Effects of modafinil on the sleep EEG depend on Val158Met genotype of COMT

Genetic Markers of Differential Vulnerability to Sleep Loss in Adults

In this review, we discuss reports of genotype-dependent interindividual differences in phenotypic neurobehavioral responses to total sleep deprivation or sleep restriction. We highlight the importance of using the candidate gene approach to further elucidate differential resilience and vulnerability to sleep deprivation in humans, although we acknowledge that other omics techniques and genome-wide association studies can also offer insights into biomarkers of such vulnerability. Specifically, we discuss polymorphisms in adenosinergic genes (ADA and ADORA2A), core circadian clock genes (BHLHE41/DEC2 and PER3), genes related to cognitive development and functioning (BDNF and COMT), dopaminergic genes (DRD2 and DAT), and immune and clearance genes (AQP4, DQB1*0602, and TNFα) as potential genetic indicators of differential vulnerability to deficits induced by sleep loss. Additionally, we review the efficacy of several countermeasures for the neurobehavioral impairments induced by sleep loss, including banking sleep, recovery sleep, caffeine, and naps. The discovery of reliable, novel genetic markers of differential vulnerability to sleep loss has critical implications for future research involving predictors, countermeasures, and treatments in the field of sleep and circadian science.

Clinical and Experimental Human Sleep-Wake Pharmacogenetics

Sleep and wakefulness are highly complex processes that are elegantly orchestrated by fine-tuned neurochemical changes among neuronal and non-neuronal ensembles, nuclei, and networks of the brain. Important neurotransmitters and neuromodulators regulating the circadian and homeostatic facets of sleep-wake physiology include melatonin, γ-aminobutyric acid, hypocretin, histamine, norepinephrine, serotonin, dopamine, and adenosine. Dysregulation of these neurochemical systems may cause sleep-wake disorders, which are commonly classified into insomnia disorder, parasomnias, circadian rhythm sleep-wake disorders, central disorders of hypersomnolence, sleep-related movement disorders, and sleep-related breathing disorders. Sleep-wake disorders can have far-reaching consequences on physical, mental, and social well-being and health and, thus, need be treated with effective and rational therapies. Apart from behavioral (e.g., cognitive behavioral therapy for insomnia), physiological (e.g., chronotherapy with bright light), and mechanical (e.g., continuous positive airway pressure treatment of obstructive sleep apnea) interventions, pharmacological treatments often are the first-line clinical option to improve disturbed sleep and wake states. Nevertheless, not all patients respond to pharmacotherapy in uniform and beneficial fashion, partly due to genetic differences. The improved understanding of the neurochemical mechanisms regulating sleep and wakefulness and the mode of action of sleep-wake therapeutics has provided a conceptual framework, to search for functional genetic variants modifying individual drug response phenotypes. This article will summarize the currently known genetic polymorphisms that modulate drug sensitivity and exposure, to partly determine individual responses to sleep-wake pharmacotherapy. In addition, a pharmacogenetic strategy will be outlined how based upon classical and opto-/chemogenetic strategies in animals, as well as human genetic associations, circuit mechanisms regulating sleep-wake functions in humans can be identified. As such, experimental human sleep-wake pharmacogenetics forms a bridge spanning basic research and clinical medicine and constitutes an essential step for the search and development of novel sleep-wake targets and therapeutics.

Effects of COMT genotype and tolcapone on lapses of sustained attention after sleep deprivation in healthy young men

Tolcapone, a brain penetrant selective inhibitor of catechol-O-methyltransferase (COMT) devoid of psychostimulant properties, improves cognition and cortical information processing in rested volunteers, depending on the genotype of the functional Val158Met polymorphism of COMT. The impact of this common genetic variant on behavioral and neurophysiological markers of increased sleep need after sleep loss is controversial. Here we investigated the potential usefulness of tolcapone to mitigate consequences of sleep deprivation on lapses of sustained attention, and tested the hypothesis that dopamine signaling in the prefrontal cortex (PFC) causally contributes to neurobehavioral and neurophysiological markers of sleep homeostasis in humans. We first quantified in 73 young male volunteers the impact of COMT genotype on the evolution of attentional lapses during 40 h of extended wakefulness. Subsequently, we tested in an independent group of 30 young men whether selective inhibition of COMT activity with tolcapone counteracts attentional and neurophysiological markers of elevated sleep need in a genotype-dependent manner. Neither COMT genotype nor tolcapone affected brain electrical activity in wakefulness and sleep. By contrast, COMT genotype and tolcapone modulated the sleep loss-induced impairment of vigilant attention. More specifically, Val/Met heterozygotes produced twice as many lapses after a night without sleep than Met/Met homozygotes. Unexpectedly, tolcapone further deteriorated the sleep loss-induced performance deficits when compared to placebo, particularly in Val/Met and Met/Met genotypes. The findings suggest that PFC dopaminergic tone regulates sustained attention after sleep loss according to an inverse U-shape relationship, independently of neurophysiological markers of elevated sleep need.

