UNC5A-D are transmembrane receptors for netrin that plays an important role in the development of the spinal cord. However, their function in the adult nervous system remains to be established. In the present study, the mRNA expression of UNC5 family was investigated in the adult rat spinal cord following a dorsal hemisection injury. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that mRNA expression of rat UNC5 family was down-regulated in the spinal cord within 3 days after the dorsal hemisection. Unc5b-d mRNA expressions returned to near normal level after a week, whereas the down-regulation of Unc5a mRNA expression was maintained until 1 month after the injury. In situ hybridization and immunofluorescent showed that both neurons and non-neuronal cells express Unc5a and b mRNAs in the adult spinal cord, and the significant long lasting down-regulation of Unc5a mRNA expression was also noticed following the spinal cord injury. This result suggests netrin/UNC5 involvement in the injury response of the adult spinal cord of the rats.