The Glymphatic System in Central Nervous System Health and Disease: Past, Present, and Future

Novel insights into non-coding RNAs and their role in hydrocephalus

A large body of evidence has highlighted the role of non-coding RNAs in neurodevelopment and neuroinflammation. This evidence has led to increasing speculation that non-coding RNAs may be involved in the pathophysiological mechanisms underlying hydrocephalus, one of the most common neurological conditions worldwide. In this review, we first outline the basic concepts and incidence of hydrocephalus along with the limitations of existing treatments for this condition. Then, we outline the definition, classification, and biological role of non-coding RNAs. Subsequently, we analyze the roles of non-coding RNAs in the formation of hydrocephalus in detail. Specifically, we have focused on the potential significance of non-coding RNAs in the pathophysiology of hydrocephalus, including glymphatic pathways, neuroinflammatory processes, and neurological dysplasia, on the basis of the existing evidence. Lastly, we review the potential of non-coding RNAs as biomarkers of hydrocephalus and for the creation of innovative treatments.

Targeting the brain's glymphatic pathway: A novel therapeutic approach for cerebral small vessel disease

Cerebral small vessel disease encompasses a group of neurological disorders characterized by injury to small blood vessels, often leading to stroke and dementia. Due to its diverse etiologies and complex pathological mechanisms, preventing and treating cerebral small vessel vasculopathy is challenging. Recent studies have shown that the glymphatic system plays a crucial role in interstitial solute clearance and the maintenance of brain homeostasis. Increasing evidence also suggests that dysfunction in glymphatic clearance is a key factor in the progression of cerebral small vessel disease. This review begins with a comprehensive introduction to the structure, function, and driving factors of the glymphatic system, highlighting its essential role in brain waste clearance. Afterwards, cerebral small vessel disease was reviewed from the perspective of the glymphatic system, after which the mechanisms underlying their correlation were summarized. Glymphatic dysfunction may lead to the accumulation of metabolic waste in the brain, thereby exacerbating the pathological processes associated with cerebral small vessel disease. The review also discussed the direct evidence of glymphatic dysfunction in patients and animal models exhibiting two subtypes of cerebral small vessel disease: arteriolosclerosis-related cerebral small vessel disease and amyloid-related cerebral small vessel disease. Diffusion tensor image analysis along the perivascular space is an important non-invasive tool for assessing the clearance function of the glymphatic system. However, the effectiveness of its parameters needs to be enhanced. Among various nervous system diseases, including cerebral small vessel disease, glymphatic failure may be a common final pathway toward dementia. Overall, this review summarizes prevention and treatment strategies that target glymphatic drainage and will offer valuable insight for developing novel treatments for cerebral small vessel disease.

Glymphatic system dysfunction in adult ADHD: Relationship to cognitive performance

OBJECTIVES

While attention-deficit/hyperactivity disorder (ADHD) persists into adulthood, the relationship between glymphatic system function and cognitive performance in adult ADHD remains unclear. This study investigated the association between glymphatic system markers and cognitive outcomes in adults with ADHD.

METHODS

This case-control study includes 41 adults with ADHD and 108 age-matched healthy controls (HCs). Glymphatic function was evaluated using choroid plexus volume (CPV), diffusion tensor imaging along the perivascular space (DTI-ALPS) index and coupling between blood‑oxygen-level-dependent signals and cerebrospinal fluid signals (BOLD-CSF coupling). Cognitive performance was measured using standardized neuropsychological tests.

RESULTS

Compared with HCs, adults with ADHD exhibited significantly lower bilateral and whole-brain ALPS indices (P < 0.05). Although CPV was increased in the ADHD group, this difference did not reach statistical significance, and no significant differences were observed in BOLD-CSF coupling between the two groups. Furthermore, whole-brain ALPS indices were positively associated with visual memory performance (r = 0.422, P = 0.005), an effect that was more pronounced in the right hemisphere (r = 0.458, P = 0.002).

LIMITATIONS

The cross-sectional design limits causal inferences, and the effects of medication were not fully accounted for.

CONCLUSIONS

These findings identify an association between glymphatic dysfunction and cognitive impairment in adults with ADHD. The observed correlation suggests that alterations in glymphatic function may underlie ADHD-related cognitive deficits. Targeting these pathways could provide novel therapeutic opportunities in the management of adult ADHD.

Estradiol effects on astrocytic aquaporin 4 and glutamate transporter 1 expression contribute to shifts in brain dynamics supporting spatial working memory

Estrogenic effects on astrocytes improve glutamate recycling and water homeostasis for neuroprotection in pathology. Estrogens also enhance spatial learning and memory. The current study looked at the effect of 17β-estradiol (E2) on astrocytic glutamate transporter 1 (GLT-1) and aquaporin 4 (AQP4) in the prelimbic cortex (PrL) and dorsal hippocampus (dHC), areas active in spatial (allocentric) working memory in comparison to dorsolateral striatum (dlStr) which is involved in response or egocentric learning. Ovariectomized, female, Long Evans rats received 0, 4.5 µg/kg, or 45 µg/kg of E2 in a sesame oil vehicle 24 and 48 h prior to a delayed spontaneous alternation task (dSA). In line with previous research dSA performance significantly improved with administration of E2 as compared to sesame oil vehicle. AQP4 and GLT-1 levels were brain area specific and E2 enhanced AQP4 and GLT-1 in brain areas associated with spatial working memory (PrL and dHC) as compared to dlStr. Additionally, AQP4 was found to have the highest density in the unmyelinated axon rich hilus while GLT-1 showed the highest density in the synaptically dense molecular layer. However, AQP4 density in the stratum radiatum was similar to the hilus after dSA, potentially supporting dynamic changes in AQP4 response to natural cognitive activity. Hilar and prelimbic AQP4 area stained was also negatively correlated with performance on the dSA, which supports the theory of increased polarity of AQP4 with healthy cognitive function. These data suggest astrocytic water and glutamate homeostasis shift with high levels of estrogens to support spatial strategies.

Therapeutic Mechanisms of Exercise in Parkinson's Disease

Despite being the second-most common neurodegenerative disease, the etiology of Parkinson's disease (PD) remains uncertain with current knowledge suggestive of multiple risk factors. Furthermore, curative treatment does not yet exist, and treatment is primarily symptomatic in nature. For this reason, supportive therapies such as exercise are a crucial tool in PD management. It is useful to better understand how exercise affects the brain and body in the context of PD to guide clinical decision-making and determine the optimal exercise intensity and modality for PD patients. This review outlines the various mechanisms by which exercise can be beneficial as a therapeutic option in PD.

Sleep disturbances are related to glymphatic dysfunction in blepharospasm

Research has shown a close relationship between sleep and glymphatic function, with impaired glymphatic function potentially contributing to sleep problems in a bidirectional way. However, its role in sleep disturbances associated with dystonia remains unknown. This cross-sectional study aimed to investigate whether glymphatic function is impaired in dystonia and to explore its relationship with sleep disturbances. We conducted structural magnetic resonance imaging and diffusion tensor imaging (DTI) on two large cohorts: patients with blepharospasm (BSP, n = 45) and cervical dystonia (CD, n = 43), alongside age- and sex-matched healthy controls (HCs). Anxiety, depression, and sleep quality were evaluated using the Hamilton Anxiety Scale (HAMA), Hamilton Depression Scale (HAMD), and Pittsburgh Sleep Quality Index (PSQI), respectively. Analysis along the perivascular space (DTI-ALPS) index and choroid plexus volume (CPV) was used to assess glymphatic function in these participants. Patients with BSP and CD had higher HAMA, HAMD, and PSQI scores than those of HCs. Patients with BSP exhibited a lower DTI-ALPS index and larger CPV than those of HCs, while no significant differences were found between CD and HCs. In BSP and CD, PSQI scores positively correlated with HAMA and HAMD scores and negatively with the DTI-ALPS index in BSP. Multivariate analysis identified the DTI-ALPS index as a dependent predictive factor of the PSQI in patients with BSP. Our findings suggest that glymphatic function varies across types of focal dystonia, with glymphatic dysfunction potentially playing an important role in the pathogenesis of sleep disturbances in BSP.

U-Net-Based Prediction of Cerebrospinal Fluid Distribution and Ventricular Reflux Grading

Previous work indicates evidence that cerebrospinal fluid (CSF) plays a crucial role in brain waste clearance processes and that altered flow patterns are associated with various diseases of the central nervous system. In this study, we investigate the potential of deep learning to predict the distribution in human brain of a gadolinium-based CSF contrast agent (tracer) administered intrathecal. For this, T1-weighted magnetic resonance imaging (MRI) scans taken at multiple time points before and after injection were utilized. We propose a U-net-based supervised learning model to predict pixel-wise signal increase at its peak after 24 h. Performance is evaluated based on different tracer distribution stages provided during training, including predictions from baseline scans taken before injection. Our findings show that training with imaging data from only the first 2-h postinjection yields tracer flow predictions comparable to models trained with additional later-stage scans. Validation against ventricular reflux gradings from neuroradiologists confirmed alignment with expert evaluations. These results demonstrate that deep learning-based methods for CSF flow prediction deserve more attention, as minimizing MR imaging without compromising clinical analysis could enhance efficiency, improve patient well-being and lower healthcare costs.

