Space flight has created a condition of total alteration of the normal input
to the balance receptors, including those of the otolith organ, the portion
of the inner ear which controls balance with respect to the excitation of gravity.
This is thought to be responsible for the space motion sickness or air sickness
syndrome that may accompany flights on both planes and spacecraft. The OFO-A
mission was prepared as part of a special program of vestibular physiology with
the purpose of studying the way in which gravitational pull affects vestibular
function. This experiment was to obtain information concerning the response
of the basic accel- eration sensor mechanism (hair cells of the otolith organ)
in weightlessness.
Two bull frogs were completely immersed in water. Action potentials were
recorded from four vestibular nerve fibers corresponding to the gravity sensors
of the inner ear. The design of the satellite kept inflight acceleration to
a maximum of 10-3 g, and an onboard centrifuge could periodically produce up
to 0.6 g of stimulation. Spike train data patterns recorded during orbital flight
and ground control experiments were compared to determine any alterations in
the basic activity of vestibular cells. EKG was continuously monitored as a
vital index of the animals' condition. Centrifuge operation was preplanned for
the first day of flight, after which it was carried out according to an experiment
routine chosen on the basis of preceding results.
EKG showed the same characteristics as on the ground; probably submersion in
water was responsible for minimizing the impact of lift off. During the first
nine hours and up to the 46th hour of weightlessness, the firing at rest slowed
down so that the average interspike interval was more than four times longer
in duration than on the ground. A rebound effect was observed starting around
the 48th hour and reaching its climax after the 72nd hour with a spontaneous
firing twice as fast as that observed in 1 g. Although there was some time shift
between specimens, the general response pattern to the centrifuge was similar:
a decrease beginning after the third day, and a return to normal by day five.
The responses during the first few days suggest an inability to distinguish
between zero input and maximum input during this period, i.e., the receptors
were not functioning. A trend towards normalization was observed following this
stage of maximum alteration. Results indicate only a partial adaptation of basic
neural control process to weightlessness while some alteration remains.
Gualtierotti, T.: Analysis of Single Vestibular Responses. Technical and Biological
Problems of Control, 1968, pp. 318-331.¥
Gualtierotti, T. and D.S. Alltucker: Prolonged Recording from Single Vestibular
Units in the Frog During Plane and Spaceflights, Its Significance and Technique.
Aerospace Medicine, vol. 38, 1967, pp. 513-517.¥
Gualtierotti, T. and F. Bracchi: OFO Experiment Techniques and Preliminary
Conclusions: Is Artificial Gravity Needed During Prolonged Weightlessness? Life
Sciences and Space Research X: Proceedings of the 14th Plenary Meeting of COSPAR,
Seattle, Wash., June 21-July 2, 1971, Akademie-Verlag, 1972, pp. 121-132.
Gualtierotti, T. et al.: Impact of the OFO-A Experiment on Space Biology. Revue
de Medecine Aeronautique et Spatiale, vol. 12, 1973, pp. 252-255.
Gualtierotti, T. et al.: Orbiting Frog Otolith Experiment (OFO). BIOSPEX: Biological
Space Experiments, NASA TM-58217, 1979, p. 108.
Gualtierotti, T. et al.: Orbiting Frog Otolith Experiment (OFO-A): Data Reduction
and Control Experimentation. NASA CR-62084, 1972, pp. 2-1-2-3.
Gualtierotti, T.: Orbital Otolith Experiment TS4: A Spaceflight Experiment
to Investigate the Effect of Weightlessness on the Activity of Single Vestibular
Unit. Proceedings of the Physiological Society, Journal of Physiology, 192,
1967, pp. 2-3.¥
Gualtierotti, T.: Orbiting Frog Otolith Experiment. AGARD, Medical and Legal
Aspects of Aviation, NASA CR-62084, 1970 .¥
¥ = publication of related ground-based study