Differential effects of controllable and uncontrollable footshock stress on sleep in mice

Slumber under pressure: REM sleep and stress response

Sleep, a state of reduced responsiveness and distinct brain activity, is crucial across the animal kingdom. This review explores the potential adaptive functions of REM sleep in adapting to stress, emphasizing its role in memory consolidation, emotional regulation, and threat processing. We further explore the underlying neural mechanisms linking stress responses to REM sleep. By synthesizing current findings, we propose that REM sleep allows animals to "rehearse" or simulate responses to danger in a secure, offline state, while also maintaining emotional balance. Environmental factors, such as predation risk and social dynamics, further influence REM sleep. This modulation may enhance survival by optimizing stress responses while fulfilling physiological needs in animals. Insights into REM sleep's role in animals may shed light on human sleep in the context of modern stressors and sleep disruptions. This review also explores the complex interplay between stress, immunity, sleep disruptions-particularly involving REM sleep-and their evolutionary underpinnings.

Sex differences in the microglial response to stress and chronic alcohol exposure in mice

BACKGROUND

Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of the neurobiological processes underlying this sex difference is still emerging. Neuroimmune signaling, particularly by microglia, the brain's macrophages, is known to contribute to dysregulation of limbic circuits following stress and alcohol exposure. Females exhibit heightened immune reactivity, so we set out to characterize sex differences in the microglial response to stress and alcohol exposure.

METHODS

Male and female C57BL/6J mice were administered alcohol over 15 or 22 trials of a modified Drinking in the Dark paradigm, with repeated exposure to inescapable footshock stress and the stress-paired context. Mice were perfused immediately after drinking and we performed immunohistochemical analyses of microglial density, morphology, and protein expression in subregions of the amygdala and hippocampus.

RESULTS

We observed dynamic sex differences in microglial phenotypes at baseline and in response to stress and alcohol. Microglia in the hippocampus displayed more prominent sex differences and heightened reactivity to stress and alcohol. Chronic alcohol exposure decreased density of amygdala microglia and lysosomal expression.

CONCLUSION

We analyzed multiple measures of microglial activation, resulting in a comprehensive assessment of microglial changes mediated by sex, stress, and alcohol. These findings highlight the complexity of microglial contributions to the development of AUD and comorbid mood and stress disorders in men and women.

Prolactin in sleep and EEG regulation: New mechanisms and sleep-related brain targets complement classical data

The role of prolactin in sleep regulation has been the subject of extensive research over the past 50 years, resulting in the identification of multiple, disparate functions for the hormone. Prolactin demonstrated a characteristic circadian release pattern with elevation during dark and diminution during light. High prolactin levels were linked to non-rapid eye movement sleep and electroencephalogram delta activity in humans. Conversely, hyperprolactinemia showed strong correlation with REM sleep in rodent studies. Prolactin may be implicated in the alterations in female sleep patterns observed during the reproductive cycle, it may play a role in the REM sleep enhancement following stress and in sleep-related immunological processes. In conclusion, prolactin appears to have a sleep-promoting role, particularly during the dark phase. However, it does not appear to play a central and coherent role in sleep regulation, as observed in some neuropeptides such as orexin. Conversely, its principal function may be to facilitate situational, yet adaptive, changes in sleep patterns in response to challenging physiological phases, such as those associated with stress, immunological challenges, or the reproductive cycle. Neuronal substrates for prolactin-mediated sleep effects remain unknown; however, recent rodent sleep studies may provide insights into the potential sites of these effects.

The daily reciprocal associations between electroencephalography measured sleep and affect

Self-report studies show that sleep and positive and negative affect are closely and bidirectionally linked. However, studies assessing sleep objectively yield more inconsistent results. This study assessed the reciprocal, daily relationship between sleep as measured with electroencephalography (EEG) and affect (measured in the evening) in a natural setting. We assessed sleep both on the macrolevel (i.e., rapid eye movement [REM] sleep and slow-wave sleep [SWS] duration) and on the microlevel (i.e., REM sleep fragmentation). In this study, 33 participants (i.e., healthy college students, mean [standard deviation] age 21.55 [3.73] years, 67% female) were followed for 2 weeks. Each participant wore an EEG headband for 15 nights and had polysomnography during 3 of the 15 nights providing 72 analysable nights of polysomnography and 271 analysable nights with the EEG headband. Every evening participants reported their momentary negative and positive affect. We examined the relationship between pre-sleep affect and the sleep variables, as well as the reverse relationship, with sleep variables predicting evening affect the next day. We detected that higher negative affect in the evening was related to more fragmented REM sleep. However, this result was only found with polysomnography and not with the EEG headband. No significant associations were found between affect and time spent in REM sleep and SWS. Overall, no support was found for the reciprocal association between negative and positive affect and EEG measured sleep. Only limited support was found for an association in one direction (i.e., evening negative affect was associated with more REM sleep fragmentation at night).

Alcohol drinking is attenuated by PDE4 inhibition but partial microglia depletion is not sufficient to block stress-induced escalation of alcohol intake in female mice

Stress is a major contributing factor to binge drinking and development of alcohol use disorders (AUD), particularly in women. Both stress and chronic ethanol can enhance neuroinflammatory processes, which may dysregulate limbic circuits involved in ethanol reinforcement. Clinical and preclinical studies have identified sex differences in alcohol intake in response to neuroinflammatory triggers. Since both cyclic AMP (cAMP) signaling and microglial activation contribute to neuroinflammation, we explored their contribution to stress-induced ethanol drinking in mice. To this end, we first trained C57BL/6J male and female mice to volitionally drink ethanol through a modified version of the "Drinking-in-the-Dark" paradigm. We then assessed whether exposure to foot shock stress followed by repeated exposure to the previously stress-paired context might alter volitional ethanol drinking. We observed that stress exposure resulted in a delayed increase in ethanol intake, but only in female mice. The anti-inflammatory drug Apremilast, an inhibitor of phosphodiesterase type 4 (PDE4; the primary enzyme for cAMP degradation in the brain), reduced ethanol intake and decreased preference for ethanol regardless of stress exposure in females. In contrast, a partial pharmacological depletion of microglia via PLX3397 treatment did not significantly alter baseline ethanol drinking or stress-induced ethanol drinking in female mice. This study shows that female mice are more susceptible to stress-induced ethanol drinking than males, and that this occurs even after partial microglial depletion. In addition, modulation of cAMP signaling by Apremilast administration reduced ethanol drinking regardless of stress exposure, supporting the idea that it might be useful for treatment of AUD.

Insomnia-related rodent models in drug discovery

Despite the widespread prevalence and important medical impact of insomnia, effective agents with few side effects are lacking in clinics. This is most likely due to relatively poor understanding of the etiology and pathophysiology of insomnia, and the lack of appropriate animal models for screening new compounds. As the main homeostatic, circadian, and neurochemical modulations of sleep remain essentially similar between humans and rodents, rodent models are often used to elucidate the mechanisms of insomnia and to develop novel therapeutic targets. In this article, we focus on several rodent models of insomnia induced by stress, diseases, drugs, disruption of the circadian clock, and other means such as genetic manipulation of specific neuronal activity, respectively, which could be used to screen for novel hypnotics. Moreover, important advantages and constraints of some animal models are discussed. Finally, this review highlights that the rodent models of insomnia may play a crucial role in novel drug development to optimize the management of insomnia.

Role of microglia in stress-induced alcohol intake in female and male mice

Rates of alcohol use disorder (AUD) have escalated in recent years, with a particular increase among women. Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of sex-specific neurobiological substrates underlying this phenomenon is still emerging. Microglia, the resident macrophages of the brain, are essential for reshaping neuronal processes, and microglial activity contributes to overall neuronal plasticity. We investigated microglial dynamics and morphology in limbic brain structures of male and female mice following exposure to stress, alcohol or both challenges. In a modified paradigm of intermittent binge drinking (repeated "drinking in the dark"), we determined that female, but not male, mice increased their alcohol consumption after exposure to a physical stressor and re-exposure trials in the stress-paired context. Ethanol (EtOH) drinking and stress altered a number of microglial parameters, including overall number, in subregions of the amygdala and hippocampus, with effects that were somewhat more pronounced in female mice. We used the CSF1R antagonist PLX3397 to deplete microglia in female mice to determine whether microglia contribute to stress-induced escalation of EtOH intake. We observed that microglial depletion attenuated stress-induced alcohol intake with no effect in the unstressed group. These findings suggest that microglial activity can contribute to alcohol intake under stressful conditions, and highlight the importance of evaluating sex-specific mechanisms that could result in tailored interventions for AUD in women.

