Optogenetic disruption of sleep continuity impairs memory consolidation

Microglial TNFα controls daily changes in synaptic GABAARs and sleep slow waves

Microglia sense the changes in their environment. How microglia actively translate these changes into suitable cues to adapt brain physiology is unknown. We reveal an activity-dependent regulation of cortical inhibitory synapses by microglia, driven by purinergic signaling acting on P2RX7 and mediated by microglia-derived TNFα. We demonstrate that sleep induces microglia-dependent synaptic enrichment of GABAARs in a manner dependent on microglial TNFα and P2RX7. We further show that microglia-specific depletion of TNFα alters slow waves during NREM sleep and blunt memory consolidation in sleep-dependent learning tasks. Together, our results reveal that microglia orchestrate sleep-intrinsic plasticity of synaptic GABAARs, sculpt sleep slow waves, and support memory consolidation.

Neurobehavioral meaning of pupil size

Pupil size is a widely used metric of brain state. It is one of the few signals originating from the brain that can be readily monitored with low-cost devices in basic science, clinical, and home settings. It is, therefore, important to investigate and generate well-defined theories related to specific interpretations of this metric. What exactly does it tell us about the brain? Pupils constrict in response to light and dilate during darkness, but the brain also controls pupil size irrespective of luminosity. Pupil size fluctuations resulting from ongoing "brain states" are used as a metric of arousal, but what is pupil-linked arousal and how should it be interpreted in neural, cognitive, and computational terms? Here, we discuss some recent findings related to these issues. We identify open questions and propose how to answer them through a combination of well-defined tasks, neurocomputational models, and neurophysiological probing of the interconnected loops of causes and consequences of pupil size.

SleepInvestigatoR: A flexible R function for analyzing scored sleep in rodents

Analyzing scored sleep is a fundamental prerequisite to understanding how sleep changes between health and disease. Classically, this is accomplished by manually calculating various measures (e.g., percent of non-rapid eye movement sleep) from a collection of scored sleep files. This process can be tedious and error prone especially when studies include a large number of animals or involve long recording sessions. To address this issue, we present SleepInvestigatoR, a versatile tool that can quickly organize and analyze multiple scored sleep files into a single output. The function is written in the open-source statistical language R and has a total of 25 parameters that can be set to match a wide variety of experimenter needs. SleepInvestigatoR delivers a total of 22 unique measures of sleep, including all measures commonly reported in the rodent literature. A simple plotting function is also provided to quickly graph and visualize the scored data. All code is designed to be implemented with little formal coding knowledge and step-by-step instructions are provided on the corresponding GitHub page. Overall, SleepInvestigatoR provides the sleep researcher a critical tool to increase efficiency, interpretation, and reproducibility in analyzing scored rodent sleep.

Regulation of stress-induced sleep fragmentation by preoptic glutamatergic neurons

Sleep disturbances are detrimental to our behavioral and emotional well-being. Stressful events disrupt sleep, in particular by inducing brief awakenings (microarousals, MAs), resulting in sleep fragmentation. The preoptic area of the hypothalamus (POA) is crucial for sleep control. However, how POA neurons contribute to the regulation of MAs and thereby impact sleep quality is unknown. Using fiber photometry in mice, we examine the activity of genetically defined POA subpopulations during sleep. We find that POA glutamatergic neurons are rhythmically activated in synchrony with an infraslow rhythm in the spindle band of the electroencephalogram during non-rapid eye movement sleep (NREMs) and are transiently activated during MAs. Optogenetic stimulation of these neurons promotes MAs and wakefulness. Exposure to acute social defeat stress fragments NREMs and significantly increases the number of transients in the calcium activity of POA glutamatergic neurons during NREMs. By reducing MAs, optogenetic inhibition during spontaneous sleep and after stress consolidates NREMs. Monosynaptically restricted rabies tracing reveals that POA glutamatergic neurons are innervated by brain regions regulating stress and sleep. In particular, presynaptic glutamatergic neurons in the lateral hypothalamus become activated after stress, and stimulating their projections to the POA promotes MAs and wakefulness. Our findings uncover a novel circuit mechanism by which POA excitatory neurons regulate sleep quality after stress.

Nesting chinstrap penguins accrue large quantities of sleep through seconds-long microsleeps

Microsleeps, the seconds-long interruptions of wakefulness by eye closure and sleep-related brain activity, are dangerous when driving and might be too short to provide the restorative functions of sleep. If microsleeps do fulfill sleep functions, then animals faced with a continuous need for vigilance might resort to this sleep strategy. We investigated electroencephalographically defined sleep in wild chinstrap penguins, at sea and while nesting in Antarctica, constantly exposed to an egg predator and aggression from other penguins. The penguins nodded off >10,000 times per day, engaging in bouts of bihemispheric and unihemispheric slow-wave sleep lasting on average only 4 seconds, but resulting in the accumulation of >11 hours of sleep for each hemisphere. The investment in microsleeps by successfully breeding penguins suggests that the benefits of sleep can accrue incrementally.

Brief Change in Dopamine Activity during Consolidation Impairs Long-Term Memory via Sleep Disruption

Sleep disturbances are associated with poor long-term memory (LTM) formation, yet the underlying cell types and neural circuits involved have not been fully decoded. Dopamine neurons (DANs) are involved in memory processing at multiple stages. Here, we show that brief activation of protocerebral anterior medial DANs (PAM-DANs) or inhibition of a pair of dorsal posterior medial (DPM) neurons during the first few hours of memory consolidation impairs 24 h LTM. Interestingly, sleep deprivation elevates the neural activity of PAM-DANs and DPM neurons, and brief thermos-activation of PAM-DANs or inactivation of DPM neurons results in sleep loss and fragmentation. Pharmacological rescue of sleep after this manipulation restores LTM. A specific subset of PAM-DANs, PAM-α1 that synapse onto DPM neurons specify the microcircuit that links sleep and memory. PAM-DANs, including PAM-α1, form functional synapses with DPM neurons mainly via Dop1R1 receptor to inhibit DPM. Our data suggest that the post-training activity of PAM(-α1)-DPM microcircuit, especially during memory consolidation, plays an essential role in maintaining the sleep necessary for LTM consolidation, providing a new cellular and circuit basis for the complex relationship between sleep and memory.

