The intermediate stage and paradoxical sleep in the rat: influence of three generations of hypnotics

Hydroalcoholic Extract of Ashwagandha Improves Sleep by Modulating GABA/Histamine Receptors and EEG Slow-Wave Pattern in In Vitro - In Vivo Experimental Models

Withania somnifera (ashwagandha) has been used traditionally as a remedy for insomnia and to enhance cognitive function. The effects of ashwagandha extract (AE, 35% withanolide glycosides, Shoden^Ⓡ) on the expression levels of γ-aminobutyric acid (GABA)_Aρ1 and histamine H3 receptors in Rattus norvegicus glioblastoma (C6) cell lines were studied using semiquantitative reverse transcriptase-polymerase chain reactions. The effects of AE on sleep onset and duration were studied in Swiss albino mice using the pentobarbital-induced sleep model. Furthermore, the effects on nonrapid eye movement (NREM) and rapid eye movement sleep patterns were studied in Wistar rats with electroencephalogram (EEG) to support the improvement in sleep quality. There was an increase in gene expression levels of GABA_Aρ1 receptor (1.38 and 1.94 folds) and histamine H3 (1.14 and 1.29 folds) receptors induced by AE at doses of 15 and 30 μg/mL compared to control. AE at doses of 10, 25, and 50 mg/kg body weight showed a significant decrease in time to sleep onset and increased total sleep duration in the pentobarbital-induced sleep model. At 50 mg/kg body weight dosage level, a 34% decrease (P<0.0001) in sleep onset time and 47% increase (P<0.0001) in sleep duration was observed. The EEG study showed significant improvement in alpha, beta, theta, delta, and gamma bands at doses of 10, 25, and 50 mg/kg body weight with delta waves showing increases of 30%, 46% (P<0.05), and 34%, respectively. The induction of sleep, GABA-mimetic action, NREM sleep, and the effects on slow-wave cycles support the calming property of AE in improving the quality of sleep.

Dose-dependent alcohol effects on electroencephalogram: Sedation/anesthesia is qualitatively distinct from sleep

Alcohol is commonly used as a sleep inducer/aid by humans. However, individuals diagnosed with alcohol use disorders have sleep problems. Few studies have examined the effect of ethanol on physiological features of sedation and anesthesia, particularly at high doses. This study used polysomnography and a rapid, unbiased scoring of vigilance states with an automated algorithm to provide a thorough characterization of dose-dependent acute ethanol effects on sleep and electroencephalogram (EEG) power spectra in C57BL/6J male mice. Ethanol had a narrow dose-response effect on sleep. Only a high dose (4.0 g/kg) produced a unique, transient state that could not be characterized in terms of canonical sleep-wake states, so we dubbed this novel state Drug-Induced State with a Characteristic Oscillation in the Theta Band (DISCO-T). After this anesthetic effect, the high dose of alcohol promoted NREM sleep by increasing the duration of NREM bouts while reducing wake. REM sleep was differentially responsive to the circadian timing of ethanol administration. EEG power spectra proved more sensitive to ethanol than sleep measures as there were clear effects of ethanol at 2.0 and 4.0 g/kg doses. Ethanol promoted delta oscillations and suppressed faster frequencies, but there were clear, differential effects on wake and REM EEG power based on the timing of the ethanol injection. Understanding the neural basis of the extreme soporific effects of high dose ethanol may aid in treating acute toxicity brought about by patterns of excessive binge consumption commonly observed in young people.

GABA Receptors and the Pharmacology of Sleep

Current GABAergic sleep-promoting medications were developed pragmatically, without making use of the immense diversity of GABA_A receptors. Pharmacogenetic experiments are leading to an understanding of the circuit mechanisms in the hypothalamus by which zolpidem and similar compounds induce sleep at α2βγ2-type GABA_A receptors. Drugs acting at more selective receptor types, for example, at receptors containing the α2 and/or α3 subunits expressed in hypothalamic and brain stem areas, could in principle be useful as hypnotics/anxiolytics. A highly promising sleep-promoting drug, gaboxadol, which activates αβδ-type receptors failed in clinical trials. Thus, for the time being, drugs such as zolpidem, which work as positive allosteric modulators at GABA_A receptors, continue to be some of the most effective compounds to treat primary insomnia.

