Diazepam-induced changes in sleep: role of the alpha 1 GABA(A) receptor subtype

Closing the gap between the molecular and systemic actions of anesthetic agents

Genetic approaches have been successfully used to relate the diverse molecular actions of anesthetic agents to their amnestic, sedative, hypnotic, and immobilizing properties. The hypnotic effect of etomidate, quantified as the duration of the loss of righting reflex in mice, is equally mediated by GABAA receptors containing β2- and β3-protein subunits. However, only β3-containing receptors are involved in producing electroencephalogram (EEG)-patterns typical of general anesthesia. The sedative action of diazepam is produced by α1-subunit-containing receptors, but these receptors do not contribute to the drug's characteristic EEG-"fingerprint." Thus, GABAA receptors with α1- and β2-subunits take a central role in causing benzodiazepine-induced sedation and etomidate-induced hypnosis, but the corresponding EEG-signature is difficult to resolve. Contrastingly, actions of etomidate and benzodiazepines mediated via α2- and β3-subunits modify rhythmic brain activity in vitro and in vivo at least in part by enhancing neuronal synchrony. The immobilizing action of GABAergic anesthetics predominantly involves β3-subunit-containing GABAA receptors in the spinal cord. Interestingly, this action is self-limiting as GABA-release is attenuated via the same receptors. Anesthetic-induced amnesia is in part mediated by GABAA receptors harboring α5-subunits that are highly enriched in the hippocampus and, in addition, by α1-containing receptors in the forebrain. Because there is accumulating evidence that in patients the expression pattern of GABAA receptor subtypes varies with age, is altered by the long-term use of drugs, and is affected by pathological conditions like inflammation and sepsis, further research is recommended to adapt the use of anesthetic agents to the specific requirements of individual patients.

Insomnia, hypnotic use, and health-related quality of life in a nationally representative sample

PURPOSE

To assess health-related quality of life (HRQoL) associated with insomnia and prescription hypnotic use.

METHODS

Primary outcomes were mental component summary (MCS) and physical component summary (PCS) scores from the 12-item Short-Form Health Survey. Using multiple regression, subjects in the 2005 through 2009 Medical Expenditure Panel Survey with diagnosed insomnia were compared against those without that diagnosis. Among subjects with diagnosed insomnia, users of prescription hypnotics were compared against nonusers.

RESULTS

Of 104,274 adults, 1.3 % (n = 1,401) had an insomnia diagnosis. Of those, 45.6 % (n = 639) used prescription hypnotics. For subjects with insomnia, mean PCS and MCS scores were 9.2 and 7.0 points lower (p < 0.001), respectively. After controlling for demographic and clinical covariates, differences remained significant (PCS:5.1;

MCS

6.2; p < 0.001). Among subjects with insomnia, HRQoL scores were not different between prescription hypnotic users (n = 639) and nonusers (n = 762). Analysis by drug class revealed lower PCS scores (difference: 7.5, p < 0.001) with benzodiazepine use (n = 129) versus benzodiazepine receptor agonist use (n = 493), but the adjusted difference was not significant (difference: 3.8, p = .018).

CONCLUSIONS

Diagnosed insomnia was associated with consistent decreases in both physical and mental HRQoL scores, regardless of whether prescription hypnotics were used. Benzodiazepine use may be associated with a further decrease in physical HRQoL scores. Although limited by its retrospective design, this study provides a first look at real-world hypnotic use outcomes at a national level. Important next steps include studies with patients serving as their own controls, and further evaluation of the sensitivity of HRQoL instruments to the effects of insomnia treatments.

Sedative-hypnotic Effect of Ash of Silver in Mice: A Reverse Pharmacological Study

Ash of silver is used in traditional systems of medicine for various neurological conditions like insomnias, neuralgias, anxiety disorders, and convulsions. The present study was conducted to evaluate the sedative-hypnotic activity of ash of silver in comparison to pentobarbitone (standard drug) in albino mice. The mice were divided into four groups as follows: Group 1 (control): Gum acacia [GA; 1% per os (p.o.)], group 2 (standard): Pentobarbitone [50 mg/kg intraperitoneal (i.p.)], group 3 (test): Ash of silver (50 mg/kg p.o.), and group 4: Ash of silver (50 mg/kg p.o.) given 30 min prior to administration of pentobarbitone (50 mg/kg i.p.). Time of onset, recovery, and total duration of loss of righting reflex were studied. Ash of silver (test) produced significant sedation (P < 0.01) compared to control (GA 1%), but the effect was significantly less compared to that of standard pentobarbitone at the doses used. Also, significant potentiation (P < 0.001) of the sedative-hypnotic effect of pentobarbitone was observed with the test drug.

EEG-β/γ spectral power elevation in rat: a translatable biomarker elicited by GABA(Aα2/3)-positive allosteric modulators at nonsedating anxiolytic doses

Benzodiazepine drugs, through interaction with GABA(Aα1), GABA(Aα2,3), and GABA(Aα5) subunits, modulate cortical network oscillations, as reflected by a complex signature in the EEG power spectrum. Recent drug discovery efforts have developed GABA(Aα2,3)-subunit-selective partial modulators in an effort to dissociate the side effect liabilities from the efficacy imparted by benzodiazepines. Here, we evaluated rat EEG and behavioral end points during dosing of nine chemically distinct compounds that we confirmed statistically to selectively to enhance GABA(Aα2,3)-mediated vs. GABA(Aα1) or GABA(Aα5) currents in voltage clamped oocytes transfected with those GABA(A) subunits. These compounds were shown with in vivo receptor occupancy techniques to competitively displace [(3)H]flumazenil in multiple brain regions following peripheral administration at increasing doses. Over the same dose range, the compounds all produced dose-dependent EEG spectral power increases in the β- and and γ-bands. Finally, the dose range that increased γ-power coincided with that eliciting punished over unpunished responding in a behavioral conflict model of anxiety, indicative of anxiolysis without sedation. EEG γ-band power increases showed a significant positive correlation to in vitro GABA(Aα2,3) modulatory intrinsic activity across the compound set, further supporting a hypothesis that this EEG signature was linked specifically to pharmacological modulation of GABA(Aα2,3) signaling. These findings encourage further evaluation of this EEG signature as a noninvasive clinical translational biomarker that could ultimately facilitate development of GABA(Aα2,3)-subtype-selective drugs for anxiety and potentially other indications.

Alcohol use disorders and current pharmacological therapies: the role of GABA(A) receptors

Alcohol use disorders (AUD) are defined as alcohol abuse and alcohol dependence, which create large problems both for society and for the drinkers themselves. To date, no therapeutic can effectively solve these problems. Understanding the underlying mechanisms leading to AUD is critically important for developing effective and safe pharmacological therapies. Benzodiazepines (BZs) are used to reduce the symptoms of alcohol withdrawal syndrome. However, frequent use of BZs causes cross-tolerance, dependence, and cross-addiction to alcohol. The FDA-approved naltrexone and acamprosate have shown mixed results in clinical trials. Naltrexone is effective to treat alcohol dependence (decreased length and frequency of drinking bouts), but its severe side effects, including withdrawal symptoms, are difficult to overcome. Acamprosate showed efficacy for treating alcohol dependence in European trials, but two large US trials have failed to confirm the efficacy. Another FDA-approved medication, disulfiram, does not diminish craving, and it causes a peripheral neuropathy. Kudzu is the only natural medication mentioned by the National Institute on Alcohol Abuse and Alcoholism, but its mechanisms of action are not yet established. It has been recently shown that dihydromyricetin, a flavonoid purified from Hovenia, has unique effects on GABAA receptors and blocks ethanol intoxication and withdrawal in alcoholic animal models. In this article, we review the role of GABAA receptors in the treatment of AUD and currently available and potentially novel pharmacological agents.

