Neuronal Modulation after long term forepaw immobilization in rats.

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Long-term immobilization by casting can occasionally cause pathologic pain states in the immobilized side. The underlying neurophysiological mechanisms of immobilization-related pain are not well understood. For this reason, we specifically examined changes of calcitonin gene-related peptide (CGRP) expression in the dorsal root ganglion (DRG), spinal dorsal horn and posterior nuclei (cuneate nuclei) ina long-term immobilization model following casting for 5 weeks. A plastic cast was wrapped around the right limb from the forearm to the forepaw to keep wrist joint at 90 degree of flexion. In this model, CGRP in immobilized (ipsilateral) side was distributed in larger DRG neurons compared with contralateral side, even though the number of CGRP-immunoreactive (CGRP-IR) neurons did not differ. Spinal laminae III-V, not laminae I-II in ipsilateral side showed significantly high CGRP expression relative to contralateral side. In addition expression of GFSP and CD11b were increased after long term immobilization. These results suggest that neuronal plastic changes were occurred after long term casting addition to joint contracture. Additional casting to sound forepaw was useful method to improve disuse behavior after the cast treatment. Thus adequate musculoskeletal rehabilitation was essential for the treatment.