Sleep deprivation impairs hippocampus-mediated contextual learning but not amygdala-mediated cued learning in rats

Could sleep be a brain/cognitive/neural reserve-builder factor? A systematic review on the cognitive effects of sleep modulation in animal models

The brain/cognitive/neural reserve concept suggests that lifelong experiences, from early life through adulthood, make the brain more resilient to neuronal damage. Modifiable lifestyle factors, such as sleep, can support the development and enhance such a reserve, helping to counteract age- or disease-related brain changes and their impact on cognition. Sleep plays a crucial role in cognitive functioning, and disruptions or disorders may increase neurodegenerative risks. This systematic review aims to explore how functional and disturbed sleep impacts cognitive functions and neuromorphological mechanisms in rodents, aiming to better understand its role in brain/cognitive/neural reserve development. This systematic review, registered on PROSPERO (ID: CRD42023423901) and conducted according to PRISMA-P guidelines, searched PubMed, Scopus, Web of Science, and Embase databases for studies up to June 2022, with terms related to sleep, rodents, and cognitive functions. Of the 28,666 articles identified, 142 met the inclusion criteria. Main results showed significant cognitive decline after sleep deprivation, especially in memory performance. These findings supports the importance of sleep as a critical factor in modulating brain/cognitive/neural reserve.

Acute sleep disruption reduces fear memories in male and female mice

Sleep problems are a prominent feature of mental health conditions including post-traumatic stress disorder (PTSD). Despite its potential importance, the role of sleep in the development of and/or recovery from trauma-related illnesses is not understood. Interestingly, there are reports that sleep disruption immediately after a traumatic experience can reduce fear memories, an effect that could be utilized therapeutically in humans. While the mechanisms of this effect are not completely understood, one possible explanation for these findings is that immediate sleep disruption interferes with consolidation of fear memories, rendering them weaker and more sensitive to intervention. Here, we allowed fear-conditioned mice to sleep immediately after fear conditioning during a time frame (18 h) that includes and extends beyond periods typically associated with memory consolidation before subjecting them to 6-h of sleep disruption. Mice exposed to this delayed regimen showed dramatic reductions in fear during tests conducted immediately after sleep disruption, as well as 24 h later. This sleep disruption regimen also increased levels of mRNA encoding brain-derived neurotrophic factor (BDNF), a molecule implicated in neuroplasticity, in the basolateral amygdala (BLA), a brain area implicated in fear and its extinction. These findings raise the possibility that the effects of our delayed sleep disruption regimen are not due to disruption of memory consolidation, but instead are caused by BDNF-mediated neuroadaptations within the BLA that actively suppress expression of fear. Treatments that safely reduce expression of fear memories would have considerable therapeutic potential in the treatment of conditions triggered by trauma.

Acute sleep deprivation reduces fear memories in male and female mice

Sleep problems are a prominent feature of mental health conditions including post-traumatic stress disorder (PTSD). Despite its potential importance, the role of sleep in the development of and/or recovery from trauma-related illnesses is not understood. Interestingly, there are reports that sleep deprivation immediately after a traumatic experience can reduce fear memories, an effect that could be utilized therapeutically in humans. While the mechanisms of this effect are not completely understood, one possible explanation for these findings is that immediate sleep deprivation interferes with consolidation of fear memories, rendering them weaker and more sensitive to intervention. Here, we allowed fear-conditioned mice to sleep immediately after fear conditioning during a time frame (18 hr) that includes and extends beyond periods typically associated with memory consolidation before subjecting them to 6 hr of sleep deprivation. Mice deprived of sleep with this delayed regimen showed dramatic reductions in fear during tests conducted immediately after sleep deprivation, as well as 24 hr later. This sleep deprivation regimen also increased levels of mRNA encoding brain-derived neurotrophic factor (BDNF), a molecule implicated in neuroplasticity, in the basolateral amygdala (BLA), a brain area implicated in fear and its extinction. These findings raise the possibility that the effects of our delayed sleep deprivation regimen are not due to disruption of memory consolidation, but instead are caused by BDNF-mediated neuroadaptations within the BLA that actively suppress expression of fear. Treatments that safely reduce expression of fear memories would have considerable therapeutic potential in the treatment of conditions triggered by trauma.

Environmental Enrichment Reverses Maternal Sleep Deprivation-Induced Anxiety-Like Behavior and Cognitive Impairment in CD-1 Mice

Preclinical studies have clearly indicated that offspring of mothers who suffered sleep deprivation during pregnancy exhibit anxiety, depression-like behaviors, and cognitive deficits. The cognitive impairment induced by maternal sleep deprivation (MSD) is currently poorly treated. Growing evidence indicates that an enriched environment (EE) improves cognition function in models of Alzheimer’s disease, schizophrenia, and lipopolysaccharide. However, the effects of EE on hippocampal-dependent learning and memory, as well as synaptic plasticity markers changes induced by MSD, are unclear. In the present study, pregnant CD-1 mice were randomly divided into a control group, MSD group, and MSD+EE group. Two different living environments, including standard environment and EE, were prepared. When male and female offspring were 2 months, the open field test and elevated plus maze were used to assess anxiety-like behavior, and the Morris water maze was used to evaluate hippocampal learning and memory. Western blotting and real-time fluorescence quantitative polymerase chain reaction were used to detect the expression of brain-derived neurotrophic factor and Synaptotagmin-1 in the hippocampus of offspring. The results revealed that MSD-induced offspring showed anxiety-like behaviors and cognitive impairment, while EE alleviated anxiety-like behavior and cognitive impairment in offspring of the MSD+EE group. The cognitive impairment induced by MSD was associated with a decreased brain-derived neurotrophic factor and an increased Synaptotagmin-1, while EE increased and decreased brain-derived neurotrophic factor and Synaptotagmin-1 in the hippocampus of mice from the MSD+EE group, respectively. Taken together, we can conclude that EE has beneficial effects on MSD-induced synaptic plasticity markers changes and can alleviate anxiety-like behaviors and cognitive impairment.

