No abstract

Increased sleep time and intensity quantified as low-frequency brain electrical activity after sleep loss demonstrate that sleep need is homeostatically regulated, yet the underlying molecular mechanisms remain elusive. We here demonstrate that metabotropic glutamate receptors of subtype 5 (mGluR5) contribute to the molecular machinery governing sleep-wake homeostasis. Using positron emission tomography, magnetic resonance spectroscopy, and electroencephalography in humans, we find that increased mGluR5 availability after sleep loss tightly correlates with behavioral and electroencephalographic biomarkers of elevated sleep need. These changes are associated with altered cortical myo-inositol and glycine levels, suggesting sleep loss-induced modifications downstream of mGluR5 signaling. Knock-out mice without functional mGluR5 exhibit severe dysregulation of sleep-wake homeostasis, including lack of recovery sleep and impaired behavioral adjustment to a novel task after sleep deprivation. The data suggest that mGluR5 contribute to the brain's coping mechanisms with sleep deprivation and point to a novel target to improve disturbed wakefulness and sleep.

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 3Ј-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 slowwave 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.

No abstract

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.

Alzheimer’s disease is a neurodegenerative disorder where pathological accumulation of amyloid-β and tau begin years before symptom onset. Emerging evidence suggests that β-blockers (β-adrenergic antagonists) increase brain clearance of these metabolites by enhancing cerebrospinal fluid flow. Our objective was to determine whether β-blockers treatments that easily cross the blood-brain barrier reduce the risk of Alzheimer’s disease compared to less permeable β-blockers. Data from the Danish national registers were used to identify a retrospective cohort of individuals with hypertension, and those treated with β-blockers were included in the analysis. Persons with indications for β-blocker use other than hypertension (e.g., heart failure) were only retained in a sensitivity analysis. β-blockers were divided into three permeability groups: low, moderate, and high. We used multivariable cause-specific Cox regression to model the effect of β-blocker blood-brain barrier permeability on time to dementia outcomes, adjusting for baseline comorbidities, demographics, and socioeconomic variables. Death was modeled as a competing risk. The 10-year standardized absolute risk was estimated as the averaged person-specific risks per treatment. In a cohort of 69,081 (median age = 64.4 years, 64.8% female) people treated with βBs for hypertension, highly BBB-permeable βBs were associated with reduced risk of Alzheimer’s disease versus low permeability βBs (−0.45%, p < 0.036). This effect was specific to Alzheimer’s diagnoses and did not extend to dementia in general. Propensity score analysis matching high and low BBB-permeable patients also detected a decreased Alzheimer’s risk (−0.92%, p < 0.001) in the high permeability group compared to the low, as did a 1-year landmark analysis (−0.57%, p < 0.029) in which events within the first year of follow-up were ignored as likely unrelated to treatment. Our results suggest that amongst people taking β-blockers for hypertension, treatment with highly blood-brain barrier permeable β-blockers reduces the risk of Alzheimer’s disease compared to low permeability drugs. Our findings support the hypothesis that highly permeable β-blockers protect against Alzheimer’s disease by promoting waste brain metabolite clearance.

Accumulation of amyloid-β is a key neuropathological feature in brain of Alzheimer's disease patients. Alterations in cerebral hemodynamics, such as arterial impulse propagation driving the (peri)vascular cerebrospinal fluid flux, predict future Alzheimer's disease progression. We now present a non-invasive method to quantify the three-dimensional propagation of cardiovascular impulses in human brain using ultrafast 10 Hz magnetic resonance encephalography. This technique revealed spatio-temporal abnormalities in impulse propagation in Alzheimer's disease. The arrival latency and propagation speed both differed in Alzheimer's disease patients. Our mapping of arterial territories revealed Alzheimer's disease-specific modifications, including reversed impulse propagation around the hippocampi and in parietal cortical areas. The findings imply that pervasive abnormality in (peri)vascular cerebrospinal fluid impulse propagation compromises vascular impulse propagation and subsequently glymphatic brain clearance of amyloid-β in Alzheimer's disease.

Oura Health Ltd.'s provided the surveillance smart rings for the study, but did not participate in the analysis. The manuscript in question is published as a preprint in bioRxiv, but we guarantee that it does not infringe any subsequent copyright or license agreement. 3We would like to thank all study subjects for their participation in the study. We also thank Tuomas Konttajärvi for assistance in measurements and preprocessing of EEG data, Jani Häkli, Annastiina Kivipää, Tarja Holtinkoski, Aleksi Rasila, Taneli Hautaniemi, Miia Lampinen and others who assisted in measurements or otherwise contributed. We are grateful for devices and data provided by Oura. We wish to acknowledge Jussi Kantola for data management and reconstruction of MREG data, the CSC -IT Center for Science Ltd.