Two weeks hindlimb immobilization causes spinal glial changes in rats

Abstract

We developed chronic pain model with the cast-immobilization to reveal mechanism of chronic pain without clear nerve injuries. This model produced the long-lasting (weeks) and widespread hyperalgesia were seen not only in immobilized side, but also in contralateral side and in tail without nerve injury. Furthermore, nerve blockade in the sciatic nerve 3 weeks after the cast removal had no effect on the contralateral hyperalgesia in the hindpaw. It is suggested that the cast-immobilization causes the central plasticity. In this study, we investigated changes in spinal glial cells with immunohistology (OX42, GFAP). We found the activation and increase in the number of microglia in L4 dorsal horn following the cast removal in the acute phase when hindpaw hyperalgesia began, while in the chronic phase that showed maximum pain behaviors we found the activation of astroglia in L4 dorsal horn and microglia in coccygeal dorsal horn. In the end of chronic phase that showed attenuated pain behaviors, both glial cells activations tended to reduce. It is suggested that microglia and astroglia are differently activated in the course of pain development in this cast-immobilization model. [J Physiol Sci. 2008;58 Suppl:S162]