Chronic antidepressant treatment rescues abnormally reduced REM sleep theta power in socially defeated rats

The effects of chronic antidepressant (AD) treatment on sleep disturbances in rodent chronic stress models have not been thoroughly investigated. Here, we show that chronic social defeat stress (SDS) in rats induces prolonged social avoidance, alterations in sleep architecture (increased total rapid eye movement [REM] sleep duration, bout, and shortened REM latency), and contextual but not cued fear memory deficits, even 1 month after the last SDS. These abnormalities were associated with changes in electroencephalography (EEG) spectral powers, including reduced REM sleep theta power during the light phase. Chronic treatment with two different classes of antidepressants (ADs), imipramine and fluoxetine, significantly ameliorated these behavioral, sleep, and EEG abnormalities. Interestingly, REM theta power was normalized by chronic (1 month) but not 1 week AD administration and solely correlated with the ratio (an objective indicator) of social interaction 1 month after the last SDS. These data suggest that reductions in REM sleep theta power, an EEG parameter that has never been directly investigated in humans, is a core sleep symptom in socially defeated rats, and, potentially, also in patients with stress-related psychiatric disorders, including major depressive and posttraumatic stress disorders.

Alteration of fear behaviors in sleep-deprived adolescent rats: increased fear expression and delayed fear extinction

Disruption of sleep due to acute or chronic stress can lead to changes in emotional memory processing. Sleep disturbances are highly prevalent in post-traumatic stress disorder (PTSD), but still, the contribution of sleep deprivation on the susceptibility to PTSD has received little attention. To determine whether rapid eye movement sleep deprivation (SD) alters the development of fear expression or fear-associated memory impairment in adolescent rats, we performed animal emotional behavior tests using an SD animal model with the flowerpot technique. SD rats showed an increase in locomotor activity frequency and a decrease in sucrose consumption compared to control rats. An increase in freezing behavior during shock trials was observed in SD rats. Noticeably, it was observed that when applying the SD condition after fear stimuli exposure, fear extinction was delayed more in SD rats than in control rats. Overall, these results indicate that SD in adolescent rats leads to increased locomotor activity and anhedonic behavior, as well as increased fear expression and delayed fear extinction, suggesting that SD would lead to increased severity of PTSD-like phenotype.

An analysis of fear inhibition and fear extinction in a sample of veterans with obstructive sleep apnea (OSA): Implications for co-morbidity with post-traumatic stress disorder (PTSD)

Obstructive sleep apnea (OSA) is a respiratory condition characterized by interrupted sleep due to repeated, temporary collapse of the soft tissue of the upper airway that can lead to a cascade of physiological and psychological adverse health outcomes. The most common therapeutic interventions for OSA patients include the application of continuous positive airway pressure (CPAP) which acts to keep the airway open and, as such, provides less interrupted and more restorative sleep. Improved sleep has been linked to more efficacious treatments for psychiatric conditions most notably those that include cognitive-behavioral elements, new learning, and memory consolidation. In the current study, we investigated the acquisition, inhibition, and extinction of conditioned fear in OSA patients, before and after CPAP therapy, using an established fear-potentiated startle paradigm. Patients with OSA displayed an intact ability to acquire, inhibit, and extinguish fear prior to CPAP treatment and this ability was significantly enhanced following CPAP usage. In addition, those patients with more severe OSA, as measured by apnea-hypopnea index (AHI), were more likely to show improved fear inhibition and extinction. Lastly, we observed impairments in discrimination between reinforced and nonreinforced conditioned stimuli, in the inhibition of fear, and in fear extinction in a subset of patients with OSA and co-morbid posttraumatic stress disorder (PTSD). These data suggest that evolving treatment algorithms for PTSD should address disrupted sleep problems prior to initiation of inhibition/extinction-based exposure therapies.

Sleep Deprivation and Neurological Disorders

Sleep plays an important role in maintaining neuronal circuitry, signalling and helps maintain overall health and wellbeing. Sleep deprivation (SD) disturbs the circadian physiology and exerts a negative impact on brain and behavioural functions. SD impairs the cellular clearance of misfolded neurotoxin proteins like α-synuclein, amyloid-β, and tau which are involved in major neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. In addition, SD is also shown to affect the glymphatic system, a glial-dependent metabolic waste clearance pathway, causing accumulation of misfolded faulty proteins in synaptic compartments resulting in cognitive decline. Also, SD affects the immunological and redox system resulting in neuroinflammation and oxidative stress. Hence, it is important to understand the molecular and biochemical alterations that are the causative factors leading to these pathophysiological effects on the neuronal system. This review is an attempt in this direction. It provides up-to-date information on the alterations in the key processes, pathways, and proteins that are negatively affected by SD and become reasons for neurological disorders over a prolonged period of time, if left unattended.

The formation of compensatory contextual fear memory in the absence of dorsal hippocampus does not change sleep architecture

Although the dorsal hippocampus (DH) plays an essential role in the consolidation of contextual fear-conditioned (CxFC) memory, this consolidation may also occur in the absence of DH. It is, however, not known if the development of a compensatory circuit for CxFC memory is time-dependent. The DH-dependent contextual fear memory influences sleep architecture, but whether the compensatory fear memory can influence sleep, is not known. Here, we have studied (a) the temporal progression of compensatory contextual fear memory in the absence of DH and (b) the influence of compensatory contextual fear memory on sleep architecture. Rats were surgically prepared for chronic polysomnographic recordings and drug injections in the DH. They were divided into four groups: DH-non-lesioned and fear-conditioned, DH-non-lesioned and non-fear-conditioned, DH-lesioned and fear-conditioned and DH-lesioned and non-fear-conditioned groups. The DH was lesioned with ibotenic acid. The animals were conditioned to contextual fear twice: 1^st training on Day 5 and testing on Day 6; 2^nd training on Day 10 and testing on Day 11. The DH-lesioned and fear-conditioned animals did not exhibit freezing response during the first testing but showed a robust freezing response when re-trained after a gap of three days. In addition, wakefulness and NREM sleep amount did not change, but REM sleep significantly decreased in the DH-dependent CxFC memory group. Interestingly, REM sleep did not decrease in the DH-independent CxFC memory group. Our findings suggest that the development of compensatory CxFC memory is a time-dependent process and the compensatory CxFC memory may not influence sleep architecture.

