Is the smell of lavender relaxing?

Aside from those with allergies, most people enjoy the smell of lavender. Found on terraces, in gardens, in cosmetic products and detergents, this plant may soon be found in hospitals as well. Before beginning any tests in humans, Japanese researchers studied its anxiolytic properties in mice in order to determine whether the smell of lavender could be effective in treating anxiety.

As the authors remind us in the introduction of their article published in Frontiers in Behavioral Neuroscience, along with pharmaceutical anxiolytic drugs, aromatic oils derived from plant extracts are already used in traditional medicine to treat anxiety. These extracts include linalool, a lavender extract. Previous research has already demonstrated the anxiolytic effects of this compound. In the current study, researchers from the departments of physiology and anesthesiology at the University of Kagoshima in Japan wanted to learn more about the neuronal mechanisms underlying the positive effects of linalool in the treatment of anxiety disorders.

A scented alcohol, linalool accounts for 26% of the composition of lavender oil and is present in nearly all lavender extracts. Kashiwadani and his colleagues wanted to study its potential anxiolytic effects (already demonstrated in classical behavioral tests) in mice. 240 male rodents participated in the study. In a custom-designed odor chamber, subjects were exposed to the odor of linalool (soaked filter paper to which the animals did not have access) for 30 minutes.

Behavioral tests were conducted after this exposure: two to measure anxiety (dark/light box and maze test), and another to measure motor coordination, balance, and fatigue (accelerated Rotarod). In the first test, the mouse was placed in the lit compartment of a box (the other compartment, separated by a small entrance, remained dark). In the second, the mouse was placed on a central platform with two open and two closed arms. In the two experiments, the subjects were filmed for 5 minutes. In the Rotarod test, the rat was placed on a drum that rotates at an increasing pace. Researchers recorded the length of time the animals remained on the drum.

The results of the different tests all point to the same conclusion. Indeed, the mice that were exposed to the linalool were (significantly) more likely to explore the lit room and the open arms of the maze, indicating a lack of anxiety. In addition, the linalool didn't alter their motor function, as indicated by the Rotarod test (no significant difference between the performances of the mice exposed to the linalool and those who had no exposure). The authors of the study therefore concluded that exposure to the scent of linalool does indeed induce anxiolytic effects without causing any motor impairment in mice.

Another interesting result: the benefits could not be replicated in a group of anosmic mice (whose olfactory glands had been neutralized). This indicated that the calming effects were indeed triggered by olfactory signals, caused by the smell of linalool. These findings present a potential alternative to the injection of linalool and its direct effects on GABAergic receptors. GABA is a chemical messenger whose natural function is to reduce the nervous activity of neurons to which it attaches, and is thus useful for controlling anxiety. But injecting linalool has a negative effect on motricity (similar to the effects of alcohol). This study thus offers a new means of allowing subjects to enjoy the benefits of linalool without the negative impact on motor skills.

According to the researchers, the odor of linalool is key: “These findings nonetheless bring us closer to clinical use of linalool to relieve anxiety - in surgery for example, where pretreatment with anxiolytics can alleviate preoperative stress and thus help to place patients under general anesthesia more smoothly.”
Source: Harada, Hideki Kashiwadani, Yuichi Kanmura et Tomoyuki Kuwaki, “Linalool Odor-Induced Anxiolytic Effects in Mice”, in Frontiers in Behavioral Neuroscience , Oct. 2018.

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