Abstract
We studied pERK expression in the trigeminal spinal nucleus caudalis (Vc) of the rats with TMJ inflammation, in order to elucidate the underlying neuronal mechanism of the trigeminal chronic pain. CFA was injected in the TMJ under pentobarbital anesthesia (50 mg/kg, i.p.). Two weeks after CFA injection, passive jaw opening (JO) was applied to the TMJ inflamed rats for 5-30 min (JO distance: 4, 6 and 15 mm). The pERK expression was studied in the medulla and upper cervical spinal cord after JO. The face temperature was significantly increased 2-3 days after CFA injection and returned to the preoperative level 7 days after that. The pERK-like immunoreactive (LI) cells were observed in the dorsal portion of the trigeminal spinal nucleus caudalis (Vc) of the TMJ inflamed rats after JO. On the other hand, we could not observe any pERK-LI cells in naive rats after 4, 6 and 15 mm JO. The number of pERK-LI cells was increased following increase in the JO duration (5, 15 and 30 min) and JO distance (4, 6 and 15 mm). The increment ratio of pERK-LI cells in Vc was significantly larger in 15 mm JO group than 4 and 6 mm JO groups following different JO duration. These findings suggest that the hyperexcitability of nociceptive neurons in the dorsal portion of the Vc would be involved in the TMJ chronic pain following TMJ inflammation through the activation of the intracellular ERK cascade. [J Physiol Sci. 2006;56 Suppl:S190]
