Outflow of cerebrospinal fluid is predominantly through lymphatic vessels and is reduced in aged mice

Meningeal lymphatics-microglia axis regulates synaptic physiology

Meningeal lymphatics serve as an outlet for cerebrospinal fluid, and their dysfunction is associated with various neurodegenerative conditions. Previous studies have demonstrated that dysfunctional meningeal lymphatics evoke behavioral changes, but the neural mechanisms underlying these changes have remained elusive. Here, we show that prolonged impairment of meningeal lymphatics alters the balance of cortical excitatory and inhibitory synaptic inputs, accompanied by deficits in memory tasks. These synaptic and behavioral alterations induced by lymphatic dysfunction are mediated by microglia, leading to increased expression of the interleukin 6 gene (Il6). IL-6 drives inhibitory synapse phenotypes via a combination of trans- and classical IL-6 signaling. Restoring meningeal lymphatic function in aged mice reverses age-associated synaptic and behavioral alterations. Our findings suggest that dysfunctional meningeal lymphatics adversely impact cortical circuitry through an IL-6-dependent mechanism and identify a potential target for treating aging-associated cognitive decline.

Border-associated macrophages as gatekeepers of brain homeostasis and immunity

The brain's border tissues serve as essential hubs for neuroimmune regulation and the trafficking of biomaterials to and from the brain. These complex tissues-including the meninges, perivascular spaces, choroid plexus, and circumventricular organs-balance the brain's need for immune privilege with immune surveillance and blood-brain communication. Macrophages are integral components of these tissues, taking up key strategic positions within the brain's circulatory system. These border-associated macrophages, or "BAMs," are therefore emerging as pivotal for brain homeostasis and disease. BAMs perform trophic functions that help to support border homeostasis but also act as immune sentinels essential for border defense. In this review, we integrate recent findings on BAM origins, cell states, and functions, aiming to provide global insights and perspectives on the complex relationship between these macrophages and their border niche.

Niche-specific therapeutic targeting of myeloid cells in the central nervous system

The central nervous system (CNS) can be subdivided into distinct anatomical and functional compartments, including the parenchyma, perivascular space, leptomeninges, and dura mater, etc. Each compartment hosts distinct immune cell populations, such as monocytes and diverse macrophages, which play critical roles in local tissue homeostasis and regional disease pathogenesis. Advances in single-cell technologies have revealed complex immune cell compositions and functions in these anatomical regions. This review summarizes the latest approaches for modulating myeloid cell subsets in a compartment-specific manner, including cellular strategies such as stem cell therapy, ex vivo gene treatment, bone marrow transplantation, as well as non-cellular strategies like antibodies, small molecules, and viral gene delivery to augment CNS immune responses and improve disease outcomes. We also discuss the challenges and requirements of translating targeting strategies from mice to humans.

Deep cervical lymphaticovenous anastomosis in Alzheimer's disease: A promising frontier or premature enthusiasm?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder marked by β-amyloid accumulation, tau pathology, and impaired metabolic waste clearance. Recent evidence suggests that meningeal lymphatic vessels (MLVs) contribute significantly to the drainage of cerebrospinal and interstitial fluid. Deep cervical lymphaticovenous anastomosis (LVA), a microsurgical technique designed to enhance this drainage, has been proposed as a potential therapeutic strategy for AD. Preliminary findings from exploratory studies in China indicate possible cognitive and biomarker improvements, but current evidence is limited by small sample sizes, non-randomized designs, and methodological variability. Without standardized protocols and rigorous clinical validation, the broader applicability of LVA remains uncertain. Further investigation through multicenter, controlled trials is essential to objectively assessing its safety, efficacy, and clinical relevance in the management of AD.

The glycosaminoglycan chains of perlecan regulate the perivascular fluid transport

BACKGROUND

The perivascular conduct pathway that connects the cerebrospinal fluid spaces with the interstitial fluid in the parenchyma are of importance for solute clearance from the brain. In this pathway, the relatively wide perivascular space (PVS) surrounding the pial arteries provides a low-resistant passage while around the perforating arteries, the solute movement is along the basement membrane (BM), that prevents the free exchange of interstitial fluids and solutes. We hypothesize that this selectivity involves specific components of the vascular BM, which is mainly composed of type IV collagen (Col IV) and laminin networks interconnected by nidogens and heparan sulphate proteoglycans (HSPGs). Perlecan is the major HSPG in the BM that binds to Col IV and laminin via glycosaminoglycan (GAG) chains to form a molecular sieve. GAGs may also provide the charge selectivity required for filtration, and also a scaffold for amyloid-β (Aβ) aggregation. The purpose of this study was the functional characterization of perivascular fluid transport and brain clearance in mice lacking perlecan GAG chains.

METHODS

We generated a novel mouse line (Hspg2∆3∆91) lacking perlecan GAG side chains and investigated perivascular flow and brain clearance in these mice using intravital multiphoton and fluorescence recovery after photobleaching techniques, and functional assays with various tracers. Potentially deleterious effects on brain homeostasis were investigated using transcriptomic, proteomic and immunohistochemical methods. The Hspg2∆3∆91 mice were crossed with a 5xFAD line to examine the importance of GAGs in Aβ aggregation.

RESULTS

We observed a delayed inflow of CSF tracer into the Hspg2∆3∆91 brain with no changes in the clearance of parenchymal injected tracers. Quantification of the Aβ plaques revealed fewer and smaller plaques in the walls of the pial arteries at six months of age, but not in the brain parenchyma. Surprisingly, perlecan GAG deficiency had no severe deleterious effects on brain homeostasis in transcriptomic and proteomic analyses.

CONCLUSIONS

Potential brain clearance mechanisms are dependent on the flow through special ECM structures. BM is mainly known for its barrier function, whereas very little is known about how passage along the perivascular ECM is established. This study shows that the GAG composition of the BM affects the solute dynamics and Aβ deposition in the periarterial space.

