Research on the antidepressant effects and mechanisms of action of geranium essential oil and basil essential oil
Depression is a chronic psychological disorder caused by multiple factors that can have a negative impact on a person’s emotions and behavior. It has the characteristics of high incidence rate and high disability rate. In recent years, with the accelerating pace of life and increasing social competition pressure, it has become one of the most common psychological disorders in modern society. Because the currently used antidepressants in clinical practice are mainly monoamine oxidase (MAO) inhibitors, selective serotonin reuptake inhibitors (SSRIs), atypical antidepressants, tricyclic and tetracyclic antidepressants, which are four major types of chemically synthesized drugs. Although they have certain therapeutic effects on various degrees of depression, they generally have drawbacks such as narrow antidepressant spectrum, high drug prices, and large side effects. On the other hand, previous studies have shown that natural aromatic herbal plants supported by traditional Chinese medicine theory have rich experience and unique therapeutic effects in treating depression. Shen et al. found that inhaling lavender essential oil in rats can affect their autonomic nervous system and regulate their emotions. Park et al. confirmed that Asarum essential oil has a certain effect on alleviating depressive symptoms in mice. Yang et al. found that sniffing sweet orange essential oil can effectively alleviate depression in experimental mice. Wang et al. preliminarily confirmed that the aroma of compound essential oils has a certain auxiliary intervention effect on the recovery of depression through human olfactory inhalation. Fernandez et al. confirmed that lavender essential oil can play a significant role in alleviating postpartum depression symptoms in women. Therefore, the exploration of highly effective and minimally toxic antidepressant medicinal active ingredients from natural aromatic Chinese herbal plants is increasingly receiving attention from scholars at home and abroad.
The two common aromatic Chinese herbal plants selected for this study, Ocimum basilicum L. and Pelargonium graveolens, both have the effect of soothing nervous tension and calming anxiety and depression. At present, research on these two plants mainly focuses on the analysis of their essential oil (EO) components, antibacterial activity, antioxidant activity, and other aspects. Regarding its antidepressant effects, apart from Khalaj et al.’s forced swimming test on mice, which found that geranium essential oil has a certain effect on relieving depression, there are few other related research reports at home and abroad. This article intends to use two “behavioral despair depression” model mice tail suspension test and mouse forced swimming test to determine the changes in immobility time of mice in each experimental group; Corticosteroid induces PC12 cell damage to simulate neuronal damage in patients with depression, and the degree of cell damage is detected by pre-treatment with relevant inhibitors. To study the antidepressant effects and possible signaling pathways of essential oils from geranium and basil at both animal and cellular levels, in order to lay the foundation for the development of aromatic herbal plant essential oil products with antidepressant effects.

The “behavioral despair depression model” is currently the most commonly used animal model for evaluating the efficacy of antidepressants. This experiment first uses this model to conduct preliminary research on the antidepressant effects of essential oils from geranium and basil. The results showed that the essential oils of geranium and basil at different experimental doses could effectively counteract the desperate behavior of these two “behavioral despair” model mice, significantly reducing their immobility time and exhibiting certain antidepressant effects. And the antidepressant effect of geranium essential oil shows a certain dose dependence, that is, the high dose of essential oil has the best effect, and the medium dose is better than or similar to the low dose. The antidepressant effect of basil essential oil is not dose-dependent, with similar effects observed in the high and medium dose groups, followed by the low-dose group. Given that research has shown that although the two “behavioral despair” depression models mentioned above have high selectivity for antidepressants, some drugs that increase animal activity may also produce false positive results. To avoid possible false positive results, this experiment also studied the effects of geranium essential oil and basil essential oil on the spontaneous activity of mice. The results showed that there was no significant increase in the number of spontaneous activities of mice in each experimental dose group of geranium essential oil and basil essential oil compared to the blank control group. In summary, it can be ruled out that false positive results of antidepressant effects may be caused by autonomous activity, indicating that the essential oils of these two aromatic plants have significant antidepressant effects on the “behavioral despair” model mice at different experimental doses.
There are also reports that using high concentrations of CORT to induce PC12 cell damage can simulate the neuronal damage state in patients with depression, and CORT induced PC12 cell damage is closely related to the PI3K/Akt signaling pathway and PKA signaling pathway in cells. Therefore, in this experiment, a corticosterone stress injury cell model was constructed by inducing PC12 cell damage with CORT, and the degree of cell damage was detected by MTT assay. The results showed that 0.1mmol/L CORT significantly reduced cell survival rate, synaptic contraction, and altered cell morphology. When given a certain dose of geranium essential oil and basil essential oil, the cell survival rate significantly increased and the cell morphology was restored, indicating that a certain dose of geranium essential oil and basil essential oil can have a certain protective effect on CORT induced PC12 cells, and the antidepressant effects of the two essential oils are not dose-dependent, with the best effect observed at a medium dose. In addition, when the PI3K/Akt signaling pathway blockers LY294002, KRX-0401, and PKA signaling pathway H-89 were intervened, it was found that the protective effects of both essential oils on CORT induced PC12 cells were significantly weakened, indicating that the protective effects of the two essential oils on CORT induced PC12 cells may be mediated by the PI3K/Akt and PKA signaling pathways.
Previous studies have reported that some volatile components of plants determine their various physiological functions. The main components of geranium essential oil, citronellol and geraniol, have been proven to have certain antidepressant effects. The volatile components of basil, such as artemisia, linalool, and caryophyllene, have also been shown to have health benefits for the human nervous system. However, it has not been explored whether other components have similar antidepressant effects.
In summary, the essential oils of geranium and basil have certain antidepressant effects, and their neuroprotective effects may be mediated by the PI3K/Akt and PKA signaling pathways. This experimental study will provide experimental support for further exploration of the antidepressant active ingredients and molecular mechanisms of these two plant essential oils in the future, and also lay an experimental foundation for the development of aromatic herbal plant essential oil products with antidepressant effects.