Delayed Granulocyte Colony-Stimulating Factor Treatment in Rats Attenuates Mechanical Allodynia Induced by Chronic Constriction Injury of the Sciatic Nerve

Study Design. Animal experimental study with intervention. Objective. The aim of this study was to elucidate therapeutic effects of delayed granulocyte colony-stimulating factor treatment for mechanical allodynia induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Summary of Background Data. Granulocyte colony-stimulating factor (G-CSF) is used clinically for patients with hematological disorders. Previous reports showed that immediate G-CSF attenuates neuropathic pain in CCI of the sciatic nerve. However, the acute treatment for neuropathic pain prior to accurate diagnosis is not realistic in clinical settings. Methods. Adult, female Sprague-Dawley rats were subjected to the CCI model. This model induces mechanical allodynia on the ipsilateral hind paw within the first week after the injury. One week after CCI, rats received intraperitoneal G-CSF (15.0 mu g/kg) for 5 consecutive days. Mechanical allodynia was assessed using the von Frey hair test. Immunohistochemistry for phosphorylated p38 mitogen-activated kinase (p-p38MAPK) and OX-42 (a marker for activated microglia) on tissue slides from a subset of rats 2 weeks after surgery. Western blot analyses were carried out to determine protein expression level of p-p38MAPK and interleukin-1 beta on spinal cord homogenates 2 weeks after CCI. Results. Results of the von Frey filament test showed that G-CSF significantly attenuates mechanical allodynia induced by the CCI model. Immunohistochemistry revealed that G-CSF reduced the number of p-p38MAPK-positive cells in the ipsilateral dorsal horn compared with that in the vehicle group rats. Immunofluorescent double staining revealed that p-p38MAPK-expressing cells in the spinal cord dorsal horn are mainly microglia. Western blot analysis indicated that G-CSF decreased the expression levels of both p-p38MAPK and interleukin-1 beta in the ipsilateral dorsal horn compared with that in the vehicle group rats. Conclusion. The present results indicate a beneficial effect of delayed G-CSF treatment in an animal model of peripheral nerve injury-induced neuropathic pain.