Meningeal lymphatic drainage: novel insights into central nervous system disease

In recent years, increasing evidence has suggested that meningeal lymphatic drainage plays a significant role in central nervous system (CNS) diseases. Studies have indicated that CNS diseases and conditions associated with meningeal lymphatic drainage dysfunction include neurodegenerative diseases, stroke, infections, traumatic brain injury, tumors, functional cranial disorders, and hydrocephalus. However, the understanding of the regulatory and damage mechanisms of meningeal lymphatics under physiological and pathological conditions is currently limited. Given the importance of a profound understanding of the interplay between meningeal lymphatic drainage and CNS diseases, this review covers seven key aspects: the development and structure of meningeal lymphatic vessels, methods for observing meningeal lymphatics, the function of meningeal lymphatics, the molecular mechanisms of meningeal lymphatic injury, the relationships between meningeal lymphatic vessels and CNS diseases, potential regulatory mechanisms of meningeal lymphatics, and conclusions and outstanding questions. We will explore the relationship between the development, structure, and function of meningeal lymphatics, review current methods for observing meningeal lymphatic vessels in both animal models and humans, and identify unresolved key points in meningeal lymphatic research. The aim of this review is to provide new directions for future research and therapeutic strategies targeting meningeal lymphatics by critically analyzing recent advancements in the field, identifying gaps in current knowledge, and proposing innovative approaches to address these gaps.

Cerebral small vessel disease: The impact of glymphopathy and sleep disorders

The glymphatic system, a vital brain perivascular network for waste clearance, hinges on the functionality of the aquaporin 4 (AQP4) water channel. Alarmingly, AQP4 single nucleotide polymorphisms (SNPs) are linked to impaired glymphatic clearance, or glymphopathy, which contributes to sleep disturbances and various age-related neurodegenerative diseases. Despite the critical role of glymphopathy and sleep disturbances in cerebral small vessel disease (CSVD) - a silent precursor to age-related neurodegenerative disorders - their interplay remains underexplored. CSVD is a major cause of stroke and dementia, yet its pathogenesis is not fully understood. Emerging evidence implicates glymphopathy and sleep disorders as pivotal factors in age-related CSVD, exacerbating the condition by hindering waste removal and compromising blood-brain barrier (BBB) integrity. Advanced imaging techniques promise to enhance diagnosis and monitoring, while lifestyle modifications and personalised medicine present promising treatment avenues. This narrative review underscores the need for a multidisciplinary approach to understanding glymphopathy and sleep disorders in CSVD. By exploring their roles, emphasising the necessity for longitudinal studies, and discussing potential therapeutic interventions, this paper aims to pave the way for new research and therapeutic directions in CSVD management.

Redefining CNS immune privilege

The central nervous system (CNS) has a unique relationship with the immune system, referred to as immune privilege. For many years it was thought that immune privilege was due to isolation of the CNS from the immune system, but recent findings have shown that this theory is flawed and that there is substantial neuroimmune communication, particularly at border sites that encase the CNS. These border sites include perivascular and subarachnoid spaces, the choroid plexus, the meninges and the vasculature, including the recently discovered meningeal lymphatic vessels. CNS border tissues have extensive interaction with the cerebrospinal fluid, which acts as an immune mediator, allowing the immune system at the CNS borders to respond to challenges within the CNS parenchyma. Together, CNS border tissues enable immune surveillance and protection against infections while preventing inflammatory damage to the parenchyma. A better understanding of the mechanisms of immune privilege as an accord, as opposed to isolation, between the two systems would help us obtain effective immunotherapies for neurological diseases.

Emerging Roles of Meningeal Lymphatic Vessels in Ischemic Stroke

This review highlights the emerging relevance of meningeal lymphatic vessels (MLVs) in the context of ischemic stroke, challenging the conventional view of a privileged immunological central nervous system. MLVs facilitate immunological surveillance by modulating the entry of peripheral immune cells into the meningeal compartment, a process not impeded by the blood-brain barrier. In ischemic stroke, these vessels play a crucial role in the neuroinflammatory cascade, contributing to immune responses by draining antigens and signals to cervical lymph nodes. Their involvement extends to potential contributions to resolving ischemia-induced cerebral edema, impacting fluid homeostasis. The dynamic interaction among MLVs, neuroinflammation, and fluid dynamics suggests promising therapeutic approaches. Targeting these vessels for immunomodulation, fluid drainage, and preserving blood-brain barrier integrity emerges as an innovative approach to improve ischemic stroke outcomes. However, successful clinical translation awaits further exploration of the therapeutic potential of these vessels. The multifaceted contributions of MLVs provide a compelling rationale for ongoing research, aiming to fully harness their therapeutic impact in ischemic stroke management.

Age-related meningeal extracellular matrix remodeling compromises CNS lymphatic function

Efficient clearance of central nervous system (CNS) waste proteins and appropriate immune surveillance is essential for brain health. These processes are facilitated by lymphatic networks present in the meninges that drain cerebrospinal fluid (CSF). Age-related impairments to meningeal lymphatic drainage contribute to CNS waste accumulation and immune dysfunction, yet the underlying mechanisms remain poorly understood. Here, we identify extracellular matrix (ECM) remodeling in the aged dura as a key driver of CSF clearance deficits, demonstrating that peri-lymphatic collagen accumulation disrupts lymphatic function. Exploring immune-derived factors contributing to this ECM remodeling, we identify transforming growth factor beta 1 (TGFβ1) as a major regulator using primary human dural fibroblasts. Using a novel mouse model with constitutively active TGFβ receptor 1 (TGFβR1) signaling in dural fibroblasts, we show that excessive peri-lymphatic collagen deposition impairs meningeal lymphatic drainage and alters meningeal immunity. Mechanistically, we reveal that ECM-associated matrix stiffness disrupts lymphatic junction integrity and impairs lymphangiogenesis in human lymphatic endothelial cells. These findings establish dural immune cell and fibroblast-mediated ECM remodeling as a critical regulator of CSF clearance and highlight it as a potential therapeutic target for restoring brain waste clearance in aging.

Vascular Contribution to Cerebral Waste Clearance Affected by Aging or Diabetes

Background: The brain's vascular system has recently been shown to provide an important efflux pathway for cerebral waste clearance (CWC). However, little is known about the influence of aging or diabetes on the CWC. The aim of the current study is to investigate the vasculature contribution to CWC under aging and diabetic conditions. Methods: Male Wistar rats under aging and diabetic conditions were evaluated using dynamic intra-cisterna superparamagnetic iron oxide-enhanced susceptibility-weighted imaging (SPIO-SWI). Theoretical analysis of the expected signal intensity using SPIO-SWI was compared with the corresponding dynamic in vivo images. Quantitative susceptibility mapping (QSM) was used to evaluate the iron-based tracer concentration in the venous system. Results: Our data demonstrated that the theoretical analysis predicted the dynamic changes in the signal intensity after SPIO infusion. The distinct hyperintense signals due to the lower concentration of the SPIO over time in cerebrospinal fluid (CSF) and meningeal lymphatic (ML) vessels likely represented the CWC through various efflux pathways, including cerebral vascular and ML vessels. The QSM analysis further revealed reduced CWC from the vasculature in both the aged and diabetic groups compared to the younger group. Conclusions: Our results demonstrated that SPIO-SWI can quantitatively evaluate the CWC efflux contributions from cerebral vascular vessels under aging or diabetic conditions.

