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Mammalian Development Team

A question to consider as you read

Recall when you were younger and all you did was crawl around - - think about some ways that your development would have been affected if you were instead floating around in space under microgravity conditions.

Vocabulary that will help you understand this section

Environmental information is detected by an animal's sensory system, translated into neural signals, and sent to the organism's central nervous system (CNS). The CNS then sends neural commands, which are translated into coordinated muscular movements. The relevant importance of environmental stimuli on the correct motor system development varies from species to species. For example, tadpoles hatched and raised in micogravity show normal swimming behavior, indicating that motor system development in aquatic organisms is not dependent upon gravity. In contrast, quail chicks develop necessary motor skills for feeding themselves unassisted, suggesting that the development of terrestrial animals is gravity dependent.

The nerve cells that make up the CNS

Objective:

The objective of the Mammalian Development Team is to provide information for understanding the effects of microgravity on the normal development of the nervous system of terrestrial animals. The series of experiments will use anatomical, physiological, molecular, and biochemical approaches to investigate the necessary processes for CNS and subsequent motor system development.

Dr. Shimizu's Study

photo of rat Dr. Shimizu's experiment focuses on an initial sensory component of the nervous system called the arterial baroreceptor reflex. Cardiovascular changes, such as declines in blood and plasma volume, changes in cardiac output, and blood flow distribution, have been documented in humans during space flight. The mechanism responsible for these adjustments is still not known. Arterial baroreceptors located in the walls of the aorta and carotid arteries are the sensors that monitor arterial pressure. Signals to the CNS based on information from the arterial baroreceptors influence the control of the heart and peripheral blood vessels. It is possible that exposure to microgravity during space flight alters the physical structure of the aortic nerve fibers, thus influencing the sensory signals sent to the CNS. Dr. Shimizu will microscopically examine the arterial baroreceptors of rats that have adjusted to microgravity, in hopes of detecting and characterizing any physical changes in this sensory component at the cellular level.

Dr.Nowakowski's Study

Dr. Nowakowski is also interested in the effects of microgravity at the cellular level. The normal progression of development of the CNS of a terrestrial animal is initiated by the production of cells in a common area. Some of these cells then migrate away from their point of production to differentiate into more specialized cells of CNS. It is unknown whether a gravitational force is necessary for normal cell production and migration during the CNS development. Using cell labeling techniques, Dr. Nowakowski will microscopically follow the production and migration of cells in mice and rats that mature in the microgravity environment of space compared to those that mature on Earth.

Drs. Raymond and Kosik's Study

Drs. Raymond and Kosik address the effects of microgravity on a developing neurosystem at both the cellular and neural circuitry levels: Dr. Raymond's experiment focuses on the vestibular receptors, which are the sensory receptors involved in an animal's perception of gravity. Dr. Kosik's experiment focuses on the hippocampus, which is part of the brain required for spatial learning. Without the presence of a gravitational force, these neural receptors and circuitry systems may develop physical differences detectable at the structural, biochemical, and molecular levels, as compared to animals which mature in the presence of gravity.

Drs. Riley, Baldwin and Walton's Study

Drs. Riley, Baldwin and Walton are studying the necessity of gravity during a critical period in the development of a terrestrial animal's motor system. The major elements of the motor system include neurons, muscle, and bone. Some of the motor system skills require the development of strength, whereas other skills require the development of coordination or dexterity. It is hypothesized that a critical period of weight bearing is necessary for the proper development of the strength component of the motor system; whether it is also necessary for the development of coordination is unknown.

Dr. Riley will microscopically analyze the motor neurons, neuromuscular junctions, and muscles fiber types of rats that matured in the microgravity of space as compared to rats that matured in the gravitational environment of Earth, to see if other development factors, such as thyroid hormones, can compensate for the absence of a weight-bearing development period. Dr. Baldwin will increase the level of growth hormones in the experimental rats to compensate for the lack of a gravitational stimulus while they mature. He will then compare their skeletal muscles to those of mature rats developed in the presence of gravity.

Dr. Walton's study also addresses the "critical period" theory for proper motor development. Using rat neonates, Dr. Walton will observe their motor development in microgravity by observing their reflexes for walking and rising in a mini jungle gym, including rope, ladder, and rod climbing. To determine if the critical period exists, Dr. Walton will also test the motor skills of the rats after they have been returned to Earth and become acclimated to the force of gravity.

Information from these experiments could be beneficial in developing treatments for people with neuromuscular disorders, such as childhood neuromuscular diseases, Alzheimer's disease, and anosagnosia (the failure to recognize body parts after a stroke).