Bottom-Up versus Top-Down Induction of Sleep by Zolpidem Acting on Histaminergic and Neocortex Neurons

Zolpidem, a GABA_A receptor-positive modulator, is the gold-standard drug for treating insomnia. Zolpidem prolongs IPSCs to decrease sleep latency and increase sleep time, effects that depend on α2 and/or α3 subunit-containing receptors. Compared with natural NREM sleep, zolpidem also decreases the EEG power, an effect that depends on α1 subunit-containing receptors, and which may make zolpidem-induced sleep less optimal. In this paper, we investigate whether zolpidem needs to potentiate only particular GABAergic pathways to induce sleep without reducing EEG power. Mice with a knock-in F77I mutation in the GABA_A receptor γ2 subunit gene are zolpidem-insensitive. Using these mice, GABA_A receptors in the frontal motor neocortex and hypothalamic (tuberomammillary nucleus) histaminergic-neurons of γ2I77 mice were made selectively sensitive to zolpidem by genetically swapping the γ2I77 subunits with γ2F77 subunits. When histamine neurons were made selectively zolpidem-sensitive, systemic administration of zolpidem shortened sleep latency and increased sleep time. But in contrast to the effect of zolpidem on wild-type mice, the power in the EEG spectra of NREM sleep was not decreased, suggesting that these EEG power-reducing effects of zolpidem do not depend on reduced histamine release. Selective potentiation of GABA_A receptors in the frontal cortex by systemic zolpidem administration also reduced sleep latency, but less so than for histamine neurons. These results could help with the design of new sedatives that induce a more natural sleep.

SIGNIFICANCE STATEMENT

Many people who find it hard to get to sleep take sedatives. Zolpidem (Ambien) is the most widely prescribed "sleeping pill." It makes the inhibitory neurotransmitter GABA work better at its receptors throughout the brain. The sleep induced by zolpidem does not resemble natural sleep because it produces a lower power in the brain waves that occur while we are sleeping. We show using mouse genetics that zolpidem only needs to work on specific parts and cell types of the brain, including histamine neurons in the hypothalamus, to induce sleep but without reducing the power of the sleep. This knowledge could help in the design of sleeping pills that induce a more natural sleep.

Pharmaco-EEG Studies in Animals: A History-Based Introduction to Contemporary Translational Applications

Current research on the effects of pharmacological agents on human neurophysiology finds its roots in animal research, which is also reflected in contemporary animal pharmaco-electroencephalography (p-EEG) applications. The contributions, present value and translational appreciation of animal p-EEG-based applications are strongly interlinked with progress in recording and neuroscience analysis methodology. After the pioneering years in the late 19th and early 20th century, animal p-EEG research flourished in the pharmaceutical industry in the early 1980s. However, around the turn of the millennium the emergence of structurally and functionally revealing imaging techniques and the increasing application of molecular biology caused a temporary reduction in the use of EEG as a window into the brain for the prediction of drug efficacy. Today, animal p-EEG is applied again for its biomarker potential - extensive databases of p-EEG and polysomnography studies in rats and mice hold EEG signatures of a broad collection of psychoactive reference and test compounds. A multitude of functional EEG measures has been investigated, ranging from simple spectral power and sleep-wake parameters to advanced neuronal connectivity and plasticity parameters. Compared to clinical p-EEG studies, where the level of vigilance can be well controlled, changes in sleep-waking behaviour are generally a prominent confounding variable in animal p-EEG studies and need to be dealt with. Contributions of rodent pharmaco-sleep EEG research are outlined to illustrate the value and limitations of such preclinical p-EEG data for pharmacodynamic and chronopharmacological drug profiling. Contemporary applications of p-EEG and pharmaco-sleep EEG recordings in animals provide a common and relatively inexpensive window into the functional brain early in the preclinical and clinical development of psychoactive drugs in comparison to other brain imaging techniques. They provide information on the impact of drugs on arousal and sleep architecture, assessing their neuropharmacological characteristics in vivo, including central exposure and information on kinetics. In view of the clear disadvantages as well as advantages of animal p-EEG as compared to clinical p-EEG, general statements about the usefulness of EEG as a biomarker to demonstrate the translatability of p-EEG effects should be made with caution, however, because they depend on the particular EEG or sleep parameter that is being studied. The contribution of animal p-EEG studies to the translational characterisation of centrally active drugs can be furthered by adherence to guidelines for methodological standardisation, which are presently under construction by the International Pharmaco-EEG Society (IPEG).

Effect of sedative-hypnotics, anesthetics and analgesics on sleep architecture in obstructive sleep apnea

The perioperative care of obstructive sleep apnea (OSA) patients is currently receiving much attention due to an increased risk for complications. It is established that postoperative changes in sleep architecture occur and this may have pathophysiological implications for OSA patients. Upper airway muscle activity decreases during rapid eye movement sleep (REMS). Severe OSA patients exhibit exaggerated chemoreceptor-driven ventilation during non-rapid eye movement sleep (NREMS), which leads to central and obstructive apnea. This article critically reviewed the literature relevant to preoperative screening for OSA, prevalence of OSA in surgical populations and changes in postoperative sleep architecture relevant to OSA patients. In particular, we addressed three questions in regard to the effects of sedative-hypnotics, anesthetics and analgesics on sleep architecture, the underlying mechanisms and the relevance to OSA. Indeed, these classes of drugs alter sleep architecture, which likely significantly contributes to abnormal postoperative sleep architecture, exacerbation of OSA and postoperative complications.