A prolonged stress rat model recapitulates some PTSD-like changes in sleep and neuronal connectivity

Chronic post-traumatic stress disorder (PTSD) exhibits psychological abnormalities during fear memory processing in rodent models. To simulate long-term impaired fear extinction in PTSD patients, we constructed a seven-day model with multiple prolonged stress (MPS) by modifying manipulation repetitions, intensity, and unpredictability of stressors. Behavioral and neural changes following MPS conveyed longitudinal PTSD-like effects in rats for 6 weeks. Extended fear memory was estimated through fear retrieval induced-freezing behavior and increased long-term serum corticosterone concentrations after MPS manipulation. Additionally, memory retrieval and behavioral anxiety tasks continued enhancing theta oscillation activity in the prefrontal cortex-basal lateral amygdala-ventral hippocampus pathway for an extended period. Moreover, MPS and remote fear retrieval stimuli disrupted sleep-wake activities to consolidate fear memory. Our prolonged fear memory, neuronal connectivity, anxiety, and sleep alteration results demonstrated integrated chronic PTSD symptoms in an MPS-induced rodent model.

Stressor control and regional inflammatory responses in the brain: regulation by the basolateral amygdala

Increasing evidence has connected the development of certain neuropsychiatric disorders, as well as neurodegenerative diseases, to stress-induced dysregulation of the immune system. We have shown that escapable (ES) and inescapable (IS) footshock stress, and memories associated with ES or IS, can differentially alter inflammatory-related gene expression in brain in a region dependent manner. We have also demonstrated that the basolateral amygdala (BLA) regulates stress- and fear memory-induced alterations in sleep, and that differential sleep and immune responses in the brain to ES and IS appear to be integrated during fear conditioning and then reproduced by fear memory recall. In this study, we investigated the role of BLA in influencing regional inflammatory responses within the hippocampus (HPC) and medial prefrontal cortex (mPFC) by optogenetically stimulating or inhibiting BLA in male C57BL/6 mice during footshock stress in our yoked shuttlebox paradigm based on ES and IS. Then, mice were immediately euthanized and RNA extracted from brain regions of interest and loaded into NanoString® Mouse Neuroinflammation Panels for compilation of gene expression profiles. Results showed differential regional effects in gene expression and activated pathways involved in inflammatory-related signaling following ES and IS, and these differences were altered depending on amygdalar excitation or inhibition. These findings demonstrate that the stress-induced immune response, or "parainflammation", is affected by stressor controllability and that BLA influences regional parainflammation to ES or IS in HPC and mPFC. The study illustrates how stress-induced parainflammation can be regulated at the neurocircuit level and suggests that this approach can be useful for uncovering circuit and immune interactions in mediating differential stress outcomes.

Modeling integrated stress, sleep, fear and neuroimmune responses: Relevance for understanding trauma and stress-related disorders

Sleep and stress have complex interactions that are implicated in both physical diseases and psychiatric disorders. These interactions can be modulated by learning and memory, and involve additional interactions with the neuroimmune system. In this paper, we propose that stressful challenges induce integrated responses across multiple systems that can vary depending on situational variables in which the initial stress was experienced, and with the ability of the individual to cope with stress- and fear-inducing challenges. Differences in coping may involve differences in resilience and vulnerability and/or whether the stressful context allows adaptive learning and responses. We provide data demonstrating both common (corticosterone, SIH and fear behaviors) and distinguishing (sleep and neuroimmune) responses that are associated with an individual's ability to respond and relative resilience and vulnerability. We discuss neurocircuitry regulating integrated stress, sleep, neuroimmune and fear responses, and show that responses can be modulated at the neural level. Finally, we discuss factors that need to be considered in models of integrated stress responses and their relevance for understanding stress-related disorders in humans.

Pontine control of rapid eye movement sleep and fear memory

AIMS

We often experience dreams of strong irrational and negative emotional contents with postural muscle paralysis during rapid eye movement (REM) sleep, but how REM sleep is generated and its function remain unclear. In this study, we investigate whether the dorsal pontine sub-laterodorsal tegmental nucleus (SLD) is necessary and sufficient for REM sleep and whether REM sleep elimination alters fear memory.

METHODS

To investigate whether activation of SLD neurons is sufficient for REM sleep induction, we expressed channelrhodopsin-2 (ChR2) in SLD neurons by bilaterally injecting AAV1-hSyn-ChR2-YFP in rats. We next selectively ablated either glutamatergic or GABAergic neurons from the SLD in mice in order to identify the neuronal subset crucial for REM sleep. We finally  investigated the role of REM sleep in consolidation of fear memory using rat model with complete SLD lesions.

RESULTS

We demonstrate the sufficiency of the SLD for REM sleep by showing that photo-activation of ChR2 transfected SLD neurons selectively promotes transitions from non-REM (NREM) sleep to REM sleep in rats. Diphtheria toxin-A (DTA) induced lesions of the SLD in rats or specific deletion of SLD glutamatergic neurons but not GABAergic neurons in mice completely abolish REM sleep, demonstrating the necessity of SLD glutamatergic neurons for REM sleep. We then show that REM sleep elimination by SLD lesions in rats significantly enhances contextual and cued fear memory consolidation by 2.5 and 1.0 folds, respectively, for at least 9 months. Conversely, fear conditioning and fear memory trigger doubled amounts of REM sleep in the following night, and chemo-activation of SLD neurons projecting to the medial septum (MS) selectively enhances hippocampal theta activity in REM sleep; this stimulation immediately after fear acquisition reduces contextual and cued fear memory consolidation by 60% and 30%, respectively.

CONCLUSION

SLD glutamatergic neurons generate REM sleep and REM sleep and SLD via the hippocampus particularly down-regulate contextual fear memory.

The influence of sleep on fear extinction in trauma-related disorders

In Posttraumatic Stress Disorder (PTSD), fear and anxiety become dysregulated following psychologically traumatic events. Regulation of fear and anxiety involves both high-level cognitive processes such as cognitive reattribution and low-level, partially automatic memory processes such as fear extinction, safety learning and habituation. These latter processes are believed to be deficient in PTSD. While insomnia and nightmares are characteristic symptoms of existing PTSD, abundant recent evidence suggests that sleep disruption prior to and acute sleep disturbance following traumatic events both can predispose an individual to develop PTSD. Sleep promotes consolidation in multiple memory systems and is believed to also do so for low-level emotion-regulatory memory processes. Consequently sleep disruption may contribute to the etiology of PTSD by interfering with consolidation in low-level emotion-regulatory memory systems. During the first weeks following a traumatic event, when in the course of everyday life resilient individuals begin to acquire and consolidate these low-level emotion-regulatory memories, those who will develop PTSD symptoms may fail to do so. This deficit may, in part, result from alterations of sleep that interfere with their consolidation, such as REM fragmentation, that have also been found to presage later PTSD symptoms. Here, sleep disruption in PTSD as well as fear extinction, safety learning and habituation and their known alterations in PTSD are first briefly reviewed. Then neural processes that occur during the early post-trauma period that might impede low-level emotion regulatory processes through alterations of sleep quality and physiology will be considered. Lastly, recent neuroimaging evidence from a fear conditioning and extinction paradigm in patient groups and their controls will be considered along with one possible neural process that may contribute to a vulnerability to PTSD following trauma.

Controllable and Uncontrollable Stress Differentially Impact Fear Conditioned Alterations in Sleep and Neuroimmune Signaling in Mice

Stress induces neuroinflammation and disrupts sleep, which together can promote a number of stress-related disorders. Fear memories associated with stress can resurface and reproduce symptoms. Our previous studies have demonstrated sleep outcomes can be modified by stressor controllability following stress and fear memory recall. However, it is unknown how stressor controllability alters neuroinflammatory signaling and its association with sleep following fear memory recall. Mice were implanted with telemetry transmitters and experienced escapable or inescapable footshock and then were re-exposed to the shuttlebox context one week later. Gene expression was assessed with Nanostring® panels using RNA extracted from the basolateral amygdala and hippocampus. Freezing and temperature were examined as behavioral measures of fear. Increased sleep after escapable stress was associated with a down-regulation in neuro-inflammatory and neuro-degenerative related genes, while decreased sleep after inescapable stress was associated with an up-regulation in these genes. Behavioral measures of fear were virtually identical. Sleep and neuroimmune responses appear to be integrated during fear conditioning and reproduced by fear memory recall. The established roles of disrupted sleep and neuroinflammation in stress-related disorders indicate that these differences may serve as informative indices of how fear memory can lead to psychopathology.

