Effects of Chronic Administration of Green Tea Ethanol Extract on Sleep Architecture in Mice: A Comparative Study with a Representative Stimulant Caffeine.

Wakefulness is defined as a state in which individuals can react to a change in situations. The number of people staying awake and compensating for lack of sleep has increased in recent years. Caffeine, a representative stimulant, is the most extensively consumed compound globally and is mainly consumed through coffee. Although green tea (Camellia sinensis L.) contains high caffeine content like coffee, its arousal-inducing effects have not yet been studied. In the present study, we aimed to identify the arousal-inducing effect of GT during a chronic administration period (three weeks) using analysis of sleep architecture. Treatment with GT (1500 mg/kg) significantly elevated the sleep latency and wakefulness throughout the treatment period, and chronic administration of GT consistently maintained an increase in wakefulness for up to 3 h. During the treatment period, the arousal-inducing effect of GT (1500 mg/kg) occurred without any change in the tolerance phenomenon or withdrawal symptoms, similar to that observed with caffeine (25 mg/kg). GT (1500 mg/kg) containing 95.6 mg/kg of caffeine did not produce a better arousal-inducing effect than caffeine at 25 mg/kg. These results indicate that the arousal-inducing effect of GT persisted for three weeks without adverse effects and that GT can control the arousal-inducing effects of caffeine due to the hypnotic effects of its other constituents.

Effects of Green Kiwifruit Peel Extract on Sleep-Wake Profiles in Mice: A Polysomnographic Study Based on Electroencephalogram and Electromyogram Recordings.

In the previous study, it was reported that green kiwifruit peel ethanol extract (GKPEE) increases sleep duration and decreases sleep latency in pentobarbital-treated mice. The pentobarbital-induced sleep test can be used to verify sleep quantity, which includes factors such as sleep duration and latency, but not sleep quality. In the present study, the sleep-promoting effects of GKPEE were investigated by the analysis of electroencephalogram (EEG) and electromyogram in mice and were compared with the results of diazepam (DZP), a representative sedative-hypnotic agent. The acute administration of GKPEE (250, 500 and 1000 mg/kg) increased the amount of non-rapid eye movement sleep (NREMS) and decreased sleep latency in a dose-dependent manner. The effect of GKPEE at 1000 mg/kg produced persistently significantly different results until the second hour of time-course changes. In particular, GKPEE did not produce any change in delta activity compared to DZP. Furthermore, sub-chronic administration (15 days) of GKPEE (500 mg/kg) continued sleep-promoting effects, whilst the EEG power density of NREMS did not show significant differences, indicating that there were no tolerance phenomena. Our findings suggest that GKPEE may be a promising natural sleep aid for treating sleep disorders. In addition, considering the number of by-products discarded each year by the food industry, the application of GKPEE here contributes to the utilization of processed kiwifruit by-products and can help to solve environmental problems.

Curcuminoids, a major turmeric component, have a sleep-enhancing effect by targeting the histamine H1 receptor.

Turmeric (Curcuma longa) had been considered as a universal panacea in functional foods and traditional medicines. In recent, the sedative-hypnotic effect of turmeric extract (TE) was reported. However, sleep-promoting compounds in TE have been not yet demonstrated. Curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) are the major constituents of turmeric being responsible for its various biological activities. Therefore, they can be first assumed to be sedative-hypnotic compounds of TE. In the present study, we aimed to investigate the effects and underlying mechanisms of curcuminoids and each constituent on the sleep-wake cycle of mice. Molecular docking studies, histamine H1 receptor (H1R) binding assays, and H1R knockout animal studies were used to investigate the molecular mechanisms underlying the sleep-promoting effects. Curcuminoids and their constituents reduced sleep latency and increased sleep duration in the pentobarbital-induced sleep test in mice. In addition, curcuminoids significantly increased the duration of NREMS and reduced sleep latency without altering the REMS and delta activity. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin were predicted to interact with H1R in the molecular model. In the binding affinity assay, we found that curcuminoids, as well as their constituents, significantly bind to H1R with the Ki value of 1.49 µg mL-1. Furthermore, sleep latency was reduced and NREMS frequency was increased following curcuminoid administration in wild-type mice but not in H1R knockout mice. Therefore, we conclude that curcuminoids reduce sleep latency and enhance the quantity of NREMS by acting as modulators of H1R, indicating their usefulness in treating insomnia.

