Effects of ketamine and midazolam on morphine induced dependence and tolerance in mice

The aim of this study was to investigate the effects of ketamine and midazolam on prevention of the development of morphine tolerance and dependence in mice. Different groups of mice received morphine (50 mg/kg, sc), morphine (50 mg/kg, sc) + ketamine (25,50,75 mg/kg, ip), morphine (50 mg/kg, sc) + midazolam (0.5,1,2 mg/kg, ip) , morphine (50 mg/kg , sc) + ketamine (50 mg/kg, ip) + midazolam (1 mg/kg, ip) once a day for four days. Tolerance was assessed by administration of morphine (9 mg/kg, ip) on fifth day. Withdrawal symptoms were assessed by administration of naloxane (4 mg/kg, ip) two hours after co-administration of morphine with either ketamine or midazolam. It was found that pretreatment with ketamine or midazolam decreased the degree of tolerance and withdrawal symptoms. Additionally co-administration of ketamine and midazolam before morphine therapy decreased the tolerance and dependence significantly. From these results it may concluded that administration of ketamine and midazolam alone or in combination could prevent the development of tolerance and dependence to morphine. These effects can be related to the N-Methyl-D-Aspartate (NMDA) receptor antagonist behavior of ketamine and GABA-receptor agonist behavior of midazolam.