Sleep architecture and regulation of male dusky antechinus, an Australian marsupial

Study Objectives

In this study, we (1) describe sleep behavior and architecture, and (2) explore how sleep is regulated in dusky antechinus (Antechinus swainsonii), a small insectivorous marsupial. Our aim is to provide the first investigation into sleep homeostasis in a marsupial.

Methods

Wild-caught male dusky antechinus (n = 4) were individually housed in large indoor cages under a natural photoperiod of 10.5 h light/13.5 h dark. Continuous recordings of EEG, EMG, and tri-axial accelerometry were performed under baseline conditions and following 4-h of extended wakefulness.

Results

Antechinus engage in SWS and REM sleep. Some aspects of these states are mammal-like, including a high amount (23%) of REM sleep, but other features are reminiscent of birds, notably, hundreds of short sleep episodes (SWS mean: 34 s; REM sleep: 10 s). Antechinus are cathemeral and sleep equally during the night and day. Immediately after the sleep deprivation ended, the animals engaged in more SWS, longer SWS episodes, and greater SWS SWA. The animals did not recover lost REM sleep.

Conclusions

Sleep architecture in dusky antechinus was broadly similar to that observed in eutherian and marsupial mammals, but with interesting peculiarities. We also provided the first evidence of SWS homeostasis in a marsupial mammal.

Social sleepers: The effects of social status on sleep in terrestrial mammals

Social status among group-living mammals can impact access to resources, such as water, food, social support, and mating opportunities, and this differential access to resources can have fitness consequences. Here, we propose that an animal's social status impacts their access to sleep opportunities, as social status may predict when an animal sleeps, where they sleep, who they sleep with, and how well they sleep. Our review of terrestrial mammals examines how sleep architecture and intensity may be impacted by (1) sleeping conditions and (2) the social experience during wakefulness. Sleeping positions vary in thermoregulatory properties, protection from predators, and exposure to parasites. Thus, if dominant individuals have priority of access to sleeping positions, they may benefit from higher quality sleeping conditions and, in turn, better sleep. With respect to waking experiences, we discuss the impacts of stress on sleep, as it has been established that specific social statuses can be characterized by stress-related physiological profiles. While much research has focused on how dominance hierarchies impact access to resources like food and mating opportunities, differential access to sleep opportunities among mammals has been largely ignored despite its potential fitness consequences.

Regulation of Dark Period Sleep by the Amygdala: A microinjection and optogenetics study

The central nucleus of the amygdala (CNA) projects to brainstem regions that generate and regulate rapid eye movement sleep (REM). We used optogenetics to assess the influence of CNA inputs into reticularis pontis oralis (RPO), pedunculopontine tegmentum (PPT) and nucleus subcoeruleus (SubC) on dark period sleep. We compared these results to effects of microinjections into CNA of the GABA_A agonist, muscimol (MUS, inhibition of cell bodies) and tetrodotoxin (TTX, inhibition of cell bodies and fibers of passage). For optogenetics, male Wistar rats received excitatory (AAV5-EF1a-DIO -hChR2(H134R)-EYFP) or inhibitory (AAV-EF1a-DIO-eNpHR3.0-EYFP; DIO-eNpHR3.0) opsins into CNA and AAV5-EF1a-mCherry-IRES-WGA-Cre into RPO, PPT, or SubC. This enabled only CNA neurons synaptically connected to each region to express opsin. Optic cannulae for light delivery into CNA and electrodes for determining sleep were implanted. Sleep was recorded with and without blue or amber light stimulation of CNA. Separate rats received MUS or TTX into CNA prior to recording sleep. Optogenetic activation of CNA neurons projecting to RPO enhanced REM and did not alter non-REM (NREM) whereas activation of CNA neurons projecting to PPT or SubC did not significantly affect sleep. Inhibition of CNA neurons projecting to any region did not significantly alter sleep. TTX inactivation of CNA decreased REM and increased NREM whereas muscimol inactivation did not significantly alter sleep. Thus, the amygdala can regulate decreases and increases in REM, and RPO is important for CNA promotion of REM. Fibers passing through CNA, likely from the basolateral nucleus of the amygdala, also play a role in regulating sleep.

Hypocretin in locus coeruleus and dorsal raphe nucleus mediates inescapable footshock stimulation (IFS)-induced REM sleep alteration

Hypocretin (hcrt) is a stress-reacting neuropeptide mediating arousal and energy homeostasis. An inescapable footshock stimulation (IFS) could initiate the hcrt release from the lateral hypothalamus (LHA) and suppresses rapid eye movement (REM) sleep in rodents. However, the effects of the IFS-induced hcrts on REM-off nuclei, the locus coeruleus (LC) and dorsal raphe nucleus (DRN), remained unclear. We hypothesized that the hcrt projections from the LHA to LC or DRN mediate IFS-induced sleep disruption. Our results demonstrated that the IFS increased hcrt expression and the neuronal activities in the LHA, hypothalamus, brainstem, thalamus, and amygdala. Suppressions of REM sleep and slow wave activity during non-REM (NREM) sleep caused by the high expression of hcrts were blocked when a non-specific and dual hcrt receptor antagonist was administered into the LC or DRN. Furthermore, the IFS also caused an elevated innate anxiety, but was limitedly influenced by the hcrt antagonist. This result suggests that the increased hcrt concentrations in the LC and DRN mediate stress-induced sleep disruptions and might partially involve IFS-induced anxiety.

The Basolateral Amygdala Mediates the Role of Rapid Eye Movement Sleep in Integrating Fear Memory Responses

The basolateral amygdala (BLA) mediates the effects of stress and fear on rapid eye movement sleep (REM) and on REM-related theta (θ) oscillatory activity in the electroencephalograph (EEG), which is implicated in fear memory consolidation. We used optogenetics to assess the potential role of BLA glutamate neurons (BLA^Glu) in regulating behavioral, stress and sleep indices of fear memory, and their relationship to altered θ. An excitatory optogenetic construct targeting glutamatergic cells (AAV-CaMKIIα-hChR2-eYFP) was injected into the BLA of mice. Telemetry was used for real-time monitoring of EEG, activity, and body temperature to determine sleep states and stress-induced hyperthermia (SIH). For 3 h following shock training (ST: 20 footshocks, 0.5 mA, 0.5 s, 1 min interval), BLA was optogenetically stimulated only during REM (REM + L) or NREM (NREM + L). Mice were then re-exposed to the fear context at 24 h, 48 h, and 1 week after ST and assessed for behavior, SIH, sleep and θ activity. Control mice were infected with a construct without ChR2 (eYFP) and studied under the same conditions. REM + L significantly reduced freezing and facilitated immediate recovery of REM tested at 24 h and 48 h post-ST during contextual re-exposures, whereas NREM + L had no significant effect. REM + L significantly reduced post-ST REM-θ, but attenuated REM-θ reductions at 24 h compared to those found in NREM + L and control mice. Fear-conditioned SIH persisted regardless of treatment. The results demonstrate that BLA^Glu activity during post-ST REM mediates the integration of behavioral and sleep indices of fear memory by processes that are associated with θ oscillations within the amygdalo-hippocampal pathway. They also demonstrate that fear memories can remain stressful (as indicated by SIH) even when fear conditioned behavior (freezing) and changes in sleep are attenuated.