Control of energy homeostasis by the lateral hypothalamic area

The lateral hypothalamic area (LHA) is a subcortical brain region that exerts control over motivated behavior, feeding, and energy balance across species. Recent single-cell sequencing studies have defined at least 30 distinct LHA neuron types. Some of these influence specific aspects of energy homeostasis; however, the functions of many LHA cell types remain unclear. This review addresses the rapidly emerging evidence from cell-type-specific investigations that the LHA leverages distinct neuron populations to regulate energy balance through complex connections with other brain regions. It will highlight recent findings demonstrating that LHA control of energy balance extends beyond mere food intake and propose outstanding questions to be addressed by future research.

Sleep and vigilance states: Embracing spatiotemporal dynamics

The classic view of sleep and vigilance states is a global stationary perspective driven by the interaction between neuromodulators and thalamocortical systems. However, recent data are challenging this view by demonstrating that vigilance states are highly dynamic and regionally complex. Spatially, sleep- and wake-like states often co-occur across distinct brain regions, as in unihemispheric sleep, local sleep in wakefulness, and during development. Temporally, dynamic switching prevails around state transitions, during extended wakefulness, and in fragmented sleep. This knowledge, together with methods monitoring brain activity across multiple regions simultaneously at millisecond resolution with cell-type specificity, is rapidly shifting how we consider vigilance states. A new perspective incorporating multiple spatial and temporal scales may have important implications for considering the governing neuromodulatory mechanisms, the functional roles of vigilance states, and their behavioral manifestations. A modular and dynamic view highlights novel avenues for finer spatiotemporal interventions to improve sleep function.

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

The Effect of Obstructive Sleep Apnea on Sleep-dependent Emotional Memory Consolidation

Rationale: A growing body of evidence suggests that sleep is critical for the adaptive processing and consolidation of emotional information into long-term memory. Previous research has indicated that emotional components of scenes particularly benefit from sleep in healthy groups, yet sleep-dependent emotional memory processes remain unexplored in clinical cohorts, including those with obstructive sleep apnea (OSA). This line of research is important as it will add to the understanding of how disrupted sleep in OSA contributes to both impaired cognition and emotion dysregulation. Objectives: To test the hypothesis that individuals with OSA will have impaired sleep-dependent memory consolidation, with the greatest impact being on memory for emotional content. Methods: In this study, a group of newly diagnosed patients with OSA (n = 26; 10 female; average age, 42.5 years) and a matched group of healthy control subjects (n = 24; 13 female; average age, 37 years) were enrolled in the study at Beth Israel Deaconess Medical Center. Participants encoded scenes with negative or neutral foreground objects placed on neutral backgrounds before a night of polysomnographically recorded sleep. In the morning, they completed a recognition test in which old and new scene objects and backgrounds, presented separately and one at a time, were judged as old, new, or similar compared with what had been previously viewed. Results: Patients with OSA had a deficit in recognition memory for the scenes. Overall recognition (the ability to recognize old items as either old or similar) was impaired across all scene elements, both negative and neutral objects and backgrounds, whereas specific recognition (correctly identifying old items as old) was impaired only for negative objects. Across all participants, successful overall recognition correlated positively with sleep efficiency and rapid eye movement (REM) sleep, whereas successful specific memory recognition correlated only with REM sleep. Conclusions: Our findings indicate that fragmented sleep and reduced REM sleep, both hallmarks of OSA, are associated with disruptions in general memory impairment and veridical memory for emotional content, which could alter emotional regulation and contribute to comorbid emotional distress in OSA.

A Review: Research Progress of Neural Probes for Brain Research and Brain-Computer Interface

Neural probes, as an invasive physiological tool at the mesoscopic scale, can decipher the code of brain connections and communications from the cellular or even molecular level, and realize information fusion between the human body and external machines. In addition to traditional electrodes, two new types of neural probes have been developed in recent years: optoprobes based on optogenetics and magnetrodes that record neural magnetic signals. In this review, we give a comprehensive overview of these three kinds of neural probes. We firstly discuss the development of microelectrodes and strategies for their flexibility, which is mainly represented by the selection of flexible substrates and new electrode materials. Subsequently, the concept of optogenetics is introduced, followed by the review of several novel structures of optoprobes, which are divided into multifunctional optoprobes integrated with microfluidic channels, artifact-free optoprobes, three-dimensional drivable optoprobes, and flexible optoprobes. At last, we introduce the fundamental perspectives of magnetoresistive (MR) sensors and then review the research progress of magnetrodes based on it.

Rapid Eye Movement Sleep Engages Melanin-Concentrating Hormone Neurons to Reduce Cocaine Seeking

BACKGROUND

Persistent sleep disruptions following withdrawal from abused drugs may hold keys to battle drug relapse. It is posited that there may be sleep signatures that predict relapse propensity, identifying which may open new avenues for treating substance use disorders.

METHODS

We trained male rats (approximately postnatal day 56) to self-administer cocaine. After long-term drug withdrawal (approximately postnatal day 100), we examined the correlations between the intensity of cocaine seeking and key sleep features. To test for causal relationships, we then used behavioral, chemogenetic, or optogenetic methods to selectively increase rapid eye movement sleep (REMS) and measured behavioral and electrophysiological outcomes to probe for cellular and circuit mechanisms underlying REMS-mediated regulation of cocaine seeking.

RESULTS

A selective set of REMS features was preferentially associated with the intensity of cue-induced cocaine seeking after drug withdrawal. Moreover, selectively increasing REMS time and continuity by environmental warming attenuated a withdrawal time-dependent intensification of cocaine seeking, or incubation of cocaine craving, suggesting that REMS may benefit withdrawal. Warming increased the activity of lateral hypothalamic melanin-concentrating hormone (MCH) neurons selectively during prolonged REMS episodes and counteracted cocaine-induced synaptic accumulation of calcium-permeable AMPA receptors in the nucleus accumbens-a critical substrate for incubation. Finally, the warming effects were partly mimicked by chemogenetic or optogenetic stimulations of MCH neurons during sleep, or intra-accumbens infusions of MCH peptide during the rat's inactive phase.

CONCLUSIONS

REMS may encode individual vulnerability to relapse, and MCH neuron activities can be selectively targeted during REMS to reduce drug relapse.