Effect of Black Pepper (Piper nigrum) Extract on Caffeine-Induced Sleep Disruption and Excitation in Mice.

Sleep is one of the most essential factors required to maintain good health. However, the global prevalence of insomnia is increasing, and caffeine intake is a major trigger. The objective of this study was to investigate the inhibitory effect of black pepper, Piper nigrum extract (PE), on caffeine-induced sleep disruption and excitation in mice. Caffeine significantly decreased sleep duration in the pentobarbital-induced sleep test. It also resulted in a significant increase in sleep onset and a decrease in non-rapid eye movement sleep. Moreover, in an open-field test, caffeine-treated mice exhibited a significantly increased time in the center zone and total distance traveled. However, the co-administration of caffeine and PE did not result in similar arousal activities. Thus, our results suggest that PE can be used as a potential therapeutic agent to treat sleep problems and excitatory status associated with caffeine intake.

Arousal-Inducing Effect of Garcinia cambogia Peel Extract in Pentobarbital-Induced Sleep Test and Electroencephalographic Analysis.

Caffeine, a natural stimulant, is known to be effective for weight loss. On this basis, we screened the arousal-inducing effect of five dietary supplements with a weight loss effect (Garcinia cambogia, Coleus forskohlii, Camellia sinensis L., Irvingia gabonensis, and Malus pumila M.), of which the G. cambogia peel extract (GC) showed a significant arousal-inducing effect in the pentobarbital-induced sleep test in mice. This characteristic of GC was further evaluated by analysis of electroencephalogram and electromyogram in C57L/6N mice, and it was compared to that of the positive control, caffeine. Administration of GC (1500 mg/kg) significantly increased wakefulness and decreased non-rapid eye movement sleep, similar to that of caffeine (25 mg/kg), with GC and caffeine showing a significant increase in wakefulness at 2 and 6 h, respectively. Compared to that of caffeine, the shorter duration of efficacy of GC could be advantageous because of the lower possibility of sleep disturbance. Furthermore, the arousal-inducing effects of GC (1500 mg/kg) and caffeine (25 mg/kg) persisted throughout the chronic (3 weeks) administration study. This study, for the first time, revealed the arousal-inducing effect of GC. Our findings suggest that GC might be a promising natural stimulant with no side effects. In addition, it is preferential to take GC as a dietary supplement for weight loss during the daytime to avoid sleep disturbances owing to its arousal-inducing effect.

A Novel Potent Sleep-Promoting Effect of Turmeric: Turmeric Increases Non-Rapid Eye Movement Sleep in Mice Via Histamine H1Receptor Blockade.

SCOPE: Turmeric has a broad spectrum of biological properties; however, the sleep-promoting effects of turmeric have not yet been reported. Thus, this study aims to investigate the effect of turmeric on sleep and the molecular mechanism underlying this effect. METHODS AND RESULTS: Pentobarbital-induce sleep test and sleep-wake profile assessment using recorded electroencephalography are used to evaluate the hypnotic effects of the turmeric extract (TE) compared to diazepam on sleep in mice. Additionally, the molecular mechanism of TE's sleep effect is investigated using ex vivo electrophysiological recordings from brain slices in histamine H1 receptor (H1 R) knockout mice. Oral administration of TE and diazepam significantly reduce sleep latency and increase non-rapid eye movement sleep (NREMS) duration without delta activity in mice. Like doxepin, TE inhibits the H1 R agonist (2-pyridylethylamine dihydrochloride)-induced increase in action potentials in the hypothalamic neurons. In animal tests using neurotransmitter agonists or antagonists, TE effect mimick H1 R antagonistic effect of doxepin. Additionally, both reduce sleep latency and increase NREMS in wild-type mice, although these effects are not observed in H1 R knockout mice. CONCLUSION: TE has a sleep-promoting effect owing to reduction in sleep latency and enhancement of NREMS via H1 R blockade; therefore, it could be useful in insomnia.

