Kazan (Volga) Federal University, Kazan, Russia, firstname.lastname@example.org
Spinal cord injury (SCI) leads to disruption of the locomotor function, in particular, neural overhaul of the injured area of the spinal cord below the injury, due tothe loss of supraspinal influence or strenghthening the plasticity mechanisms. The main violations that limit the possibilitIes of restoring the functions of the musculoskeletal system are called spasticity and imbalance between excitatory and inhibitory systems of the spinal cord, providing locomotion.
The aim was the neurophysiological study of the functional state of the rat's neuro-motor apparatus central section in conditions of a non-communicating motor centers to the periphery on the model of spinal injury. The experiments were performed in compliance with the bioethical standards. We used the method monosynaptic testing.
The period of spinal shock on electrophysiological parameters was caused by decrease in the excitability of spinal motoneurons. We observed a decrease in the amplitude of M - and H - answers that was shown in other studies. Recovery from spinal shock was reflected in the increase of excitability of the flexor tendon reflexes and muscle tone of the rat's hind limb muscles (rated on a scale Ashworth), as noted in the literature. These clinical changes were combined with electromyographic indicators changes. Our results showed an increase in the amplitude of H-reflex and the Hmax/Mmax in this period. In our study, we observed an increase in the amplitude of the H-response in 14 days after spinal cord injury, the maximum relief to the H-reflex was observed on 45TH day after spinal cord injury, after which the amplitude of the H-reflex was unchanged, and in some cases decreased. We also demonstrated a reduction in the effect of the H-reflex depression during repetitive stimulation after spinal injury. One more important indicator of spinal neurons recovery excitability, in our opinion, is the appearance of the electrical activity of muscles of the rat´s hind limb in response to a stimulus and polyphase answers during repetitive stimulation that integrate inputs from the muscles, joints and skin afferents on common interneurons. In the chronic phase of SCI we have not observed significant changes in thresholds, the maximum amplitude and duration of the H-response. The ratio of Hmax/Mmax increases, but this can be explained by the decrease in the amplitude of the M-response. However, the increase in the excitability of motor neurons in this period can be identified using other methods. Thus, we observed an increase in the muscles electrical activity under tension and the appearance of high-frequency discharges of individual motor units in response to a stimulus.
Our results extend the current understanding of the hyperexcitability mechanisms, demonstrating that all the links in the neuro-motor apparatus may be involved in the formation of spastic syndrome.