Continuous theta burst stimulation facilitates the clearance efficiency of the glymphatic pathway in a mouse model of sleep deprivation

Measuring glymphatic function: Assessing the toolkit

Glymphatic flow has been proposed to clear brain waste while we sleep. Cerebrospinal fluid moves from periarterial to perivenous spaces through the parenchyma, with subsequent cerebrospinal fluid drainage to dural lymphatics. Glymphatic disruption is associated with neurological conditions such as Alzheimer's disease and traumatic brain injury. Therefore, investigating its structure and function may improve understanding of pathophysiology. The recent controversy on whether glymphatic flow increases or decreases during sleep demonstrates that the glymphatic hypothesis remains contentious. However, discrepancies between different studies could be due to limitations of the specific techniques used and confounding factors. Here, we review the methods used to study glymphatic function and provide a toolkit from which researchers can choose. We conclude that tracer analysis has been useful, ex vivo techniques are unreliable, and in vivo imaging is still limited. Finally, we explore the potential for future methods and highlight the need for in vitro models, such as microfluidic devices, which may address technique limitations and enable progression of the field.

In vivo two-photon microscopy imaging of focused ultrasound-mediated glymphatic transport in the mouse brain

The glymphatic system regulates cerebrospinal fluid (CSF) transport and brain waste clearance. Focused ultrasound combined with microbubbles (FUSMB) has shown feasibility for manipulating glymphatic transport, yet its mechanisms remain poorly understood. In this work, we used in vivo two-photon microscopy to reveal how FUSMB manipulates the CSF tracer transport in the mouse brain. A FUS transducer was confocally aligned with the objective of a two-photon microscope. Fluorescently labeled albumin was infused into the CSF via cisterna magna. FUS sonication was applied following an intravenous injection of microbubbles. Dynamic imaging was performed through a cranial window to record local changes in vessel and tracer dynamics. The fluorescence intensity of the CSF tracer within the treated region decreased rapidly upon FUSMB treatment. Concurrently, vessel deformation was observed, and the fastest diameter changes were observed during FUSMB treatment. A linear correlation was identified between the rate of vessel diameter change and the rate of tracer intensity change. Moreover, given the same rate of vessel diameter change, the tracer intensity changed faster around larger vessels than smaller vessels. These findings offer insight into the potential biophysical mechanism of FUSMB-mediated glymphatic transport.

New perspectives on the glymphatic system and the relationship between glymphatic system and neurodegenerative diseases

Neurodegenerative diseases (ND) are characterized by the accumulation of aggregated proteins. The glymphatic system, through its rapid exchange mechanisms between cerebrospinal fluid (CSF) and interstitial fluid (ISF), facilitates the movement of metabolic substances within the brain, serving functions akin to those of the peripheral lymphatic system. This emerging waste clearance mechanism offers a novel perspective on the removal of pathological substances in ND. This article elucidates recent discoveries regarding the glymphatic system and updates relevant concepts within its model. It discusses the potential roles of the glymphatic system in ND, including Alzheimer's disease (AD), Parkinson's disease (PD), and multiple system atrophy (MSA), and proposes the glymphatic system as a novel therapeutic target for these conditions.

Diffusion Tensor Imaging Analysis Along the Perivascular Space (DTI-ALPS) Demonstrates That Sleep Disorders Exacerbate Glymphatic Circulatory Impairment and Cognitive Impairment in Patients with Alzheimer's Disease

Objective

Sleep disorders are common in Alzheimer's disease (AD) patients and can impair the glymphatic system, leading to cognitive decline. This study aimed to investigate whether AD patients with sleep disorders exhibit worse glymphatic function and more severe cognitive impairment compared to those without sleep disorders and to explore the underlying molecular imaging mechanisms.

Methods

This study included 40 AD patients with sleep disorders (ADSD), 39 cognitively matched AD patients without sleep disorders (ADNSD), and 25 healthy middle-aged and elderly controls (NC). Participants underwent functional magnetic resonance imaging (fMRI), and cognitive and sleep assessments. The ALPS (Along the Perivascular Space) index was calculated, followed by intergroup comparisons, correlation analyses, and mediation analyses. The diagnostic utility of the ALPS index was assessed using a receiver operating characteristic (ROC) curve.

Results

The ALPS index was lower in the ADNSD and ADSD groups compared to the NC group. In the ADSD group, PSQI scores were negatively correlated with MMSE scores. The ALPS index was positively correlated with MMSE scores and negatively with PSQI scores. Mediation analyses indicated that the ALPS index partially mediated the effect of sleep disturbances on cognitive impairment (indirect effect = -0.134; mediation effect = 30.505%). The area under the ROC curve (AUROC) for distinguishing ADSD from ADNSD was 0.86, with a cutoff ALPS index value 1.309.

Conclusion

Sleep disorders worsen glymphatic function and cognitive impairment in AD patients. The ALPS index partially mediates the impact of sleep disorders on cognitive function and shows moderate accuracy in distinguishing between patients with ADSD and ADNSD.

Gray Matter Reserve Modulates the Association between Glymphatic System Function and Cognition in Patients with Type 2 Diabetes Mellitus

INTRODUCTION

The glymphatic system is regarded as a key factor in the pathogenesis of neurodegenerative diseases. Given the heightened risk of cognitive impairment in patients with type 2 diabetes mellitus (T2DM), the possible alterations in the glymphatic system in T2DM patients remain to be explored. Diffusion tensor imaging (DTI) analysis along the perivascular space (ALPS) index can be utilized to model the glymphatic system in humans. Our aim was to explore the relationship between the ALPS index and cognitive function in patients with T2DM and whether this relationship is modulated by gray matter (GM) integrity anchored by the ALPS index.

METHODS

All participants underwent evaluation using a comprehensive cognitive assessment scale to determine their neurocognitive status. The ALPS index was calculated based on DTI data, and the disparity in ALPS index values between patients with T2DM and healthy controls (HCs) was examined. Furthermore, multiple linear regression analysis was conducted in the T2DM group to identify the GM regions associated with the ALPS index, and the volumes of the GM partitions were extracted. The volume of GM partitions was used as the regulating variable, the ALPS index was used as the independent variable, and cognitive test scores were used as the dependent variable in our analysis.

RESULTS

The ALPS index differed significantly between the two groups, and the ALPS index in patients with T2DM was significantly lower than that in HCs. In addition, our analysis revealed a correlation between the ALPS index and GM volume in the insular region, consistent with the observed GM atrophy in the patient cohort. Moreover, a significant negative correlation was observed between the ALPS index in patients and performance on the Trail-Making Test-A (TMT-A), and this relationship was moderated by GM integrity. In patients with more severe GM atrophy, the ALPS index was more strongly correlated with cognitive function.

CONCLUSIONS

In this study, a decreased ALPS index was found in T2DM patients, indicating impaired glymphatic function in this population. Furthermore, a significant association was detected between the ALPS index and cognitive performance in T2DM patients, and this correlation was influenced by GM integrity. Therefore, the ALPS index has the potential to be used as a biomarker of cognitive impairment in diabetic patients. Further studies are needed to investigate the diagnostic and therapeutic implications of glymphatic dysfunction in T2DM patients with cognitive impairment.

