Anxiolytic-like effects of essential oil from Thymus vulgaris was increased during stress

Aromas Influencing the GABAergic System

Aromas have a powerful influence in our everyday life and are known to exhibit an array of pharmacological properties, including anxiolytic, anti-stress, relaxing, and sedative effects. Numerous animal and human studies support the use of aromas and their constituents to reduce anxiety-related symptoms and/or behaviours. Although the exact mechanism of how these aromas exert their anxiolytic effects is not fully understood, the GABAergic system is thought to be primarily involved. The fragrance emitted from a number of plant essential oils has shown promise in recent studies in modulating GABAergic neurotransmission, with GABA_A receptors being the primary therapeutic target. This review will explore the anxiolytic and sedative properties of aromas found in common beverages, such as coffee, tea, and whisky as well aromas found in food, spices, volatile organic compounds, and popular botanicals and their constituents. In doing so, this review will focus on these aromas and their influence on the GABAergic system and provide greater insight into viable anxiety treatment options.

Smell and Stress Response in the Brain: Review of the Connection between Chemistry and Neuropharmacology

The stress response in the brain is not fully understood, although stress is one of the risk factors for developing mental disorders. On the other hand, the stimulation of the olfactory system can influence stress levels, and a certain smell has been empirically known to have a stress-suppressing effect, indeed. In this review, we first outline what stress is and previous studies on stress-responsive biomarkers (stress markers) in the brain. Subsequently, we confirm the olfactory system and review previous studies on the relationship between smell and stress response by species, such as humans, rats, and mice. Numerous studies demonstrated the stress-suppressing effects of aroma. There are also investigations showing the effects of odor that induce stress in experimental animals. In addition, we introduce recent studies on the effects of aroma of coffee beans and essential oils, such as lavender, cypress, α-pinene, and thyme linalool on the behavior and the expression of stress marker candidates in the brain. The transfer of volatile components into the brain is also discussed while using the results of thyme linalool as an example. These studies may provide a good opportunity to connect chemical research at the molecular level with neuropharmacological approaches in the future.

Anxiolytic Effect of Essential Oils and Their Constituents: A Review

Essential oils are usually used in aromatherapy to alleviate anxiety symptoms. In comparison to traditional drugs, essential oils have fewer side effects and more diversified application ways, including inhalation. This review provides a comprehensive overview of studies on anxiolytic effects of essential oils in preclinical and clinical trials. Most of the essential oils used in clinical studies have been proven to be anxiolytic in animal models. Inhalation and oral administration were two common methods for essential oil administration in preclinical and clinical trials. Massage was only used in the clinical trials, while intraperitoneal injection was only used in the preclinical trails. In addition to essential oils that are commonly used in aromatherapy, essential oils from many folk medicinal plants have also been reported to be anxiolytic. More than 20 compounds derived from essential oils have shown an anxiolytic effect in rodents, while two-thirds of them are alcohols and terpenes. Monoamine neurotransmitters, amino acid neurotransmitters, and the hypothalamic-pituitary-adrenal axis are thought to play important roles in the anxiolytic effects of essential oils.

Effects of Inhalation of Geranium Essential Oil on Blood Pressure and Heart Rate in Mice

For a better scientific understanding of the basics of aromatherapy, our research group attempted to clarify the effectiveness of the essential oil from Pelargonium graveolens (EOPG, geranium essential oil), which is used to try and balance the mind-body connection. In order to eliminate any possible placebo effect, we used animal experiments that are considered to be insensitive to the placebo effect. Measurements of blood pressure and heart rate in the mouse tail artery were used as a reflection of the mind-body balance. Thirty minutes after inhalation of EOPG (5 µL/L air) for 90 minutes, blood pressure and heart rate of the mice were measured. EOPG significantly reduced blood pressure and heart rate. To further clarify the factors responsible for these effects, gas chromatography analysis was performed in order to determine the components transferred into the brain after the EOPG inhalation. Linalool, citronellol, and geraniol were detected at concentrations around 0.1 nL/L tissue from the brain after 10 µL/L air inhalation of EOPG. However, these were not detected after a 5 µL/L air inhalation of EOPG, as the levels were below the detection limit. These results suggest EOPG inhalation might lower blood pressure and heart rate, with the expressed effects associated with the transfer of components such as linalool into the brain.