40 Hz light flickering promotes sleep through cortical adenosine signaling

State of the art indicators for imaging purinergic dynamics in vitro and in vivo

Purinergic neurotransmission, a dynamic signaling system using adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine (ADO), uridine diphosphate (UDP), and others, plays a crucial role in brain function. Purinergic signaling is involved in regulating synaptic communication to influence sleep and neuroprotection; malfunction of purinergic signaling contributes to various neurological disorders like pain, epilepsy, and depression. Effective detection methods are crucial for a comprehensive understanding of the multifaceted roles of purinergic signaling in the brain. This review sheds light on advancements in fluorescent indicators, a powerful toolkit for visualizing purinergic activities in living animals. We explore the diverse applications of these indicators in studying purinergic transmission both in health and in diseases. Despite their current strengths, we emphasize the need for continuous development of fluorescent indicators to achieve an even more comprehensive, specific, and quantitative detection of purinergic signaling.

A high-performance fluorescent sensor spatiotemporally reveals cell-type specific regulation of intracellular adenosine in vivo

Adenosine (Ado), a nucleoside bridging intracellular metabolism with intercellular communication, plays an essential role in regulating processes such as sleep and seizure. While the functions of extracellular Ado ("eAdo") are well documented, our knowledge about the distribution and regulatory functions of intracellular Ado ("iAdo") is limited by a lack of methods for detecting iAdo in vivo. Here, we develop HypnoS, a genetically encoded fluorescent sensor for iAdo characterized by its high sensitivity, specificity, spatiotemporal resolution, and rapid response (sub-seconds). HypnoS enables real-time visualization of iAdo dynamics in live cultures, acute brain slices, flies, and freely moving mice. Using HypnoS for dual-color mesoscopic imaging in mice, we show that seizure-induced iAdo waves propagated across the cortex, following calcium signals. Additionally, two-photon imaging reveals that iAdo decays more rapidly in astrocytes than in neurons during seizures. Moreover, by recording iAdo dynamics in the basal forebrain during the sleep-wake cycle, we observe that iAdo signals are present during wakefulness and rapid eye movement (REM) sleep, regulated by equilibrative nucleoside transporters (ENT1/2). Thus, HypnoS is a versatile and powerful tool for investigating the biological functions of iAdo across a range of physiological and pathological states.

Dysregulation of Astrocytic ATP/Adenosine Release in the Hippocampus Cause Cognitive and Affective Disorders: Molecular Mechanisms, Diagnosis, and Therapy

The gliotransmitter adenosine 5'-triphosphate (ATP) and its enzymatic degradation product adenosine play a major role in orchestrating in the hippocampus cognitive and affective functions via P2 purinoceptors (P2X, P2Y) and P1 adenosine receptors (A1, A2A). Although numerous reviews exist on purinoceptors that modulate these functions, there is an apparent gap relating to the involvement of astrocyte-derived extracellular ATP. Our review focuses on the following issues: An impeded release of ATP from hippocampal astrocytes through vesicular mechanisms or connexin hemichannels and pannexin channels interferes with spatial working memory in rodents. The pharmacological blockade of P2Y1 receptors (P2Y1Rs) reverses the deficits in learning/memory performance in mouse models of familial Alzheimer's disease (AD). Similarly, in mouse models of major depressive disorder (MDD), based on acute or chronic stress-induced development of depressive-like behavior, a reduced exocytotic/channel-mediated ATP release from hippocampal astrocytes results in the deterioration of these behavioral responses. However, on the opposite, the increased stimulation of the microglial/astrocytic P2X7R-channel by ATP causes neuroinflammation and in consequence depressive-like behavior. In conclusion, there is strong evidence for the assumption that gliotransmitter ATP is intimately involved in the pathophysiology of cognitive and affective neuron/astrocyte-based human illnesses opening new diagnostic and therapeutic vistas for AD and MDD.

