Purpose: To determine whether upregulation of inducible nitric oxide synthase (iNOS) transcription and translation is related to radicular pain in a model of lumbar disc herniation. Also, to investigate the temporal changes of mRNA expression of iNOS and the identity of iNOS and transient receptor potential vanilloid (TRPV) 1 channel expression cells in dorsal root ganglion (DRG) of a model of lumbar disc herniation. Methods: A lumbar disc herniated rat model was developed by implantation of the autologous nucleus pulposus, harvested from the coccygeal vertebra of each tail, on the left L5 nerve root just proximal to the DRG. Rats were tested for mechanical allodynia of the plantar surface of both hind paws 2 days before surgery and 1, 5, 10, 20 and 30 days postoperatively. Reverse transcription polymerase chain reaction (RT-PCR) was used to follow iNOS mRNA expression. To stain iNOS and TRPV1 in DRG, an immunohistochemical study was done 10 days after surgery. Results: A significant drop in mechanical withdrawal threshold on the ipsilateral and contralateral hind paws was observed 1 day after surgery and was prolonged to 30 days in rats with lumbar disc herniation. The expression of mRNA for iNOS peaked at postoperative day 10 on both sides of the DRG. iNOS-positive sensory neurons in the DRG varied in size from large to small diameter cells. A majority of small and intermediate sensory neurons were TRPV1-positive cells. Double immunofluorescence staining for TRPV1 and iNOS revealed that most intermediate TRPV1-positive sensory neurons co-localized with iNOS-positive neurons. Conclusion: Nucleus pulposus-induced mechanical allodynia can be generated without mechanical compression. This pain is related to temporal changes in expression of iNOS mRNA in the DRG. Co-localization of TRPV1 and iNOS in intermediate neurons of the DRG is correlated with pain modality and intensity.