Adenosine, caffeine, and performance: from cognitive neuroscience of sleep to sleep pharmacogenetics

Biomathematical modeling of fatigue due to sleep inertia

Biomathematical models of fatigue capture the physiology of sleep/wake regulation and circadian rhythmicity to predict changes in neurobehavioral functioning over time. We used a biomathematical model of fatigue linked to the adenosinergic neuromodulator/receptor system in the brain as a framework to predict sleep inertia, that is, the transient neurobehavioral impairment experienced immediately after awakening. Based on evidence of an adenosinergic basis for sleep inertia, we expanded the biomathematical model with novel differential equations to predict the propensity for sleep inertia during sleep and its manifestation after awakening. Using datasets from large laboratory studies of sleep loss and circadian misalignment, we calibrated the model by fitting just two new parameters and then validated the model's predictions against independent data. The expanded model was found to predict the magnitude and time course of sleep inertia with generally high accuracy. Analysis of the model's dynamics revealed a bifurcation in the predicted manifestation of sleep inertia in sustained sleep restriction paradigms, which reflects the observed escalation of the magnitude of sleep inertia in scenarios with sleep restriction to less than ∼ 4 h per day. Another emergent property of the model involves a rapid increase in the predicted propensity for sleep inertia in the early part of sleep followed by a gradual decline in the later part of the sleep period, which matches what would be expected based on the adenosinergic regulation of non-rapid eye movement (NREM) sleep and its known influence on sleep inertia. These dynamic behaviors provide confidence in the validity of our approach and underscore the predictive potential of the model. The expanded model provides a useful tool for predicting sleep inertia and managing impairment in 24/7 settings where people may need to perform critical tasks immediately after awakening, such as on-demand operations in safety and security, emergency response, and health care.

Adora2A downregulation promotes caffeine neuroprotective effect against LPS-induced neuroinflammation in the hippocampus

Caffeine has been extensively studied in the context of CNS pathologies as many researchers have shown that consuming it reduces pro-inflammatory biomarkers, potentially delaying the progression of neurodegenerative pathologies. Several lines of evidence suggest that adenosine receptors, especially A1 and A2A receptors, are the main targets of its neuroprotective action. We found that caffeine pretreatment 15 min before LPS administration reduced the expression of Il1b in the hippocampus and striatum. The harmful modulation of caffeine-induced inflammatory response involved the downregulation of the expression of A2A receptors, especially in the hippocampus. Caffeine treatment alone promoted the downregulation of the adenosinergic receptor Adora2A; however, this promotion effect was reversed by LPS. Although administering caffeine increased the expression of the enzymes DNA methyltransferases 1 and 3A and decreased the expression of the demethylase enzyme Tet1, this effect was reversed by LPS in the hippocampus of mice that were administered Caffeine + LPS, relative to the basal condition; no significant differences were observed in the methylation status of the promoter regions of adenosine receptors. Finally, the bioinformatics analysis of the expanded network demonstrated the following results: the Adora2B gene connects the extended networks of the adenosine receptors Adora1 and Adora2A; the Mapk3 and Esr1 genes connect the extended Adora1 network; the Mapk4 and Arrb2 genes connect the extended Adora2A network with the extended network of the proinflammatory cytokine Il1β. These results indicated that the anti-inflammatory effects of acute caffeine administration in the hippocampus may be mediated by a complex network of interdependencies between the Adora2B and Adora2A genes.

Repeated caffeine intake suppresses cerebral grey matter responses to chronic sleep restriction in an A1 adenosine receptor-dependent manner: a double-blind randomized controlled study with PET-MRI

Evidence has shown that both sleep loss and daily caffeine intake can induce changes in grey matter (GM). Caffeine is frequently used to combat sleepiness and impaired performance caused by insufficient sleep. It is unclear (1) whether daily use of caffeine could prevent or exacerbate the GM alterations induced by 5-day sleep restriction (i.e. chronic sleep restriction, CSR), and (2) whether the potential impact on GM plasticity depends on individual differences in the availability of adenosine receptors, which are involved in mediating effects of caffeine on sleep and waking function. Thirty-six healthy adults participated in this double-blind, randomized, controlled study (age = 28.9 ± 5.2 y/; F:M = 15:21; habitual level of caffeine intake < 450 mg; 29 homozygous C/C allele carriers of rs5751876 of ADORA2A, an A2A adenosine receptor gene variant). Each participant underwent a 9-day laboratory visit consisting of one adaptation day, 2 baseline days (BL), 5-day sleep restriction (5 h time-in-bed), and a recovery day (REC) after an 8-h sleep opportunity. Nineteen participants received 300 mg caffeine in coffee through the 5 days of CSR (CAFF group), while 17 matched participants received decaffeinated coffee (DECAF group). We examined GM changes on the 2nd BL Day, 5th CSR Day, and REC Day using magnetic resonance imaging and voxel-based morphometry. Moreover, we used positron emission tomography with [18F]-CPFPX to quantify the baseline availability of A1 adenosine receptors (A1R) and its relation to the GM plasticity. The results from the voxel-wise multimodal whole-brain analysis on the Jacobian-modulated T1-weighted images controlled for variances of cerebral blood flow indicated a significant interaction effect between caffeine and CSR in four brain regions: (a) right temporal-occipital region, (b) right dorsomedial prefrontal cortex (DmPFC), (c) left dorsolateral prefrontal cortex (DLPFC), and (d) right thalamus. The post-hoc analyses on the signal intensity of these GM clusters indicated that, compared to BL, GM on the CSR day was increased in the DECAF group in all clusters  but decreased in the thalamus, DmPFC, and DLPFC in the CAFF group. Furthermore, lower baseline subcortical A1R availability predicted a larger GM reduction in the CAFF group after CSR of all brain regions except for the thalamus. In conclusion, our data suggest an adaptive GM upregulation after 5-day CSR, while concomitant use of caffeine instead leads to a GM reduction. The lack of consistent association with individual A1R availability may suggest that CSR and caffeine affect thalamic GM plasticity predominantly by a different mechanism. Future studies on the role of adenosine A2A receptors in CSR-induced GM plasticity are warranted.

Effectiveness of caffeine and blue-enriched light on cognitive performance and electroencephalography correlates of alertness in a spaceflight robotics simulation

Human cognitive impairment associated with sleep loss, circadian misalignment and work overload is a major concern in any high stress occupation but has potentially catastrophic consequences during spaceflight human robotic interactions. Two safe, wake-promoting countermeasures, caffeine and blue-enriched white light have been studied on Earth and are available on the International Space Station. We therefore conducted a randomized, placebo-controlled, cross-over trial examining the impact of regularly timed low-dose caffeine (0.3 mg per kg per h) and moderate illuminance blue-enriched white light (~90 lux, ~88 melEDI lux, 6300 K) as countermeasures, separately and combined, in a multi-night simulation of sleep-wake shifts experienced during spaceflight among 16 participants (7 F, ages 26-55). We find that chronic administration of low-dose caffeine improves subjective and objective correlates of alertness and performance during an overnight work schedule involving chronic sleep loss and circadian misalignment, although we also find that caffeine disrupts subsequent sleep. We further find that 90 lux of blue-enriched light moderately reduces electroencephalogram (EEG) power in the theta and delta regions, which are associated with sleepiness. These findings support the use of low-dose caffeine and potentially blue-enriched white light to enhance alertness and performance among astronauts and shiftworking populations.

Current therapeutic targets and multifaceted physiological impacts of caffeine

Caffeine, which shares consubstantial structural similarity with purine adenosine, has been demonstrated as a nonselective adenosine receptor antagonist for eliciting most of the biological functions at physiologically relevant dosages. Accumulating evidence supports caffeine's beneficial effects against different disorders, such as total cardiovascular diseases and type 2 diabetes. Conversely, paradoxical effects are also linked to caffeine ingestion in humans including hypertension-hypotension and tachycardia-bradycardia. These observations suggest the association of caffeine action with its ingested concentration and/or concurrent interaction with preferential molecular targets to direct explicit events in the human body. Thus, a coherent analysis of the functional targets of caffeine, relevant to normal physiology, and disease pathophysiology, is required to understand the pharmacology of caffeine. This review provides a broad overview of the experimentally validated targets of caffeine, particularly those of therapeutic interest, and the impacts of caffeine on organ-specific physiology and pathophysiology. Overall, the available empirical and epidemiological evidence supports the dose-dependent functional activities of caffeine and advocates for further studies to get insights into the caffeine-induced changes under specific conditions, such as asthma, DNA repair, and cancer, in view of its therapeutic applications.