The translocator protein ligands as mitochondrial functional modulators for the potential anti-Alzheimer agents.

Small molecule modulators of mitochondrial function have been attracted much attention in recent years due to their potential therapeutic applications for neurodegenerative diseases. The mitochondrial translocator protein (TSPO) is a promising target for such compounds, given its involvement in the formation of the mitochondrial permeability transition pore in response to mitochondrial stress. In this study, we performed a ligand-based pharmacophore design and virtual screening, and identified a potent hit compound, 7 (VH34) as a TSPO ligand. After validating its biological activity against amyloid-ß (Aß) induced mitochondrial dysfunction and in acute and transgenic Alzheimer's disease (AD) model mice, we developed a library of analogs, and we found two most active compounds, 31 and 44, which restored the mitochondrial membrane potential, ATP production, and cell viability under Aß-induced mitochondrial toxicity. These compounds recovered learning and memory function in acute AD model mice with improved pharmacokinetic properties.

Dieckol is a natural positive allosteric modulator of GABAA-benzodiazepine receptors and enhances inhibitory synaptic activity in cultured neurons.

Phlorotannin supplement (PS) is a natural hypnotic substrate that modulates γ-aminobutyric acid type A (GABAA)-benzodiazepine (BZD) receptors. However, there is a lack of functional data assessing the role of individual components of PS, such as Dieckol, as allosteric activators of GABAA receptors (GABAAR). Using the whole cell patch clamp technique, we demonstrated that PS functionally enhanced the activity of GABAA-BZD receptors in a heterologous system and in primary cultured neurons. Application of diazepam (DZP) or Dieckol (1) increased GABAAR-mediated inward current in HEK293T cells containing the α1 subunit in a dose-dependent manner, (2) which was blocked by co-treatment with the selective benzodiazepine site antagonist, flumazenil (FLZ); it also (3) increased the amplitude of GABAA-BZD receptors in primary cultured neurons, which was blocked by FLZ and (4) attenuated spontaneous activity in cultured neurons. These results indicate that PS and Dieckol act as positive allosteric activators of GABAA-BZD receptors, which might be the underlying mechanism of the sedative-hypnotic effect of PS. To our knowledge, this is the first study to directly link Dieckol-induced GABAAR activation via the BZD site binding and suppression of spontaneous neuronal activity in vitro.

Rice bran extract supplement improves sleep efficiency and sleep onset in adults with sleep disturbance: A randomized, double-blind, placebo-controlled, polysomnographic study.

We previously reported that rice bran extract supplement (RBS) administration to mice decreased sleep latency and induced non-rapid eye movement (NREM) sleep via inhibition of the histamine H1 receptor. Based on this, we performed the first clinical trial to investigate whether RBS would be beneficial to subjects with disturbed sleep. We performed a randomized, double-blinded, placebo-controlled, 2-week study. Fifty subjects with sleep disturbance were enrolled and received either RBS (1,000 mg/day) or placebo. Polysomnography was performed, and Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale (ESS), and Fatigue Severity Scale were administered at the initiation and termination of the study. Compared with the placebo, RBS led to significant polysomnographic changes, including decreased sleep latency (adjusted, P = 0.047), increased total sleep time (P = 0.019), and improved sleep efficiency (P = 0.010). Additionally, the amount of stage 2 sleep significantly increased in the RBS group. When adjusted for caffeine intake, wakefulness after sleep onset, total wake time, and delta activity tended to decrease in the RBS group. RBS administration decreased ESS scores. There were no reported serious adverse events in both groups. RBS improved sleep in adults with sleep disturbance. Trial registration: WHO ICTRP, KCT0001893.