Brain alterations and neurologic disorder progression induced by lymphatic dysfunction in the head and neck region

The potential negative impact of lymphatic dysfunction caused by head and neck cancer treatment remains underexplored. Emerging evidence suggests that waste clearance and fluidic balance in the brain are connected to the peripheral lymphatic system in the head and neck region, implying that lymphatic injury in this area could contribute to brain damage. This study aimed to investigate the pathological alterations in the brain induced by peripheral lymphatic dysfunction in the head and neck region using the lymphatic obstruction animal model. An animal model underwent cervical lymph node dissection combined with radiation therapy to simulate the condition with the peripheral lymphatic dysfunction in the head and neck region after cancer treatment. Lymphatic drainage impairment in the head and neck region was associated with significant swelling, disrupted lymphatic drainage, and immune cell infiltration in the white matter. The imaging techniques revealed ventricular enlargement and increased brain water content caused by fluid imbalance leading to significant structural alterations in the brain. Histopathological analysis demonstrated structural brain alterations similar to that of hydrocephalus and cerebral edema, while rotarod tests showed a substantial decline in motor performance. These findings highlight the impact of peripheral lymphatic dysfunction on brain integrity and function. This study provides evidence that brain damage in head and neck cancer patients may be influenced not only by chemotherapy or radiotherapy but also by lymphatic dysfunction caused by surgical interventions. Lymphatic injury in the head and neck region emerges as a potential risk factor for brain damage, underscoring the need for further research into preventive and therapeutic strategies.

CSF outflow from the human spinal canal: preliminary results from an anatomical specimen-based model

BACKGROUND

Recent discoveries focused on the role of cerebrospinal fluid (CSF) in metabolite clearance have initiated intense research on CSF circulation and outflow pathways. These studies have focused on the cranial subarachnoid space, whereas spinal outflow has been relatively less investigated. Moreover, most studies have been performed on rodent models, which allows thorough anatomical investigation, whereas evidence from humans has been generated primarily from in vivo neuroimaging techniques. In this paper, we introduce an anatomical specimen-based preparation for studying spinal CSF outflow in humans and present preliminary results from our initial studies.

METHODS

Unfixed anatomical specimens of the thoracolumbar spinal dural sac along with the spinal nerves were obtained from cadavers. Experiments involving low-pressure infusion of contrast medium (barium sulfate) into the spinal subarachnoid space with video recording of contrast spread were performed. After fixation, contrast agent distribution of the samples was assessed via histological and radiological analyses including 3D X-ray microscopy.

RESULTS

Five human anatomical specimens of the dural sac were assessed. Filling of spaces extending to the spinal dura (arachnoid granulations, cuffs around the proximal spinal nerves) and unrestricted outflow from postganglionic spinal nerve cross-sections were both observed. Histological and radiological results confirmed the presence of contrast around the spinal nerve fascicles under the perineurium, in the arachnoid granulations and within the lumens of vessels within the dura or in the surrounding epidural adipose tissue.

CONCLUSIONS

The described model makes it possible to examine CSF outflow routes from the human spinal subarachnoid space. The methodology is reproducible, feasible, and does not require specialized equipment. Preliminary results have revealed two potential CSF outflow pathways that have been previously observed in animal models: along the spinal nerves and to the epidural tissue and vessels.

Cerebrospinal fluid flow within ventricles and subarachnoid space evaluated by velocity selective spin labeling MRI

This study aims to evaluate cerebrospinal fluid (CSF) flow dynamics within ventricles, and the subarachnoid space (SAS) using the velocity selective spin labeling (VSSL) MRI method with Fourier-transform-based velocity selective inversion preparation. The study included healthy volunteers who underwent MRI scanning with specific VSSL parameters optimized for CSF flow quantification. The VSSL sequence was calibrated against phase-contrast MRI (PC-MRI) to ensure accurate flow velocity measurements. The CSF flow patterns observed in the ventricles were consistent with those obtained using 3D amplified MRI and other advanced MRI techniques, verifying the reliability of the VSSL method. The VSSL method successfully measured CSF flow in the SAS along major arteries, including the middle cerebral artery (MCA), anterior cerebral artery (ACA), and posterior cerebral artery (PCA), with an average flow velocity of 0.339±0.117cm/s. The diffusion component was well suppressed by flow-compensated gradients, enabling comprehensive mapping of the rapid CSF flow pattern in the SAS system and ventricles. The flow pattern in the SAS system closely resembles the recently discovered perivascular subarachnoid space (PVSAS) system. CSF flow around the MCA, PCA, and ACA arteries in the SAS exhibited a weak orientation dependency. CSF flow in the ventricles was also measured, with an average flow velocity of0.309±0.116cm/s, and the highest velocity observed along the superior-inferior direction. This study underscores the potential of VSSL MRI as a non-invasive tool for investigating CSF dynamics in both SAS and ventricles.

Exercise-Induced Cardiac Lymphatic Remodeling Mitigates Inflammation in the Aging Heart

The lymphatic vasculature plays essential roles in fluid balance, immunity, and lipid transport. Chronic, low-grade inflammation in peripheral tissues develops when lymphatic structure or function is impaired, as observed during aging. While aging has been associated with a broad range of heart pathophysiology, its effect on cardiac lymphatic vasculature has not been characterized. Here, we analyzed cardiac lymphatics in aged 20-month-old mice versus young 2-month-old mice. Aged hearts showed reduced lymphatic vascular density, more dilated vessels, and increased inflammation and fibrosis in peri-lymphatic zones. As exercise has shown benefits in several different models of age-related heart disease, we further investigated the effects of aerobic training on cardiac lymphatics. Eight weeks of voluntary wheel running attenuated age-associated adverse remodeling of the cardiac lymphatics, including reversing their dilation, increasing lymph vessel density and branching, and reducing perilymphatic inflammation and fibrosis. Intravital lymphangiography demonstrated improved cardiac lymphatic flow after exercise training. Our findings illustrate that aging leads to cardiac lymphatic dysfunction, and that exercise can improve lymphatic health in aged animals.

