Effects of hydroalcoholic extract of Melilotus officinalis L. on chronic immobility stress-induced depression in adult male rats

Stress affects the body's systems and can lead to many disorders, including depression. To deal with stress and depression, the use of medicinal plants that have fewer side effects than chemical drugs has attracted the attention of researchers. Melilotus officinalis L. contains compounds such as coumarin, flavonoids, triterpene, saponin, and volatile oils with anti-inflammatory and antioxidant effects. The present study investigated the effect of the hydroalcoholic extract of the M. officinalis plant on depression caused by chronic immobility stress in adult male rats.

In this experimental study, 48 male Wistar rats weighing 250-300 grams were used. The rats were randomly divided into 6 groups of 8 (n=8) including control (intact), sham (under chronic immobility stress and receiving normal saline), experimental groups (under chronic immobility stress and subjected to doses 25, 50, and 100 mg.kg-1 of M. officinalis extract), and the positive control group (under chronic immobility stress and receiving fluoxetine). To establish an animal model of chronic immobility stress, the rats were placed in the restraint device daily for 2 hours, for 3 weeks. Injections were made intraperitoneally (IP), 30 minutes before stress induction. The depression model was evaluated by the Forced Swimming Test (FST) and motor activity by the Open Field Test (OFT). Then with deep anesthesia in the animals, blood was taken from the heart. By separating the serum, the amount of corticosterone in the rats’ blood was evaluated and measured using special kits and the ELISA method.

The results of this research showed that in the sham group, the duration of immobility in the FST increased significantly in comparison to the control group (P<0.001). In the experimental groups, a high dose of M. officinalis extract led to a significant increase in the duration of immobility in the FST (P<0.01). However, the lower doses of the extract led to a significant decrease in immobility duration compared to the sham group (P<0.001) (P<0.01). The fluoxetine-receiving group also showed a significant reduction in immobility duration compared to the sham group (P<0.01). Lower doses of M. officinalis extract caused a significant increase in blood corticosterone relative to the sham group (P<0.001). Administration of fluoxetine also caused a significant increase in corticosterone levels in the blood in comparison to the sham group (P<0.001). In the OFT, the number of crossing lines in the sham group showed a significant increase relative to the control group (P<0.01) in the experimental groups, a high dose of M. officinalis extract resulted in a significant decrease in the number of times the rats crossed the lines in comparison to the sham group (P<0.01).

Phytochemical studies have shown some active substances, such as quercetin and phenolic acids in M. officinalis, which have antioxidant and antidepressant activity by inhibiting monoamine oxidase and increasing dopamine and serotonin. Therefore, due to active biological molecules, M. officinalis can play a vital role in preventing depression. The results have also shown that M. officinalis extract, particularly in lower doses, has better antidepressant effects in rats under chronic stress.