Aim: To study the distribution of NADPH-diaphorase positive neurons in periaqueductal gray matter(PAG) and dorsal raphe nucleus (DR), and the correlation between nitric oxide and peripheral nociception at supraspinal level.
Methods: 20 Sprague-Dawley rats were randomly divided into two groups. In experimental group (n = 10), formalin (5%, 0.1 ml) was injected subcutaneously into the plantar surface of the unilateral hindpaw, and in control group (n = 10), normal saline solution was used alike. The rats were perfused after 2 hours, and the midbrain were removed. Frozen seriate transverse sections were divided into three sets, all of which were processed for NADPH-d histochemistry. Subsequently, the first set that contained NADPH-diaphorase positive neurons were stained with neutral red, and the other two sets were processed for c-fos immunohistochemistry.
Results: NADPH-diaphorase positive neurons were densely distributed in CGLD, CGLV and DR. NADPH-d, Fos and NADPH/Fos double-labeled neurons appeared in CGLD, CGLV and DR after injection of formalin in the rat hindpaw.
Conclusion: At supraspinal level NO may play an important role in the modulation of nociception in PAG and DR.