Benzodiazepine site agonists differentially alter acetylcholine release in rat amygdala

BACKGROUND

Agonist binding at the benzodiazepine site of γ-aminobutric acid type A receptors diminishes anxiety and insomnia by actions in the amygdala. The neurochemical effects of benzodiazepine site agonists remain incompletely understood. Cholinergic neurotransmission modulates amygdala function, and this study tested the hypothesis that benzodiazepine site agonists alter acetylcholine (ACh) release in the amygdala.

METHODS

Microdialysis and high-performance liquid chromatography quantified ACh release in the amygdala of Sprague-Dawley rats (n = 33). ACh was measured before and after IV administration (3 mg/kg) of midazolam or eszopiclone, with and without anesthesia. ACh in isoflurane-anesthetized rats during dialysis with Ringer's solution (control) was compared with ACh release during dialysis with Ringer's solution containing (100 μM) midazolam, diazepam, eszopiclone, or zolpidem.

RESULTS

In unanesthetized rats, ACh in the amygdala was decreased by IV midazolam (-51.1%; P = 0.0029; 95% confidence interval [CI], -73.0% to -29.2%) and eszopiclone (-39.6%; P = 0.0222; 95% CI, -69.8% to -9.3%). In anesthetized rats, ACh in the amygdala was decreased by IV administration of midazolam (-46.2%; P = 0.0041; 95% CI, -67.9% to -24.5%) and eszopiclone (-34.0%; P = 0.0009; 95% CI, -44.7% to -23.3%), and increased by amygdala delivery of diazepam (43.2%; P = 0.0434; 95% CI, 2.1% to 84.3%) and eszopiclone (222.2%; P = 0.0159; 95% CI, 68.5% to 375.8%).

CONCLUSIONS

ACh release in the amygdala was decreased by IV delivery of midazolam and eszopiclone. Dialysis delivery directly into the amygdala caused either increased (eszopiclone and diazepam) or likely no significant change (midazolam and zolpidem) in ACh release. These contrasting effects of delivery route on ACh release support the interpretation that systemically administered midazolam and eszopiclone decrease ACh release in the amygdala by acting on neuronal systems outside the amygdala.

The behavioral pharmacology of zolpidem: evidence for the functional significance of α1-containing GABA(A) receptors

RATIONALE

Zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) with preferential binding affinity and efficacy for α1-subunit containing GABA(A) receptors (α1-GABA(A)Rs). Over the last three decades, a variety of animal models and experimental procedures have been used in an attempt to relate the behavioral profile of zolpidem and classic benzodiazepines (BZs) to their interaction with α1-GABA(A)Rs.

OBJECTIVES

This paper reviews the results of rodent and non-human primate studies that have evaluated the effects of zolpidem on motor behaviors, anxiety, memory, food and fluid intake, and electroencephalogram (EEG) sleep patterns. Also included are studies that examined zolpidem's discriminative, reinforcing, and anticonvulsant effects as well as behavioral signs of tolerance and withdrawal.

RESULTS

The literature reviewed indicates that α1-GABA(A)Rs play a principle role in mediating the hypothermic, ataxic-like, locomotor- and memory-impairing effects of zolpidem and BZs. Evidence also suggests that α1-GABA(A)Rs play partial roles in the hypnotic, EEG sleep, anticonvulsant effects, and anxiolytic-like of zolpidem and diazepam. These studies also indicate that α1-GABA(A)Rs play a more prominent role in mediating the discriminative stimulus, reinforcing, hyperphagic, and withdrawal effects of zolpidem and BZs in primates than in rodents.

CONCLUSIONS

The psychopharmacological data from both rodents and non-human primates suggest that zolpidem has a unique pharmacological profile when compared with classic BZs. The literature reviewed here provides an important framework for studying the role of different GABA(A)R subtypes in the behavioral effects of BZ-type drugs and helps guide the development of new pharmaceutical agents for disorders currently treated with BZ-type drugs.

GABA transporter-1 inhibitor NO-711 alters the EEG power spectra and enhances non-rapid eye movement sleep during the active phase in mice

GABA transporter subtype 1 (GAT1) constructs high affinity reuptake sites for GABA in the CNS and regulates GABAergic transmission. Compounds that inhibit GAT1 are targets often used for the treatment of epilepsy; however sedation has been reported as a side effect of these agents, indicating potential sedative and/or hypnotic uses for these compounds. In the current study, we observed the sleep behaviors of mice treated with NO-711, a selective GAT1 inhibitor, in order to elucidate the role of GAT1 in sleep-wake regulation during the active phase. The data revealed that NO-711 at a high dose of 10 mg/kg caused a marked enhancement of EEG activity in the frequency ranges of 3-25 Hz during wakefulness as well as rapid eye movement (REM) sleep. During the non-REM (NREM) sleep, NO-711 (10 mg/kg) elevated EEG activity in the frequency ranges of 1.5-6.75 Hz. Similar changes were found in mice treated with a low dose of 3 mg/kg. NO-711 administered i.p. at a dose of 1, 3 or 10 mg/kg significantly shortened the sleep latency of NREM sleep, increased the amount of NREM sleep and the number of NREM sleep episodes. NO-711 did not affect the sleep latency and the amount of REM sleep. NO-711 dose-dependently increased c-Fos expression in sleep-promoting nucleus of the ventrolateral preoptic area and median preoptic area. However, c-Fos expression was decreased in the wake-promoting nuclei, tuberomammillary nucleus and lateral hypothalamus. These results indicate that NO-711 can increase NREM sleep in mice.

The α1 adrenoceptor antagonist prazosin enhances sleep continuity in fear-conditioned Wistar-Kyoto rats

Fragmentation of rapid eye movement sleep (REMS) is well described in individuals with posttraumatic stress disorder (PTSD) and likely has significant functional consequences. Fear-conditioned rodents may offer an attractive model of the changes in sleep that characterize PTSD. Following fear conditioning (FC), Wistar-Kyoto (WKY) rats, a strain known to be particularly stress-sensitive, have increased REMS fragmentation that can be quantified as a shift in the distribution of REMS episodes towards the more frequent occurrence of sequential REMS (inter-REMS episode interval≤3 min) vs. single REMS (interval>3 min). The α1 adrenoceptor antagonist prazosin has demonstrated efficacy in normalizing sleep in PTSD. To determine the utility of fear-conditioned WKY rats as a model of sleep disturbances typical of PTSD and as a platform for the development of new treatments, we tested the hypothesis that prazosin would reduce REMS fragmentation in fear-conditioned WKY rats. Sleep parameters and freezing (a standard measure of anxiety in rodents) were quantified at baseline and on Days 1, 7, and 14 following FC, with either prazosin (0.01mg/kg, i.p.) or vehicle injections administered prior to testing in a between-group design. Fear conditioning was achieved by pairing tones with a mild electric foot shock (1.0mA, 0.5s). One, 7, and 14 days following FC, prazosin or vehicle was injected, the tone was presented, freezing was measured, and then sleep was recorded from 11 AM to 3 PM. WKY rats given prazosin, compared to those given vehicle, had a lower amount of seq-REMS relative to total REMS time 14 days after FC. They also had a shorter non-REMS latency and fewer non-REMS arousals at baseline and on Days 1 and 7 after FC. Thus, in FC rats, prazosin reduced both REMS fragmentation and non-REMS discontinuity.

