NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women

Abstract

As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.

Corticospinal excitability after 5-day Dry Immersion in women

“…Previously, for the first time, a comprehensive experiment to study the effects of 3-day support unloading on the sensorimotor system in women of reproductive age was carried out. It showed the possibility and safety of such exposure, as well as the comparability of the results with data obtained in similar experiments with the participation of male volunteers (Amirova et al, 2021 ; Tomilovskaya et al, 2021 ; Nosikova et al, 2021a ).…”

The State of the Organs of the Female Reproductive System after a 5-Day “Dry” Immersion

“…Exposure under the conditions of “dry” immersion for 5 days was carried out exactly as described earlier for a 3-day immersion [ 37 ]. It is known that most physiological systems under the conditions of a “dry” immersion respond after 3 days, and the maximum acute changes are observed after 5–7 days [ 14 ].…”

“…The average time spend outside the immersion bath (for hygiene procedures and certain experimental examinations) did not exceed 30 min per day. The crew, consisting of a doctor, an assistant, and a technician, provided 24 h monitoring of participants’ health and the working conditions of the technical equipment [ 37 ].…”

Impact of different ground-based microgravity models on human sensorimotor system

“…A landmark event for this model was the first 3-day DI experiment with the participation of six female subjects in 2020 in Russia ( Nosikova I. et al, 2021 ; Tomilovskaya et al, 2021 ) since earlier DI experiments were performed only in males. Experiments involving females continue.…”