Insights into the Role of the Glymphatic System in the Pathogenesis of Post-hemorrhagic Hydrocephalus

Recently, it has been well-established that the glymphatic or glial-lymphatic system plays a vital role in the pathophysiology of various neurological compromise, especially hydrocephalus (HCP). Till now, the complete pathway is not yet fully understood, and little evidence is available from the literature that links hydrocephalus to disorders of the glymphatic system. Most published molecular studies and animal research have shown that, in models with hydrocephalus, the drainage of cerebrospinal fluid (CSF) via the glymphatic system is disrupted. This is strongly observed in normal pressure and post-hemorrhagic hydrocephalus cases. A thorough search of the literature to date yields scarce evidence on studies conducted on humans. Despite major similarities between non-human and human glymphatic pathways, the need for studies conducted on humans is becoming more urgent as the glymphatic pathway has been shown to be a good candidate for therapeutic intervention. In this review, we collect and report the most updated evidence addressing the glymphatic drainage pathways and their associations with the development of various types of hydrocephalus. In addition, we reveal the current scientific gap in human studies and our recommendations for the conduction of future clinical studies.

Widespread and prolonged pain may reduce brain clearance capacity only via sleep impairment: Evidence from participants with knee pain

The brain is key in the pain-sleep relationship, and sleep is needed for glymphatic clearance. However, no studies have examined how pain relates to the glymphatic system (GS). Characterizing the GS alongside sleep quality in well-characterized pain samples is essential for advancing this understanding. Non-invasive MRI techniques, such as Diffusion Tensor Imaging-Analysis aLong the Perivascular Space (DTI-ALPS), are particularly valuable as they are approved for humans. Although the relationship between the DTI-ALPS index and the GS is primarily deductive, the index may be a proxy for waste clearance capacity in deep white matter. Its sensitivity to interstitial space changes-known to be modulated by norepinephrine-offers a unique opportunity to investigate how sleep impairment and chronic pain regulation affect specific components of brain waste clearance. We thus fitted two longitudinal models linking pain, sleep quality and the DTI-ALPS index. We hypothesized that variations in pain characteristics would predict DTI-ALPS index changes, either directly or mediated by sleep quality changes. Alternatively, we hypothesized that variations in sleep quality would predict changes in pain characteristics via DTI-ALPS index modifications. Knee pain participants (n=87) completed an MRI and self-reported measures of pain and sleep impairment at baseline and two years later. We only found evidence supporting that more widespread and longer pain at baseline significantly influenced decreases in the DTI-ALPS index in the left hemisphere through increased sleep impairment two years later (p=0.039, corrected). PERSPECTIVE: Findings highlight the need for research on the relationship between pain and sleep quality and its implications for brain health.

Extracellular vesicles as precision therapeutics for psychiatric conditions: targeting interactions among neuronal, glial, and immune networks

The critical role of the immune system in brain function and dysfunction is well recognized, yet development of immune therapies for psychiatric diseases has been slow due to concerns about iatrogenic immune deficiencies. These concerns are emphasized by the lack of objective diagnostic tools in psychiatry. A promise to resolve this conundrum lies in the exploitation of extracellular vesicles (EVs) that are physiologically produced or can be synthetized. EVs regulate recipient cell functions and offer potential for EVs-based therapies. Intranasal EVs administration enables the targeting of specific brain regions and functions, thereby facilitating the design of precise treatments for psychiatric diseases. The development of such therapies requires navigating four dynamically interacting networks: neuronal, glial, immune, and EVs. These networks are profoundly influenced by brain fluid distribution. They are crucial for homeostasis, cellular functions, and intercellular communication. Fluid abnormalities, like edema or altered cerebrospinal fluid (CSF) dynamics, disrupt these networks, thereby negatively impacting brain health. A deeper understanding of the above-mentioned four dynamically interacting networks is vital for creating diagnostic biomarker panels to identify distinct patient subsets with similar neuro-behavioral symptoms. Testing the functional pathways of these biomarkers could lead to new therapeutic tools. Regulatory approval will depend on robust preclinical data reflecting progress in these interdisciplinary areas, which could pave the way for the design of innovative and precise treatments. Highly collaborative interdisciplinary teams will be needed to achieve these ambitious goals.

Glymphatic system dysfunction and cerebrospinal fluid retention in gliomas: evidence from perivascular space diffusion and volumetric analysis

BACKGROUND

Gliomas may impair glymphatic function and alter cerebrospinal fluid (CSF) dynamics through structural brain changes, potentially affecting peritumoral brain edema (PTBE) and fluid clearance. This study investigated the impact of gliomas on glymphatic system function and CSF volume via diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) and volumetric magnetic resonance imaging (MRI), which clarified the relationships between tumor characteristics and glymphatic system disruption.

METHODS

In this prospective study, 112 glioma patients and 56 healthy controls underwent MRI to calculate DTI-ALPS indices and perform volumetric analyses of CSF, tumor, and PTBE. Statistical analyses were used to assess the relationships between the DTI-ALPS index, tumor volume, PTBE volume, and clinical characteristics.

RESULTS

Glioma patients had significantly lower DTI-ALPS indices (1.266 ± 0.258 vs. 1.395 ± 0.174, p < 0.001) and greater CSF volumes (174.53 ± 34.89 cm³ vs. 154.25 ± 20.89 cm³, p < 0.001) than controls did. The DTI-ALPS index was inversely correlated with tumor volume (r = -0.353, p < 0.001) and PTBE volume (r = -0.266, p = 0.015). High-grade gliomas were associated with lower DTI-ALPS indices and larger PTBE volumes (all p < 0.001). Tumor grade emerged as an independent predictor of the DTI-ALPS index in multivariate analysis (β = -0.244, p = 0.011).

CONCLUSION

Gliomas are associated with significant glymphatic dysfunction, as evidenced by reduced DTI-ALPS indices and increased CSF and PTBE volumes. The DTI-ALPS index serves as a potential biomarker of glymphatic disruption in glioma patients, offering insights into tumor-related fluid changes and the pathophysiology of brain-tumor interactions.

Total cerebral blood volume changes drive macroscopic cerebrospinal fluid flux in humans

In the mammalian brain, the directed motion of cerebrospinal fluid (CSF-flux) is instrumental in the distribution and removal of solutes. Changes in total cerebral blood volume (CBV) have been hypothesized to drive CSF-flux. We tested this hypothesis in two multimodal brain imaging experiments in healthy humans, in which we drove large changes in total CBV by neuronal burst-suppression under anesthesia or by transient global vasodilation in a hypercapnic challenge. We indirectly monitored CBV changes with a high temporal resolution based on associated changes in total brain volume by functional MRI (fMRI) and measured cerebral blood flow by arterial spin-labeling. Relating CBV-sensitive signals to fMRI-derived measures of macroscopic CSF flow across the basal cisternae, we demonstrate that increasing total CBV extrudes CSF from the skull and decreasing CBV allows its influx. Moreover, CSF largely stagnates when CBV is stable. Together, our results establish the direct coupling between total CBV changes and CSF-flux.

Glymphatic system dysfunction in pediatric tourette syndrome Neuroimaging evidence from MRI metrics

BACKGROUND AND OBJECTIVES

The glymphatic system, vital for brain waste clearance, is implicated in neurodevelopmental diseases, but its role in pediatric Tourette syndrome (TS) is not well understood. This study investigates structural and functional alterations in the glymphatic system in pediatric TS using non-invasive MRI techniques.

METHODS

This case-control study included 37 children with Tourette syndrome (TS) and 37 age- and gender-matched typically developing (TD) controls. We assessed brain volumetric differences and glymphatic function using two MRI metrics: perivascular space (PVS) burden for glymphatic influx and the DTI-ALPS index for waste clearance, with PVS quantified via semi-automated analysis of axial T2-weighted images. Correlations between MRI metrics and clinical symptoms in TS children were analyzed using partial correlations.

RESULTS

Children with Tourette syndrome (TS) exhibited significant reductions in brain parenchymal and white matter volume compared to typically developing (TD) children (all PFDR < 0.001), along with a higher perivascular space (PVS) volume (6.29 ± 3.62 mL vs. 4.76 ± 2.13 mL; PFDR = 0.046), indicating impaired glymphatic influx. The DTI-ALPS index was lower in TS (1.21 ± 0.18 vs. 1.46 ± 0.12; PFDR < 0.001), reflecting reduced waste clearance, and Dzassoc and Dzproj metrics were positively correlated with motor tic severity in TS (all P ≤ 0.02).