In Situ Mass Spectrometry Imaging to Elucidate the Effects of an Adenosine A2A Receptor Agonist and Alprazolam on Sleep Regulation

Alprazolam (Alp), a commonly used sleep medication in clinical practice, has several potential limitations, including a narrow therapeutic dosage range and a delayed sleep onset. CGS21680 (CGS), a selective agonist of the adenosine A2A receptor, exhibits neuroinhibitory properties. This study aimed to evaluate the effects of CGS on the sleep properties of Alp. The sleep-inducing effects of Alp were assessed through the righting reflex, while the sedative effects of CGS were evaluated by spontaneous activity detection. The synergistic effect of CGS on Alp was evaluated by using electroencephalography and electromyography. The results indicate that we optimized and selected ED5 dose of Alp and ED50 dose of CGS for coadministration. CGS reduced the sleep latency induced by Alp and extended the sleep duration. The distribution of Alp in the brain was assessed through mass spectrometry imaging (MSI). The blood-brain barrier (BBB) model was established to evaluate the impact of CGS on the transmittance of Alp. The results indicated that CGS influenced the distribution of Alp across various brain regions and increased Alp's transmittance across the BBB. The metabolic pathways of GABA, glutamate, and glutamine were assessed through MSI and enzyme activity verification. The coadministration of Alp and CGS resulted in the regulation of GABA, glutamate, and glutamine during the sleep latency and sleep maintenance periods, respectively. In conclusion, the potentiating effect of CGS on the sleep-inducing properties of Alp is attributed to its ability to modulate the distribution of Alp in the brain by enhancing BBB permeability and its influence on Alp-induced neurotransmitter release.

40 Hz visual stimulation during sleep evokes neuronal gamma activity in NREM and REM stages

STUDY OBJECTIVES

Visual stimulation (VS) at 40 Hz is being tested as a non-invasive approach against dementias such as Alzheimer's disease. Applying it during sleep could increase the convenience, duration, and efficacy of stimulation. Here, we tested the feasibility of 40 Hz VS during sleep in a proof-of-concept study.

METHODS

Thirty healthy participants underwent one control and one experimental night of polysomnography at the sleep laboratory. 40 Hz VS was delivered in wakefulness (W), NREM sleep stages 2 and 3, and REM sleep.

RESULTS

As expected, 40 Hz EEG spectral power was increased in all four stages in the experimental condition, compared to control. It was highest in W and similar across NREM 2, NREM 3, and REM, with large and medium effect sizes, respectively. Steady-state visually evoked potential (SSVEP) analyses in the time domain confirmed the specificity of the effect. Secondary analyses revealed that the intervention did not impair objective and subjective sleep quality beyond the first-night effect.

CONCLUSIONS

40 Hz VS during sleep effectively evoked neuronal gamma activity at stimulation frequency without degrading sleep quality, supporting the feasibility of this approach. These findings lay the groundwork for optimizing gamma-band sensory stimulation as a tool to causally study cognitive functions and as a scalable, non-invasive intervention against dementias.

Longitudinal Effects of Lifetime Caffeine Consumption on Levels of Depression, Anxiety, and Stress: A Comprehensive Review

PURPOSE OF REVIEW

Caffeine has high bioavailability and a purine-like alkaloid structure. It exerts wide-ranging physiological effects by binding to adenosine receptors throughout the human body. Through the activation of those receptors, it can regulate many physiological events in the body. The impact of caffeine consumption on depression, anxiety, stress, and human health remains unclear, constituting an important knowledge gap. This review was conducted to examine the effects of caffeine consumption on depression, anxiety, and stress levels and to offer some recommendations for its future use.

RECENT FINDINGS

We performed a comprehensive literature search using PubMed, Web of Science and Google Scholar databases for original articles published in recent years on "caffeine metabolism", "caffeine mechanism", "anxiety", "depression", "stress". Caffeine, which has an antagonistic effect on adenosine, can reduce the risk and symptoms of depression and improve general mental health by modulating the central nervous system and neurotransmitter systems. However, increases in anxiety and stress levels, which are often seen together with depression, are observed due to high-dose caffeine consumption. Caffeine's effects on depression, anxiety, and stress may vary depending on different factors, but the level of consumption is particularly important and attention should be paid to upper limits and reference values while evaluating consumption amounts.