Basolateral Amygdala Regulates EEG Theta-activity During Rapid Eye Movement Sleep

Pharmacological and optogenetic studies have demonstrated that the basolateral amygdala (BLA) plays a pivotal role in regulating fear-conditioned changes in sleep, in particular, rapid eye movement sleep (REM). However, the linkage between BLA and REM regulation has been minimally examined. In this study, we optogenetically activated or inhibited BLA selectively during spontaneous REM, and determined the effects on REM amounts and on hippocampus regulated EEG-theta (θ) activity. Excitatory (CaMKIIα-hChR2 (E123A)-eYFP-WPRE) or inhibitory (CaMKIIα-eNpHR3.0-eYFP-WPRE) optogenetic constructs were stereotaxically delivered targeting glutamatergic cells in BLA (BLA^Glu) of mice. Viral constructs without opsin (CaMKIIα-eYFP-WPRE) were used as controls. All mice were implanted with telemetry transmitters for monitoring electroencephalography (EEG), activity, and body temperature, and with optic cannulas for light delivery to the BLA. BLA^Glu were optogenetically activated by blue light (473 nm), or inhibited by green light (532 nm), in 10 s epochs during REM, or non-REM (NREM), in undisturbed mice. Sleep amounts and EEG activity were analyzed. Projections from BLA^Glu to neurons in hippocampus were immunohistochemically (IHC) examined. Brief optogenetic activation of BLA^Glu during REM immediately reduced EEG theta activity (5-8 Hz, REM-θ), without affecting overall amount and propensity of sleep, while optogenetic inhibition increased REM-θ. Stimulation during NREM had no effect on EEG spectra or sleep. IHC results showed that glutamatergic and GABAergic cells in CA3 of the hippocampus received inputs from BLA^Glu projection neurons. Activation of BLA^Glu reduced, and inhibition increased, REM-θ without otherwise altering sleep. Optogenetic stimulation of BLA^Glu may be useful for systematically manipulating sleep-related amygdalo-hippocampal interactions.

The European starling (Sturnus vulgaris) shows signs of NREM sleep homeostasis but has very little REM sleep and no REM sleep homeostasis

Most of our knowledge about the regulation and function of sleep is based on studies in a restricted number of mammalian species, particularly nocturnal rodents. Hence, there is still much to learn from comparative studies in other species. Birds are interesting because they appear to share key aspects of sleep with mammals, including the presence of two different forms of sleep, i.e. non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. We examined sleep architecture and sleep homeostasis in the European starling, using miniature dataloggers for electroencephalogram (EEG) recordings. Under controlled laboratory conditions with a 12:12 h light-dark cycle, the birds displayed a pronounced daily rhythm in sleep and wakefulness with most sleep occurring during the dark phase. Sleep mainly consisted of NREM sleep. In fact, the amount of REM sleep added up to only 1~2% of total sleep time. Animals were subjected to 4 or 8 h sleep deprivation to assess sleep homeostatic responses. Sleep deprivation induced changes in subsequent NREM sleep EEG spectral qualities for several hours, with increased spectral power from 1.17 Hz up to at least 25 Hz. In contrast, power below 1.17 Hz was decreased after sleep deprivation. Sleep deprivation also resulted in a small compensatory increase in NREM sleep time the next day. Changes in EEG spectral power and sleep time were largely similar after 4 and 8 h sleep deprivation. REM sleep was not noticeably compensated after sleep deprivation. In conclusion, starlings display signs of NREM sleep homeostasis but the results do not support the notion of important REM sleep functions.

Homeostatic sleep regulation in the absence of the circadian sleep-regulating component: effect of short light-dark cycles on sleep-wake stages and slow waves

BACKGROUND

Aside from the homeostatic and circadian components, light has itself an important, direct as well as indirect role in sleep regulation. Light exerts indirect sleep effect by modulating the circadian rhythms. Exposure to short light-dark cycle (LD 1:1, 1:1 h light - dark) eliminates the circadian sleep regulatory component but direct sleep effect of light could prevail. The aim of the present study was to examine the interaction between the light and the homeostatic influences regarding sleep regulation in a rat model.

METHODS

Spontaneous sleep-wake and homeostatic sleep regulation by sleep deprivation (SD) and analysis of slow waves (SW) were examined in Wistar rats exposed to LD1:1 condition using LD12:12 regime as control.

RESULTS

Slow wave sleep (SWS) and REM sleep were both enhanced, while wakefulness (W) was attenuated in LD1:1. SWS recovery after 6-h total SD was more intense in LD1:1 compared to LD12:12 and SWS compensation was augmented in the bright hours. Delta power increment during recovery was caused by the increase of SW number in both cases. More SW was seen during baseline in the second half of the day in LD1:1 and after SD compared to the LD12:12. Increase of SW number was greater in the bright hours compared to the dark ones after SD in LD1:1. Lights ON evoked immediate increase in W and decrease in both SWS and REM sleep during baseline LD1:1 condition, while these changes ceased after SD. Moreover, the initial decrease seen in SWS after lights ON, turned to an increase in the next 6-min bin and this increase was stronger after SD. These alterations were caused by the change of the epoch number in W, but not in case of SWS or REM sleep. Lights OFF did not alter sleep-wake times immediately, except W, which was increased by lights OFF after SD.

CONCLUSIONS

Present results show the complex interaction between light and homeostatic sleep regulation in the absence of the circadian component and indicate the decoupling of SW from the homeostatic sleep drive in LD1:1 lighting condition.

Group II metabotropic glutamate receptor activation in the basolateral amygdala mediates individual differences in stress-induced changes in rapid eye movement sleep

Group II metabotropic glutamate receptors (mGluR2/3s) have been implicated in stress and trauma related disorders including post-traumatic stress disorder (PTSD). PTSD is characterized by flashbacks, anxiety, and sleep disturbances. While many people are exposed to trauma in their lifetime, only a small percentage go on to develop PTSD, indicating individual differences in stress and emotional processing. Wistar strain rats display directionally different rapid-eye movement sleep (REM) responses to footshock stress, with resilient rats having no change or an increase in REM and vulnerable rats having a significant reduction in REM compared to baseline. The basolateral nucleus of the amygdala (BLA) is key in regulating individual differences in stress-induced alterations in sleep. Group II metabotropic glutamate receptors (mGluR2/3s) negatively modulate glutamate and are implicated in fear, fear memory, and sleep. The current study evaluated the effect of mGluR2/3 agonist LY379268 (LY37) in BLA on stress and fear memory induced changes in sleep, EEG spectra, behavioral fear expression and physiological stress. These data indicate that vulnerable rats treated with LY37 have an attenuation of the REM reductions generally seen in vulnerable rats. Furthermore, LY37 altered EEG spectra in the delta (0.5-4.5 Hz) and theta (5-9.5 Hz) frequency. LY37 did not impact behavioral fear expression or physiological stress. Therefore, mGluR2/3s within BLA are implicated in regulating individual differences in sleep responses to fear- and stress-related memories.

[A Review of the Posttraumatic Stress Disorder and Sleep Disturbances]

Post-traumatic stress disorder (PTSD) is characterized by intrusive emotional memory, alertness and avoidance after individuals suffer from one or more traumatic events. With the exception of manifestations, sleep disturbances are also considered to be the core symptoms of PTSD. This article mainly discussed insomnia, nightmares, obstructive sleep apnea (OSA), and periodic limb movement during sleep (PLMS) in patients with PTSD. Existing evidence suggested that insomnia is a predictor of the development of PTSD. Cognitive behavioral therapy for insomnia is an important research direction for treating insomnia in PTSD patients. Nightmares are also the core symptom of PTSD. Prazosin and image rehearsal therapy are effective therapies to treat post-traumatic nightmares. The co-occurrence of obstructive sleep apnea (OSA) is over 40% in patients with PTSD. Preliminary studies have shown that continuous positive airway pressure therapy can improve PTSD symptoms in patients with PTSD comorbid OSA. In the process of diagnosis and treatment of PTSD patients, it is important to firstly evaluate whether PTSD patient comorbid OSA or insomnia, and then clinicians could further develop an appropriate treatment plan for these patients.

