The influence of neuromodulation effects on the functional state of the neuromotor apparatus of the soleus muscle in middle-aged male rats under conditions of long-term hindlimb unloading

The study of the nature of motor pathologies is one of the most important areas in physiology and medicine. The purpose of this work was to assess the functional state of the neuromotor apparatus of the soleus muscle (SM) in middle-aged male rats under conditions of long-term hindlimb unloading (HU). Experiments were carried out in strict accordance with accepted bioethical standards. The animals were divided into three groups: hinlimb unloading (HU), HU with magnetic stimulation (HU+MS), and the electrical stimulation of the spinal cord (HU+ES). Parameters of motor and reflex responses were recorded. The threshold of the SM reflex response was reduced to 81±8% (p<0.05) in the HU group, 77±10% (p<0.05) in the HU+ES group, and 73±16% (p<0.05) in the HU+MS group. The amplitude of the SM H-response increased to 130±15% (p<0.05)in the HU group, 121±9% (p<0.05) in the HU+ES group, and 120±10% (p<0.05) in the HU+MS group. The amplitude of the M response was 73±11% (p<0.05) in the HU group, 76±9% (p<0.05) in the HU+ES group, and 70±15% (p<0.05) in the HU+MS group. Thus, during long-term hindlimb unloading, we recorded an increase in the reflex excitability of the spinal motor center of the SM. And we also found that spinal cord stimulation prevented changes in the threshold of the M-response of the SM, but did not exclude a decrease in amplitude. The research was funded by a grant from the Russian Science Foundation and the Academy of Sciences of the Republic of Tatarstan under project no. 23-25-10065.