Fast-Acting Sublingual Zolpidem for Middle-of-the-Night Wakefulness

Sleep disorders (somnipathies) are conditions characterized by disruptions of sleep quality or of sleep pattern. They can involve difficulty falling asleep (prolonged sleep onset latency), difficulty staying asleep (disturbance of sleep maintenance), sleep of poor quality (unrefreshing), or combinations of these and can lead to poor health and quality of life problems. A subtype of sleep-maintenance insomnia is middle-of-the-night wakefulness, a relatively common occurrence. Zolpidem, a nonbenzodiazepine benzodiazepine receptor agonist, allosterically modulates an ion channel and increases the influx of Cl(-), thereby dampening the effect of excitatory (sleep disrupting) input. Recently, product label changes to some zolpidem containing products have been implemented by the FDA in order to reduce the risk associated with their morning after residual side effects. A new formulation of zolpidem tartrate (Intermezzo) sublingual tablet, an approved product indicated exclusively for the treatment of middle-of-the-night wakefulness and difficulty returning to sleep, did not have its label changed. We present a short summary of its basic science and clinical attributes in light of the recent regulatory changes for zolpidem products.

Sedative and hypnotic activity of N(6)-(3-methoxyl-4-hydroxybenzyl) adenine riboside (B2), an adenosine analog

N(6)-(3-methoxyl-4-hydroxybenzyl) adenine riboside (B2) is an N(6)-substitued adenosine analog. Previous studies have shown that B2 binds to the adenosine A1 and A2A receptors with moderate affinity and produces protective effects on serum deprivation-induced cell damage. However, central nervous system effects of B2 have not been studied. We aimed to investigate the sedative and hypnotic effects and the mechanism of action of B2 in mice. Our behavioral studies showed that oral administration of B2 decreased spontaneous locomotor activity and potentiated the hypnotic effect of pentobarbital in mice. Sleep architecture analyses revealed that B2 decreased wakefulness and increased non-rapid eye movement (NREM) sleep in both normal mice and mice with caffeine-induced insomnia. Using immunohistochemistry, we showed that B2 increased c-Fos expression, a cellular marker for neuronal activity, in the ventrolateral preoptic (VLPO) area, a sleep center in the anterior hypothalamus. Altogether, these results indicate that oral administration of B2 produces sedative and hypnotic effects. Furthermore, the activation of VLPO neurons may be involved in the central depressant effects of B2.

Orexin receptor antagonists differ from standard sleep drugs by promoting sleep at doses that do not disrupt cognition

Current treatments for insomnia, such as zolpidem (Ambien) and eszopiclone (Lunesta), are γ-aminobutyric acid type A (GABAA)-positive allosteric modulators that carry a number of side effects including the potential to disrupt cognition. In an effort to develop better tolerated medicines, we have identified dual orexin 1 and 2 receptor antagonists (DORAs), which promote sleep in preclinical animal models and humans. We compare the effects of orally administered eszopiclone, zolpidem, and diazepam to the dual orexin receptor antagonist DORA-22 on sleep and the novel object recognition test in rat, and on sleep and two cognition tests (delayed match to sample and serial choice reaction time) in the rhesus monkey. Each compound's minimal dose that promoted sleep versus the minimal dose that exerted deficits in these cognitive tests was determined, and a therapeutic margin was established. We found that DORA-22 has a wider therapeutic margin for sleep versus cognitive impairment in rat and rhesus monkey compared to the other compounds tested. These data were further supported with the demonstration of a wider therapeutic margin for DORA-22 compared to the other compounds on sleep versus the expression of hippocampal activity-regulated cytoskeletal-associated protein (Arc), an immediate-early gene product involved in synaptic plasticity. These findings suggest that DORAs might provide an effective treatment for insomnia with a greater therapeutic margin for sleep versus cognitive disturbances compared to the GABAA-positive allosteric modulators currently in use.

Can pharmaco-electroencephalography help improve survival of central nervous system drugs in early clinical development?

Pharmaco-electroencephalography has significant yet unrealised promise as a translatable intermediate biomarker of central pharmacodynamic activity that could help reduce Phase 2 attrition in the development of central nervous system drugs. In an effort to understand its true potential, a framework for decision-making was proposed and the utility of pharmaco-electroencephalography was assessed through several case studies. A key finding was that lack of standardisation reduces the value of data pooling and meta-analyses and renders assessment of translatability difficult, limiting utility in all but simple cases. Pre-competitive collaboration is essential both to improving understanding of translation and developing modern signal processing techniques.

Maternal Separation during Breastfeeding Induces Gender-Dependent Changes in Anxiety and the GABA-A Receptor Alpha-Subunit in Adult Wistar Rats

Different models of rodent maternal separation (MS) have been used to investigate long-term neurobiological and behavioral changes, associated with early stress. However, few studies have involved the analysis of sex-related differences in central anxiety modulation. This study investigated whether MS during breastfeeding affected adult males and females in terms of anxiety and brain GABA-A receptor-alpha-subunit immunoreactivity. The brain areas analyzed were the amygdale (AM), hippocampus (HP), medial prefrontal cortex (mPFC), medial preoptic area (POA) and paraventricular nucleus (PVN). Rats were housed under a reversed light/dark cycle (lights off at 7∶00 h) with access to water and food ad libitum. Animals underwent MS twice daily during the dark cycle from postnatal day 1 to postnatal day 21. Behavior was tested when rats were 65-70 days old using the elevated plus maze and after brains were treated for immunohistochemistry. We found that separated females spent more time in the open arms and showed more head dipping behavior compared with controls. The separated males spent more time in the center of the maze and engaged in more stretching behavior than the controls. Immunohistochemistry showed that separated females had less immunostained cells in the HP, mPFC, PVN and POA, while separated males had fewer immunolabeled cells in the PFC, PVN and AM. These results could indicate that MS has gender-specific effects on anxiety behaviors and that these effects are likely related to developmental alterations involving GABA-A neurotransmission.

Delirium: is sleep important?

