Sleep Homeostatic and Waking Behavioral Phenotypes in Egr3-Deficient Mice Associated with Serotonin Receptor 5-HT2 Deficits

Effects of clozapine-N-oxide and compound 21 on sleep in laboratory mice

Designer receptors exclusively activated by designer drugs (DREADDs) are chemogenetic tools for remote control of targeted cell populations using chemical actuators that bind to modified receptors. Despite the popularity of DREADDs in neuroscience and sleep research, potential effects of the DREADD actuator clozapine-N-oxide (CNO) on sleep have never been systematically tested. Here, we show that intraperitoneal injections of commonly used CNO doses (1, 5, and 10 mg/kg) alter sleep in wild-type male laboratory mice. Using electroencephalography (EEG) and electromyography (EMG) to analyse sleep, we found a dose-dependent suppression of rapid eye movement (REM) sleep, changes in EEG spectral power during non-REM (NREM) sleep, and altered sleep architecture in a pattern previously reported for clozapine. Effects of CNO on sleep could arise from back-metabolism to clozapine or binding to endogenous neurotransmitter receptors. Interestingly, we found that the novel DREADD actuator, compound 21 (C21, 3 mg/kg), similarly modulates sleep despite a lack of back-metabolism to clozapine. Our results demonstrate that both CNO and C21 can modulate sleep of mice not expressing DREADD receptors. This implies that back-metabolism to clozapine is not the sole mechanism underlying side effects of chemogenetic actuators. Therefore, any chemogenetic experiment should include a DREADD-free control group injected with the same CNO, C21, or newly developed actuator. We suggest that electrophysiological sleep assessment could serve as a sensitive tool to test the biological inertness of novel chemogenetic actuators.

Utilizing network pharmacology and experimental validation to explore the potential molecular mechanisms of BanXia-YiYiRen in treating insomnia

BanXia-YiYiRen (Pinellia Ternata and Coix Seed, BX-YYR) has been clinically proven to be an effective Chinese medicine compatible with the treatment of insomnia. However, the underlying mechanism of BX-YYR against insomnia remains unclear. This study aimed to explore the pharmacological mechanisms of BX-YYR in treating insomnia based on network pharmacology and experimental validation. The drug-disease targets were obtained using publicly available databases. The analysis revealed 21 active compounds and 101 potential targets of BX-YYR from the pharmacological database of Chinese medicine system and analysis platform (TCMSP) and 1020 related targets of insomnia from the GeneCards and Online Mendelian Inheritance in Man (OMIM) databases. Furthermore, 38 common targets of BX-YYR against insomnia were identified, and these common targets were used to construct a protein–protein interaction (PPI) network. The visual PPI network was constructed by Cytoscape software. The top three genes from PPI according to degree value are FOS, AKT1, and CASP3. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were applied to reveal the potential targets and signaling pathways involved in BX-YYR against insomnia, especially the serotonergic pathway. In addition, molecular docking revealed that baicalein, beta-sitosterol, and stigmasterol displayed strong binding to AKT1, FOS, PRKCA, and VEGFA. Experimental study found that BX-YYR against insomnia might play a role in improving sleep by modulating the serotonergic pathway. In summary, our findings revealed the underlying mechanism of BX-YYR against insomnia and provided an objective basis for further experimental study and clinical application.

Changes in Locomotor Activity and Oxidative Stress-Related Factors after the Administration of an Amino Acid Mixture by Generation and Age

Amino acids, as nutrients, are expected to improve sleep disorders. This study aimed to evaluate the generation- and age-dependent sleep-improving effects of γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP) coadministration. The differentially expressed genes and generation-related behavior after the administration of a GABA/5-HTP mixture were measured in a Drosophila model, while age-related changes in gene expression and oxidative stress-related parameters were measured in a mouse model. The GABA/5-HTP-treated group showed significant behavioral changes compared to the other groups. Sequencing revealed that the GABA/5-HTP mixture influenced changes in nervous system-related genes, including those involved in the regulation of the expression of behavioral and synaptic genes. Additionally, total sleep time increased with age, and nighttime sleep time in the first- and third-generation flies was significantly different from that of the control groups. The GABA/5-HTP mixture induced significant changes in the expression of sleep-related receptors in both models. Furthermore, the GABA/5-HTP mixture reduced levels of ROS and ROS reaction products in an age-dependent manner. Therefore, the increase in behavioral changes caused by GABA/5-HTP mixture administration was effective in eliminating ROS activity across generations and ages.