Genetics of caffeine and brain-related outcomes - a systematic review of observational studies and randomized trials

CONTEXT

Although the stimulant and anxiogenic properties of caffeine are widely accepted, research on its specific effects on the brain remains controversial. Growing evidence shows that interindividual differences in caffeine response may be partly due to variations in genes such as CYP1A2 and ADORA2A, which have been used to identify individuals as "fast" or "slow" caffeine metabolizers and as having a "high" or "low" caffeine sensitivity, respectively.

OBJECTIVE

The objective of this review was to identify, evaluate, and discuss current evidence on the associations between common genetic variants, caffeine consumption, and brain-related outcomes in humans.

DATA SOURCES

PubMed and Embase databases were searched for relevant reports based on a predetermined search strategy.

DATA EXTRACTION

Reports of observational and experimental studies on healthy adults who underwent (a) genetic analysis for polymorphisms in genes associated with caffeine metabolism and effects and (b) measurements of brain-related effects such as anxiety, insomnia, and cognitive performance associated with the consumption of caffeine (habitual intake or supplementation) were included.

DATA ANALYSIS

Of the 22 records included, 15 were randomized controlled trials, 6 were cross-sectional studies, and 1 was a genome-wide association study. The main outcomes identified were cognitive performance (n = 9), anxiety (n = 7), and sleep disturbance/insomnia (n = 6). Polymorphisms in the CYP1A2 gene were associated with cognitive function, while variations in the ADORA2A gene were associated with anxiety and sleep disturbance.

CONCLUSION

The present review has provided evidence that variability in the CYP1A2 and the ADORA2A genes may modulate the association between caffeine and brain-related outcomes. Future studies are warranted to investigate the specific polymorphisms implicated in each brain outcome, which cognitive functions are particularly related to caffeine (simple vs complex), whether there are gender differences in anxiety effects, and how habitual caffeine intake may influence the acute effects of caffeine.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42021257556.

A genetic variation in the adenosine A2A receptor gene contributes to variability in oscillatory alpha power in wake and sleep EEG and A1 adenosine receptor availability in the human brain

The EEG alpha rhythm (∼ 8-13 Hz) is one of the most salient human brain activity rhythms, modulated by the level of attention and vigilance and related to cerebral energy metabolism. Spectral power in the alpha range in wakefulness and sleep strongly varies among individuals based on genetic predisposition. Knowledge about the underlying genes is scarce, yet small studies indicated that the variant rs5751876 of the gene encoding A2A adenosine receptors (ADORA2A) may contribute to the inter-individual variation. The neuromodulator adenosine is directly linked to energy metabolism as product of adenosine tri-phosphate breakdown and acts as a sleep promoting molecule by activating A1 and A2A adenosine receptors. We performed sleep and positron emission tomography studies in 59 healthy carriers of different rs5751876 alleles, and quantified EEG oscillatory alpha power in wakefulness and sleep, as well as A1 adenosine receptor availability with 18F-CPFPX. Oscillatory alpha power was higher in homozygous C-allele carriers (n = 27, 11 females) compared to heterozygous and homozygous carriers of the T-allele (n(C/T) = 23, n(T/T) = 5, 13 females) (F(18,37) = 2.35, p = 0.014, Wilk's Λ = 0.487). Furthermore, a modulatory effect of ADORA2A genotype on A1 adenosine receptor binding potential was found across all considered brain regions (F(18,40) = 2.62, p = 0.006, Wilk's Λ = 0.459), which remained significant for circumscribed occipital region of calcarine fissures after correction for multiple comparisons. In female participants, a correlation between individual differences in oscillatory alpha power and A1 receptor availability was observed. In conclusion, we confirmed that a genetic variant of ADORA2A affects individual alpha power, while a direct modulatory effect via A1 adenosine receptors in females is suggested.

Exploring Astrocyte-Mediated Mechanisms in Sleep Disorders and Comorbidity

Astrocytes, the most abundant cells in the brain, are integral to sleep regulation. In the context of a healthy neural environment, these glial cells exert a profound influence on the sleep-wake cycle, modulating both rapid eye movement (REM) and non-REM sleep phases. However, emerging literature underscores perturbations in astrocytic function as potential etiological factors in sleep disorders, either as protopathy or comorbidity. As known, sleep disorders significantly increase the risk of neurodegenerative, cardiovascular, metabolic, or psychiatric diseases. Meanwhile, sleep disorders are commonly screened as comorbidities in various neurodegenerative diseases, epilepsy, and others. Building on existing research that examines the role of astrocytes in sleep disorders, this review aims to elucidate the potential mechanisms by which astrocytes influence sleep regulation and contribute to sleep disorders in the varied settings of brain diseases. The review emphasizes the significance of astrocyte-mediated mechanisms in sleep disorders and their associated comorbidities, highlighting the need for further research.

Sleep Deprivation and Gut Microbiota Dysbiosis: Current Understandings and Implications

Gut microbiota comprises the microbial communities inhabiting our gastrointestinal (GI) tracts. Accordingly, these complex communities play a fundamental role in many host processes and are closely implicated in human health and diseases. Sleep deprivation (SD) has become increasingly common in modern society, partly owing to the rising pressure of work and the diversification of entertainment. It is well documented that sleep loss is a significant cause of various adverse outcomes on human health including immune-related and metabolic diseases. Furthermore, accumulating evidence suggests that gut microbiota dysbiosis is associated with these SD-induced human diseases. In this review, we summarize the gut microbiota dysbiosis caused by SD and the succedent diseases ranging from the immune system and metabolic system to various organs and highlight the critical roles of gut microbiota in these diseases. The implications and possible strategies to alleviate SD-related human diseases are also provided.

Brain activity during a working memory task after daily caffeine intake and caffeine withdrawal: a randomized double-blind placebo-controlled trial

Acute caffeine intake has been found to increase working memory (WM)-related brain activity in healthy adults without improving behavioral performances. The impact of daily caffeine intake-a ritual shared by 80% of the population worldwide-and of its discontinuation on working memory and its neural correlates remained unknown. In this double-blind, randomized, crossover study, we examined working memory functions in 20 young healthy non-smokers (age: 26.4 ± 4.0 years; body mass index: 22.7 ± 1.4 kg/m²; and habitual caffeine intake: 474.1 ± 107.5 mg/day) in a 10-day caffeine (150 mg × 3 times/day), a 10-day placebo (3 times/day), and a withdrawal condition (9-day caffeine followed by 1-day placebo). Throughout the 10th day of each condition, participants performed four times a working memory task (N-Back, comprising 3- and 0-back), and task-related blood-oxygen-level-dependent (BOLD) activity was measured in the last session with functional magnetic resonance imaging. Compared to placebo, participants showed a higher error rate and a longer reaction time in 3- against 0-back trials in the caffeine condition; also, in the withdrawal condition we observed a higher error rate compared to placebo. However, task-related BOLD activity, i.e., an increased attention network and decreased default mode network activity in 3- versus 0-back, did not show significant differences among three conditions. Interestingly, irrespective of 3- or 0-back, BOLD activity was reduced in the right hippocampus in the caffeine condition compared to placebo. Adding to the earlier evidence showing increasing cerebral metabolic demands for WM function after acute caffeine intake, our data suggest that such demands might be impeded over daily intake and therefore result in a worse performance. Finally, the reduced hippocampal activity may reflect caffeine-associated hippocampal grey matter plasticity reported in the previous analysis. The findings of this study reveal an adapted neurocognitive response to daily caffeine exposure and highlight the importance of classifying impacts of caffeine on clinical and healthy populations.