A review of cerebrospinal fluid circulation with respect to Chiari-like malformation and syringomyelia in brachycephalic dogs

Cerebrospinal fluid (CSF) plays a crucial role in maintaining brain homeostasis by facilitating the clearance of metabolic waste and regulating intracranial pressure. Dysregulation of CSF flow can lead to conditions like syringomyelia, and hydrocephalus. This review details the anatomy of CSF flow, examining its contribution to waste clearance within the brain and spinal cord. The review integrates data from human, canine, and other mammalian studies, with a particular focus on brachycephalic dogs. Certain dog breeds exhibit a high prevalence of CSF-related conditions due to artificial selection for neotenous traits, making them valuable models for studying analogous human conditions, such as Chiari-like malformation and syringomyelia associated with craniosynostosis. This review discusses the anatomical features specific to some brachycephalic breeds and the impact of skull and cranial cervical conformation on CSF flow patterns, providing insights into the pathophysiology and potential modelling approaches for these conditions.

Lymphatic transport in anti-tumor immunity and metastasis

Although lymphatic vessels (LVs) are present in many tumors, their importance in cancer has long been underestimated. In contrast to the well-studied tumor-associated blood vessels, LVs were previously considered to function as passive conduits for tumor metastasis. However, emerging evidence over the last two decades has shed light on their critical role in locally shaping the tumor microenvironment (TME). Here we review the involvement of LVs in tumor progression, metastasis, and modulation of anti-tumor immune response.

A Proposed Role for Lymphatic Supermicrosurgery in the Management of Alzheimer's Disease: A Primer for Reconstructive Microsurgeons

The relatively recent discovery of a novel lymphatic system within the brain meninges has spurred interest in how waste products generated by neurons and glial cells-including proteins associated with Alzheimer's disease (AD) pathology such as amyloid beta (Aβ) and tau-are disposed of. Evidence is building that suggests disease progression in AD and other cognitive impairments could be explained by dysfunction in the brain's lymphatic system or obstruction of drainage. An interesting implication of this hypothesis is that, by relieving the obstruction of flow, lymphatic reconstruction along the drainage pathway could serve as a potential novel treatment. Should this concept prove true, it could represent a surgical solution to a problem for which only medical solutions have thus far been considered. This study is meant to serve as a primer for reconstructive microsurgeons, introducing the topic and current hypotheses about the potential role of lymphatic drainage in AD. A preview of current research evaluating the feasibility of lymphatic reconstruction as a surgical approach to improving Aβ clearance is provided, with the aim of inspiring others to design robust preclinical and clinical investigations into this intriguing hypothesis.

Impact of Subarachnoid Hemorrhage on Human Glymphatic Function: A Time-Evolution Magnetic Resonance Imaging Study

BACKGROUND

Subarachnoid hemorrhage (SAH) is associated with significant mortality and morbidity. The impact of SAH on human glymphatic function remains unknown.

METHODS

This prospective, controlled study investigated whether human glymphatic function is altered after SAH, how it differs over time, and possible underlying mechanisms. Glymphatic enrichment was examined by intrathecal contrast-enhanced magnetic resonance imaging (MRI, glymphatic MRI), utilizing the MRI contrast agent gadobutrol (Gadovist, Bayer AG, GE; 0.50 mmol) as a cerebrospinal fluid (CSF) tracer. The distribution of the tracer in the brain and the subarachnoid and ventricular CSF spaces was assessed using standardized multi-phase MRI T1 sequences, and between-group differences in percentage change of standardized T1 signal unit ratios over time were analyzed by linear mixed models.

RESULTS

The study comprised 27 patients with SAH (19 female/8 male; 59.3±10.2 years) who were examined <3 months (n=5), 3 to 6 months (n=10), 6 to 12 months (n=5), or >12 months (n=7) after bleed. A sex- and age-matched control group of 22 individuals (15 female/7 male; 55.5±10.5 years) underwent the same glymphatic MRI protocol but had no neurological or CSF disease. The patients with SAH showed a marked impairment of glymphatic enrichment throughout the brain (particularly addressing the cerebral cortex and subcortical white matter), especially after 24 hours. The glymphatic impairment was accompanied by redistribution of CSF tracer from subarachnoid spaces toward ventricles. These alterations were most pronounced after 3 to 6 months and less after 12 months, though with interindividual variation. CSF tracer transport within perivascular subarachnoid spaces was impaired and coincided with impaired glymphatic enrichment.

CONCLUSIONS

Human glymphatic function is severely impaired by SAH, particularly shortly after the event. Glymphatic failure is associated with redistribution of CSF from subarachnoid spaces toward ventricles. SAH-related impairment of fluid transport within perivascular subarachnoid spaces may contribute to reduced glymphatic influx. Since patient groups are small, care should be made when concluding about the impact of time on glymphatic function.

Spaceflight Associated Neuro-ocular Syndrome (SANS) and its countermeasures

Astronauts can develop a distinct collection of neuro-ophthalmic findings during long duration spaceflight, collectively known as Spaceflight Associated Neuro-ocular Syndrome (SANS). These clinical characteristics include optic disc edema, hyperopic refractive shifts, globe flattening, and chorioretinal folds, which may pose a health risk for future space exploration. Obtaining knowledge of SANS and countermeasures for its prevention is crucial for upcoming crewed space missions and warrants a multidisciplinary approach. This review examines the potential causes and countermeasures of SANS, including space anticipation glasses, lower body negative pressure, venoconstrictive thigh cuffs, impedance threshold devices, translaminar pressure gradient modulation, centrifugation, artificial gravity, pharmaceuticals, and precision nutritional supplementation. This paper highlights future research directions for understanding the genetic, anthropometric, behavioral, and environmental susceptibilities to SANS as well as how to use terrestrial analogs for testing future mitigation strategies.

Hourly Variations in Glymphatic Function Based on MRI Scan Times in Cognitively Normal Individuals

RATIONALE AND OBJECTIVES

This study evaluated glymphatic function changes according to MRI scan time over a 24-hour cycle, using diffusion tensor image analysis along the perivascular space (DTI-ALPS) to assess interstitial fluid dynamics.