Bidirectional influence of amygdala β1-adrenoceptors blockade on cannabinoid signaling in contextual and auditory fear memory

The basolateral amygdala (BLA) is a major target and modulator of stress and has a critical role in the neural circuitry presenting learned fear behaviors. On the other hand, both the endocannabinoid and noradrenergic systems may be involved in regulating the stress responses, fear, and anxiety. Considering the aforementioned, we have investigated the involvement of the BLA β₁-adrenoceptors in conditioned fear responses induced by ACPA, a CB1 receptor (CB1R) agonist. In adult male NMRI mice, freezing responses to context and cue were measured using a Pavlovian fear conditioning apparatus. Pre-training intra-BLA microinjection of xamoterol (0.01 and 0.02 µg/mouse), a partial β₁-adrenoceptor agonist, or atenolol (0.5 µg/mouse), a β₁-adrenoceptor antagonist, decreased freezing behavior, which suggests an impairment of contextual and auditory fear retrieval. Similar results were found with pre-training intraperitoneal administration of ACPA (0.5 mg/kg). A sub-threshold dose of xamoterol, infused into the BLA, decreased ACPA (0.005 and 0.05 mg/kg) effect on both memories, while atenolol increased ACPA response to the context at the middle dose and decreased ACPA response to the tone at the lower dose. It can be concluded that the blockade of BLA β₁-adrenoceptors differentially affects ACPA response on the contextual and auditory conditioned fear memories.

Declarative virtual water maze learning and emotional fear conditioning in primary insomnia

Healthy sleep restores the brain's ability to adapt to novel input through memory formation based on activity-dependent refinements of the strength of neural transmission across synapses (synaptic plasticity). In line with this framework, patients with primary insomnia often report subjective memory impairment. However, investigations of memory performance did not produce conclusive results. The aim of this study was to further investigate memory performance in patients with primary insomnia in comparison to healthy controls, using two well-characterized learning tasks, a declarative virtual water maze task and emotional fear conditioning. Twenty patients with primary insomnia according to DSM-IV criteria (17 females, three males, 43.5 ± 13.0 years) and 20 good sleeper controls (17 females, three males, 41.7 ± 12.8 years) were investigated in a parallel-group study. All participants completed a hippocampus-dependent virtual Morris water maze task and amygdala-dependent classical fear conditioning. Patients with insomnia showed significantly delayed memory acquisition in the virtual water maze task, but no significant difference in fear acquisition compared with controls. These findings are consistent with the notion that memory processes that emerge from synaptic refinements in a hippocampal-neocortical network are particularly sensitive to chronic disruptions of sleep, while those in a basic emotional amygdala-dependent network may be more resilient.

Light and Cognition: Roles for Circadian Rhythms, Sleep, and Arousal

Light exerts a wide range of effects on mammalian physiology and behavior. As well as synchronizing circadian rhythms to the external environment, light has been shown to modulate autonomic and neuroendocrine responses as well as regulating sleep and influencing cognitive processes such as attention, arousal, and performance. The last two decades have seen major advances in our understanding of the retinal photoreceptors that mediate these non-image forming responses to light, as well as the neural pathways and molecular mechanisms by which circadian rhythms are generated and entrained to the external light/dark (LD) cycle. By contrast, our understanding of the mechanisms by which lighting influences cognitive processes is more equivocal. The effects of light on different cognitive processes are complex. As well as the direct effects of light on alertness, indirect effects may also occur due to disrupted circadian entrainment. Despite the widespread use of disrupted LD cycles to study the role circadian rhythms on cognition, the different experimental protocols used have subtly different effects on circadian function which are not always comparable. Moreover, these protocols will also disrupt sleep and alter physiological arousal, both of which are known to modulate cognition. Studies have used different assays that are dependent on different cognitive and sensory processes, which may also contribute to their variable findings. Here, we propose that studies addressing the effects of different lighting conditions on cognitive processes must also account for their effects on circadian rhythms, sleep, and arousal if we are to fully understand the physiological basis of these responses.

Good night, sleep tight: The effects of sleep deprivation on spatial associative learning in zebrafish

Learning and memory are vital to an animal's survival, and numerous factors can disrupt cognitive performance. Sleep is an evolutionarily conserved physiological process known to be important for the consolidation of learning and memory. The zebrafish has emerged as a powerful model organism sharing organizational and functional characteristics with other vertebrates, providing great translational relevance. In our study, we used a simple spatial associative learning task to quantify the effects of sleep deprivation (partial vs. total) on learning performance in zebrafish, using an animated conspecific shoal image as a reward. Control animals maintained on a regular light:dark cycle were able to acquire the association between the unconditioned and conditioned stimulus, reinforcing zebrafish as a valid and reliable model for appetitive conditioning tasks. Notably, sleep deprivation did not alter the perception of and response to the conspecific image. In contrast, although partial sleep deprivation did not impair cognitive performance, total sleep deprivation significantly impaired performance on the associative learning task. Our results suggest that sleep is important for learning and memory, and that the effects of sleep deprivation on these processes can be investigated in zebrafish.

