• Shigeru Ebisawa, Tsugunobu Andoh, Yutaka Shimada, and Yasushi Kuraishi.
• Department of Japanese Oriental Medicine, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama 930-0194, Japan.
• Evid Based Compl Alt. 2015 Jan 1; 2015: 870687.

AbstractNeuropathic pain is caused by nerve injury. Yokukansan (Yi-Gan San), a traditional Japanese (Kampo) medicine, has been widely used for neuropathic pain control. However, the analgesic mechanisms remain unknown. In this study, we investigated the analgesic mechanisms of yokukansan in a mouse model of neuropathic pain. Partial sciatic nerve ligation (PSL) induced mechanical allodynia in mice. Repetitive oral administration of the extracts of yokukansan and the constituent herbal medicine Atractylodis Lanceae Rhizoma, but not Glycyrrhizae Radix, relieved mechanical allodynia in the PSL mice and inhibited the PSL-induced expression of interleukin- (IL-) 6 mRNA in the spinal cord. Yokukansan did not attenuate intrathecal IL-6-induced mechanical allodynia. IL-6 immunoreactivity was detected in microglia and astrocytes in the spinal dorsal horn. These results suggest that yokukansan relieves mechanical allodynia in PSL mice by regulating the expression of IL-6 in astrocytes and/or microglia in the spinal cord. In addition, the components of Atractylodis Lanceae Rhizoma, one of the constituent herbal medicines in yokukansan, may play an important role in the regulation of IL-6 expression and neuropathic pain control.

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