From Fundamentals to Innovation in Alzheimer's Disease: Molecular Findings and Revolutionary Therapies

Alzheimer's disease (AD) is a global health concern and the leading cause of dementia in the elderly. The prevalence of this neurodegenerative condition is projected to increase concomitantly with increased life expectancy, resulting in a significant economic burden. With very few FDA-approved disease-modifying drugs available for AD, there is an urgent need to develop new compounds capable of impeding the progression of the disease. Given the unclear etiopathogenesis of AD, this review emphasizes the underlying mechanisms of this condition. It explores not only well-studied aspects, such as the accumulation of Aβ plaques and neurofibrillary tangles, but also novel areas, including glymphatic and lymphatic pathways, microbiota and the gut-brain axis, serotoninergic and autophagy alterations, vascular dysfunction, the metal hypothesis, the olfactory pathway, and oral health. Furthermore, the potential molecular targets arising from all these mechanisms have been reviewed, along with novel promising approaches such as nanoparticle-based therapy, neural stem cell transplantation, vaccines, and CRISPR-Cas9-mediated genome editing techniques. Taking into account the overlap of these various mechanisms, individual and combination therapies emerge as the future direction in the AD strategy.

Continuous Theta Burst Stimulation Inhibits Oxidative Stress-Induced Inflammation and Autophagy in Hippocampal Neurons by Activating Glutathione Synthesis Pathway, Improving Cognitive Impairment in Sleep-Deprived Mice

Sleep deprivation (SD) has been reported to have a negative impact on cognitive function. Continuous theta burst stimulation (cTBS) shows certain effects in improving sleep and neurological diseases, and its molecular or cellular role in SD-induced cognition impairment still need further exploration. In this study, C57BL/6 mice were subjected to 48 h of SD and cTBS treatment, and cTBS treatment significantly improved SD-triggered impairment of spatial learning and memory abilities in mice. Additionally, cTBS reduced malondialdehyde levels, increased superoxide dismutase activities, and inhibited the production of inflammatory cytokines, alleviating oxidative stress and inflammation levels in hippocampal tissues of SD model mice. cTBS decreased LC3II/LC3I ratio, Beclin1 protein levels, and LC3B puncta intensity, and elevated p62 protein levels to suppress excessive autophagy in hippocampal tissues of SD-stimulated mice. Then, we proved that inhibiting oxidative stress alleviated inflammation, autophagy, and death of hippocampal neuron cells through an in vitro cellular model for oxidative stress, and cTBS treatment promoted the production of glutathione (GSH), the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and the mRNA expression of GSH synthesis-related genes to enhance antioxidant capacity in hippocampal tissues of SD mice. An Nrf2 inhibitor ML385 or a GSH synthesis inhibitor BSO reversed the alleviating effects of cTBS treatment on oxidative stress-associated damage of hippocampal tissues and cognitive impairment in SD model mice. Altogether, our study demonstrated that cTBS mitigates oxidative stress-associated inflammation and autophagy through activating the Nrf2-mediated GSH synthesis pathway, improving cognitive impairment in SD mice.

The Glymphatic System and its Relationship to Migraine

PURPOSE OF REVIEW

We aim to critically review animal and human studies of the glymphatic system in migraine and propose a model for how the glymphatic system may function in migraine, based on the available evidence.

RECENT FINDINGS

Early studies in animal models report migraine attacks temporarily disrupt glymphatic flow. Human imaging studies suggest chronic migraine may be associated with alterations in glymphatic system function, albeit with conflicting results. Presently, it remains unknown whether repetitive migraine attacks or frequent nights of insomnia impair glymphatic system function over time in those with migraine, and whether alterations in glymphatic function could contribute to worsening migraine disability or risk for cognitive disease. Longitudinal studies of glymphatic function in patients with migraine and insomnia, with inclusion of cognitive assessments, may be informative.

Sleep Apnea and Amyotrophic Lateral Sclerosis: Cause, Correlation, Any Relation?

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease with progressive neurodegeneration, affecting both the cortical and the spinal component of the motor neuron circuitry in patients. The cellular and molecular basis of selective neuronal vulnerability is beginning to emerge. Yet, there are no effective cures for ALS, which affects more than 200,000 people worldwide each year. Recent studies highlight the importance of the glymphatic system and its proper function for the clearance of the cerebral spinal fluid, which is achieved mostly during the sleep period. Therefore, a potential link between problems with sleep and neurodegenerative diseases has been postulated. This paper discusses the present understanding of this potential correlation.

Influencing factors of glymphatic system during perioperative period

The glymphatic system is a functional cerebrospinal fluid circulatory system that uses peri-arterial space for inflow of cerebrospinal fluid and peri-venous space for efflux of cerebrospinal fluid from brain parenchyma. This brain-wide fluid transport pathway facilitates the exchange between cerebrospinal fluid and interstitial fluid and clears metabolic waste from the metabolically active brain. Multiple lines of work show that the glymphatic system is crucial to normal brain functions, and the dysfunction of the glymphatic system is closely associated with various neurological disorders, including aging, neurodegeneration, and acute brain injury. Currently, it is common to explore the functional and molecular mechanisms of the glymphatic system based on animal models. The function of glymphatic system during perioperative period is affected by many factors such as physiological, pathological, anesthetic and operative methods. To provide a reference for the interpretation of the results of glymphatic system studies during perioperative period, this article comprehensively reviews the physiological and pathological factors that interfere with the function of the glymphatic system during perioperative period, investigates the effects of anesthetic drugs on glymphatic system function and the potential underlying mechanisms, describes operative methods that interfere with the function of the glymphatic system, and potential intervention strategies based on the glymphatic system. Future, these variables should be taken into account as critical covariates in the design of functional studies on the glymphatic system.

Chronic sleep fragmentation impairs brain interstitial clearance in young wildtype mice

Accumulating evidence shows that most chronic neurological diseases have a link with sleep disturbances, and that patients with chronically poor sleep undergo an accelerated cognitive decline. Indeed, a single-night of sleep deprivation may increase metabolic waste levels in cerebrospinal fluid. However, it remains unknown how chronic sleep disturbances in isolation from an underlying neurological disease may affect the glymphatic system. Clearance of brain interstitial waste by the glymphatic system occurs primarily during sleep, driven by multiple oscillators including arterial pulsatility, and vasomotion. Herein, we induced sleep fragmentation in young wildtype mice and assessed the effects on glymphatic activity and cognitive functions. Chronic sleep fragmentation reduced glymphatic function and impaired cognitive functions in healthy mice. A mechanistic analysis showed that the chronic sleep fragmentation suppressed slow vasomotion, without altering cardiac-driven pulsations. Taken together, results of this study document that chronic sleep fragmentation suppresses brain metabolite clearance and impairs cognition, even in the absence of disease.

