A focal traumatic injury to the spinal cord causes an immediate and massive spreading depolarization sustained by chloride ions, with transient network dysfunction and remote cortical glia changes.

Abstract

In clinics, physical injuries to the spinal cord cause a temporary motor areflexia below lesion, known as spinal shock. This topic is still underexplored due to the lack of preclinical SCI models that do not use anesthesia, which would affect spinal excitability. Our innovative design considered a custom-made micro impactor that provides localized and calibrated strikes to the ventral surface of the thoracic spinal cord of the entire CNS isolated from neonatal rats. Before and after injury, multiple ventral root (VR) recordings continuously traced respiratory rhythm, baseline spontaneous activities, and electrically-induced reflex responses. As early as 200 ms after impact, an immediate transient depolarization spread from the injury site to the whole spinal cord with distinct segmental velocities. Stronger strikes induced higher potentials causing, at the site of injury, a transient drop in tissue oxygen levels and a massive cell death with complete disconnection of longitudinal tracts. Below the impact site, expiratory rhythm and spontaneous lumbar activity were suppressed. On lumbar VRs, reflex responses transiently halted but later recovered to control values, while electrically-induced fictive locomotion remained perturbed. Moreover, low-ion modified Krebs solutions differently influenced impact-induced depolarizations, the magnitude of which amplified in low-Cl-. Moreover, remote changes in cortical glia occurred soon after spinal damage. Overall, our novel in vitro platform traces the immediate functional consequences of impacts to the spinal cord during development. This basic study provides insights on the SCI pathophysiology, unveiling an immediate chloride dysregulation and transient remote glial changes in the cortex.