A review of the current state of knowledge on sex differences in sleep and circadian phenotypes in rodents

Sleep is a vital part of our lives as it is required to maintain health and optimal cognition. In humans, sex differences are relatively well-established for many sleep phenotypes. However, precise differences in sleep phenotypes between male and female rodents are less documented. The main goal of this article is to review sex differences in sleep architecture and electroencephalographic (EEG) activity during wakefulness and sleep in rodents. The effects of acute sleep deprivation on sleep duration and EEG activity in male and female rodents will also be covered, in addition to sex differences in specific circadian phenotypes. When possible, the contribution of the female estrous cycle to the observed differences between males and females will be described. In general, male rodents spend more time in non-rapid eye movement sleep (NREMS) in comparison to females, while other differences between sexes in sleep phenotypes are species- and estrous cycle phase-dependent. Altogether, the review illustrates the need for a sex-based perspective in basic sleep and circadian research, including the consideration of sex chromosomes and gonadal hormones in sleep and circadian phenotypes.

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In rodents, males spend less time awake, and more time in NREMS than females.

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The recovery from sleep deprivation is also dependent on biological sex.

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Gonadal hormones modulate sleep and circadian phenotypes in rodents.

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A more systematic comparison of sex in basic sleep/circadian research is needed.

Are Circadian Disturbances a Core Pathophysiological Component of Schizophrenia?

Schizophrenia is a multifactorial disorder caused by a combination of genetic variations and exposure to environmental insults. Sleep and circadian rhythm disturbances are a prominent and ubiquitous feature of many psychiatric disorders, including schizophrenia. There is growing interest in uncovering the mechanistic link between schizophrenia and circadian rhythms, which may directly affect disorder outcomes. In this review, we explore the interaction between schizophrenia and circadian rhythms from 2 complementary angles. First, we review evidence that sleep and circadian rhythm disturbances constitute a fundamental component of schizophrenia, as supported by both human studies and animal models with genetic mutations related to schizophrenia. Second, we discuss the idea that circadian rhythm disruption interacts with existing risk factors for schizophrenia to promote schizophrenia-relevant behavioral and neurobiological abnormalities. Understanding the mechanistic link between schizophrenia and circadian rhythms will have implications for mitigating risk to the disorder and informing the development of circadian-based therapies.

Inhibition of NR2B-containing NMDA receptors during nitrogen narcosis

INTRODUCTION

When humans breathe compressed air or N₂-O₂ mixtures at three to four atmospheres pressure, they will experience nitrogen narcosis that may possibly lead to a diving accident, but the underlying mechanisms remain unclear.

METHODS

Mice were exposed to 1.6 MPa breathing a N₂-O₂ mixture adjusted to deliver an inspired PO₂ of 32-42 kPa. The electroencephalogram (EEG) and forced swimming test were used to evaluate the narcotic effect of nitrogen. Neuronal activity was observed via c-Fos expression in cortex and hippocampus tissue after decompressing to the surface. To further investigate underlying molecular mechanisms, we incubated cultured hippocampal neurons with various NMDA concentrations, and measured expression of NMDA receptors and its down-stream signal with or without 1.6 MPa N₂-O₂ exposure.

RESULTS

Both the frequency of the EEG and the drowning time using the forced swimming test were significantly decreased during exposure to 1.6 MPa N₂-O₂ (P < 0.001). Additionally, in cultured hippocampal neurons, the increased levels of phosphorylated NR2B and cAMP-response element binding protein (CREB) induced by NMDA stimulation were significantly inhibited by exposure to 1.6 MPa N₂-O₂.

CONCLUSIONS

Our findings indicated that NR2B-containing NMDA receptors were inhibited during nitrogen narcosis.