The effect of sleep deprivation on the encoding of contextual and non-contextual aspects of emotional memory

Sleep loss affects emotional memory, but the specific effects on its contextual and non-contextual aspects are unknown. In this study we investigated the possible differential influence of one night of sleep deprivation on the encoding and subsequent recall of these two aspects of emotional information. Forty-eight healthy subjects, divided in a sleep deprivation (SD) and a well-rested group (WR), completed two testing sessions: the encoding session took place after one night of sleep for the WR and after one night of sleep deprivation for the SD group; the recall session after two nights of recovery sleep for both groups. During the encoding session, 6 clips of films of different valence (2 positive, 2 neutral and 2 negative) were presented to the participants. During the recall session, the non-contextual emotional memory was assessed by a recognition task, while the contextual emotional memory was evaluated by a temporal order task. The SD group showed a worst non-contextual recognition of positive and neutral events compared to WR subjects, while recognition of negative items was similar in the two groups. Instead, the encoding of the temporal order resulted deteriorated in the SD participants, independent of the emotional valence of the items. These results indicate that sleep deprivation severely impairs the encoding of both contextual and non-contextual aspects of memory, resulting in significantly worse retention two days later. However, the preserved recognition of negative non-contextual events in sleep deprived subjects suggests that the encoding of negative stimuli is more "resistant" to the disruptive effects of sleep deprivation.

Caffeine/sleep-deprivation interaction in mice produces complex memory effects

BACKGROUND

Sleep deprivation negatively impacts memory, causing deficits in memory processes. Of interest is any agent that can offset such deficits. Mice were given varying doses of caffeine for 14 days and then deprived of sleep for 6 hours by the 'gentle handling' method. Memory was assessed using the Novel Object Recognition Test and Y maze alternation.

PURPOSE

The study was designed to ascertain the impact of varying doses of caffeine combined with total sleep-deprivation on spatial and non spatial memory in mice.

METHODS

Adult Swiss Webster mice of both sexes were assigned to six groups viz., vehicle (distilled water), or one of five selected doses of caffeine (10, 20, 40, 80 and 120 mg/kg) for 14 days via the oral route. Open field novel object recognition test and Y maze spatial working memory tests were carried out on day 14. Results were analysed using multi-factorial ANOVA followed by Tukey HSD test and expressed as mean ± S.E.M, with p values less than 0.05 were considered statistically significant.

RESULTS

Novel object recognition tests (NOR) revealed that pre-training and pre-test sleep deprivation and caffeine combination impaired non spatial and spatial memory in male and female mice.

CONCLUSION

The study shows the complex interactions with memory that may arise when total sleep deprivation is superimposed on caffeine administration.

Differential effects of duration of sleep fragmentation on spatial learning and synaptic plasticity in pubertal mice

STUDY OBJECTIVE

To examine the differential effects of acute and chronic sleep fragmentation (SF) on spatial learning and memory, and hippocampal long-term potentiation (LTP) in pubertal mice.

METHODS

Two studies were performed during which adolescent C57/Bl6 mice were subjected to acute-SF 24h a day × 3 days or chronic-SF for 12h a day × 2 weeks using a programmable rotating lever that provides tactile stimulus with controls housed in similar cages. Spatial learning and memory was examined using the Morris water maze, and long-term potentiation (LTP) was evaluated after stimulation of Schaffer collaterals in CA1 hippocampus post SF. Actigraphy was used during the period of SF to monitor rest-activity patterns. Electroencephalographic (EEG) recordings were acquired for analysis of vigilance state patterns and delta-power. Serum corticosterone was measured to assess stress levels.

RESULTS

Acute-SF via tactile stimulation negatively impacted spatial learning, as well as LTP maintenance, compared to controls with no tactile stimulation. While actigraphy showed significantly increased motor activity during SF in both groups, EEG data indicated that overall sleep efficiency did not differ between baseline and SF days, but significant increases in number of wakeful bouts and decreases in average NREM and REM bout lengths were seen during lights-on. Acute sleep fragmentation did not impact corticosterone levels.

CONCLUSIONS

The current results indicate that, during development in pubertal mice, acute-SF for 24h a day × 3 days negatively impacted spatial learning and synaptic plasticity. Further studies are needed to determine if any inherent long-term homeostatic mechanisms in the adolescent brain afford greater resistance to the deleterious effects of chronic-SF.

Sleep deprivation and hippocampal vulnerability: changes in neuronal plasticity, neurogenesis and cognitive function

Despite the ongoing fundamental controversy about the physiological function of sleep, there is general consensus that sleep benefits neuronal plasticity, which ultimately supports brain function and cognition. In agreement with this are numerous studies showing that sleep deprivation (SD) results in learning and memory impairments. Interestingly, such impairments appear to occur particularly when these learning and memory processes require the hippocampus, suggesting that this brain region may be particularly sensitive to the consequences of sleep loss. Although the molecular mechanisms underlying sleep and memory formation remain to be investigated, available evidence suggests that SD may impair hippocampal neuronal plasticity and memory processes by attenuating intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling which may lead to alterations in cAMP response element binding protein (CREB)-mediated gene transcription, neurotrophic signaling, and glutamate receptor expression. When restricted sleep becomes a chronic condition, it causes a reduction of hippocampal cell proliferation and neurogenesis, which may eventually lead to a reduction in hippocampal volume. Ultimately, by impairing hippocampal plasticity and function, chronically restricted and disrupted sleep contributes to cognitive disorders and psychiatric diseases.

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

Orexin neuropeptides contribute to the development and persistence of generalized avoidance behavior in the rat

RATIONALE

Avoidance of contexts directly associated with fearful experiences represents an adaptive behavioral survival strategy. Over-interpretation of contextual cues leading to generalized avoidance of situations that are only remotely similar to the original fear context represents a pathologic process that contributes to anxiety disorders. Orexin neuropeptides modulate anxiety-like behavioral and physiological responses.

OBJECTIVE

The objective of this paper was to investigate the impact of pharmacological orexin receptor blockade on generalized avoidance behavior.

