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A question to consider as you read . . .When you're put in a swimming pool, what are some of the ways you adjust your body, muscle movements, etc. to account for the perceived change in gravity? How do you think this might be similar (or perhaps different) to what's going on at the molecular level with neurons?
Vocabulary that will help you understand this sectionThe nervous system monitors and controls the various functions such as body temperature and metabolism that allow an animal to regulate its internal environment and to sense and react appropriately to its external environment or surroundings. The fundamental component of the nervous system is the neuron, a nerve cell composed of three parts: sensors which receive stimuli, a cell body which holds the nucleus and is the control center of the neuron, and a nerve fiber that transmits signals to other neurons.
Drs. Holstein and McNaughton's StudyWhen one neuron sends a signal to another neuron, it does so by releasing a chemical message from its nerve fiber. This chemical stimuli travels a short distance, and is then picked up by the sensory portion of the receiving neuron. Dr. Holstein will study the vestibular synaptic circuits in rat cerebellar cortex to determine to what extent these neurons reorganize themselves to adapt to microgravity, and again to normal gravity after being returned to Earth. In addition to the circuitry, Dr. Holstein will examine the chemical messages sent by the circuitry.Dr. McNaughton will be studying the neural activity of rats after they have adapted to microgravity. He will focus on the neural messages in the hippocampal and thalamic neurons, which are responsible for self-orientation with respect to three-dimensional spatial relationships; in addition to detecting the force of gravity, macular receptors also detect linear acceleration, such as forward and backward movement. Macular receptors in a rat, like the gravity sensory organs of other species, are composed of tiny hair cells that are triggered by the relative weight and movement of an overlying mineral mass. It is anticipated that upon introduction to microgravity, the macular receptors will try to compensate for perceived decrease of trigger weight by increasing the number of hair cells. Furthermore, after reentry to gravity on Earth, the additional hair cells generated in space will eventually disappear, as they are no longer needed in normal gravity.
Dr. Fuller's StudyAn animal's circadian rhythm is its internal clock, which is based on the 24-hour cycle and affects physiological patterns such as sleeping. The animal's internal clock is based on cues from the outside environment, such as the natural light/dark cycles of day and night. Dr. Fuller will seek to determine if space flight affects the phase and amplitude of circadian rhythms by monitoring the body temperature, heart rare, feeding, drinking, and physical activity in rates under different light cycles. The effects of light/dark stimuli can be observed by measuring the corresponding chemical messengers are c-Fos and Jun-B; the levels of these chemicals will be correlated with the rat's physiological patterns during space flight.
Dr. Pompeiano's StudyDr. Pompeiano will also be studying circadian rhythm as dictated by neural functioning. Immediate early genes (IEGs) contain instructions for the expression of proteins and can be used as markers of neuronal activity. Activation of the genes is induced by physiological stimuli. Specifically, it has been determined that there is a relationship between a stage of sleep called rapid eye movement (REM) and vestibular (self-orientation, balance) mechanisms. It is these relationship that Dr. Pompeiano is studying by motoring the expression of IEGs in the vestibular system of rats in microgravity.Data gathered from the vestibular adaptation experiments of Drs. Holstein, McNaughton, Pompeiano, and Ross will be beneficial in developing treatments for a number of clinical conditions on Earth, including balance disorders such as vertigo and dizziness, which affect more than 90 million Americans. And, because deficits in human circadian timing systems are associated with various Earth-based disorders, the data collected by Dr. Fuller and Pompeiano should be of clinical use as well. Circadian timing disorders include jet lag, insomnia, and mental disorders such as winter depression. In addition, innovative virtual computer-based test methods being developed by the investigators for the experiments are expected to be used by Earth's scientific and medical communities.
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