Evaluation of a piezoelectric system as an alternative to electroencephalogram/ electromyogram recordings in mouse sleep studies

STUDY OBJECTIVES

Traditionally, sleep studies in mammals are performed using electroencephalogram/electromyogram (EEG/EMG) recordings to determine sleep-wake state. In laboratory animals, this requires surgery and recovery time and causes discomfort to the animal. In this study, we evaluated the performance of an alternative, noninvasive approach utilizing piezoelectric films to determine sleep and wakefulness in mice by simultaneous EEG/EMG recordings. The piezoelectric films detect the animal's movements with high sensitivity and the regularity of the piezo output signal, related to the regular breathing movements characteristic of sleep, serves to automatically determine sleep. Although the system is commercially available (Signal Solutions LLC, Lexington, KY), this is the first statistical validation of various aspects of sleep.

DESIGN

EEG/EMG and piezo signals were recorded simultaneously during 48 h.

SETTING

Mouse sleep laboratory.

PARTICIPANTS

Nine male and nine female CFW outbred mice.

INTERVENTIONS

EEG/EMG surgery.

MEASUREMENTS AND RESULTS

The results showed a high correspondence between EEG/EMG-determined and piezo-determined total sleep time and the distribution of sleep over a 48-h baseline recording with 18 mice. Moreover, the piezo system was capable of assessing sleep quality (i.e., sleep consolidation) and interesting observations at transitions to and from rapid eye movement sleep were made that could be exploited in the future to also distinguish the two sleep states.

CONCLUSIONS

The piezo system proved to be a reliable alternative to electroencephalogram/electromyogram recording in the mouse and will be useful for first-pass, large-scale sleep screens for genetic or pharmacological studies.

CITATION

Mang GM, Nicod J, Emmenegger Y, Donohue KD, O'Hara BF, Franken P. Evaluation of a piezoelectric system as an alternative to electroencephalogram/electromyogram recordings in mouse sleep studies.

Optogenetically induced sleep spindle rhythms alter sleep architectures in mice

Sleep spindles are rhythmic patterns of neuronal activity generated within the thalamocortical circuit. Although spindles have been hypothesized to protect sleep by reducing the influence of external stimuli, it remains to be confirmed experimentally whether there is a direct relationship between sleep spindles and the stability of sleep. We have addressed this issue by using in vivo photostimulation of the thalamic reticular nucleus of mice to generate spindle oscillations that are structurally and functionally similar to spontaneous sleep spindles. Such optogenetic generation of sleep spindles increased the duration of non-rapid eye movement (NREM) sleep. Furthermore, the density of sleep spindles was correlated with the amount of NREM sleep. These findings establish a causal relationship between sleep spindles and the stability of NREM sleep, strongly supporting a role for the thalamocortical circuit in sleep regulation.

Global slowing of network oscillations in mouse neocortex by diazepam

Benzodiazepines have a broad spectrum of clinical applications including sedation, anti-anxiety, and anticonvulsive therapy. At the cellular level, benzodiazepines are allosteric modulators of GABA(A) receptors; they increase the efficacy of inhibition in neuronal networks by prolonging the duration of inhibitory postsynaptic potentials. This mechanism of action predicts that benzodiazepines reduce the frequency of inhibition-driven network oscillations, consistent with observations from human and animal EEG. However, most of existing data are restricted to frequency bands below ∼30 Hz. Recent data suggest that faster cortical network rhythms are critically involved in several behavioral and cognitive tasks. We therefore analyzed diazepam effects on a large range of cortical network oscillations in freely moving mice, including theta (4-12 Hz), gamma (40-100 Hz) and fast gamma (120-160 Hz) oscillations. We also investigated diazepam effects over the coupling between theta phase and the amplitude fast oscillations. We report that diazepam causes a global slowing of oscillatory activity in all frequency domains. Oscillation power was changed differently for each frequency domain, with characteristic differences between active wakefulness, slow-wave sleep and REM sleep. Cross-frequency coupling strength, in contrast, was mostly unaffected by diazepam. Such state- and frequency-dependent actions of benzodiazepines on cortical network oscillations may be relevant for their specific cognitive effects. They also underline the strong interaction between local network oscillations and global brain states.

