Neuropathic pain, a debilitating chronic pain condition, is a common consequence of damage to the nervous system. A growing body of evidence indicates that peripheral nerve injury converts spinal microglia into reactive cells that are essential for neuropathic pain. Recent studies have shown that after peripheral nerve injury, bone marrow (BM)-derived cells migrate into the dorsal horn, express microglial markers and showed microglia-like morphology. However, the ability of BM cells to migrate into the parenchyma of the CNS remains controversial because of experimental manipulations such as irradiation and exogenously injected donor cells. In the present study, we used myeloablation and parabiosis approaches to evaluate the recruitment of BM cells to the spinal dorsal horn. We found that irradiated mice that had been injected with EGFP-expressing BM cells had only few EGFP-positive microglia in the dorsal horn after nerve injury. A similar result was obtained by flow cytometry analysis. Furthermore, EGFP-expressing cells in the dorsal horn was also absent in parabionts (C57BL/6J mice) that had been surgically joined with EGFP mice. These results indicate that the origin of activated spinal microglia after peripheral nerve injury might be CNS-resident cells but not BM-derived cells.