MATERIAL AND METHODS

This single-center retrospective cohort study included cognitively normal participants between January and August 2023. Participants were grouped by MRI scan time: dawn, early morning, daytime, and evening/night. Glymphatic function was assessed via the ALPS index calculated from DTI. ALPS index values were compared among groups using one-way ANOVA with post hoc pairwise independent t-tests. Multiple linear regression analysis adjusted for age, sex, and mini-mental state examination scores was used to compare daytime ALPS index with other groups. Paired t-tests assessed ALPS index changes in participants with follow-up MRIs.

RESULTS

Among 539 participants (age: 70 ± 10 years, 41.4% male), the dawn group had the highest mean ALPS index, followed by early morning, evening/night, and daytime groups (P =0.024). Daytime ALPS index was significantly lower than dawn (P =0.0036) and early morning (P =0.018). Multiple linear regression confirmed lower daytime ALPS index, with the dawn group showing the largest difference (0.067, 95% CI: 0.025-0.108; P =0.002). No significant difference was observed in ALPS index for follow-up scans from dawn or evening/night to daytime (P =0.353).

CONCLUSION

Glymphatic function varies diurnally, with lower values during daytime. These findings emphasize the importance of circadian timing in evaluating glymphatic function using DTI-ALPS. Further studies are needed to explore intra-individual glymphatic variations.

Dual role of vascular endothelial growth factor-C in post-stroke recovery

Cerebrospinal fluid (CSF), antigens, and antigen-presenting cells drain from the central nervous system (CNS) into lymphatic vessels near the cribriform plate and dura, yet the role of these vessels during stroke is unclear. Using a mouse model of ischemic stroke, transient middle cerebral artery occlusion (tMCAO), we demonstrate stroke-induced lymphangiogenesis near the cribriform plate, peaking at day 7 and regressing by day 14. Lymphangiogenesis is restricted to the cribriform plate and deep cervical lymph nodes and is regulated by VEGF-C/VEGFR-3 signaling. The use of a VEGFR-3 inhibitor prevented lymphangiogenesis and led to improved stroke outcomes at earlier time points, with no effects at later time points. VEGF-C delivery after tMCAO did not further increase post-stroke lymphangiogenesis, but instead induced larger brain infarcts. Our data support the damaging role of VEGF-C acutely and a pro-angiogenic role chronically. This nuanced understanding of VEGFR-3 and VEGF-C in stroke pathology advises caution regarding therapeutic VEGF-C use in stroke.

Glymphatic function decline as a mediator of core memory-related brain structures atrophy in aging

Background and Objectives

This study aimed to elucidate the role of the glymphatic system-a crucial pathway for clearing waste in the brain-in the aging process and its contribution to cognitive decline. We specifically focused on the diffusion tensor imaging analysis along the perivascular space (ALPS) index as a noninvasive biomarker of glymphatic function.

Methods

Data were drawn from the Alzheimers Disease Neuroimaging Initiative (ADNI) database and a separate validation cohort to analyze the ALPS index in cognitively normal older adults. The relationships among the ALPS index, brain morphometry, and memory performance were examined.

Results

As a biomarker of glymphatic function, the ALPS index appeared to decline with age in both cohorts. According to the brain morphology analysis, the ALPS index was positively correlated with the thickness of the left entorhinal cortex (r = 0.258, P false discovery rate (FDR) = 2.96 × 10-4), and it played a mediating role between aging and left entorhinal cortex thinning. The independent cohort further validated the correlation between the ALPS index and the left entorhinal cortex thickness (r = 0.414, P FDR = 0.042). Additionally, in both the primary and validation cohorts, the ALPS index played a significant mediating role in the relationship between age and durable or delayed memory decline.

Conclusion

This study highlights the ALPS index as a promising biomarker for glymphatic function and links it to atrophy of the core memory brain regions during aging. Furthermore, these results suggest that targeting glymphatic dysfunction could represent a novel therapeutic approach to mitigate age-related memory decline.

The optic nerve in spaceflight: novel concepts in the pathogenesis of optic disc edema in microgravity

PURPOSE OF REVIEW

Spaceflight-associated neuro-ocular syndrome (SANS) encompasses a unique constellation of neuro-ocular findings in astronauts, including optic disc edema (ODE), globe flattening, chorioretinal folds, and hyperopic refractive shift. Although there are numerous neuro-ocular findings in SANS, the purpose of this review is to describe the novel, emerging concepts of the pathogenesis for the ODE specifically in SANS.

RECENT FINDINGS

While the initial hypotheses on the pathogenesis of ODE in SANS focused on possible elevated intracranial pressures (i.e., papilledema), the most prominent current hypothesis is microgravity-induced cephalad fluid shift. More recent studies however suggest that the pathogenesis of the ODE in SANS is likely multifactorial including possible underlying metabolic and genetic components.

SUMMARY

We review the literature on ODE in SANS including recent work integrating the complex physiologic interactions of microgravity-induced disruption in intracerebral and intraocular fluid dynamics, vascular congestion, cellular stress responses, and genetic predisposition. We believe that the development of ODE in SANS is likely multifactorial in origin, and further understanding of the mechanical, cellular, metabolic, and genetic components is of utmost importance to develop future countermeasures in preparation for possible future crewed missions to the moon, the asteroid belt, and Mars.

The Brain Toxin Cleansing of Sleep Achieved During Wakefulness

A primary purpose of sleep for humans is to remove toxins and metabolic wastes from the brain (e.g., Aβ, tau, lactate) that would otherwise build up and compromise brain functionality. There are currently no drugs or devices that have been clinically shown in humans to enhance brain toxin removal, either during sleep or wakefulness. This perspective article focuses on a recently (re)discovered major route of toxin drainage from the human brain through meningeal lymphatic vessels (mLVs) and the primary enhancer of their flow-the cytokine Vascular Endothelial Growth Factor (VEGF). The purpose of this perspective article is to present pre-clinical and clinical evidence relevant to a new bioengineered technology (Transcranial Radiofrequency Treatment; TRFT) that appears to enhance mLV flow to increase brain toxin cleansing in humans during wakefulness. In being both safe and non-invasive, TRFT is administered in-home, presently through a device called "MemorEM". Two months of daily TRFT during wakefulness increased the typically low plasma/brain levels of VEGF in Alzheimer's Disease (AD) subjects, which was associated with increased Aβ and tau toxin removal from their brains during wakefulness-ostensibly through VEGF-increased mLV flow. Even irrespective of baseline VEGF levels, brain toxin cleansing was increased by TRFT in AD subjects, who also experienced a notable reversal of their cognitive impairment after TRFT. Additional clinical studies are nonetheless required to firmly establish TRFT's brain cleansing abilities during wakefulness. In performing a major duty of sleep, TRFT during wakefulness is proposed as a viable intervention to counter the decline in nighttime brain toxin cleansing that occurs with aging and in multiple brain diseases, most notably Alzheimer's Disease. The implications of TRFT for insomnia and for sleep deprivation are also discussed, as is the potential for TRFT to extend healthy human longevity.