Experimental Models to Study End-Organ Morbidity in Sleep Apnea: Lessons Learned and Future Directions

Sleep apnea (SA) is a very prevalent sleep breathing disorder mainly characterized by intermittent hypoxemia and sleep fragmentation, with ensuing systemic inflammation, oxidative stress, and immune deregulation. These perturbations promote the risk of end-organ morbidity, such that SA patients are at increased risk of cardiovascular, neurocognitive, metabolic and malignant disorders. Investigating the potential mechanisms underlying SA-induced end-organ dysfunction requires the use of comprehensive experimental models at the cell, animal and human levels. This review is primarily focused on the experimental models employed to date in the study of the consequences of SA and tackles 3 different approaches. First, cell culture systems whereby controlled patterns of intermittent hypoxia cycling fast enough to mimic the rates of episodic hypoxemia experienced by patients with SA. Second, animal models consisting of implementing realistic upper airway obstruction patterns, intermittent hypoxia, or sleep fragmentation such as to reproduce the noxious events characterizing SA. Finally, human SA models, which consist either in subjecting healthy volunteers to intermittent hypoxia or sleep fragmentation, or alternatively applying oxygen supplementation or temporary nasal pressure therapy withdrawal to SA patients. The advantages, limitations, and potential improvements of these models along with some of their pertinent findings are reviewed.

A noradrenergic-hypothalamic neural substrate for stress-induced sleep disturbances

In our daily life, we are exposed to uncontrollable and stressful events that disrupt our sleep. However, the underlying neural mechanisms deteriorating the quality of non-rapid eye movement sleep (NREMs) and REM sleep are largely unknown. Here, we show in mice that acute psychosocial stress disrupts sleep by increasing brief arousals (microarousals [MAs]), reducing sleep spindles, and impairing infraslow oscillations in the spindle band of the electroencephalogram during NREMs, while reducing REMs. This poor sleep quality was reflected in an increased number of calcium transients in the activity of noradrenergic (NE) neurons in the locus coeruleus (LC) during NREMs. Opto- and chemogenetic LC-NE activation in naïve mice is sufficient to change the sleep microarchitecture similar to stress. Conversely, chemogenetically inhibiting LC-NE neurons reduced MAs during NREMs and normalized their number after stress. Specifically inhibiting LC-NE neurons projecting to the preoptic area of the hypothalamus (POA) decreased MAs and enhanced spindles and REMs after stress. Optrode recordings revealed that stimulating LC-NE fibers in the POA indeed suppressed the spiking activity of POA neurons that are activated during sleep spindles and REMs and inactivated during MAs. Our findings reveal that changes in the dynamics of the stress-regulatory LC-NE neurons during sleep negatively affect sleep quality, partially through their interaction with the POA.

Adolescent sleep shapes social novelty preference in mice

Sleep disturbances frequently occur in neurodevelopmental disorders such as autism, but the developmental role of sleep is largely unexplored, and a causal relationship between developmental sleep defects and behavioral consequences in adulthood remains elusive. Here, we show that in mice, sleep disruption (SD) in adolescence, but not in adulthood, causes long-lasting impairment in social novelty preference. Furthermore, adolescent SD alters the activation and release patterns of dopaminergic neurons in the ventral tegmental area (VTA) in response to social novelty. This developmental sleep function is mediated by balanced VTA activity during adolescence; chemogenetic excitation mimics, whereas silencing rescues, the social deficits of adolescent SD. Finally, we show that in Shank3-mutant mice, improving sleep or rectifying VTA activity during adolescence ameliorates adult social deficits. Together, our results identify a critical role of sleep and dopaminergic activity in the development of social interaction behavior.

The Combined Influences of Exercise, Diet and Sleep on Neuroplasticity

Neuroplasticity refers to the brain's ability to undergo structural and functional adaptations in response to experience, and this process is associated with learning, memory and improvements in cognitive function. The brain's propensity for neuroplasticity is influenced by lifestyle factors including exercise, diet and sleep. This review gathers evidence from molecular, systems and behavioral neuroscience to explain how these three key lifestyle factors influence neuroplasticity alone and in combination with one another. This review collected results from human studies as well as animal models. This information will have implications for research, educational, fitness and neurorehabilitation settings.

Abdominal Obesity: An Independent Influencing Factor of Visuospatial and Executive/Language Ability and the Serum Levels of Aβ40/Aβ42/Tau Protein

Background

Although obesity affects human health and cognitive function, the influence of abdominal obesity on cognitive function is still unclear.

Methods

The MoCA scale was used to evaluate the overall cognitive function and the function of each subitem of 196 subjects, as well as the SDMT and TMT-A scales for evaluating the attention and information processing speed. In addition, radioimmunoassay was used to detect the serum levels of Aβ40, Aβ42, and tau protein in 45 subjects. Subjects were divided into abdominal and nonabdominal obesity groups. Before and after correcting confounding factors, the differences in cognitive scale evaluation indexes and three protein levels between the two groups were compared. We also explore further the correlation between various cognitive abilities and the waist circumference/levels of the three proteins. Linear regression was used to identify the independent influencing factors of various cognitive functions and three protein levels.

Results

After correcting for multiple factors, we observed the lower scores of visuospatial function, execution, and language in the MoCA scale, as well as higher levels of Aβ40 and tau protein in the abdominal obesity group, supported by the results of correlation analysis. Abdominal obesity was identified as an independent negative influencing factor of MoCA visual space, executive power, and language scores and an independent positive influencing factor of Aβ40, Aβ42, and tau protein levels.

Conclusion

Abdominal obesity may play a negative role in visuospatial, executive ability, and language function and a positive role in the Aβ40, Aβ42, and tau protein serum levels.

Regulation of REM sleep by inhibitory neurons in the dorsomedial medulla

The two major stages of mammalian sleep-rapid eye movement sleep (REMs) and non-REM sleep (NREMs)-are characterized by distinct brain rhythms ranging from millisecond to minute-long (infraslow) oscillations. The mechanisms controlling transitions between sleep stages and how they are synchronized with infraslow rhythms remain poorly understood. Using opto- and chemogenetic manipulation in mice, we show that GABAergic neurons in the dorsomedial medulla (dmM) promote the initiation and maintenance of REMs, in part through their projections to the dorsal and median raphe nuclei. Fiber photometry revealed that their activity is strongly increased during REMs and fluctuates during NREMs in close synchrony with infraslow oscillations in the sleep spindle band of the electroencephalogram. The phase of this rhythm influenced the latency and probability with which dmM activation induced REMs. Thus, dmM inhibitory neurons strongly promote REMs, and their slow activity fluctuations may coordinate the timing of REMs episodes with infraslow brain rhythms.

Major role of MT2 receptors in the beneficial effect of melatonin on long-term recognition memory in C57BL/6J male mice

Melatonin, a major signal of the circadian system, is also involved in brain functions such as learning and memory. Chronic melatonin treatment is known to improve memory performances, but the respective contribution of its central receptors, MT₁ and MT₂, is still unclear. Here, we used new single receptor deficient MT₁^-/- and MT₂^-/- mice to investigate the contribution of each receptor in the positive effect of chronic melatonin treatment on long-term recognition memory. The lack of MT₂ receptor precluded memory-enhancing effect of melatonin in the object recognition task and to a lesser extent in the object location task, whereas the lack of MT₁ receptor mitigated its effect in the object location task only. Our findings support a key role of MT₂ in mediating melatonin's beneficial action on long-term object recognition memory, whereas MT₁ may contribute to the effect on object location memory.

