[The effect of microgravity on the state of compensation in one-side labyrinthisized newts]. / Vliianie nevesomosti na sostoianie kompensatsii u odnostoronne delabirintirovannykh tritonov.

Experiments were performed on newts Pleurodeles waltii subjected to one-side labyrinthectomy 1, 2, 5, and 6 mos prior to a spaceflight on board the orbital complex Mir. Duration of the exposure in microgravity was 8, 31 and 73 days. Destruction of one labyrinth in the newts brought about a number of characteristic reactions, i.e. rollover, circling and sideway movements with the head on a solid substrate and spinning about the longitudinal body axis when in water. These reactions were directed exclusively towards the labyrinthectomized side, their intensity faded, and typically in 1.5 mos. following surgery the motor activity of the newts was close to the norm. In the weight-free conditions the animals appeared to lose compensation they had formed on Earth. During 1.5 days of return the newts were unable to walk and their heads were turned towards the labyrinthectomized side. Immersed in water, the animals started spinning also towards this side. Two days later, they regained the ability to walk without assistance but with evident signs of ataxia. In 40 days after flight, the animals still exhibited locomotor disturbances during walk and swimming.

[Interlabyrinthine asymmetry, vestibular dysfunction and space motion sickness]. / Mezhlabirintnaia asimmetriia, vestibuliarnaia disfunktsiia i kosmicheskaia bolezn' dvizheniia.

The data available suggest that a disorder in the labyrinthine paired function can be regarded as a factor responsible for the initiation and development of space motion sickness. This concept is based on the assumption that in the norm the vestibular function is to a certain extent asymmetric which is made for by a compensatory center in the central nervous system. Exposure to an unusual space environment leads to a disorder of this compensation and development of a "new" vestibular asymmetry. This exposure involves: elimination of the difference in the weight of otolith membranes, disorder of the canal-otolith interaction, asymmetric blood-CSF changes, distinct interhemispheric asymmetry, general stress. Vestibular asymmetry that develops in the weightless state may become sufficient for the generalization of afferent impulsation to normal stimuli and development of a strong reaction. Adaptation to weightlessness occurs due to rearrangements of the compensatory center which are responsible for lower vestibular asymmetry. The compensatory mechanisms that have evolved in weightlessness continue to function during a certain time interval after recovery. They facilitate a re-initiation of vestibular asymmetry and motion sickness that is mainly provoked by head movements, as in the weightless state.

[Human vestibular reactions to galvanic stimulation of the labyrinths]. / Vestibuliarnye reaktsii cheloveka na gal'vanicheskoe razdrazhenie labirintov.

The development of illusionary movements and oscillations of the total body mass center in response to labyrinthine stimulation by ascending and descending current was investigated in 37 healthy test subjects. The stimulation of each labyrinth separately or both labyrinths by the current of opposite direction caused illusionary sensations of tilts, turns and tumbles in various planes. When the test subjects were on the stabilographic platform, their total body mass center shifted toward the anode. Simultaneous stimulation of both labyrinths by the current of one direction produced qualitatively new reactions, such as illusionary movement and displacement of the mass center toward the sagittal plane.

[Effect of limited mobility on vestibular function]. / Vliianie ogranicheniia podvizhnosti na vestibuliarnuiu funktsiiu.

The hypokinetic effect on the nystagmic reaction and illusory sensations upon caloric and galvanic stimulations of the labyrinths was studied on six test subjects (professional gymnasts). Under normal conditions the sportsmen predominantly showed the nystagmic response to the caloric irritation of the left labyrinth. A 10-day hypokinetic exposure produced a noticeable decrease of the above asymmetric nystagmic reaction to the caloric irritation of both labyrinths. Simultaneously an enhancement of illusory sensations and a decrease of their thresholds in response to the firect current labyrinthine stimulation were noted. The above changes can be attributed to the hypokinesia-induced decline of mechanisms of vestibular adaptation of sportsmen.