Intraspinal Electrical Stimulation Reliably Triggers Respiratory Activity in the in situ Rodent Model

Abstract

Cervical spinal cord injury impairs ventilation by preventing brainstem generated respiratory activity from reaching motor pools in the spinal cord which drive respiratory pump muscles. Epidural high frequency thoracic spinal cord stimulation is a method of producing respiratory efforts independent of centrally generated signals, which is effective at eliciting diaphragmatic EMG in anesthetized animal preparations. However, the exact spinal pathways and circuitry involved in producing these respiratory efforts are unknown. We hypothesize that targeted electrical stimulation within the spinal cord will identify pathways relaying the stimulus to the phrenic motoneurons. To investigate this, we monitored bilateral phrenic nerve activity (PNA) in the in situ rat preparation (n=6) and applied either bipolar epidural or intraspinal stimulation (ISS) (300ms, 100‐300Hz, 200μs pd) in the rostral thoracic spinal cord (T2‐6). Our initial findings demonstrated that epidural stimulation was only intermittently effective in eliciting PNA, while ISS reliably produced site and current dependent (10‐500μA) responses. We conclude that, in comparison to epidural stimulation, low current thoracic ISS more efficiently and reliably activates the phrenic motor circuit in the in situ model. Ongoing studies are focused on identifying the neural circuits activated by ISS. Funded by the UF College of Veterinary Medicine, APS UGSRF, and NIH 1R01NS080180‐01A1