Sleep disruption elevates oxidative stress in parvalbumin-positive cells of the rat cerebral cortex

We used a novel automated sleep disruption (SD) apparatus to determine the impact of SD on sleep and molecular markers of oxidative stress in parvalbumin (PV) neurons in the rat prefrontal cortex (PFC). Rats were subjected to two 6 hr SD sessions from zeitgeber time (ZT) 0 to ZT6, one by the gentle handling method and the other by an automated agitator running the length of the rat's home cage floor (a novel SD method). The same rats were later subjected to a 12 hr SD session from ZT0 to ZT12. Sleep was disrupted with both methods, although rats slept less during gentle handling than during the automated condition. Immediately after both SD sessions, rats displayed compensatory sleep characterized by elevated slow-wave activity. We measured in the prelimbic prefrontal cortex (prelimbic PFC; 6 and 12 hr SD) and orbital frontal cortex (12 hr SD) the intensity of the oxidative stress marker, 8-oxo-2'-deoxyguanosine (8-oxo-dG) as well as the staining intensity of PV and the PV cell-associated perineuronal net marker, Wisteria floribunda agglutinin (WFA). In the prelimbic PFC, 6 hr SD increased the intensity of 8-oxo-dG, PV, and WFA. After 12 hr SD, the intensity of 8-oxo-dG was elevated in all neurons. PV intensity was elevated only in neurons colabeled with 8-oxo-dG or WFA, and no changes were found in WFA intensity. We conclude that in association with SD-induced sleep drive, PV neurons in the prelimbic PFC exhibit oxidative stress.

Dopamine and Wakefulness: Pharmacology, Genetics, and Circuitry

Over the period of decades in the mid to late twentieth century, arousal-promoting functions were attributed to neuromodulators including serotonin, hypocretin, histamine, and noradrenaline. For some time, a relatively minor role in regulating sleep and wake states was ascribed to dopamine and the dopamine-producing cells of the ventral tegmental area, despite the fact that dopaminergic signaling is a major target, if not the primary target, for wake-promoting agents. In recent years, due to observations from human genetic studies, pharmacogenetic studies in animal models, and the increasingly sophisticated methods used to manipulate the nervous systems of experimental animals, it has become clear that dopaminergic signaling is central to the regulation of arousal. This chapter reviews this central role of dopaminergic signaling, and in particular its antagonistic interaction with adenosinergic signaling, in maintaining vigilance and in the response to wake-promoting therapeutics.

Influence of Schizophrenia-Associated Gene Egr3 on Sleep Behavior and Circadian Rhythms in Mice

Up to 80% of people meeting DSM-IV definitions for schizophrenia will exhibit difficulties with sleep, along with a breakdown in circadian entrainment and rhythmicity. The changes to the sleep and circadian systems in this population are thought to be interdependent, as evidenced by the frequent use of the combined term "sleep and circadian rhythm disruption" or "SCRD" to describe their occurrence. To understand links between sleep and circadian problems in the schizophrenia population, we analyzed the duration and rhythmicity of sleep behavior in mice lacking function of the immediate early gene early growth response 3 ( Egr3). EGR3 has been associated with schizophrenia risk in humans, and Egr3-deficient (-/-) mice display various features of schizophrenia that are responsive to antipsychotic treatment. While Egr3-/- mice slept less than their wildtype (WT) littermates, they showed no evidence of circadian disorganization; in fact, circadian rhythms of activity were more robust in these mice compared with WT, as measured by time series analysis and the relative amplitude index of Van Someren's suite of non-parametric circadian rhythm analyses. Differences in circadian robustness were maintained when the animals were transferred to several weeks of housing under constant darkness or constant light. Together, our results suggest that Egr3-/- mice retain control over the circadian timekeeping of sleep and wake, while showing impaired sleep. The findings are compatible with those from a surprising array of mouse models of schizophrenia and raise the possibility that SCRD may be 2 separate disorders in the schizophrenia population requiring different treatment strategies.