Sleep disturbance in rodent models and its sex-specific implications

Sleep disturbances, encompassing altered sleep physiology or disorders like insomnia and sleep apnea, profoundly impact physiological functions and elevate disease risk. Despite extensive research, the underlying mechanisms and sex-specific differences in sleep disorders remain elusive. While polysomnography serves as a cornerstone for human sleep studies, animal models provide invaluable insights into sleep mechanisms. However, the availability of animal models of sleep disorders is limited, with each model often representing a specific sleep issue or mechanism. Therefore, selecting appropriate animal models for sleep research is critical. Given the significant sex differences in sleep patterns and disorders, incorporating both male and female subjects in studies is essential for uncovering sex-specific mechanisms with clinical relevance. This review provides a comprehensive overview of various rodent models of sleep disturbance, including sleep deprivation, sleep fragmentation, and circadian rhythm dysfunction. We evaluate the advantages and disadvantages of each model and discuss sex differences in sleep and sleep disorders, along with potential mechanisms. We aim to advance our understanding of sleep disorders and facilitate sex-specific interventions.

Functional aspects of the brain lymphatic drainage system in aging and neurodegenerative diseases

The phenomenon of an aging population is advancing at a precipitous rate. Alzheimer's disease (AD) and Parkinson's disease (PD) are two of the most common age-associated neurodegenerative diseases, both of which are primarily characterized by the accumulation of toxic proteins and the progressive demise of neuronal structures. Recent discoveries about the brain lymphatic drainage system have precipitated a growing body of investigations substantiating its novel roles, including the clearance of macromolecular waste and the trafficking of immune cells. Notably, aquaporin 4-mediated glymphatic transport, crucial for maintaining neural homeostasis, becomes disrupted during the aging process and is further compromised in the pathogenesis of AD and PD. Functional meningeal lymphatic vessels, which facilitate the drainage of cerebrospinal fluid into the deep cervical lymph nodes, are integral in bridging the central nervous system with peripheral immune responses. Dysfunction in these meningeal lymphatic vessels exacerbates pathological trajectory of the age-related neurodegenerative disease. This review explores modulatory influence of the glymphatic system and meningeal lymphatic vessels on the aging brain and its associated neurodegenerative disorders. It also encapsulates the insights of potential mechanisms and prospects of the targeted non-pharmacological interventions.

Aquaporin-4 and Parkinson's Disease

The water-selective channel aquaporin-4 (AQP4) is implicated in water homeostasis and the functioning of the glymphatic system, which eliminates various metabolites from the brain tissue, including amyloidogenic proteins. Misfolding of the α-synuclein protein and its post-translational modifications play a crucial role in the development of Parkinson's disease (PD) and other synucleopathies, leading to the formation of cytotoxic oligomers and aggregates that cause neurodegeneration. Human and animal studies have shown an interconnection between AQP4 dysfunction and α-synuclein accumulation; however, the specific role of AQP4 in these mechanisms remains unclear. This review summarizes the current knowledge on the role of AQP4 dysfunction in the progression of α-synuclein pathology, considering the possible effects of AQP4 dysregulation on brain molecular mechanisms that can impact α-synuclein modification, accumulation and aggregation. It also highlights future directions that can help study the role of AQP4 in the functioning of the protective mechanisms of the brain during the development of PD and other neurodegenerative diseases.

Deregulation of the Glymphatic System in Alzheimer's Disease: Genetic and Non-Genetic Factors

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive degeneration of brain function. AD gradually affects the parts of the brain that control thoughts, language, behavior and mental function, severely impacting a person's ability to carry out daily activities and ultimately leading to death. The accumulation of extracellular amyloid-β peptide (Aβ) and the aggregation of intracellular hyperphosphorylated tau are the two key pathological hallmarks of AD. AD is a complex condition that involves both non-genetic risk factors (35%) and genetic risk factors (58-79%). The glymphatic system plays an essential role in clearing metabolic waste, transporting tissue fluid, and participating in the immune response. Both non-genetic and genetic risk factors affect the glymphatic system to varying degrees. The main purpose of this review is to summarize the underlying mechanisms involved in the deregulation of the glymphatic system during the progression of AD, especially concerning the diverse contributions of non-genetic and genetic risk factors. In the future, new targets and interventions that modulate these interrelated mechanisms will be beneficial for the prevention and treatment of AD.

Glymphatic System and Psychiatric Disorders: A Rapid Comprehensive Scoping Review

BACKGROUND

Since discovering the glymphatic system, there has been a looming interest in exploring its relationship with psychiatric disorders. Recently, increasing evidence suggests an involvement of the glymphatic system in the pathophysiology of psychiatric disorders. However, clear data are still lacking. In this context, this rapid comprehensive PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) scoping review aims to identify and analyze current evidence about the relation between the glymphatic system and psychiatric disorders.

METHODS

We conducted a comprehensive review of the literature and then proceeded to discuss the findings narratively. Tables were then constructed and articles were sorted according to authors, year, title, location of study, sample size, psychiatric disorder, the aim of the study, principal findings, implications.

RESULTS

Twenty papers were identified as eligible, among which 2 articles on Schizophrenia, 1 on Autism Spectrum Disorders, 2 on Depression, 1 on Depression and Trauma-related Disorders, 1 on Depression and Anxiety, 2 on Anxiety and Sleep Disorders, 8 on Sleep Disorders, 2 on Alcohol use disorder and 1 on Cocaine Use Disorder.

CONCLUSION

This review suggests a correlation between the glymphatic system and several psychiatric disorders: Schizophrenia, Depression, Anxiety Disorders, Sleep Disorders, Alcohol Use Disorder, Cocaine Use Disorder, Trauma-Related Disorders, and Autism Spectrum Disorders. Impairment of the glymphatic system could play a role in Trauma-Related Disorders, Alcohol Use Disorders, Cocaine Use Disorders, Sleep Disorders, Depression, and Autism Spectrum Disorders. It is important to implement research on this topic and adopt standardized markers and radio diagnostic tools.

Aquaporin 4 beyond a water channel; participation in motor, sensory, cognitive and psychological performances, a comprehensive review

Aquaporin 4 (AQP4) is a protein highly expressed in the central nervous system (CNS) and peripheral nervous system (PNS) as well as various other organs, whose different sites of action indicate its importance in various functions. AQP4 has a variety of essential roles beyond water homeostasis. In this article, we have for the first time summarized different roles of AQP4 in motor and sensory functions, besides cognitive and psychological performances, and most importantly, possible physiological mechanisms by which AQP4 can exert its effects. Furthermore, we demonstrated that AQP4 participates in pathology of different neurological disorders, various effects depending on the disease type. Since neurological diseases involve a spectrum of dysfunctions and due to the difficulty of obtaining a treatment that can simultaneously affect these deficits, it is therefore suggested that future studies consider the role of this protein in different functional impairments related to neurological disorders simultaneously or separately by targeting AQP4 expression and/or polarity modulation.

The Effect of Continuous Theta Burst Stimulation over the Right Dorsolateral Prefrontal Cortex on Cognitive Function and Emotional Regulation in Patients with Cerebral Small Vessel Disease

OBJECTIVES

Cognitive impairment in cerebral small vessel disease (CSVD) is a common cause of vascular dementia and is often accompanied by mental disorders. The purpose of this study was to investigate the effect of continuous theta burst stimulation (cTBS) over the right dorsolateral prefrontal cortex (DLPFC) on the cognitive function and Hamilton depression (HAMD) scores in patients with CSVD.