CONCLUSIONS

Our findings suggest significant glymphatic dysfunction in pediatric TS, indicating its role in the disorder's pathogenesis. Increased PVS burden and decreased DTI-ALPS index may serve as non-invasive biomarkers for diagnosing and understanding TS mechanisms.

Beyond the cerebellum: perivascular space burden in spinocerebellar ataxia type 3 extends to multiple brain regions

Spinocerebellar ataxia type 3 (SCA3) is an uncommon inherited (autosomal dominant) neurodegenerative disorder caused by abnormal accumulation of ataxin-3 protein. The perivascular space (PVS) burden reflects protein clearance and may worsen in SCA3 disease. This study aimed to quantify the PVS burden and investigate the relationship between the PVS burden and clinical characteristics in individuals with SCA3. This study enrolled 43 SCA3 patients and 43 age- and sex-matched healthy controls (HCs). The cross-sectional study assessed the severity of ataxia in SCA3 patients using the Scale for the Assessment and Rating of Ataxia (SARA) and the International Cooperative Ataxia Rating Scale (ICARS). Various cognitive functions were evaluated in all subjects using the Montreal Cognitive Assessment (MoCA), Rapid Verbal Retrieval (RAR) and Digital Span Test (DST) scales. MRI was used to automatically segment the PVS in all subjects and quantify the PVS burden in 15 brain regions. Compared with the HCs, the SCA3 patients showed a significantly higher PVS burden in the basal ganglia, temporal lobe, right parietal lobe and right cerebellum. There was a positive correlation in motor dysfunction between the PVS volume in the left parietal lobe, right cerebellum and PVS number in the right cerebellum with the SARA and ICARS scores. This study showed that SCA3 patients have an increased PVS burden in many brain regions, leading to motor impairment. The PVS burden could be a new imaging biomarker for disease monitoring and a therapeutic target for SCA3.

Reactive Astrocytes in Glioma: Emerging Opportunities and Challenges

Gliomas are the most prevalent malignant tumors in the adult central nervous system (CNS). Glioblastoma (GBM) accounts for approximately 60-70% of primary gliomas. It is a great challenge to human health because of its high degree of malignancy, rapid progression, short survival time, and susceptibility to recurrence. Owing to the specificity of the CNS, the glioma microenvironment often contains numerous glial cells. Astrocytes are most widely distributed in the human brain and form reactive astrocyte proliferation regions around glioma tissue. In addition, astrocytes are activated under pathological conditions and regulate tumor and microenvironmental cells through cell-to-cell contact or the secretion of active substances. Therefore, astrocytes have attracted attention as important components of the glioma microenvironment. Here, we focus on the mechanisms of reactive astrocyte activation under glioma conditions, their contribution to the mechanisms of glioma genesis and progression, and their potential value as targets for clinical intervention in gliomas.

Radiation-Induced Brain Injury with Special Reference to Astrocytes as a Therapeutic Target

Radiotherapy is one of the primary modalities for oncologic treatment and has been utilized at least once in over half of newly diagnosed cancer patients. Cranial radiotherapy has significantly enhanced the long-term survival rates of patients with brain tumors. However, radiation-induced brain injury, particularly hippocampal neuronal damage along with impairment of neurogenesis, inflammation, and gliosis, adversely affects the quality of life for these patients. Astrocytes, a type of glial cell that are abundant in the brain, play essential roles in maintaining brain homeostasis and function. Despite their importance, the pathophysiological changes in astrocytes induced by radiation have not been thoroughly investigated, and no systematic or comprehensive review addressing the effects of radiation on astrocytes and related diseases has been conducted. In this paper, we review current studies on the neurophysiological roles of astrocytes following radiation exposure. We describe the pathophysiological changes in astrocytes, including astrogliosis, astrosenescence, and the associated cellular and molecular mechanisms. Additionally, we summarize the roles of astrocytes in radiation-induced impairments of neurogenesis and the blood-brain barrier (BBB). Based on current research, we propose that brain astrocytes may serve as potential therapeutic targets for treating radiation-induced brain injury (RIBI) and subsequent neurological and neuropsychiatric disorders.

Glymphatic system dysfunction in cerebral infarction: advances and perspectives based on DTI-derived ALPS measures

The glymphatic pathway plays a crucial role in the clearance of metabolic byproducts and solutes from cerebral tissue. Dysfunction of the glymphatic pathway has been associated with various neurological disorders, including ischemic stroke. Diffusion tensor imaging (DTI) and the derived Analysis aLong the Perivascular Space (ALPS) have emerged as promising tools for evaluating glymphatic pathway function. This review aims to summarize the current evidence on the use of DTI-derived ALPS measures in assessing glymphatic dysfunction in ischemic stroke patients, and to explore their potential implications for diagnosis, prognostication, and treatment monitoring in this patient population.

Meningeal Lymphatic and Glymphatic Structures in a Pelagic Delphinid (Delphinus delphis)

The glymphatic system, an analog of the peripheral lymphatic system in the brain, and the meningeal lymphatic system are critical to central nervous system health. The glymphatic system functions to distribute cerebrospinal fluid and important compounds throughout the brain and to remove metabolic waste. The flow of cerebrospinal fluid through this system is affected by changes in cerebral blood flow, intracranial pressure, and vascular tone. Cetaceans experience profound cardiorespiratory alterations while diving that can directly affect cerebrospinal fluid and blood flow and, thus, glymphatic function. Our goal was to investigate glymphatic and lymphatic system structures, including perivascular spaces, aquaporin-4 water channels, meningeal lymphatic, and dural venous sinus vessels in the common dolphin (Delphinus delphis), using immunofluorescent labeling, histochemical staining, and postmortem computed tomography (CT) angiography. We highlight perivascular spaces and aquaporin-4 water channels surrounding blood vessels in the parenchyma and demonstrate evidence of meningeal lymphatic vessels and associated dural venous sinuses. These results demonstrate that common dolphins possess the key anatomical structures required for functional glymphatic and meningeal lymphatic systems. Future studies can build upon these anatomical discoveries to study the function and role of these systems in brain health in this species.

Clinical neurocardiology: defining the value of neuroscience-based cardiovascular therapeutics - 2024 update

The intricate role of the autonomic nervous system (ANS) in regulating cardiac physiology has long been recognized. Aberrant function of the ANS is central to the pathophysiology of cardiovascular diseases. It stands to reason, therefore, that neuroscience-based cardiovascular therapeutics hold great promise in the treatment of cardiovascular diseases in humans. A decade after the inaugural edition, this White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology and pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Emerging Technologies to Track and Improve Sleep Health

This review explores cutting-edge advancements, including wearable sleep trackers, brain age assessments, transcranial electrical stimulation (TES), acoustic stimulation, and glymphatic system modulation. Sleep trackers provide continuous monitoring of sleep patterns, while brain age estimation offers insights into brain health and early detection of accelerated aging. TES shows promise in improving mood, memory, and sleep. Acoustic stimulation during slow-wave sleep has been demonstrated to enhance memory consolidation. Additionally, optimizing the glymphatic system may facilitate brain waste clearance, crucial in preventing neurodegenerative diseases like Alzheimer's. However, significant challenges remain, including the need for rigorous longitudinal studies to validate these technologies' efficacy and safety.

Neuropathological features of cerebrovascular diseases

Optimal blood flow through a patent cerebral circulation is critical for supply of oxygen and nutrients for brain function. The integrity of vascular elements within arterial vessels of any calibre can be compromised by various disease processes. Pathological changes in the walls of veins and the venous system may also alter the dynamics of cerebral perfusion. The consequences of both systemic vascular and cerebrovascular diseases range from acute focal changes to irreversible chronic restructuring of the brain parenchyma. Cerebral infarcts of different sizes may instigate a cascade of programmed cell death mechanisms including autophagy and mitophagy and processes that range from necroptosis to ferroptosis. Recent advances also emphasise the role of the vascular inflammasome in the pathology of cerebral infarction. Here, we summarise current knowledge on frequencies, epidemiological features and the neuropathology of common cerebrovascular disorders among which cerebral small vessel diseases have become of particular interest. We also highlight the current spectrum of monogenic and polygenic genetic disorders affecting the intracranial vasculature. With the advent of DNA screening technologies, it is now realised that several cerebrovascular disorders exhibit strong genetic traits. Whilst several gene defects and their aberrant products are identified, the precise role or mechanisms of how they influence angiogenesis, vasculogenesis, vessel integrity or the extracellular matrix remain largely unclear. Despite such genetic advances, histopathological examination remains the gold standard for diagnosis and characterisation of most cerebrovascular disorders.