Near-Infrared Imaging of Glymphatic Clearance in a Pre-Clinical Model of Repetitive Closed Head Traumatic Brain Injury

Traumatic brain injury (TBI) is a major health disorder for which there are few treatments. The glymphatic system is the brain's inbuilt lymphatic-like system that is thought to be responsible for clearing waste products from the brain to the lymph nodes. Although there is evidence that glymphatic drainage is crucial for brain homeostasis, its role in TBI pathogenesis remains elusive. Here, we investigated how glymphatic clearance is altered following TBI in rats using real-time non-invasive imaging. Twenty-four hours following repetitive closed-head TBI or sham conditions, we injected infrared dye intraventricularly and used near-infrared (NIR) imaging to quantify signal intensity, intensity over time, and appearance time of NIR dye in different brain regions. TBI yielded a lower NIR signal and lower rate of NIR dye change in the lateral ventricle and surrounding parietal cortex compared with sham conditions, indicating reduced cerebrospinal fluid perfusion. NIR dye appearance took significantly longer to reach the anterior regions of the brain, while perfusion to the posterior of the brain was faster in TBI compared with sham animals. Aquaporin-4 (AQP4) expression was reduced 24 h after TBI across all cortical regions examined in the posterior of the brain and in the ventral cortex at all coronal levels, suggesting a complex relationship between AQP4 and glymph function. Furthermore, NIR imaging revealed that NIR dye was detectable in the cervical lymph nodes (CLNs) of sham animals but not in TBI animals, yet there was evidence of blood accumulation in the CLNs of TBI animals, suggesting that TBI-related extravascular blood is removed through the glymph system. These data indicate that TBI disrupts normal brain efflux kinetics and reduces glymphatic drainage to the CLNs, demonstrating that restoring glymphatic function may be a promising therapeutic target.

The pathobiology of neurovascular aging

As global life expectancy increases, age-related brain diseases such as stroke and dementia have become leading causes of death and disability. The aging of the neurovasculature is a critical determinant of brain aging and disease risk. Neurovascular cells are particularly vulnerable to aging, which induces significant structural and functional changes in arterial, venous, and lymphatic vessels. Consequently, neurovascular aging impairs oxygen and glucose delivery to active brain regions, disrupts endothelial transport mechanisms essential for blood-brain exchange, compromises proteostasis by reducing the clearance of potentially toxic proteins, weakens immune surveillance and privilege, and deprives the brain of key growth factors required for repair and renewal. In this review, we examine the effects of neurovascular aging on brain function and its role in stroke, vascular cognitive impairment, and Alzheimer's disease. Finally, we discuss key unanswered questions that must be addressed to develop neurovascular strategies aimed at promoting healthy brain aging.

Tertiary Lymphoid Structures in Central Nervous System Disorders

The central nervous system (CNS) constitutes a tightly regulated milieu, where immune responses are strictly controlled to prevent neurological damage. This poses considerable challenges to the therapeutic management of CNS pathologies, such as autoimmune disorders and cancer. Tertiary lymphoid structures (TLS) are ectopic, lymph node-like structures containing B- and T-cells, often associated with chronic inflammation or cancer, which have been shown to be detrimental in autoimmunity but beneficial in cancer. In-depth studies of TLS induction in CNS disorders, as well as their precise role in regulating adaptive immune responses in this context, will be paramount to the development of novel TLS-targeting therapies. In the present chapter, we review the anatomical and physiological peculiarities shaping TLS formation in the CNS, their relevance in autoimmunity and cancer, as well as their implications for the development of novel therapeutic modalities for these patients.

Angiotensin-converting enzyme inhibitors: a therapeutic option for controlling blood pressure associated with delayed cognitive processing speed

Antihypertensive treatment (AT) is essential for preventing hypertension-related cognitive decline. The goals of this observational study were to compare cognitive performance (CP) between non-hypertensive (NH) volunteers and hypertensive patients and to evaluate the correlation between CP and antihypertensive drugs (AHD). Three groups were constituted: NH (n = 30) [group 1], hypertensive with systolic blood pressure (SBP) < 140 mmHg and diastolic blood pressure (DBP) < 90 mmHg (n = 54) [group 2] and hypertensive with SBP ≥ 140 or DBP ≥ 90 (n = 31) [group 3]. To analyze the cognitive domains, a neuropsychological battery was applied and the raw performance values in these tests were transformed into z-scores. The domain was considered impaired if it presented a z-score below -1.5 SD. Compared to group 1, both groups of hypertensive were older (51 [ ± 12] years) and showed a worse CP in episodic memory (p = 0.014), language (p = 0.003) and processing speed (PS) [p = 0.05]. Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB) were the most used AHD (46.3%, p = 0.01 [group 2] and 64.5%, p = 0.005 [group 3]) and showed correlations with PS. Linear regression models revealed a negative association of PS with the use of ACEi (β = -0.230, p = 0.004), but not with the use of ARB (β = 0.208, p = 0.008). The effect of AT on cognition appears to go beyond the search for lower blood pressure targets and also includes the mechanism of action of AHD on the brain, so that additional benefits may possibly be achieved with simple adaptations in the treatment regimen, particularly in patients without clinically manifest cognitive impairment.

Multifaceted role of thrombin in subarachnoid hemorrhage: Focusing on cerebrospinal fluid circulation disorder

Subarachnoid hemorrhage (SAH) is a severe neurological condition characterized by high morbidity and mortality. The unfavorable prognosis of SAH is closely associated with early brain injury (EBI) and delayed cerebral ischemia (DCI), wherein thrombin plays a role as part of the secondary injury components following hemorrhage in these two pathological processes. Additionally, thrombin contributes to disruptions in the circulation of cerebrospinal fluid (CSF), thereby giving rise to a spectrum of sequelae following SAH, including cerebral edema, hydrocephalus, cognitive impairments, and depressive symptoms. This review aims to provide a comprehensive understanding of the pathological role of thrombin in EBI, DCI, and CSF circulation following SAH, with a specific focus on its impact on the glymphatic-meningeal lymphatic system-a crucial mechanism for waste clearance and neurohomeostatic regulation. Additionally, this review offers an overview of current pharmacological interventions and treatment modalities targeting pathogenic mechanisms, aiming to mitigate brain injury and promote neurological recovery post-SAH.

