Effect of Lemon Verbena on Memory of Male Rats

Lemon verbena (Lippia citriodora) has been known to have various pharmacologic activities. Lemon verbena leaves are used to make an herbal tea, which is traditionally used for treating spasms, common cold, severe abdominal pain, indigestion, insomnia, anxiety, and headache. Although it has been known to have various pharmacologic activities, no scientific study has been done to assess its effects yet. In this study aimed to assess the effect of the aqueous extract of lemon verbena on memory of male rats by using the passive avoidance task. In this study, Wistar male rats (weight, 180-250 g) were recruited. Aqueous extract of lemon verbena leaves was prepared. A total of 40 Wistar male rats were randomly allocated to five groups (n = 8). Saline for control group and aqueous extract of lemon verbena in four experimental groups were administered intraperitoneally (respectively 10, 100, 500, and 1000 mg/kg) for seven days. Then passive avoidance learning test was used to evaluate learning and memory. On the seventh day, acquisition test was performed an hour after treatment and the retention test was performed on the next day. Analysis of data showed that in comparison to controls, treatment with the aqueous extract of lemon verbena (≥ 100 mg/kg) had decreased the step-through latency (STL) (P < 0.001). Moreover, treatment of the rats with the extract doses of ≥ 500 mg/kg had increased the total time spent in the dark compartment (TDC) in comparison to controls (P < 0.001). These results indicated that aqueous extract of lemon verbena (≥ 100 mg/kg) has undesirable effects on memory; however, understanding the underling mechanisms needs further investigation.