Anatomical Studies of Vestibular Adaptation
Understanding How Astronauts Adapt to Space and to Earth
Significant changes take place in the nervous systems of astronauts during
and following exposure to microgravity. These changes, particularly in the part
of the brain that controls balance, the vestibular system, can cause sensations
of rotation, dizziness, and vertigo, as well as space adaptation syndrome. Adaptation
to the microgravity environment usually occurs within one week, and a subsequent
re-adaptation period of several days is often required upon return to Earth. In
order to realize long-term spaceflight, effective countermeasures for these symptoms
must be developed.
The structural changes that take place in one of the vestibular regions of
the brain (the cerebellar cortex) during the process of adaptation to Earth’s
gravity remain unclear and are the subject of an experiment being conducted on
STS–107 by Dr. Gay Holstein of the Mount Sinai School of Medicine in New
York. Using the rat as a model, Dr. Holstein and her team will seek to identify
the cellular changes underlying the vestibular changes experienced by astronauts.
Above: Electron micrographs of the cerebellar
cortex from a rat after 24 hours of spaceflight. One unusual change observed in
the ultrastructure of the Purkinje cells was the presence of extensive enlargements
of the cisternal membranes into organelles called lamellar bodies (A, arrows).
Panel B illustrates electron-dense degeneration in Purkinje cell dendrites (asterisks).
Synaptic contacts with the degenerated cells are indicated by black arrows. The
scale bar is 0.5 mm long. These observations will be further studied on STS–107.
Photo credit - Holstein 
Background Information
For this experiment, five flight and five ground control animals will be housed
in two Animal Enclosure Modules (AEMs). The five flight animals will be flown
aboard the Shuttle in one AEM, for a total of 16 days. Ground based 72-hour delayed
control rats will be housed in the other AEM. Ultrastructural studies will then
be carried out using electron microscopy. The results of this experiment will
help to identify the cellular bases underlying the vestibular changes experienced
by astronauts during periods of adaptation and re-adaptation to altered gravitational
forces, and may provide insights for the development of effective pharmacotherapeutic
countermeasures.
Earth Benefits and Applications
The results of this experiment will help to identify the cellular bases underlying
vestibular changes that occur during periods of adaptation and re-adaptation to
different gravitational forces. In that light, the findings may provide insights
for the development of effective pharmacotherapeutic countermeasures for vestibular
changes during spaceflight. In addition, since the short- and long-term changes
in neural structure and connectivity that occur during adaptation to microgravity
mimic the neuronal alterations that occur in many progressive neurological disorders
such as stroke and Parkinson’s Disease, findings from this study using a
rat model could offer guidance in the development of strategies for neurorehabilitation
and treatment of these disorders.
Science Discipline Supported
This experiment supports NASA’s priorities for research aimed at understanding
fundamental biological processes in which gravity is known to play a direct role
and alleviating problems that may limit astronauts’ ability to survive and/or
function during prolonged spaceflight.
Previous Results
The results from a previous experiment flown on STS–90 suggest that immediately
following exposure to spaceflight, substantial structural reorganization takes
place in the regions of the brain involved in controlling balance and equilibrium.
Observations of brain tissue obtained after 24 hours of spaceflight indicate that
several structural alterations occur in specific regions and cells of the rat
brain. These alterations are not apparent in the cage control animals. The primary
goal of the present project is to study these ultrastructural alterations in greater
detail.
Hardware
Above: This experiment is part of the Fundamental Rodent
Experiments Supporting Health (FRESH)-02 payload which consists of 13 rats housed
in 3 AEMs. The animals, which will be shared among several different investigators,
will experience microgravity for 16 days on board the Shuttle Columbia. The AEMs
have been used successfully on many previous shuttle flights. Photo credit - Ames
Research Center
The AEMs is a rodent habitat that provides ventilation, continuous filtered
air flow to control waste and odor, timed lighting, food in the form of foodbars
attached to the side of the cage, and a water supply which can be refilled as
required. Rodents in the cage compartment of the AEM are not accessible but can
be viewed through the clear lexan cover. This also allows for viewing of water
level remaining in the AEM water box.
The AEM has been designed for minimum crew interaction and the animals adapt
very well to this virtually self-contained system. The only nominal operations
required are a daily hardware check, a daily visual animal health check, and periodic
water refills.
Principal Investigator: Dr. Gay Holstein,
Mount Sinai School of Medicine, New York, New York
Project Scientist: Marilyn Vasques,
NASA Ames Research Center, Mountain View, CA
Project Manager: Rudy Aquilina,
NASA Ames Research Center, Mountain View, CA
Visit Anatomical Studies
for a printable PDF version of this research.
Visit http://spaceresearch.nasa.gov/sts-107/overview.html
to learn more about the other OBPR investigations flying on STS-107.
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