Voluntary locomotion induces an early and remote hemodynamic decrease in the large cerebral veins

Significance

Behavior regulates dural and cerebral vessels, with spontaneous locomotion inducing dural vessel constriction and increasing stimulus-evoked cerebral hemodynamic responses. It is vital to investigate the function of different vascular network components, surrounding and within the brain, to better understand the role of the neurovascular unit in health and neurodegeneration.

Aim

We characterized locomotion-induced hemodynamic responses across vascular compartments of the whisker barrel cortex: artery, vein, parenchyma, draining, and meningeal vein.

Approach

Using 2D-OIS, hemodynamic responses during locomotion were recorded in 9- to 12-month-old awake mice: wild-type, Alzheimer's disease (AD), atherosclerosis, or mixed (atherosclerosis/AD) models. Within the somatosensory cortex, responses were taken from pial vessels inside the whisker barrel region [(WBR): "whisker artery" and "whisker vein"], a large vein from the sagittal sinus adjacent to the WBR (draining vein), and meningeal vessels from the dura mater (which do not penetrate cortical tissue).

Results

We demonstrate that locomotion evokes an initial decrease in total hemoglobin (HbT) within the draining vein before the increase in HbT within WBR vessels. The locomotion event size influences the magnitude of the HbT increase in the pial vessels of the WBR but not of the early HbT decrease within the draining veins. Following locomotion onset, an early HbT decrease was also observed in the overlying meningeal vessels, which unlike within the cortex did not go on to exceed baseline HbT levels during the remainder of the locomotion response. We show that locomotion-induced hemodynamic responses are altered in disease in the draining vein and whisker artery, suggesting this could be an important neurodegeneration biomarker.

Conclusions

This initial reduction in HbT within the draining and meningeal veins potentially serves as a "space-saving" mechanism, allowing for large increases in cortical HbT associated with locomotion. Given this mechanism is impacted by disease, it may provide an important target for vascular-based therapeutic interventions.

Association of Glymphatic and White Matter Impairment With the Postoperative Outcome of Pediatric Hydrocephalus

BACKGROUND AND OBJECTIVES

Assessment of postoperative outcomes on pediatric hydrocephalus is critical for adjusting treatment strategies. The aim of this work was to investigate the ability of MRI metrics to predict postoperative outcomes.

METHODS

A total of 55 children with hydrocephalus who underwent MRI and ventriculoperitoneal shunt surgery were prospectively enrolled. MRI was also performed at 6 months postoperatively in 33 of the 55 children. A total of 92 controls matched for age and sex were enrolled and divided into preoperative and postoperative control groups. We calculated the diffusion tensor imaging along the perivascular space (DTI-ALPS) index, Evans index, and diffusion tensor imaging metrics. The ability of various metrics to predict postoperative outcomes was assessed using receiver operating characteristic curve analysis.

RESULTS

The DTI-ALPS index was significantly lower in patients with hydrocephalus than in controls. The abnormal DTI-ALPS index trended toward the normal range after surgery. Patients with lower preoperative DTI-ALPS index, lower fractional anisotropy (FA), and higher radial diffusivity in association fibers had less favorable short-term outcomes. Patients with worse long-term outcomes had lower postoperative DTI-ALPS index, higher postoperative Evans index, and lower FA and higher radial diffusivity in association fibers. Predictive performance was better when the DTI-ALPS index and FA in association fibers were used in combination than when either of these metrics was used alone.

CONCLUSION

The DTI-ALPS index and FA in association fibers provided complementary information for prognostic assessment after the ventriculoperitoneal shunt surgery on pediatric hydrocephalus. A combination of DTI-ALPS index and FA would improve our ability to predict postoperative outcomes in these patients.

Neuroinflammatory pathways and potential therapeutic targets in neonatal post-hemorrhagic hydrocephalus

BACKGROUND

Post-hemorrhagic hydrocephalus (PHH) is a severe complication in premature infants following intraventricular hemorrhage (IVH). It is characterized by abnormal cerebrospinal fluid (CSF) accumulation, disrupted CSF dynamics, and elevated intracranial pressure (ICP), leading to significant neurological impairments.

OBJECTIVE

This review provides an overview of recent molecular insights into the pathophysiology of PHH and evaluates emerging therapeutic approaches aimed at addressing its underlying mechanisms.

METHODS

Recent studies were reviewed, focusing on molecular and cellular mechanisms implicated in PHH, including neuroinflammatory pathways, immune mediators, and regulatory genes. The potential of advanced technologies such as whole genome/exome sequencing, proteomics, epigenetics, and single-cell transcriptomics to identify key molecular targets was also analyzed.

RESULTS

PHH has been strongly linked to neuroinflammatory processes triggered by the degradation of blood byproducts. These processes involve cytokines, chemokines, the complement system, and other immune mediators, as well as regulatory genes and epigenetic mechanisms. Current treatments, primarily surgical CSF diversion, do not address the underlying molecular pathology. Emerging therapies, such as mesenchymal stem cell-based interventions, show promise in modulating immune responses and mitigating neurological damage. However, concerns about the safety of these novel approaches in neonatal populations and their potential effects on brain development remain unresolved.

CONCLUSIONS

Advanced molecular tools and emerging therapies have the potential to transform the treatment of PHH by targeting its underlying pathophysiology. Further research is needed to validate these approaches, enhance their safety profiles, and improve outcomes for infants with PHH.

IMPACT STATEMENT

1. This review elucidates the molecular complexities of post-hemorrhagic hydrocephalus (PHH) by examining specific immune pathways and their impact on disease pathogenesis and progression. 2. It outlines the application of genomic, epigenomic, and proteomic technologies to identify critical molecular targets in PHH, setting the stage for innovative, targeted therapeutic approaches that could improve the outcomes of neonates affected by PHH. 3. It discusses the potential of gene and stem cell therapies in treating PHH, offering non-surgical alternatives and focusing on the underlying neuroinflammatory mechanisms.

