Ipsilateral inspiratory intercostal activity persists after C2 hemisection

Upper cervical spinal cord injury (C2 hemisection) results in paralysis of the ipsilateral hemidiaphragm due to the interruption of descending respiratory premotor neurons. After C2 hemisection, however, it is not clear what happens to inspiratory intercostal muscle activity. Innervation of the diaphragm primarily involves monosynaptic bulbospinal premotor neurons, whereas innervation of thoracic intercostal muscles involves primarily respiratory thoracic interneurons. Studies show that at least 60% of the respiratory interneurons project to the contralateral ventral horn. Therefore, we hypothesized that intercostal activity may persist ipsilateral to a C2 spinal cord hemisection. Female, Sprague Dawley rats were anesthetized with urethane and inspiratory intercostal EMG activity (1‐10 spaces) was recorded in control rats, immediately after hemisection (within minutes), and in chronic‐injured rats (16wks post injury). In control rats, inspiratory intercostal activity was present in all thoracic spaces examined. Immediately after hemisection, intercostal inspiratory activity did not change contralateral to the hemisection, but was significantly reduced ipsilateral to the hemisection. There was no difference between acutely injured rats and chronically injured rats; intercostal inspiratory activity did not change contralateral to hemisection but was reduced ipsilateral to injury. This study demonstrates that inspiratory intercostal activity persists after spinal cord injury although at significantly reduced amounts and may contribute toward ventilation after spinal cord injury.