A Standardized Phlorotannin Supplement Attenuates Caffeine-Induced Sleep Disruption in Mice.

In our previous studies, a standardized phlorotannin (brown seaweed polyphenol) supplement (PS) exhibited sleep-promoting effects via type A γ-aminobutyric acid-benzodiazepine receptors in mice. In addition, in human clinical trials, it decreased wake after sleep onset in adults with sleep disturbance. In this follow-up study, we investigated whether PS attenuates caffeine-induced sleep disruption in mice. The effects of PS were evaluated in a caffeine model by analyzing sleep architecture based on electroencephalogram and electromyogram findings, and were compared with the effects of a well-known sedative-hypnotic drug zolpidem (ZPD). As expected, oral administration of caffeine (25 mg/kg) significantly increased sleep latency and decreased the amount of non-rapid eye movement sleep (NREMS). In the caffeine + PS and caffeine + ZPD groups, PS (500 mg/kg) attenuated caffeine-induced sleep disruption, and its effects were comparable with those of ZPD (10 mg/kg). In particular, PS inhibited the arousal effects of caffeine without change in delta activity during NREMS, whereas ZPD produced a decrease in the delta activity. Considering global trends in coffee and energy drink consumption, our finding suggest that PS may be useful to relieve transitory insomnia symptoms caused by caffeine consumption, unlike the prescription drug ZPD.

Standardized Citrus unshiu peel extract ameliorates dexamethasone-induced neurotoxicity and depressive-like behaviors in mice.

Dried Citrus unshiu peel, also known as Chinpi, have been commonly used as a traditional medicine to improve for allergy, inflammation and hepatopathy. Many previously studies have reported that citrus flavonoids show neuroprotective activities. However, the antidepressant-related effects of C. unshiu peels have not been well characterized. Here, the antidepressant-like effects of standardized C. unshiu peel extract (SCP) were evaluated in in vivo and in vitro depression models induced by dexamethasone (DEX), a synthetic glucocorticoid. Male ICR mice (9-week-old) were injected the DEX (40 mg/kg) and were orally given SCP daily (30, 100, and 300 mg/kg) for 14 consecutive days. The depressive-like behaviors were determined by use of open filed test (OFT), sucrose preference test (SPT), tail suspension test (TST), and forced swim test (FST). We show that treatment with SCP significantly alleviated DEX-induced depressive-like behaviors and reduced neurotoxicity in a concentration dependent manner in SH-SY5Y cells. Additionally, repeated DEX injection markedly decreased brain derived neurotrophic factor (BDNF) level, tropomyosin receptor kinase B (TrkB), and cyclic AMP-response element-binding protein (CREB), while SCP treatment improved these levels in the cerebral cortex and hippocampus regions. Our findings suggest that SCP exhibits significant antidepressant-like effects in the DEX-induced depressive animal model, and this activity may be mediated by preventing corticosterone-induced neurotoxicity.

Rice bran supplement prevents UVB-induced skin photoaging in vivo.

Although rice bran consumption is reportedly has numerous beneficial effects on human health, the relationship between rice bran and the prevention of photoaging has not been investigated in detail. We sought to investigate whether consumption of rice bran supplement (RBS) can elicit preventive effects against UVB-induced photoaging in vivo. Dorsal skin sections of hairless mice were exposed to UVB over 16 weeks. RBS consumption suppressed UVB-induced wrinkle formation and inhibited the loss of water content and epidermal thickening in the mouse skin. Western blot and immunohistochemical analyses revealed that repeated exposure to UVB upregulated matrix metalloproteinase-13 (MMP-13) and cyclooxygenase-2 (COX-2) expression, while consumption of RBS suppressed MMP-13 and COX-2 expression, as well as mitogen-activated protein kinase (MAPK) signaling pathways. These findings suggest that RBS could be a potential bioactive ingredient in nutricosmetics to inhibit wrinkle formation and water content loss via the suppression of COX-2 and MMP-13 expression.