METHODS

Rats received a single electric foot-shock in the dark side of a two-compartment shuttle box followed by situational context reminders. After shock, rats were treated chronically (3 weeks) with the orexin receptor antagonist almorexant or with the selective serotonin reuptake inhibitor sertraline, used as positive anxiolytic control. In week 3, avoidance behavior was measured under conditions of high (dark-light (DL)-box) and low (elevated plus maze (EPM)) similarity to the original shock context. Avoidance behavior was re-assessed 5 and 17 weeks after treatment termination.

RESULTS

Avoidance in the DL box (contextual fear memory) remained unaffected by any treatment and lasted 20 weeks post-shock exposure. Avoidance in the EPM (neophobic fear generalization) was partially attenuated during treatment with almorexant and sertraline at week 3. Following 5 and 17 weeks of drug washout, avoidance in the EPM was significantly reduced in almorexant- but not in sertraline-treated rats. Almorexant also reduced persistent avoidance in the EPM upon treatment initiation 3 weeks after shock exposure.

CONCLUSION

Chronic orexin receptor blockade in rats reduces both the development and persistence of generalized avoidance in situations with low similarity to the initial shock context.

Effects of sleep deprivation and aging on long-term and remote memory in mice

Sleep deprivation (SD) following hippocampus-dependent learning in young mice impairs memory when tested the following day. Here, we examined the effects of SD on remote memory in both young and aged mice. In young mice, we found that memory is still impaired 1 mo after training. SD also impaired memory in aged mice 1 d after training, but, by a month after training, sleep-deprived and control aged animals performed similarly, primarily due to remote memory decay in the control aged animals. Gene expression analysis supported the finding that SD has similar effects on the hippocampus in young and aged mice.

Chronically restricted or disrupted sleep as a causal factor in the development of depression

Sleep problems are a common complaint in the majority of people suffering from depression. While sleep complaints were traditionally seen as a symptom of mood disorders, accumulating evidence suggests that in many cases the relationship may be reverse as well. A long list of longitudinal studies shows that sleep complaints often precede the onset of depression and constitute an independent risk factor for the development of the disorder. Additionally, experimental studies in animals show that chronically restricted or disrupted sleep may gradually induce neurobiological changes that are very similar to what has been reported for depressed patients. The mechanisms through which insufficient sleep increases the risk for depression are poorly understood but may include effects of sleep disturbance on neuroendocrine stress systems, serotonergic neurotransmission, and various interacting signaling pathways involved in the regulation of neuronal plasticity and neurogenesis. Because sleep is considered to play a crucial role in regulating neuronal plasticity and synaptic strength, chronically insufficient sleep may contribute to depression through an impairment of these plasticity processes leading to altered connectivity and communication within and between brain regions involved in the regulation of mood.

Animal studies on the role of sleep in memory: from behavioral performance to molecular mechanisms

Although the exact functions of sleep remain a topic of debate, several hypotheses propose that sleep benefits neuronal plasticity, which ultimately supports brain function and cognition . For over a century, researchers have applied a wide variety of behavioral, electrophysiological, biochemical, and molecular approaches to study how memory processes are promoted by sleep and perturbed by sleep loss. Interestingly, experimental studies indicate that cognitive impairments as a consequence of sleep deprivation appear to be most severe with learning and memory processes that require the hippocampus , which suggests that this brain region is particularly sensitive to the consequences of sleep loss. Moreover, recent studies in laboratory rodents indicate that sleep deprivation impairs hippocampal neuronal plasticity and memory processes by attenuating intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling. Attenuated cAMP-PKA signaling can lead to a reduced activity of the transcription factor cAMP response element binding protein (CREB) and ultimately affect the expression of genes and proteins involved in neuronal plasticity and memory formation. Pharmacogenetic experiments in mice show that memory deficits following sleep deprivation can be prevented by specifically boosting cAMP signaling in excitatory neurons of the hippocampus. Given the high incidence of sleep disturbance and sleep restriction in our 24/7 society, understanding the consequences of sleep loss and unraveling the underlying molecular mechanisms is of great importance.

Effects of sleep deprivation on cognitive functions

Sleep deprivation (SD) is a common condition that afflicts many people in modern life. Deficits in daytime performance due to SD are experienced universally. Recent evidence indicates that SD causes impairments in cognitive functions. However, the mechanisms that SD impairs cognitive functions are not clear. This review will focus on the behavioral and neural effects of SD with the aim to elucidate the possible mechanisms of SD-induced deterioration in cognitive functions and to identify directions for future research.

Cognitive behavioural therapy for anxiety disorders and insomnia: a commentary on future directions

Anxiety disorders and insomnia significantly impair daily functioning. Similar underlying mechanisms may account for the high comorbidity of both disorders, and respective treatments share pharmacological and behavioural features. This review suggests the utility of an integrated CBT approach in the treatment of generalized anxiety, post-traumatic stress, and panic disorders, and comorbid insomnia. Other anxiety disorders were not explored because current data are limited or inconsistent. A comprehensive, non-systematic review of the literature was conducted to evaluate the treatment of comorbid anxiety and insomnia disorders, and data reveal shared pharmacological and behavioural features of insomnia and anxiety disorders treatment. However, research demonstrates that CBT maintains successful treatment results longer than drug therapies. Despite similar treatment approaches, there is a paucity of research that explores integrated CBT approaches for comorbid anxiety and insomnia disorders. This review suggests that future research should assess the impact of combined therapeutic approaches on the simultaneous reduction of anxiety disorders, insomnia, and relapse rates.