Enhancing sleep after training improves memory in Down syndrome model mice

Down syndrome (DS) is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. DS is associated with cognitive disabilities, for which there are no drug therapies. In spite of significant behavioral and pharmacological efforts to treat cognitive disabilities, new and continued efforts are still necessary. Over sixty percent of children with DS are reported to have sleep apnea that disrupt normal sleep. Normal and adequate sleep is necessary to maintain optimal cognitive functions. Therefore, we asked whether improved quality and/or quantity of sleep could improve cognitive capacities of people with DS. To investigate this possibility, we used the Ts65Dn mouse model of DS and applied two methods for enhancing their sleep following training on mouse memory tasks. A behavioral method was to impose sleep deprivation prior to training resulting in sleep rebound following the training. A pharmacologic method, hypocretin receptor 2 antagonist, was used immediately after the training to enhance subsequent sleep knowing that hypocretin is involved in the maintenance of wake. Our behavioral method resulted in a sleep reorganization that decreased wake and increased REM sleep following the training associated with an improvement of recognition memory and spatial memory in the DS model mice. Our pharmacologic approach decreased wake and increased NREM sleep and was associated with improvement only in the spatial memory task. These results show that enhancing sleep after the training in a memory task improves memory consolidation in a mouse model of DS.

Dim light in the evening causes coordinated realignment of circadian rhythms, sleep, and short-term memory

In modern societies, people are regularly exposed to artificial light (e.g., light-emitting electronic devices). Dim light in the evening (DLE) imposes an artificial extension of the solar day, increasing our alertness before bedtime, delaying melatonin timing and sleep onset, and increasing sleepiness in the next morning. Using laboratory mice as a model organism, we show that 2 wk of 4-h, 20-lux DLE postpones rest–activity rhythms, delays molecular rhythms in the brain and body, and reverses the diurnal pattern of short-term memory performance. These results highlight the biological impact of DLE and emphasize the need to optimize our evening light exposure if we are to avoid shifting our biological clocks.

Light provides the primary signal for entraining circadian rhythms to the day/night cycle. In addition to rods and cones, the retina contains a small population of photosensitive retinal ganglion cells (pRGCs) expressing the photopigment melanopsin (OPN4). Concerns have been raised that exposure to dim artificial lighting in the evening (DLE) may perturb circadian rhythms and sleep patterns, and OPN4 is presumed to mediate these effects. Here, we examine the effects of 4-h, 20-lux DLE on circadian physiology and behavior in mice and the role of OPN4 in these responses. We show that 2 wk of DLE induces a phase delay of ∼2 to 3 h in mice, comparable to that reported in humans. DLE-induced phase shifts are unaffected in Opn4^−/− mice, indicating that rods and cones are capable of driving these responses in the absence of melanopsin. DLE delays molecular clock rhythms in the heart, liver, adrenal gland, and dorsal hippocampus. It also reverses short-term recognition memory performance, which is associated with changes in preceding sleep history. In addition, DLE modifies patterns of hypothalamic and cortical cFos signals, a molecular correlate of recent neuronal activity. Together, our data show that DLE causes coordinated realignment of circadian rhythms, sleep patterns, and short-term memory process in mice. These effects are particularly relevant as DLE conditions―due to artificial light exposure―are experienced by the majority of the populace on a daily basis.

Clinical applicability of optogenetic gene regulation

The field of optogenetics is rapidly growing in relevance and number of developed tools. Among other things, the optogenetic repertoire includes light-responsive ion channels and methods for gene regulation. This review will be confined to the optogenetic control of gene expression in mammalian cells as suitable models for clinical applications. Here optogenetic gene regulation might offer an excellent method for spatially and timely regulated gene and protein expression in cell therapeutic approaches. Well-known systems for gene regulation, such as the LOV-, CRY2/CIB-, PhyB/PIF-systems, as well as other, in mammalian cells not yet fully established systems, will be described. Advantages and disadvantages with regard to clinical applications are outlined in detail. Among the many unanswered questions concerning the application of optogenetics, we discuss items such as the use of exogenous chromophores and their effects on the biology of the cells and methods for a gentle, but effective gene transfection method for optogenetic tools for in vivo applications.

Shining a Light on the Mechanisms of Sleep for Memory Consolidation

Purpose of review

This paper reviews all optogenetic studies that directly test various sleep states, traits, and circuit-level activity profiles for the consolidation of different learning tasks.

Recent findings

Inhibiting or exciting neurons involved either in the production of sleep states or in the encoding and consolidation of memories reveals sleep states and traits that are essential for memory. REM sleep, NREM sleep, and the N2 transition to REM (characterized by sleep spindles) are integral to memory consolidation. Neural activity during sharp-wave ripples, slow oscillations, theta waves, and spindles are the mediators of this process.

Summary

These studies lend strong support to the hypothesis that sleep is essential to the consolidation of memories from the hippocampus and the consolidation of motor learning which does not necessarily involve the hippocampus. Future research can further probe the types of memory dependent on sleep-related traits and on the neurotransmitters and neuromodulators required.

An anti-narcolepsy drug reveals behavioral and fitness costs of extreme activity cycles in arctic-breeding songbirds

Sleep loss impairs cognitive function, immunological responses and general well-being in humans. However, sleep requirements in mammals and birds vary dramatically. In circumpolar regions with continuous summer light, daily sleep duration is reduced, particularly in breeding birds. The effect of an anti-narcolepsy drug (modafinil) to putatively extend wakefulness was examined in two species of closely related arctic-breeding passerine birds: Lapland longspurs (Calcarius lapponicus) and snow buntings (Plectrophenax nivalis). Free-living adult males were implanted during the nestling phase on day 4 (D4; 4 days post-hatching) with osmotic pumps containing either vehicle or modafinil to extend the active period for 72 h. Nestlings were weighed on D2 and D7 to measure growth rates. Additionally, focal observations were conducted on D6. Male longspurs receiving modafinil made fewer feeding visits and spent less time at the nest but tended to spend more time near the nest than controls. We observed no change in longspur nestling growth rates, but fledging occurred significantly later when males received modafinil, suggesting a fitness cost. In contrast, modafinil had no measurable impact on male or female snow bunting behavior, nestling growth rates or time to fledging. We suggest male longspurs compromise and maintain vigilance at their nests in lieu of sleeping because of the increased predation risk that is characteristic of their tundra nesting habitat. Snow buntings are cavity nesters, and their nests do not require the same vigilance, allowing males to presumably rest following provisioning. These life-history differences between species highlight the role of predation risk in mediating behavioral modifications to prolonged wakefulness in arctic-breeding songbirds.

