Diaphragm motor evoked potential induced by cervical magnetic stimulation following cervical spinal cord contusion in the rat

Abstract

Cervical spinal cord injury is usually associated with respiratory impairments due to damage of bulbospinal respiratory pathways and cervical phrenic motoneurons. The magnetic stimulation is a non-invasive and safe approach to evaluate and modulate the central and peripheral nervous system. The purpose of the present study was to examine whether cervical magnetic stimulation can be applied to evaluate the diaphragmatic motor outputs in a pre-clinical rodent model of cervical spinal cord injury. The bilateral diaphragm electromyogram was measured in anesthetized rats at the acute, subchronic and chronic stage following left mid-cervical spinal cord contusion. The center of figure-of-eight coil was placed 20 mm caudal to the Bregma to stimulate the cervical spinal cord. The results demonstrated that cervical magnetic stimulation can evoke a significant diaphragm motor evoked potential in uninjured animals when the coil was placed at the lateral position (3 cm right or left to the midline). The spontaneous bursting of diaphragm was significantly attenuated by cervical spinal cord contusion at all-time points post-injury. However, the threshold of diaphragm motor evoked potential was reduced and the amplitude of diaphragm motor evoked potential was augmented in response to cervical magnetic stimulation at the acute injured stage. In addition, the motor evoked potential of bilateral diaphragm in contused animals was generally greater when the coil was placed at the left spinal cord at the subchronic and chronic injured stages. These results suggested that cervical magnetic stimulation can be used to examine the excitability of phrenic motor outputs, and the lateral cervical magnetic stimulation may be more effective to trigger the diaphragm motor evoked potential.