Spinal ephrinB/EphB signalling contributed to remifentanil-induced hyperalgesia via NMDA receptor.

BACKGROUND: One of the major unresolved issues in treating pain is the paradoxical hyperalgesia produced by opiates, and accumulating evidence implicate that EphBs receptors and ephrinBs ligands are involved in mediation of spinal nociceptive information and central sensitization, but the manner in which ephrinB/EphB signalling acts on spinal nociceptive information networks to produce hyperalgesia remains enigmatic. The objective of this research was to investigate the role of ephrinB/EphB signalling in remifentanil-induced hyperalgesia (RIH) and its downstream effector. METHODS: We characterized the remifentanil-induced pain behaviours by evaluating thermal hyperalgesia and mechanical allodynia in a rat hind paw incisional model. Protein expression of EphB1 receptor and ephrinB1 ligand in spinal dorsal horn cord was determined by Western blotting, and Fos was determined by immunohistochemistry assay, respectively. To figure out the manner in which ephrinB/EphB signalling acts with N-methyl-d-aspartic acid (NMDA) receptor, we used MK-801, an antagonist of NMDA receptor, trying to suppressed the hyperalgesia induced by ephrinB1-Fc, an agonist of ephrinB/EphB. RESULTS: Continuing infusion of remifentanil produced a thermal hyperalgesia and mechanical allodynia, which was accompanied with increased protein expression of spinal-level EphB1 receptor, ephrinB1 ligand and Fos; what appeared above was suppressed by pretreatment with EphB1-Fc, an antagonist of ephrinB/EphB or MK-801, and increased pain behaviours induced by intrathecal injection of ephrinB1-Fc, an agonist of ephrinB/EphB, were suppressed by MK-801. CONCLUSIONS: Our findings indicated that ephrinB/EphB signalling is involved in RIH. EphrinB/EphB signalling might be the upstream of NMDA receptor.

EphrinB-EphB receptor signaling contributes to bone cancer pain via Toll-like receptor and proinflammatory cytokines in rat spinal cord.

Treating bone cancer pain poses a major clinical challenge, and the mechanisms underlying bone cancer pain remain elusive. EphrinB-EphB receptor signaling may contribute to bone cancer pain through N-methyl-d-aspartate receptor neuronal mechanisms. Here, we report that ephrinB-EphB signaling may also act through a Toll-like receptor 4 (TLR4)-glial cell mechanism in the spinal cord. Bone cancer pain was induced by tibia bone cavity tumor cell implantation (TCI) in rats. TCI increased the expression of TLR4 and the EphB1 receptor, the activation of astrocytes and microglial cells, and increased levels of interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α). The increased expression of TLR4 and EphB1 were colocalized with each other in astrocytes and microglial cells. Spinal knockdown of TLR4 suppressed TCI-induced behavioral signs of bone cancer pain. The TCI-induced activation of astrocytes and microglial cells, as well as the increased levels of IL-1ß and TNF-α, were inhibited by intrathecal administration of TLR4-targeting siRNA2 and the EphB receptor antagonist EphB2-Fc, respectively. The administration of EphB2-Fc suppressed the TCI-induced increase of TLR4 expression but siRNA2 failed to affect TCI-induced EphB1 expression. Intrathecal administration of an exogenous EphB1 receptor activator, ephrinB2-Fc, increased the expression of TLR4 and the levels of IL-1ß and TNF-α, activated astrocytes and microglial cells, and induced thermal hypersensitivity. These ephrinB2-Fc-induced alterations were suppressed by spinal knockdown of TLR4. This study suggests that TLR4 may be a potential target for preventing or reversing bone cancer pain and other similar painful processes mediated by ephrinB-EphB receptor signaling.

EphrinB2 induces tyrosine phosphorylation of NR2B via Src-family kinases during inflammatory hyperalgesia.

In recent years a role for EphB receptor tyrosine kinases and their ephrinB ligands in activity-dependent synaptic plasticity in the CNS has been identified. The aim of the present study was to test the hypothesis that EphB receptor activation in the adult rat spinal cord is involved in synaptic plasticity and processing of nociceptive inputs, through modulation of the function of the glutamate ionotropic receptor NMDA (N-methyl-D-aspartate). In particular, EphB receptor activation would induce phosphorylation of the NR2B subunit of the NMDA receptor by a Src family non-receptor tyrosine kinase. Intrathecal administration of ephrinB2-Fc in adult rats, which can bind to and activate EphB receptors and induce behavioral thermal hyperalgesia, led to NR2B tyrosine phosphorylation, which could be blocked by the Src family kinase inhibitor PP2. Furthermore animals pre-treated with PP2 did not develop behavioral thermal hyperalgesia following EphrinB2-Fc administration, suggesting that this pathway is functionally significant. Indeed, EphB1-Fc administration, which competes with the endogenous receptor for ephrinB2 binding and prevents behavioral allodynia and hyperalgesia in the carrageenan model of inflammation, also inhibited NR2B phosphorylation in this model. Taken together these findings support the hypothesis that EphB-ephrinB interactions play an important role in NMDA-dependent, activity-dependent synaptic plasticity in the adult spinal cord, inducing the phosphorylation of the NR2B subunit of the receptor via Src family kinases, thus contributing to chronic pain states.