Nicotinamide adenine dinucleotide phosphate-diaphorase and c-fos expression in spinal cord neurons following noxious stimulation

Objectives: To investigate nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and fos expression in spinal cord dorsal horn neurons following noxious peripheral stimulation. Methods: Expression of the immediate-early gene c-fos and nitric oxide containing neurons one hour after unilateral formalin injection to the dorsal hind paw was investigated in rat lumbar spinal cord, using fos immunohistochemistry and NADPH-d histochemical techniques. The experiments were performed in 2004 and 2006 at Ege University Center for Brain Research in Izmir, Turkey. Results: In 10 adult male Sprague-Dawley rats, an increase in fos-immunoreactive neurons was observed ipsilateral, and NADPH-d positive neurons equally ipsi- and contralateral to the formalin injection site. Approximately 20% of fos-immunoreactive neurons were NADPH-d positive ipsilateral to the formalin injection, whereas no double labeling was observed in the contralateral side. Also, a close relation of NADPH-d positive processes with fos-immunoreactive nuclei were also observed. Conclusion: The results of this study support the hypothesis that nitric oxide synthase blocking agents may serve as a possible alternative in treatment of hyperalgesia following inflammation and peripheral nerve injury.