Brain Networks are Independently Modulated by Donepezil, Sleep, and Sleep Deprivation

Resting-state connectivity has been widely studied in the healthy and pathological brain. Less well-characterized are the brain networks altered during pharmacological interventions and their possible interaction with vigilance. In the hopes of finding new biomarkers which can be used to identify cortical activity and cognitive processes linked to the effects of drugs to treat neurodegenerative diseases such as Alzheimer's disease, the analysis of networks altered by medication would be particularly interesting. Eleven healthy subjects were recruited in the context of the European Innovative Medicines Initiative 'PharmaCog'. Each underwent five sessions of simultaneous EEG-fMRI in order to investigate the effects of donepezil and memantine before and after sleep deprivation (SD). The SD approach has been previously proposed as a model for cognitive impairment in healthy subjects. By applying network based statistics (NBS), we observed altered brain networks significantly linked to donepezil intake and sleep deprivation. Taking into account the sleep stages extracted from the EEG data we revealed that a network linked to sleep is interacting with sleep deprivation but not with medication intake. We successfully extracted the functional resting-state networks modified by donepezil intake, sleep and SD. We observed donepezil induced whole brain connectivity alterations forming a network separated from the changes induced by sleep and SD, a result which shows the utility of this approach to check for the validity of pharmacological resting-state analysis of the tested medications without the need of taking into account the subject specific vigilance.

Time to wake up: No impact of COMT Val158Met gene variation on circadian preferences, arousal regulation and sleep

Dopamine has been implicated in the regulation of sleep-wake states and the circadian rhythm. However, there is no consensus on the impact of two established dopaminergic gene variants: the catechol-O-methyltransferase Val158Met (COMT Val158Met; rs4680) and the dopamine D4 receptor Exon III variable-number-of-tandem-repeat polymorphism (DRD4 VNTR). Pursuing a multi-method approach, we examined their potential effects on circadian preferences, arousal regulation and sleep. Subjects underwent a 7-day actigraphy assessment (SenseWear Pro3), a 20-minute resting EEG (analyzed using VIGALL 2.0) and a body mass index (BMI) assessment. Further, they completed the Morningness-Eveningness Questionnaire (MEQ), the Epworth Sleepiness Scale (ESS) and the Pittsburgh Sleep Quality Index (PSQI). The sample comprised 4625 subjects (19-82 years) genotyped for COMT Val158Met, and 689 elderly subjects (64-82 years) genotyped for DRD4 VNTR. The number of subjects varied across phenotypes. Power calculations revealed a minimum required phenotypic variance explained by genotype ranging between 0.5% and 1.5% for COMT Val158Met and between 3.3% and 6.0% for DRD4 VNTR. Analyses did not reveal significant genotype effects on MEQ, ESS, PSQI, BMI, actigraphy and EEG variables. Additionally, we found no compelling evidence in sex- and age-stratified subsamples. Few associations surpassed the threshold of nominal significance (p < .05), providing some indication for a link between DRD4 VNTR and daytime sleepiness. Taken together, in light of the statistical power obtained in the present study, our data particularly suggest no impact of the COMT Val158Met polymorphism on circadian preferences, arousal regulation and sleep. The suggestive link between DRD4 VNTR and daytime sleepiness, on the other hand, might be worth investigation in a sample enriched with younger adults.