Phlorotannin supplement decreases wake after sleep onset in adults with self-reported sleep disturbance: A randomized, controlled, double-blind clinical and polysomnographic study.

Our previous study demonstrated that phlorotannin supplement had a sleep-promoting effect in rodents. In the present study, we investigated whether the phlorotannin supplement could improve sleep in subjects with self-reported sleep disturbances. In a randomized, double-blind, placebo-controlled trial, 24 subjects consumed either a placebo or phlorotannin supplement (500 mg/day) for 1 week, 30-60 min prior to bedtime. Sleep parameters were assessed at baseline and at 1 week with sleep questionnaires and polysomnography. At the end of the treatment period, the complete sets of sleep parameters from 20 subjects. Phlorotannin resulted in a significant increase in "Sleep duration" scores compared to the placebo (p = .044), although there were no significant differences on the total PSQI scores. Polysomnography revealed that wakefulness after sleep onset was significantly lower in the phlorotannin group compared to the placebo group (phlorotannin vs. placebo, -25.5 ± 30.5 vs. -1.7 ± 14.9; p = .045) as well as total wake time (phlorotannin vs. placebo, -0.9 ± 3.0 vs. -6.1 ± 6.8; p = .048). Additionally, the respiratory disturbance index during supine rapid eye movement sleep was significantly lower in the phlorotannin group (p = .035). There were no serious adverse effects in either group. Our data suggest that the phlorotannin supplement improved sleep maintenance (WHO ICTRP: KCT0001892).

A novel neurological function of rice bran: a standardized rice bran supplement promotes non-rapid eye movement sleep in mice through histamine H1 receptors.

SCOPE: Although rice bran has been shown to be associated with a wide spectrum of health benefits, to date, there are no reports on its effects on sleep. We investigated the effect of rice bran on sleep and the mechanism underlying this effect. METHODS AND RESULTS: Electroencephalography was used to evaluate the effects of standardized rice bran supplement (RBS) and doxepin hydrochloride (DH), a histamine H1 receptor (H1 R) antagonist used as a positive control, on sleep in mice. The mechanism of RBS action was investigated using knockout (KO) mice and ex vivo electrophysiological recordings. Oral administration of RBS and DH significantly decreased sleep latency and increased the amount of non-rapid eye movement sleep (NREMS) in mice. Similar to DH, RBS fully inhibited H1 R agonist-induced increase in action potential frequency in tuberomammillary nucleus neurons. In H1 R KO mice, neither RBS nor DH administration led to the increase in NREMS and decrease in sleep latency observed in WT mice. These results indicate that the sleep-promoting effect of RBS is completely dependent on H1 R antagonism. CONCLUSIONS: RBS decreases sleep latency and promotes NREMS through the inhibition of H1 R, suggesting that it could be a promising therapeutic agent for insomnia.

Sleep-Promoting Effects and Possible Mechanisms of Action Associated with a Standardized Rice Bran Supplement.

Natural sleep aids are becoming more popular due to the widespread occurrence of sleep disorders. The objective of this study was to assess the sleep-promoting effects of rice bran-a product that is considered as a functional ingredient. To evaluate the sleep-promoting effects of a standardized rice bran supplement (RBS), we employed a pentobarbital-induced sleep test and conducted analyses of sleep architecture. In addition, the effect of RBS on a caffeine-induced sleep disturbance was investigated. Oral administration of RBS (500 and 1000 mg/kg) produced a significant decrease in sleep latency and increase in sleep duration in pentobarbital-induced sleep in mice. Moreover, both RBS (1000 mg/kg) and doxepin hydrochloride (histamine H1 receptor antagonist, 30 mg/kg) counteracted a caffeine-induced sleep disturbance in mice. In terms of sleep phases, RBS (500 mg/kg) promoted non-rapid eye movement sleep for the first 3 h following its administration. Lastly, we unveiled a possible mechanism for RBS action as the hypnotic effect of RBS was blocked by a histamine H1 receptor agonist. The present study revealed sleep-promoting effects of RBS using various animal assays. Such effects seem to be mediated through the histaminergic system. Our findings suggest that RBS may be a promising natural aid for relieving sleep problems.

