The Effect of Intrahippocampal Injection of Ghrelin on Morphine-Induced Amnesia by Passive Avoidance Task in Male Laboratory Rats

Background and Objectives: Ghrelin is a peptide hormone, which is secreted by stomach cells and has an important role in the metabolism and energy homeostasis. This hormone crosses the blood-brain barrier and enters the hippocampus, where it affects the learning process and memory. In the present study, the effect of intrahippocampal injection of ghrelin on morphine-induced amnesia was investigated using passive avoidance learning model in experimental male rats.   Methods: In this experimental study, the animals were implanted with cannula in the CA1 region, and morphine was injected subcutaneously and ghrelin was locally injected into the CA1 region. Then, memory retrieval was assessed by a passive avoidance task.   Results: Post-training subcutaneous administration of different doses of morphine (0.5, 2.5, 5, 7.5mg/kg body weight) reduced step-through latency in a dose dependent manner, indicating morphine-induced amnesia. Injection of different doses of ghrelin into the CA1 region together with the effective dose of morphine (dose, 7.5mg/kg body weight) significantly increased memory retrieval compared to the morphine group (dose, 7.5mg/kg body weight).   Conclusion: The findings of this study revealed that injection of ghrelin into the hippocampal region inhibits the morphine-induced amnesia in the passive avoidance learning model; therefore, it can be considered in the improvement of morphine-induced memory impairment. &nbsp