METHODS

A total of 30 CSVD patients who met the inclusion criteria were randomly assigned to either the sham or cTBS group. The patients in both groups received routine cognitive function training. All the patients were under treatment for 14 sessions, with one session per day (each cTBS conditioning session consisted of three-pulse bursts at 50 Hz repeated at 5 Hz, 80% MT, and 600 pulses). Before and after the treatment, the patients in both groups were evaluated using the Montreal Cognitive Assessment (MoCA), Stroop Color-Word Test (SCWT), Trail Marking Test (TMT), Digital Span Test (DST), and HAMD test. The time to complete the SCWT and TMT were recorded. The scores of the MoCA, DST and HAMD test were recorded.

RESULTS

The HAMD scores in the cTBS group decreased significantly compared to the control (p < 0.05). There were no significant differences in the MoCA (including the MoCA subitems) or DST scores or in the SCWT or TMT completion times between the two groups (p > 0.05). For the HAMD scores and the MoCA subitem visuospatial/executive scores, the SCWT-B and SCWT-C completion times in the two groups both improved significantly before and after treatment (p < 0.05). For the MoCA scores, the DST-backward scores and the TMT-B completion times in the cTBS group improved significantly before and after treatment (p < 0.05). There was no significant difference in the SCWT-A, TMT-A completion times and MoCA subitems naming, attention, language, abstraction, delayed recall, and orientation scores either before or after treatment in the two groups or between the two groups (p > 0.05).

CONCLUSIONS

In this study, cTBS over the right DLPFC decreased the HAMD scores significantly in patients with CSVD but had no significant improvement or impairment effects on cognitive function. cTBS over the right DLPFC could be used to treat CSVD patients with depression symptoms.

Assessment of factors influencing glymphatic activity and implications for clinical medicine

The glymphatic system is a highly specialized fluid transport system in the central nervous system. It enables the exchange of the intercellular fluid of the brain, regulation of the movement of this fluid, clearance of unnecessary metabolic products, and, potentially, brain immunity. In this review, based on the latest scientific reports, we present the mechanism of action and function of the glymphatic system and look at the role of factors influencing its activity. Sleep habits, eating patterns, coexisting stress or hypertension, and physical activity can significantly affect glymphatic activity. Modifying them can help to change lives for the better. In the next section of the review, we discuss the connection between the glymphatic system and neurological disorders. Its association with many disease entities suggests that it plays a major role in the physiology of the whole brain, linking many pathophysiological pathways of individual diseases.

Recovery of glymphatic system function in patients with temporal lobe epilepsy after surgery

OBJECTIVES

To investigate the recovery of human glymphatic system (GS) function in patients with temporal lobe epilepsy (TLE) after successful anterior temporal lobectomy (ATL) using diffusion tensor image analysis along the perivascular space (DTI-ALPS).

METHODS

We retrospectively analysed DTI-ALPS index in 13 patients with unilateral TLE before and after ATL, and compared the index with 20 healthy controls (HCs). Two-sample t tests and paired t tests were performed to analyse differences in the DTI-ALPS index between patients and HCs. The Pearson correlation analysis was used to observe the relationship between the disease duration and GS function.

RESULTS

The DTI-ALPS index before ATL was significantly lower in the hemisphere ipsilateral to the epileptogenic foci than in the contralateral hemisphere of the patients (p < 0.001, t =  - 4.81) and in the ipsilateral hemisphere of the HCs (p = 0.007, t =  - 2.90). A significant increase in the DTI-ALPS index was found in the hemisphere ipsilateral to the epileptogenic foci after successful ATL (p = 0.01, t =  - 3.01). In addition, the DTI-ALPS index of the lesion side before ATL was significantly correlated with disease duration (p = 0.04, r =  - 0.59).

CONCLUSIONS

DTI-ALPS may be used as a quantitative biomarker evaluating surgical outcomes and TLE disease duration. DTI-ALPS index may also help localise epileptogenic foci in unilateral TLE. Overall, our study suggests that GS may potentially serve as a new method for the management of TLE and a new direction for investigating the mechanism of epilepsy.

KEY POINTS

• DTI-ALPS index may contribute to epileptogenic foci lateralisation in TLE. • DTI-ALPS index is a potential quantitative feature evaluating surgical outcomes and TLE disease duration. • The GS provides a new perspective for the study of TLE.

Chronic inhibition of astrocytic aquaporin-4 induces autistic-like behavior in control rat offspring similar to maternal exposure to valproic acid

Social communication and interaction deficits, memory impairment, and anxiety-like behavior are characterized in many people identified with autism spectrum disorder (ASD). A thorough understanding of the specific aspects that contribute to the deficiencies associated with ASD can aid research into the etiology of the disorder while also providing targets for more effective intervention. As part of the ASD pathophysiology, alterations in synaptogenesis and abnormal network connections were seen in high-order brain areas, which control social behavior and communication. The early emergence of microglia during nervous system development may contribute to synaptic dysfunction and the pathobiology of ASD. Since aquaporin-4 (AQP4) appears to be required for the basic procedures of synapse activation, certain behavioral and cognitive impairments as well as disturbance in water homeostasis might likely arise from AQP4 deficiency. Here, through the measurement of the water content of the hippocampus and behavioral experiments we aim to explore the contribution of astrocytic AQP4 to the autism-like behavior induced by prenatal valproic acid (VPA) exposure and whether inhibition of AQP4 per se can induce autistic-like behavior in control rats. Microinjection of TGN-020 (10µM, i.c.v), a specific AQP4 inhibitor, for 7 successive days before behavioral tasks from postnatal day 28 to 35 revealed that inhibition of AQP4 in the control offspring caused lower social interaction and locomotor activity, higher anxiety, and decreased ability to recognize novel objects, very similar to the behavioral changes observed in offspring prenatally exposed to VPA. However, VPA-exposed offspring treated with TGN-020, showed no further remarkable behavioral impairments than those detected in the autistic-like rats. Furthermore, both control offspring treated with TGN-020 and offspring exposed to VPA had a considerable accumulation of water in their hippocampi. But AQP4 inhibition did not affect the water status of the autistic-like rats. The findings of this study revealed that control offspring exhibited similar hippocampal water retention and behavioral impairments that were observed in maternal VPA-exposed offspring following inhibition of astrocytic AQP4, whereas, in autistic-like rats, it did not produce any significant change in water content and behaviors. Findings suggest that AQP4 deficiency could be associated with autistic disorder and may be a potential pharmaceutical target for treating autism in the future.

Phototherapy of Alzheimer's Disease: Photostimulation of Brain Lymphatics during Sleep: A Systematic Review

The global number of people with Alzheimer's disease (AD) doubles every 5 years. It has been established that unless an effective treatment for AD is found, the incidence of AD will triple by 2060. However, pharmacological therapies for AD have failed to show effectiveness and safety. Therefore, the search for alternative methods for treating AD is an urgent problem in medicine. The lymphatic drainage and removal system of the brain (LDRSB) plays an important role in resistance to the progression of AD. The development of methods for augmentation of the LDRSB functions may contribute to progress in AD therapy. Photobiomodulation (PBM) is considered to be a non-pharmacological and safe approach for AD therapy. Here, we highlight the most recent and relevant studies of PBM for AD. We focus on emerging evidence that indicates the potential benefits of PBM during sleep for modulation of natural activation of the LDRSB at nighttime, providing effective removal of metabolites, including amyloid-β, from the brain, leading to reduced progression of AD. Our review creates a new niche in the therapy of brain diseases during sleep and sheds light on the development of smart sleep technologies for neurodegenerative diseases.

