Role of nitric oxide in the regulation of pain after nociceptive stimuli in rat spinal cord
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Purpose: In this study, we examined the responses of the neurons in the lumbar segments of the spinal cord to nociceptive stimuli induced by formalin using c-fos immunohistochemistry and NADPH-d histochemistry Materials and Methods: Thirteen male, Wistar albino rats were used. The rats were divided into 3 groups. Group 1: pain group (n=5). Group 2: sham group (n=5). Group 3: control group (n=3). In group 1, 50 mu l of 30% formalin solution was injected subcutaneously unilaterally on the dorsal surface of the right foot. In group 2, phosphate buffered saline was injected subcutaneously unilaterally on the dorsal surface of the right foot. In group 3, no treatment was given. For each group lumbar spinal cord (SC) samples were taken. Samples were stained with c-fos and NADPH-d histochemistry and c-fos/NADPH-d double-labeling methods and evaluated under light microscope. Results: We noted that cells on spinal cord sections stained with c-fos, NADPH-d and both became prominent with nociceptive stimuli. There were significant increases in the numbers of c-fos (+), NADPH-d (+) and double-labeled cells in pain group comparison to sham group. In group 1, NADPH was significantly increased in the Laminae I-IV of the lumbar segments of the SC on both sides and laminae VIII, IX and X on the same side. Conclusion: The findings suggest that NO is associated with formalin-induced FOS-ir in the spinal cord, that it may play an important role in the regulation of pain and that the nociceptive function is related to increased nitric oxide synthase (+) neurons in the spinal cord.
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C-FOS , DORSAL-HORN , NERVE INJURY , NADPH-D , EXPRESSION , IMMUNOREACTIVITY , ACTIVATION , INDUCTION , INJECTION , SYNTHASE