Brain Health in Sleep Disorders

Sleep is a critical determinant of brain health, influencing cognitive, emotional, and physiologic functions. The complex bidirectional relationship between sleep and brain health underscores the importance of sleep in maintaining cognitive function, regulating brain homeostasis, and facilitating the clearance of metabolic waste through the glymphatic system. Chronic sleep deprivation and sleep disorders such as insomnia and obstructive sleep apnea have been shown to negatively impact brain structures and functions. This review discusses the impact of sleep disorders on brain health. It also explores the implications of impaired sleep on cardiovascular health, immune function, and neuroplasticity.

Cortical Morphology Alterations Mediate the Relationship Between Glymphatic System Function and the Severity of Asthenopia

Objectives: This study is aimed at assessing glymphatic function by diffusion tensor image analysis along the perivascular space (DTI-ALPS) and its associations with cortical morphological changes and severity of accommodative asthenopia (AA). Methods: We prospectively enrolled 50 patients with AA and 47 healthy controls (HCs). All participants underwent diffusion tensor imaging (DTI) and T1-weighted imaging and completed the asthenopia survey scale (ASS). Differences in brain morphometry and the analysis along the perivascular space (ALPS) index between the two groups were compared. The correlation and mediation analyses were conducted to explore the relationships between them. Results: Compared to HCs, patients with AA exhibited significantly increased sulcal depth in the left superior occipital gyrus (SOG.L) and increased cortical thickness in the left superior temporal gyrus (STG.L), left middle occipital gyrus (MOG.L), left postcentral gyrus (PoCG.L), and left precuneus (PCUN.L). Additionally, patients with AA had a significantly lower ALPS index than HCs. The sulcal depth of the SOG.L was significantly positively correlated with the ASS score in patients with AA, and a positive correlation was found between the cortical thickness of the MOG.L and ASS score. The ALPS index was negatively associated with the sulcal depth of the SOG.L and cortical thickness of the MOG.L. Mediation analysis revealed that the sulcal depth of SOG.L and cortical thickness of MOG.L partially mediated the impact of the DTI-ALPS index on the ASS score. Conclusion: Our findings suggested that patients with AA exhibit impaired glymphatic function, which may contribute to the severity of asthenopia through its influence on cortical morphological changes. The ALPS index is anticipated to become a potential imaging biomarker for patients with AA. Trial Registration: Chinese Registry of Clinical Trials: ChiCTR1900028306.

Fading Blue: Exploring the Causes of Locus Coeruleus Damage Across the Lifespan

Locus Coeruleus (LC) is a brain nucleus that is involved in a variety of key functions (ranging from attention modulation to sleep-wake cycle regulation, to memory encoding); its proper function is necessary both during brain development and for brain integrity maintenance, and both at the microscale and macroscale level. Due to their specific intrinsic and extrinsic features, LC cells are considered particularly susceptible to damage concerning a variety of insults. This explains LC involvement in degenerative diseases not only in adults (in the context of neurodegenerative disease, mainly), but also in children (in relation to early hypoxic damage and Down's Syndrome, among others). In this narrative review, we dissect the potential mechanisms through which LC is affected in different diseases, with a special emphasis on the high rate of activity it is subjected to and the oxidative stress associated with it. Further research aimed at deepening our understanding of these mechanisms is needed to enable the development of potential strategies in the future that could slow down LC degeneration in subjects predisposed to specific brain disorders.

Altered immune landscape of cervical lymph nodes reveals Epstein-Barr virus signature in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, and Epstein-Barr virus (EBV) infection is a prerequisite for developing the disease. However, the pathogenic mechanisms that lead to MS remain to be determined. Here, we characterized the immune landscape of deep cervical lymph nodes (dcLNs) in newly diagnosed untreated patients with MS (pwMS) using fine-needle aspirations. By combining single-cell RNA sequencing and cellular indexing of transcriptomes and epitopes by sequencing, we observed increased memory B cells and reduced germinal center B cells with decreased clonality in pwMS. Double-negative memory B cells were increased in pwMS that transcriptionally resembled B cells with a lytic EBV infection. Moreover, EBV-targeting memory CD8 T cells were detected in a subset of pwMS. We also detected increased EBV DNA in dcLNs and elevated viral loads in patient saliva. These findings suggest that EBV-driven B cell dysregulation is a critical mechanism in MS pathogenesis.

In vivo imaging markers of glymphatic dysfunction in amyotrophic lateral sclerosis: Analysis of ALPS index and choroid plexus volume

BACKGROUND

The glymphatic system, essential for brain waste clearance, has been implicated in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Emerging imaging markers, such as the analysis along the perivascular space (ALPS) index and choroid plexus volume (CPV), may provide insights into glymphatic function, but their relevance to ALS remains unclear.

OBJECTIVE

To assess glymphatic dysfunction in ALS patients using the ALPS index and CPV.

METHODS

In this prospective single-center study, we analyzed 51 ALS patients and 51 age- and sex-matched healthy controls (HC). The ALPS index was calculated using diffusion tensor imaging, and 3D T1-weighted MRI was used for automated estimation of CPV and its fraction (CPV/total intracranial volume). Diagnostic performance was assessed using area under the receiver operating curve (AUC). Correlations between imaging markers and clinical parameters were also examined.

RESULTS

ALS patients had a significantly lower ALPS index (ALS: 1.45 ± 0.15; HC: 1.55 ± 0.16; p = 0.002) and higher CPV fraction (ALS: 0.12 ± 0.04 %; HC: 0.10 ± 0.02 %; p < 0.001). The ALPS index and CPV fraction had AUCs of 0.70 and 0.72, respectively. A significant inverse correlation was observed between the ALPS index and CPV fraction (r = -0.31, p = 0.002). Both markers correlated with aging but not with clinical disability or progression rate.

CONCLUSION

This study identifies glymphatic dysfunction in ALS, as evidenced by changes in the ALPS index and CPV. Larger studies are warranted to validate these findings and assess their potential as biomarkers for ALS.

Blood Flow in the Internal Jugular Veins in the Lateral Decubitus Body Position in the Healthy People

Background: Some studies have suggested that the lateral decubitus position during sleep may protect the brain from neurodegenerative processes. Although the mechanisms of such possible protection are not known, an optimal venous outflow may be responsible. Venous outflow from the cranial cavity is dependent on the body's position. However, to date, flow in the internal jugular veins (IJVs) in the lateral position has not been studied quantitatively. Methods: Using ultrasonography, we measured the cross-sectional areas and flow volumes in the IJVs in a group of 25 healthy individuals aged 20-52 ± 12.1 years. These measurements were performed in the supine, upright, and lateral decubitus positions. Results: In the lateral decubitus position, we revealed a collapse of the IJV located higher, dilatation of the opposite vein, and a shift in flow from one vein to the opposite. In the right lateral position, the mean cross-sectional area and flow in the right IJV were 88.6 ± 71.1 mm2 and 74.3 ± 97.5 mL/min, in the left IJV: 37.2 ± 33.4 mm2 and 48.8 ± 82.8 mL/min. In the left lateral position, the right IJV was 38.4 ± 30.7 mm2 and 56.7 ± 56.1 mL/min, and the left IJV was 75.9 ± 51.9 mm2 and 99.7 ± 123.9 mL/min. However, there was also a high heterogeneity of the cross-sectional area changes, and in many participants, this pattern was not observed. Regarding flow volumes in the lateral body positions, in comparison with the supine position, the total outflow through both internal jugular veins was not significantly different. Conclusions: In terms of venous outflow, the lateral decubitus position did not differ significantly from the supine position. The working hypothesis of a potentially protective effect of this body position during sleep against neurodegeneration through improved venous outflow has not been proven, at least in healthy individuals.

Immersive gamma music as a tool for enhancing glymphatic clearance in astronauts while improving their mental well-being

Spaceflight occurs under extreme environmental conditions that pose significant risks to the physical and mental health and well-being of astronauts. Certain factors, such as prolonged isolation, monotony, disrupted circadian rhythms, heavy workload, and weightlessness in space, can trigger psychological distress and may contribute to a variety of mental health problems, including mood and anxiety disturbances. Recent findings regarding spaceflight-associated alterations in cerebrospinal fluid spaces, demonstrating enlargement of the brain's perivascular spaces from preflight to postflight, at least suggest reduced glymphatic clearance in microgravity, and have raised concerns about long-term cognitive health in astronauts. Therefore, it is critical for future long-duration human exploration missions to identify, develop and validate all potentially effective long-term countermeasures capable of reducing the risk of perivascular space enlargement and impaired glymphatic transport in space mission crews. Furthermore, it is crucial to implement effective strategies that would allow crew members to maintain optimal psychological well-being during future long-duration space exploration. In the present paper, we propose "immersive gamma music" as an add-on countermeasure that in combination with existing countermeasures can optimize glymphatic clearance in astronauts while improving their mental well-being. If confirmed, this approach could enrich the practice of space medicine, and might become increasingly important, given the plans for future human missions, including a return to the Moon and manned missions to Mars.