Sleep loss effects on physiological and cognitive responses to systemic environmental hypoxia

In the course of their missions or training, alpinists, but also mountain combat forces and mountain security services, professional miners, aircrew, aircraft and glider pilots and helicopter crews are regularly exposed to altitude without oxygen supplementation. At altitude, humans are exposed to systemic environmental hypoxia induced by the decrease in barometric pressure (<1,013 hPa) which decreases the inspired partial pressure of oxygen (PIO₂), while the oxygen fraction is constant (equal to approximately 20.9%). Effects of altitude on humans occur gradually and depend on the duration of exposure and the altitude level. From 1,500 m altitude (response threshold), several adaptive responses offset the effects of hypoxia, involving the respiratory and the cardiovascular systems, and the oxygen transport capacity of the blood. Fatigue and cognitive and sensory disorders are usually observed from 2,500 m (threshold of prolonged hypoxia). Above 3,500 m (the threshold for disorders), the effects are not completely compensated and maladaptive responses occur and individuals develop altitude headache or acute altitude illness [Acute Mountain Sickness (AMS)]. The magnitude of effects varies considerably between different physiological systems and exhibits significant inter-individual variability. In addition to comorbidities, the factors of vulnerability are still little known. They can be constitutive (genetic) or circumstantial (sleep deprivation, fatigue, speed of ascent.). In particular, sleep loss, a condition that is often encountered in real-life settings, could have an impact on the physiological and cognitive responses to hypoxia. In this review, we report the current state of knowledge on the impact of sleep loss on responses to environmental hypoxia in humans, with the aim of identifying possible consequences for AMS risk and cognition, as well as the value of behavioral and non-pharmacological countermeasures.

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Supporting Professionals in Critical Care Medicine: Burnout, Resiliency, and System-Level Change

Burnout is occurring in epidemic proportions among intensive care unit physicians and other health-care professionals-accelerated by pandemic-driven stress. The impact of burnout is far-reaching, threatening the health of individual workers, the safety and quality of care our patients receive, and eroding the infrastructure of health care in general. Drivers of burnout include excessive quantity of work (nights, weekends, and acuity surges); excessive menial tasks; incivility, poor communication, and challenges to team success; and frequent moral distress and end-of-life issues. This article provides system-based practice and individual strategies to address these drivers and improve the well-being of our team and our patients.

Possible Neuropathology of Sleep Disturbance Linking to Alzheimer's Disease: Astrocytic and Microglial Roles

Sleep disturbances not only deteriorate Alzheimer’s disease (AD) progress by affecting cognitive states but also accelerate the neuropathological changes of AD. Astrocytes and microglia are the principal players in the regulation of both sleep and AD. We proposed that possible astrocyte-mediated and microglia-mediated neuropathological changes of sleep disturbances linked to AD, such as astrocytic adenosinergic A1, A2, and A3 regulation; astrocytic dopamine and serotonin; astrocyte-mediated proinflammatory status (TNFα); sleep disturbance-attenuated microglial CX3CR1 and P2Y12; microglial Iba-1 and astrocytic glial fibrillary acidic protein (GFAP); and microglia-mediated proinflammatory status (IL-1b, IL-6, IL-10, and TNFα). Furthermore, astrocytic and microglial amyloid beta (Aβ) and tau in AD were reviewed, such as astrocytic Aβ interaction in AD; astrocyte-mediated proinflammation in AD; astrocytic interaction with Aβ in the central nervous system (CNS); astrocytic apolipoprotein E (ApoE)-induced Aβ clearance in AD, as well as microglial Aβ clearance and aggregation in AD; proinflammation-induced microglial Aβ aggregation in AD; microglial-accumulated tau in AD; and microglial ApoE and TREM2 in AD. We reviewed astrocytic and microglial roles in AD and sleep, such as astrocyte/microglial-mediated proinflammation in AD and sleep; astrocytic ApoE in sleep and AD; and accumulated Aβ-triggered synaptic abnormalities in sleep disturbance. This review will provide a possible astrocytic and microglial mechanism of sleep disturbance linked to AD.

Effect of Adenosine Receptor Antagonists on Adenosine-Pretreated PC12 Cells Exposed to Paraquat

Previous studies evaluated the adenosine receptor antagonists alone to determine their effects on oxidative stress, but little is known about adenosine’s protective efficacy when oxidative injury occurs in vivo. Adenosine is a crucial signaling molecule recognized by four distinct G-protein-coupled receptors (GPCRs) (i.e., A1R, A2AR, A2BR, and A3R) and protects cells against pathological conditions. The present study was performed to evaluate the role of antagonist modulation in the setting of paraquat toxicity with adenosine pretreatment. First, PC12 cells were exposed to paraquat (850 μM) and adenosine (30 μM) to develop an in vitro model for the antagonist effect assay. Second, we found that the A1R antagonist DPCPX enhanced the viability of paraquat-induced PC12 cells that underwent adenosine pretreatment. Moreover, the A2AR antagonist ZM241385 decreased the viability of paraquat-induced PC12 cells that underwent adenosine pretreatment. Our findings indicate that adenosine protection requires a dual blockade of A1R and activation of A2AR to work at its full potential, and the A2B and A3 adenosine receptor antagonists increased paraquat-induced oxidative damage. This represents a novel pharmacological strategy based on A1/A2A interactions and can assist in clarifying the role played by AR antagonists in the treatment of neurodegenerative diseases.

Characterization of sleep-related neurochemicals in the different developmental stages and insomnia models of Drosophila melanogaster

Neurotransmitters play an important role in regulating the physiological activity of the animal, especially in emotion and sleep. While nucleotides are involved in almost all cellular processes. However, the characteristics of sleep-related neurochemicals under different life cycles and environment remain poorly understood. A rapid and sensitive analytical method was established with LC-MS/MS to determine eight endogenous neurochemicals in Drosophila melanogaster and the levels of neurochemicals in the different developmental stages of Drosophila melanogaster were evaluated. The results indicated that there were significant discrepancies among different stages, especially from pupal stage to adult. The levels of these compounds in caffeine-induced insomnia model of Drosophila melanogaster were investigated. Compared with normal group the eight endogenous metabolites did not fluctuate significantly in insomnia Drosophila melanogaster, which may be due to the mechanism of caffeine-induced insomnia through other pathways, such as adenosine. The results provide a reference for decoding of neurochemicals involved in the development of the full cycle of mammalian life and exploration of insomnia even other mental diseases induced by exogenous substances in the future.

Effects of Caffeine Intake on Cognitive Performance Related to Total Sleep Deprivation and Time on Task: A Randomized Cross-Over Double-Blind Study

INTRODUCTION

It is widely admitted that both total sleep deprivation (TSD) and extended task engagement (Time-On-Task, TOT) induce a cognitive fatigue state in healthy subjects. Even if EEG theta activity and adenosine both increase with cognitive fatigue, it remains unclear if these modifications are common mechanisms for both sustained attention and executive processes.

METHODS

We performed a double-blind counter-balanced (placebo (PCBO) and caffeine (CAF) - 2×2.5 mg/kg/24 h)) study on 24 healthy subjects (33.7 ± 5.9 y). Subjects participated in an experimental protocol including an habituation/training day followed by a baseline day (D0 and D1) and a total sleep deprivation (TSD) day beginning on D1 at 23:00 until D2 at 21:00. Subjects performed the psychomotor vigilance test (PVT) assessing sustained attention, followed by the executive Go-NoGo inhibition task and the 2-NBack working memory task at 09:15 on D1 and D2.

RESULTS

We showed differential contributions of TSD and TOT on deficits in sustained attention and both executive processes. An alleviating effect of caffeine intake is only observed on sustained attention deficits related to TSD and not at all on TOT effect. The caffeine dose slows down the triggering of sustained attention deficits related to TOT effect.

DISCUSSION

These results suggest that sustained attention deficits induced by TSD rely on the adenosinergic mechanism whereas TOT effect observed for both sustained attention and executive would not.

Electroacupuncture promotes the survival and synaptic plasticity of hippocampal neurons and improvement of sleep deprivation-induced spatial memory impairment

Aims

This study aimed to investigate whether electroacupuncture (EA) promotes the survival and synaptic plasticity of hippocampal neurons by activating brain‐derived neurotrophic factor (BDNF)/tyrosine receptor kinase (TrkB)/extracellular signal‐regulated kinase (Erk) signaling, thereby improving spatial memory deficits in rats under SD.