State-Dependent Modulation of Visual Evoked Potentials in a Rodent Genetic Model of Electroencephalographic Instability

Despite normal sleep timing and duration, Egr3-deficient (Egr3^−/−) mice exhibit electroencephalographic (EEG) characteristics of reduced arousal, including elevated slow wave (1–4 Hz) activity during wakefulness. Here we show that these mice exhibit state-dependent instability in the EEG. Intermittent surges in EEG power were found in Egr3^−/− mice during wakefulness and rapid eye movement sleep, most prominently in the beta (15–35 Hz) range compared to wild type (Egr3^+/+) mice. Such surges did not coincide with sleep onset, as the surges were not associated with cessation of electromyographic tone. Cortical processing of sensory information by visual evoked responses (VEP) were found to vary as a function of vigilance state, being of higher magnitude during slow wave sleep (SWS) than wakefulness and rapid eye movement sleep. VEP responses were significantly larger during quiet wakefulness than active wakefulness, in both Egr3^−/− mice and Egr3^+/+ mice. EEG synchronization in the beta range, previously linked to the accumulation of sleep need over time, predicted VEP magnitude. Egr3^−/− mice not only displayed elevated beta activity, but in quiet wake, this elevated beta activity coincides with an elevated evoked response similar to that of animals in SWS. These data confirm that (a) VEPs vary as a function of vigilance state, and (b) beta activity in the EEG is a predictor of state-dependent modulation of visual information processing. The phenotype of Egr3^−/− mice indicates that Egr3 is a genetic regulator of these phenomena.

Nitrogen narcosis induced by repetitive hyperbaric nitrogen oxygen mixture exposure impairs long-term cognitive function in newborn mice

Human beings are exposed to compressed air or a nitrogen-oxygen mixture, they will produce signs and symptoms of nitrogen narcosis such as amnesia or even loss of memory, which may be disappeared once back to the normobaric environment. This study was designed to investigate the effect of nitrogen narcosis induced by repetitive hyperbaric nitrogen-oxygen mixture exposure on long-term cognitive function in newborn mice and the underlying mechanisms. The electroencephalogram frequency was decreased while the amplitude was increased in a pressure-dependent manner during 0.6, 1.2, 1.8 MPa (million pascal) nitrogen-oxygen mixture exposures in adult mice. Nitrogen narcosis in postnatal days 7-9 mice but not in adult mice induced by repetitive hyperbaric exposure prolonged the latency to find the platform and decreased the number of platform-site crossovers during Morris water maze tests, and reduced the time in the center during the open field tests. An increase in the expression of cleaved caspase-3 in the hippocampus and cortex were observed immediately on the first day after hyperbaric exposure, and this lasted for seven days. Additionally, nitrogen narcosis induced loss of the dendritic spines but not of the neurons, which may mainly account for the cognitive dysfunction. Nitrogen narcosis induced long-term cognitive and emotional dysfunction in the postnatal mice but not in the adult mice, which may result from neuronal apoptosis and especially reduction of dendritic spines of neurons.

Plasticity-Related Gene Expression During Eszopiclone-Induced Sleep

Study Objectives

Experimental evidence suggests that restorative processes depend on synaptic plasticity changes in the brain during sleep. We used the expression of plasticity-related genes to assess synaptic plasticity changes during drug-induced sleep.

Methods

We first characterized sleep induced by eszopiclone in mice during baseline conditions and during the recovery from sleep deprivation. We then compared the expression of 18 genes and two miRNAs critically involved in synaptic plasticity in these mice. Gene expression was assessed in the cerebral cortex and hippocampus by the TaqMan reverse transcription polymerase chain reaction and correlated with sleep parameters.

Results

Eszopiclone reduced the latency to nonrapid eye movement (NREM) sleep and increased NREM sleep amounts. Eszopiclone had no effect on slow wave activity (SWA) during baseline conditions but reduced the SWA increase during recovery sleep (RS) after sleep deprivation. Gene expression analyses revealed three distinct patterns: (1) four genes had higher expression either in the cortex or hippocampus in the group of mice with increased amounts of wakefulness; (2) a large proportion of plasticity-related genes (7 out of 18 genes) had higher expression during RS in the cortex but not in the hippocampus; and (3) six genes and the two miRNAs showed no significant changes across conditions. Even at a relatively high dose (20 mg/kg), eszopiclone did not reduce the expression of plasticity-related genes during RS period in the cortex.

Conclusions

These results indicate that gene expression associated with synaptic plasticity occurs in the cortex in the presence of a hypnotic medication.