Aquaporin-4 activation facilitates glymphatic system function and hematoma clearance post-intracerebral hemorrhage

Efficient clearance of hematomas is crucial for improving clinical outcomes in patients with intracerebral hemorrhage (ICH). The glymphatic system, facilitated by aquaporin-4 (AQP4), plays a crucial role in cerebrospinal fluid (CSF) entry and metabolic waste clearance. This study examined the role of the glymphatic system in ICH pathology, with a focus on AQP4. Collagenase-induced ICH models were established, with AQP4 expression regulated through mifepristone as an agonist, TGN-020 as an inhibitor, and Aqp4 gene knockout. Fluorescence tracing and multimodal magnetic resonance imaging (MRI) were employed to observe glymphatic system functionality, hematoma, and edema volumes. Neurological deficit scoring was performed using the modified Garcia Scale. AQP4 expression was quantified using RT-qPCR and Western blotting, and cellular localization was explored using immunofluorescence. The brain tissue sections were examined for neuronal morphology, degenerative changes, and iron deposition. Three days post-ICH, the AQP4 agonist group showed increased AQP4 protein expression and perivascular polarization, decreased hemoglobin levels, and reduced iron deposition. Conversely, the inhibition group exhibited contrasting trends. AQP4 activation improved glymphatic system function, leading to a wider distribution, improved neurological function, and reduced hematoma. Pharmacological inhibition and genetic knockout of AQP4 have opposing effects. The glymphatic system, facilitated by AQP4, plays a crucial role in hematoma clearance following cerebral hemorrhage. Upregulation of AQP4 improves glymphatic system function, facilitates hematoma clearance, and promotes brain tissue recovery.

Evaluation of Plasma Neurodegenerative Biomarkers for Diagnosing Minimal Hepatic Encephalopathy and Predicting Overt Hepatic Encephalopathy in Chinese Patients with Hepatic Cirrhosis

Background and Aims

The performance of neurodegenerative biomarkers-neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), tau, and ubiquitin carboxy-terminal hydrolase L1 (UCHL1)-in diagnosing minimal hepatic encephalopathy (MHE) has not been systematically evaluated, simultaneously, nor have their associations with the development of overt hepatic encephalopathy (OHE). This study aimed to evaluate the performance of plasma NfL, GFAP, tau, and UCHL1 in diagnosing MHE and predicting the development of OHE in Chinese patients with hepatic cirrhosis.

Methods

In this prospective study, 124 patients with hepatic cirrhosis were recruited. The Psychometric Hepatic Encephalopathy Score was used to diagnose MHE, and OHE development was observed during a 30-day follow-up period. Plasma levels of NfL, GFAP, tau, and UCHL1 were measured using the highly sensitive single-molecule array when MHE was diagnosed. Additionally, serum interleukin-6 (IL-6) levels and the model for end-stage liver disease (MELD) and MELD-Na scores were also measured.

Results

MHE was diagnosed in 57 (46.0%) patients. Patients with MHE had significantly higher plasma levels of NfL and GFAP (34.2 vs. 22.4 pg/mL and 173 vs. 97.6 pg/mL, respectively; both p < 0.001) and lower tau levels (8.4 vs. 11.6 pg/mL, p = 0.048) compared to those without MHE. Plasma NfL (odds ratios = 1.027, 95% confidence interval [CI]: 1.006-1.048; p = 0.013) and serum ammonia levels (odds ratios = 1.021, 95% CI: 1.006-1.036; p = 0.007) were independently associated with MHE occurrence. A combination of NfL, GFAP, tau, and UCHL1 was effective in diagnosing MHE in all cirrhotic patients (area under the receiver operating characteristic curve [hereinafter referred to as AUROC]: 0.748, 95% CI: 0.662-0.821), with an accuracy, sensitivity, and specificity of 71.0%, 71.9%, and 71.6%, respectively. In patients without previous OHE, the combination had an AUROC of 0.764 (95% CI: 0.673-0.840), with an accuracy, sensitivity, and specificity of 72.5%, 71.7%, and 73.0%, respectively. Furthermore, GFAP (hazard ratio (HR) = 1.003, 95% CI: 1.000-1.005; p = 0.044), IL-6 (HR = 1.003, 95% CI: 1.001-1.004; p < 0.001), and MELD score (HR = 1.139, 95% CI: 1.072-1.210; p < 0.001)-but not NfL, tau, and UCHL1-were identified as risk factors for 30-day OHE development.

Conclusions

The combination of plasma levels of NfL, GFAP, tau, and UCHL1 performs well in diagnosing MHE. Additionally, MELD score, IL-6, and GFAP appear to be significant predictors of OHE development in patients with hepatic cirrhosis.

An Improved Method for Extracting Rat Cerebrospinal Fluid with Repeatable Large-Scale Collection

The aim of this study was to explore an improved method for extracting rat cerebrospinal fluid (CSF), observing the impact on animal health under conditions of large-scale CSF collection and evaluating the feasibility of repeated collections. A total of 20 rats were anesthetized and fixed in a stereotactic frame. A 26G scalp needle, combined with a 1 mL syringe, was used to puncture the atlanto-occipital membrane and collect approximately 170 μL of CSF. CSF was collected twice within 14 days. During the study, animals were monitored daily for food intake, body weight, and hematological parameters, and at the end of the study, histopathological examination was performed. The health of the animals remained good, and repeated CSF collections were feasible. The success rate of the procedure was 100%, with blood contamination in the CSF decreasing from 70% in the first collection to 35% in the second. This technique is convenient, accurate, and suitable for widespread applications.

Targeting the glymphatic system to promote α-synuclein clearance: a novel therapeutic strategy for Parkinson's disease

ABSTRACT

The excessive buildup of neurotoxic α-synuclein plays a pivotal role in the pathogenesis of Parkinson's disease, highlighting the urgent need for innovative therapeutic strategies to promote α-synuclein clearance, particularly given the current lack of disease-modifying treatments. The glymphatic system, a recently identified perivascular fluid transport network, is crucial for clearing neurotoxic proteins. This review aims to synthesize current knowledge on the role of the glymphatic system in α-synuclein clearance and its implications for the pathology of Parkinson's disease while emphasizing potential therapeutic strategies and areas for future research. The review begins with an overview of the glymphatic system and details its anatomical structure and physiological functions that facilitate cerebrospinal fluid circulation and waste clearance. It summarizes emerging evidence from neuroimaging and experimental studies that highlight the close correlation between the glymphatic system and clinical symptom severity in patients with Parkinson's disease, as well as the effect of glymphatic dysfunction on α-synuclein accumulation in Parkinson's disease models. Subsequently, the review summarizes the mechanisms of glymphatic system impairment in Parkinson's disease, including sleep disturbances, aquaporin-4 impairment, and mitochondrial dysfunction, all of which diminish glymphatic system efficiency. This creates a vicious cycle that exacerbates α-synuclein accumulation and worsens Parkinson's disease. The therapeutic perspectives section outlines strategies for enhancing glymphatic activity, such as improving sleep quality and pharmacologically targeting aquaporin-4 or its subcellular localization. Promising interventions include deep brain stimulation, melatonin supplementation, γ-aminobutyric acid modulation, and non-invasive methods (such as exercise and bright-light therapy), multisensory γ stimulation, and ultrasound therapy. Moreover, identifying neuroimaging biomarkers to assess glymphatic flow as an indicator of α-synuclein burden could refine Parkinson's disease diagnosis and track disease progression. In conclusion, the review highlights the critical role of the glymphatic system in α-synuclein clearance and its potential as a therapeutic target in Parkinson's disease. It advocates for further research to elucidate the specific mechanisms by which the glymphatic system clears misfolded α-synuclein and the development of imaging biomarkers to monitor glymphatic activity in patients with Parkinson's disease. Findings from this review suggest that enhancing glymphatic clearance is a promising strategy for reducing α-synuclein deposits and mitigating the progression of Parkinson's disease.

Anatomical correlates for the newly discovered meningeal layer in the existing literature: A systematic review

The existence of a previously unrecognized subarachnoid lymphatic-like membrane (SLYM) was reported in a recent study. SLYM is described as an intermediate leptomeningeal layer between the arachnoid and pia mater in mouse and human brains, which divides the subarachnoid space (SAS) into two functional compartments. Being a macroscopic structure, having missed detection in previous studies is surprising. We systematically reviewed the published reports in animals and humans to explore whether prior descriptions of this meningeal layer were reported in some way. A comprehensive search was conducted in PubMed/Medline, EMBASE, Google Scholar, Science Direct, and Web of Science databases using combinations of MeSH terms and keywords with Boolean operators from inception until 31 December 2023. We found at least eight studies that provided structural evidence of an intermediate leptomeningeal layer in the brain or spinal cord. However, unequivocal descriptions for this layer all along the central nervous system were scarce. Obscure names like the epipial, intermediate meningeal, outer pial layers, or intermediate lamella were used to describe it. Its microscopic/ultrastructural details closely resemble the recently reported SLYM. We further examined the counterarguments in current literature that are skeptical of the existence of this layer. The potential physiological and clinical implications of this new meningeal layer are significant, underscoring the urgent need for further exploration of its structural and functional details.