Elimination kinetics of the novel prodrug cinazepam possessing psychotropic activity in mice

The kinetics of excretion of the novel tranquilizer cinazepam (3-hydroxy-7-bromo-5-(ortho-chlorophenyl)-1,2-dihydro-3H-1,4-benzdiazepin-2-one hemisuccinate (I)) in mice after a single administration and different schemes of multiple administration were determined. Mass balance was studied daily in excretions of mice (feces and urine) for 5-10 days. We observed that monoexponential renal excretion of (14)C-cinazepam and its metabolites predominated with all dosage regimens. Cinazepam and its metabolites were almost fully (> 90%) eliminated in urine and feces over the period of study (5-10 days), which means that no significant accumulation of the drug in the body occurred. The kinetic parameters of drug excretion were not significantly different after a single injection compared with those following multiple doses of (14)C-cinazepam administration. This finding suggests the absence of induction (repression) of enzymatic systems after multiple administration and lack of influence on the kinetic scheme of cinazepam elimination from mice. In our work, we also presented a modification of the Mansgeldorf's method for analysis of kinetic parameters during multiple administration of the tranquilizer. We demonstrated that our modified approach could be equally and efficiently applied for interpreting experimental data during a single dose administration and after chronic administration of xenobiotics. The use of this method made it possible to evaluate the relative efficiency of elimination processes and to find current values for excretion constants during sampling intervals.

Effects of GF-015535-00, a novel α1 GABA A receptor ligand, on the sleep-wake cycle in mice, with reference to zolpidem

STUDY OBJECTIVES

Novel, safe, and efficient hypnotic compounds capable of enhancing physiological sleep are still in great demand in the therapy of insomnia. This study compares the sleep-wake effects of a new α1 GABA(A) receptor subunit ligand, GF-015535-00, with those of zolpidem, the widely utilized hypnotic compound.

METHODS

Nine C57Bl6/J male mice were chronically implanted with electrodes for EEG and sleep-wake monitoring. Each mouse received 3 doses of GF-015535-00 and zolpidem. Time spent in sleep-wake states and cortical EEG power spectra were analyzed.

RESULTS

Both zolpidem and GF-015535-00 prominently enhanced slow wave sleep and paradoxical sleep in the mouse. However, as compared with zolpidem, GF-015535-00 showed several important differences: (1) a comparable sleep-enhancing effect was obtained with a 10 fold smaller dose; (2) the induced sleep was less fragmented; (3) the risk of subsequent wake rebound was less prominent; and (4) the cortical EEG power ratio between slow wave sleep and wake was similar to that of natural sleep and thus compatible with physiological sleep.

CONCLUSION

The characteristics of the sleep-wake effects of GF-015535-00 in mice could be potentially beneficial for its use as a therapeutic compound in the treatment of insomnia. Further investigations are required to assess whether the same characteristics are conserved in other animal models and humans.

Promotion of non-rapid eye movement sleep and activation of reticular thalamic neurons by a novel MT2 melatonin receptor ligand

Melatonin activates two brain G-protein coupled receptors, MT(1) and MT(2), whose differential roles in the sleep-wake cycle remain to be defined. The novel MT(2) receptor partial agonist, N-{2-[(3-methoxyphenyl) phenylamino] ethyl} acetamide (UCM765), is here shown to selectively promote non-rapid eye movement sleep (NREMS) in rats and mice. The enhancement of NREMS by UCM765 is nullified by the pharmacological blockade or genetic deletion of MT(2) receptors. MT(2), but not MT(1), knock-out mice show a decrease in NREMS compared to the wild strain. Immunohistochemical labeling reveals that MT(2) receptors are localized in sleep-related brain regions, and notably the reticular thalamic nucleus (Rt). Microinfusion of UCM765 in the Rt promotes NREMS, and its systemic administration induces an increase in firing and rhythmic burst activity of Rt neurons, which is blocked by the MT(2) antagonist 4-phenyl-2-propionamidotetralin. Since developing hypnotics that increase NREMS without altering sleep architecture remains a medical challenge, MT(2) receptors may represent a novel target for the treatment of sleep disorders.

Comparative analysis of the neurophysiological profile of group II metabotropic glutamate receptor activators and diazepam: effects on hippocampal and cortical EEG patterns in rats

Selective activation of the Group II metabotropic glutamate receptors 2/3 (mGlu2/3) by either full agonists or positive allosteric modulators (PAMs) show anxiolytic activity. In the present study the anxiolytic profile of mGlu2/3 receptor agonists LY-354740 and LY-404039 and the mGlu2 receptor PAM 1-methyl-2-((cis-3-methyl-4-(4-trifluoromethyl-2-methoxy)-phenyl)piperidin-1-yl)-1H-imidazo[4,5-b]pyridine (MTFIP) were evaluated using neurophysiology-based assays. Activation of mGlu2/3 receptors by these compounds, as well as the positive control diazepam, significantly decreased the frequency of hippocampal theta oscillation elicited by stimulation of the brainstem nucleus pontis oralis (nPO), a characteristic action of anxiolytic compounds. Since the nPO is a critical region involved in regulation of rapid eye movement sleep, mGlu2/3 receptor activators were also tested on sleep parameters, as well as on cortical and hippocampal encephalography (EEG) activity. Both mGlu2/3 agonists and the mGlu2 PAM significantly prolonged REM sleep latency and reduced total REM sleep duration while during the active awake state all compounds lowered hippocampal peak theta frequency. However, diazepam and mGlu2/3 agonists/PAM elicited opposite changes in cortical EEG delta and beta bands. Delta power significantly increased after any of the mGlu2/3 compounds but decreased after diazepam. In the beta band, mGlu2/3 receptor agonists dose-dependently decreased beta power in contrast to the well-known beta activation by diazepam. These effects lasted 3-4h and could not be explained by modest, transient changes (<1h) in waking and slow wave sleep. The current observations support the role of mGlu2/3 receptor activators as potential anxiolytic compounds, but indicate a distinct action on cortical EEG activity which is different from the effects of GABA(A) PAMs. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Eszopiclone facilitation of the antidepressant efficacy of fluoxetine using a social defeat stress model

