Effect of Yokukansan on sleep disturbance and neuropathic pain in chronic constriction injury using a rat model

Patients with chronic pain develop peripheral neuropathy and experience sleep disturbance. Yokukansan is used to treat insomnia and control neuropathic pain. We studied if Yokukansan affects neuropathic pain and sleep disturbance using a rat model of chronic constriction injury (CCI). Male Wistar rats (4-week age) were divided into the following groups (n = 7, per group): CCI rats fed normal chow (CCI-0); CCI rats fed powdered chow mixed with 1% Yokukansan (CCI-1); CCI rats fed powdered chow mixed with 3% Yokukansan (CCI-3); and sham-operated control rats fed normal chow (SHAM). We examined sleep duration and quality using electroencephalograms and assessed pain using the von Frey and Hargreaves tests. Results were analyzed by one-way analysis of variance and Bonferroni post hoc tests. The CCI-0 group exhibited an increased wake period, decreased non-rapid eye movement (REM) sleep time, and no change in REM sleep time in comparison to the SHAM group. The CCI-1 group exhibited a decreased wake period, increased non-REM sleep time, and no change in REM sleep time compared to the CCI-0 group. The CCI-3 group exhibited increased non-REM sleep time but no changes in wake and REM sleep times compared to the CCI-1 group. The von Frey and Hargreaves test findings revealed an increase in the pain threshold in the CCI-1 group compared to the CCI-0 group. There was no difference in pain threshold between the CCI-1 and CCI-3 groups. In our rat model of CCI, sleep disturbance was reflected. Yokukansan inhibited CCI-induced sleep disturbance.