Circadian gene variants influence sleep and the sleep electroencephalogram in humans

The sleep electroencephalogram (EEG) is highly heritable in humans and yet little is known about the genetic basis of inter-individual differences in sleep architecture. The aim of this study was to identify associations between candidate circadian gene variants and the polysomnogram, recorded under highly controlled laboratory conditions during a baseline, overnight, 8 h sleep opportunity. A candidate gene approach was employed to analyze single-nucleotide polymorphisms from five circadian-related genes in a two-phase analysis of 84 healthy young adults (28 F; 23.21 ± 2.97 years) of European ancestry. A common variant in Period2 (PER2) was associated with 20 min less slow-wave sleep (SWS) in carriers of the minor allele than in noncarriers, representing a 22% reduction in SWS duration. Moreover, spectral analysis in a subset of participants (n = 37) showed the same PER2 polymorphism was associated with reduced EEG power density in the low delta range (0.25-1.0 Hz) during non-REM sleep and lower slow-wave activity (0.75-4.5 Hz) in the early part of the sleep episode. These results indicate the involvement of PER2 in the homeostatic process of sleep. Additionally, a rare variant in Melatonin Receptor 1B was associated with longer REM sleep latency, with minor allele carriers exhibiting an average of 65 min (87%) longer latency from sleep onset to REM sleep, compared to noncarriers. These findings suggest that circadian-related genes can modulate sleep architecture and the sleep EEG, including specific parameters previously implicated in the homeostatic regulation of sleep.

Nutraceuticals for body-weight management: The role of green tea catechins

Green tea catechins mixed with caffeine have been proposed as adjuvants for maintaining or enhancing energy expenditure and for increasing fat oxidation, in the context of prevention and treatment of obesity. These catechins-caffeine mixtures seem to counteract the decrease in metabolic rate that occurs during weight loss. Their effects are of particular importance during weight maintenance after weight loss. Other metabolic targets may be fat absorption and the gut microbiota composition, but these effects still need further investigation in combination with weight loss. Limitations for the effects of green tea catechins are moderating factors such as genetic predisposition related to COMT-activity, habitual caffeine intake, and ingestion combined with dietary protein. In conclusion, a mixture of green tea catechins and caffeine has a beneficial effect on body-weight management, especially by sustained energy expenditure, fat oxidation, and preservation of fat free body-mass, after energy restriction induced body-weight loss, when taking the limitations into account.

Sleep and plasticity in schizophrenia

Schizophrenia is a devastating mental illness with a worldwide prevalence of approximately 1%. Although the clinical features of the disorder were described over one hundred years ago, its neurobiology is still largely elusive despite several decades of research. Schizophrenia is associated with marked sleep disturbances and memory impairment. Above and beyond altered sleep architecture, sleep rhythms including slow waves and spindles are disrupted in schizophrenia. In the healthy brain, these rhythms reflect and participate in plastic processes during sleep. This chapter discusses evidence that schizophrenia patients exhibit dysfunction of sleep-mediated plasticity on a behavioral, cellular, and molecular level and offers suggestions on how the study of sleeping brain activity can shed light on the pathophysiological mechanisms of the disorder.

Duration of activity and mode of action of modafinil: Studies on sleep and wakefulness in humans

The duration of activity of modafinil was investigated in healthy male volunteers in two double-blind crossover studies. Mode of action was explored using a statistical model concerned with the relationship between total sleep duration and that of rapid eye movement (REM) sleep. Nocturnal sleep (23:00-07:00) followed by next-day performance (09:00-17:00) was studied in 12 subjects administered 100, 200, 300 mg modafinil and placebo, 0.5 h before bedtime. Performance overnight (19:00-08:45) followed by sleep (09:15-15:15) was studied in nine subjects administered 100, 200, 300, 400 mg modafinil, 300 mg caffeine and placebo at 22:15. Modafinil dose-dependently reduced sleep duration (nocturnal: 200 mg, p<0.05; 300 mg, p<0.001; morning: 300 and 400 mg, p<0.05) and REM sleep (nocturnal: 300 mg; morning: 400 mg; p<0.05). The statistical model revealed that reduced REM sleep was due to alerting activity, with no evidence of direct suppression of REM sleep, suggesting dopaminergic activity. Enhanced performance with modafinil during overnight work varied with dose (200 mg>100 mg; 300, 400 mg>200, 100 mg, caffeine). However, in the study of next-day performance, the enhancement was attenuated at the highest dose (300 mg) by the greater disturbance of prior sleep. These findings indicate that modafinil has a long duration of action, with alerting properties arising predominantly from dopaminergic activity.