This study analyzed the interaction of the sleep aid eszopiclone (ESZ) and antidepressant fluoxetine (FLX) on social defeat stress (SDS) in the mouse. Beta adrenoreceptors, brain-derived neurotrophic factor (BDNF) and cAMP response element binding protein (CREB) expression in the hippocampus and frontal cortex were also analyzed. Subjects were adult male 'intruder' C57/B6 mice that were exposed to a retired 'resident' male breeder ICR mouse in this animal's home cage for a 5 min period for each of 10 consecutive days, and the resident established physical dominance. The following day, all animals were assigned to one of four drug treatment groups, and treatment was given for up to 18 days: vehicle, ESZ only (3mg/kg), FLX (10mg/kg) only, or ESZ+FLX. A social interaction test was given on days 1, 5, 10, and 15 of drug treatment to assess SDS. Results showed that the ESZ+FLX group spent less time in avoidance zones during the interaction test at days 1 and 5, and more time in the interaction zone at day 5 compared to defeated mice given vehicle. All drug treatment groups spent more time in the interaction zone compared to defeated mice given vehicle on day 1 as well as day 10. SDS completely dissipated by the fourth interaction test according to both behavioral measures. Neurochemically, SDS did not produce changes in any marker analyzed. This study shows the combination of ESZ and FLX alleviated SDS, but a neurochemical correlate remains elusive.

Does arousal interfere with operant conditioning of spike-wave discharges in genetic epileptic rats?

One of the ways in which brain computer interfaces can be used is neurofeedback (NF). Subjects use their brain activation to control an external device, and with this technique it is also possible to learn to control aspects of the brain activity by operant conditioning. Beneficial effects of NF training on seizure occurrence have been described in epileptic patients. Little research has been done about differentiating NF effectiveness by type of epilepsy, particularly, whether idiopathic generalized seizures are susceptible to NF. In this experiment, seizures that manifest themselves as spike-wave discharges (SWDs) in the EEG were reinforced during 10 sessions in 6 rats of the WAG/Rij strain, an animal model for absence epilepsy. EEG's were recorded before and after the training sessions. Reinforcing SWDs let to decreased SWD occurrences during training; however, the changes during training were not persistent in the post-training sessions. Because behavioural states are known to have an influence on the occurrence of SWDs, it is proposed that the reinforcement situation increased arousal which resulted in fewer SWDs. Additional tests supported this hypothesis. The outcomes have implications for the possibility to train SWDs with operant learning techniques.

Effects of eszopiclone and zolpidem on sleep-wake behavior, anxiety-like behavior and contextual memory in rats

At present, eszopiclone and zolpidem are the most commonly prescribed drugs for treating insomnia. Despite the established relationship between sleep disturbance and anxiety, it remains unknown whether targeted treatment for insomnia may affect acute anxiety. Therefore, the objective of this study was to examine the effects of three different doses (1, 3, and 10mg/kg) of eszopiclone and zolpidem on the states of sleep and wakefulness, levels of anxiety-like behavior, and long-term contextual memory in footshock-induced anxious rats. The results of this study demonstrated that the administration of eszopiclone and zolpidem both were equally effective in attenuating footshock stressor-induced suppression of slow-wave sleep (SWS). The administration of eszopiclone at 1mg/kg or zolpidem at 1 and 3mg/kg doses showed a tendency for attenuating stressor-induced suppression of REM sleep. However, the REM sleep attenuating effects of these drugs disappeared when they were administered at higher doses. The administration of eszopiclone at 3 and 10mg/kg doses and zolpidem at all three doses reduced the power of electroencephalographic theta band frequencies during wakefulness. In addition, the administration of eszopiclone at 1 and 3mg/kg doses suppressed stressor-induced anxiety-like behavior. The administration of zolpidem at 1, 3, or 10mg/kg doses was not effective in attenuating stressor-induced anxiety-like behavior. Contextual memory after administration of eszopiclone at 1mg/kg dose had no effects, but was reduced significantly with increased dosage. Contextual memory after administration of zolpidem, at all three doses, was severely disrupted. The results of this study suggest that eszopiclone at a low dose could be used effectively to control anxiety and anxiety-induced insomnia.

