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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 A 2A 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 A 1 and A 2A 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 A 1 adenosine receptor availability with 18 F-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 A 1 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 A 1 receptor availability was observed. In conclusion, we confirmed that a genetic variant of ADORA2A affects individual alpha power, while a direct modulatory effect via A 1 adenosine receptors in females is suggested., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Sleep deprivation (SD) could amplify the temporal fluctuation of spontaneous brain activities that reflect different arousal levels using a dynamic functional connectivity (dFC) approach. Therefore, we intended to evaluate the test-retest reliability of dFC characteristics during rested wakefulness (RW), and to explore how the properties of these dynamic connectivity states were affected by extended durations of acute sleep loss (28/52 hr). We acquired resting-state fMRI and neuropsychological datasets in two independent studies: (a) twice during RW and once after 28 hr of SD (n = 15) and (b) after 52 hr of SD and after 14 hr of recovery sleep (RS; n = 14). Sliding-window correlations approach was applied to estimate their covariance matrices and corresponding three connectivity states were generated. The test-retest reliability of dFC properties demonstrated mean dwell time and fraction of connectivity states were reliable. After SD, the mean dwell time of a specific state, featured by strong subcortical-cortical anticorrelations, was significantly increased. Conversely, another globally hypoconnected state was significantly decreased. Subjective sleepiness and objective performances were separately positive and negative correlated with the increased and decreased state. Two brain connectivity states and their alterations might be sufficiently sensitive to reflect changes in the dynamics of brain mental activities after sleep loss., (© 2019 The Authors. Human Brain Mapping published by Wiley Periodicals, Inc.)

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 A 1 adenosine receptors (A 1 ARs), 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 A 1 AR availability were measured in 10 healthy male volunteers (31 ± 9 years) with [ 18 F]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). A 1 AR 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 A 1 AR availability, pointing to a potential common molecular response mechanism., Competing Interests: The authors declare no conflict of interest.

Adenosine and functional A 1 adenosine receptor (A 1 AR) availability are supposed to mediate sleep-wake regulation and cognitive performance. We hypothesized that cerebral A 1 AR availability after an extended wake period decreases to a well-rested state after recovery sleep. [ 18 F]CPFPX positron emission tomography was used to quantify A 1 AR availability in 15 healthy male adults after 52 h of sleep deprivation and following 14 h of recovery sleep. Data were additionally compared with A 1 AR 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 A 1 AR availability in several brain regions, ranging from 11% (insula) to 14% (striatum). A 1 AR 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 A 1 AR availability. Sleep deprivation resulted in a higher A 1 AR 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 A 1 AR availability were more resilient to sleep-loss effects than those with a subtle increase. This pattern implies that differences in endogenous adenosine and A 1 AR availability might be causal for individual responses to sleep loss., Competing Interests: The authors declare no conflict of interest.

The metabotrophic subtype 5 glutamate receptor (mGluR5) plays a critical role in synaptic plasticity besides its involvement in numerous neurological disorders, such as depression. As mGluR5 availability in humans is altered in sleep deprivation, we hypothesized that mGluR5 availability underlies a circadian variation. To investigate whether mGluR5 underlies potential circadian changes we measured its density in a randomized fashion at six different daytimes in 11 adult Sprague-Dawley rats. mGluR5 density was quantified by positron emission tomography (PET) using the radioactive ligand [ 11 C]ABP688. [ 11 C]ABP688 uptake was quantified in nine regions of interest with a reference tissue model. Significant differences in the binding potential (BP ND ) and therefore mGluR5 availability between the different circadian times were found in cortex, cingulate cortex, amygdala, caudate putamen and nucleus accumbens. Further post-hoc statistical analysis (Tukey-Kramer test) of the different time-points revealed significant changes in BP ND between 07:00 hours (start of light-on phase) and 15:00 hours (last time-point of the light-on phase) in the caudate putamen. This study shows that mGluR5 availability is increased during the light-on, or sleep phase, of rodents by approximately 10%. Given that altered mGluR5 densities play a role in psychiatric disorders, further investigation is warranted to evaluate their circadian involvement in mood changes in humans., (© 2016 European Sleep Research Society.)