Neural and Homeostatic Regulation of REM Sleep

Rapid eye movement (REM) sleep is a distinct, homeostatically controlled brain state characterized by an activated electroencephalogram (EEG) in combination with paralysis of skeletal muscles and is associated with vivid dreaming. Understanding how REM sleep is controlled requires identification of the neural circuits underlying its initiation and maintenance, and delineation of the homeostatic processes regulating its expression on multiple timescales. Soon after its discovery in humans in 1953, the pons was demonstrated to be necessary and sufficient for the generation of REM sleep. But, especially within the last decade, researchers have identified further neural populations in the hypothalamus, midbrain, and medulla that regulate REM sleep by either promoting or suppressing this brain state. The discovery of these populations was greatly facilitated by the availability of novel technologies for the dissection of neural circuits. Recent quantitative models integrate findings about the activity and connectivity of key neurons and knowledge about homeostatic mechanisms to explain the dynamics underlying the recurrence of REM sleep. For the future, combining quantitative with experimental approaches to directly test model predictions and to refine existing models will greatly advance our understanding of the neural and homeostatic processes governing the regulation of REM sleep.

Differential behavioral, stress, and sleep responses in mice with different delays of fear extinction

STUDY OBJECTIVES

Sleep, in particular rapid eye movement (REM), has been linked to fear learning and extinction; however, their relationship is poorly understood. We determined how different delays of extinction training (ET) impact fear-conditioned behaviors, changes in sleep, and stress responses.

METHODS

EEG activity, movement, and body temperature in mice were monitored via telemetry. Following contextual fear conditioning (shock training [ST]), separate groups of mice were reexposed to the context at 24-hour post-ST (24h ET-1) and at 48-hour post-ST (48h ET-1). Post-ET sleep amount and sleep-associated EEG (delta and theta) activity were compared to baseline and to post-ST sleep. Freezing, locomotion, grooming, and rearing were monitored to determine effects of ET on fear behaviors. Body temperature immediately after ET was monitored to assess stress-induced hyperthermia (SIH).

RESULTS

24h ET-1 and 48h ET-1 produced similar freezing and REM reductions, but dissimilar rearing activity and SIH. 24h ET-1 was followed by periods of suppressed REM-associated theta (REM-θ) activity, immediately after ET and during the subsequent dark period. Suppressed REM-θ was specific to sleep after 24h ET-1, and did not occur after ST, nor after 48h ET-1.

CONCLUSIONS

ET-1 at 24 and 48 hours after ST was associated with similar freezing and REM amounts, but with differences in other overt behaviors, in REM-θ, and in SIH. Freezing was not predictive of changes in other fear-associated responses. This study demonstrated that consideration of time delay from fear acquisition to extinction is important when assessing the relationships between extinction and behavior, sleep, and stress responses.

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.

Hypocretin in median raphe nucleus modulates footshock stimuli-induced REM sleep alteration

Stress is one of major factors that cause sleep problems. Hypocretin represents a stress-related neuropeptide and is well known in maintaining physiological wakefulness. The hypocretinergic neurons originate in the lateral hypothalamic area (LHA) and transmit to several brain regions, including the median raphe nuclei (MRNs). The MRNs modulate both fear responses and sleep-wake activity; however, it remains unclear whether stress alters the levels of hypocretin to regulate MRNs and consequently disrupt sleep. In this paper, we employed the inescapable footshock stimuli (IFS) as a stressor and hypothesized that the IFS-induced sleep disruption is mediated by increased hypocretins in the MRNs. Our results demonstrate that the concentrations of hypocretin in the hypothalamus increased after IFS. Rapid eye movement (REM) sleep was reduced after footshock, and microinjection of non-selective hypocretin receptor antagonist TCS-1102 into the MRNs blocked the IFS-induced decrease of REM sleep. Furthermore, administration of hypocretins into the MRNs mimicked the IFS-induced REM sleep reduction. These results conclude that the increased levels of hypocretins in the MRNs mediate the IFS-induced REM sleep reduction.

Animal Models of PTSD: A Critical Review

The goals of animal research in post-traumatic stress disorder (PTSD) include better understanding the neurophysiological etiology of PTSD, identifying potential targets for novel pharmacotherapies, and screening drugs for their potential use as PTSD treatment in humans. Diagnosis of PTSD relies on a patient interview and, as evidenced by changes to the diagnostic criteria in the DSM-5, an adequate description of this disorder in humans is a moving target. Therefore, it may seem insurmountable to model the construct of PTSD in animals such as rodents. Fortunately, the neural circuitry involved in fear and anxiety, thought to be essential to the etiology of PTSD in humans, is highly conserved throughout evolution. Furthermore, many symptoms can be modeled using behavioral tests that have face, construct, and predictive validity. Because PTSD is precipitated by a definite traumatic experience, animal models can simulate the induction of PTSD, and test causal factors with longitudinal designs. Accordingly, several animal models of physical and psychological trauma have been established. This review discusses the widely used animal models of PTSD in rodents, and overviews their strengths and weaknesses in terms of face, construct, and predictive validity.

Acute Social Defeat Stress Increases Sleep in Mice

Social conflict is a major source of stress in humans. Animals also experience social conflicts and cope with them by stress responses that facilitate arousal and activate sympathetic and neuroendocrine systems. The effect of acute social defeat (SoD) stress on the sleep/wake behavior of mice has been reported in several models based on a resident-intruder paradigm. However, the post-SoD stress sleep/wake effects vary between the studies and the contribution of specific effects in response to SoD or non-specific effects of the SoD procedure (e.g., sleep deprivation) is not well established. In this study, we established a mouse model of acute SoD stress based on strong aggressive mouse behavior toward unfamiliar intruders. In our model, we prevented severe attacks of resident mice on submissive intruder mice to minimize behavioral variations during SoD. In response to SoD, slow-wave sleep (SWS) strongly increased during 9 h. Although some sleep changes after SoD stress can be attributed to non-specific effects of the SoD procedure, most of the SWS increase is likely a specific response to SoD. Slow-wave activity was only enhanced for a short period after SoD and dissipated long before the SWS returned to baseline. Moreover, SoD evoked a strong corticosterone response that may indicate a high stress level in the intruder mice after SoD. Our SoD model may be useful for studying the mechanisms and functions of sleep in response to social stress.

Modelling posttraumatic stress disorders in animals

Animal models of posttraumatic stress disorder are useful tools to reveal the neurobiological basis of the vulnerability to traumatic events, and to develop new treatment strategies, as well as predicting treatment response contributing to personalized medicine approach. Different models have different construct, face and predictive validity and they model different symptoms of the disease. The most prevalent models are the single prolonged stress, electric foot-shock and predator odor. Freezing as 're-experiencing' in cluster B and startle as 'arousal' in cluster E according to DSM-5 are the most frequently studied parameters; however, several other symptoms related to mood, cognitive and social skills are part of the examinations. Beside behavioral characteristics, symptoms of exaggerated sympathetic activity and hypothalamic-pituitary-adrenocortical axis as well as signs of sleep disturbances are also warranted. Test battery rather than a single test is required to describe a model properly and the results should be interpreted in a comprehensive way, e.g. creating a z-score. Research is shifting to study larger populations and identifying the features of the resilient and vulnerable individuals, which cannot be easily done in humans. Incorporation of the "three hit theory" in animal models may lead to a better animal model of vulnerability and resilience. As women are twice as vulnerable as men, more emphasize should be taken to include female animals. Moreover, hypothesis free testing and big data analysis may help to identify an array of biomarkers instead of a single variable for identification of vulnerability and for the purpose of personalized medicine.

The low-down on sleeping down low: pigeons shift to lighter forms of sleep when sleeping near the ground

Sleep in birds is composed of two distinct sub-states, remarkably similar to mammalian slow-wave sleep (SWS) and rapid eye movement (REM) sleep. However, it is unclear whether all aspects of mammalian sleep are present in birds. We examined whether birds suppress REM sleep in response to changes in sleeping conditions that presumably evoke an increase in perceived predation risk, as observed previously in rodents. Although pigeons sometimes sleep on the ground, they prefer to sleep on elevated perches at night, probably to avoid nocturnal mammalian ground predators. Few studies to date have investigated how roosting sites affect sleep architecture. We compared sleep in captive pigeons on days with and without access to high perches. On the first (baseline) day, low and high perches were available; on the second day, the high perches were removed; and on the third (recovery) day, the high perches were returned. The total time spent sleeping did not vary significantly between conditions; however, the time spent in REM sleep declined on the low-perch night and increased above baseline when the pigeons slept on the high perch during the recovery night. Although the amount of SWS did not vary significantly between conditions, SWS intensity was lower on the low-perch night, particularly early in the night. The similarity of these responses between birds and mammals suggests that REM sleep is influenced by at least some ecological factors in a similar manner in both groups of animals.

