Abstract
It is well known that the phosphorylation of extracellular signal-regulated protein kinase (pERK) in dorsal horn neurons is induced by noxious stimulation of the peripheral structures. The pERK is thought to be a good marker of the excitability of nociceptive neurons. This study was designed to elucidate the central mechanism of tooth pulp pain by use of pERK immunohistochemistry. The right upper maxillary tooth pulp was stimulated by 10 mM capsaicin (CAP) or vehcle (Veh) solution in the anesthetized rat. Rats were perfused at 2, 5, 10, 30 and 120 min after the stimulation. The number of pERK-like immunoreactive (LI) cells in the medulla and the upper cervical cord was counted in CAP or Veh groups. In addition, electromiographic (EMG) activities of digastric and masseter muscles were analyzed following the stimulation. Five min after CAP, a number of pERK-LI cells were expressed bilaterally in the trigeminal subnuclei interpolaris/caudalis (Vi/Vc) zone and paratrigeminal nucleus (Pa5). In the ipsilateral caudal subnucleus caudalis/upper cervical dorsal horn (C1/C2) zone, the pERK-LI cells were expressed significantly larger 5 min after CAP. EMG activities of the digastric and masseter muscles were significantly increased immediately after CAP.These results suggest that C1/C2 zone contribute directly to the tooth pulp pain, and the Pa5 and Vi/Vc zone would be involved in the other functions instead of tooth pain. [Jpn J Physiol 55 Suppl:S161 (2005)]
