Activation of ERK1/2 in spinal cord contributes to the development of acute cystic pain in rabbits.

Objective To investigate the role of activated extracellular signal-regulated kinase 1/2 (ERK1/2) in spinal cord in the development of cystic pain in rabbit. Methods We observed the relationship between the activation of ERK1/2 in spinal cord and nociceptive behaviors, as well as the effect of U0126, a mitogen-activated protein kinase (MEK, upstream protein of ERK1/2) inhibitor, on cystic pain in rabbits by behavioral test, immunohistochemistry and western blot analysis. Results After injecting 0.5 ml formalin into gallbladder, the behaviors such as grasping of the cheek and licking of the abdomen increased in 30 min, with a significant increase in pERK1/2 expression in the spinal cord, as well as the pERK1/2 immunoreactive cells located in laminae V-VII and X of the dorsal horn and ventral horn of T6 spinal cord. Administration of U0126 (100 - 400 mu g/kg body weight, i.v., 10 min before instillation of formalin) could attenuated nociceptive behaviors dose-dependently, but could not restrain the nociceptive behaviors completely even at the maximal efficient dose of 400 mu g/kg body weight. Conclusion Activated ERK1/2 in the spinal cord at least partly participates in the development of acute inflammatory cystic pain induced by formalin in rabbits.