Light/Clock Influences Membrane Potential Dynamics to Regulate Sleep States

The circadian rhythm is a fundamental process that regulates the sleep-wake cycle. This rhythm is regulated by core clock genes that oscillate to create a physiological rhythm of circadian neuronal activity. However, we do not know much about the mechanism by which circadian inputs influence neurons involved in sleep-wake architecture. One possible mechanism involves the photoreceptor cryptochrome (CRY). In Drosophila, CRY is receptive to blue light and resets the circadian rhythm. CRY also influences membrane potential dynamics that regulate neural activity of circadian clock neurons in Drosophila, including the temporal structure in sequences of spikes, by interacting with subunits of the voltage-dependent potassium channel. Moreover, several core clock molecules interact with voltage-dependent/independent channels, channel-binding protein, and subunits of the electrogenic ion pump. These components cooperatively regulate mechanisms that translate circadian photoreception and the timing of clock genes into changes in membrane excitability, such as neural firing activity and polarization sensitivity. In clock neurons expressing CRY, these mechanisms also influence synaptic plasticity. In this review, we propose that membrane potential dynamics created by circadian photoreception and core clock molecules are critical for generating the set point of synaptic plasticity that depend on neural coding. In this way, membrane potential dynamics drive formation of baseline sleep architecture, light-driven arousal, and memory processing. We also discuss the machinery that coordinates membrane excitability in circadian networks found in Drosophila, and we compare this machinery to that found in mammalian systems. Based on this body of work, we propose future studies that can better delineate how neural codes impact molecular/cellular signaling and contribute to sleep, memory processing, and neurological disorders.

The persistence of sleep disturbance and its correlates in children with moderate to severe traumatic brain injury: A longitudinal study

OBJECTIVES

The primary aim was to examine whether sleep disturbances persist in children in the chronic stage of recovery from moderate or severe traumatic brain injury (TBI). The secondary aim was to examine whether memory difficulties and/or other previously identified factors relate to sleep disturbances in children with moderate to severe TBI.

METHODS

This longitudinal study included 21 children with moderate to severe TBI, 8-18 years old, recruited from an urban tertiary paediatric specialised brain injury rehabilitation unit. Participants were seen 5 years and again 7 years post-injury, on average. Sleep disturbances were assessed with Sleep Disturbance Scale for Children (SDSC). Correlates that were considered included indicators of TBI severity, and questionnaires assessing everyday memory, fatigue, internalizing and externalizing behaviors and pain intensity.

RESULTS

The SDSC scores of children with moderate to severe TBI indicated greater disturbances in initiating and maintaining sleep, arousal, sleep-wake transition, and excessive somnolence relative to the norms, at follow-up. The mean SDSC scores and the number of participants with subclinical to clinical sleep disturbances on the SDSC remained unchanged from baseline to follow-up. At follow-up, the SDSC initiating and maintaining sleep, and excessive somnolence scales were associated with poorer everyday memory and greater fatigue.

CONCLUSIONS

Children with moderate to severe TBI experience ongoing sleep disturbances for years post-injury. Greater sleep disturbances are associated with worse functional outcomes. Further research into sleep disturbances and development of treatments is important, as it could improve the outcomes of children with TBI.

Premature Aging Among Trauma Survivors-The Longitudinal Implications of Sleep Disruptions on Telomere Length and Cognitive Performance

OBJECTIVES

Sleep is necessary for brain function as well as physical and cognitive processes. Sleep disruptions, common with aging, intensify among trauma survivors. Moreover, former prisoners-of-war (ex-POWs) often experience premature aging. This study investigates the longitudinal effects of sleep disruptions for ex-POWs in relation to cognitive performance and telomere length as well as between cognition and telomeres.

METHOD

This study included Israeli veterans from the 1973 Yom Kippur War who participated in four assessments (1991, 2003, 2008, 2015): (a) ex-POWs (n = 99), and (b) veterans who not were captured (controls) (n = 101). Among both groups, sleep disruptions were assessed using a self-report item in all four assessments. Cognitive performance was assessed using the Montreal Cognitive Assessment (MOCA) and telomere length was assessed via total white blood cells (leukocytes) from whole blood samples using Southern blot, both were measured only among ex-POWs in 2015. We conducted descriptive statistics, repeated measures, correlations, and path analyses.

RESULTS

Sleep disruptions were related to lower cognitive performance but not to shorter telomeres. Moreover, cognitive performance and telomere length were found to be related when sleep disruptions were taken into consideration.

CONCLUSION

Interpersonal trauma was shown to be a unique experience resulting in sleep disruptions over time, leading to cognitive impairment. These findings highlight the importance of viewing trauma survivors at high-risk for sleep disruptions. Therefore, it is imperative to inquire about sleep and diagnose cognitive disorders to help identify and treat premature aging.

Sleep Deprivation Aggravates Cognitive Impairment by the Alteration of Hippocampal Neuronal Activity and the Density of Dendritic Spine in Isoflurane-Exposed Mice

Isoflurane contributes to cognitive deficits when used as a general anesthetic, and so does sleep deprivation (SD). Patients usually suffer from insomnia before an operation due to anxiety, fear, and other factors. It remains unclear whether preoperative SD exacerbates cognitive impairment induced by isoflurane. In this study, we observed the effects of pretreated 24-h SD in adult isoflurane-exposed mice on the cognitive behaviors, the Ca²⁺ signals of dorsal hippocampal CA1 (dCA1) neurons in vivo with fiber photometry, and the density of dendritic spines in hippocampal neurons. Our results showed that in cognitive behavior tasks, short-term memory damages were more severe with SD followed by isoflurane exposure than that with SD or isoflurane exposure separately, and interestingly, severe long-term memory deficits were induced only by SD followed by isoflurane exposure. Only the treatment of SD followed by isoflurane exposure could reversibly decrease the amplitude of Ca²⁺ signals when mice were freely moving and increase the duration of Ca²⁺ signals during the long-term memory behavior test. The density of dendritic spines with both SD and isoflurane exposure was lower than that with SD alone. This study suggests that SD should be avoided preoperatively in patients undergoing elective surgery under isoflurane anesthesia.