Effects of sleep deprivation on different phases of memory in the rat: dissociation between contextual and tone fear conditioning tasks

Numerous studies show that sleep deprivation (SD) impacts negatively on cognitive processes, including learning and memory. Memory formation encompasses distinct phases of which acquisition, consolidation and retrieval are better known. Previous studies with pre-training SD induced by the platform method have shown impairment in fear conditioning tasks. Nonetheless, pre-training manipulations do not allow the distinction between effects on acquisition and/or consolidation, interfering, ultimately, on recall of/performance in the task. In the present study, animals were first trained in contextual and tone fear conditioning (TFC) tasks and then submitted to SD with the purpose to evaluate the effect of this manipulation on different stages of the learning process, e.g., in the uptake of (new) information during learning, its encoding and stabilization, and the recall of stored memories. Besides, we also investigated the effect of SD in the extinction of fear memory and a possible state-dependent learning induced by this manipulation. For each task (contextual or TFC), animals were trained and then distributed into control, not sleep-deprived (CTL) and SD groups, the latter being submitted to the modified multiple platform paradigm for 96 h. Subsets of eight rats in each group/experiment were submitted to the test of the tasks, either immediately or at different time intervals after SD. The results indicated that (a) pre- but not post-training SD impaired recall in the contextual and TFC; (b) this impairment was not state-dependent; and (c) in the contextual fear conditioning (CFC), pre-test SD prevented extinction of the learned task. Overall, these results suggest that SD interferes with acquisition, recall and extinction, but not necessarily with consolidation of emotional memory.

Dietary therapy mitigates persistent wake deficits caused by mild traumatic brain injury

Sleep disorders are highly prevalent in patients with traumatic brain injury (TBI) and can significantly impair cognitive rehabilitation. No proven therapies exist to mitigate the neurocognitive consequences of TBI. We show that mild brain injury in mice causes a persistent inability to maintain wakefulness and decreases orexin neuron activation during wakefulness. We gave mice a dietary supplement of branched-chain amino acids (BCAAs), precursors for de novo glutamate synthesis in the brain. BCAA therapy reinstated activation of orexin neurons and improved wake deficits in mice with mild brain injury. Our data suggest that dietary BCAA intervention, acting in part through orexin, can ameliorate injury-induced sleep disturbances and may facilitate cognitive rehabilitation after brain injury.

Dorsal subcoeruleus nucleus (SubCD) involvement in context-associated fear memory consolidation

The neurobiological mechanisms of emotional memory processing can be investigated using classical fear conditioning as a model system, and evidence from multiple lines of research suggests that sleep influences consolidation of emotional memory. In rodents, some of this evidence comes from a common finding that sleep deprivation from 0 to 6 h after fear conditioning training impairs processing of conditioned fear memory. Here, we show that during a 6-h session of sleep-wake (S-W) recording, immediately after a session of context-associated fear conditioning training, rats spent more time in wakefulness (W) and less time in slow-wave sleep (SWS) and rapid eye movement (REM) sleep. This context-associated fear conditioning training-induced reduction in SWS lasts for 2 h, and the REM sleep reduction lasts throughout the entire 6-h post-training S-W recording period. Interestingly, these reductions in SWS and REM sleep during this 6-h period did not impair memory consolidation for context-associated fear conditioning. The results of this study show, for the first time, that lesions within the dorsal part of the subcoeruleus nucleus (SubCD), which were unintentionally caused by the implantation of bipolar recording electrodes, impair consolidation of context-associated fear conditioning memory. Together, the results of these experiments suggest that emotional memory processing associated with fear conditioning can be completed successfully within less than a normal amount of sleep, but it requires a structurally and functionally intact SubCD, an area in the brain stem where phasic pontine wave (P-wave) generating cells are located.

Experimental sleep deprivation as a tool to test memory deficits in rodents

Paradigms of sleep deprivation (SD) and memory testing in rodents (laboratory rats and mice) are here reviewed. The vast majority of these studies have been aimed at understanding the contribution of sleep to cognition, and in particular to memory. Relatively little attention, instead, has been devoted to SD as a challenge to induce a transient memory impairment, and therefore as a tool to test cognitive enhancers in drug discovery. Studies that have accurately described methodological aspects of the SD protocol are first reviewed, followed by procedures to investigate SD-induced impairment of learning and memory consolidation in order to propose SD protocols that could be employed as cognitive challenge. Thus, a platform of knowledge is provided for laboratory protocols that could be used to assess the efficacy of drugs designed to improve memory performance in rodents, including rodent models of neurodegenerative diseases that cause cognitive deficits, and Alzheimer's disease in particular. Issues in the interpretation of such preclinical data and their predictive value for clinical translation are also discussed.

The impact of sleep loss on hippocampal function

Hippocampal cellular and molecular processes critical for memory consolidation are affected by the amount and quality of sleep attained. Questions remain with regard to how sleep enhances memory, what parameters of sleep after learning are optimal for memory consolidation, and what underlying hippocampal molecular players are targeted by sleep deprivation to impair memory consolidation and plasticity. In this review, we address these topics with a focus on the detrimental effects of post-learning sleep deprivation on memory consolidation. Obtaining adequate sleep is challenging in a society that values "work around the clock." Therefore, the development of interventions to combat the negative cognitive effects of sleep deprivation is key. However, there are a limited number of therapeutics that are able to enhance cognition in the face of insufficient sleep. The identification of molecular pathways implicated in the deleterious effects of sleep deprivation on memory could potentially yield new targets for the development of more effective drugs.

Regular treadmill exercise prevents sleep deprivation-induced disruption of synaptic plasticity and associated signaling cascade in the dentate gyrus

STUDY OBJECTIVES

Evidence suggests that regular exercise can protect against learning and memory impairment in the presence of insults such as sleep deprivation. The dentate gyrus (DG) area of the hippocampus is a key staging area for learning and memory processes and is particularly sensitive to sleep deprivation. The purpose of this study was to determine the effect of regular exercise on early-phase long-term potentiation (E-LTP) and its signaling cascade in the presence of sleep deprivation.

EXPERIMENTAL DESIGN

Rats were exposed to 4 weeks of regular treadmill exercise then subsequently sleep-deprived for 24h using the modified multiple platform model before experimentation. We tested the effects of exercise and/or sleep deprivation using electrophysiological recording in the DG to measure synaptic plasticity; and Western blot analysis to quantify the levels of key signaling proteins related to E-LTP.