Mechanically manipulating glymphatic transport by ultrasound combined with microbubbles

The glymphatic system is a perivascular fluid transport system for waste clearance. Glymphatic transport is believed to be driven by the perivascular pumping effect created by the pulsation of the arterial wall caused by the cardiac cycle. Ultrasound sonication of circulating microbubbles (MBs) in the cerebral vasculature induces volumetric expansion and contraction of MBs that push and pull on the vessel wall to generate a MB pumping effect. The objective of this study was to evaluate whether glymphatic transport can be mechanically manipulated by focused ultrasound (FUS) sonication of MBs. The glymphatic pathway in intact mouse brains was studied using intranasal administration of fluorescently labeled albumin as fluid tracers, followed by FUS sonication at a deep brain target (thalamus) in the presence of intravenously injected MBs. Intracisternal magna injection, the conventional technique used in studying glymphatic transport, was employed to provide a comparative reference. Three-dimensional confocal microscopy imaging of optically cleared brain tissue revealed that FUS sonication enhanced the transport of fluorescently labeled albumin tracer in the perivascular space (PVS) along microvessels, primarily the arterioles. We also obtained evidence of FUS-enhanced penetration of the albumin tracer from the PVS into the interstitial space. This study revealed that ultrasound combined with circulating MBs could mechanically enhance glymphatic transport in the brain.

Leveraging the glymphatic and meningeal lymphatic systems as therapeutic strategies in Alzheimer's disease: an updated overview of nonpharmacological therapies

Understanding and treating Alzheimer's disease (AD) has been a remarkable challenge for both scientists and physicians. Although the amyloid-beta and tau protein hypothesis have largely explained the key pathological features of the disease, the mechanisms by which such proteins accumulate and lead to disease progression are still unknown. Such lack of understanding disrupts the development of disease-modifying interventions, leaving a therapeutic gap that remains unsolved. Nonetheless, the recent discoveries of the glymphatic pathway and the meningeal lymphatic system as key components driving central solute clearance revealed another mechanism underlying AD pathogenesis. In this regard, this narrative review integrates the glymphatic and meningeal lymphatic systems as essential components involved in AD pathogenesis. Moreover, it discusses the emerging evidence suggesting that nutritional supplementation, non-invasive brain stimulation, and traditional Chinese medicine can improve the pathophysiology of the disease by increasing glymphatic and/or meningeal lymphatic function. Given that physical exercise is a well-regarded preventive and pro-cognitive intervention for dementia, we summarize the evidence suggesting the glymphatic system as a mediating mechanism of the physical exercise therapeutic effects in AD. Targeting these central solute clearance systems holds the promise of more effective treatment strategies.

The Relationships Among Metal Homeostasis, Mitochondria, and Locus Coeruleus in Psychiatric and Neurodegenerative Disorders: Potential Pathogenetic Mechanism and Therapeutic Implications

While alterations in the locus coeruleus-noradrenergic system are present during early stages of neuropsychiatric disorders, it is unclear what causes these changes and how they contribute to other pathologies in these conditions. Data suggest that the onset of major depressive disorder and schizophrenia is associated with metal dyshomeostasis that causes glial cell mitochondrial dysfunction and hyperactivation in the locus coeruleus. The effect of the overactive locus coeruleus on the hippocampus, amygdala, thalamus, and prefrontal cortex can be responsible for some of the psychiatric symptoms. Although locus coeruleus overactivation may diminish over time, neuroinflammation-induced alterations are presumably ongoing due to continued metal dyshomeostasis and mitochondrial dysfunction. In early Alzheimer's and Parkinson's diseases, metal dyshomeostasis and mitochondrial dysfunction likely induce locus coeruleus hyperactivation, pathological tau or α-synuclein formation, and neurodegeneration, while reduction of glymphatic and cerebrospinal fluid flow might be responsible for β-amyloid aggregation in the olfactory regions before the onset of dementia. It is possible that the overactive noradrenergic system stimulates the apoptosis signaling pathway and pathogenic protein formation, leading to further pathological changes which can occur in the presence or absence of locus coeruleus hypoactivation. Data are presented in this review indicating that although locus coeruleus hyperactivation is involved in pathological changes at prodromal and early stages of these neuropsychiatric disorders, metal dyshomeostasis and mitochondrial dysfunction are critical factors in maintaining ongoing neuropathology throughout the course of these conditions. The proposed mechanistic model includes multiple pharmacological sites that may be targeted for the treatment of neuropsychiatric disorders commonly.

Glymphatic pathway in sporadic cerebral small vessel diseases: From bench to bedside

Cerebral small vessel diseases (CSVD) consist of a group of diseases with high heterogeneity induced by pathologies of intracranial small blood vessels. Endothelium dysfunction, bloodbrain barrier leakage and the inflammatory response are traditionally considered to participate in the pathogenesis of CSVD. However, these features cannot fully explain the complex syndrome and related neuroimaging characteristics. In recent years, the glymphatic pathway has been discovered to play a pivotal role in clearing perivascular fluid and metabolic solutes, which has provided novel insights into neurological disorders. Researchers have also explored the potential role of perivascular clearance dysfunction in CSVD. In this review, we presented a brief overview of CSVD and the glymphatic pathway. In addition, we elucidated CSVD pathogenesis from the perspective of glymphatic failure, including basic animal models and clinical neuroimaging markers. Finally, we proposed forthcoming clinical applications targeting the glymphatic pathway, hoping to provide novel ideas on promising therapies and preventions of CSVD.

Preclinical Research on Focused Ultrasound-Mediated Blood-Brain Barrier Opening for Neurological Disorders: A Review

Several therapeutic agents for neurological disorders are usually not delivered to the brain owing to the presence of the blood-brain barrier (BBB), a special structure present in the central nervous system (CNS). Focused ultrasound (FUS) combined with microbubbles can reversibly and temporarily open the BBB, enabling the application of various therapeutic agents in patients with neurological disorders. In the past 20 years, many preclinical studies on drug delivery through FUS-mediated BBB opening have been conducted, and the use of this method in clinical applications has recently gained popularity. As the clinical application of FUS-mediated BBB opening expands, it is crucial to understand the molecular and cellular effects of FUS-induced microenvironmental changes in the brain so that the efficacy of treatment can be ensured, and new treatment strategies established. This review describes the latest research trends in FUS-mediated BBB opening, including the biological effects and applications in representative neurological disorders, and suggests future directions.