Brain mechanisms of insomnia: new perspectives on causes and consequences

While insomnia is the second most common mental disorder, progress in our understanding of underlying neurobiological mechanisms has been limited. The present review addresses the definition and prevalence of insomnia and explores its subjective and objective characteristics across the 24-hour day. Subsequently, the review extensively addresses how the vulnerability to develop insomnia is affected by genetic variants, early life stress, major life events, and brain structure and function. Further supported by the clear mental health risks conveyed by insomnia, the integrated findings suggest that the vulnerability to develop insomnia could rather be found in brain circuits regulating emotion and arousal than in circuits involved in circadian and homeostatic sleep regulation. Finally, a testable model is presented. The model proposes that in people with a vulnerability to develop insomnia, the locus coeruleus is more sensitive to-or receives more input from-the salience network and related circuits, even during rapid eye movement sleep, when it should normally be sound asleep. This vulnerability may ignite a downward spiral of insufficient overnight adaptation to distress, resulting in accumulating hyperarousal, which, in turn, impedes restful sleep and moreover increases the risk of other mental health adversity. Sensitized brain circuits are likely to be subjectively experienced as "sleeping with one eye open". The proposed model opens up the possibility for novel intervention studies and animal studies, thus accelerating the ignition of a neuroscience of insomnia, which is direly needed for better treatment.

Daily Rhythms of Female Self-maintenance Correlate with Predation Risk and Male Nest Attendance in a Biparental Wader

Parents make tradeoffs between care for offspring and themselves. Such a tradeoff should be reduced in biparental species, when both parents provide parental care. However, in some biparental species, the contribution of one sex varies greatly over time or between pairs. How this variation in parental care influences self-maintenance rhythms is often unclear. In this study, we used continuous video recording to investigate the daily rhythms of sleep and feather preening in incubating females of the Northern Lapwing (Vanellus vanellus), a wader with a highly variable male contribution to incubation. We found that the female's sleep frequency peaked after sunrise and before sunset but was low in the middle of the day and especially during the night. In contrast, preening frequency followed a 24-h rhythm and peaked in the middle of the day. Taken together, incubating females rarely slept or preened during the night, when the predation pressure was highest. Moreover, the sleeping and preening rhythms were modulated by the male contribution to incubation. Females that were paired with more contributing males showed a stronger sleep rhythm but also a weaker preening rhythm. If more incubating males also invest more in nest guarding and deterring daylight predators, their females may afford more sleep on the nest during the day and preen more when they are off the nest. Whether the lack of sleep in females paired with less caregiving males has fitness consequences awaits future investigation.

Ablation of Ventral Midbrain/Pons GABA Neurons Induces Mania-like Behaviors with Altered Sleep Homeostasis and Dopamine D2R-mediated Sleep Reduction

Individuals with the neuropsychiatric disorder mania exhibit hyperactivity, elevated mood, and a decreased need for sleep. The brain areas and neuronal populations involved in mania-like behaviors, however, have not been elucidated. In this study, we found that ablating the ventral medial midbrain/pons (VMP) GABAergic neurons induced mania-like behaviors in mice, including hyperactivity, anti-depressive behaviors, reduced anxiety, increased risk-taking behaviors, distractibility, and an extremely shortened sleep time. Strikingly, these mice also showed no rebound sleep after sleep deprivation, suggesting abnormal sleep homeostatic regulation. Dopamine D₂ receptor deficiency largely abolished the sleep reduction induced by ablating the VMP GABAergic neurons without affecting the hyperactivity and anti-depressive behaviors. Our data demonstrate that VMP GABAergic neurons are involved in the expression of mania-like behaviors, which can be segregated to the short-sleep and other phenotypes on the basis of the dopamine D₂ receptors.

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Hyperactivity and anti-depressive behaviors are induced by loss of VMP GABA neurons

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Homeostatic sleep rebound is lost together with largely shorten daily sleep

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Dopamine D₂ receptors mediate the daytime sleep loss

Destabilization of light NREM sleep by thalamic PLCβ4 deletion impairs sleep-dependent memory consolidation

Sleep abnormality often accompanies the impairment of cognitive function. Both rapid eye movement (REM) and non-REM (NREM) sleep have associated with improved memory performance. However, the role of composition in NREM sleep, consisting of light and deep NREM, for memory formation is not fully understood. We investigated how the dynamics of NREM sleep states influence memory consolidation. Thalamocortical (TC) neuron-specific phospholipase C β4 (PLCβ4) knockout (KO) increased the total duration of NREM sleep, consisting of destabilized light NREM and stabilized deep NREM. Surprisingly, the longer NREM sleep did not improve memory consolidation but rather impaired it in TC-specific PLCβ4 KO mice. Memory function was positively correlated with the stability of light NREM and spindle activity occurring in maintained light NREM period. Our study suggests that a single molecule, PLCβ4, in TC neurons is critical for tuning the NREM sleep states and thus affects sleep-dependent memory formation.

Effect of sleep loss on executive function and plasma corticosterone levels in an arctic-breeding songbird, the Lapland longspur (Calcarius lapponicus)

Sleep is a fundamental component of vertebrate life, although its exact functions remain unclear. Animals deprived of sleep typically show reduced neurobiological performance, health, and in some cases, survival. However, a number of vertebrate taxa exhibit adaptations that permit normal activities even when sleep is reduced. Lapland longspurs (Calcarius lapponicus), arctic-breeding passerine birds, exhibit around-the-clock activity during their short breeding season, with an inactive period of ca. 4 h/day. Whether behavioral or physiological costs occur from sleep loss (SL) in this species is unknown. To assess the effects of SL, wild-caught male longspurs were placed in captivity (12L:12D) and trained for one month to successfully learn color association and spatial memory tasks. Birds were then placed in automated sleep fragmentation cages that utilize a moving wire to force movement every 1 min (60 arousals/h) during 12D (inactive period) or control conditions (during 12L; active period). After SL (or control) treatment, birds were presented with color association and spatial memory tasks a final time to assess executive function. Baseline plasma corticosterone concentration, body mass, and satiety were also measured. SL significantly elevated corticosterone levels and increased accuracy during color association recall but did not affect the overall time required to complete the task. SL had no effect upon spatial memory, body mass, or satiety. Taken together, these results suggest that Lapland longspurs exhibit a degree of behavioral, but not physiological, insensitivity to acute SL. Whether elevated plasma concentrations of corticosterone play a direct role in ameliorating cognitive deficits from SL require additional study.