Methods

In vivo, Morris water maze (MWM) was used to detect the effect of EA on learning and memory, at the same time Western blotting (WB), immunofluorescence (IF), and transmission electron microscopy (TEM) were used to explore the plasticity of hippocampal neurons and synapses, and the expression of BDNF/TrkB/Erk signaling. In vitro, cultured hippocampal neurons were treated with exogenous BDNF and the TrkB inhibitor K252a to confirm the relationship between BDNF/TrkB/Erk signaling and synaptic plasticity.

Results

Our results showed that EA mitigated the loss of hippocampal neurons and synapses, stimulated hippocampal neurogenesis, and improved learning and memory of rats under SD accompanied by upregulation of BDNF and increased phosphorylation of TrkB and Erk. In cultured hippocampal neurons, exogenous BDNF enhanced the expression of synaptic proteins, the frequency of the postsynaptic currents, and the phosphorylation of TrkB and Erk; these effects were reversed by treatment with K252a.

Conclusions

Electroacupuncture alleviates SD‐induced spatial memory impairment by promoting hippocampal neurogenesis and synaptic plasticity via activation of BDNF/TrkB/Erk signaling, which provided evidence for EA as a therapeutic strategy for countering the adverse effects of SD on cognition.

The Effect of Experimental Recuperative and Appetitive Post-lunch Nap Opportunities, With or Without Caffeine, on Mood and Reaction Time in Highly Trained Athletes

Purpose: To investigate the effects of placebo (PLA), 20 min nap opportunity (N20), 5mg·kg-1 of caffeine (CAF), and their combination (CAF+N20) on sleepiness, mood and reaction-time after partial sleep deprivation (PSD; 04h30 of time in bed; study 1 ) or after normal sleep night (NSN; 08h30 of time in bed; study 2 ). Methods: Twenty-three highly trained athletes ( study 1 ; 9 and study 2 ; 14) performed four test sessions (PLA, CAF, N20 and CAF+N20) in double-blind, counterbalanced and randomized order. Simple (SRT) and two-choice (2CRT) reaction time, subjective sleepiness (ESS) and mood state (POMS) were assessed twice, pre- and post-intervention. Results: SRT was lower (i.e., better performance) during CAF condition after PSD (pre: 336 ± 15 ms vs. post: 312 ± 9 ms; p < 0.001; d = 2.07; Δ% = 7.26) and NSN (pre: 350 ± 39 ms vs. post: 323 ± 32 ms; p < 0.001; d = 0.72; Δ% = 7.71) compared to pre-intervention. N20 decreased 2CRT after PSD (pre: 411 ± 13 ms vs. post: 366 ± 20 ms; p < 0.001; d = 2.89; Δ% = 10.81) and NSN (pre: 418 ± 29 ms vs. post: 375 ± 40 ms; p < 0.001; d = 1.23; Δ% = 10.23). Similarly, 2CRT was shorter during CAF+N20 sessions after PSD (pre: 406 ± 26 ms vs. post: 357 ± 17 ms; p < 0.001; d = 2.17; Δ% = 12.02) and after NSN (pre: 386 ± 33 ms vs. post: 352 ± 30 ms; p < 0.001; d = 1.09; Δ% = 8.68). After PSD, POMS score decreased after CAF (p < 0.001; d = 2.38; Δ% = 66.97) and CAF+N20 (p < 0.001; d = 1.68; Δ% = 46.68). However, after NSN, only N20 reduced POMS (p < 0.001; d = 1.05; Δ% = 78.65) and ESS (p < 0.01; d = 0.71; Δ% = 19.11). Conclusion: After PSD, all interventions reduced sleepiness and only CAF enhanced mood with or without napping. However, only N20 enhanced mood and reduced sleepiness after NSN. Caffeine ingestion enhanced SRT performance regardless of sleep deprivation. N20, with or without caffeine ingestion, enhanced 2CRT independently of sleep deprivation. This suggests a different mode of action of napping and caffeine on sleepiness, mood and reaction time.

Deletion of CD73 increases exercise power in mice

Ecto-5'-nucleotidase or CD73 is the main source of extracellular adenosine involved in the activation of adenosine A2A receptors, responsible for the ergogenic effects of caffeine. We now investigated the role of CD73 in exercise by comparing female wild-type (WT) and CD73 knockout (KO) mice in a treadmill-graded test to evaluate running power, oxygen uptake (V̇O2), and respiratory exchange ratio (RER) - the gold standards characterizing physical performance. Spontaneous locomotion in the open field and submaximal running power and V̇O2 in the treadmill were similar between CD73-KO and WT mice; V̇O2max also demonstrated equivalent aerobic power, but CD73-KO mice displayed a 43.7 ± 4.2% larger critical power (large effect size, P < 0.05) and 3.8 ± 0.4% increase of maximum RER (small effect size, P < 0.05). Thus, KO of CD73 was ergogenic; i.e., it increased physical performance.

Relationships of beverage consumption and actigraphy-assessed sleep parameters among urban-dwelling youth from Mexico

OBJECTIVE

To examine whether usual beverage intake was associated with sleep timing, duration and fragmentation among adolescents.

DESIGN

Usual beverage intake was assessed with a FFQ. Outcomes included sleep duration, midpoint (median of bed and wake times) and fragmentation, assessed with 7-d actigraphy. Sex-stratified linear regression was conducted with sleep characteristics as separate outcomes and quantiles of energy-adjusted beverage intake as exposures, accounting for age, maternal education, physical activity and smoking.

SETTING

Mexico City.

PARTICIPANTS

528 adolescents residing in Mexico City enrolled in a longitudinal cohort.

RESULTS

The mean age (sd) was 14·4 (2·1) years; 48 % were male. Among males, milk and water consumption were associated with longer weekday sleep duration (25 (95 % CI 1, 48) and 26 (95 % CI 4, 47) more minutes, in the 4th compared to the 1st quartile); and higher 100 % fruit juice consumption was related to earlier weekday sleep timing (-22 (95 % CI -28, 1) minutes in the 1st compared to the last quantile; P = 0·03). Among females, soda was associated with higher sleep fragmentation (1·6 (95 % CI 0·4, 2·8) % in the 4th compared to the 1st), and coffee/tea consumption was related to shorter weekend sleep duration (-23 (95 % CI -44, 2) minutes in the 4th compared to the 1st).

CONCLUSIONS

Among females, adverse associations with sleep were observed for caffeinated drinks, while males with higher consumption of healthier beverage options (water, milk and 100 % juice) had evidence of longer and earlier-timed sleep. Potential mechanisms involving melatonin and tryptophan should be further investigated.

Daily Caffeine Intake Induces Concentration-Dependent Medial Temporal Plasticity in Humans: A Multimodal Double-Blind Randomized Controlled Trial

Caffeine is commonly used to combat high sleep pressure on a daily basis. However, interference with sleep-wake regulation could disturb neural homeostasis and insufficient sleep could lead to alterations in human gray matter. Hence, in this double-blind, randomized, cross-over study, we examined the impact of 10-day caffeine (3 × 150 mg/day) on human gray matter volumes (GMVs) and cerebral blood flow (CBF) by fMRI MP-RAGE and arterial spin-labeling sequences in 20 habitual caffeine consumers, compared with 10-day placebo (3 × 150 mg/day). Sleep pressure was quantified by electroencephalographic slow-wave activity (SWA) in the previous nighttime sleep. Nonparametric voxel-based analyses revealed a significant reduction in GMV in the medial temporal lobe (mTL) after 10 days of caffeine intake compared with 10 days of placebo, voxel-wisely adjusted for CBF considering the decreased perfusion after caffeine intake compared with placebo. Larger GMV reductions were associated with higher individual concentrations of caffeine and paraxanthine. Sleep SWA was, however, neither different between conditions nor associated with caffeine-induced GMV reductions. Therefore, the data do not suggest a link between sleep depth during daily caffeine intake and changes in brain morphology. In conclusion, daily caffeine intake might induce neural plasticity in the mTL depending on individual metabolic processes.

