Effect of repeated morphine and tramadol administration on the motor behavior in the neonatal period

Motor behavior and coordination impairment are known side effects of opioid treatment, yet very few studies have investigated the effects of tramadol on motor behavior, or compared its effect with the effect of an opioid. This study investigates the effects of chronic injection of morphine and tramadol on rat motor function during infancy. Neonate rats (n=56) were randomly divided into three groups. On postnatal days 8-14, one group received saline and two other groups received tramadol and morphine with a dose-dependent manner. On postnatal day 21, each group was divided into subgroups, which received morphine, tramadol or saline again on postnatal days 22-26. Finally, on postnatal days of 22 and 26, the motor behavior was studied. On postnatal day 23, tramadol caused an increase the falling rate from Rotarod (P<0.001), But there was not any significant difference between morphine groups. On postnatal day 26 rat, there was a significant difference only for morphine groups that received additive doses. The last dose of morphine (15 mg/kg) interferes with motor behavior of immature rats, whereas tramadol with additive doses on the first two days (3-6 mg/kg) caused an impairment in motor behavior of immature rats, but could not maintain this ability for the rest of the days of the injection (until 26 day).