Genetic polymorphisms of DAT1 and COMT differentially associate with actigraphy-derived sleep-wake cycles in young adults

Accumulating evidence suggests that dopamine plays a key role in sleep-wake regulation. Cerebral dopamine levels are regulated primarily by the dopamine transporter (DAT) in the striatum and by catechol-O-methyl-transferase (COMT) in the prefrontal cortex. We hypothesized that the variable-number-tandem-repeat (VNTR) polymorphism in the 3'-untranslated region of the gene encoding DAT (DAT1, SLC6A3; rs28363170) and the Val158Met polymorphism of COMT (rs4680) differently affect actigraphy-derived rest-activity cycles and sleep estimates in healthy adults (65 men; 45 women; age range: 19-35 years). Daytime sleepiness, continuous rest-actigraphy and sleep diary data during roughly 4-weeks were analyzed. Nine-repeat (9R) allele carriers of DAT1 (n = 48) more often reported elevated sleepiness (Epworth sleepiness score ≥10) than 10-repeat (10R) allele homozygotes (n = 62, p < 0.02). Moreover, male 9R allele carriers showed higher wrist activity, whereas this difference was not present in women ("DAT1 genotype" × "gender" interaction: p < 0.005). Rest-activity patterns did not differ among COMT genotypes. Nevertheless, a significant "COMT genotype" × "type of day" (workdays vs. rest days) interaction for sleep duration was observed (p = 0.04). The Val/Val (n = 36) and Met/Met (n = 24) homozygotes habitually prolonged sleep on rest days compared to workdays by more than 30 min, while Val/Met heterozygotes (n = 50) did not significantly extend their sleep (mean difference: 7 min). Moreover, whereas the proportion of women among the genotype groups did not differ, COMT genotype affected body-mass-index (BMI), such that Val/Met individuals had lower BMI than the homozygous genotypes (p < 0.04). While awaiting independent replication and confirmation, our data support an association of genetically-determined differences in cerebral dopaminergic neurotransmission with daytime sleepiness and individual rest-activity profiles, as well as other sleep-associated health characteristics such as the regulation of BMI. The differential associations of DAT1 and COMT polymorphisms may reflect the distinct local expression of the encoded proteins in the brain.

Dopaminergic role in regulating neurophysiological markers of sleep homeostasis in humans

While dopamine affects fundamental brain processes such as movement control, emotional responses, addiction, and pain, the roles for this neurotransmitter in regulating wakefulness and sleep are incompletely understood. Genetically modified animal models with reduced dopamine clearance exhibit hypersensitivity to caffeine, reduced-responsiveness to modafinil, and increased homeostatic response to prolonged wakefulness when compared with wild-type animals. Here we studied sleep-wake regulation in humans and combined pharmacogenetic and neurophysiologic methods to analyze the effects of the 3'-UTR variable-number-tandem-repeat polymorphism of the gene (DAT1, SLC6A3) encoding dopamine transporter (DAT). Previous research demonstrated that healthy homozygous 10-repeat (10R/10R) allele carriers of this genetic variant have reduced striatal DAT protein expression when compared with 9-repeat (9R) allele carriers. Objective and subjective estimates of caffeine sensitivity were higher in 10R allele homozygotes than in carriers of the 9R allele. Moreover, caffeine and modafinil affected wakefulness-induced changes in functional bands (delta, sigma, beta) of rhythmic brain activity in wakefulness and sleep in a DAT1 genotype-dependent manner. Finally, the sleep deprivation-induced increase in well established neurophysiologic markers of sleep homeostasis, including slow-wave sleep, electroencephalographic slow-wave activity (0.5-4.5 Hz), and number of low-frequency (0.5-2.0 Hz) oscillations in non-rapid-eye-movement sleep, was significantly larger in the 10R/10R genotype than in the 9R allele carriers of DAT1. Together, the data suggest that the dopamine transporter contributes to homeostatic sleep-wake regulation in humans.