Effects of stressor controllability on transcriptional levels of c-fos, Arc, and brain-derived neurotrophic factor in mouse amygdala and medial prefrontal cortex

Controllability is an important factor in determining stress outcomes. Uncontrollable stress is associated with the development of psychopathology such as post-traumatic stress disorder, whereas controllable stress is associated with adaptive stress responses and positive outcomes. In this study, we investigated how controllability affects poststress neurobiology by assessing transcriptional levels of activity-dependent genes in medial prefrontal cortex (mPFC) and amygdala, regions important in mediating stress outcomes. Mice were subjected to either escapable shock (ES) or yoked inescapable shock (IS) as models of controllable and uncontrollable stress, respectively. Immediately (0 h) or at 2 h after shock training (20 trials; 0.5 mA, 5.0 s maximum duration; 1.0 min interstimulus interval), mice were killed, and we interrogated expression levels of the immediate-early genes, c-fos and Arc, and a delayed primary response gene, brain-derived neurotrophic factor, in mPFC, amygdala, and somatosensory cortex (a control region), using real-time reverse transcription quantitative PCR (RT qPCR). We found ES-associated up-regulation of brain-derived neurotrophic factor in amygdala as well as in mPFC. IS suppressed c-fos in mPFC (0 h) but induced more Arc in amygdala (2 h) in comparison with ES. Freezing, an index of fear memory, and serum level corticosterone, an index of the stress response, did not differ between mice trained with ES or IS. The data are discussed with respect to the potential functional involvements of the amygdala and mPFC in mediating differential outcomes of controllable and uncontrollable stress.

Controllable and uncontrollable stress differentially impact pathogenicity and survival in a mouse model of viral encephalitis

Intranasal instillation of vesicular stomatitis virus (VSV) into mice given controllable stress (modeled by escapable foot shock, ES) resulted in enhanced pathogenicity and decreased survival relative to infected mice given uncontrollable stress (modeled by inescapable foot shock, IS) and non-shocked control mice. Survival likely reflected differential cytokine gene expression that may have been regulated by miR146a, a predicted stress-responsive upstream regulator. Controllability also enhanced the accumulation of brain T resident memory cells that persisted long after viral clearance. The unexpected facilitatory effect of ES on antiviral neuroimmune responses and pathogenicity may arise from differential immunoactivating and immunosuppressive effects of uncontrollable and controllable stress.

Antagonism of corticotropin releasing factor in the basolateral amygdala of resilient and vulnerable rats: Effects on fear-conditioned sleep, temperature and freezing

The basolateral nucleus of the amygdala (BLA) plays a significant role in mediating individual differences in the effects of fear memory on sleep. Here, we assessed the effects of antagonizing corticotropin releasing factor receptor 1 (CRFR1) after shock training (ST) on fear-conditioned behaviors and sleep. Outbred Wistar rats were surgically implanted with electrodes for recording EEG and EMG and with bilateral guide cannulae directed at BLA. Data loggers were placed intraperitoneally to record core body temperature. The CRFR1 antagonist, antalarmin (ANT; 4.82 mM) was microinjected into BLA after shock training (ST: 20 footshocks, 0.8 mA, 0.5 s duration, 60 s interstimulus interval), and the effects on sleep, freezing and the stress response (stress-induced hyperthermia, SIH) were examined after ST and fearful context re-exposure alone at 7 days (CTX1) and 21 days (CTX2) post-ST. EEG and EMG recordings were scored for non-rapid eye movement sleep (NREM), rapid eye movement sleep (REM) and wakefulness. The rats were separated into 4 groups: Vehicle-vulnerable (Veh-Vul; n = 10), Veh-resilient (Veh-Res; n = 11), ANT-vulnerable (ANT-Vul; n = 8) and ANT-resilient (ANT-Res; n = 8) based on whether, compared to baseline, the rats showed a decrease or no change/increase in REM during the first 4 h following ST. Post-ST ANT microinjected into BLA attenuated the fear-conditioned reduction in REM in ANT-Vul rats on CTX1, but did not significantly alter REM in ANT-Res rats. However, compared to Veh treated rats, REM was reduced in ANT treated rats on CTX2. There were no group differences in freezing or SIH across conditions. Therefore, CRFR1 in BLA plays a role in mediating individual differences in sleep responses to stress and in the extinction of fear conditioned changes in sleep.

Consolidative mechanisms of emotional processing in REM sleep and PTSD

Research suggests sleep plays a role in the consolidation of recently acquired memories for long-term storage. rapid eye movement (REM) sleep has been shown to play a complex role in emotional-memory processing, and may be involved in subsequent waking-day emotional reactivity and amygdala responsivity. Interaction of the hippocampus and basolateral amygdala with the medial-prefrontal cortex is associated with sleep-dependent learning and emotional memory processing. REM is also implicated in post-traumatic stress disorder (PTSD), which is characterized by sleep disturbance, heightened reactivity to fearful stimuli, and nightmares. Many suffers of PTSD also exhibit dampened medial-prefrontal cortex activity. However, the effects of PTSD-related brain changes on REM-dependent consolidation or the notion of 'over-consolidation' (strengthening of memory traces to such a degree that they become resistant to extinction) have been minimally explored. Here, we posit that (in addition to sleep architecture changes) the memory functions of REM must also be altered in PTSD. We propose a model of REM-dependent consolidation of learned fear in PTSD and examine how PTSD-related brain changes might interact with fear learning. We argue that reduced efficacy of inhibitory medial-prefrontal pathways may lead to maladaptive processing of traumatic memories in the early stages of consolidation after trauma.

Effects of Optogenetic inhibition of BLA on Sleep Brief Optogenetic Inhibition of the Basolateral Amygdala in Mice Alters Effects of Stressful Experiences on Rapid Eye Movement Sleep

Study Objectives

Stressful events can directly produce significant alterations in subsequent sleep, in particular rapid eye movement sleep (REM); however, the neural mechanisms underlying the process are not fully known. Here, we investigated the role of the basolateral nuclei of the amygdala (BLA) in regulating the effects of stressful experience on sleep.

Methods

We used optogenetics to briefly inhibit glutamatergic cells in BLA during the presentation of inescapable footshock (IS) and assessed effects on sleep, the acute stress response, and fear memory. c-Fos expression was also assessed in the amygdala and the medial prefrontal cortex (mPFC), both regions involved in coping with stress, and in brain stem regions implicated in the regulation of REM.

Results

Compared to control mice, peri-shock inhibition of BLA attenuated an immediate reduction in REM after IS and produced a significant overall increase in REM. Moreover, upon exposure to the shock context alone, mice receiving peri-shock inhibition of BLA during training showed increased REM without altered freezing (an index of fear memory) or stress-induced hyperthermia (an index of acute stress response). Inhibition of BLA during REM under freely sleeping conditions enhanced REM only when body temperature was high, suggesting the effect was influenced by stress. Peri-shock inhibition of BLA also led to elevated c-Fos expression in the central nucleus of the amygdala and mPFC and differentially altered c-Fos activity in the selected brain stem regions.

Conclusions

Glutamatergic cells in BLA can modulate the effects of stress on REM and can mediate effects of fear memory on sleep that can be independent of behavioral fear.

Brain prolactin is involved in stress-induced REM sleep rebound

REM sleep rebound is a common behavioural response to some stressors and represents an adaptive coping strategy. Animals submitted to multiple, intermittent, footshock stress (FS) sessions during 96h of REM sleep deprivation (REMSD) display increased REM sleep rebound (when compared to the only REMSD ones, without FS), which is correlated to high plasma prolactin levels. To investigate whether brain prolactin plays a role in stress-induced REM sleep rebound two experiments were carried out. In experiment 1, rats were either not sleep-deprived (NSD) or submitted to 96h of REMSD associated or not to FS and brains were evaluated for PRL immunoreactivity (PRL-ir) and determination of PRL concentrations in the lateral hypothalamus and dorsal raphe nucleus. In experiment 2, rats were implanted with cannulas in the dorsal raphe nucleus for prolactin infusion and were sleep-recorded. REMSD associated with FS increased PRL-ir and content in the lateral hypothalamus and all manipulations increased prolactin content in the dorsal raphe nucleus compared to the NSD group. Prolactin infusion in the dorsal raphe nucleus increased the time and length of REM sleep episodes 3h after the infusion until the end of the light phase of the day cycle. Based on these results we concluded that brain prolactin is a major mediator of stress-induced REMS. The effect of PRL infusion in the dorsal raphe nucleus is discussed in light of the existence of a bidirectional relationship between this hormone and serotonin as regulators of stress-induced REM sleep rebound.

