Effect of Morphine on Passive Avoidance Memory in Cholestatic Rats

Background and purpose: Morphine as an opioid compound has different and sometimes conflicting effects on memory and learning process. Bile duct ligation causes cholestasis, which disrupts liver function. It is known that opioid systems are involved in cholestasis. The aim of this study was to investigate the possible effect of morphine on the memory of cholestatic rats. Materials and methods: In this experimental study, the cholestatic model in male Wistar rats (weighing 200-250 g) was induced by bile duct ligation (BDL). The animals were injected with morphine (4 and 6 mg/kg, ip), naloxone (0.6 and 0.8 mg/kg, ip), and morphine and naloxone in different groups. Passive avoidance memory was evaluated on day 7 after BDL by shuttle box test.  Data were analyzed by PRISM software and ANOVA. Results: Naloxone (0.6 and 0.8 mg/kg), 30 min before the test, did not show significant changes in the memory of the cholestatic rats compared to the BDL group, whereas, morphine (4 and 6 mg/kg) showed significant increase in step-through latency (P<0.05). Also, naloxone (0.6 mg/kg, ip) 15 minutes before injection of morphine (6 mg/kg( showed a significant increase in acquired memory on day 7 after BDL (P<0.0001). Conclusion: According to findings, morphine had a protective effect on memory impairment induced by cholestasis.