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

An intricate interplay between circadian and sleep-wake homeostatic processes regulate cognitive performance on specific tasks, and individual differences in circadian preference and sleep pressure may contribute to individual differences in distinct neurocognitive functions. Attentional performance appears to be particularly sensitive to time of day modulations and the effects of sleep deprivation. Consistent with the notion that the neuromodulator, adenosine , plays an important role in regulating sleep pressure, pharmacologic and genetic data in animals and humans demonstrate that differences in adenosinergic tone affect sleepiness, arousal and vigilant attention in rested and sleep-deprived states. Caffeine--the most often consumed stimulant in the world--blocks adenosine receptors and normally attenuates the consequences of sleep deprivation on arousal, vigilance, and attention. Nevertheless, caffeine cannot substitute for sleep, and is virtually ineffective in mitigating the impact of severe sleep loss on higher-order cognitive functions. Thus, the available evidence suggests that adenosinergic mechanisms, in particular adenosine A2A receptor-mediated signal transduction, contribute to waking-induced impairments of attentional processes, whereas additional mechanisms must be involved in higher-order cognitive consequences of sleep deprivation. Future investigations should further clarify the exact types of cognitive processes affected by inappropriate sleep. This research will aid in the quest to better understand the role of different brain systems (e.g., adenosine and adenosine receptors) in regulating sleep, and sleep-related subjective state, and cognitive processes. Furthermore, it will provide more detail on the underlying mechanisms of the detrimental effects of extended wakefulness, as well as lead to the development of effective, evidence-based countermeasures against the health consequences of circadian misalignment and chronic sleep restriction.

Catechin- and caffeine-rich teas for control of body weight in humans

Maintaining the level of daily energy expenditure during weight loss and weight maintenance is as important as maintaining satiety while decreasing energy intake. In this context, different catechin- and caffeine-rich teas (CCRTs), such as green, oolong, and white teas, as well as caffeine have been proposed as tools for maintaining or enhancing energy expenditure and for increasing fat oxidation. Tea polyphenols have been proposed to counteract the decrease in metabolic rate that is usually present during weight loss. Their effects may be of particular importance during weight maintenance after weight loss. Although the thermogenic effect of CCRT has the potential to produce significant effects on these metabolic targets as well as on fat absorption and energy intake, possibly via its impact on the gut microbiota and gene expression, a clinically meaningful outcome also depends on compliance by the subjects. Limitations to this approach require further examination, including moderating factors such as genetic predisposition, habitual caffeine intake, and catechin composition and dose. Nevertheless, CCRTs may be useful agents that could help in preventing a positive energy balance and obesity.

About sleep's role in memory

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

Predicting Risk in Space: Genetic Markers for Differential Vulnerability to Sleep Restriction

Several laboratories have found large, highly reliable individual differences in the magnitude of cognitive performance, fatigue and sleepiness, and sleep homeostatic vulnerability to acute total sleep deprivation and to chronic sleep restriction in healthy adults. Such individual differences in neurobehavioral performance are also observed in space flight as a result of sleep loss. The reasons for these stable phenotypic differential vulnerabilities are unknown: such differences are not yet accounted for by demographic factors, IQ or sleep need, and moreover, psychometric scales do not predict those individuals cognitively vulnerable to sleep loss. The stable, trait-like (phenotypic) inter-individual differences observed in response to sleep loss-with intraclass correlation coefficients accounting for 58%-92% of the variance in neurobehavioral measures- point to an underlying genetic component. To this end, we utilized multi-day highly controlled laboratory studies to investigate the role of various common candidate gene variants-each independently-in relation to cumulative neurobehavioral and sleep homeostatic responses to sleep restriction. These data suggest that common genetic variations (polymorphisms) involved in sleep-wake, circadian, and cognitive regulation may serve as markers for prediction of inter-individual differences in sleep homeostatic and neurobehavioral vulnerability to sleep restriction in healthy adults. Identification of genetic predictors of differential vulnerability to sleep restriction-as determined from candidate gene studies-will help identify astronauts most in need of fatigue countermeasures in space flight and inform medical standards for obtaining adequate sleep in space. This review summarizes individual differences in neurobehavioral vulnerability to sleep deprivation and ongoing genetic efforts to identify markers of such differences.

