Effects of intrathecal injection of strychnine on analgesic effect of etomidate in mice

Objective To investigate the analgesic effect of etomidate(ET),and to explore the effects of intrathecal injection of strychnine(Stry) on analgesic effect of etomidate in mice.Methods Two hundred and forty Kunming mice were randomly divided into two groups:hot-plate group and writhing group,each group was randomly divided into three subgroups:Stry group,ET group and Stry+ET group,and then each subgroup was divided into four subgroups(n=10 each group) according to different doses of etomidate or strychnine.Etomiate was intravenously injected and strychnine was intrathecally injected after the etomidate injection.Then hot-plate test and acetic acid-induced writhing test were employed to evaluate the pain index in hot-plate test(HPPI) and the writhing times.Results Etomidate 0.5 mg/kg had no effect on HPPI and writhing times in mice(P0.05),while etomidate 1.0 mg/kg and 2.0 mg/kg increased the HPPI(P0.05) and decreased the writhing times(P0.05).Strychnine 0.1 μg and 0.2 μg had no effect on HPPI and writhing times in mice in Stry+ET group(P0.05),while strychnine 0.4 μg decreased the HPPI(P0.05) but had no effects on writhing times(P0.05).Conclusion Etomidate has analgesic effect and its mechanism may be different in hot-plate test and acetic acid-induced writhing test.The former may exert the effects through glycine receptor,but the latter is not related to glycine receptor.