Caffeine Use or Napping to Enhance Repeated Sprint Performance After Partial Sleep Deprivation: Why Not Both?

PURPOSE

To compare the effect of a 20-minute nap opportunity (N20), a moderate dose of caffeine (CAF; 5 mg·kg-1), or a moderate dose of caffeine before N20 (CAF+N) as possible countermeasures to the decreased performance and the partial sleep deprivation-induced muscle damage.

METHODS

Nine male, highly trained judokas were randomly assigned to either baseline normal sleep night, placebo, N20, CAF, or CAF+N. Test sessions included the running-based anaerobic sprint test, from which the maximum (Pmax), mean (Pmean), and minimum (Pmin) powers were calculated. Biomarkers of muscle, hepatic, and cardiac damage and of enzymatic and nonenzymatic antioxidants were measured at rest and after the exercise.

RESULTS

N20 increased Pmax compared with placebo (P < .01, d = 0.75). CAF+N increased Pmax (P < .001, d = 1.5; d = 0.94), Pmin (P < .001, d = 2.79; d = 2.6), and Pmean (P < .001, d = 1.93; d = 1.79) compared with placebo and CAF, respectively. Postexercise creatine kinase increased whenever caffeine was added, that is, after CAF (P < .001, d = 1.19) and CAF+N (P < .001, d = 1.36). Postexercise uric acid increased whenever participants napped, that is, after N20 (P < .001, d = 2.19) and CAF+N (P < .001, d = 2.50) and decreased after CAF (P < .001, d = 2.96).

CONCLUSION

Napping improved repeated-sprint performance and antioxidant defense after partial sleep deprivation. Contrarily, caffeine increased muscle damage without improving performance. For sleep-deprived athletes, caffeine before a short nap opportunity would be more beneficial for repeated sprint performance than each treatment alone.

Changed signals of blood adenosine and cytokines are associated with parameters of sleep and/or cognition in the patients with chronic insomnia disorder

OBJECTIVES

This study aimed to investigate whether plasma levels of adenosine, adenosine deaminase (ADA), and certain cytokines change in patients with chronic insomnia disorder (CID), and if so, whether these alterations are associated with poor sleep quality and cognitive dysfunction.

METHODS

Fifty-five CID patients were selected for the study, along with fifty-five healthy controls (HC) matched to the patients according to their basic data. All subjects completed sleep, emotion, and cognition assessments, with some CID patients also completing an overnight polysomnography. The plasma level of adenosine was measured using liquid chromatography-tandem mass spectrometry, while ADA level was quantified using a quantitative sandwich enzyme-linked immunosorbent assay. Levels of cytokines, including IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12, TNF-α, and IFN-γ, were measured using Luminex liquid chip technology.

RESULTS

CID patients had a lower adenosine level, and higher levels of ADA and some of the cytokines (IL-1β, IL-2, IL-6, IL-10 and TNF-α) compared with controls. In the CID group, plasma concentrations of adenosine were negatively correlated with Pittsburgh Sleep Quality Index scores, while concentrations of IL-1β, IL-6 and TNF-α were positively correlated with these scores. Concentrations of IL-1β and TNF-α were negatively correlated with scores on the Chinese-Beijing Version of the Montreal Cognitive Assessment. Moreover, levels of IL-1β, TNF-α, IL-6, and IL-2 were positively correlated with memory test errors by CID patients after controlling for confounding factors.

CONCLUSIONS

The reduced adenosine and elevated cytokine levels of CID patients were associated with the severity of insomnia and/or cognitive dysfunction.

International society of sports nutrition position stand: caffeine and exercise performance

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

Wide awake at bedtime? Effects of caffeine on sleep and circadian timing in male adolescents - A randomized crossover trial

Adolescents often suffer from short and mistimed sleep. To counteract the resulting daytime sleepiness they frequently consume caffeine. However, caffeine intake may exaggerate sleep problems by disturbing sleep and circadian timing. In a 28-hour double-blind randomized crossover study, we investigated to what extent caffeine disturbs slow-wave sleep (SWS) and delays circadian timing in teenagers. Following a 6-day ambulatory phase of caffeine abstinence and fixed sleep-wake cycles, 18 male teenagers (14-17 years old) ingested 80 mg caffeine vs. placebo in the laboratory four hours prior to an electro-encephalographically (EEG) recorded nighttime sleep episode. Data were analyzed using both frequentist and Bayesian statistics. The analyses suggest that subjective sleepiness is reduced after caffeine compared to placebo. However, we did not observe a strong caffeine-induced reduction in subjective sleep quality or SWS, but rather a high inter-individual variability in caffeine-induced SWS changes. Exploratory analyses suggest that particularly those individuals with a higher level of SWS during placebo reduced SWS in response to caffeine. Regarding salivary melatonin onsets, caffeine-induced delays were not evident at group level, and only observed in participants exposed to a higher caffeine dose relative to individual bodyweight (i.e., a dose > 1.3 mg/kg). Together, the results suggest that 80 mg caffeine are sufficient to induce alertness at a subjective level. However, particularly teenagers with a strong need for deep sleep might pay for these subjective benefits by a loss of SWS during the night. Thus, caffeine-induced sleep-disruptions might change along with the maturation of sleep need.

Association between coffee, tobacco, and alcohol daily consumption and sleep/wake cycle: an actigraphy study in euthymic patients with bipolar disorders

Individuals with bipolar disorder (BD) have higher than average rates of coffee, tobacco and alcohol use. These substances may have deleterious effects on sleep quality and quantity, which may destabilize sleep/wake cycles and negatively impact the clinical course and prognosis of BD. The use of these substances may also be perceived as a self-medication attempt, for example, to induce sleep or to increase vigilance during the day. The objective of the current study was to investigate associations between the self-reported daily use of coffee, tobacco, and alcohol, and objective measures of sleep and activity patterns in adult individuals with BD. A sample of 147 euthymic individuals with BD were assessed for daily coffee, tobacco and alcohol consumption and 21 days of actigraphy monitoring. Actigraphic measures of sleep quantity and daytime activity were compared between groups classified as coffee+/coffee-, tobacco+/tobacco- and alcohol+/alcohol-, defined according to their current daily use. Then, we examined potential correlations between sleep/wake cycle parameters and the amount of daily consumption of each substance. Multivariable analyses identified associations between the use of coffee, tobacco, and alcohol and several sleep and activity parameters, such as between coffee, alcohol, and the relative amplitude of activity (respectively, p = .003 and p = .005), between alcohol and M10 onset (onset time of the 10 most active hours during the 24-h cycle) (p = .003), and between coffee and sleep duration (p = .047). This study supports the hypothesis that there is a relationship, whose direction would be bidirectional, between the daily use of these substances and the sleep/wake cycle in euthymic individuals with BD. These preliminary results require replications in other retrospective and prospective samples. They may have a clinical impact on psycho-education strategies to be proposed to individuals with BD.

Arousal and sleep circuits

The principal neurons of the arousal and sleep circuits are comprised by glutamate and GABA neurons, which are distributed within the reticular core of the brain and, through local and distant projections and interactions, regulate cortical activity and behavior across wake-sleep states. These are in turn modulated by the neuromodulatory systems that are comprised by acetylcholine, noradrenaline, dopamine, serotonin, histamine, orexin (hypocretin), and melanin-concentrating hormone (MCH) neurons. Glutamate and GABA neurons are heterogeneous in their profiles of discharge, forming distinct functional cell types by selective or maximal discharge during (1) waking and paradoxical (REM) sleep, (2) during slow wave sleep, (3) during waking, or (4) during paradoxical (REM) sleep. The neuromodulatory systems are each homogeneous in their profile of discharge, the majority discharging maximally during waking and paradoxical sleep or during waking. Only MCH neurons discharge maximally during sleep. They each exert their modulatory influence upon other neurons through excitatory and inhibitory receptors thus effecting a concerted differential change in the functionally different cell groups. Both arousal and sleep circuit neurons are homeostatically regulated as a function of their activity in part through changes in receptors. The major pharmacological agents used for the treatment of wake and sleep disorders act upon GABA and neuromodulatory transmission.

