The antagonism of intrathecal injection of yohimbine on the analgesia by ketamine

Objective To observe the effect of α2 receptor blocker yohimbine on the analgesia by ketamine at the spinal cord level. Methods 120 mice were randomly divided into 2 large groups (hot water tail-flick group and writhing group),each of which was further divided into 6 groups with 10 mice in each group:NS group,ketamine group,15 μg yohimbine group,5 μg yohimbine group,ketamine plus 15 μg yohimbine group,and ketamine plus 5 μg yohimbine group. Using tail-flick test and writhing test,the effect of intrathecal injection (IT) of yohimbine at different concentrations on the analgesic action of ketamine was observed. Results Subcutaneous injection of ketamine had obvious analgesic effect (P0.01). IT of yohimbine (15 μg or 5 μg) alone had no marked effect on the pain threshold of tail-flick and the writhing times (P0.05). Of the above two methods,15 μg yohimbine could obviously reduce the analgesia by ketamine (P0.01). For the mice under ketamine,5 μg yohimbine (IT) had no obvious effect on the pain threshold in tail-flick test (P0.05),but could increase the writhing times (P0.05). Conclusion Analgesic effect of ketamine is closely correlated with α2 receptor of norepinephrine in the spinal cord.