The relationship between visual impairment and insomnia among people middle-aged and older in India

The correlation between insomnia and visual impairment has not been extensively studied. This study aims to investigate this relationship among individuals aged 45 and above in India. This investigation utilized data from the 2017-2018 Wave 1 of the Longitudinal Aging Study in India (LASI). Visual impairment was self-reported, including presbyopia, cataracts, glaucoma, myopia, and hyperopia. Insomnia symptoms were determined by at least one of the following: difficulty in initiating sleep (DIS), difficulty in maintaining sleep (DMS), or early morning awakening (EMA) occurring three or more times per week. Analytical methods involved multivariate logistic regression, subgroup analyses, and interaction tests to interpret the data. In our cohort of 65,840 participants, 29.6% reporting insomnia symptoms demonstrated a higher risk for visual impairment. There was a significant association between visual impairment and increased risk of insomnia symptoms after adjustment for confounders. Furthermore, age in the relationship between insomnia and cataracts, sex in the relationship between insomnia and myopia, and age, sex, and smoking status in the relationship between insomnia and hyperopia, was found to have a significant interaction effect, respectively. Visual impairment was significantly associated with a higher incidence of insomnia among middle-aged and older adults in India. These findings underscore the importance of timely interventions to improve sleep quality and overall well-being in visually impaired populations.

The role of cholinergic signaling in multi-sensory gamma stimulation induced perivascular clearance of amyloid

Modulatory neurotransmitters exert powerful control over neurons and the brain vasculature. Gamma Entrainment Using Sensory Stimuli (GENUS) promotes amyloid clearance via increased perivascular cerebral spinal fluid (CSF) flux in mouse models of Alzheimer's Disease. Here we use whole-brain activity mapping to identify the cholinergic basal forebrain as a key region responding to GENUS. In line with this, GENUS promoted cortical acetylcholine release, vascular dilation, vasomotion and perivascular clearance. Inhibiting cholinergic signaling abolished the effects of GENUS, including the promotion of arterial pulsatility, periarterial CSF influx, and the reduction of cortical amyloid levels. Our findings establish cholinergic signaling as an essential component of the brain's ability to promote perivascular amyloid clearance via non-invasive sensory stimulation.

The gamma rhythm as a guardian of brain health

Gamma oscillations in brain activity (30-150 Hz) have been studied for over 80 years. Although in the past three decades significant progress has been made to try to understand their functional role, a definitive answer regarding their causal implication in perception, cognition, and behavior still lies ahead of us. Here, we first review the basic neural mechanisms that give rise to gamma oscillations and then focus on two main pillars of exploration. The first pillar examines the major theories regarding their functional role in information processing in the brain, also highlighting critical viewpoints. The second pillar reviews a novel research direction that proposes a therapeutic role for gamma oscillations, namely the gamma entrainment using sensory stimulation (GENUS). We extensively discuss both the positive findings and the issues regarding reproducibility of GENUS. Going beyond the functional and therapeutic role of gamma, we propose a third pillar of exploration, where gamma, generated endogenously by cortical circuits, is essential for maintenance of healthy circuit function. We propose that four classes of interneurons, namely those expressing parvalbumin (PV), vasointestinal peptide (VIP), somatostatin (SST), and nitric oxide synthase (NOS) take advantage of endogenous gamma to perform active vasomotor control that maintains homeostasis in the neuronal tissue. According to this hypothesis, which we call GAMER (GAmma MEdiated ciRcuit maintenance), gamma oscillations act as a 'servicing' rhythm that enables efficient translation of neural activity into vascular responses that are essential for optimal neurometabolic processes. GAMER is an extension of GENUS, where endogenous rather than entrained gamma plays a fundamental role. Finally, we propose several critical experiments to test the GAMER hypothesis.

40 Hz light preserves synaptic plasticity and mitochondrial function in Alzheimer's disease model

Alzheimer's disease (AD) is the most prevalent type of dementia. Its causes are not fully understood, but it is now known that factors like mitochondrial dysfunction, oxidative stress, and compromised ion channels contribute to its onset and progression. Flickering light therapy has shown promise in AD treatment, though its mechanisms remain unclear. In this study, we used a rat model of streptozotocin (STZ)-induced AD to evaluate the effects of 40 Hz flickering light therapy. Rats received intracerebroventricular (ICV) STZ injections, and 7 days after, they were exposed to 40 Hz flickering light for 15 min daily over seven days. Cognitive and memory functions were assessed using Morris water maze, novel object recognition, and passive avoidance tests. STZ-induced AD rats exhibited cognitive decline, elevated reactive oxygen species, amyloid beta accumulation, decreased serotonin and dopamine levels, and impaired mitochondrial function. However, light therapy prevented these effects, preserving cognitive function and synaptic plasticity. Additionally, flickering light restored mitochondrial metabolites and normalized ATP-insensitive mitochondrial calcium-sensitive potassium (mitoBKCa) channel activity, which was otherwise downregulated in AD rats. Our findings suggest that 40 Hz flickering light therapy could be a promising treatment for neurodegenerative disorders like AD by preserving synaptic and mitochondrial function.