Transient neonatal sleep fragmentation results in long-term neuroinflammation and cognitive impairment in a rabbit model

Sleep fragmentation is an increase in sleep-wake transitions without an overall decrease in total sleep time. Sleep fragmentation is well documented during acute and chronic hospitalization and can result in delirium and memory problems in children. Sleep fragmentation is also often noted in neurodevelopmental disorders. However, it is unclear how sleep fragmentation independent of disease affects brain development and function. We hypothesized that acute sleep fragmentation during the neonatal period in otherwise healthy animals would result in neuroinflammation and would be associated with abnormalities in cognitive development. The orbital shaker method was used to fragment sleep for 72 h in postnatal day 3 New Zealand white rabbit kits (fragmentation group). To control for maternal separation, the sham group was separated from the dam and maintained in the same conditions without undergoing sleep fragmentation. A naïve control group remained with the dam. Kits underwent behavioral testing with novel object recognition and spontaneous alternation T-maze tests at 2-3 weeks post-fragmentation and were sacrificed 3-50 days after fragmentation. Sleep fragmentation resulted in acute and chronic changes in microglial morphology in the hippocampus and cortex, and regional differences in mRNA expression of pro- and anti-inflammatory cytokines at 3, 7 and 50 days post-fragmentation. Impaired novel object recognition and a longer latency in T-maze task completion were noted in the fragmented kits. This was in spite of normalization of sleep architecture noted at 2 months of age in these kits. The results indicate that transient neonatal sleep fragmentation results in short-term and long-term immune alterations in the brain, along with diminished performance in cognitive tasks long-term.

Impacts of Sleep Loss versus Waking Experience on Brain Plasticity: Parallel or Orthogonal?

Recent studies on the effects of sleep deprivation on synaptic plasticity have yielded discrepant results. Sleep deprivation studies using novelty exposure as a means to keep animals awake suggests that sleep (compared with wake) leads to widespread reductions in net synaptic strength. By contrast, sleep deprivation studies using approaches avoiding novelty-induced arousal (i.e., gentle handling) suggest that sleep can promote synaptic growth and strengthening. How can these discrepant findings be reconciled? Here, we discuss how varying methodologies for the experimental disruption of sleep (with differential introduction of novel experiences) could fundamentally alter the experimental outcome with regard to synaptic plasticity. Thus, data from experiments aimed at assessing the relative impact of sleep versus wake on the brain may instead reflect the quality of the waking experience itself. The highlighted work suggests that brain plasticity resulting from novel experiences versus wake per se has unique and distinct features.

Differential modulation of NREM sleep regulation and EEG topography by chronic sleep restriction in mice

Compensatory elevation in NREM sleep EEG delta power has been typically observed following prolonged wakefulness and widely used as a sleep homeostasis indicator. However, recent evidence in human and rodent chronic sleep restriction (CSR) studies suggests that NREM delta power is not progressively increased despite of accumulated sleep loss over days. In addition, there has been little progress in understanding how sleep EEG in different brain regions responds to CSR. Using novel high-density EEG electrode arrays in the mouse model of CSR where mice underwent 18-h sleep deprivation per day for 5 consecutive days, we performed an extensive analysis of topographical NREM sleep EEG responses to the CSR condition, including period-amplitude analysis of individual slow waves. As previously reported in our analysis of REM sleep responses, we found different patterns of changes: (i) progressive decrease in NREM sleep duration and consolidation, (ii) persistent enhancement in NREM delta power especially in the frontal and parietal regions, and (iii) progressive increases in individual slow wave slope and frontal fast oscillation power. These results suggest that multiple sleep-wake regulatory systems exist in a brain region-specific manner, which can be modulated independently, especially in the CSR condition.

A Serotonin-Modulated Circuit Controls Sleep Architecture to Regulate Cognitive Function Independent of Total Sleep in Drosophila

Both the structure and the amount of sleep are important for brain function. Entry into deep, restorative stages of sleep is time dependent; short sleep bouts selectively eliminate these states. Fragmentation-induced cognitive dysfunction is a feature of many common human sleep pathologies. Whether sleep structure is normally regulated independent of the amount of sleep is unknown. Here, we show that in Drosophila melanogaster, activation of a subset of serotonergic neurons fragments sleep without major changes in the total amount of sleep, dramatically reducing long episodes that may correspond to deep sleep states. Disruption of sleep structure results in learning deficits that can be rescued by pharmacologically or genetically consolidating sleep. We identify two reciprocally connected sets of ellipsoid body neurons that form the heart of a serotonin-modulated circuit that controls sleep architecture. Taken together, these findings define a circuit essential for controlling the structure of sleep independent of its amount.

Increasing the expression level of ChR2 enhances the optogenetic excitability of cochlear neurons

Optogenetics comprise a promising alternative to electrical stimulation for characterization of neural circuits and for the next generation of neural prostheses. Optogenetic stimulation relies on expression of photosensitive microbial proteins in animal cells to initiate a flow of ions into the cells in response to visible light. Here, we generated a novel transgenic mouse model in which we studied the optogenetic activation of spiral ganglion neurons, the primary afferent neurons of the auditory system, and showed a strong optogenetic response, with a similar amplitude as the acoustically evoked response. A twofold increase in the level of channelrhodopsin expression significantly increased the photosensitivity at both the single cell and organismal levels but also partially compromised the native electrophysiological properties of the neurons. The importance of channelrhodopsin expression level to optogenetic stimulation, revealed by these quantitative measurements, will be significant for the characterization of neural circuitry and for the use of optogenetics in neural prostheses.NEW & NOTEWORTHY This study reveals a dose-response relationship between channelrhodopsin expression and optogenetic excitation. Both single cell and organismal responses depend on the expression level of the heterologous protein. Expression level of the opsin is thus an important variable in determining the outcome of an optogenetic experiment. These results are key to the implementation of neural prostheses based on optogenetics, such as next generation cochlear implants, which would use light to elicit a neural response to sound.

Pharmacosynthetic Deconstruction of Sleep-Wake Circuits in the Brain

Over the past decade, basic sleep research investigating the circuitry controlling sleep and wakefulness has been boosted by pharmacosynthetic approaches, including chemogenetic techniques using designed receptors exclusively activated by designer drugs (DREADD). DREADD offers a series of tools that selectively control neuronal activity as a way to probe causal relationship between neuronal sub-populations and the regulation of the sleep-wake cycle. Following the path opened by optogenetics, DREADD tools applied to discrete neuronal sub-populations in numerous brain areas quickly made their contribution to the discovery and the expansion of our understanding of critical brain structures involved in a wide variety of behaviors and in the control of vigilance state architecture.