Neuroendocrine and Peptidergic Regulation of Stress-Induced REM Sleep Rebound

Sleep homeostasis depends on the length and quality (occurrence of stressful events, for instance) of the preceding waking time. Forced wakefulness (sleep deprivation or sleep restriction) is one of the main tools used for the understanding of mechanisms that play a role in homeostatic processes involved in sleep regulation and their interrelations. Interestingly, forced wakefulness for periods longer than 24 h activates stress response systems, whereas stressful events impact on sleep pattern. Hypothalamic peptides (corticotropin-releasing hormone, prolactin, and the CLIP/ACTH18-39) play an important role in the expression of stress-induced sleep effects, essentially by modulating rapid eye movement sleep, which has been claimed to affect the organism resilience to the deleterious effects of stress. Some of the mechanisms involved in the generation and regulation of sleep and the main peptides/hypothalamic hormones involved in these responses will be discussed in this review.

The basolateral amygdala can mediate the effects of fear memory on sleep independently of fear behavior and the peripheral stress response

Fear conditioning associated with inescapable shock training (ST) and fearful context re-exposure (CR) alone can produce significant behavioral fear, a stress response and alterations in subsequent REM sleep. These alterations may vary among animals and are mediated by the basolateral nucleus of the amygdala (BLA). Here, we used the GABA_A agonist, muscimol (Mus), to inactivate BLA prior to CR and examined the effects on sleep, freezing and stress-induced hyperthermia (SIH). Wistar rats (n=28) were implanted with electrodes for recording sleep, data loggers for recording core body temperature, and with cannulae aimed bilaterally into BLA. After recovery, the animals were habituated to the injection procedure and baseline sleep was recorded. On experimental day 1, rats received ST (20 footshocks, 0.8mA, 0.5s duration, 60s interstimulus interval). On experimental day 7, the rats received microinjections (0.5μl) into BLA of either Mus (1.0μM; n=13) or vehicle (Veh; n=15) prior to CR (CR1). On experimental day 21, the animals experienced a second CR (CR2) without Mus. For analysis, the rats were separated into 4 groups: (Veh-vulnerable (Veh-Vul; n=8), Veh-resilient (Veh-Res; n=7), Mus-vulnerable (Mus-Vul; n=7), and Mus-resilient (Mus-Res; n=6)) based on whether or not REM was decreased, compared to baseline, during the first 4h following ST. Pre-CR1 inactivation of BLA did not alter freezing or SIH, but did block the reduction in REM in the Mus-Vul group compared to the Veh-Vul group. These data indicate that BLA is an important region for mediating the effects of fearful memories on sleep.

Voluntary Sleep Loss in Rats

STUDY OBJECTIVES

Animal sleep deprivation (SDEP), in contrast to human SDEP, is involuntary and involves repeated exposure to aversive stimuli including the inability of the animal to control the waking stimulus. Therefore, we explored intracranial self-stimulation (ICSS), an operant behavior, as a method for voluntary SDEP in rodents.

METHODS

Male Sprague-Dawley rats were implanted with electroencephalography/electromyography (EEG/EMG) recording electrodes and a unilateral bipolar electrode into the lateral hypothalamus. Rats were allowed to self-stimulate, or underwent gentle handling-induced SDEP (GH-SDEP), during the first 6 h of the light phase, after which they were allowed to sleep. Other rats performed the 6 h ICSS and 1 w later were subjected to 6 h of noncontingent stimulation (NCS). During NCS the individual stimulation patterns recorded during ICSS were replayed.

RESULTS

After GH-SDEP, ICSS, or NCS, time in nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep increased. Further, in the 24 h after SDEP, rats recovered all of the REM sleep lost during SDEP, but only 75% to 80% of the NREM sleep lost, regardless of the SDEP method. The magnitude of EEG slow wave responses occurring during NREM sleep also increased after SDEP treatments. However, NREM sleep EEG slow wave activity (SWA) responses were attenuated following ICSS, compared to GH-SDEP and NCS.

CONCLUSIONS

We conclude that ICSS and NCS can be used to sleep deprive rats. Changes in rebound NREM sleep EEG SWA occurring after ICSS, NCS, and GH-SDEP suggest that nonspecific effects of the SDEP procedure differentially affect recovery sleep phenotypes.

Individual Differences in Animal Stress Models: Considering Resilience, Vulnerability, and the Amygdala in Mediating the Effects of Stress and Conditioned Fear on Sleep

STUDY OBJECTIVES

To examine the REM sleep response to stress and fearful memories as a potential marker of stress resilience and vulnerability and to assess the role of the basolateral amygdala (BLA) in mediating the effects of fear memory on sleep.

METHODS

Outbred Wistar rats were surgically implanted with electrodes for recording EEG and EMG and with bilateral guide cannulae directed at the BLA. Data loggers were placed intraperitoneally to record core body temperature. After recovery from surgery, the rats received shock training (ST: 20 footshocks, 0.8 mA, 0.5-s duration, 60-s interstimulus interval) and afterwards received microinjections of the GABAA agonist muscimol (MUS; 1.0 μM) to inactivate BLA or microinjections of vehicle (VEH) alone. Subsequently, the rats were separated into 4 groups (VEH-vulnerable (VEH-Vul; n = 14), VEH-resilient (VEH-Res; n = 13), MUS-vulnerable (MUS-Vul; n = 8), and MUS-resilient (MUS-Res; n = 11) based on whether or not REM was decreased, compared to baseline, during the first 4 h following ST. We then compared sleep, freezing, and the stress response (stress-induced hyperthermia, SIH) across groups to determine the effects of ST and fearful context re-exposure alone (CTX).

RESULTS

REM was significantly reduced on the ST day in both VEH-Vul and MUS-Vul rats; however, post-ST MUS blocked the reduction in REM on the CTX day in the MUS-Vul group. The VEH-Res and MUS-Res rats showed similar levels of REM on both ST and CTX days. The effects of post-ST inactivation of BLA on freezing and SIH were minimal.

CONCLUSIONS

Outbred Wistar rats can show significant individual differences in the effects of stress on REM that are mediated by BLA. These differences in REM can be independent of behavioral fear and the peripheral stress response, and may be an important biomarker of stress resilience and vulnerability.

Diurnal Emotional States Impact the Sleep Course

BACKGROUND

Diurnal emotional experiences seem to affect several characteristics of sleep architecture. However, this influence remains unclear, especially for positive emotions. In addition, electrodermal activity (EDA), a sympathetic robust indicator of emotional arousal, differs depending on the sleep stage. The present research has a double aim: to identify the specific effects of pre-sleep emotional states on the architecture of the subsequent sleep period; to relate such states to the sympathetic activation during the same sleep period.

METHODS

Twelve healthy volunteers (20.1 ± 1.0 yo.) participated in the experiment and each one slept 9 nights at the laboratory, divided into 3 sessions, one per week. Each session was organized over three nights. A reference night, allowing baseline pre-sleep and sleep recordings, preceded an experimental night before which participants watched a negative, neutral, or positive movie. The third and last night was devoted to analyzing the potential recovery or persistence of emotional effects induced before the experimental night. Standard polysomnography and EDA were recorded during all the nights.

RESULTS

Firstly, we found that experimental pre-sleep emotional induction increased the Rapid Eye Movement (REM) sleep rate following both negative and positive movies. While this increase was spread over the whole night for positive induction, it was limited to the second half of the sleep period for negative induction. Secondly, the valence of the pre-sleep movie also impacted the sympathetic activation during Non-REM stage 3 sleep, which increased after negative induction and decreased after positive induction.

CONCLUSION

Pre-sleep controlled emotional states impacted the subsequent REM sleep rate and modulated the sympathetic activity during the sleep period. The outcomes of this study offer interesting perspectives related to the effect of diurnal emotional influences on sleep regulation and open new avenues for potential practices designed to alleviate sleep disturbances.

