The scent of lavender reduces anxiety through odor receptors

Traditional medicine has long used aromatic compounds derived from plants, such as lavender extract, to treat anxiety, but it is still unclear how these compounds could act at the neuronal level. In Japan, a team of scientists has demonstrated that the smell of linalool, an aromatic alcohol derived from lavender, exerts anxiolytic effects in mice by acting on the same receptors for gamma-aminobutyric acid A (GABA)._ARs) who respond to the anti-anxiety drug benzodiazepam. However, while diazepam in the blood acts directly on GABA_A The team from Kagoshima University discovered that linalool vapor was acting via the animal's olfactory system. Its relaxing effects were not obvious in mice that did not smell.

The researchers, led by Hideki Kashiwadani, Ph.D., of Kagoshima University, suggest that further studies will be needed to further evaluate the target, effects and potential side effects of linalool, but that new discoveries indicate that the compound could actually be used. be used to help reduce the anxiety of patients in a clinical setting. "These results nevertheless bring us closer to the clinical use of linalool to relieve anxiety, for example in surgery where pretreatment with anxiolytics can alleviate preoperative stress and thus help to place patients under general anesthesia more easily. Says Dr. Kashiwadani. "Sprayed linalol could also be a safe alternative for patients who have difficulty with the administration of oral or suppository anxiolytics, such as confused infants or seniors."

The findings of the team are reported in Borders in behavioral neuroscience, in an article entitled "Anxiolytic Effects Induced by Linalool Odor in Mice".

The authors say that anxiety disorders are one of the most common types of mental health disorders. First-line drug therapies include azapirons and selective serotonin reuptake inhibitors (SSRIs) that affect serotonergic synaptic transmission, as well as benzodiazepines that act by GABAergic transmission. However, the team notes that the side effects of these medications may be worse than the anxiety itself.

Aromatic compounds of plant origin, including lavender extract, are used in traditional medicines to treat anxiety for many years. "However, the neural mechanisms underlying reported anxiolytic effects of odorous compounds have not yet been fully revealed," the team said. "Previously, several studies have shown that inhalation of linalool induces anxiolytic effects. However, since the contribution of the olfactory system has not been directly examined, the nature of how linalool can induce effects has not been revealed. "

Researchers are now reporting on studies involving conventional anxiety tests in male mice, immediately following exposure of animals to linalool vapor. The light / black box test results and the elevated labyrinth plus test suggest that exposure to linalool vapor produces dose-related anxiolytic effects that, in some cases, are comparable to those produced by the product. treatment with diazepam. However, unlike injections of benzodiazepam or linalool, linalol odor exposure did not cause motor disturbances and test results suggested that linalool odor effects were rather anxiolytic than sedatives.

Significantly, linalool vapor exerts its effects only in mice that have a sense of smell. Exposure to linalool vapor had anxiolytic effects in anosmic mice. These animals had been pretreated with a compound destroying their olfactory receptors. Similarly, animals pretreated with a flumazenil compound, which blocks the benzodiazepine site on GABA_ARS, also, did not respond to linalool vapor, "indicating that GABAergic transmission via GABA-sensitive benzodiazepine_ARs was essential for anxiolytic effects, "say the authors. "When combined, these results suggest that linalool does not act directly on GABA_A Receptors like benzodiazepines do, but have to activate them through olfactory neurons located in the nose to produce its relaxing effects, "notes Dr. Kashiwadani.

Interestingly, previous studies have shown that other odors, including (+) – limonene, present in citrus peels, also have anxiolytic effects when inhaled. However, in the case of (+) – limonene, pretreatment with flumazenil does not block its relaxing effects. "Given our findings, it is possible that there are at least two parallel anxiolytic pathways involving benzodiazepine-sensitive GABA._ARs-dependent, and independent-systems evoked by olfactory entry. "

Previous research had shown that systemic administration of linalool by intraperitoneal injection also induced anxiolytic effects, suggesting that inhaled linalool acts via glutamatergic neurotransmission after it enters the bloodstream via airway absorption. However, according to Dr. Kashiwadani, "our study opens the possibility that the relaxation observed in linalool-fed or linalool-fed mice may actually be due to the smell of the compound emitted in their expired breath" .

"These findings provide information on the potential central neural mechanisms underlying odor-induced anxiolytic effects and provide the foundation for exploring the clinical application of linalool odor in cancer treatments." "Anxiety," write the authors. "The anxiolytic effects induced by the odor of linalool can be applied to preoperative patients, as pretreatment with anxiolytics can alleviate preoperative stress and thus contribute to better undergoing general anesthesia of patients. In addition, for patients who may have difficulty with the administration of oral or suppository anxiolytics, such as infants, the use of the linalool odor to reduce anxiety may be a practical alternative and promising. "