Medicinal plants for the management of post-COVID-19 fatigue: A literature review on the role and mechanisms

Background

COVID-19 infection has a lasting impact on human health, which is known as post-COVID-19 conditions. Fatigue is one of the most commonly reported post-COVID-19 conditions. Management of fatigue in the post-COVID-19 era is necessary and emerging. The use of medicinal plants may provide a strategy for the management of post-COVID-19 fatigue.

Methods

A literature search has been conducted by using PubMed, Embase and Cochrane library databases is performed for studies published up to March 2024. Keywords, such as "post-COVID-19 conditions, persistent COVID-19 symptoms, chronic COVID-19, long-term sequelae, fatigue, post-COVID-19 fatigue, herbal plants, medicinal herbs, traditional Chinese medicine, pharmacological mechanisms, pharmacological actions" are thoroughly searched in Englsih and Chinese. This study reviews the pathophysiology of post-COVID-19 fatigue and potential herbal plants for managing post-COVID-19 fatigue.

Results and conclusion

Representative medicinal plants that have been extensively investigated by previous studies are presented in the study. Three common mechanisms among the most extensively studied for post-COVID-19 fatigue, with each mechanism having medicinal plants as an example. The latest clinical studies concerning the management of post-COVID-19 fatigue using medicinal plants have also been summarized. The study shows the potential for improving post-COVID-19 fatigue by consuming medicinal plants.

Plasma brain-related biomarkers and potential therapeutic targets in pediatric ECMO

Extracorporeal membrane oxygenation (ECMO) is a technique used to support severe cardiopulmonary failure. Its potential life-saving benefits are tempered by the significant risk for acute brain injury (ABI), from both primary pathophysiologic factors and ECMO-related complications through central nervous system cellular injury, blood-brain barrier dysfunction (BBB), systemic inflammation and neuroinflammation, and coagulopathy. Plasma biomarkers are an emerging tool used to stratify risk for and diagnose ABI, and prognosticate neurofunctional outcomes. Components of the neurovascular unit have been rational targets for this inquiry in ECMO. Central nervous system (CNS) neuronal and astroglial cellular-derived neuron-specific enolase (NSE), tau, glial fibrillary acidic protein (GFAP) and S100β elevations have been detected in ABI and are associated with poorer outcomes. Evidence of BBB breakdown through peripheral blood detection of CNS cellular components NSE, GFAP, and S100β, as well as evidence of elevated BBB components vWF and PDGFRβ are associated with higher mortality and worse neurofunctional outcomes. Higher concentrations of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, TNF-α) are associated with abnormal neuroimaging, and proteomic expression panels reveal different coagulation and inflammatory responses. Abnormal coagulation profiles are common in ECMO with ongoing studies attempting to describe specific abnormalities either being causal or associated with neurologic outcomes; vWF has shown some promise. Understanding these mechanisms of injury through biomarker analysis supports potential neuroprotective strategies such as individualized blood pressure targets, judicious hypercarbia and hypoxemia correction, and immunomodulation (inhaled hydrogen and N-acetylcysteine). Further research continues to elucidate the role of biomarkers as predictors, prognosticators, and therapeutic targets.

Adenosine-Dependent Arousal Induced by Astrocytes in a Brainstem Circuit

Astrocytes play a crucial role in regulating sleep-wake behavior. However, how astrocytes govern a specific sleep-arousal circuit remains unknown. Here, the authors show that parafacial zone (PZ) astrocytes responded to sleep-wake cycles with state-differential Ca2+ activity, peaking during transitions from sleep to wakefulness. Using chemogenetic and optogenetic approaches, they find that activating PZ astrocytes elicited and sustained wakefulness by prolonging arousal episodes while impeding transitions from wakefulness to non-rapid eye movement (NREM) sleep. Activation of PZ astrocytes specially induced the elevation of extracellular adenosine through the ATP hydrolysis pathway but not equilibrative nucleoside transporter (ENT) mediated transportation. Strikingly, the rise in adenosine levels induced arousal by activating A1 receptors, suggesting a distinct role for adenosine in the PZ beyond its conventional sleep homeostasis modulation observed in the basal forebrain (BF) and cortex. Moreover, at the circuit level, PZ astrocyte activation induced arousal by suppressing the GABA release from the PZGABA neurons, which promote NREM sleep and project to the parabrachial nucleus (PB). Thus, their study unveils a distinctive arousal-promoting effect of astrocytes within the PZ through extracellular adenosine and elucidates the underlying mechanism at the neural circuit level.

Simulating the impact of tumor mechanical forces on glymphatic networks in the brain parenchyma

The brain glymphatic system is currently being explored in the context of many neurological disorders and diseases, including traumatic brain injury, Alzheimer's disease, and ischemic stroke. However, little is known about the impact of brain tumors on glymphatic function. Mechanical forces generated during tumor development and growth may be responsible for compromised glymphatic transport pathways, reducing waste clearance and cerebrospinal fluid (CSF) transport in the brain parenchyma. One such force is solid stress, i.e., growth-induced forces from cell hyperproliferation and excess matrix deposition. Because there are no prior studies assessing the impact of tumor-derived solid stress on glymphatic system structure and performance in the brain parenchyma, this study serves to fill an important gap in the field. We adapted a previously developed Electrical Analog Model using MATLAB Simulink for glymphatic transport coupled with Finite Element Analysis for tumor mechanical stresses and strains in COMSOL. This allowed simulation of the impact of tumor mechanical force generation on fluid transport within brain parenchymal glymphatic units-which include perivascular spaces, astrocytic networks, interstitial spaces, and capillary basement membranes. We conducted a parametric analysis to compare the contributions of tumor size, tumor proximity, and ratio of glymphatic subunits to the stress and strain experienced by the glymphatic unit and corresponding reduction in flow rate of CSF. Mechanical stresses intensify with proximity to the tumor and increasing tumor size, highlighting the vulnerability of nearby glymphatic units to tumor-derived forces. Our stress and strain profiles reveal compressive deformation of these surrounding glymphatics and demonstrate that varying the relative contributions of astrocytes vs. interstitial spaces impact the resulting glymphatic structure significantly under tumor mechanical forces. Increased tumor size and proximity caused increased stress and strain across all glymphatic subunits, as does decreased astrocyte composition. Indeed, our model reveals an inverse correlation between extent of astrocyte contribution to the composition of the glymphatic unit and the resulting mechanical stress. This increased mechanical strain across the glymphatic unit decreases the venous efflux rate of CSF, dependent on the degree of strain and the specific glymphatic subunit of interest. For example, a 20% mechanical strain on capillary basement membranes does not significantly decrease venous efflux (2% decrease in flow rates), while the same magnitude of strain on astrocyte networks and interstitial spaces decreases efflux flow rates by 7% and 22%, respectively. Our simulations reveal that solid stress from growing brain tumors directly reduces glymphatic fluid transport, independently from biochemical effects from cancer cells. Understanding these pathophysiological implications is crucial for developing targeted interventions aimed at restoring effective waste clearance mechanisms in the brain. This study opens potential avenues for future experimental research in brain tumor-related glymphatic dysfunction.

Neuroinflammation modifies the relationship between stress and perivascular spaces in an elderly population with different levels of cognitive impairment

Background

Perivascular spaces (PVS) are fluid-filled spaces surrounding the brain parenchymal vasculature. Literature suggests that PVS may play a significant role in aging and neurological disorders, including Alzheimer's disease (AD). The aim of this study is to investigate whether the relationship between MRI-visible PVS and stress is influenced by neuroinflammation in an elderly population with different levels of cognitive impairment.

Methods

Using brain MRI scans acquired at 1.5 T, PVS were quantified in a cohort of 461 individuals, consisting of cognitively healthy controls (n = 48), people with mild cognitive impairment (MCI, n = 322) and Alzheimer's disease (AD, n = 91). PVS volume fraction was calculated in the basal ganglia and centrum semiovale using a semi-automated segmentation approach. Stress was quantified with levels of salivary cortisol. Inflammatory biomarkers measured from plasma included cytokines, matrix metalloproteinases and C-reactive protein. General linear models were used to test the relationship between PVS and cortisol, when interacting with inflammatory markers. This was done on the whole cohort and within each clinical cognitive group.