Sleep changes following intensive cognitive activity

Studies over the last 40 years have mainly investigated sleep structure changes as a result of wake duration, in the frame of the classical sleep regulation theories. However, wake intervals of the same duration can profoundly differ in their intensity, which actually reflects the degree of cognitive and physical activity. Data on how sleep can be modified by wake intensity changes (initially sparse and of little consistence) have become much more substantial, especially in the frame of the intense research debate on sleep-memory relationships. Our aim is to examine the vast repertoire of sleep modifications that depend on waking cognitive manipulations, highlighting the sleep features that appear most affected. By systematically addressing this issue, we want to set the basis for future research exploring both the specific nature of the mechanisms involved and the applicative psychosocial and clinical fall-outs, in terms of possible behavioural interventions for sleep quality improvement.

The Effect of Cognitive Activity on Sleep Maintenance in a Subsequent Daytime Nap

Background/Objective: The aim of this study is to assess the effects of a learning task on the characteristics of a subsequent daytime nap. Participants and Methods: Thirty-eight subjects were administered a control nap (C) and one preceded by a cognitive training session (TR). Results: Relative to C, TR naps showed significantly increased sleep duration with decreased sleep latency, as well as significantly increased sleep efficiency due to reduced awakening frequency. Meaningful trends were also found toward an increase of Stage 2 sleep proportion and a reduction of Stage 1 sleep, percentage of wake after sleep onset (WASO), and frequency of state transitions. Conclusions: Our results indicate that presleep learning favors sleep propensity and maintenance, offering the possibility to explore planned cognitive training as a low-cost treatment for sleep impairments.

Chemogenetic activation of orexin/hypocretin neurons ameliorates aging-induced changes in behavior and energy expenditure

Aging affects numerous physiological processes, as well as behavior. A large number of these processes are regulated, at least partially, by hypothalamic orexin neurons, and orexin tone may decrease with normal aging. In this study, we hypothesized that designer receptors exclusively activated by designer drugs (DREADD) stimulation of orexin neuronal activity will ameliorate the effect of aging on behavioral and metabolic alterations in young and middle-aged mice. DREADD targeting was achieved by stereotaxic injection of AAV vectors (AAV2-hSyn-DIO-hM3D(Gq)-mCherry) into the lateral hypothalamus of 5- and 12-mo old orexin-cre female mice and was confirmed by immunohistochemistry (IHC) analysis of orexin A and mCherry expression. After recovery, animals were subjected to a behavioral test battery consisting of the elevated plus maze (EPM), open field (OFT), and novel object recognition tests (NORT) to assess effects of aging on anxiety-like behavior, general locomotion, and working memory. A comprehensive laboratory animal monitoring system (CLAMS) was used to measure spontaneous physical activity (SPA) and energy expenditure (EE). The results indicate that activation of orexin neurons mitigates aging-induced reductions in anxiety-like behavior in middle-aged mice (P < 0.005) and increases locomotion in both young and middle-aged mice (P < 0.05). Activation of orexin neurons increases SPA (P < 0.01) and EE (P < 0.005) in middle-aged mice, restoring the levels to that observed in young animals. Results from this study identify orexin neurons as potential therapeutic targets for age-related impairments in cognitive and anxiety-related behavior, and energy balance.

Sleep and circadian rhythm disruption and stress intersect in Alzheimer's disease

Alzheimer's disease (AD) was discovered and the pathological hallmarks were revealed more than a century ago. Subsequently, many remarkable discoveries and breakthroughs provided us with mechanistic insights into the pathogenesis of AD. The identification of the molecular underpinning of the disease not only provided the framework of AD pathogenesis but also targets for therapeutic inventions. Despite all the initial successes, no effective treatment for AD has emerged yet as all the late stages of clinical trials have failed. Many factors ranging from genetic to environmental factors have been critically appraised as the potential causes of AD. In particular, the role of stress on AD has been intensively studied while the relationship between sleep and circadian rhythm disruption (SCRD) and AD have recently emerged. SCRD has always been thought to be a corollary of AD pathologies until recently, multiple lines of evidence converge on the notion that SCRD might be a contributing factor in AD pathogenesis. More importantly, how stress and SCRD intersect and make their concerted contributions to AD phenotypes has not been reviewed. The goal of this literature review is to examine at multiple levels - molecular, cellular (e.g. microglia, gut microbiota) and holistic - how the interaction between stress and SCRD bi-directionally and synergistically exacerbate AD pathologies and cognitive impairment. AD, in turn, worsens stress and SCRD and forms the vicious cycle that perpetuates and amplifies AD.

Does Increased Consolidated Nighttime Sleep Facilitate Attentional Control? A Pilot Study of Nap Restriction in Preschoolers

OBJECTIVE

The aim of this study is to understand the impact of a 5-day period of nap restriction on sleep patterns and cognitive function in typically developing preschoolers, aged 3 to 4 years.

METHOD

Following 1 week of baseline assessment, 28 children were randomly assigned to either a "napping as usual" group ( n = 15) or a 5-day period of nap restriction ( n = 13). Sleep was assessed with sleep logs and actigraphy; cognition was assessed at baseline and at the end of the intervention week.

RESULTS

No group differences in sleep or cognitive function were observed at baseline. For the no-nap group, the 5-day period of daytime nap restriction resulted in increased nighttime sleep. Children in the no-nap group also showed a significant improvement in attentional control compared with baseline, whereas no such changes were observed among children in the napping-as-usual group.

CONCLUSION

In preschool children who typically take naps, short-term nap restriction is associated with increased nighttime sleep and may contribute to improved attentional function.

Orexins as Novel Therapeutic Targets in Inflammatory and Neurodegenerative Diseases

Orexins [orexin-A (OXA) and orexin-B (OXB)] are two isoforms of neuropeptides produced by the hypothalamus. The main biological actions of orexins, focused on the central nervous system, are to control the sleep/wake process, appetite and feeding, energy homeostasis, drug addiction, and cognitive processes. These effects are mediated by two G protein-coupled receptor (GPCR) subtypes named OX1R and OX2R. In accordance with the synergic and dynamic relationship between the nervous and immune systems, orexins also have neuroprotective and immuno-regulatory (i.e., anti-inflammatory) properties. The present review gathers recent data demonstrating that orexins may have a therapeutic potential in several pathologies with an immune component including multiple sclerosis, Alzheimer's disease, narcolepsy, obesity, intestinal bowel diseases, septic shock, and cancers.