Background and Objectives: Hippocampus is the most important part of learning and memory in the brain. Melissa officinalis naturally affects the nervous system and induces calmness. Lorazepam is also used in the treatment of insomnia and anxiety. In this study, the effect of Lorazepam and aqueous extract of Melissa officinalis (AEMO) was investigated on hippocampus tissue and spatial memory in male rats using radial maze method.

Methods: In this experimental study, 24 male Wistar rats were randomly divided into four groups. Control group received normal diet and water, the second group received lorazepam (dose. 10mg/kg), and two other groups received AEMO (at doses of 10 and 100mg/kg) by gavage for 18 days. Then, their spatial memory were tested in an 8 arm radial maze (RAM). The level of lipid peroxidation of homogenized brain tissue was assessed, and hippocampal tissue sections were prepared and after H&E staining, DG area was investigated under a microscope. Data were analyzed using one-way ANOVA and Tukey statistical tests. The level of significance was set at p<0.05.

Results: There was no significant difference in learning level between animals received lorazepam and control group. The results of the experiments showed the positive effect of low dose of AEMO (10mg/kg) on spatial memory, while high dose of Melissa officinalis (100mg/kg) prevented memory formation.

Conclusion: The results of this research showed that AEMO can increase short-term memory at low dose (10mg/kg), but it may prevent spatial memory formation at high doses.