Adenosine Metabolism Pathway Alterations in Frontal Cortical Neurons in Schizophrenia

Schizophrenia is a neuropsychiatric illness characterized by altered neurotransmission, in which adenosine, a modulator of glutamate and dopamine, plays a critical role that is relatively unexplored in the human brain. In the present study, postmortem human brain tissue from the anterior cingulate cortex (ACC) of individuals with schizophrenia (n = 20) and sex- and age-matched control subjects without psychiatric illness (n = 20) was obtained from the Bronx-Mount Sinai NIH Brain and Tissue Repository. Enriched populations of ACC pyramidal neurons were isolated using laser microdissection (LMD). The mRNA expression levels of six key adenosine pathway components-adenosine kinase (ADK), equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2), ectonucleoside triphosphate diphosphohydrolases 1 and 3 (ENTPD1 and ENTPD3), and ecto-5'-nucleotidase (NT5E)-were quantified using real-time PCR (qPCR) in neurons from these individuals. No significant mRNA expression differences were observed between the schizophrenia and control groups (p > 0.05). However, a significant sex difference was found in ADK mRNA expression, with higher levels in male compared with female subjects (Mann-Whitney U = 86; p < 0.05), a finding significantly driven by disease (t(17) = 3.289; p < 0.05). Correlation analyses also demonstrated significant associations (n = 12) between the expression of several adenosine pathway components (p < 0.05). In our dementia severity analysis, ENTPD1 mRNA expression was significantly higher in males in the "mild" clinical dementia rating (CDR) bin compared with males in the "none" CDR bin (F(2, 13) = 5.212; p < 0.05). Lastly, antipsychotic analysis revealed no significant impact on the expression of adenosine pathway components between medicated and non-medicated schizophrenia subjects (p > 0.05). The observed sex-specific variations and inter-component correlations highlight the value of investigating sex differences in disease and contribute to the molecular basis of schizophrenia's pathology.

Rhythmic gamma frequency light flickering ameliorates stress-related behaviors and cognitive deficits by modulating neuroinflammatory response through IL-12-Mediated cytokines production in chronic stress-induced mice

Chronic stress enhances the risk for psychiatric disorders and induces depression and cognitive impairment. Gamma oscillations are essential for neurocircuit function, emotion, and cognition. However, the influence of gamma entrainment by sensory stimuli on specific aspects of chronic stress-induced responses remains unclear. Mice were subjected to corticosterone (CORT) administration and chronic restraint stress (CRS) for weeks, followed by rhythmic gamma frequency light flickering exposure. Local field potentials (LFPs) were recorded from the V1, CA1, and PFC regions to verify the light flicker on gamma oscillations. Behavioral tests were used to examine stress-related and memory-related behaviors. Golgi staining was performed to observe changes in spine morphology. Synaptosomes were isolated to determine the expression of synapse-related proteins through immunoblotting. RNA sequencing (RNA-seq) was applied to explore specific changes in the transcriptome. Immunofluorescence staining, real-time quantitative polymerase chain reaction (qPCR), and ELISA were used to evaluate microglial activation and cytokine levels. In this study, we demonstrated that rhythmic 40 Hz LF attenuated stress-related behavior and cognitive impairments by ameliorating the microstructural alterations in spine morphology and increasing the expression of GluN2A and GluA1 in chronically stressed mice. Transcriptome analysis revealed that significantly downregulated genes in LF-exposed CRS mice were enriched in neuroimmune-related signaling pathways. Rhythmic 40 Hz LF exposure significantly decreased the number of Iba1-positive microglia in the PFC and hippocampus, and the expression levels of the M1 markers of microglia iNOS and CD68 were reduced significantly in CRS mice. In addition, 40 Hz LF exposure suppressed the secretion of cytokines IL-12, which could regulate the production of IFN-γ and IL-10 in stressed mice. Our results demonstrate that exposure to rhythmic 40 Hz LF induces the neuroimmune response and downregulation of neuroinflammation with attenuated stress-related behaviors and cognitive function in CRS-induced mice. Our findings highlight the importance of sensory-evoked gamma entrainment as a potential therapeutic strategy for stress-related disorders treatment. Abbreviations: CORT, Chronic corticosterone treatment; CRS, Chronic restraint stress; IACUC, Institutional Animal Care and Use Committee; LF, light flickers; FST, Forced swim test; NSFT, Novelty-suppressed feeding test; SPT, Sucrose preference test; NSFT, Novelty-suppressed feeding; qPCR, Quantitative real-time polymerase chain reaction; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; PVDF, polyvinylidene fluoride; PBS, phosphate-buffered saline; PBS-T, phosphate-buffered saline plus 0.1% Tween 20; PVDF, polyvinylidene fluoride; GFAP, Glial fibrillary acidic protein; DAPI, 4',6-Diamid- ino-2-phenylindole; Iba1, Ionized calcium-binding adaptor molecule 1; iNOS, Inducible nitric oxide synthase; IL-10, Interleukin-10; IL6, Interleukin 6; IL-1β, Interleukin 1β; IL-12, Interleukin 12; TNF-α, Tumor necrosis factor alpha; IFN-γ, Interferon-gamma; TLR6 and 9, Toll-like Receptor 6 and 9.