Results

In the centrum semiovale, higher inflammation levels reduced the relationship of cortisol with PVS. In basal ganglia, higher levels of C-reactive protein reduced the negative relationship of cortisol with PVS. All analyses were accounted for age, sex, body mass index (BMI) and total hippocampal volume. There was a significant interaction effect between cortisol and C-reactive protein on PVS volume fraction in the MCI group.

Discussion

These findings suggest an influence of neuroinflammation on the PVS structure in Alzheimer's disease spectrum, and offer insight for better understanding physiological processes of cognitive impairment onset.

A Histopathologic Correlation Study Evaluating Glymphatic Function in Brain Tumors by Multiparametric MRI

PURPOSE

This study aimed to elucidate the impact of brain tumors on cerebral edema and glymphatic drainage by leveraging advanced MRI techniques to explore the relationships among tumor characteristics, glymphatic function, and aquaporin-4 (AQP4) expression levels.

EXPERIMENTAL DESIGN

In a prospective cohort from March 2022 to April 2023, patients with glioblastoma, brain metastases, and aggressive meningiomas, alongside age- and sex-matched healthy controls, underwent 3.0T MRI, including diffusion tensor imaging analysis along the perivascular space (DTI-ALPS) index and multiparametric MRI for quantitative brain mapping. Tumor and peritumor tissues were analyzed for AQP4 expression levels via immunofluorescence. Correlations among MRI parameters, glymphatic function (DTI-ALPS index), and AQP4 expression levels were statistically assessed.

RESULTS

Among 84 patients (mean age: 55 ± 12 years; 38 males) and 59 controls (mean age: 54 ± 8 years; 23 males), patients with brain tumor exhibited significantly reduced glymphatic function (DTI-ALPS index: 2.315 vs. 2.879; P = 0.001) and increased cerebrospinal fluid volume (201.376 cm³ vs. 115.957 cm³; P = 0.001). A negative correlation was observed between tumor volume and the DTI-ALPS index (r: -0.715, P < 0.001), whereas AQP4 expression levels correlated positively with peritumoral brain edema volume (r: 0.989, P < 0.001) and negatively with proton density in peritumoral brain edema areas (ρ: -0.506, P < 0.001).

CONCLUSIONS

Our findings highlight the interplay among tumor-induced compression, glymphatic dysfunction, and altered fluid dynamics, demonstrating the utility of DTI-ALPS and multiparametric MRI in understanding the pathophysiology of tumor-related cerebral edema. These insights provide a radiological foundation for further neuro-oncological investigations into the glymphatic system. See related commentary by Surov and Borggrefe, p. 4813.

Evaluation of Glymphatic System Development in Neonatal Brain via Diffusion Analysis along the Perivascular Space Index

OBJECTIVE

Glymphatic system is a recently discovered macroscopic waste clearance system associated with numerous neurological diseases. However, little is known about glymphatic system development in neonates. We sought to evaluate diffusion along the perivascular space (ALPS) index, a proxy for glymphatic system function, in neonates and investigate its potential associations with maturation, sex, and preterm birth.

METHODS

Diffusion magnetic resonance imaging (MRI) data in 418 neonates, including 92 preterm neonates (57 males) and 326 term neonates (175 males), from the Developing Human Connectome Project were used for evaluating ALPS index. Linear regression modeling was performed to assess group differences in the ALPS index according to preterm birth and sex. Pearson's and partial correlation analysis were performed to assess the association between the ALPS index and gestational age (GA) as well as postmenstrual age (PMA) at MRI. Moderation analysis was performed to assess the moderation effect of preterm birth on the relationship between the ALPS index and PMA.

RESULTS

Compared to term neonates, preterm neonates exhibited lower ALPS indices (p < 0.001). The ALPS index positively correlated with PMA (p = 0.004) and GA (p < 0.001). Preterm birth (p = 0.013) had a significant moderation effect on the relationship between the ALPS index and PMA. Sex had no significant direct effect (p = 0.639) or moderation effect (p = 0.333) on ALPS index.

INTERPRETATION

Glymphatic system development is a dynamic process in neonates, which can be moderated by preterm birth, the ALPS index could serve as a sensitive biomarker for monitoring this process. ANN NEUROL 2024;96:970-980.

The Effects of Vitamin D on Movement and Cognitive Function in Senile Mice After Sevoflurane Anaesthesia

BACKGROUND

Vitamin D (VD) is a neuroactive steroid involved in many brain functions, such as neurotrophic, neuroimmune control and neurotransmission, which affects the growth and function of the brain. The purpose of this study is to explore the effect of VD on motor and cognitive function of aged mice after sevoflurane anesthesia.

METHOD

We established sevoflurane anesthesia model and VD(-) and VD(+) mice model. The VD concentration of mice in each group was determined by enzyme-linked immunosorbent assay (ELISA). An open-field test was used to evaluate the mice's capacity for movement and exploration. A Y-maze test was used to gauge the mice's short-term memory. The primary purpose of the water-maze experiment was to examine mice's long-term spatial memory.

RESULTS

The ELISA results showed that the model was successfully constructed. In the open-field test, VD increased the exercise distance of mice (P < .05). In the Y-maze experiment, VD improved short-term memory impairment in mice (P < .05). In the water-maze test, VD increased the activity time and platform crossing number of mice in the target quadrant. (P < .05).

CONCLUSION

Sevoflurane anesthesia caused cognitive dysfunction in aged mice, including reduced learning ability, memory loss, lower motor and exploratory abilities and depression, and VD deficiency aggravated these impairments. By supplementing with VD, learning ability and long-term memory were enhanced, motor and exploratory abilities were improved, and depression levels were reduced. Anxiety was also improved.

The impact of neuroinflammation on neuronal integrity

Neuroinflammation, characterized by a complex interplay among innate and adaptive immune responses within the central nervous system (CNS), is crucial in responding to infections, injuries, and disease pathologies. However, the dysregulation of the neuroinflammatory response could significantly affect neurons in terms of function and structure, leading to profound health implications. Although tremendous progress has been made in understanding the relationship between neuroinflammatory processes and alterations in neuronal integrity, the specific implications concerning both structure and function have not been extensively covered, with the exception of perspectives on glial activation and neurodegeneration. Thus, this review aims to provide a comprehensive overview of the multifaceted interactions among neurons and key inflammatory players, exploring mechanisms through which inflammation influences neuronal functionality and structural integrity in the CNS. Further, it will discuss how these inflammatory mechanisms lead to impairment in neuronal functions and architecture and highlight the consequences caused by dysregulated neuronal functions, such as cognitive dysfunction and mood disorders. By integrating insights from recent research findings, this review will enhance our understanding of the neuroinflammatory landscape and set the stage for future interventions that could transform current approaches to preserve neuronal integrity and function in CNS-related inflammatory conditions.

Enlarged perivascular spaces in alcohol-related brain damage induced by dyslipidemia

Perivascular spaces (PVSs) as the anatomical basis of the glymphatic system, are increasingly recognized as potential imaging biomarkers of neurological conditions. However, it is not clear whether enlarged PVSs are associated with alcohol-related brain damage (ARBD). We aimed to investigate the effect of long-term alcohol exposure on dyslipidemia and the glymphatic system in ARBD. We found that patients with ARBD exhibited significantly enlargement of PVSs in the frontal cortex and basal ganglia, as well as a notable increased levels of total cholesterol (TC) and triglycerides (TG). The anatomical changes of the glymphatic drainage system mentioned above were positively associated with TC and TG. To further explore whether enlarged PVSs affects the function of the glymphatic system in ARBD, we constructed long alcohol exposure and high fat diet mice models. The mouse model of long alcohol exposure exhibited increased levels of TC and TG, enlarged PVSs, the loss of aquaporin-4 polarity caused by reactive astrocytes and impaired glymphatic drainage function which ultimately caused cognitive deficits, in a similar way as high fat diet leading to impairment in glymphatic drainage. Our study highlights the contribution of dyslipidemia due to long-term alcohol abuse in the impairment of the glymphatic drainage system.

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Astrocyte-Mediated Neuroinflammation in Neurological Conditions

Astrocytes are one of the key glial types of the central nervous system (CNS), accounting for over 20% of total glial cells in the brain. Extensive evidence has established their indispensable functions in the maintenance of CNS homeostasis, as well as their broad involvement in neurological conditions. In particular, astrocytes can participate in various neuroinflammatory processes, e.g., releasing a repertoire of cytokines and chemokines or specific neurotrophic factors, which result in both beneficial and detrimental effects. It has become increasingly clear that such astrocyte-mediated neuroinflammation, together with its complex crosstalk with other glial cells or immune cells, designates neuronal survival and the functional integrity of neurocircuits, thus critically contributing to disease onset and progression. In this review, we focus on the current knowledge of the neuroinflammatory responses of astrocytes, summarizing their common features in neurological conditions. Moreover, we highlight several vital questions for future research that promise novel insights into diagnostic or therapeutic strategies against those debilitating CNS diseases.

