The effects of transcranial functional magnetic stimulation on motor recovery in rats after spinal cord injury

Abstract

Objective: Magnetic stimulation is a non-invasive technique which stimulates the central nervous system through pulsed magnetic fields without direct effect on the neurons. Although a positive effect of repetitive magnetic stimulation on neuronal regeneration had been reported recently, no studies for the effects of transcranial functional magnetic stimulation on in vivo spinal cord injury could be found. The objective of this study was to investigate whether transcranial functional magnetic stimulation could facilitate spinal cord regeneration and improve motor function in rats after spinal cord injury. Method: Functional magnetic stimulation was applied daily 5 days per week for 5 weeks from 4 days after contusion injury at the spinal level of T9 using the NYU Impactor. Magnetic stimulation was delivered by a magnetic stimulator(Biocon-1000P, Mcube Technology) through a round prototype coil( 7cm diameter) which was positioned around the bregma in the distance of 1cm from skull. Stimulator parameters were set as follows: The intensity of 100 % stimulation= 2.2 kG, repetition rate=10 Hz, on-time=3 sec, off-time=3 sec, stimulated time= 20 min. The hindlimb motor function was monitored by assigning BBB test and inclined plane test weekly. To assess motor axon pathway, the retrograde neuronal tracing was performed by using 4% fluorogold (FG) injection into the dorsal funniculus at the spinal level of L1. The animals were sacrificed at 5 weeks after magnetic stimulation, and the degree of spared axon was assessed by immunohistochemistry. Results: Behavioral tests showed that functional magnetic stimulated group improved some degrees of motor functional recovery compared to controls. Retrograde labeling study showed that, the number of FG-labeled neurons in the brain stem was increased in magnetic stimulated rats compared to controls. Conclusion: Our result demonstrate that transcranial functional magnetic stimulation may have beneficial effects on motor function recovery in rat contusion models of spinal cord injury. These results may be due to facilitating the motor axonal regeneration by pulsed magnetic field.