40 Hz light flickering facilitates the glymphatic flow via adenosine signaling in mice

The glymphatic-lymphatic system is increasingly recognized as fundamental for the homeostasis of the brain milieu since it defines cerebral spinal fluid flow in the brain parenchyma and eliminates metabolic waste. Animal and human studies have uncovered several important physiological factors regulating the glymphatic system including sleep, aquaporin-4, and hemodynamic factors. Yet, our understanding of the modulation of the glymphatic system is limited, which has hindered the development of glymphatic-based treatment for aging and neurodegenerative disorders. Here, we present the evidence from fluorescence tracing, two-photon recording, and dynamic contrast-enhanced magnetic resonance imaging analyses that 40 Hz light flickering enhanced glymphatic influx and efflux independently of anesthesia and sleep, an effect attributed to increased astrocytic aquaporin-4 polarization and enhanced vasomotion. Adenosine-A2A receptor (A2AR) signaling emerged as the neurochemical underpinning of 40 Hz flickering-induced enhancement of glymphatic flow, based on increased cerebrofluid adenosine levels, the abolishment of enhanced glymphatic flow by pharmacological or genetic inactivation of equilibrative nucleotide transporters-2 or of A2AR, and by the physical and functional A2AR-aquaporin-4 interaction in astrocytes. These findings establish 40 Hz light flickering as a novel non-invasive strategy of enhanced glymphatic flow, with translational potential to relieve brain disorders.

Optochemical control of slow-wave sleep in the nucleus accumbens of male mice by a photoactivatable allosteric modulator of adenosine A2A receptors

Optochemistry, an emerging pharmacologic approach in which light is used to selectively activate or deactivate molecules, has the potential to alleviate symptoms, cure diseases, and improve quality of life while preventing uncontrolled drug effects. The development of in-vivo applications for optochemistry to render brain cells photoresponsive without relying on genetic engineering has been progressing slowly. The nucleus accumbens (NAc) is a region for the regulation of slow-wave sleep (SWS) through the integration of motivational stimuli. Adenosine emerges as a promising candidate molecule for activating indirect pathway neurons of the NAc expressing adenosine A2A receptors (A2ARs) to induce SWS. Here, we developed a brain-permeable positive allosteric modulator of A2ARs (A2AR PAM) that can be rapidly photoactivated with visible light (λ > 400 nm) and used it optoallosterically to induce SWS in the NAc of freely behaving male mice by increasing the activity of extracellular adenosine derived from astrocytic and neuronal activity.

Study on Gamma sensory flicker for Insomnia

OBJECTIVES

Insomnia has been the subject of much systematic research because it is a risk factor for a variety of diseases. There is some evidence that gamma sensory stimulation therapy has also been demonstrated to improve sleep quality for people with Alzheimer's disease. However, it is unclear whether this method is effective for treating insomnia. The principal objective of this project was to investigate the efficacy and safety of gamma sensory flicker in improving the sleep quality of insomnia patients.

METHODS

Thirty-seven participants with insomnia were recruited for this prospective observational study. For a duration of 8 weeks, participants were exposed to flicker stimulation through a light and sound device.

RESULTS

During the main phase of the study, adherence rates averaged 92.21%. Additionally, no severe adverse events were reported for flicker treatment. Analysis of sleep diaries indicated that 40 Hz flickers can enhance sleep quality by reducing sleep onset latencies, and arousals, and increasing total sleep duration.

CONCLUSIONS

Gamma sensory flicker improves sleep quality in people suffering from insomnia.