Potentiating effect of eszopiclone on GABA(A) receptor-mediated responses in pedunculopontine neurons

The pedunculopontine nucleus (PPN) is part of the cholinergic arm of the reticular activating system, which is mostly active during waking and REM sleep. GABAergic modulation of this area appears to regulate sleep-wake cycles. Eszopiclone (ESZ), a nonbenzodiazepine hypnotic agent, appears to modulate GABAergic receptors. However, the action site of ESZ in the brain is still unresolved. We tested the hypothesis that ESZ acts by potentiating GABA(A) receptors on PPN neurons. Wholecell voltage clamp recordings were performed on PPN neurons in 7-15 day rat brainstem slices, and the potentiating effects of ESZ on the responses to the GABA(A) receptor agonist isoguvacine (IGV), and on GABA(A) receptor-mediated inhibitory post-synaptic currents (IPSCs), were determined. In the presence of tetrodotoxin, ESZ (1) increased the amplitude of the outward current induced by IGV, (2) increased its duration, and (3) enhanced the IGV-induced decrease in input resistance (Rin). The GABA(A) receptor antagonist gabazine (GBZ) blocked these effects. ESZ alone did not induce detectable currents or change Rin at a holding potential of -60 mV, but when held at 0 mV, ESZ induced an outward current in 13/21 PPN cells, an effect blocked by GBZ. ESZ also increased the amplitude (n = 18/21), duration (n = 17/21), and frequency (n = 13/15) of IPSCs. ESZ may potentiate GABA(A) inhibition in the PPN via pre- and post-synaptic modulation, which may underlie the hypnotic effects of ESZ. The differential effects of ESZ on both pre- and post-synaptic sites may partially explain why it has less significant side effects compared to other hypnotic agents.

Characterisation of the effects of caffeine on sleep in the rat: a potential model of sleep disruption

Caffeine is known to disrupt sleep and its administration to human subjects has been used to model sleep disruption. We previously showed that its effects on sleep onset latency are comparable between rats and humans. This study evaluated the potential use of caffeine as a model of sleep disruption in the rat, by assessing its effects on sleep architecture and electroencephalogram (EEG) frequency spectrum, and using sleep-promoting drugs to reverse these effects. Rats were implanted with radiotelemetry devices for body temperature, EEG, electromyogram and locomotor activity. Following recovery, animals were dosed with caffeine (10 mg/kg) alone or in combination with zolpidem (10 mg/kg) or trazodone (20 mg/kg). Sleep was scored for the subsequent 12 h using automated analysis software. Caffeine dose-dependently disrupted sleep: it increased WAKE time, decreased NREM (non-REM) sleep time and NREM bout duration (but not bout number), and decreased delta activity in NREM sleep. It also dose-dependently increased locomotor activity and body temperature. When given alone, zolpidem suppressed REM whilst trazodone increased NREM sleep time at the expense of WAKE, increased NREM bout duration, increased delta activity in NREM sleep and reduced body temperature. In combination, zolpidem attenuated caffeine's effects on WAKE, whilst trazodone attenuated its effects on NREM sleep, NREM bout duration, delta activity, body temperature and locomotor activity. Caffeine administration produced many of the signs of insomnia that were improved by two of its most successful current treatments. This model may therefore be useful in the study of new drugs for the treatment of sleep disturbance.

The impact of age on the hypnotic effects of eszopiclone and zolpidem in the guinea pig

RATIONALE

Eszopiclone and zolpidem are hypnotics that differentially affect sleep and waking states in adult animals. Therefore, it was of interest to compare their effects on the states of sleep and wakefulness in aged animals.

OBJECTIVES

Our objective was to determine the responses to eszopiclone and zolpidem vis-à-vis sleep and waking states in aged guinea pigs and to compare them with the effects of these hypnotics in adult animals.

METHODS

Aged guinea pigs were prepared to monitor sleep and waking states and to perform a frequency analysis of the EEG. Eszopiclone and zolpidem were administered intraperitoneally (1, 3, and 10 mg/kg).

RESULTS

Eszopiclone produced a more rapid and greater increase in NREM sleep as well as longer duration episodes of NREM sleep compared with zolpidem. There was also a significant increase in the latency to REM sleep with eszopiclone, but not with zolpidem. EEG power during NREM sleep increased in the delta band and decreased in the theta band following eszopiclone administration, whereas zolpidem had no effect on any of the frequency bands analyzed.

CONCLUSIONS

In aged as well as adult guinea pigs, eszopiclone is a more effective hypnotic insofar as it produces a shorter latency to NREM sleep, a greater amount of NREM sleep and EEG delta waves. Differences in the effects produced by eszopiclone and zolpidem as a function of the aging process likely reflect the fact that they bind to different subunits of the GABA(A) receptors, which are differentially reactive to the aging process.

