The Effect of 5HT3 Agonist Receptor of the Lateral Hippocampal on Amnesia Induce by Morphine in Mice

Background and Objective: It has been shown that the opioidergic system exerts widespread effects on cognitive functions. Interactions between opioid and serotonin receptors have been reported in some brain structures such as the dorsal hippocampus, thus a functional interaction between opioids and serotonin seems possible concerning memory control. The purpose of this study was to assess the effects of CA1 5-HT3 receptor agonist on memory acquisition deficit induced by morphine. Materials and Methods: In this study, we used 96NMRI mice. These mice were divided into twelve equal groups that received different doses of 5-HT3recepto ragonist, different doses of morphine and a combination of morphine and serotonin 5-HT3 receptor agonist. Morphine was injected into the peritoneum, while 5-HT3 receptor agonist M-Chlorophenylbiguanide (M-chl) was administered via intra-hippocampal injection. A step-down passive avoidance test was used for the evaluation of memory. Results: Pre-training intra-peritoneal administration of morphine (5 mg/kg) induced amnesia. Moreover, pre-training intra-CA1 administration of 5-HT3 receptor agonist (M-Chl) (0.5 ng/mouse) impaired memory acquisition. Furthermore, intra-CA1 injection of M-Chl (0.005ng/mouse) reversed impairment of memory acquisition induced by morphine (5 mg/kg). Conclusion: The results demonstrated the existence of a synergistic effect between hippocampal 5-HT3 receptor agonists and opioidergic receptors.