Delirium and poor sleep quality are common and often co-exist in hospitalised patients. A link between these disorders has been hypothesised but whether this link is a cause-and-effect relationship or simply an association resulting from shared mechanisms is yet to be determined. Potential shared mechanisms include: abnormalities of neurotransmitters, tissue ischaemia, inflammation and sedative exposure. Sedatives, while decreasing sleep latency, often cause a decrease in slow wave sleep and stage rapid eye movement (REM) sleep and therefore may not provide the same restorative properties as natural sleep. Mechanical ventilation, an important cause of sleep disruption in intensive care unit (ICU) patients, may lead to sleep disruption not only from the discomfort of the endotracheal tube but also as a result of ineffective respiratory efforts and by inducing central apnoea events if not properly adjusted for the patient's physiologic needs. When possible, efforts should be made to optimise the patient-ventilator interaction to minimise sleep disruptions.

Honokiol promotes non-rapid eye movement sleep via the benzodiazepine site of the GABA(A) receptor in mice

BACKGROUND AND PURPOSE

Decoctions of the Chinese herb houpu contain honokiol and are used to treat a variety of mental disorders, including depression. Depression commonly presents alongside sleep disorders and sleep disturbances, which appear to be a major risk factor for depression. Here, we have evaluated the somnogenic effect of honokiol and the mechanisms involved.

EXPERIMENTAL APPROACH

Honokiol was administered i.p. at 20:00 h in mice. Flumazenil, an antagonist at the benzodiazepine site of the GABA(A) receptor, was administered i.p. 15 min before honokiol. The effects of honokiol were measured by EEG and electromyogram (EMG), c-Fos expression and in vitro electrophysiology.

KEY RESULTS

Honokiol (10 and 20 mg·kg⁻¹) significantly shortened the sleep latency to non-rapid eye movement (non-REM, NREM) sleep and increased the amount of NREM sleep. Honokiol increased the number of state transitions from wakefulness to NREM sleep and, subsequently, from NREM sleep to wakefulness. However, honokiol had no effect on either the amount of REM sleep or EEG power density of both NREM and REM sleep. Honokiol increased c-Fos expression in ventrolateral preoptic area (VLPO) neurons, as examined by immunostaining, and excited sleep-promoting neurons in the VLPO by whole-cell patch clamping in the brain slice. Pretreatment with flumazenil abolished the somnogenic effects and activation of the VLPO neurons by honokiol.

CONCLUSION AND IMPLICATIONS

Honokiol promoted NREM sleep by modulating the benzodiazepine site of the GABA(A) receptor, suggesting potential applications in the treatment of insomnia, especially for patients who experience difficulty in falling and staying asleep.

Flavonoid Myricetin Modulates GABA(A) Receptor Activity through Activation of Ca(2+) Channels and CaMK-II Pathway

The flavonoid myricetin is found in several sedative herbs, for example, the St. John's Wort, but its influence on sedation and its possible mechanism of action are unknown. Using patch-clamp technique on a brain slice preparation, the present study found that myricetin promoted GABAergic activity in the neurons of hypothalamic paraventricular nucleus (PVN) by increasing the decay time and frequency of the inhibitory currents mediated by GABA_A receptor. This effect of myricetin was not blocked by the GABA_A receptor benzodiazepine- (BZ-) binding site antagonist flumazenil, but by KN-62, a specific inhibitor of the Ca²⁺/calmodulin-stimulated protein kinase II (CaMK-II). Patch clamp and live Ca²⁺ imaging studies found that myricetin could increase Ca²⁺ current and intracellular Ca²⁺ concentration, respectively, via T- and L-type Ca²⁺ channels in rat PVN neurons and hypothalamic primary culture neurons. Immunofluorescence staining showed increased phosphorylation of CaMK-II after myricetin incubation in primary culture of rat hypothalamic neurons, and the myricetin-induced CaMK-II phosphorylation was further confirmed by Western blotting in PC-12 cells. The present results suggest that myricetin enhances GABA_A receptor activity via calcium channel/CaMK-II dependent mechanism, which is distinctively different from that of most existing BZ-binding site agonists of GABA_A receptor.

Determination of GABA(Aα1) and GABA (B1) receptor subunits expression in tissues of gilts during the late gestation

GABA(Aα1) and GABA(B1) receptor subunits are responsible for most behavioral, physiological and pharmacological effects of GABA receptors. We investigated the expression of GABA(Aα1) and GABA(B1) receptor subunits in different tissues of gilts during late pregnancy in hot summer. The mRNA abundance of GABA(Aα1) receptor subunit in different tissues of gilts at d 90 and d 110 of gestation was as follows: d 90: brain > lung > liver > ovary > spleen > kidney > heart; d 110: brain > lung > spleen > liver > ovary > kidney > heart. And, the mRNA abundance of GABA(B1) receptor subunit was as follows: d 90: spleen > lung > brain > kidney > ovary > liver > heart; d 110: spleen > lung > kidney > brain > ovary > liver > heart. The results in this trial indicated that the GABA(Aα1) receptor subunit was abundantly expressed in brain, while GABA(B1) receptor subunit was abundant in spleen and lung of gilts during late gestation. There were no gestation stage-dependent effects on GABA(Aα1) and GABA(B1) receptor subunits expression in all tissues.

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.

Anxioselective anxiolytics: on a quest for the Holy Grail

The discovery of benzodiazepine receptors provided the impetus to discover and develop anxioselective anxiolytics ('Valium without the side effects'). The market potential for an anxioselective based on the γ-aminobutyric acid A (GABA(A)) receptor resulted in clinical trials of multiple compounds. In contrast to the anxioselective profile displayed in preclinical models, compounds such as bretazenil, TPA023, and MRK 409 produced benzodiazepine-like side effects (sedation, dizziness) in Phase I studies, whereas alpidem and ocinaplon exhibited many of the characteristics of an anxioselective in the clinic. Alpidem was briefly marketed for the treatment of anxiety, but was withdrawn because of liver toxicity. Reversible elevations in liver enzymes halted development of ocinaplon in Phase III. The clinical profiles of these two molecules demonstrate that it is possible to develop GABA(A) receptor-based anxioselectives. However, despite the formidable molecular toolbox at our disposal, we are no better informed about the GABA(A) receptors responsible for an anxioselective profile in the clinic. Here, I discuss the evolution of a quest, spanning four decades, for molecules that retain the rapid and robust anti-anxiety actions of benzodiazepines without the side effects that limit their usefulness.

A novel GABA(A) receptor pharmacology: drugs interacting with the α(+) β(-) interface

GABA(A) receptors are ligand-gated chloride channels composed of five subunits that can belong to different subunit classes. The existence of 19 different subunits gives rise to a multiplicity of GABA(A) receptor subtypes with distinct subunit composition; regional, cellular and subcellular distribution; and pharmacology. Most of these receptors are composed of two α, two β and one γ2 subunits. GABA(A) receptors are the site of action of a variety of pharmacologically and clinically important drugs, such as benzodiazepines, barbiturates, neuroactive steroids, anaesthetics and convulsants. Whereas GABA acts at the two extracellular β(+) α(-) interfaces of GABA(A) receptors, the allosteric modulatory benzodiazepines interact with the extracellular α(+) γ2(-) interface. In contrast, barbiturates, neuroactive steroids and anaesthetics seem to interact with solvent accessible pockets in the transmembrane domain. Several benzodiazepine site ligands have been identified that selectively interact with GABA(A) receptor subtypes containing α2βγ2, α3βγ2 or α5βγ2 subunits. This indicates that the different α subunit types present in these receptors convey sufficient structural differences to the benzodiazepine binding site to allow specific interaction with certain benzodiazepine site ligands. Recently, a novel drug binding site was identified at the α(+) β(-) interface. This binding site is homologous to the benzodiazepine binding site at the α(+) γ2(-) interface and is thus also strongly influenced by the type of α subunit present in the receptor. Drugs interacting with this binding site cannot directly activate but only allosterically modulate GABA(A) receptors. The possible importance of such drugs addressing a spectrum of receptor subtypes completely different from that of benzodiazepines is discussed.

