An innovative spinal cord injury model for the study of locomotor networks

An acute lesion to the spinal cord triggers complex mechanisms responsible for amplification of the initial damage and its chronicity. In vitro preparations of the rodent spinal cord retain the intrinsic ability to produce locomotor-like discharges from lumbar ventral roots and, thus, offer the opportunity to study the still unclear process of lesion progression in relation to cell number and topography. In addition, these models enable a detailed approach to the molecular mechanisms of damage and to pharmacological tools to counteract them. Using the rat spinal cord in vitro, our laboratory has shown how to reliably produce discrete lesions by applying the glutamate agonist kainate that evokes delayed neuronal loss via a non-apoptotic cell death mechanism termed parthanatos. Parthanatos is believed to be due to mitochondrial damage and exhaustion of cell energy stores caused by hyperactivation of enzymatic systems initially set to repair DNA damage. Locomotor network activity is irreversibly destroyed by kainate in a virtually all-or-none manner, suggesting destruction of a highly-vulnerable cell population crucial for the expression of locomotion. Hypoxic challenge to the spinal cord together with toxic radicals primarily damages white matter cells with deficit (without full suppression) of locomotor network function, while neurons are less vulnerable. Pharmacological agents to inhibit different targets involved in the early pathophysiology of spinal injury provided limited success, indicating that novel approaches based on newly identified steps in the biochemical cascade leading to cell death should be investigated for their potential to improve the outcome of spinal cord injury.