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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 spinal cord injury (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 the lowering of the impactor, an immediate transient depolarization spread from the injury site to the whole spinal cord with distinct segmental velocities. Stronger strikes induced higher potentials causing, close by the site of injury, a transient drop in spinal cord oxygenation (SCO 2 ) and a massive cell death with a complete functional disconnection of input along the cord. 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 - . Overall, our novel ex vivo 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., Competing Interests: Declarations. Competing Interests: The authors have no relevant financial or non-financial interest to disclose. The impactor adopted in the study is currently being patented by SISSA and is available upon request. The authors declare no competing interests. Ethical Approval: The study was performed in line with the principles of the Italian Animal Welfare Act 24/3/2014 n. 26 implementing the European Union directive on animal experimentation (2010/63/ EU). The study complied with the ARRIVE guidelines. The animal protocol was approved by the Italian Ministry of Health with the notification. 22DAB.N.52 M dated Oct 30th, 2019, and approved by SISSA ACUC (OPBA) committee (verbale n.17/3019). Consent to Participate: All authors give their formal consent to participate to the present manuscript. Consent for Publication: All authors give their formal consent for the publication of the present manuscript. Preprint Disclosure Statement: This manuscript was previously published as a pre-print on bioRxiv, available at https://doi.org/10.1101/2024.07.15.603535 , on 17 July 2024., (© 2024. The Author(s).)