MEASUREMENTS AND RESULTS

Regular exercise prevented the sleep deprivation-induced impairment of E-LTP in the DG area as well as the sleep deprivation-associated decrease in basal protein levels of phosphorylated and total α calcium/calmodulin-dependent protein kinase II (P/total-CaMKII) and brain-derived neurotrophic factor (BDNF). High frequency stimulation (HFS) to the DG area was used to model learning stimuli and increased the P-CaMKII and BDNF levels in normal animals: yet failed to change these levels in sleep-deprived rats. However, HFS in control and sleep-deprived rats increased the levels of the phosphatase calcineurin. In contrast, exercise increased BDNF and P-CaMKII levels in exercised/sleep-deprived rats.

CONCLUSIONS

Regular exercise appears to exert a protective effect against sleep deprivation-induced spatial memory impairment by inducing hippocampal signaling cascades that positively modulate basal and stimulated levels of key effectors such as P-CaMKII and BDNF, while attenuating increases in the protein phosphatase calcineurin.

Sleep deprivation impairs spatial retrieval but not spatial learning in the non-human primate grey mouse lemur

A bulk of studies in rodents and humans suggest that sleep facilitates different phases of learning and memory process, while sleep deprivation (SD) impairs these processes. Here we tested the hypothesis that SD could alter spatial learning and memory processing in a non-human primate, the grey mouse lemur (Microcebus murinus), which is an interesting model of aging and Alzheimer's disease (AD). Two sets of experiments were performed. In a first set of experiments, we investigated the effects of SD on spatial learning and memory retrieval after one day of training in a circular platform task. Eleven male mouse lemurs aged between 2 to 3 years were tested in three different conditions: without SD as a baseline reference, 8 h of SD before the training and 8 h of SD before the testing. The SD was confirmed by electroencephalographic recordings. Results showed no effect of SD on learning when SD was applied before the training. When the SD was applied before the testing, it induced an increase of the amount of errors and of the latency prior to reach the target. In a second set of experiments, we tested the effect of 8 h of SD on spatial memory retrieval after 3 days of training. Twenty male mouse lemurs aged between 2 to 3 years were tested in this set of experiments. In this condition, the SD did not affect memory retrieval. This is the first study that documents the disruptive effects of the SD on spatial memory retrieval in this primate which may serve as a new validated challenge to investigate the effects of new compounds along physiological and pathological aging.

Neurobiological consequences of sleep deprivation

Although the physiological function of sleep is not completely understood, it is well documented that it contributes significantly to the process of learning and memory. Ample evidence suggests that adequate sleep is essential for fostering connections among neuronal networks for memory consolidation in the hippocampus. Sleep deprivation studies are extremely valuable in understanding why we sleep and what are the consequences of sleep loss. Experimental sleep deprivation in animals allows us to gain insight into the mechanism of sleep at levels not possible to study in human subjects. Many useful approaches have been utilized to evaluate the effect of sleep loss on cognitive function, each with relative advantages and disadvantages. In this review we discuss sleep and the detrimental effects of sleep deprivation mostly in experimental animals. The negative effects of sleep deprivation on various aspects of brain function including learning and memory, synaptic plasticity and the state of cognition-related signaling molecules are discussed.

Sleep deprivation impairs consolidation of cued fear memory in rats

Post-learning sleep facilitates negative memory consolidation and also helps preserve it over several years. It is believed, therefore, that sleep deprivation may help prevent consolidation of fearful memory. Its effect, however, on consolidation of negative/frightening memories is not known. Cued fear-conditioning (CuFC) is a widely used model to understand the neural basis of negative memory associated with anxiety disorders. In this study, we first determined the suitable circadian timing for consolidation of CuFC memory and changes in sleep architecture after CuFC. Thereafter, we studied the effect of sleep deprivation on CuFC memory consolidation. Three sets of experiments were performed in male Wistar rat (n = 51). In experiment-I, animals were conditioned to cued-fear by presenting ten tone-shock paired stimuli during lights-on (7 AM) (n = 9) and lights-off (7 PM) (n = 9) periods. In experiment-II, animals were prepared for polysomnographic recording (n = 8) and changes in sleep architecture after CuFC was determined. Further in experiment-III, animals were cued fear-conditioned during the lights-off period and were randomly divided into four groups: Sleep-Deprived (SD) (n = 9), Non-Sleep Deprived (NSD) (n = 9), Stress Control (SC) (n = 9) and Tone Control (n = 7). Percent freezing amount, a hallmark of fear, was compared statistically in these groups. Rats trained during the lights-off period exhibited significantly more freezing compared to lights-on period. In CuFC trained animals, total sleep amount did not change, however, REM sleep decreased significantly. Further, out of total sleep time, animals spent proportionately more time in NREM sleep. Nevertheless, SD animals exhibited significantly less freezing compared to NSD and SC groups. These data suggest that sleep plays an important role in the consolidation of cued fear-conditioned memory.

Genomic analysis of sleep deprivation reveals translational regulation in the hippocampus

Sleep deprivation is a common problem of considerable health and economic impact in today's society. Sleep loss is associated with deleterious effects on cognitive functions such as memory and has a high comorbidity with many neurodegenerative and neuropsychiatric disorders. Therefore, it is crucial to understand the molecular basis of the effect of sleep deprivation in the brain. In this study, we combined genome-wide and traditional molecular biological approaches to determine the cellular and molecular impacts of sleep deprivation in the mouse hippocampus, a brain area crucial for many forms of memory. Microarray analysis examining the effects of 5 h of sleep deprivation on gene expression in the mouse hippocampus found 533 genes with altered expression. Bioinformatic analysis revealed that a prominent effect of sleep deprivation was to downregulate translation, potentially mediated through components of the insulin signaling pathway such as the mammalian target of rapamycin (mTOR), a key regulator of protein synthesis. Consistent with this analysis, sleep deprivation reduced levels of total and phosphorylated mTOR, and levels returned to baseline after 2.5 h of recovery sleep. Our findings represent the first genome-wide analysis of the effects of sleep deprivation on the mouse hippocampus, and they suggest that the detrimental effects of sleep deprivation may be mediated by reductions in protein synthesis via downregulation of mTOR. Because protein synthesis and mTOR activation are required for long-term memory formation, our study improves our understanding of the molecular mechanisms underlying the memory impairments induced by sleep deprivation.

