Resumo

Aim: Glial cells have an important role in inflammatory processes, through the release of several mediators. In order to explore the involvement of glia in the nitric oxide(NO)-mediated nociception, the present study was undertaken to investigate the NO synthase (NOS) expression in the spinal cord during the process of acute myositis induced by carrageenan in rats. In addition, we will also evaluate the effect of fluorocitrate (FC), an inhibitor of glial metabolism, on NOS expression. Methods: Myositis was induced by the administration of 400µg of carrageenan (Cg) in the right gastrocnemius (GS) muscle of rats, with saline (150µL) as control. Immunohistochemical assays to evaluate nNOS expression were performed in the lumbar dorsal horn and central canal of spinal cord 2h after the myositis-induced. The activity of all NOS isoforms was detected by NADPH-d histochemistry staining. Intrathecal injection of fluorocitrate was used to examine potential spinal glial mediation in this model. Results: The immunohistochemical data showed that carrageenan up-regulated nNOS expression 2h after acute myositis, as immunostaining to nNOS was significantly higher in animals injected with Cg when compared with controls groups. Fluorocitrate, a glial inhibitor, when administered by intrathecal route, was not able to decrease nNOS expression in rats with myositis. Regarding NADPH-d, we also observed and increase of NO positive cells after carrageenan injections when compared with control animals. Conclusions: Our results suggest that in the process of acute muscle inflammation occurs the release of NO, through the activation of positive NOS neurons in the dorsal horn and central canal of the spinal cord. Understanding the role of glial cells during myositis-induced nociception may lead to new strategies for management of muscle pain, one of the most frequent types of clinically relevant pain. Acknowledgments: Supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).