Abstract
The organization of phosphorylated extracellular signal-regulated kinase-like immunoreactive cells (pERK-LI cells) in the trigeminal spinal nucleus and the upper cervical cord were studied following capsaicin stimulation of the orofacial regions in rats. Rats were perfused 5 minutes after capsaicin injection and sections from the medulla and upper cervical cord were processed with pERK immunohistochemistry. A large number of pERK-LI cells were expressed in the rostro-caudally middle portion of ipsilateral the trigeminal spinal nucleus interpolaris and caudalis transition zone (Vi/Vc zone) after capsaicin injection into the vibrissal pad and snout. On the other hand, those were restricted in the ventrolateral portion of the Vc/C2 zone following orbital injection. Following capsaicin injection into the tongue, lower or upper lip, pERK-LI cells were expressed in the dorsomedial portion of the ipsilateral Vi/Vc and Vc/C2 zone. The present findings suggest that the face nociceptive information was processed in the trigeminal nociceptive neurons restricted in the Vi/Vc zone, whereas those from the intra-oral structures were processed in nociceptive neurons distributed in wide area of the Vi/Vc and Vc/C2 zones through activation of the MAP kinase intracellular signal transduction pathway. [J Physiol Sci. 2007;57 Suppl:S154]
