Ephrinli/EphB signaling contributes to spinal nociceptive processing via calpain-1 and caspase-3

Previous studies have indicated that an important subfamily of receptor tyrosine kinases, ephrins and their receptors, are important in pain signaling, particularly in spinal nociceptive processing. In the present study, the role of the ephrin/Eph signaling pathway was confirmed, and it was shown that this signaling was also involved in spinal nociceptive processing through the actions of calpain-1 and caspase-3. First, the ephrinB ligands, ephrinBl-Fc or ephrinB2-Fc, were introduced into experimental mice via intrathecal injection, and it was found that this injection induced marked time- and dose-dependent mechanical allodynia and thermal hyperalgesia, accompanied by increased levels of calpain-1 and caspase-3 in the spinal cord. MDL28170, an inhibitor of calpain-1, reversed the behavioral effects and ameliorated the increases in calpain-1 and caspase-3. Second, it was found that the administration of EphB1 between L5 and L6 in mice inhibited the mechanical allodynia and thermal hyperalgesia induced by chronic constrictive injury. In addition, to demonstrate the cell phenotypes responsible for the increased levels of calpain-1 and caspase-3 in the spinal cord following injection with ephrinB2-Fc, double immunofluorescent labeling was performed, which indicated that calpain-1 and caspase-3 were localized in neurons, but not in astrocytes or microglial cells. In conclusion, the present study suggested that ephrinB/EphB signaling contributes to spinal nociceptive processing via the actions of calpain-1 and caspase-3.