Abstract
The aim of present study is to clarify the neuronal mechanisms of an inhibition of swallowing reflex following capsaicin injection into the whisker pad region and masseter muscle in the anesthetized rats. We analyzed the number of swallowing reflexes induced by intraoral water application and the effect of capsaicin injection into the whisker pad region or master muscle (1,10,30mM) on occurrence of swallowing reflex was precisely analyzed. The pERK immunohistochemistry in the trigeminal spinal nuclei (Vi/Vc and Vc) and the nucleus of solitary tract (NTS) was also carried out in capsaicin-treated rats.In summary:1) The number of swallowing reflexes following capsaicin injection into the whisker pad region or masseter muscle was decreased in dose dependent manner. 2) The pERK-LI cells in Vi/Vc-Vc and NTS neurons were significantly higher in the rats with capsaicin treatment compared with vehicle-treated rats.3) The number of swallowing reflexes following capsaicin (10mM) injection was significantly increased folllowing PD98059 (MEK1/2inhibitor) intrathecal administration. 4) The pERK-LI cells were significantly decreased in PD98059-treated rats.These findings suggest that the ERK phosphorylation in Vi/Vc-Vc and NTS neurons would be involved in an inhibition of swallowing reflex following noxious stimulation of the facial skin or deep muscles. [J Physiol Sci. 2008;58 Suppl:S197]