Perivascular spaces as a potential biomarker of Alzheimer's disease

Alzheimer's disease (AD) is a highly damaging disease that affects one's cognition and memory and presents an increasing societal and economic burden globally. Considerable research has gone into understanding AD; however, there is still a lack of effective biomarkers that aid in early diagnosis and intervention. The recent discovery of the glymphatic system and associated Perivascular Spaces (PVS) has led to the theory that enlarged PVS (ePVS) may be an indicator of AD progression and act as an early diagnostic marker. Visible on Magnetic Resonance Imaging (MRI), PVS appear to enlarge when known biomarkers of AD, amyloid-β and tau, accumulate. The central goal of ePVS and AD research is to determine when ePVS occurs in AD progression and if ePVS are causal or epiphenomena. Furthermore, if ePVS are indeed causative, interventions promoting glymphatic clearance are an attractive target for research. However, it is necessary first to ascertain where on the pathological progression of AD ePVS occurs. This review aims to examine the knowledge gap that exists in understanding the contribution of ePVS to AD. It is essential to understand whether ePVS in the brain correlate with increased regional tau distribution and global or regional Amyloid-β distribution and to determine if these spaces increase proportionally over time as individuals experience neurodegeneration. This review demonstrates that ePVS are associated with reduced glymphatic clearance and that this reduced clearance is associated with an increase in amyloid-β. However, it is not yet understood if ePVS are the outcome or driver of protein accumulation. Further, it is not yet clear if ePVS volume and number change longitudinally. Ultimately, it is vital to determine early diagnostic criteria and early interventions for AD to ease the burden it presents to the world; ePVS may be able to fulfill this role and therefore merit further research.

Continuous Theta-Burst Stimulation Promotes Paravascular CSF-Interstitial Fluid Exchange through Regulation of Aquaporin-4 Polarization in APP/PS1 Mice

Amyloid-β (Aβ) deposition plays a crucial role in the occurrence and development of Alzheimer's disease (AD), and impaired Aβ clearance is the leading cause of Aβ deposition. Recently, studies have found that the glymphatic system performs similar functions to the peripheral lymphatic system. Glymphatic fluid transport mainly consists of cerebrospinal fluid (CSF) entering the brain from the paravascular space (PVS) by penetrating arteries and CSF and interstitial fluid exchanging mediated by aquaporin-4 (AQP4). This system promotes the drainage of interstitial fluid (ISF) in the parenchyma and removes metabolic waste, including Aβ, in the brain. Glymphatic system dysfunction plays an essential role in the occurrence and progression of AD. Regulation of glymphatic fluid transport may be a critical target for AD therapy. This study explored the regulatory effects of continuous theta-burst stimulation (CTBS) on the glymphatic system in APPswe/PS1dE9 (APP/PS1) mice with two-photon imaging. The results demonstrated that CTBS could increase glymphatic fluid transport, especially CSF and ISF exchange, mediated by improved AQP4 polarization. In addition, the accelerated glymphatic pathway reduced Aβ deposition and enhanced spatial memory cognition. It provided new insight into the clinical prevention and treatment of Aβ deposition-related diseases.

Impaired Glymphatic System Actions in Obstructive Sleep Apnea Adults

Study Objectives

Obstructive sleep apnea (OSA) is accompanied by sleep fragmentation and altered sleep architecture, which can potentially hinder the glymphatic system, increasing risks for Alzheimer's disease (AD), but the status is unclear in OSA. Our aim was to investigate the glymphatic system in OSA subjects and examine the relationships between OSA disease severity, sleep symptoms, and glymphatic system indices in OSA using diffusion tensor imaging (DTI).

Methods

We acquired DTI data from 59 OSA and 62 controls using a 3.0-Tesla MRI and examined OSA disease severity and sleep symptoms with the Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS). Diffusivity maps in the x-axis (Dxx), y-axis (Dyy), and z-axis (Dzz), as well as in x-y axis (Dxy), y-z axis (Dyz), and x-z axis (Dxz) were calculated, diffusion values for the projection and association fibers extracted, and the DTI analyses along the perivascular space (DTI-ALPS index) were performed. The glymphatic system indices were compared between groups and correlated with disease severity and sleep symptoms in OSA subjects.

Results

Dzz values, derived from projection fiber areas, Dyy and Dzz values from association fiber areas, as well as ALPS and Dyzmean values were significantly reduced in OSA over controls. Significant correlations emerged between disease severity, sleep symptoms, and Dxy, Dxx, and Dzz values in OSA subjects.

Conclusion

OSA patients show abnormal glymphatic system function that may contribute to increased risks for AD. The findings suggest that the APLS method can be used to assess the glymphatic system in OSA patients.

Barbeau E, Pariente J, Dahan L, Valton L. Sleep: The Tip of the Iceberg in the Bidirectional Link Between Alzheimer's Disease and Epilepsy

The observation that a pathophysiological link might exist between Alzheimer's disease (AD) and epilepsy dates back to the identification of the first cases of the pathology itself and is now strongly supported by an ever-increasing mountain of literature. An overwhelming majority of data suggests not only a higher prevalence of epilepsy in Alzheimer's disease compared to healthy aging, but also that AD patients with a comorbid epileptic syndrome, even subclinical, have a steeper cognitive decline. Moreover, clinical and preclinical investigations have revealed a marked sleep-related increase in the frequency of epileptic activities. This characteristic might provide clues to the pathophysiological pathways underlying this comorbidity. Furthermore, the preferential sleep-related occurrence of epileptic events opens up the possibility that they might hasten cognitive decline by interfering with the delicately orchestrated synchrony of oscillatory activities implicated in sleep-related memory consolidation. Therefore, we scrutinized the literature for mechanisms that might promote sleep-related epileptic activity in AD and, possibly dementia onset in epilepsy, and we also aimed to determine to what degree and through which processes such events might alter the progression of AD. Finally, we discuss the implications for patient care and try to identify a common basis for methodological considerations for future research and clinical practice.

Photobiomodulation Therapy and the Glymphatic System: Promising Applications for Augmenting the Brain Lymphatic Drainage System

The glymphatic system is a glial-dependent waste clearance pathway in the central nervous system, devoted to drain away waste metabolic products and soluble proteins such as amyloid-beta. An impaired brain glymphatic system can increase the incidence of neurovascular, neuroinflammatory, and neurodegenerative diseases. Photobiomodulation (PBM) therapy can serve as a non-invasive neuroprotective strategy for maintaining and optimizing effective brain waste clearance. In this review, we discuss the crucial role of the glymphatic drainage system in removing toxins and waste metabolites from the brain. We review recent animal research on the neurotherapeutic benefits of PBM therapy on glymphatic drainage and clearance. We also highlight cellular mechanisms of PBM on the cerebral glymphatic system. Animal research has shed light on the beneficial effects of PBM on the cerebral drainage system through the clearance of amyloid-beta via meningeal lymphatic vessels. Finally, PBM-mediated increase in the blood–brain barrier permeability with a subsequent rise in Aβ clearance from PBM-induced relaxation of lymphatic vessels via a vasodilation process will be discussed. We conclude that PBM promotion of cranial and extracranial lymphatic system function might be a promising strategy for the treatment of brain diseases associated with cerebrospinal fluid outflow abnormality.

Aquaporin-4 and Cognitive Disorders

Aquaporin-4 (AQP4) is the most abundantly expressed aquaporin in the central nervous system (CNS) and is an integral part of the glymphatic system that cannot be ignored. The CNS has the glymphatic system instead of the conventional lymphatic system. The glymphatic system plays an essential role in the pathophysiological processes of many cognitive disorders. AQP4 shows noteworthy changes in various cognitive disorders and is part of the pathogenesis of these diseases. For this reason, AQP4 has attracted attention as a potential and promising target for regulating and even reversing cognitive dysfunction. This review will summarize the role of AQP4 in the pathophysiological processes of several cognitive disorders as reported in recent studies.