The Impact of Genetic Variations in ADORA2A in the Association between Caffeine Consumption and Sleep

ADORA2A has been shown to be responsible for the wakefulness-promoting effect of caffeine and the 1976T>C genotype (SNP rs5751876, formerly 1083T>C) to contribute to individual sensitivity to caffeine effects on sleep. We investigate the association between six single nucleotide polymorphisms (SNP) from ADORA2A and self-reported sleep characteristics and caffeine consumption in 1023 active workers of European ancestry aged 18-60 years. Three groups of caffeine consumers were delineated: low (0-50 mg/day, less than one expresso per day), moderate (51-300 mg/day), and high (>300 mg/day). We found that at caffeine levels higher than 300 mg/day, total sleep time (TST) decreased (F = 13.9, p < 0.01), with an increase of insomnia (ORa [95%CI] = 1.5 [1.1-1.9]) and sleep complaints (ORa [95%CI] = 1.9 [1.1-3.3]), whatever the ADORA2A polymorphism. Odds ratios were adjusted (ORa) for sex, age, and tobacco. However, in low caffeine consumers, lower TST was observed in the T allele compared to homozygote rs5751876 and rs3761422 C carriers. Conversely, higher TST was observed in rs2298383 T allele compared to C and in rs4822492G allele compared to the homozygote C (p < 0.05). These 4 SNPs are in strong linkage disequilibrium. Haplotype analysis confirmed the influence of multiple ADORA2a SNPs on TST. In addition, the rs2298383 T and rs4822492 G alleles were associated with higher risk of sleep complaints (Ora = 1.9 [1.2-3.1] and Ora = 1.5 [1.1-2.1]) and insomnia (Ora = 1.5 [1.3-2.5] and Ora = 1.9 [1.3-3.2). The rs5751876 T allele was associated with a decreased risk of sleep complaints (Ora = 0.7 [0.3-0.9]) and insomnia (Ora = 0.5 [0.3-0.9]). Our results identified ADORA2A polymorphism influences in the less-than-300-mg-per-day caffeine consumers. This opens perspectives on the diagnosis and pharmacology of sleep complaints and caffeine chronic consumption.

Fatigue, Sleep, and Autoimmune and Related Disorders

Profound and debilitating fatigue is the most common complaint reported among individuals with autoimmune disease, such as systemic lupus erythematosus, multiple sclerosis, type 1 diabetes, celiac disease, chronic fatigue syndrome, and rheumatoid arthritis. Fatigue is multi-faceted and broadly defined, which makes understanding the cause of its manifestations especially difficult in conditions with diverse pathology including autoimmune diseases. In general, fatigue is defined by debilitating periods of exhaustion that interfere with normal activities. The severity and duration of fatigue episodes vary, but fatigue can cause difficulty for even simple tasks like climbing stairs or crossing the room. The exact mechanisms of fatigue are not well-understood, perhaps due to its broad definition. Nevertheless, physiological processes known to play a role in fatigue include oxygen/nutrient supply, metabolism, mood, motivation, and sleepiness-all which are affected by inflammation. Additionally, an important contributing element to fatigue is the central nervous system-a region impacted either directly or indirectly in numerous autoimmune and related disorders. This review describes how inflammation and the central nervous system contribute to fatigue and suggests potential mechanisms involved in fatigue that are likely exhibited in autoimmune and related diseases.

Research progress on adenosine in central nervous system diseases

As an endogenous neuroprotectant agent, adenosine is extensively distributed and is particularly abundant in the central nervous system (CNS). Under physiological conditions, the concentration of adenosine is low intra- and extracellularly, but increases significantly in response to stress. The majority of adenosine functions are receptor-mediated, and primarily include the A1, A2A, A2B, and A3 receptors (A1R, A2AR, A2BR, and A3R). Adenosine is currently widely used in the treatment of diseases of the CNS and the cardiovascular systems, and the mechanisms are related to the disease types, disease locations, and the adenosine receptors distribution in the CNS. For example, the main infarction sites of cerebral ischemia are cortex and striatum, which have high levels of A1 and A2A receptors. Cerebral ischemia is manifested with A1R decrease and A2AR increase, as well as reduction in the A1R-mediated inhibitory processes and enhancement of the A2AR-mediated excitatory process. Adenosine receptor dysfunction is also involved in the pathology of Alzheimer's disease (AD), depression, and epilepsy. Thus, the adenosine receptor balance theory is important for brain disease treatment. The concentration of adenosine can be increased by endogenous or exogenous pathways due to its short half-life and high inactivation properties. Therefore, we will discuss the function of adenosine and its receptors, adenosine formation, and metabolism, and its role for the treatment of CNS diseases (such as cerebral ischemia, AD, depression, Parkinson's disease, epilepsy, and sleep disorders). This article will provide a scientific basis for the development of novel adenosine derivatives through adenosine structure modification, which will lead to experimental applications.

Effects of strategic early-morning caffeine gum administration on association between salivary alpha-amylase and neurobehavioural performance during 50 h of sleep deprivation

Self-assessment is the most common method for monitoring performance and safety in the workplace. However, discrepancies between subjective and objective measures have increased interest in physiological assessment of performance. In a double-blind placebo-controlled study, 23 healthy adults were randomly assigned to either a placebo (n = 11; 5 F, 6 M) or caffeine condition (n = 12; 4 F, 8 M) while undergoing 50 h (i.e. two days) of total sleep deprivation. In previous work, higher salivary alpha-amylase (sAA) levels were associated with improved psychomotor vigilance and simulated driving performance in the placebo condition. In this follow-up article, the effects of strategic caffeine administration on the previously reported diurnal profiles of sAA and performance, and the association between sAA and neurobehavioural performance were investigated. Participants were given a 10 h baseline sleep opportunity (monitored via standard polysomnography techniques) prior to undergoing sleep deprivation (total sleep time: placebo = 8.83 ± 0.48 h; caffeine = 9.01 ± 0.48 h). During sleep deprivation, caffeine gum (200 mg) was administered at 01:00 h, 03:00 h, 05:00 h, and 07:00 h to participants in the caffeine condition (n = 12). This strategic administration of caffeine gum (200 mg) has been shown to be effective at maintaining cognitive performance during extended wakefulness. Saliva samples were collected, and psychomotor vigilance and simulated driving performance assessed at three-hour intervals throughout wakefulness. Caffeine effects on diurnal variability were compared with previously reported findings in the placebo condition (n = 11). The impact of caffeine on the circadian profile of sAA coincided with changes in neurobehavioural performance. Higher sAA levels were associated with improved performance on the psychomotor vigilance test during the first 24 h of wakefulness in the caffeine condition. However, only the association between sAA and response speed (i.e. reciprocal-transform of mean reaction time) was consistent across both days of sleep deprivation. The association between sAA and driving performance was not consistent across both days of sleep deprivation. Results show that the relationship between sAA and reciprocal-transform of mean reaction time on the psychomotor vigilance test persisted in the presence of caffeine, however the association was relatively weaker as compared with the placebo condition.

Staying awake to stay alive: A circuit controlling starvation-induced waking

The balance of sleep and wake is plastic and changes to meet environmental demands. Mechanisms that allow an animal to suppress sleep and maintain waking in potentially adverse situations could serve adaptive functions in evolution. The fruit fly, Drosophila melanogaster, is well poised as a system in which to explore these questions. The environment changes sleep and wake in flies, e.g., starvation induces waking in Drosophila as it does in many animals. Further, the sophisticated neurobiological toolkit available to Drosophila researchers gives the fly a great advantage as a system to investigate the precise neurobiological mechanisms underlying these adaptive changes. In a paper in this issue of PLOS Biology, Yurgel and colleagues elegantly exploit the advantages of the Drosophila model to map starvation-induced wakefulness to a single pair of peptidergic neurons and their partners.

