Figure 9.
The inhibitory effects of ChTX on LPA-induced microglial hyperactivation and tactile allodynia and a schematic representation of the nerve injury-induced reactions of spinal microglia. A, Immunoblot analyses for the LPA (10 μm)-induced increased level of mIL-1β in cultured MG6 microglia in the absence and presence of ChTX (100 μm). B, The time course changes in the PWT after the intrathecal administration of saline, LPA (1 nmol in 5 μl), and combination of LPA with ChTX (100 nm). Each circle and vertical bar represent the mean ± SEM. The asterisks indicate a statistically significant difference from saline group (***p < 0.001). The daggers indicate a statistically significant difference from LPA-treated group (††p < 0.01; †††p < 0.001). C, Schematic representation of a series of sequential signalings in spinal microglia following nerve injury and the pharmacological target of S-ketamine. LPA stimulates the increased synthesis of BDNF in the microglia through upregulation of P2X4 receptors and then enhances nociceptive neurotransmission (1: gray arrow). The current study shows that LPA enhances the production of mIL-1β through the activation of BK channels in the spinal microglia (2: black arrow). Finally, secreted mIL-1β or BDNF itself further enhances the expression levels of P2X4 receptors and the activities of BK channels (3: dashed arrow), leading to the development of neuropathic pain. Therefore, through the inhibition of BK channels, S-ketamine suppresses the nerve injury-induced production of mIL-1β, expression of P2X4 receptors, and BDNF synthesis in the spinal microglia, and finally the development of neuropathic pain (4: open arrow).