Improvement of two-way active avoidance memory requires protein kinase a activation and brain-derived neurotrophic factor expression in the dorsal hippocampus

Previous studies have shown that two-way active avoidance (TWAA) memory processing involves a functional interaction between the pontine wave (P wave) generator and the CA3 region of the dorsal hippocampus (DH-CA3). The present experiments examined whether the interaction between P wave generator activity and the DH-CA3 involves the intracellular protein kinase A (PKA) signaling system. In the first series of experiments, rats were subjected to a session of TWAA training followed immediately by bilateral microinjection of either the PKA activation inhibitor (KT-5720) or vehicle control into the DH-CA3 and tested for TWAA memory 24 h later. The results indicated that immediate KT-5720 infusion impaired improvement of TWAA performance. Additional experiments showed that KT-5720 infusion also blocked TWAA training-induced BDNF expression in the DH-CA3. Together, these findings suggest that the PKA activation and BDNF expression in the DH-CA3 is essential for the improvement of TWAA memory.

Synaptic plasticity along the sleep-wake cycle: implications for epilepsy

Activity-dependent changes in synaptic efficacy (i.e., synaptic plasticity) can alter the way neurons communicate and process information as a result of experience. Synaptic plasticity mechanisms involve both molecular and structural modifications that affect synaptic functioning, either enhancing or depressing neuronal transmission. They include redistribution of postsynaptic receptors, activation of intracellular signaling cascades, and formation/retraction of dendritic spines, among others. During the sleep-wake cycle, as the result of particular neurochemical and neuronal firing modes, distinct oscillatory patterns organize the activity of neuronal populations, modulating synaptic plasticity. Such modulation, for example, has been shown in the visual cortex following sleep deprivation and in the ability to induce hippocampal long-term potentiation during sleep. In epilepsy, synchronized behavioral states tend to contribute to the initiation of paroxystic discharges and are considered more epileptogenic than desynchronized states. Here, we review some of the current understandings of synaptic plasticity changes in wake and sleep states and how sleep may affect epileptic seizures.

Anxiolytic profile of pregabalin on elicited hippocampal theta oscillation

Previous published work with the novel anticonvulsant, analgesic and anti-anxiety medication, pregabalin (Lyrica), has shown that it has anxiolytic-like actions in several animal behavioral models. However, pregabalin is structurally and pharmacologically different from other classes of known anxiolytic drugs, and the mechanisms that alter brain activity to produce anxiolytic-like actions are not well understood. In an effort to determine more about the cellular mechanisms of pregabalin, we studied its effects on hippocampal theta activity of urethane-anesthetized rats that was elicited by electrical stimulation of the nucleus pontis oralis (nPO) in the brainstem. We found that systemic administration of pregabalin significantly reduced the frequency of stimulation-induced hippocampal theta activity similarly to the effects of diazepam. In addition, pregabalin (but not diazepam) significantly altered the stimulus intensity/frequency relationship, and increased slow delta oscillation (<3.0Hz) in spontaneous hippocampal EEG in a dose-dependent manner. Our findings suggest that pregabalin may alter evoked theta frequency activity in the hippocampus by reducing neurotransmitter-mediated activation of either the septal nucleus or the hippocampus, and that its actions are unlikely to be mediated by direct activation of GABA neurotransmitter systems. These observations provide further insight to the action of pregabalin, and support the utilization of stimulation-induced theta model in discovery of novel anxiolytic drugs.

Sleep-stabilizing effects of E-6199, compared to zopiclone, zolpidem and THIP in mice

Gamma aminobutyric acid (GABA)A receptor modulators constitute the majority of clinically used sedative-hypnotics. These compounds have the capacity to initiate and maintain sleep, but decrease REM sleep and delta activity within NREM sleep. In order to avoid such sleep adverse effects, the development of novel compounds remains of interest.

STUDY OBJECTIVES

The present study aimed at characterizing the acute effects of a novel putative hypnotic compound, E-6199, compared to zopiclone, zolpidem, and THIP on sleep-wakefulness patterns in mice. We also investigated whether repeated administration (daily injection during 10 days) of E-6199 was associated with tolerance and sleep disturbances at cessation of treatment.

MEASUREMENTS AND RESULTS

Polygraphic recordings were performed during 8 h after acute treatment with the various compounds. Under such conditions, E-6199 (5-20 mg/kg i.p.), zopiclone and zolpidem (2-10 mg/kg i.p.), but not THIP (2-10 mg/kg i.p.), exerted a marked sleep-promoting effect. Furthermore, E-6199 specifically increased the duration of NREM and markedly improved sleep continuity by lengthening NREM sleep episodes and reducing short awakenings and microarousal frequency. It also intensified NREM sleep by enhancing the slow wave activity within NREM at wake-NREM transitions. These effects were sustained and became even larger during chronic administration. Finally, abrupt E-6199 withdrawal did not elicit negative sleep effects.