Effects of corticotropin releasing factor (CRF) on sleep and temperature following predictable controllable and uncontrollable stress in mice

Corticotropin releasing factor (CRF) is a major mediator of central nervous system responses to stressors, including alterations in wakefulness and sleep. However, its role in mediating stress-induced alterations in sleep has not been fully delineated. In this study, we assessed the role of CRF and the non-specific CRF antagonist, astressin (AST), in regulating changes in sleep produced by signaled, escapable shock (SES) and signaled inescapable shock (SIS), two stressors that can increase or decrease sleep, respectively. Male BALB/cJ mice were surgically implanted with transmitters (DataSciences ETA10-F20) for recording EEG, activity and core body temperature by telemetry and a cannula for intracerebroventricular (ICV) microinjections. After baseline (Base) sleep recording, mice were presented tones (90 dB, 2 kHz) that started 5.0 s prior to and co-terminated with footshock (0.5 mA; 5.0 s maximum duration). SES mice (n = 9) always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. Yoked SIS mice (n = 9) were treated identically, but could not alter shock duration. Training with SES or SIS was conducted over 2 days to stabilize responses. Afterwards, the mice received saline, CRF [0.4 μg (0.42 mM) or AST (1.0 μg (1.4 mM)] prior to SES or SIS. Sleep was analyzed over 20 h post-stress recordings. After administration of saline, REM was significantly greater in SES mice than in SIS mice whereas after CRF or AST, REM was similar in both groups. Total 20 h NREM did not vary across condition or group. However, after administration of saline and CRF, NREM episode duration was significantly decreased, and NREM episode number significantly increased, in SIS mice compared to SES animals. SES and SIS mice showed similar stress induced hyperthermia (SIH) across all conditions. These data demonstrate that CRF can mediate stress-induced changes in sleep independently of SIH, an index of hypothalamic-pituitary-adrenal axis activation.

Deep sleep after social stress: NREM sleep slow-wave activity is enhanced in both winners and losers of a conflict

Sleep is considered to be a recovery process of prior wakefulness. Not only duration of the waking period affects sleep architecture and sleep EEG, the quality of wakefulness is also highly important. Studies in rats have shown that social defeat stress, in which experimental animals are attacked and defeated by a dominant conspecific, is followed by an acute increase in NREM sleep EEG slow wave activity (SWA). However, it is not known whether this effect is specific for the stress of social defeat or a result of the conflict per se. In the present experiment, we examined how sleep is affected in both the winners and losers of a social conflict. Sleep-wake patterns and sleep EEG were recorded in male wild-type Groningen rats that were subjected to 1h of social conflict in the middle of the light phase. All animals were confronted with a conspecific of similar aggression level and the conflict took place in a neutral arena where both individuals had an equal chance to either win or lose the conflict. NREM sleep SWA was significantly increased after the social conflict compared to baseline values and a gentle stimulation control condition. REM sleep was significantly suppressed in the first hours after the conflict. Winners and losers did not differ significantly in NREM sleep time, NREM sleep SWA and REM sleep time immediately after the conflict. Losers tended to have slightly more NREM sleep later in the recovery period. This study shows that in rats a social conflict with an unpredictable outcome has quantitatively and qualitatively largely similar acute effects on subsequent sleep in winners and losers.

Sleep and REM sleep disturbance in the pathophysiology of PTSD: the role of extinction memory

Post-traumatic stress disorder (PTSD) is accompanied by disturbed sleep and an impaired ability to learn and remember extinction of conditioned fear. Following a traumatic event, the full spectrum of PTSD symptoms typically requires several months to develop. During this time, sleep disturbances such as insomnia, nightmares, and fragmented rapid eye movement sleep predict later development of PTSD symptoms. Only a minority of individuals exposed to trauma go on to develop PTSD. We hypothesize that sleep disturbance resulting from an acute trauma, or predating the traumatic experience, may contribute to the etiology of PTSD. Because symptoms can worsen over time, we suggest that continued sleep disturbances can also maintain and exacerbate PTSD. Sleep disturbance may result in failure of extinction memory to persist and generalize, and we suggest that this constitutes one, non-exclusive mechanism by which poor sleep contributes to the development and perpetuation of PTSD. Also reviewed are neuroendocrine systems that show abnormalities in PTSD, and in which stress responses and sleep disturbance potentially produce synergistic effects that interfere with extinction learning and memory. Preliminary evidence that insomnia alone can disrupt sleep-dependent emotional processes including consolidation of extinction memory is also discussed. We suggest that optimizing sleep quality following trauma, and even strategically timing sleep to strengthen extinction memories therapeutically instantiated during exposure therapy, may allow sleep itself to be recruited in the treatment of PTSD and other trauma and stress-related disorders.

Effects of sleep on memory for conditioned fear and fear extinction

Learning and memory for extinction of conditioned fear is a basic mammalian mechanism for regulating negative emotion. Sleep promotes both the consolidation of memory and the regulation of emotion. Sleep can influence consolidation and modification of memories associated with both fear and its extinction. After brief overviews of the behavior and neural circuitry associated with fear conditioning, extinction learning, and extinction memory in the rodent and human, interactions of sleep with these processes will be examined. Animal and human studies suggest that sleep can serve to consolidate both fear and extinction memory. In humans, sleep also promotes generalization of extinction memory. Time-of-day effects on extinction learning and generalization are also seen. Rapid eye movement (REM) may be a sleep stage of particular importance for the consolidation of both fear and extinction memory as evidenced by selective REM deprivation experiments. REM sleep is accompanied by selective activation of the same limbic structures implicated in the learning and memory of fear and extinction. Preliminary evidence also suggests extinction learning can take place during slow wave sleep. Study of low-level processes such as conditioning, extinction, and habituation may allow sleep effects on emotional memory to be identified and inform study of sleep's effects on more complex, emotionally salient declarative memories. Anxiety disorders are marked by impairments of both sleep and extinction memory. Improving sleep quality may ameliorate anxiety disorders by strengthening naturally acquired extinction. Strategically timed sleep may be used to enhance treatment of anxiety by strengthening therapeutic extinction learned via exposure therapy. (PsycINFO Database Record

Stress, arousal, and sleep

Stress is considered to be an important cause of disrupted sleep and insomnia. However, controlled and experimental studies in rodents indicate that effects of stress on sleep-wake regulation are complex and may strongly depend on the nature of the stressor. While most stressors are associated with at least a brief period of arousal and wakefulness, the subsequent amount and architecture of recovery sleep can vary dramatically across conditions even though classical markers of acute stress such as corticosterone are virtually the same. Sleep after stress appears to be highly influenced by situational variables including whether the stressor was controllable and/or predictable, whether the individual had the possibility to learn and adapt, and by the relative resilience and vulnerability of the individual experiencing stress. There are multiple brain regions and neurochemical systems linking stress and sleep, and the specific balance and interactions between these systems may ultimately determine the alterations in sleep-wake architecture. Factors that appear to play an important role in stress-induced wakefulness and sleep changes include various monominergic neurotransmitters, hypocretins, corticotropin releasing factor, and prolactin. In addition to the brain regions directly involved in stress responses such as the hypothalamus, the locus coeruleus, and the amygdala, differential effects of stressor controllability on behavior and sleep may be mediated by the medial prefrontal cortex. These various brain regions interact and influence each other and in turn affect the activity of sleep-wake controlling centers in the brain. Also, these regions likely play significant roles in memory processes and participate in the way stressful memories may affect arousal and sleep. Finally, stress-induced changes in sleep-architecture may affect sleep-related neuronal plasticity processes and thereby contribute to cognitive dysfunction and psychiatric disorders.

The truncated TrkB receptor influences mammalian sleep

Brain-derived neurotrophic factor (BDNF) is a neurotrophin hypothesized to play an important role in mammalian sleep expression and regulation. In order to investigate the role of the truncated receptor for BDNF, TrkB.T1, in mammalian sleep, we examined sleep architecture and sleep regulation in adult mice constitutively lacking this receptor. We find that TrkB.T1 knockout mice have increased REM sleep time, reduced REM sleep latency, and reduced sleep continuity. These results demonstrate a novel role for the TrkB.T1 receptor in sleep expression and provide new insights into the relationship between BDNF, psychiatric illness, and sleep.