Specific Features of the Motor Potentials of the Leg Muscles Induced by Magnetic Stimulation under the Conditions of a Five-Day “Dry” Immersion in Healthy Volunteers

Abstract

The aim of this study was to analyze the mechanisms of the development of hypogravitational hyperreflexia in the motoneuron pool of gravity-dependent muscles such as the gastrocnemius and soleus muscles of the leg under the conditions of five-day “dry” immersion in healthy volunteers using the method of transcranial and trans-spinal magnetic stimulation. The essence of the method lies in the stimulation of the areas of interest (motor areas of the cerebral cortex and lumbosacral thickening) with an electromagnetic stimulus. The study involved 10 subjects at the age of 29.9 ± 6.9 years, with no history of movement disorders or neurological diseases. The excitability of the motor neuron pool in both muscles was judged by the values of the thresholds and amplitudes of the motor response caused by transcranial and trans-spinal magnetic stimulations. A general pattern manifested in a significant decrease in thresholds and an increase in the amplitudes of motor responses caused by trans-spinal magnetic stimulation in both muscles gas been discovered. Specifically, the threshold of spinal evoked motor responses in both muscles decreased by 20%, and the amplitude increased by 150% after the end of immersion. The data obtained during the experiment confirm the spinal nature of the origin of hypogravitational hyperreflexia.

Corticospinal excitability after 5-day Dry Immersion in women

“…The results of our study correspond with the data obtained in the 5-day DI experiment with the participation of male volunteers (Nosikova et al, 2021b ). In the male group, a significant decrease in spinal MEP thresholds and a tendency to decrease in cortical MEP thresholds were also observed.…”

“…In our study, baseline TMS sessions were conducted at the early follicular phase; the session on the day of DI completion coincided with the ovulation phase; and the sessions in the recovery period fell within the luteal phase ( Figure 2 ). Since the dynamics of MEP characteristics in our study largely correlated with the data obtained in the experiment with the participation of men (Nosikova et al, 2021b ), hormonal fluctuations during MC probably did not significantly affect the recorded values compared with the effects of immersion. Nevertheless, high MEP amplitudes' variability and a tendency of amplitude values on the 6th day of the recovery period to return to the state of the day of DI completion ( Figures 5 , 6 ) in women may be associated with both the hormonal level fluctuations and individual aspects of the nervous system's adaptation to the experimental conditions.…”

“…The decrease in MEP thresholds for both trans-spinal and transcranial MS and the increase in spinal MEP amplitudes in the majority of the group reflect the phenomenon of hypogravitational hyperreflexia (Kozlovskaya et al, 1988 ), which develops in the microgravity environment. Previously, hypogravitational hyperreflexia development on the spinal level was shown in similar immersion experiments: 5-day DI with the participation of male volunteers (Nosikova et al, 2021b ) and 3-day DI with the participation of female volunteers (Nosikova et al, 2021a ). There is also evidence of an increase in spinal excitability in the model of unilateral lower limb suspension (Clark et al, 2006 , 2007 ).…”

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

“…A recent study of the excitability of the motor neuron pool in the soleus and gastrocnemius muscles in terms of values of the thresholds and amplitudes of the motor response to transcranial and transspinal magnetic stimulation after DI confirms the spinal nature of the development of hypogravitational hyperreflexia. At the same time, the authors noted that a decrease or increase in the amplitudes of the motor response is possible, but not necessary for the state of hypogravitational hyperreflexia, while a decrease in reflex thresholds can be considered as a hallmark of this phenomenon ( Nosikova I. N. et al, 2021 ). This phenomenon is part of pictures of “gravitational ataxia” and “muscular hypogravity detraining” syndromes, which were described earlier based on the studies performed in SF, onground models, and animal experiments ( Kozlovskaya, 1983 ; 1988 ; Shenkman et al, 1997 ; Recktenwald et al, 1999 ; Ohira et al, 2002 ; Kakueva and Kaplanskii, 2005 ; Reschke et al, 2009 ).…”

“…Electroneurographic findings have suggested decreased tibial nerve M-responses after second and fourth mouth of HDBR ( Ruegg et al, 2003 ), similar to DI ( Zakirova et al, 2015 ). After 5 days of DI, the maximum amplitude of the motor evoked potential of the soleus muscle while transcranial magnetic stimulation was almost twice the baseline values ( Nosikova I. N. et al, 2021 ). At the same time, in a study by Yamanaka et al (1999) and Miyazaki et al (2002) there were no significant differences between the average amplitudes of the motor evoked potential of the same muscle before and after HDBR.…”