β-adrenergic signaling regulates evolutionarily derived sleep loss in the Mexican cavefish

Sleep is a fundamental behavior exhibited almost universally throughout the animal kingdom. The required amount and circadian timing of sleep differs greatly between species in accordance with habitats and evolutionary history. The Mexican blind cavefish, Astyanax mexicanus, is a model organism for the study of adaptive morphological and behavioral traits. In addition to loss of eyes and pigmentation, cave populations of A. mexicanus exhibit evolutionarily derived sleep loss and increased vibration attraction behavior, presumably to cope with a nutrient-poor environment. Understanding the neural mechanisms of evolutionarily derived sleep loss in this system may reveal critical insights into the regulation of sleep in vertebrates. Here we report that blockade of β-adrenergic receptors with propranolol rescues the decreased-sleep phenotype of cavefish. This effect was not seen with α-adrenergic antagonists. Treatment with selective β1-, β2-, and β3-antagonists revealed that the increased sleep observed with propranolol could partially be explained via the β1-adrenergic system. Morphological analysis of catecholamine circuitry revealed conservation of gross catecholaminergic neuroanatomy between surface and cave morphs. Taken together, these findings suggest that evolutionarily derived changes in adrenergic signaling underlie the reduced sleep of cave populations.

α2-containing GABA(A) receptors: a target for the development of novel treatment strategies for CNS disorders

GABA(A) receptors have important physiological functions, as revealed by pharmacological studies and experiments involving gene-targeted mouse models, and are the target of widely used drugs such as the benzodiazepines. In this review, we are summarizing current knowledge about the function of α2-containing GABA(A) receptors, a receptor subtype representing approximately 15-20% of all GABA(A) receptors. This receptor subtype mediates anxiolytic-like, reward-enhancing, and antihyperalgesic actions of diazepam, and has antidepressant-like properties. Secondary insufficiency of α2-containing GABA(A) receptors has been postulated to play a role in the pathogenesis of schizophrenia, and may be involved in cognitive impairment in other disorders. Moreover, polymorphisms in the GABRA2 gene encoding the GABA(A) receptor α2 subunit have been found to be linked to chronic alcohol dependence and to polydrug abuse. Thus, α2-containing GABA(A) receptors are involved in the regulation and/or modulation of emotional behaviors and of chronic pain, and appear to be a valid target for novel therapeutic approaches for the treatment of anxiety, depression, schizophrenia and chronic pain.

Magnolol, a major bioactive constituent of the bark of Magnolia officinalis, induces sleep via the benzodiazepine site of GABA(A) receptor in mice

Magnolol (6,6',7,12-tetramethoxy-2,2'-dimethyl-1-beta-berbaman, C(18)H(18)O(2)), an active ingredient of the bark of Magnolia officinalis, has been reported to exert potent anti-epileptic effects via the GABA(A) receptor. The receptor also mediates sleep in humans and animals. The aim of this study was to determine whether magnolol could modulate sleep behaviors by recording EEG and electromyogram in mice. The results showed that magnolol administered i.p. at a dose of 5 or 25 mg/kg could significantly shorten the sleep latency, increase the amount of non-rapid eye movement (non-REM, NREM) and rapid eye movement (REM) sleep for 3 h after administration with an increase in the number of NREM and REM sleep episodes. Magnolol at doses of 5 and 25 mg/kg increased the number of bouts of wakefulness but decreased their duration. On the other hand, magnolol increased the number of state transitions from wakefulness to NREM sleep and subsequently from NREM sleep to wakefulness. Immunohistochemical study showed that magnolol increased c-Fos expression in the neurons of ventrolateral preoptic area, a sleep center in the anterior hypothalamus, and decreased c-Fos expression in the arousal tuberomammillary nucleus, which was located in the caudolateral hypothalamus. The sleep-promoting effects and changes in c-Fos induced by magnolol were reversed by flumazenil, an antagonist at the benzodiazepine site of the GABA(A) receptor. These results indicate that magnolol increased NREM and REM sleep via the GABA(A) receptor.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

NHBA isolated from Gastrodia elata exerts sedative and hypnotic effects in sodium pentobarbital-treated mice

The rhizomes of Gastrodia elata have been used for the treatment of insomnia in oriental countries. N⁶-(4-hydroxybenzyl) adenine riboside (NHBA) was originally isolated from G. elata. For the first time we report a detailed study on the effects and mechanisms of NHBA on its sedative and hypnotic activity. Adenosine, an endogenous sleep factor, regulates sleep-wake cycle via interacting with adenosine A₁/A(2A) receptors. Using radioligand binding studies and cAMP accumulation assays, our results show that NHBA may be a functional ligand for the adenosine A₁ and A(2A) receptors. NHBA significantly decreases spontaneous locomotor activity and potentiates the hypnotic effect of sodium pentobarbital in mice. Sleep architecture analyses reveal that NHBA significantly decreases wakefulness time and increases NREM sleep times. However, NHBA does not affect the amount of REM sleep. Pretreatment with the adenosine A₁ receptor antagonist DPCPX or the A(2A) receptor antagonist SCH 58261 significantly reverses the increase in sleeping time induced by NHBA in sodium pentobarbital treated mice. Immunohistochemical studies show that NHBA increases c-Fos expression in GABAergic neurons of the ventrolateral preoptic area (VLPO), which suggests that NHBA activates the sleep center in the anterior hypothalamus. Altogether, these results indicate that NHBA produces significant sedative and hypnotic effects. Such effects might be mediated by the activation of adenosine A₁/A(2A) receptors and stimulation of the sleep center VLPO.

Enhancement of pentobarbital-induced sleep by apigenin through chloride ion channel activation

This experiment was performed to investigate whether apigenin has hypnotic effects and/or enhances pentobarbital-induced sleep behaviors through the GABAergic systems. Apigenin prolonged sleep time induced by pentobarbital similar to muscimol, a GABA(A) receptors agonist. Apigenin also increased sleep rate and sleep time in the combined administration with pentobarbital at the sub-hypnotic dosage, and showed synergic effects with muscimol in potentiating sleep onset and enhancing sleep time induced by pentobarbital. In addition, both of apigeinin and pentobarbital increased chloride influx in primary cultured cerebellar granule cells. Apigenin increased glutamate decarboxylase (GAD) and had no effect on the expression of GABA(A) receptor α-, β-, γ-subunits in n hippocampus of mouse brain, showing different expression of subunits from pentobarbital treatment group. In conclusion, it is suggested that apigenin augments pentobarbital-induced sleep behaviors through chloride ion channel activation.

