ラット孤束核および三叉神経傍核ニューロンは口腔顔面領域の侵害刺激によるERK のリン酸化を介して嚥下反射を抑制する

抄録

   The aim of present study is to clarify neuronal mechanisms of an inhibition of swallowing reflex following capsaicin injection into the whisker pad skin or lingual muscle in anesthetized rats.　We analyzed the number of swallows induced by topical administration of 0.1 ml of water to the pharyngeal mucosa following capsaicin injection into the whisker pad skin or lingual muscle. The phosphorylated extracellular signal-regulated kinase (pERK) immunohistochemistry in the medulla and upper cervical spinal cord was also carried out in 10 mM capsaicin-treated rats.We also studied the effect of MAP kinase (MEK)1/2 inhibitor, PD98059, on pERK expression and swallowing reflex following 10 mM capsaicin injection into the whisker pad skin or lingual muscle.
   The number of swallows decreased in dose dependent manner following capsaicin injection into the whisker pad skin or lingual muscle. The number of pERK-like immunoreactive (pERK-LI) cells in the nucleus tractus solitarii (NTS), trigeminal spinal subnucleus caudalis (Vc) and paratrigeminal nucleus (Pa5) was significantly larger in the rats with capsaicin treatment compared to vehicle-treated rats. After intrathecal (i.t.) injection of PD98059 in the rats with capsaicin treatment, the number of pERK-LI cells was significantly depressed compared to vehicle-treated rats.Swallowing reflex was significantly enhanced in PD98059-treated rats compared to vehicle-treated rats.
   These findings suggest that the ERK phosphorylation in NTS and Pa5 neurons is involved in modulation of swallowing reflex following noxious stimulation of the orofacial regions.