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.

Effects of Essential Oil from Hinoki Cypress, Chamaecyparis obtusa, on Physiology and Behavior of Flies

Phytoncides, which are volatile substances emitted from plants for protection against plant pathogens and insects, are known to have insecticidal, antimicrobial, and antifungal activities. In contrast to their negative effects on microorganisms and insects, phytoncides have been shown to have beneficial effects on human health. Essential oil from Hinoki cypress (Chamaecyparis obtusa) is mostly used in commercial products such as air purifiers. However, the physiological/behavioral impact of essential oil from C. obtusa on insects is not established. In this study, we tested the effects of essential oil extracted from C. obtusa on the physiologies and behaviors of Drosophila melanogaster and Musca domestica. Exposure to essential oil from C. obtusa decreased the lifespan, fecundity, locomotive activity, and developmental success rate of D. melanogaster. In addition, both fruit flies and house flies showed strong repellent behavioral responses to the essential oil, with duration times of about 5 hours at 70 μg/ml. These results suggest that essential oil from C. obtusa can be used as a ‘human-friendly’ alternative insect repellent.

Intracerebral Distribution of α-Pinene and the Anxiolytic-like Effect in Mice following Inhaled Administration of Essential Oil from Chamaecyparis Obtusa

The anxiolytic-like and stress reduction effects following inhaled administration of essential oil from Chamaecyparis obtusa (EOCO) have been reported. Volatile components are thought to produce these effects of EOCO by neurological transfer and pharmacological transfer. The regions of the brain in which inhaled compounds are found due to pharmacological transfer of EOCO are not known. This research was undertaken to clarify the relationship between the intracerebral distribution of α-pinene, which is the main component of EOCO, and emotional behavior. α-Pinene was detected as the main component of volatile EOCO. The amount of α-pinene in each region of the brain was measured following inhaled administration of EOCO. The amount of α-pinene was different in each region of the brain. With inhaled administration of 32 μL/L air EOCO, a high concentration of α-pinene was observed. However, no significant differences in the concentration of α-pinene among brain regions were found. A therapeutic concentration of α-pinene (8 μL/L air EOCO) in each region of the brain may induce an anxiolytic-like effect, and a high concentration of α-pinene (32 μL/L air EOCO) in each region of the brain may induce an excitatory-like effect. The increases in the concentration of α-pinene from 8 to 32 μL/L air EOCO in the striatum and the hippocampus were significantly lower compared with the increases in other brain regions. These results indicate that regions besides the striatum and the hippocampus participated in the increase in locomotor activity due to the high concentration of α-pinene in the brain.

Effect of Hinoki and Meniki Essential Oils on Human Autonomic Nervous System Activity and Mood States

Meniki ( Chamecyparis formosensis) and Hinoki ( C. obtusa) are precious conifers with excellent wood properties and distinctive fragrances that make these species popular in Taiwan for construction, interiors and furniture. In the present study, the compositions of essential oils prepared from Meniki and Hinoki were analyzed by gas chromatography-mass spectrometry (GC/MS). Thirty-six compounds were identified from the wood essential oil of Meniki, including 5-cadinene, y-cadinene, 5-cadinol, α-muurolene, calamenene, linalyl acetate and myrtenol; 29 compounds were identified from Hinoki, including α-terpineol, α-pinene, 8-cadinene, borneol, terpinolene, and limonene. Next, we examined the effect of Meniki and Hinoki essential oils on human autonomic nervous system activity. Sixteen healthy adults received Meniki or Hinoki by inhalation for 5 min, and the physiological and psychological effects were examined. After inhaling Meniki essential oil, participant's systolic blood pressure and heart rate (HR) were decreased, and diastolic blood pressure increased. In addition, sympathetic nervous activity (SNS) was significantly decreased, and parasympathetic activity (PSNS) was significantly increased. On the other hand, after inhaling Hinoki essential oil, systolic blood pressure, heart rate and PSNS were decreased, whereas SNA was increased. Indeed, both Meniki and Hinoki essential oils increased heart rate variability (HRV) in tested adults. Furthermore, in the Profile of Mood States (POMS) test, both Meniki and Hinoki wood essential oils stimulated a pleasant mood status. Our results strongly suggest that Meniki and Hinoki essential oils could be suitable agents for the development of regulators of sympathetic nervous system dysfunctions.