Evidence for a role of inhibition of orexinergic neurons in the anxiolytic and sedative effects of diazepam: A c-Fos study

The classical benzodiazepine diazepam (DZ) induces anxiolysis at low doses and sedation and hypnosis at higher doses. Different brain areas and neuronal populations most likely mediate these different behavioral effects. We used c-Fos immunohistochemistry as an indirect way to study neuronal activation or inhibition induced by DZ at anxiolytic and sedative doses (0.5 and 5mg/kg, respectively) in various brain areas involved in anxiety, arousal, sedation and addiction in C57BL/6J mice. We also focused on the two neuronal populations, orexinergic and dopaminergic neuronal populations, with the help of double-immunohistochemistry using c-Fos and orexin-A antibodies and c-Fos and tyrosine hydroxylase antibodies. We found that different brain areas of unhabituated mice reacted differently to the mild stress induced by vehicle injection. Also the response to anxiolytic or sedative doses of DZ differed between the areas, suggesting that distinct brain areas mediate the behavioral effects of low and high DZ doses. Our findings propose a role for inhibition of orexin neurons in the anxiolytic and sleep-promoting effects of DZ. In addition, the activation of central amygdala neurons by DZ treatment was associated with anxiolytic and sedative effects. On the other hand, the ventral hippocampus, basolateral amygdala, ventral tegmental area and prefrontal cortex were sensitive even to the mild injection stress, but not to the anxiolytic dose of DZ.

Sedation and sleep disturbances in the ICU

Sedation in the ICU is, paradoxically, both a cause and a potential treatment for the sleep disruption almost universally observed in the critically ill. A patient-focused sedation strategy that minimizes unnecessary medication, avoids medication withdrawal, addresses the specific impediments to sleep, and serves as an adjunct to attentive environmental control may ultimately serve patients best.

A Comparison of the α2/3/5 Selective Positive Allosteric Modulators L-838,417 and TPA023 in Preclinical Models of Inflammatory and Neuropathic Pain

GABA(A) receptors containing α2/3 subunits are current targets in the battle to develop new pain medications, as they are expressed in the spinal cord where increasing inhibitory drive should result in analgesia. However, this approach is prone to a range of side effects including sedation, cognitive impairment, and abuse as a consequence of the widespread influence of GABA. The ability to make subtype selective low-efficacy benzodiazepine compounds, which potentiate the action of GABA at specific α subunits, has the potential to reduce this side effect profile. In this study, we have investigated the effects of the medium-efficacy positive allosteric modulator (PAM) L-838,417 and the low-efficacy PAM TPA023 in a number of preclinical inflammatory and neuropathic pain models. We conclude that either the higher level of efficacy at α2/3 or efficacy at α5 is required for compounds to have a significant analgesic effect in a range of models, and, therefore, although the side-effect profile of compounds can be reduced compared to typical benzodiazepines, it is unlikely that it can be completely eliminated.

Anaesthetic potency of diazepam is resistant to cholinergic overstimulation

Patients suffering from organophosphorus intoxication are compromised by generalised seizures and respiratory insufficiency, either being potentially lethal. In these patients induction of general anaesthesia to allow artificial ventilation is an important therapeutic option. Previously, it has been demonstrated that cholinergic overstimulation impaired network depressing effects of etomidate and sevoflurane. In this study we tested the impact of cholinergic overstimulation on inhibitory effects of diazepam in organotypic slice cultures of cerebrocortical neurons. Effects of clinically relevant concentrations of diazepam on spontaneous action potential activity were assessed by extracellular action potential recordings under basal cholinergic tone as well as in the presence of acetylcholine (1 μM). Diazepam at anaesthetic concentrations (25-500 μM) impeded spontaneous network activity in a concentration dependent manner (EC₅₀ 80.5±8.0 μM). In the presence of 1 μM acetylcholine the potency of diazepam was not significantly altered (EC₅₀ 83.6±8.4 μM). The results demonstrate that the potency of diazepam to depress neocortical network-excitability is not significantly impaired by cholinergic overstimulation. Diazepam thereby differs from other anaesthetics like etomidate or sevoflurane whose potencies and efficacies were severely attenuated. Hence diazepam might be preferable for induction and maintenance of general anaesthesia in patients suffering from nerve agent intoxication.

Absence of tolerance to the anticonvulsant and neuroprotective effects of imidazenil against DFP-induced seizure and neuronal damage

The clinical use of diazepam or midazolam to control organophosphate (OP) nerve agent-induced seizure activity is limited by their unwanted effects including sedation, amnesia, withdrawal, and anticonvulsant tolerance. Imidazenil is an imidazo-benzodiazepine derivative with high intrinsic efficacy and selectivity for α2-, α3-, and α5- but low intrinsic efficacy for α1-containing GABA(A) receptors. We have previously shown that imidazenil is more efficacious than diazepam at protecting rats and mice from diisopropyl fluorophosphate (DFP)-induced seizures and neuronal damage without producing sedation. In the present study, we compared the tolerance liability of imidazenil and diazepam to attenuate the seizure activity and neurotoxic effects of DFP. Rats received protracted (14 days) oral treatment with increasing doses of imidazenil (1-4 mg/kg), diazepam (5-20 mg/kg), or vehicle. Eighteen hours after the last dose of the protracted treatment schedule, rats were tested for anticonvulsant tolerance after a 30 min pretreatment with a single test dose of imidazenil (0.5 mg/kg) or diazepam (5 mg/kg) prior to a DFP challenge (1.5 mg/kg). The anticonvulsant (modified Racine score scale) and neuroprotective (fluoro-jade B staining) effects of diazepam were significantly reduced in protracted diazepam-treated animals whereas the effects of imidazenil were not altered in protracted imidazenil-treated animals. The present findings indicate that protracted imidazenil treatment does not produce tolerance to its protective action against the neurotoxic effects of OP exposure.

Beyond classical benzodiazepines: novel therapeutic potential of GABAA receptor subtypes

GABA(A) (γ-aminobutyric acid, type A) receptors are a family of ligand-gated ion channels that are essential for the regulation of central nervous system function. Benzodiazepines - which non-selectively target GABA(A) receptors containing the α1, α2, α3 or α5 subunits - have been in clinical use for decades and are still among the most widely prescribed drugs for the treatment of insomnia and anxiety disorders. However, their use is limited by side effects and the risk of drug dependence. In the past decade, the identification of separable key functions of GABA(A) receptor subtypes suggests that receptor subtype-selective compounds could overcome the limitations of classical benzodiazepines; furthermore, they might be valuable for novel indications such as chronic pain, depression, schizophrenia, cognitive enhancement and stroke.