Control of sleep and wakefulness

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

The impact of sleep deprivation on neuronal and glial signaling pathways important for memory and synaptic plasticity

Sleep deprivation is a common feature in modern society, and one of the consequences of sleep loss is the impairment of cognitive function. Although it has been widely accepted that sleep deprivation affects learning and memory, only recently has research begun to address which molecular signaling pathways are altered by sleep loss and, more importantly, which pathways can be targeted to reverse the memory impairments resulting from sleep deprivation. In this review, we discuss the different methods used to sleep deprive animals and the effects of different durations of sleep deprivation on learning and memory with an emphasis on hippocampus-dependent memory. We then review the molecular signaling pathways that are sensitive to sleep loss, with a focus on those thought to play a critical role in the memory and synaptic plasticity deficits observed after sleep deprivation. Finally, we highlight several recent attempts to reverse the effects of sleep deprivation on memory and synaptic plasticity. Future research building on these studies promises to contribute to the development of novel strategies to ameliorate the effects of sleep loss on cognition.

Astrocyte-derived adenosine and A1 receptor activity contribute to sleep loss-induced deficits in hippocampal synaptic plasticity and memory in mice

Sleep deprivation (SD) can have a negative impact on cognitive function, but the mechanism(s) by which SD modulates memory remains unclear. We have previously shown that astrocyte-derived adenosine is a candidate molecule involved in the cognitive deficits following a brief period of SD (Halassa et al., 2009). In this study, we examined whether genetic disruption of soluble N-ethylmaleimide-sensitive factor attached protein (SNARE)-dependent exocytosis in astrocytes (dnSNARE mice) or pharmacological blockade of A1 receptor signaling using an adenosine A1 receptor (A1R) antagonist, 8-cyclopentyl-1,3-dimethylxanthine (CPT), could prevent the negative effects of 6 h of SD on hippocampal late-phase long-term potentiation (L-LTP) and hippocampus-dependent spatial object recognition memory. We found that SD impaired L-LTP in wild-type mice but not in dnSNARE mice. Similarly, this deficit in L-LTP resulting from SD was prevented by a chronic infusion of CPT. Consistent with these results, we found that hippocampus-dependent memory deficits produced by SD were rescued in dnSNARE mice and CPT-treated mice. These data provide the first evidence that astrocytic ATP and adenosine A1R activity contribute to the effects of SD on hippocampal synaptic plasticity and hippocampus-dependent memory, and suggest a new therapeutic target to reverse the hippocampus-related cognitive deficits induced by sleep loss.

Neuropsychological effects of sleep loss: implication for neuropsychologists

There is rapidly accumulating evidence of a close relationship between sleep loss and cognition. Neuropsychologists need to become aware of this body of knowledge as the effects of sleep loss on brain functions are significant. The current study (a) outlines the extent to which insufficient sleep affects performance on cognitive tasks in otherwise healthy people, (b) discusses the relationship between sleep and neurocognitive disorders, and (c) highlights key issues that merit consideration for neuropsychologists. This review shows that sleep loss has a measurable impact on performance through decreases in cognitive functions and effects on biological pathways that support cognitive performance. Sleep loss reliably produces reductions in speed of processing and attention. Higher order cognitive functions are affected to a lesser extent, and there is sparing on tasks of crystallized abilities. Deficits worsen with increasing time awake, but may be overturned after normal sleep is resumed. The review also shows that sleep disorders are a major feature of neuropsychological conditions contributing to the pattern of cognitive impairment. Overall, neuropsychologists must be alert to sleep problems in their clients, so that sleep interventions, or referrals, are put in place in the rehabilitation plan of individuals with cognitive dysfunctions. Recommendations also include routine screening of sleep as part of cognitive assessment.

Sleep disorders in patients with traumatic brain injury: a review

Traumatic brain injury (TBI) is a global problem and causes long-term disability in millions of individuals. This is a major problem for both military- and civilian-related populations. The prevalence of sleep disorders in individuals with TBI is very high, yet mostly unrecognized. Approximately 46% of all chronic TBI patients have sleep disorders, which require nocturnal polysomnography and the Multiple Sleep Latency Test for diagnosis. These disorders include sleep apnoea (23% of all TBI patients), post-traumatic hypersomnia (11%), narcolepsy (6%) and periodic limb movements (7%). Over half of all TBI patients will have insomnia complaints, most often with less severe injury and after personal assault, and half of these may be related to a circadian rhythm disorder. Hypothalamic injury with decreased levels of wake-promoting neurotransmitters such as hypocretin (orexin) and histamine may be involved in the pathophysiology of excessive sleepiness associated with TBI. These sleep disorders result in additional neurocognitive deficits and functional impairment, which might be attributed to the original brain injury itself and thus be left without specific treatment. Most standard treatment regimens of sleep disorders appear to be effective in these patients, including continuous positive airway pressure for sleep apnoea, pramipexole for periodic limb movements and cognitive behavioural therapy for insomnia. The role of wake-promoting agents and CNS stimulants for TBI-associated narcolepsy, post-traumatic hypersomnia and excessive daytime sleepiness requires further study with larger numbers of patients to determine effectiveness and benefit in this population. Future research with multiple collaborating centres should attempt to delineate the pathophysiology of TBI-associated sleep disorders, including CNS-derived hypersomnia and circadian rhythm disturbances, and determine definitive, effective treatment for associated sleep disorders.