Abstract
BackgroundElectrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury.MethodsHere 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).ResultsIn 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.ConclusionThese findings demonstrated that dCMS could improve functionality of corticomotoneuronal pathway and thus it may have therapeutic potential.
Highlights
After a spinal cord injury (SCI), spared regions of the central nervous system are spontaneously capable of repairing the damaged pathway, the process is very limited
Behavioral assessment A contusion lesion of the spinal cord resulted in the appearance of signs of spasticity syndrome such as crossing of both limbs and fanning of the paws
Abnormal pattern scale (APS) showed substantial increase for both on (APSon 9.8 ± 0.70) and off (APSoff 9.8 ± 0.70) ground conditions. These postural abnormalities were accompanied by reduction in Basso Mouse Scale (BMS) scores from 9 in control mouse to 1.2 ± 0.47 and 1.0 ± 0.63 for right and left hindlimb in SCI mouse (n = 15), respectively
Summary
After a spinal cord injury (SCI), spared regions of the central nervous system are spontaneously capable of repairing the damaged pathway, the process is very limited. It is well known that spared axons sprout after an SCI [1,2,3], but fine-tuning of this process as well as synapse stabilization might be dependent on precise pathway-selective activity. Electrical stimulation is an effective method that promotes reactive sprouting through which an increase in the number of functional connections may be possible [3]. Electrical stimulation can improve functional connections by strengthening the weak existing synapses and/or by promoting synaptogenesis. Electrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury
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