Netrin-1, secreted by floor plate cells, orients axon extension in relation to the ventral midline of the embryonic spinal cord. Oligodendrocyte precursor (OP) cells are born close to the ventral midline and migrate away from the floor plate. Here we show that OP cells, identified by expression of the platelet-derived growth factor alpha receptor, express the netrin receptors dcc and unc5h1 but do not express netrin-1. Using a microchemotaxis assay, we demonstrate that migrating OPs are repelled by a gradient of netrin-1 in vitro. Furthermore, application of netrin-1 to OPs in vitro triggers retraction of OP processes. In the absence of netrin-1 or Deleted in Colorectal Cancer (DCC) function in vivo, fewer OP cells migrate from the ventral to the dorsal embryonic spinal cord, consistent with netrin-1 acting as a repellent. In addition to their role regulating cell movement, DCC and UNC-5 homologs have been suggested to function as proapoptotic dependence receptors, triggering cell death in the absence of netrin-1. In contrast, we report no evidence of increased OP cell death in vivo or in vitro in the absence of either netrin-1 or DCC. These findings indicate that netrin-1 is a repellent cue for migrating OPs in the embryonic spinal cord.

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Background: Spinal cord injury without radiographic abnormality (SCIWORA) represents a traumatic myelopathy, either transient or permanent, that is not associated with visible vertebral fractures or ligamentous abnormalities on plain radiographs or CT. MRI has become essential in the diagnosis and evaluation of trauma patients and in predicting the long-term neurological outcome. Methods: The medical charts of 578 children with vertebral trauma at the Children’s Hospital of Eastern Ontario and the Hospital for Sick Children were retrospectively reviewed. Results: Forty-five patients were identified as having traumatic myelopathy. Three of these patients had SCIWORA. Two sustained thoracic spinal cord injuries as a result of motor vehicle accidents and permanent neurological deficits. The third was involved in a sports-related injury and sustained a cervical spine injury that improved in 48 h. Conclusions: SCIWORA is uncommon. The serious neurological sequelae that can result from a missed diagnosis merit more attention in identifying a spinal lesion in children with traumatic myelopathy. MRI has played a valuable role in this respect and may be even more predictive of outcome than the presenting neurological findings. The SCIWORA acronym can be modified to SCIWONA (spinal cord injury without neuroimaging abnormality) in order to highlight the importance of MRI in the prognosis.