Sport Nutrigenomics: Personalized Nutrition for Athletic Performance

An individual's dietary and supplement strategies can influence markedly their physical performance. Personalized nutrition in athletic populations aims to optimize health, body composition, and exercise performance by targeting dietary recommendations to an individual's genetic profile. Sport dietitians and nutritionists have long been adept at placing additional scrutiny on the one-size-fits-all general population dietary guidelines to accommodate various sporting populations. However, generic "one-size-fits-all" recommendations still remain. Genetic differences are known to impact absorption, metabolism, uptake, utilization and excretion of nutrients and food bioactives, which ultimately affects a number of metabolic pathways. Nutrigenomics and nutrigenetics are experimental approaches that use genomic information and genetic testing technologies to examine the role of individual genetic differences in modifying an athlete's response to nutrients and other food components. Although there have been few randomized, controlled trials examining the effects of genetic variation on performance in response to an ergogenic aid, there is a growing foundation of research linking gene-diet interactions on biomarkers of nutritional status, which impact exercise and sport performance. This foundation forms the basis from which the field of sport nutrigenomics continues to develop. We review the science of genetic modifiers of various dietary factors that impact an athlete's nutritional status, body composition and, ultimately athletic performance.

Transcranial Direct Current Stimulation Does Not Counteract Cognitive Fatigue, but Induces Sleepiness and an Inter-Hemispheric Shift in Brain Oxygenation

Sustained cognitive demands may result in cognitive fatigue (CF), eventually leading to decreased behavioral performance and compromised brain resources. In the present study, we tested the hypothesis that transcranial direct current stimulation (tDCS) would counteract the behavioral and neurophysiological effects of CF. Twenty young healthy participants were tested in a within-subject counterbalanced order across two different days. Anodal tDCS (real vs. sham) was applied over the left prefrontal cortex. In the real tDCS condition, a current of 1.5 mA was delivered for 25 min. Cortical oxygenation changes were measured using functional Near Infrared Spectroscopy (fNIRS) on the frontal cortices. CF was triggered using the TloadDback task, a sustained working memory paradigm that allows tailoring task demands according to each individual's maximal cognitive capacity. Sustained cognitive load-related effects were assessed using pre- versus post-task subjective fatigue and sleepiness scales, evolution of performance accuracy within the task, indirect markers of dopaminergic activity (eye blinks), and cortical oxygenation changes (fNIRS) both during the task and pre- and post-task resting state periods. Results consistently disclosed significant CF-related effects on performance. Transcranial DCS was not effective to counteract the behavioral effects of CF. In the control (sham tDCS) condition, cerebral oxygen exchange (COE) levels significantly increased in the right hemisphere during the resting state immediately after the induction of CF, suggesting a depletion of brain resources. In contrast, tDCS combined with CF induction significantly shifted interhemispheric oxygenation balance during the post-training resting state. Additionally, increased self-reported sleepiness was associated with brain activity in the stimulated hemisphere after recovery from CF during the tDCS condition only, which might reflect a negative middle-term effect of tDCS application.

Sleep-Wake Neurochemistry

The regulated alternations between wakefulness and sleep states reflect complex behavioral processes, orchestrated by distinct neurochemical changes in brain parenchyma. No single neurotransmitter or neuromodulator controls the sleep-wake states in isolation. Rather, fine-tuned interactions within organized neuronal circuits regulate waking and sleep states and drive their transitions. Structural or functional dysregulation and medications interfering with these ensembles can lead to sleep-wake disorders and exert wanted or unwanted pharmacological actions on sleep-wake states. Knowledge of the neurochemical bases of sleep-wake states, which will be discussed in this article, provides the conceptual framework for understanding pharmacological effects on sleep and wake.

A systems genetics resource and analysis of sleep regulation in the mouse

Sleep is essential for optimal brain functioning and health, but the biological substrates through which sleep delivers these beneficial effects remain largely unknown. We used a systems genetics approach in the BXD genetic reference population (GRP) of mice and assembled a comprehensive experimental knowledge base comprising a deep "sleep-wake" phenome, central and peripheral transcriptomes, and plasma metabolome data, collected under undisturbed baseline conditions and after sleep deprivation (SD). We present analytical tools to interactively interrogate the database, visualize the molecular networks altered by sleep loss, and prioritize candidate genes. We found that a one-time, short disruption of sleep already extensively reshaped the systems genetics landscape by altering 60%-78% of the transcriptomes and the metabolome, with numerous genetic loci affecting the magnitude and direction of change. Systems genetics integrative analyses drawing on all levels of organization imply α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor trafficking and fatty acid turnover as substrates of the negative effects of insufficient sleep. Our analyses demonstrate that genetic heterogeneity and the effects of insufficient sleep itself on the transcriptome and metabolome are far more widespread than previously reported.

Cognitive impairments by alcohol and sleep deprivation indicate trait characteristics and a potential role for adenosine A1 receptors

Trait-like differences in cognitive performance after sleep loss put some individuals more at risk than others, the basis of such disparities remaining largely unknown. Similarly, interindividual differences in impairment in response to alcohol intake have been observed. We tested whether performance impairments due to either acute or chronic sleep loss can be predicted by an individual's vulnerability to acute alcohol intake. Also, we used positron emission tomography (PET) to test whether acute alcohol infusion results in an up-regulation of cerebral A₁ adenosine receptors (A₁ARs), similar to the changes previously observed following sleep deprivation. Sustained attention in the psychomotor vigilance task (PVT) was tested in 49 healthy volunteers (26 ± 5 SD years; 15 females) (i) under baseline conditions: (ii) after ethanol intake, and after either (iii) total sleep deprivation (TSD; 35 hours awake; n = 35) or (iv) partial sleep deprivation (PSD; four nights with 5 hours scheduled sleep; n = 14). Ethanol- versus placebo-induced changes in cerebral A₁AR availability were measured in 10 healthy male volunteers (31 ± 9 years) with [¹⁸F]8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine (CPFPX) PET. Highly significant correlations between the performance impairments induced by ethanol and sleep deprivation were found for various PVT parameters, including mean speed (TSD, r = 0.62; PSD, r = 0.84). A₁AR availability increased up to 26% in several brain regions with ethanol infusion. Our studies revealed individual trait characteristics for being either vulnerable or resilient to both alcohol and to sleep deprivation. Both interventions induce gradual increases in cerebral A₁AR availability, pointing to a potential common molecular response mechanism.

Optogenetic Dissection of Sleep-Wake States In Vitro and In Vivo

Optogenetic tools have revolutionized insights into the fundamentals of brain function. This is particularly true for our current understanding of sleep-wake regulation and sleep rhythms. This is illustrated here through a comprehensive and step-by-step review over the major brain areas involved in transitions between sleep and wake states and in sleep rhythmogenesis.

Purinergic Signaling in Neuron-Astrocyte Interactions, Circadian Rhythms, and Alcohol Use Disorder

Alcohol use disorder (AUD) is a debilitating condition marked by cyclic patterns of craving, use, and withdrawal. These pathological behaviors are mediated by multiple neurotransmitter systems utilizing glutamate, GABA, dopamine, ATP, and adenosine. In particular, purines such as ATP and adenosine have been demonstrated to alter the phase and function of the circadian clock and are reciprocally regulated by the clock itself. Importantly, chronic ethanol intake has been demonstrated to disrupt the molecular circadian clock and is associated with altered circadian patterns of activity and sleep. Moreover, ethanol has been demonstrated to disrupt purinergic signaling, while dysfunction of the purinergic system has been implicated in conditions of drug abuse such as AUD. In this review, we summarize our current knowledge regarding circadian disruption by ethanol, focusing on the reciprocal relationship that exists between oscillatory neurotransmission and the molecular circadian clock. In particular, we offer detailed explanations and hypotheses regarding the concerted regulation of purinergic signaling and circadian oscillations by neurons and astrocytes, and review the diverse mechanisms by which purinergic dysfuction may contribute to circadian disruption or alcohol abuse. Finally, we describe the mechanisms by which ethanol may disrupt or hijack endogenous circadian rhythms to induce the maladaptive behavioral patterns associated with AUD.