CONCLUSIONS

Our findings demonstrate that E-6199 may be an effective hypnotic compound that promotes and improves NREMS, without producing EEG side effects, tolerance or withdrawal phenomena, when administered under chronic conditions.

A translational, caffeine-induced model of onset insomnia in rats and healthy volunteers

RATIONALE

Insomnia is a common and disabling complaint for which there is a need for improved treatments. Successful drug discovery relies on the use of appropriate animal models to assess likely outcome in the clinic.

OBJECTIVES

The purpose of this study was to develop a translational, caffeine-induced model of insomnia in rats and healthy volunteers. We used sleep onset latency (SOL) as a comparable sleep measure between the two species. The model was validated by two effective sleep-promoting agents with different pharmacology, zolpidem and trazodone, which have GABA-ergic and serotonergic mechanisms, respectively.

MATERIALS AND METHODS

In rats, radiotelemetry transmitters with electroencephalogram and electromyogram electrodes were implanted for sleep recording. Animals were administered with caffeine alone (10 mg/kg) or in combination with zolpidem (10 mg/kg) or trazodone (20 mg/kg), or vehicle, in crossover experiments. Home polysomnography was performed in 12 healthy male volunteers in a randomised, placebo-controlled, 4-week crossover study. Subjects received placebo, caffeine (150 mg) or caffeine in combination with zolpidem (10 mg) or trazodone (100 mg). Subjective sleep effects in volunteers were assessed using the Leeds Sleep Evaluation Questionnaire.

RESULTS

Caffeine caused a significant prolongation in objective SOL in rats and humans. This effect was sensitive to zolpidem and trazodone, both of which attenuated the caffeine-induced increase in SOL. Furthermore, both hypnotics restored the disruption in subjective measures of sleep onset caused by caffeine in volunteers.

CONCLUSIONS

This model therefore provides a promising paradigm in which we can study novel treatments for sleep disorders and an opportunity for direct comparison of results between rodents and humans.

Sub-chronic administration of zolpidem affects modifications to rat sleep architecture

Gamma-aminobutyric acidA receptor (GABAAR) modulators constitute the majority of clinically relevant sedative-hypnotics. Animal studies have clearly demonstrated sedative efficacy for these compounds in acute studies. However, relatively less is known regarding their efficacy under brief periods of repeat administration or following intermittent dosing. Therefore zolpidem, a short-acting GABAAR modulator with selectivity for the type-I (omega1) benzodiazepine receptor, was studied for efficacy in altering rat sleep architecture as determined by electrocorticogram (ECoG) and electromyogram (EMG) activity over a 7-day sub-chronic administration period. Zolpidem caused significant reductions in wakefulness entries and rapid eye movement (REM) sleep entries and duration, with increases in Delta sleep duration throughout the administration period. Examination of sleep architecture 24 h after cessation of sub-chronic zolpidem administration revealed a decrease in Delta sleep, suggesting that repeated zolpidem administration might elicit enduring modifications to sleep organization. This was not seen following similar dosing of diazepam. The efficacy of sub-chronic administration of zolpidem to alter sleep architecture was enhanced when the administration regimen was repeated following a 7-day hiatus. Significant increases in Delta sleep duration, with significant decreases in light sleep and wakefulness were observed during the repeated exposure to zolpidem. Therefore, sub-chronic administration of zolpidem affected lasting modifications in sleep organization that appeared both 1 day following administration and during reiterated administration without eliciting tolerance.

GABA mechanisms and sleep

GABA is the main inhibitory neurotransmitter of the CNS. It is well established that activation of GABA(A) receptors favors sleep. Three generations of hypnotics are based on these GABA(A) receptor-mediated inhibitory processes. The first and second generation of hypnotics (barbiturates and benzodiazepines respectively) decrease waking, increase slow-wave sleep and enhance the intermediate stage situated between slow-wave sleep and paradoxical sleep, at the expense of this last sleep stage. The third generation of hypnotics (imidazopyridines and cyclopyrrolones) act similarly on waking and slow-wave sleep but the slight decrease of paradoxical sleep during the first hours does not result from an increase of the intermediate stage. It has been shown that GABA(B) receptor antagonists increase brain-activated behavioral states (waking and paradoxical sleep: dreaming stage). Recently, a specific GABA(C) receptor antagonist was synthesized and found by i.c.v. infusion to increase waking at the expense of slow-wave sleep and paradoxical sleep. Since the sensitivity of GABA(C) receptors for GABA is higher than that of GABA(A) and GABA(B) receptors, GABA(C) receptor agonists and antagonists, when available for clinical practice, could open up a new era for therapy of troubles such as insomnia, epilepsy and narcolepsy. They could possibly act at lower doses, with fewer side effects than currently used drugs. This paper reviews the influence of different kinds of molecules that affect sleep and waking by acting on GABA receptors.