Analysing humanly generated random number sequences: a pattern-based approach

In a random number generation task, participants are asked to generate a random sequence of numbers, most typically the digits 1 to 9. Such number sequences are not mathematically random, and both extent and type of bias allow one to characterize the brain's “internal random number generator”. We assume that certain patterns and their variations will frequently occur in humanly generated random number sequences. Thus, we introduce a pattern-based analysis of random number sequences. Twenty healthy subjects randomly generated two sequences of 300 numbers each. Sequences were analysed to identify the patterns of numbers predominantly used by the subjects and to calculate the frequency of a specific pattern and its variations within the number sequence. This pattern analysis is based on the Damerau-Levenshtein distance, which counts the number of edit operations that are needed to convert one string into another. We built a model that predicts not only the next item in a humanly generated random number sequence based on the item′s immediate history, but also the deployment of patterns in another sequence generated by the same subject. When a history of seven items was computed, the mean correct prediction rate rose up to 27% (with an individual maximum of 46%, chance performance of 11%). Furthermore, we assumed that when predicting one subject′s sequence, predictions based on statistical information from the same subject should yield a higher success rate than predictions based on statistical information from a different subject. When provided with two sequences from the same subject and one from a different subject, an algorithm identifies the foreign sequence in up to 88% of the cases. In conclusion, the pattern-based analysis using the Levenshtein-Damarau distance is both able to predict humanly generated random number sequences and to identify person-specific information within a humanly generated random number sequence.

Reduced neurobehavioral impairment from sleep deprivation in older adults: contribution of adenosinergic mechanisms

A night without sleep is followed by enhanced sleepiness, increased low-frequency activity in the waking EEG, and reduced vigilant attention. The magnitude of these changes is highly variable among healthy individuals. Findings in young men of low and high subjective caffeine sensitivity suggest that adenosinergic mechanisms contribute to inter-individual differences in sleep deprivation-induced changes in EEG theta activity, as well as optimal performance on the psychomotor vigilance task (PVT). In comparison to young subjects, healthy adults of older age typically feel less sleepy after sleep deprivation, and show fewer response lapses, and faster reaction times on the PVT, especially in the morning after the night without sleep. We hypothesized that age-related changes in adenosine signal transmission underlie reduced vulnerability to sleep deprivation in older individuals. To test this hypothesis, the combined effects of prolonged wakefulness and the adenosine receptor antagonist, caffeine, on an antero-posterior power gradient in EEG theta activity and PVT performance were analyzed in healthy older and caffeine-insensitive and -sensitive young men. The results show that age-related differences in sleep loss-induced changes in brain rhythmic activity and neurobehavioral functions are mirrored in young individuals of low and high sensitivity to the stimulant effects of caffeine. Moreover, the effects of sleep deprivation and caffeine on regional theta power and vigilant attention are inversely correlated across older and young age groups. Genetic variants of the adenosine A_2A receptor gene contribute to individual differences in neurobehavioral performance in rested and sleep deprived state, and modulate the actions of caffeine in wakefulness and sleep. Based upon this evidence, we propose that age-related differences in A_2A receptor-mediated signal transduction could be involved in age-related changes in the vulnerability to acute sleep deprivation.

Influence of chronic dopamine transporter inhibition by RTI-336 on motor behavior, sleep, and hormone levels in rhesus monkeys

Dopamine transporter (DAT) inhibitors have been developed as a promising treatment approach for cocaine dependence. However, the stimulant effects of DAT inhibitors have the potential to disrupt sleep patterns, and the influence of long-term treatment on dopamine neurochemistry is still unknown. The objectives of this study were to (1) explore the stimulant-related effects of chronic DAT inhibitor (RTI-336) treatment on motor activity and sleep-like measures in male rhesus monkeys (Macaca mulatta; n = 4) and (2) to determine the effect of drug treatment on prolactin and cortisol levels. Subjects were fitted with a collar-mounted activity monitor to evaluate their motor activity, with 4 days of baseline recording preceding 21 days of daily saline or RTI-336 (1 mg/kg/day; intramuscular) injections. Blood samples were collected immediately prior to and following chronic treatment to assess hormone levels. RTI-336 produced a significant increase in locomotor activity at the end of the daytime period compared to saline administration. During the 3-week treatment period, sleep efficiency was decreased and the fragmentation index and latency to sleep onset were significantly increased. Hormone levels were not changed throughout the study. Chronic treatment with RTI-336 has a mild but significant stimulant effect, as evidenced by the significant increase in activity during the evening period which may cause minor disruptions in sleep measures.