Context dependent benzodiazepine modulation of GABA(A) receptor opening frequency

The anxiolytic, hypnotic, and anti-convulsant properties of benzodiazepines (BDZs) require modulation of distinct GABA_A receptor α-subtypes. BDZ modulation of GABA_A receptors is often described in terms of increased opening frequency, and contrasted with the increased open durations occurring with barbiturate modulation. Several studies spanning single channel, rapid kinetic, and whole cell techniques have suggested that BDZs effect this observed change in frequency through increased affinity for GABA. BDZ-sensitive αβγ isoforms exist at extrasynaptic as well as synaptic locations, where they encounter markedly different concentration and time-course of GABA exposure. Interestingly, this affinity-based mechanism (specifically, decreasing the GABA unbinding rate) is only predicted to increase opening frequency under conditions that allow the unbinding and rebinding cycles typical of prolonged exposure to low GABA concentrations, which are more likely to occur at extrasynaptic GABA_A receptors. In contrast, when rebinding is less likely, such as may occur in certain synaptic conditions, the number, but not the frequency, of channel openings increases in response to BDZ modulation. In conclusion, not only can multiple kinetic mechanisms alter channel opening frequency, but a single mechanism – increased affinity – impacts opening frequency differently under different contexts of GABA_A receptor activation.

Ethanol Extract of the Flower Chrysanthemum morifolium Augments Pentobarbital-Induced Sleep Behaviors: Involvement of Cl Channel Activation

Dried Chrysanthemum morifolium flowers have traditionally been used in Korea for the treatment of insomnia. This study was performed to investigate whether the ethanol extract of Chrysanthemum morifolium flowers (EFC) enhances pentobarbital-induced sleep behaviors. EFC prolonged sleep time induced by pentobarbital similar to muscimol, a GABA_A receptors agonist. EFC also increased sleep rate and sleep time when administrated with pentobarbital at a subhypnotic dosage. Both EFC and pentobarbital increased chloride (Cl⁻) influx in primary cultured cerebellar granule cells. EFC increased glutamic acid decarboxylase (GAD) expression levels, but had no effect on the expression of α1-, β2-, and γ2-subunits of the GABA_A receptor in the hippocampus of a mouse brain. This is in contrast to treatment with pentobarbital, which showed decreased α1-subunit expression and no change in GAD expression. In conclusion, EFC augments pentobarbital-induced sleep behaviors; these effects may result from Cl⁻ channel activation.

Quantitative analyses of [¹¹C]Ro15-4513 binding to subunits of GABAA/benzodiazepine receptor in the living human brain

BACKGROUND

Gamma-aminobutyric acid (GABA)A/benzodiazepine (BZ) receptor chloride channel consists of several subunits. The diversity of the α subunits results in the various ligand selectivity and functionally different properties of the GABAA/BZ receptor. Although [¹¹C] Ro15-4513 is reported to be a radioligand that has relatively high affinity for α5 subunit-containing GABAA/BZ receptor, it remained to be evaluated fully.

AIM

The aim of this study was to evaluate the quantitative analyses of [¹¹C]Ro15-4513 in the living human brain.

METHODS

Positron emission tomography examinations were performed in eight healthy male volunteers after intravenous injection of [¹¹C]Ro15-4513. Kinetic analysis of data was performed with the two-compartment and three-compartment models using arterial input function. Linear graphical analysis and the simplified reference tissue model analysis (SRTM) were also performed using pons as a reference region. In a simulation study, the effects of noise to the estimation of binding potentials were evaluated.

RESULTS

The accumulation of [¹¹C]Ro15-4513 in the limbic system was relatively higher than in other cortex. The bindings were well described by the three-compartment model in the regions with specific binding. Binding potentials obtained from the graphical method and SRTM correlated well with those obtained from the three-compartment model. In the simulation study, estimated parameters from SRTM were less affected by noise compared with those from the graphical method.

CONCLUSION

The reference tissue methods using pons as a reference region can be used for quantitative analysis of [¹¹C]Ro15-4513 binding. SRTM seemed less susceptible to noise than does graphical analysis.

Contribution of sedative-hypnotic agents to delirium via modulation of the sleep pathway

Purpose

To review the mechanisms of sedative-hypnotic action with respect to the risk of delirium imparted by drugs that act on γ-amino-butyric-acid type A receptors or α₂ adrenoceptors.

Source

MEDLINE was searched for relevant articles.

Principal findings

Development of the acute confusional state of delirium is associated with longer intensive care unit (ICU) and hospital lengths of stay, significantly higher risk of functional decline, and increased mortality. Disruption of sleep is a modifiable risk factor that may contribute to delirium and cognitive dysfunction in ICU patients. Among the functions of sleep are repair of defective processes and restoration of the brain to a state in which it is ready to acquire new knowledge. It is logical that disruption of these processes may produce acute confusion. Delirium develops through a complex interaction between the patient’s baseline vulnerability (patient’s predisposing risk factors before hospitalization) and precipitating factors or insults (modifiable events that occur during hospitalization). The latter factors include both sleep disruption and sedation. We present a hypothesis that these two factors are causally linked through effects on memory. Our hypothesis explains why patients randomized to receive an α₂ adrenoceptor agonist are less likely to develop delirium (and the attendant cognitive dysfunction) than those randomized to receive benzodiazepines.

Conclusion

Herein we present our hypothesis that alternate mechanisms of hypnotic action may differentiate the deleriogenic properties of the two classes of sedatives. Future studies should focus on whether a causal relationship can be established between sedative administration, sleep disruption, and delirium.

Searching for perfect sleep: the continuing evolution of GABAA receptor modulators as hypnotics

The non-benzodiazepine GABA(A) receptor modulators ('Z-drugs') - zaleplon, zolpidem, zopiclone and eszopiclone - have become the accepted treatments for insomnia where they are available. However, recent randomized, placebo-controlled trials suggest that, for these drugs, there may be particular efficacy and tolerability profiles and distinct clinical outcomes in specific patient populations. This is particularly apparent when hypnotic/ selective serotonin reuptake inhibitor co-therapy is used to treat patients with co-morbid insomnia and psychiatric disorders, as patient recovery appears to be accelerated and enhanced by some drugs but not others. Emerging evidence of why this should be the case is that these hypnotic drugs may differ significantly from each other in their pharmacodynamic and pharmacokinetic profiles. Functional selectivity for specific GABA(A) receptor subtypes may determine each drug's clinical attributes, while the pharmacokinetic characteristics of Z-drugs also determine to a large extent how they perform in the clinic. For example, activity at GABA(A) alpha 1 receptor subtypes may be associated with sedative effects, whereas activity at alpha 2 and alpha 3 receptor subtypes may be associated with anxiolytic and antidepressant effects. In summary, the distinct clinical outcomes of zaleplon, zolpidem, zopiclone and eszopiclone may be explained by each drug's unique GABA(A) receptor subunit selectivity and pharmacokinetic profile. Further investigation of GABA( A) receptor subtype effects would help to increase understanding of current hypnotic drug effects, while knowledge of each drug's specific binding profile should enable clinicians to tailor treatment to individual patient's needs.