Cells of the Blood-Brain Barrier: An Overview of the Neurovascular Unit in Health and Disease

The brain is endowed with highly specialized vasculature that is both structurally and functionally unique compared to vasculature supplying peripheral organs. The blood-brain barrier (BBB) is formed by endothelial cells of the cerebral vasculature and prevents extravasation of blood products into the brain to protect neural tissue and maintain a homeostatic environment. The BBB functions as part of the neurovascular unit (NVU), which is composed of neurons, astrocytes, and microglia in addition to the specialized endothelial cells, mural cells, and the basement membrane. Through coordinated intercellular signaling, these cells function as a dynamic unit to tightly regulate brain blood flow, vascular function, neuroimmune responses, and waste clearance. In this chapter, we review the functions of individual NVU components, describe neurovascular coupling as a classic example of NVU function, and discuss archetypal NVU pathophysiology during disease.

Cerebral Microcirculation, Perivascular Unit, and Glymphatic System: Role of Aquaporin-4 as the Gatekeeper for Water Homeostasis

In the past, water homeostasis of the brain was understood as a certain quantitative equilibrium of water content between intravascular, interstitial, and intracellular spaces governed mostly by hydrostatic effects i.e., strictly by physical laws. The recent achievements in molecular bioscience have led to substantial changes in this regard. Some new concepts elaborate the idea that all compartments involved in cerebral fluid homeostasis create a functional continuum with an active and precise regulation of fluid exchange between them rather than only serving as separate fluid receptacles with mere passive diffusion mechanisms, based on hydrostatic pressure. According to these concepts, aquaporin-4 (AQP4) plays the central role in cerebral fluid homeostasis, acting as a water channel protein. The AQP4 not only enables water permeability through the blood-brain barrier but also regulates water exchange between perivascular spaces and the rest of the glymphatic system, described as pan-cerebral fluid pathway interlacing macroscopic cerebrospinal fluid (CSF) spaces with the interstitial fluid of brain tissue. With regards to this, AQP4 makes water shift strongly dependent on active processes including changes in cerebral microcirculation and autoregulation of brain vessels capacity. In this paper, the role of the AQP4 as the gatekeeper, regulating the water exchange between intracellular space, glymphatic system (including the so-called neurovascular units), and intravascular compartment is reviewed. In addition, the new concepts of brain edema as a misbalance in water homeostasis are critically appraised based on the newly described role of AQP4 for fluid permeation. Finally, the relevance of these hypotheses for clinical conditions (including brain trauma and stroke) and for both new and old therapy concepts are analyzed.

Achieving brain clearance and preventing neurodegenerative diseases-A glymphatic perspective

Age-related neurodegenerative diseases are a growing burden to society, and many are sporadic, meaning that the environment, diet and lifestyle play significant roles. Cerebrospinal fluid (CSF)-mediated clearing of brain waste products via perivascular pathways, named the glymphatic system, is receiving increasing interest, as it offers unexplored perspectives on understanding neurodegenerative diseases. The glymphatic system is involved in clearance of metabolic by-products such as amyloid-β from the brain, and its function is believed to lower the risk of developing some of the most common neurodegenerative diseases. Here, we present magnetic resonance imaging (MRI) data on the heart cycle's control of CSF flow in humans which corroborates findings from animal studies. We also review the importance of sleep, diet, vascular health for glymphatic clearance and find that these factors are also known players in brain longevity.

Sleep, neuronal hyperexcitability, inflammation and neurodegeneration: Does early chronic short sleep trigger and is it the key to overcoming Alzheimer's disease?

Evidence links neuroinflammation to Alzheimer's disease (AD); however, its exact contribution to the onset and progression of the disease is poorly understood. Symptoms of AD can be seen as the tip of an iceberg, consisting of a neuropathological build-up in the brain of extracellular amyloid-β (Aβ) plaques and intraneuronal hyperphosphorylated aggregates of Tau (pTau), which are thought to stem from an imbalance between its production and clearance resulting in loss of synaptic health and dysfunctional cortical connectivity. The glymphatic drainage system, which is particularly active during sleep, plays a key role in the clearance of proteinopathies. Poor sleep can cause hyperexcitability and promote Aβ and tau pathology leading to systemic inflammation. The early neuronal hyperexcitability of γ-aminobutyric acid (GABA)-ergic inhibitory interneurons and impaired inhibitory control of cortical pyramidal neurons lie at the crossroads of excitatory/inhibitory imbalance and inflammation. We outline, with a prospective framework, a possible vicious spiral linking early chronic short sleep, neuronal hyperexcitability, inflammation and neurodegeneration. Understanding the early predictors of AD, through an integrative approach, may hold promise for reducing attrition in the late stages of neuroprotective drug development.

Glymphatic system, AQP4, and their implications in Alzheimer's disease

Lacking conventional lymphatic system, the central nervous system requires alternative clearance systems, such as the glymphatic system, which promotes clearance of interstitial solutes. Aquaporin-4 water channels (AQP4) are an integral part of this system and related to neuropathologies, such as Alzheimer's disease (AD). The clearance of Alzheimer's associated proteins amyloid β and tau is diminished by glymphatic system impairment, due to lack of AQP4. Even though AQP4 mislocalisation (which affects its activity) is a phenotype of AD, it remains a controversial topic, as it is still unclear if it is a phenotype-promoting factor or a consequence of this pathology. This review provides important and updated knowledge about glymphatic system, AQP4 itself, and their link with Alzheimer's disease. Finally, AQP4 as a therapeutic target is proposed to ameliorate Alzheimer's Disease and other neuropathologies AQP4-related.

Enlarged Perivascular Space and Its Correlation with Polysomnography Indicators of Obstructive Sleep Apnea

PURPOSE

There is increasing evidence of a causal interaction between obstructive sleep apnea (OSA) and white matter hyperintensity (WMH). WMH and enlarged perivascular space (EPVS) are the neuroimaging markers for cerebral small vessel disease (CSVD). Thus, this study aimed to determine whether a contextual relationship existed between OSA and EPVS.

PARTICIPANTS AND METHODS

In this study, 107 participants underwent 1-night polysomnography, brain magnetic resonance imaging (MRI) and health screening examinations and were classified as 63 OSA patients (mild, moderate, and severe groups), and 44 healthy controls. We assessed the sleep characteristics in OSA group, quantified the total EPVS from MRI and related them to the measures of polysomnography-obtained sleep parameters.

RESULTS

Polysomnography revealed that 63 OSA patients had sleep architecture alteration. A higher proportion of N2 phase sleep (N2%), lower percentage of N3 sleep (N3%) and REM sleep (REM%), as well as increased arousal index (AI), oxygen desaturation index (ODI) and decreased lowest arterial oxygen saturation (LSaO2) were detected. The results also indicated a higher prevalence and a larger number of EPVS, and a lower Mini Mental State Scale (MMSE) scale score in OSA group. LSaO2, N3% and REM% were negatively correlated with the total EPVS, whereas ODI, AI and N2% were positively correlated with the total EPVS.

CONCLUSION

The findings suggested that OSA patients had sleep disturbances with a higher incidence and more severe EPVS. Furthermore, the EPVS in OSA might be secondary to sleep disturbances, intermittent hypoxemia and the respiratory event-related hemodynamic changes. Thus, our findings highlighted that increased risk for EPVS in OSA is a potential contributor to increased stroke risk in OSA.