The effects of sleep deprivation on item and associative recognition memory

Sleep deprivation adversely affects the ability to perform cognitive tasks, but theories range from predicting an overall decline in cognitive functioning because of reduced stability in attentional networks to specific deficits in various cognitive domains or processes. We measured the effects of sleep deprivation on two memory tasks, item recognition ("was this word in the list studied") and associative recognition ("were these two words studied in the same pair"). These tasks test memory for information encoded a few minutes earlier and so do not address effects of sleep deprivation on working memory or consolidation after sleep. A diffusion model was used to decompose accuracy and response time distributions to produce parameter estimates of components of cognitive processing. The model assumes that over time, noisy evidence from the task stimulus is accumulated to one of two decision criteria, and parameters governing this process are extracted and interpreted in terms of distinct cognitive processes. Results showed that sleep deprivation reduces drift rate (evidence used in the decision process), with little effect on the other components of the decision process. These results contrast with the effects of aging, which show little decline in item recognition but large declines in associative recognition. The results suggest that sleep deprivation degrades the quality of information stored in memory and that this may occur through degraded attentional processes. (PsycINFO Database Record

Activating adenosine A1 receptor accelerates PC12 cell injury via ADORA1/PKC/KATP pathway after intermittent hypoxia exposure

Obstructive sleep apnea hypopnea syndrome (OSAHS) is associated with the neurocognitive deficits as a result of the neuronal cell injury. Previous studies have shown that adenosine A1 receptor (ADORA1) played an important role against hypoxia exposure, such as controlling the metabolic recovery in rat hippocampal slices and increasing the resistance in the combined effects of hypoxia and hypercapnia. However, little is known about whether ADORA1 takes part in the course of neuronal cell injury after intermittent hypoxia exposure which was the main pathological characteristic of OSAHS. The present study is performed to explore the underlying mechanism of neuronal cell injury which was induced by intermittent hypoxia exposure in PC12 cells. In our research, we find that the stimulation of the ADORA1 by CCPA accelerated the injury of PC12 cells as well as upregulated the expression of PKC, inwardly rectifying potassium channel 6.2(Kir6.2) and sulfonylurea receptor 1(SUR1) while inhibition of the ADORA1 by DPCPX alleviated the injury of PC12 cells as well as downregulated the expression of PKC, Kir6.2, and SUR1. Moreover, inhibition of the PKC by CHE, also mitigated the injury of PC12 cells, suppressed the Kir6.2 and SUR1 expressions induced by PKC. Taken together, our findings indicate that ADORA1 accelerated PC12 cells injury after intermittent hypoxia exposure via ADORA1/PKC/K_ATP signaling pathway.

Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition

Caffeine use is widespread in sport, with a strong evidence base demonstrating its ergogenic effect. Based on existing research, current guidelines recommend ingestion of 3-9 mg/kg approximately 60 min prior to exercise. However, the magnitude of performance enhancement following caffeine ingestion differs substantially between individuals, with the spectrum of responses ranging between highly ergogenic to ergolytic. These extensive inter-individual response distinctions are mediated by variation in individual genotype, environmental factors, and the legacy of prior experiences partially mediated via epigenetic mechanisms. Here, we briefly review the drivers of this inter-individual variation in caffeine response, focusing on the impact of common polymorphisms within two genes, CYP1A2 and ADORA2A. Contemporary evidence suggests current standardised guidelines are optimal for only a sub-set of the athlete population. Clearer understanding of the factors underpinning inter-individual variation potentially facilitates a more nuanced, and individually and context-specific customisation of caffeine ingestion guidelines, specific to an individual's biology, history, and competitive situation. Finally, we identify current knowledge deficits in this area, along with future associated research questions.

Skin temperature, sleep, and vigilance

A large number of studies have shown a close association between the 24-hour rhythms in core body temperature and sleep propensity. More recently, studies have have begun to elucidate an intriguing association of sleep with skin temperature as well. The present chapter addresses the association of sleep and alertness with skin temperature. It discusses whether the association could reflect common underlying drivers of both sleep propensity and skin vasodilation; whether it could reflect efferents of sleep-regulating brain circuits to thermoregulatory circuits; and whether skin temperature could provide afferent input to sleep-regulating brain circuits. Sleep regulation and concomitant changes in skin temperature are systematically discussed and three parallel factors suggested: a circadian clock mechanism, a homeostatic hourglass mechanism, and a third set of sleep-permissive and wake-promoting factors that gate the effectiveness of signals from the clock and hourglass in the actual induction of sleep or maintenance of alert wakefulness. The chapter moreover discusses how the association between skin temperature and arousal can change with sleep deprivation and insomnia. Finally it addresses whether the promising laboratory findings on the effects of skin temperature manipulations on vigilance can be applied to improve sleep in everyday life.

Recovery sleep after extended wakefulness restores elevated A1 adenosine receptor availability in the human brain

Adenosine and functional A₁ adenosine receptor (A₁AR) availability are supposed to mediate sleep-wake regulation and cognitive performance. We hypothesized that cerebral A₁AR availability after an extended wake period decreases to a well-rested state after recovery sleep. [¹⁸F]CPFPX positron emission tomography was used to quantify A₁AR availability in 15 healthy male adults after 52 h of sleep deprivation and following 14 h of recovery sleep. Data were additionally compared with A₁AR values after 8 h of baseline sleep from an earlier dataset. Polysomnography, cognitive performance, and sleepiness were monitored. Recovery from sleep deprivation was associated with a decrease in A₁AR availability in several brain regions, ranging from 11% (insula) to 14% (striatum). A₁AR availabilities after recovery did not differ from baseline sleep in the control group. The degree of performance impairment, sleepiness, and homeostatic sleep-pressure response to sleep deprivation correlated negatively with the decrease in A₁AR availability. Sleep deprivation resulted in a higher A₁AR availability in the human brain. The increase that was observed after 52 h of wakefulness was restored to control levels during a 14-h recovery sleep episode. Individuals with a large increase in A₁AR availability were more resilient to sleep-loss effects than those with a subtle increase. This pattern implies that differences in endogenous adenosine and A₁AR availability might be causal for individual responses to sleep loss.

Adenosine Shifts Plasticity Regimes between Associative and Homeostatic by Modulating Heterosynaptic Changes

Endogenous extracellular adenosine level fluctuates in an activity-dependent manner and with sleep-wake cycle, modulating synaptic transmission and short-term plasticity. Hebbian-type long-term plasticity introduces intrinsic positive feedback on synaptic weight changes, making them prone to runaway dynamics. We previously demonstrated that co-occurring, weight-dependent heterosynaptic plasticity can robustly prevent runaway dynamics. Here we show that at neocortical synapses in slices from rat visual cortex, adenosine modulates the weight dependence of heterosynaptic plasticity: blockade of adenosine A₁ receptors abolished weight dependence, while increased adenosine level strengthened it. Using model simulations, we found that the strength of weight dependence determines the ability of heterosynaptic plasticity to prevent runaway dynamics of synaptic weights imposed by Hebbian-type learning. Changing the weight dependence of heterosynaptic plasticity within an experimentally observed range gradually shifted the operating point of neurons between an unbalancing regime dominated by associative plasticity and a homeostatic regime of tightly constrained synaptic changes. Because adenosine tone is a natural correlate of activity level (activity increases adenosine tone) and brain state (elevated adenosine tone increases sleep pressure), modulation of heterosynaptic plasticity by adenosine represents an endogenous mechanism that translates changes of the brain state into a shift of the regime of synaptic plasticity and learning. We speculate that adenosine modulation may provide a mechanism for fine-tuning of plasticity and learning according to brain state and activity.SIGNIFICANCE STATEMENT Associative learning depends on brain state and is impaired when the subject is sleepy or tired. However, the link between changes of brain state and modulation of synaptic plasticity and learning remains elusive. Here we show that adenosine regulates weight dependence of heterosynaptic plasticity: adenosine strengthened weight dependence of heterosynaptic plasticity; blockade of adenosine A1 receptors abolished it. In model neurons, such changes of the weight dependence of heterosynaptic plasticity shifted their operating point between regimes dominated by associative plasticity or by synaptic homeostasis. Because adenosine tone is a natural correlate of activity level and brain state, modulation of plasticity by adenosine represents an endogenous mechanism for translation of brain state changes into a shift of the regime of synaptic plasticity and learning.