Benzodiazepine receptor agonists cause drug-specific and state-specific alterations in EEG power and acetylcholine release in rat pontine reticular formation

STUDY OBJECTIVES

Benzodiazepine (BDZ) and non-benzodiazepine (NBDZ) hypnotics enhance GABAergic transmission and are widely used for the treatment of insomnia. In the pontine reticular formation (PRF), GABA inhibits rapid eye movement (REM) sleep and acetylcholine (ACh) release. No previous studies have characterized the effects of BDZ and NBDZ hypnotics on ACh release in the PRF. This study tested 2 hypotheses: (1) that microdialysis delivery of zolpidem, eszopiclone, and diazepam to rat PRF alters ACh release in PRF and electroencephalographic (EEG) delta power and (2) that intravenous (i.v.) administration of eszopiclone to non-anesthetized rat alters ACh release in the PRF, sleep, and EEG delta power.

DESIGN

A within- and between-groups experimental design.

SETTING

University of Michigan.

PATIENTS OR PARTICIPANTS

Adult male Crl:CD*(SD) (Sprague-Dawley) rats (n = 57).

INTERVENTIONS

In vivo microdialysis of the PRF in rats anesthetized with isoflurane was used to derive the concentration-response effects of zolpidem, eszopiclone, and diazepam on ACh release. Chronically instrumented rats were used to quantify the effects of eszopiclone (3 mg/kg, i.v.) on ACh release in the PRF, sleep-wake states, and cortical EEG power.

MEASUREMENTS AND RESULTS

ACh release was significantly increased by microdialysis delivery to the PRF of zolpidem and eszopiclone but not diazepam. EEG delta power was increased by zolpidem and diazepam but not by eszopiclone administered to the PRF. Eszopiclone (i.v.) decreased ACh release in the PRF of both anesthetized and non-anesthetized rats. Eszopiclone (i.v.) prevented REM sleep and increased EEG delta power.

CONCLUSION

The concentration-response data provide the first functional evidence that multiple GABA(A) receptor subtypes are present in rat PRF. Intravenously administered eszopiclone prevented REM sleep, decreased ACh release in the PRF, and increased EEG delta power. The effects of eszopiclone are consistent with evidence that ACh release in the PRF is lower during NREM sleep than during REM sleep, and with data showing that cholinergic stimulation of the PRF activates the cortical EEG.

Genetic analysis of sleep

Almost 20 years ago, the gene underlying fatal familial insomnia was discovered, and first suggested the concept that a single gene can regulate sleep. In the two decades since, there have been many advances in the field of behavioral genetics, but it is only in the past 10 years that the genetic analysis of sleep has emerged as an important discipline. Major findings include the discovery of a single gene underlying the sleep disorder narcolepsy, and identification of loci that make quantitative contributions to sleep characteristics. The sleep field has also expanded its focus from mammalian model organisms to Drosophila, zebrafish, and worms, which is allowing the application of novel genetic approaches. Researchers have undertaken large-scale screens to identify new genes that regulate sleep, and are also probing questions of sleep circuitry and sleep function on a molecular level. As genetic tools continue to be refined in each model organism, the genes that support a specific function in sleep will become more apparent. Thus, while our understanding of sleep still remains rudimentary, rapid progress is expected from these recently initiated studies.

Role of GABAA receptors in cognition

Complex brains have developed specialized mechanisms for the grouping of principal cells into temporal coalitions of local or distant networks: the inhibitory interneuron ‘clocking’ networks. They consist of GABAergic (where GABA is γ-aminobutyric acid) interneurons of a rich diversity. In cortical circuits, these neurons control spike timing of the principal cells, sculpt neuronal rhythms, select cell assemblies and implement brain states. On the basis of these considerations, the deficits in cognition, emotion and perception in psychiatric disorders such as anxiety, depression or schizophrenia are considered to manifest themselves through a dysregulation of the inhibitory interneuron ‘clocking’ network as a final common denominator, irrespective of the diverse underlying disease pathologies. The diversity of GABAergic interneurons is paralleled by a corresponding diversity of GABAA receptors in network regulation. The region-, cell- and domain-specific location of these receptor subtypes offers the possibility to gain functional insights into the role of behaviourally relevant neuronal circuits. Using genetic manipulation, the regulation of anxiety behaviour was attributed to neuronal circuits characterized by the expression of α2-GABAA receptors. Neurons expressing α3-GABAA receptors, located mainly in aminergic and basal forebrain cholinergic neurons, were related to a hyperdopaminergic phenotype, typical of schizophrenic symptoms. Temporal and spatial memory were selectively modulated by extrasynaptic α5-GABAA receptors. Chronic pathological pain was under the regulation of spinal and cortical α2- (and α3-) GABAA receptors. Thus the relevance of the diversity of inhibitory GABAA receptor subtypes for the regulation of cognition, emotion and memory is increasingly being recognized. The clinical proof-of-concept of a subtype-specific pharmacology is most advanced for the alleviation of cognitive dysfunctions in schizophrenia, based on the treatment of patients with an α2/α3-GABAA receptor ligand.

Sedation and sleep disturbances in the ICU

The need for compassionate care of the critically ill often compels clinicians to treat these patients with pharmacologic sedation. Although patients may appear to be asleep under the influence of these sedating medications, the relationship between sleep and sedation is complex and not fully understood. These medications exert their effects at different points along the central nervous system's natural sleep pathway, leading to similarities and differences between the two states. This relationship is important because critically ill patients sleep poorly and this phenomenon has been linked to poor intensive care unit outcomes. Therefore, greater awareness of the effects of these medications on sleep may lead to sedation protocols that further improve outcomes. This article reviews the relationship between sedation and sleep from physiologic and clinical perspectives.

Discovery of 1-[1-(1-methylcyclooctyl)-4-piperidinyl]-2-[(3R)-3-piperidinyl]-1H-benzimidazole: integrated drug-design and structure-activity relationships for orally potent, metabolically stable and potential-risk reduced novel non-peptide nociceptin/orphanin FQ receptor agonist as antianxiety drug

Anxiety disorders, caused by continuous or acute stress or fear, have been highly prevailing psychiatric disorders. For the acute treatment of the disorders, benzodiazepines have been widely used despite having liabilities that limit their utility. Alternatively, endogenous nociceptin/orphanin FQ and nociceptin/orphanin FQ peptide receptor (or opioid-receptor-like-1 receptor) have important roles in the integration of emotional components, e.g. anxiolytic activity is the key behavioral action of nociceptin/orphanin FQ in brain. In our preceding study, various structurally novel 1,2-disubstituted benzimidazole derivatives were designed and synthesized as highly potent nociceptin/orphanin FQ peptide receptor selective full agonists in vitro with high or moderate nociceptin/orphanin FQ peptide receptor occupancy in the mice brain per os based on appropriate physicochemical properties for the oral brain activity [Hayashi et al. (2009) J Med Chem;52:610-625]. In the present study, drug design and structure-activity relationships for Vogel anticonflict activities in mice per os, metabolic stabilities in human liver microsome, CYP2D6 inhibitions, serum protein bindings, and human ether-a-go-go related gene binding affinities of novel nociceptin/orphanin FQ peptide receptor agonists were investigated. Through the series of coherent drug discovery studies, the strongest nociceptin/orphanin FQ peptide receptor agonist, 1-[1-(1-methylcyclooctyl)-4-piperidinyl]-2-[(3R)-3-piperidinyl]-1H-benzimidazole was designed and identified as a new-class orally potent anxiolytic with little side-effects, as significant findings.