Inhaled β-myrcene alleviates insomnia in mice by modulating 5-HT1A/PKA signaling and the gut microbiota

Background and Objectives Insomnia is a major public health issue that impairs daily functions and quality of life. Sleep-onset difficulty, a common complaint among patients, is accompanied by reduced central serotonin (5-HT) function. β-myrcene from lavender has sedative–hypnotic effects via serotonergic pathways, but most previous studies used intraperitoneal injection, which causes stress and limits clinical translation. Here, we asked whether non-invasive inhalation of β-myrcene produced similar effects in a mouse model of insomnia with low 5-HT function, and explored the underlying mechanisms.Methods β-myrcene was given to PCPA-induced insomnia mice by inhalation (with intraperitoneal injection as a pharmacodynamic control). In the inhalation group, sleep and behavior were evaluated using the amobarbital sodium sleep test and spontaneous locomotor activity test. ELISA, RT-qPCR, Western blot, and 16S rRNA sequencing were applied to study mechanisms.Results Inhaled β-myrcene shortened sleep latency and prolonged sleep duration. It also reduced oxidative stress and modulated GABA, 5-HT, and glutamate levels. These changes were accompanied by upregulation of mRNAs such as GABAARγ2 and 5-HT1A, as well as proteins including GAD65/67 and PKA, suggesting involvement of 5-HT1A/PKA signaling. Additionally, inhalation of β-myrcene was correlated with alterations in gut microbiota composition in PCPA-induced insomnia mice.Conclusions Our findings indicate that inhaled β-myrcene is associated with sedative–hypnotic effects and alterations in gut microbiota composition in PCPA-induced insomnia mice, potentially involving modulation of 5-HT1A/PKA signaling.