. Eggs were rotated in their sample holders once an hour to imitate the turning they would receive if tended by a hen. Once completed, ADF automatically injected the eggs with a fixative. Within hours of landing, the eggs were removed from the ADF and delivered to the researchers for analysis.
The inner ear bones in the embryos that developed in microgravity appear to be larger than those found in the controls that remained on Earth. There are some indications that the fan-shaped arrangement of receptor cells may also be altered under the influence of microgravity. Conclusive data from this investigation are pending further analysis (Increment 4 One Year Postflight Report). (Evans et al. 2009)
Ground Based Results Publications
Hughes I, Blasiole B, Huss D, Warchol ME, Rath NP, Hurle B, Ignatova E, Dickman JD, Dickman JD, Thalmann R, Levenson R, Ornitz DM. Otopetrin is required for otolith formation in the zebra fish Danio rerio. Developmental Biology. 2004; 276(2): 391-402.
Washington University, Department of Anatomy and Neurobiology
Exploration Systems Mission Directorate Education Outreach
NASA Fact Sheet
One of two ADF carousels, each featuring 18 sample containers. During space missions, one carousel rotates at 77.3 RPMs to simulate a 1g gravity field. The other carousel remains motionless to provide a microgravity environment for the specimens inside. Besides eggs, the ADF can carry fish, plants, insects or cells in its sample containers. Image courtesy of Ames Research Center.
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Scanning electron micrographs of fused otoconial stones from embryonic day 12 quail embryos. Three saccule stones are shown, one each from an embryo raised from fertilization in 0g (left), 1g flight (middle), and 2g laboratory centrifugation (right). Image courtesy of J. David Dickman.
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