Реферат: Hypogravitational spinal hyperreflexia is a key component of the motor syndrome occurring during microgravity exposure and is primarily associated with proprioceptive deafferentation due to reduced motor activity and support unloading. Dry Immersion (DI) is one of the most adequate ground-based models for simulating microgravity effects, reproducing support and motor unloading (Tomilovskaya et al., 2019). Understanding spinal reflex adaptation to altered gravity is essential for elucidating hyperreflexia mechanisms (Kozlovskaya et al., 2002; Reschke et al., 2009). The aim was to investigate the temporal dynamics and mechanisms of hypogravitational spinal hyperreflexia using DI. Spinal hyperreflexia was assessed using H-reflex recruitment curves in leg extensor muscles. A 14-day DI experiment was conducted (n=8, 31.2±7.3 years) with measurements in the mm. soleus and gastrocnemius muscles before DI, after 5 hours, on days 3, 5, 7, 9, 11, 13, 15 of DI, and on days 2 and 5 after DI completion. Additionally, during a separate 5-day DI, transcutaneous spinal cord stimulation (TSS) at the T11-T12 level was performed to assess multisegmental spinal excitability (mm. soleus, tibialis anterior, semitendinosus, vastus lateralis) under two conditions: directly in the immersion tank (supportless) and on the platform after being lifted out of the water (weight-bearing). H-reflex thresholds in the m. soleus decreased within 5 hours after DI start, with a maximum decrease on day 3. In the m. gastrocnemius maximum threshold decrease was observed on day 5. Thresholds remained below baseline, returning to baseline values 2 days after DI completion. H-reflex amplitude in both muscles increased by day 5 and remained above baseline until the end of exposure. After day 5, no progressive changes were observed. TSS revealed that evoked potential thresholds decreased by day 3, with thresholds consistently higher on the platform than in the immersion tank. Changes in amplitude were different in the flexor and extensor muscles with a more pronounced increase in extensors (mm. soleus and vastus lateralis) compared to flexors (mm. tibialis anterior and semitendinosus). Hypogravitational spinal hyperreflexia is characterized by rapid development. Its dynamics are biphasic: acute hyperreflexia followed by chronic compensation after day 5, manifested by reflex parameter stabilization. The key trigger is support afferentation removal, confirmed by TSS showing higher thresholds under weight-bearing versus supportless conditions. These results reveal fundamental mechanisms of spinal motor center plasticity under conditions of gravitational unloading. The study was supported by the Russian Science Foundation grant № 24-15-00309, https://rscf.ru/en/project/24-15-00309/.

Библиографическая ссылка: Shigueva T.A. , Artamonova N.M.A. , Urbanskaya A.D. , Riabova A.M. , Kitov V.V. , Sayenko D.G. , Tomilovskaya E.S.
Hypogravitational spinal hyperreflexia: results of ground-based model experiments
24th IAA Humans in Space Symposium, Montecatini, Italy, 20-24 April 2026 20-24 Apr 2026