Continuous theta burst stimulation dilates meningeal lymphatic vessels by up-regulating VEGF-C in meninges

BACKGROUND

Lymphatic vessels (LVs) of meninges and lymphatic drainage in the brain have been investigated previously. Here, we examined the role of continuous theta burst stimulation (CTBS) in the modulation of meningeal LVs.

METHODS

To explore the effects of CTBS on meningeal LVs, the diameters of LVs were measured between a real CTBS group and sham CTBS group of wild-type male mice. Vascular endothelial growth factor-C (VEGF-C) expression was subsequently calculated in both groups to account for lymphatic changes after CTBS. Sunitinib was administered by 3-day oral gavage to inhibit the VEGF receptor (VEGFR), and the effects of CTBS were further examined in the following groups: vehicle with real CTBS, vehicle with sham CTBS, sunitinib treatment with real CTBS, and sunitinib treatment with sham CTBS.

RESULTS

The lymphatic vessels were augmented, and the level of VEGF-C in meninges increased after CTBS. CTBS dilated meningeal lymphatic vessels were impaired after the VEGF-C/VEGFR3 pathway was blocked.

CONCLUSIONS

CTBS can dilate meningeal lymphatic vessels by up-regulating VEGF-C in meninges.

Brain Glymphatic/Lymphatic Imaging by MRI and PET

Since glymphatic was proposed and meningeal lymphatic was discovered, MRI and even PET were introduced to investigate brain parenchymal interstitial fluid (ISF), cerebrospinal fluid (CSF), and lymphatic outflow in rodents and humans. Previous findings by ex vivo fluorescent microscopic, and in vivo two-photon imaging in rodents were reproduced using intrathecal contrast (gadobutrol and the similar)-enhanced MRI in rodents and further in humans. On dynamic MRI of meningeal lymphatics, in contrast to rodents, humans use mainly dorsal meningeal lymphatic pathways of ISF-CSF-lymphatic efflux. In mice, ISF-CSF exchange was examined thoroughly using an intra-cistern injection of fluorescent tracers during sleep, aging, and neurodegeneration yielding many details. CSF to lymphatic efflux is across arachnoid barrier cells over the dorsal dura in rodents and in humans. Meningeal lymphatic efflux to cervical lymph nodes and systemic circulation is also well-delineated especially in humans onintrathecal contrast MRI. Sleep- or anesthesia-related changes of glymphatic-lymphatic flow and the coupling of ISF-CSF-lymphatic drainage are major confounders ininterpreting brain glymphatic/lymphatic outflow in rodents. PET imaging in humans should be interpreted based on human anatomy and physiology, different in some aspects, using MRI recently. Based on the summary in this review, we propose non-invasive and longer-term intrathecal SPECT/PET or MRI studies to unravel the roles of brain glymphatic/lymphatic in diseases.

Sleep deprivation and its association with diseases- a review

Sleep deprivation, a consequence of multiple health problems or a cause of many major health risks, is a significant public health concern in this era. In the recent years, numerous reports have been added to the literature to provide explanation and to answer previously unanswered questions on this important topic but comprehensive updates and reviews in this aspect remain scarce. The present study identified 135 papers that investigated the association between sleep deprivation and health risks, including cardiovascular, respiratory, neurological, gastrointestinal, immunology, dermatology, endocrine, and reproductive health. In this review, we aimed to provide insight into the association between sleep deprivation and the development of diseases. We reviewed the latest updates available in the literature and particular attention was paid to reports that detailed all possible causal relationships involving both extrinsic and intrinsic factors that may be relevant to this topic. Various mechanisms by which sleep deprivation may affect health were presented and discussed, and this review hopes to serve as a platform for ideas generation for future research.

Continuous theta burst stimulation provides neuroprotection by accelerating local cerebral blood flow and inhibiting inflammation in a mouse model of acute ischemic stroke

Acute ischemic stroke is a leading cause of disability with limited therapeutic options. Continuous theta burst stimulation (cTBS) has recently been shown to be a promising noninvasive therapeutic strategy for neuroprotection in ischemic stroke patients. Here, we investigated the protective effects of cTBS following acute infarction using a photothrombotic stroke (PTS) model in the right posterior parietal cortex (PPC) of C57BL/6 mice. Treatment with cTBS resulted in a reduction in the volume of the infarct region and significantly increased vascular diameter and blood flow velocity in peri-infarct region, as well as decreased the numbers of calcium binding adapter molecule 1 (Iba-1)-positive microglia and glial fibrillary acidic protein (GFAP)-positive astrocytes. Moreover, the number of CD16/32 positive microglia was decreased, whereas the number of CD206 positive microglia was increased. In addition, performance in a water maze task was significantly improved. These results indicated that cTBS protected against PPC infarct region, leading to an improvement in spatial cognitive function, possibly as a result of changes to cerebral microvascular function and inflammatory responses.

Aquaporin 4 deletion exacerbates brain impairments in a mouse model of chronic sleep disruption

AIMS

As a normal physiological process, sleep has recently been shown to facilitate clearance of macromolecular metabolic wastes from the brain via the glymphatic system. The aim of the present study was to investigate pathophysiological roles of astroglial aquaporin 4 (AQP4), a functional regulator of glymphatic clearance, in a mouse model of chronic sleep disruption (SD).

METHODS

Adult AQP4 null mice and wild-type (WT) mice were given 7 days of SD using the improved rotating rod method, and then received behavioral, neuropathological, and neurochemical analyses.

RESULTS

Aquaporin 4 deletion resulted in an impairment of glymphatic transport and accumulation of β-amyloid and Tau proteins in the brain following SD. AQP4 null SD mice exhibited severe activation of microglia, neuroinflammation, and synaptic protein loss in the hippocampus, as well as decreased working memory, compared with WT-SD mice.

CONCLUSION

These results demonstrate that AQP4-mediated glymphatic clearance ameliorates brain impairments caused by abnormal accumulation of metabolic wastes following chronic SD, thus serving as a potential target for sleep-related disorders.

The Paravascular Pathway for Brain Waste Clearance: Current Understanding, Significance and Controversy

The paravascular pathway, also known as the “glymphatic” pathway, is a recently described system for waste clearance in the brain. According to this model, cerebrospinal fluid (CSF) enters the paravascular spaces surrounding penetrating arteries of the brain, mixes with interstitial fluid (ISF) and solutes in the parenchyma, and exits along paravascular spaces of draining veins. Studies have shown that metabolic waste products and solutes, including proteins involved in the pathogenesis of neurodegenerative diseases such as amyloid-beta, may be cleared by this pathway. Consequently, a growing body of research has begun to explore the association between glymphatic dysfunction and various disease states. However, significant controversy exists in the literature regarding both the direction of waste clearance as well as the anatomical space in which the waste-fluid mixture is contained. Some studies have found no evidence of interstitial solute clearance along the paravascular space of veins. Rather, they demonstrate a perivascular pathway in which waste is cleared from the brain along an anatomically distinct perivascular space in a direction opposite to that of paravascular flow. Although possible explanations have been offered, none have been able to fully reconcile the discrepancies in the literature, and many questions remain. Given the therapeutic potential that a comprehensive understanding of brain waste clearance pathways might offer, further research and clarification is highly warranted.