The diazepam-like sedative effects of vaporized essential oil from the Okinawan Kabuchii citrus fruit

Kabuchii (Citrus keraji var. kabuchii hort. ex Tanaka, Rutaceae) is a citrus fruit peculiar to the Japanese island of Okinawa. Although local citrus fruit farmers report that its fragrance is highly relaxing, few studies have addressed either the chemical composition or the biological effects of its essential oil. In this study, the authors investigated the chemical composition and the sedative effects of kabuchii essential oil (KBEO). The effects of the oil and its components were determined via an open field test, a rotarod test and a pentobarbital sleep test using diazepam as a positive control. In the open field test, both volatilized KBEO (0.03 - 3mg/cage, calculated conc. ca. 0.003 - 0.3mg/L) and diazepam reduced spontaneous motor activity dose-dependently. The reduction in the 0.3mg/cage KBEO group was greater than that in the 1mg/kg (p.o.) diazepam group. In rotarod testing, KBEO did not affect motor performance even at the highest dosage applied (3mg/cage), whereas diazepam reduced it dose-dependently. The effects of the major or characteristic components of kabuchii (d-limonen, γ-terpinene, thymol and p-cymene) were also evaluated via open field and rotarod testing. The results showed that γ-terpinene and thymol significantly reduced spontaneous motor activity at a dosage of 0.3mg/cage without affecting motor performance. In pentobarbital sleep testing, both volatilized KBEO and diazepam reduced sleep latency and increased sleep duration. These effects for both treatments were similarly inhibited by pretreatment with flumazenil (a benzodiazepine receptor antagonist). γ-terpinene exhibited similar potentiating effects on pentobarbital-induced sleep. Thus, it was demonstrated that volatilized kabuchii essential oil (KBEO) have diazepam-like sedative effects and sleep improvement effects.