Immediate changes in CNS networks triggered by a physical trauma to the spinal cord

Spinal cord injury (SCI) results in irreversible functional impairments due to intricate molecular and cellular processes, leading to neuronal damage. Despite its significance, the immediate consequences of SCI, including the transient disappearance of reflex responses below the injury site, termed as spinal shock, have been underexplored due to the lack of consistent preclinical models. In the first part of this PhD thesis project, an in vitro preparation of the isolated central nervous system (CNS) from neonatal rats was characterized. This preparation exhibited stable respiratory rhythms, evoked motor responses, fictive locomotor (FL) activities, and functional ascending and descending pathways. The in vitro CNS showed the crucial role of suprapontine centers in the modulation of spontaneous respiratory rhythms, electrically evoked reflexes, and spinal network activity. The second part of the project adopts a novel custom-made micro impactor to deliver a calibrated impact to the ventral surface of the thoracic spinal cord. Ventral root (VR) recordings continuously monitored baseline spontaneous activities and electrically-induced reflex responses before and after injury. Following the impact, an immediate transient depolarization occurred, coinciding with a rapid drop in tissue oxygen levels and significant cell death at the injury site, alongside complete disconnection of longitudinal tracts. Reflex responses were temporarily abolished, mimicking the progression of the spinal shock, while the coordination among motor pools during FL was affected. Perfusion with low chloride-modified Krebs medium amplified the depolarization, suggesting that chloride ions are implicated in the peak of the injury potential. Furthermore, remote changes in cortical glial cells were observed shortly after spinal injury. Eventually, various pharmacological agents were tested to mitigate injury-induced depolarization. Notably, only Transient Receptor Potential Vanilloid 4 (TRPV4) antagonism successfully reduced the depolarization amplitude, indicating for the first time that mechanoreceptors sustain the immediate depolarization after a spinal trauma. The reappearance of VR reflexes was accelerated through the blockade of TRPV4 channels, gap junctions, and GABAergic transmission, although with distinct timing and yield. In conclusion, this study provides a novel experimental platform for investigating the immediate events following traumatic SCI, revealing the pivotal roles of chloride imbalance and mechanoreceptors in the cascade of pathological events that characterize acute SCI pathophysiology.