Sleep-promoting activity of lotus (Nelumbo nucifera) rhizome water extract via GABA_A receptors

Context: The sleep-promoting activity of Nelumbo nucifera Gaertn. (Nymphaeaceae) alkaloids in leaves or seeds are well known. However, the sleep-promoting activity of the lotus rhizome (LE), which is used mainly as food, has not yet been evaluated. Objective: We investigated the sleep-promoting activity of LE water extract. Materials and methods: Institute of Cancer Research (ICR) mice (n = 8) were subject to a pentobarbital-induced sleep test to assess changes in sleep latency and duration following the administration of LE (80–150 mg/kg). In addition, electroencephalography analysis was performed to determine the sleep quality after LE treatment as well as the sleep recovery effect of LE using a caffeine-induced insomnia SD rat model. Real-time PCR and western blot analysis were performed to investigate the expression of neurotransmitter receptors, and the GABA_A receptor antagonists were used for receptor binding analysis. Results: An oral administration of 150 mg/kg LE significantly increased sleep duration by 24% compared to the control. Furthermore, LE increased nonrapid eye movement (NREM) sleep by increasing theta and delta powers. In the insomnia model, LE increased sleep time by increasing NREM sleep. Moreover, treatment with picrotoxin and flumazenil decreased the sleep time by 33% and 23%, respectively, indicating an involvement of the GABA_A receptor in the sleep-enhancing activity of LE. The expression of GABA_A receptors and the concentration of GABA in the brain were increased by LE. Discussion and conclusions: The results suggest that the sleep-promoting activity of LE was via the GABA_A receptor. Collectively, these data show that LE may promote sleep.