Polymorphisms of ADORA2A modulate psychomotor vigilance and the effects of caffeine on neurobehavioural performance and sleep EEG after sleep deprivation

BACKGROUND AND PURPOSE

Prolonged wakefulness impairs sustained vigilant attention, measured with the psychomotor vigilance task (PVT), and induces a compensatory increase in sleep intensity in recovery sleep, quantified by slow-wave activity (SWA) in the sleep electroencephalogram (EEG). These effects of sleep deprivation are counteracted by the adenosine receptor antagonist caffeine, implying involvement of the adenosine neuromodulator/receptor system. To examine a role for adenosine A(2A) receptors, we investigated whether variation of the A(2A) receptor gene (ADORA2A) modified effects of caffeine on PVT and SWA after sleep deprivation.

EXPERIMENTAL APPROACH

A haplotype analysis of eight single-nucleotide polymorphisms of ADORA2A was performed in 82 volunteers. In 45 young men carrying five different allele combinations, we investigated the effects of prolonged waking and 2 × 200 mg caffeine or 2 × 100 mg modafinil on psychomotor vigilance, sleepiness, and the waking and sleep EEG.

KEY RESULTS

Throughout extended wakefulness, the carriers of haplotype HT4 performed faster on the PVT than carriers of non-HT4 haplotype alleles. In haplotype HT4, caffeine failed to counteract the waking-induced impairment of PVT performance and the rebound of SWA in recovery sleep. However, caffeine was effective in non-HT4 allele carriers, and modafinil reduced the consequences of prolonged waking, independently of ADORA2A haplotype.

CONCLUSIONS AND IMPLICATIONS

Common genetic variation of ADORA2A is an important determinant of psychomotor vigilance in rested and sleep-deprived state. It also modulates individual responses to caffeine after sleep deprivation. These findings demonstrate a role for adenosine A(2A) receptors in the effects of prolonged wakefulness on vigilant attention and the sleep EEG.

Catechol-O-methyltransferase Val158Met polymorphism associates with individual differences in sleep physiologic responses to chronic sleep loss

BACKGROUND

The COMT Val158Met polymorphism modulates cortical dopaminergic catabolism, and predicts individual differences in prefrontal executive functioning in healthy adults and schizophrenic patients, and associates with EEG differences during sleep loss. We assessed whether the COMT Val158Met polymorphism was a novel marker in healthy adults of differential vulnerability to chronic partial sleep deprivation (PSD), a condition distinct from total sleep loss and one experienced by millions on a daily and persistent basis.

METHODOLOGY/PRINCIPAL FINDINGS

20 Met/Met, 64 Val/Met, and 45 Val/Val subjects participated in a protocol of two baseline 10h time in bed (TIB) nights followed by five consecutive 4 h TIB nights. Met/Met subjects showed differentially steeper declines in non-REM EEG slow-wave energy (SWE)-the putative homeostatic marker of sleep drive-during PSD, despite comparable baseline SWE declines. Val/Val subjects showed differentially smaller increases in slow-wave sleep and smaller reductions in stage 2 sleep during PSD, and had more stage 1 sleep across nights and a shorter baseline REM sleep latency. The genotypes, however, did not differ in performance across various executive function and cognitive tasks and showed comparable increases in subjective and physiological sleepiness in response to chronic sleep loss. Met/Met genotypic and Met allelic frequencies were higher in whites than African Americans.

CONCLUSIONS/SIGNIFICANCE

The COMT Val158Met polymorphism may be a genetic biomarker for predicting individual differences in sleep physiology-but not in cognitive and executive functioning-resulting from sleep loss in a healthy, racially-diverse adult population of men and women. Beyond healthy sleepers, our results may also provide insight for predicting sleep loss responses in patients with schizophrenia and other psychiatric disorders, since these groups repeatedly experience chronically-curtailed sleep and demonstrate COMT-related treatment responses and risk factors for symptom exacerbation.