Tibia fracture in rats evokes nociceptive, vascular, and bone changes resembling complex regional pain syndrome (CRPS). Substance P (SP) signaling contributes to the hindpaw warmth, increased vascular permeability, and edema observed in this model, suggesting that neurogenic inflammatory responses could be enhanced after fracture. Four weeks after tibia fracture we measured SP and calcitonin gene-related peptide (CGRP) protein levels in the sciatic nerve and serum. Hindpaw skin extravasation responses and SP receptor (NK1), CGRP receptor (calcitonin receptor-like receptor, CRLR) and neutral endopeptidase (NEP) protein levels were also determined. Gene expression levels of these peptides, receptors, and peptidase were examined in the DRG and skin. Spontaneous and intravenous SP-evoked extravasation responses were increased ipsilateral, but not contralateral to the fracture. Fracture increased SP and CGRP gene expression in the ipsilateral L4,L5 DRG and neuropeptide protein levels in the sciatic nerve and in serum, but had no effect on electrically evoked SP and CGRP release. NK1 receptor expression was increased in the ipsilateral hindpaw skin keratinocytes and endothelial cells after injury, but CRLR and NEP expression were unchanged. Fracture also increased epidermal thickness, but had no effect on epidermal skin neurite counts. These results demonstrate that spontaneous and intravenous SP-evoked extravasation responses are enhanced in the ipsilateral hindlimb after fracture and that fracture chronically increases the expression of endothelial and keratinocyte NK1 receptors in the injured limb. We postulate that SP activation of these up-regulated NK1 receptors results in skin warmth, protein leakage, edema, and keratinocyte proliferation in the injured limb.
aPhysical Medicine and Rehabilitation Service, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA, USA
bDepartment of Orthopedic Surgery, Stanford University School of Medicine, Stanford, CA, USA
cAnesthesiology Service, Veterans Affairs Palo Alto Health Care System Palo Alto, CA, USA
dDepartment of Anesthesiology, Stanford University School of Medicine, Stanford, CA, USA
eDepartments of Neurology and Pathology, Harvard Medical School, Boston, MA, USA
fDepartment of Anesthesiology and Intensive Care Medicine, University of Heidelberg, Mannheim, Germany
*Corresponding author. Address: Physical Medicine and Rehabilitation Service (117), Veterans Affairs Palo Alto Health Care System, 3801 Miranda Ave., Palo Alto, CA 94304. Tel.: +1 650 493 5000x64768; fax: +1 650 852 3470.
Received October 2, 2008
Received in revised form April 2, 2009
Accepted April 20, 2009.