α-Pinene, a Major Constituent of Pine Tree Oils, Enhances Non-Rapid Eye Movement Sleep in Mice through GABAA-benzodiazepine Receptors.

α-Pinene is a major monoterpene of the pine tree essential oils. It has been reported that α-pinene shows anxiolytic and hypnotic effects upon inhaled administration. However, hypnotic effect by oral supplementation and the molecular mechanism of α-pinene have not been determined yet. By combining in vivo sleep behavior, ex vivo electrophysiological recording from brain slices, and in silico molecular modeling, we demonstrate that (-)-α-pinene shows sleep enhancing property through a direct binding to GABAA-benzodiazepine (BZD) receptors by acting as a partial modulator at the BZD binding site. The effect of (-)-α-pinene on sleep-wake profiles was evaluated by recording electroencephalogram and electromyogram. The molecular mechanism of (-)-α-pinene was investigated by electrophysiology and molecular docking study. (-)-α-pinene significantly increased the duration of non-rapid eye movement sleep (NREMS) and reduced the sleep latency by oral administration without affecting duration of rapid eye movement sleep and delta activity. (-)-α-pinene potentiated the GABAA receptor-mediated synaptic response by increasing the decay time constant of sIPSCs in hippocampal CA1 pyramidal neurons. These effects of (-)-α-pinene on sleep and inhibitory synaptic response were mimicked by zolpidem, acting as a modulator for GABAA-BZD receptors, and fully antagonized by flumazenil, an antagonist for GABAA-BZD receptor. (-)-α-pinene was found to bind to aromatic residues of α1- and -γ2 subunits of GABAA-BZD receptors in the molecular model. We conclude that (-)-α-pinene enhances the quantity of NREMS without affecting the intensity of NREMS by prolonging GABAergic synaptic transmission, acting as a partial modulator of GABAA-BZD receptors and directly binding to the BZD binding site of GABAA receptor.

Antidepressant-Like Effects of Lindera obtusiloba Extracts on the Immobility Behavior of Rats in the Forced Swim Test.

Lindera obtusiloba extracts are commonly used as an alternative medicine due to its numerous health benefits in Korea. However, the antidepressant-like effects of L. obtusiloba extracts have not been fully elucidated. In this study, we aimed to determine whether L. obtusiloba extracts exhibited antidepressant-like activity in rats subjected to forced swim test (FST)-induced depression. Acute treatment of rats with L. obtusiloba extracts (200 mg/kg, p.o.) significantly reduced immobility time and increased swimming time without any significant change in climbing. Rats treated with L. obtusiloba extracts also exhibited a decrease in the limbic hypothalamic-pituitary-adrenal (HPA) axis response to the FST, as indicated by attenuation of the corticosterone response and decreased c-Fos immunoreactivity in the hippocampus CA3 region. In addition, L. obtusiloba extracts, at concentrations that were not affected by cell viability, significantly decreased luciferase activity in response to cortisol in a concentration-dependent manner by the glucocorticoid binding assay in HeLa cells. Our findings suggested that the antidepressant-like effects of L. obtusiloba extracts were likely mediated via the glucocorticoid receptor (GR). Further studies are needed to evaluate the potential of L. obtusiloba extracts as an alternative therapeutic approach for the treatment of depression.

The edible brown seaweed Ecklonia cava reduces hypersensitivity in postoperative and neuropathic pain models in rats.

