Spinal MCP-1 Contributes to Central Post-stroke Pain by Inducing Central Sensitization in Rats.

Central post-stroke pain (CPSP) is a highly refractory form of central neuropathic pain that has been poorly studied mechanistically. Recent observations have emphasized the critical role of the spinal dorsal horn in CPSP. However, the underlying mechanisms remain unclear. In this study, rats were subjected to thalamic hemorrhage to investigate the role of spinal monocyte chemoattractant protein-1 (MCP-1) and C-C motif chemokine receptor 2 (CCR2) in the development of CPSP. Immunohistochemical staining and ELISA were used to assess the expression changes of c-Fos, Iba-1, GFAP, MCP-1, and CCR2 in the dorsal horn of the lumbar spinal cord following thalamic hemorrhage, and the involvement of spinal MCP-1 in CPSP was examined by performing intrathecal anti-MCP-1 mAb injection to neutralize the spinal extracellular MCP-1. We demonstrated that intra-thalamic collagenase microinjection induced persistent bilateral mechanical pain hypersensitivity and facilitated the spontaneous pain behaviors evoked by intraplantar bee venom injection. Accompanying CPSP, the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn was significantly increased up to 28 days post-intra-thalamic collagenase microinjection. Intrathecal injection of minocycline and fluorocitrate dramatically reverses the bilateral mechanical pain hypersensitivity. Moreover, intra-thalamic collagenase microinjection dramatically induced the up-regulation of MCP-1 but had no effect on the expression of CCR2 in the bilateral lumbar spinal dorsal horn, and MCP-1 was primarily localized in the neuron. Intrathecal injection of anti-MCP-1 mAb was also able to reverse CPSP and reduce the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn. These findings indicated that spinal MCP-1 contributes to CPSP by mediating the activation of spinal neurons and glial cells following thalamic hemorrhage stroke, which may provide insights into pharmacologic treatment for CPSP.

Ropivacaine-induced seizures evoked pain sensitization in rats: Participation of 5-HT/5-HT3R.

Due to the increasing use of local anesthetic techniques in various healthcare settings, local anesthetic toxicity still occurs. Seizures are the most common symptom of local anesthetic toxicity. The relationship between local anesthetic-induced seizures and the sensation of pain has not been established till now. Here, we assessed the development of pain hypersensitivity after ropivacaine-induced seizures (RIS) and the influence of RIS on incision-induced postsurgical pain and formalin-induced acute inflammatory pain. In addition, the involvement of spinal 5-HT/5-HT3R in RIS-induced pain sensitization was investigated. According to a sequential exploratory experimental strategy, we first calculated the 50% seizure dosage of ropivacaine to be 42.66 mg/kg (95% confidence interval: 40.19-45.28 mg/kg). We showed that RIS induced significant bilateral mechanical pain hypersensitivity that lasted around 5 days, accompanied by an increase in spinal 5-HT. Moreover, RIS considerably protracted postsurgical pain and enhanced formalin-induced spontaneous flinching in the second phase. Depletion of spinal 5-HT with intrathecal injection of 5,7-dihydroxytryptamine (5,7-DHT) reduced RIS-induced pain hypersensitivity and prevented the prolonging of postsurgical pain following RIS. Likewise, blocking spinal 5-HT3R by intrathecal administration of ondansetron reversed RIS-induced pain hypersensitivity and attenuated the pronociception of RIS in the formalin test. Our findings revealed that acute RIS led to pain hypersensitivity and had pronociceptive effects on incision-induced postsurgical pain and formalin-induced acute inflammatory pain. Moreover, our data implied that RIS-induced pain sensitization depends on spinal 5-HT/5-HT3R signaling. Thus, targeting the descending serotonergic facilitation system should be an important element of the precise treatment for local anesthetic toxicity.