Effect of a hydro-alcoholic extract of Melissa officinalis on passive avoidance learning and memory

Introduction: Melissa officinalis (MO) or lemon balm is traditionally used as a sedative and anti-spasm herbal medicine. There is also evidence that this plant has effects on learning and memory. This study examined the effect of a hydro-alcoholic extract of MO on passive avoidance learning (PAL) and memory in male rats. Methods: A total of ۴۰ adult male Wistar rats were randomly distributed into four groups (۲۰۰ to ۲۲۰ g; n = ۱۰ per group); three dose groups (۵۰, ۱۰۰, and ۲۰۰ mg/kg of the hydro-alcoholic extract of MO) and vehicle control (saline) group. Saline or doses of extract were administered daily for ۱۴ days by oral gavage. The rats were trained to enter the shuttle box to record their behavior in the PAL task. A retrieval test was performed ۲۴ hours following training. Results: A significant difference was seen in performance among MO groups and the control. MO administered animals had a decreased number of acquisition trials (P < ۰.۰۵). In the retention task, MO administered animals had an increased step-through latency (SLT) (P < ۰.۰۱), and a decreased latency in the dark compartment (P < ۰.۰۰۱) compared to the control group. Conclusion: The results of the study show that MO can improve learning and memory in the PAL task. Further investigation is needed to enhance our understanding of the neurobiological mechanisms of the MO extract and its effects on learning and memory.