Repair capacity of motor neurons in spinal muscular atrophy
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Progressive muscular atrophy
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Spinal cord injury is often followed by disuse muscle atrophy. The effect of disuse muscle atrophy on motor neurons below the level of spinal cord lesions is not fully understood. We produced spinal contusions in the mid-thoracic segment (Th7/8) of rats. To promote disuse muscle atrophy, their hind limbs were immobilized. Alpha-motor neurons in L4/5 at 3 weeks postinjury showed signs of degeneration associated with disuse muscle atrophy. Muscle atrophy alone did not produce a significant α-motor neuronal degeneration. Our results demonstrate that disuse muscle atrophy within the context of spinal cord injury exacerbates motor neuronal degeneration in caudal regions remote from the injury.
Muscle Atrophy
Degeneration (medical)
Hindlimb
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Progressive muscular atrophy
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In experiments on models of spinal injuries and spinal cord in 79 laboratory rats, we found changes in reflexes revealed by electromyographic evaluation of spinal cord function during the recovery process. It is established that the parameters of calf muscle reflex responses change immediately after spinal cord injury and that the severity of changes in motor responses in the late posttraumatic period depends on the degree of damage. These data suggest a restriction of supraspinal control caused by spinal cord injury. There is a gradual recovery of the reflex excitability of the motor neurons of spinal motor centers, but the state of the peripheral part of the neuro-motor system is deteriorated. This work may be useful for the formation of ideas about the mechanisms of motor disorders and their correction in patients with a spinal cord injury with changing and descending influences on spinal afferent motor centers. This research was supported by the Russian Foundation for Basic Research 13-04-01746 a.
Motor System
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Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by degeneration of spinal cord motoneurons and it is associated with muscle paralysis and atrophy. Based on symptom onset and disease severity, SMA is classified in three subtype; type I (severe), type II (intermediate) and type III (mild). All of these are due to loss or mutation of the telomeric survival of motor neurons gene (SMN1). SMN1 is duplicated with a highly homologous copy called SMN2 and both genes are transcribed. The pathophysiology of SMA remains unknown and no cure is available due to the paucity of reliable animal models. In this study we firstly characterized the anatomy and behaviour of a type III SMA mice. Our transgenic SMA model is characterized by the genotype Smn1 -/-, Smn2 +/+, Smn1A2G +/-. The motor test used are Rotarod test, the Paw Grip Endurance and the stride length test. All mice presented a progressive motor worsening evidenced by the rotarod test. Analysis of the spinal cord of Smn1 -/-, Smn2 +/+ e Smn1A2G +/-, at lumbar level, shows severe cell death involving motor neurons within the lamina IX. The size of spared motor neurons is augmented in SMA mice. We found that chronic autophagy stimulation delayed disease onset and progression.
SMN1
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Progressive muscular atrophy
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Motor impairment
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Electrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury.Here we described a new configuration of electrical stimulation as it was tested in anesthetized control and spinal cord injury (SCI) mice. Constant voltage output was delivered through two electrodes. While the negative voltage output (ranging from -1.8 to -2.6 V) was delivered to the muscle via transverse wire electrodes (diameter, 500 μm) located at opposite ends of the muscle, the positive output (ranging from + 2.4 to +3.2 V) was delivered to the primary motor cortex (M1) (electrode tip, 100 μm). The configuration was named dipolar cortico-muscular stimulation (dCMS) and consisted of 100 pulses (1 ms pulse duration, 1 Hz frequency).In SCI animals, after dCMS, cortically-elicited muscle contraction improved markedly at the contralateral (456%) and ipsilateral (457%) gastrocnemius muscles. The improvement persisted for the duration of the experiment (60 min). The enhancement of cortically-elicited muscle contraction was accompanied by the reduction of M1 maximal threshold and the potentiation of spinal motoneuronal evoked responses at the contralateral (313%) and ipsilateral (292%) sides of the spinal cord. Moreover, spontaneous activity recorded from single spinal motoneurons was substantially increased contralaterally (121%) and ipsilaterally (54%). Interestingly, spinal motoneuronal responses and muscle twitches evoked by the test stimulation of non-treated M1 (received no dCMS) were significantly enhanced as well. Similar results obtained from normal animals albeit the changes were relatively smaller.These findings demonstrated that dCMS could improve functionality of corticomotoneuronal pathway and thus it may have therapeutic potential.
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