In the present study, expression of neuronal nitric oxide synthase (n-NOS) was investigated during postnatal development of ependymal cells which lien the central canal of the rat spinal cord. In ependymal cells, progressive decrease was seen in NOS expression with increasing postnatal age. Low level of NOS expression was present from day 2 and this expression totally disappeared by postnatal 20 (P20) days. Formation of the central canal was also found to be completed at P16. These observation suggest that NO may play a role in the formation of ependymal cells and concequently in the formation of the central canal.