The current study was designed to investigate whether edible brown seaweed Ecklonia cava extracts exhibits analgesic effects in plantar incision and spared nerve injury (SNI) rats. To evaluate pain-related behavior, we performed the mechanical withdrawal threshold (MWT) and thermal hypersensitivity tests measured by von Frey filaments and a hot/cold plate analgesia meter. Pain-related behavior was also determined through analysis of ultrasonic vocalization. The results of experiments showed MWT values of the group that was treated with E. cava extracts by 300 mg/kg significantly increased; on the contrary, number of ultrasonic distress vocalization of the treated group was reduced at 6 h and 24 h after plantar incision operation (62.8%, p < 0.05). Moreover, E. cava 300 mg/kg treated group increased the paw withdrawal latency in hot-and cold-plate tests in the plantar incision rats. After 15 days of continuous treatment with E. cava extracts at 300 mg/kg, the treated group showed significantly alleviated SNI-induced hypersensitivity response by MWT compared with the control group. In conclusion, these results suggest that E. cava extracts have potential analgesic effects in the case of postoperative pain and neuropathic pain in rats.

Marine polyphenol phlorotannins promote non-rapid eye movement sleep in mice via the benzodiazepine site of the GABAA receptor.

RATIONALE: In psychopharmacology, researchers have been interested in the hypnotic effects of terrestrial plant polyphenols and their synthetic derivatives. Phlorotannins, a marine plant polyphenol, could have potential as a source of novel hypnotic drugs. OBJECTIVES: The effects of phlorotannins and major phlorotannin constituent eckstolonol on sleep-wake profiles in mice were evaluated in comparison with diazepam, and their hypnotic mechanism was also investigated. METHODS: The effects of phlorotannin preparation (PRT) and eckstolonol orally given on sleep-wake profiles were measured by recording electroencephalograms (EEG) and electromyograms in C57BL/6N mice. Flumazenil, a GABAA-benzodiazepine (BZD) receptor antagonist, was injected 15 min before PRT and eckstolonol to reveal its hypnotic mechanism. RESULTS: PRT administration (>250 mg/kg) produced a significant decrease in sleep latency and an increase in the amount of non-rapid eye movement sleep (NREMS). Eckstolonol significantly decreased sleep latency (>12.5 mg/kg) and increased the amount of NREMS (50 mg/kg). PRT and eckstolonol had no effect on EEG power density of NREMS. The hypnotic effects of PRT or eckstolonol were completely abolished by pretreatment with flumazenil. CONCLUSIONS: We demonstrated that phlorotannins promote NREMS by modulating the BZD site of the GABAA receptor. These results suggest that phlorotannins can be potentially used as an herbal medicine for insomnia and as a promising structure for developing novel sedative-hypnotics.

Potentiating effect of glabridin on GABAA receptor-mediated responses in dorsal raphe neurons.

Flavonoid-rich ethanol extracts of licorice root have sedative and anxiolytic effects. Glabridin is a major flavonoid component from licorice which we evaluated by examining GABA responses in acutely isolated dorsal raphe neurons of the rat. Neurons were recorded with patch-clamp methods at a holding potential of - 50 mV. Glabridin potentiated GABA-induced responses by positively modulating GABAA receptor responses with different concentration range. GABA (2 × 10(-6) M)-evoked currents were potentiated in a stepwise pattern increasing glabridin concentration. Between 10(-12) and 10(-8) M glabridin increased GABA responses by about 140 % of the control. At concentrations above 10(-7) M, a much larger, dose-dependent potentiation occurred before reaching a plateau at 3 × 10-6 M glabridin. A hypnotic drug, zolpidem, also induced biphasic concentration-potentiation relationship. The glabridin potentiation ratio was 2.2 times larger than the maximum potentiation to the benzodiazepine receptor full agonist diazepam. Benzodiazepine receptor antagonist, flumazenil (3 × 10(-7) M), failed to inhibit glabridin (3 × 10(-7) M)-induced potentiation. This result implies that glabridin may exhibit sedative and hypnotic effects by potentiating GABAergic inhibition in dorsal raphe neurons by GABAA receptor actions.