c-Jun activation has been implicated not only in neuronal degeneration, but also in survival and regeneration. Here, we investigated c-Jun activation in injured motoneurons by using a nerve crush model in neonatal rats. We identified two distinct subpopulations of motoneurons: about 60% underwent degeneration following injury whereas the remaining 40% survived and induced a regeneration response at 3 weeks post injury. However, all motoneurons examined expressed phosphorylated-c-Jun-immunoreactivity (p-c-Jun-IR) at the early stage of 3 days following injury. These results suggest that active c-Jun was induced in all neonatal motoneurons following nerve crush injury, regardless of whether they were destined to degenerate or undergo successful regeneration at a later stage. Our findings therefore support the hypothesis that active c-Jun is involved in both neuronal degeneration and regeneration.