Ativação de receptores NMDA no gânglio da raiz dorsal de ratos na dor aguda: envolvimento de fibras do tipo C

Abstract

The objective of this study was to evaluate the participation of NMDA receptors present in satellite cells of the dorsal root ganglion in models of acute pain and hiperalgesia and to determine the types of nociceptive fibers involved in the process. It was also intended to advance in the mechanisms involved in the communication between primary nociceptive neurons and satellite glial cells. For this, in vivo behavioral experiments and dorsal root ganglion cultures were performed to investigate the mechanisms involved in neuronal/glia interaction in vitro. We used intraganglionic (L5) administration of the NMDA receptor antagonist, AP-5, in order to assess the receptor in the dorsal root ganglion in acute pain (nociception) induced by capsaicin and in PGE2-induced sensitization (hyperalgesia). In addition it was tested the selective destruction of C-fibers by intrathecal injection of capsaicin in the inflammatory hyperalgesia induced by PGE2. We have found that preferential destruction of fibers by administration of capsaicin as well as intraganglion administration of AP-5 does not affect basal mechanical sensitivity while PGE2-induced sensitization was reduced. Intraganglionic administration of AP-5 inhibited the nociceptive behavior induced by intraplantar capsaicin administration. Taken together, results suggest that NMDA receptors present in satellite glial cells are involved in processing acute pain. This process seems to depend on activation of type C fibers. We have found that in dorsal root ganglion primary cultures the activation of NMDA receptors in satellite glial cells induces depolarization in the neuronal resting potential, suggesting a mechanism by which activation of glial NMDA receptors influences neural excitability and, therefore, the nociceptive signal transmission.