Expression of neuronal NOS, c-jun and c-fos in spinal motoneurons following axonal damage were investigated in the present study. Although either distal spinal root axotomy or root avulsion induced expression of c-jun, expression of c-jun was predominantly found in distal root-axotomized motoneurons. In contrast, expression of NOS was exclusively observed in avulsed motoneurons. c-fos was not expressed in spinal motoneurons following either distal root axotomy or root avulsion. The different expression patterns of c-jun and NOS in the injured neurons suggest that these molecules may involve in different cellular processes and might play different roles in response to the injury. Since distal root axotomy did not cause motoneuron death and root avulsion did, expression of c-jun is likely related to regenerative process while induction of NOS may be involved in the degenerative process.