Lifetime history of head injury is associated with reduced perivascular space number in acute mild traumatic brain injury

Traumatic brain injury impairs function of the glymphatic system, a perivascular network involved in waste clearance. Enlarged perivascular spaces visible on MRI are an emerging biomarker of glymphatic function. This study characterized enlarged perivascular spaces in acute head injury with 7 T MRI. Healthy controls (n = 8) and patients (n = 11) with mild traumatic brain injury underwent MRI within 7 days of injury and were evaluated for lifetime history of head injury, neurobehavioral symptoms and sleep disturbances. MRI-visible perivascular spaces were quantified and assessed according to published criteria. The number of enlarged perivascular spaces was significantly higher in traumatic brain injury patients than controls (P = 0.015). Among healthy controls, 6/8 scored 'none' or 'mild' on the perivascular space rating scale, while 10/11 patients scored 'moderate', 'frequent' or 'severe'. There was an inverse relationship between perivascular space number and number of lifetime head injuries. Patients with more prior head injuries exhibited fewer enlarged perivascular spaces (P = 0.014). These results indicate that mild head injury results in acute alterations in perivascular space number, and this effect is mediated by previous head injury history. Enlarged perivascular spaces may reflect a glymphatic response that is diminished after multiple head injuries, although this will require further study.

Therapeutic approaches to CNS diseases via the meningeal lymphatic and glymphatic system: prospects and challenges

The brain has traditionally been considered an "immune-privileged" organ lacking a lymphatic system. However, recent studies have challenged this view by identifying the presence of the glymphatic system and meningeal lymphatic vessels (MLVs). These discoveries offer new opportunities for waste clearance and treatment of central nervous system (CNS) diseases. Various strategies have been developed based on these pathways, including modulation of glymphatic system function, enhancement of meningeal lymphatic drainage, and utilization of these routes for drug delivery. Consequently, this review explores the developmental features and physiological roles of the cerebral lymphatic system as well as its significance in various CNS disorders. Notably, strategies for ameliorating CNS diseases have been discussed with a focus on enhancing glymphatic system and MLVs functionality through modulation of physiological factors along with implementing pharmacological and physical treatments. Additionally, emphasis is placed on the potential use of the CNS lymphatic system in drug delivery while envisioning future directions in terms of mechanisms, applications, and translational research.

Correlation between glymphatic dysfunction and cranial defect in severe traumatic brain injury: a retrospective case-control study based on a diffusion tensor image analysis along the perivascular space (DTI-ALPS) investigation

Background

To date, limited research has been conducted on the functionality of the glymphatic system during the recovery phase of severe traumatic brain injury (sTBI). This study aimed to use a diffusion tensor image analysis along the perivascular space (DTI-ALPS) to evaluate glymphatic system function in patients recovering from sTBI who underwent unilateral decompressive craniectomy, and to examine the correlation between the ALPS index and the size of the cranial defect. We hypothesized that assessments would reveal ongoing impairments in glymphatic system function among sTBI patients during the recovery phase.

Methods

A total of 23 patients with a history of sTBI who had previously undergone unilateral decompressive craniectomy at Xiangya Hospital of Central South University from January 2020 to December 2020 were enrolled in the study, along with 33 healthy control (HC) subjects. All the subjects underwent magnetic resonance imaging (MRI) with DTI scans, and the ALPS index was subsequently calculated to assess glymphatic system functionality. Additionally, the circumference and sectional area of the cranial defect were measured for each patient. An analysis of variance (ANOVA) was used to compare the ALPS index values between the sTBI patients and HC subjects, while a Pearson correlation analysis was used to examine the correlation between the ALPS index and cranial defect characteristics.

Results

The ALPS index values of both the craniectomy side (t=-9.08, P<0.001) and non-craniectomy side (t=-5.06, P<0.001) of the sTBI group were significantly lower than those of the HC group. However, no statistically significant differences were observed between the ALPS index values of the craniectomy and non-craniectomy sides. Additionally, no significant differences were observed in the ALPS index values of both the craniectomy and non-craniectomy sides among the early, intermediate, and late recovery phases. In the sTBI patients, a moderately strong negative correlation was found between the circumference of the cranial defect and the ALPS index of the craniectomy side (r=-0.62, P=0.002), and a moderately negative correlation was found between the sectional area of the cranial defect and the ALPS index of the craniectomy side (r=-0.56, P=0.005).

Conclusions

The non-invasive DTI-ALPS technique revealed significantly reduced ALPS index values during the recovery phase of sTBI, indicating persistent impairment in glymphatic system function. A significant negative correlation was found between the ALPS index value of the craniectomy side and the size of the cranial defect. These findings suggest that the ALPS index may serve as a valuable prognostic factor in the recovery phase of sTBI.

Machine Learning-Based Perivascular Space Volumetry in Alzheimer Disease

OBJECTIVES

Impaired perivascular clearance has been suggested as a contributing factor to the pathogenesis of Alzheimer disease (AD). However, it remains unresolved when the anatomy of the perivascular space (PVS) is altered during AD progression. Therefore, this study investigates the association between PVS volume and AD progression in cognitively unimpaired (CU) individuals, both with and without subjective cognitive decline (SCD), and in those clinically diagnosed with mild cognitive impairment (MCI) or mild AD.

MATERIALS AND METHODS

A convolutional neural network was trained using manually corrected, filter-based segmentations (n = 1000) to automatically segment the PVS in the centrum semiovale from interpolated, coronal T2-weighted magnetic resonance imaging scans (n = 894). These scans were sourced from the national German Center for Neurodegenerative Diseases Longitudinal Cognitive Impairment and Dementia Study. Convolutional neural network-based segmentations and those performed by a human rater were compared in terms of segmentation volume, identified PVS clusters, as well as Dice score. The comparison revealed good segmentation quality (Pearson correlation coefficient r = 0.70 with P < 0.0001 for PVS volume, detection rate in cluster analysis = 84.3%, and Dice score = 59.0%). Subsequent multivariate linear regression analysis, adjusted for participants' age, was performed to correlate PVS volume with clinical diagnoses, disease progression, cerebrospinal fluid biomarkers, lifestyle factors, and cognitive function. Cognitive function was assessed using the Mini-Mental State Examination, the Comprehensive Neuropsychological Test Battery, and the Cognitive Subscale of the 13-Item Alzheimer's Disease Assessment Scale.

RESULTS

Multivariate analysis, adjusted for age, revealed that participants with AD and MCI, but not those with SCD, had significantly higher PVS volumes compared with CU participants without SCD ( P = 0.001 for each group). Furthermore, CU participants who developed incident MCI within 4.5 years after the baseline assessment showed significantly higher PVS volumes at baseline compared with those who did not progress to MCI ( P = 0.03). Cognitive function was negatively correlated with PVS volume across all participant groups ( P ≤ 0.005 for each). No significant correlation was found between PVS volume and any of the following parameters: cerebrospinal fluid biomarkers, sleep quality, body mass index, nicotine consumption, or alcohol abuse.

CONCLUSIONS

The very early changes of PVS volume may suggest that alterations in PVS function are involved in the pathophysiology of AD. Overall, the volumetric assessment of centrum semiovale PVS represents a very early imaging biomarker for AD.

Neurological glycogen storage diseases and emerging therapeutics

Glycogen storage diseases (GSDs) comprise a group of inherited metabolic disorders characterized by defects in glycogen metabolism, leading to abnormal glycogen accumulation in multiple tissues, most notably affecting the liver, skeletal muscle, and heart. Recent findings have uncovered the importance of glycogen metabolism in the brain, sustaining a myriad of physiological functions and linking its perturbation to central nervous system (CNS) pathology. This link resulted in classification of neurological-GSDs (n-GSDs), a group of diseases with shared deficits in neurological glycogen metabolism. The n-GSD patients exhibit a spectrum of clinical presentations with common etiology while requiring tailored therapeutic approaches from the traditional GSDs. Recent research has elucidated the genetic and biochemical mechanisms and pathophysiological basis underlying different n-GSDs. Further, the last decade has witnessed some promising developments in novel therapeutic approaches, including enzyme replacement therapy (ERT), substrate reduction therapy (SRT), small molecule drugs, and gene therapy targeting key aspects of glycogen metabolism in specific n-GSDs. This preclinical progress has generated noticeable success in potentially modifying disease course and improving clinical outcomes in patients. Herein, we provide an overview of current perspectives on n-GSDs, emphasizing recent advances in understanding their molecular basis, therapeutic developments, underscore key challenges and the need to deepen our understanding of n-GSDs pathogenesis to develop better therapeutic strategies that could offer improved treatment and sustainable benefits to the patients.