Divergent brain solute clearance in rat models of cerebral amyloid angiopathy and Alzheimer's disease

Brain waste clearance from the interstitial fluid environment is challenging to measure, which has contributed to controversy regarding the significance of glymphatic transport impairment for neurodegenerative processes. Dynamic contrast enhanced MRI (DCE-MRI) with cerebrospinal fluid administration of Gd-tagged tracers is often used to assess glymphatic system function. We previously quantified glymphatic transport from DCE-MRI data utilizing regularized optimal mass transport (rOMT) analysis, however, information specific to glymphatic clearance was not directly derived. To fill this knowledge gap, we here implemented unbalanced rOMT analysis which allows for assessment of both influx and clearance. Dynamic influx/clearance brain maps were derived from rTg-DI rats with cerebral amyloid angiopathy (CAA) and TgSD-AD rats with Alzheimer's disease (AD). The rTg-DI rats with severe CAA disease exhibited abnormal influx/clearance kinetics, while TgSD-AD rats with a moderate Aβ plaque load exhibited normal transport suggesting that different Aβ lesions and their overall burden differentially impact glymphatic system function.

Lumped parameter simulations of cervical lymphatic vessels: dynamics of murine cerebrospinal fluid efflux from the skull

BACKGROUND

Growing evidence suggests that for rodents, a substantial fraction of cerebrospinal fluid (CSF) drains by crossing the cribriform plate into the nasopharyngeal lymphatics, eventually reaching the cervical lymphatic vessels (CLVs). Disruption of this drainage pathway is associated with various neurological disorders.

METHODS

We employ a lumped parameter method to numerically model CSF drainage across the cribriform plate to CLVs. Our model uses intracranial pressure as an inlet pressure and central venous blood pressure as an outlet pressure. The model incorporates initial lymphatic vessels (modeling those in the nasal region) that absorb the CSF and collecting lymphatic vessels (modeling CLVs) to transport the CSF against an adverse pressure gradient. To determine unknown parameters such as wall stiffness and valve properties, we utilize a Monte Carlo approach and validate our simulation against recent in vivo experimental measurements.

RESULTS

Our parameter analysis reveals the physical characteristics of CLVs. Our results suggest that the stiffness of the vessel wall and the closing state of the valve are crucial for maintaining the vessel size and volume flow rate observed in vivo. We find that a decreased contraction amplitude and frequency leads to a reduction in volume flow rate, and we test the effects of varying the different pressures acting on the CLVs. Finally, we provide evidence that branching of initial lymphatic vessels may deviate from Murray's law to reduce sensitivity to elevated intracranial pressure.

CONCLUSIONS

This is the first numerical study of CSF drainage through CLVs. Our comprehensive parameter analysis offers guidance for future numerical modeling of CLVs. This study also provides a foundation for understanding physiology of CSF drainage, helping guide future experimental studies aimed at identifying causal mechanisms of reduction in CLV transport and potential therapeutic approaches to enhance flow.

Association between telomere length and idiopathic normal pressure hydrocephalus: a Mendelian randomization study

Objective

Idiopathic normal pressure hydrocephalus (iNPH) is highly prevalent among elderly individuals, and there is a strong correlation between telomere length and biological aging. However, there is limited evidence to elucidate the relationship between telomere length and iNPH. This study aimed to investigate the associations between telomere length and iNPH using the Mendelian randomization (MR) method.

Methods

The genetic variants of telomere length were obtained from 472,174 UK Biobank individuals. Summary level data of iNPH were acquired from 218,365 individuals of the FinnGen consortium. Five MR estimation methods, including inverse-variance weighting (IVW), MR-Egger regression, weighted median, weighted mode and simple mode, were used for causal inference. Comprehensive sensitivity analyses were conducted to test the robustness of the results. In addition, multivariable MR was further implemented to identify potential mechanisms in the causal pathway from telomere length to iNPH.

Results

Genetically determined longer telomere length was significantly associated with decreased risk of iNPH (OR = 0.44, 95% CI 0.24-0.80; p = 0.008). No evident heterogeneity (Cochran Q = 138.11, p = 0.386) and pleiotropy (MR Egger intercept = 0.01, p = 0.514) were observed in the sensitivity analysis. In addition, multivariable MR indicated that the observed association was attenuated after adjustment for several vascular risk factors, including essential hypertension (IVW OR = 0.55, 95% CI 0.30-1.03; p = 0.061), type 2 diabetes (IVW OR = 0.71, 95% CI 0.09-5.39; p = 0.740) and coronary artery disease (IVW OR = 0.58, 95% CI 0.31-1.07; p = 0.082).

Conclusion

Our MR study revealed a strong negative correlation of telomere length with iNPH. The causal relationship might be driven by several vascular risk factors.

Mechanisms of hydrocephalus after intraventricular haemorrhage: a review

Intraventricular haemorrhage (IVH) is bleeding within the ventricular system, which in adults is usually mainly secondary to cerebral haemorrhage and subarachnoid haemorrhage. Hydrocephalus is one of the most common complications of intraventricular haemorrhage, which is characterised by an increase in intracranial pressure due to an increased accumulation of cerebrospinal fluid within the ventricular system, and is closely related to the patient's prognosis. Surgical methods such as shunt surgery have been used to treat secondary hydrocephalus in recent years and have been effective in improving the survival and prognosis of patients with hydrocephalus. However, complications such as shunt blockage and intracranial infection are often faced after surgery. Moreover, little is known about the mechanism of hydrocephalus secondary to intraventricular haemorrhage. This review discusses the mechanisms regarding the occurrence of secondary hydrocephalus after intraventricular haemorrhage in adults in terms of blood clot obstruction, altered cerebrospinal fluid dynamics, inflammation, and blood composition.

Cerebrospinal Fluid Flow within Ventricles and Subarachnoid Space Evaluated by Velocity Selective Spin Labeling MRI

This study aims to evaluate cerebrospinal fluid (CSF) flow dynamics within ventricles, and the subarachnoid space (SAS) using the velocity selective spin labeling (VSSL) MRI method with Fourier-transform-based velocity selective inversion preparation. The study included healthy volunteers who underwent MRI scanning with specific VSSL parameters optimized for CSF flow quantification. The VSSL sequence was calibrated against phase-contrast MRI (PC-MRI) to ensure accurate flow velocity measurements. The CSF flow patterns observed in the ventricles were consistent with those obtained using 3D amplified MRI and other advanced MRI techniques, verifying the reliability of the VSSL method. The VSSL method successfully measured CSF flow in the SAS along major arteries, including the middle cerebral artery (MCA), anterior cerebral artery (ACA), and posterior cerebral artery (PCA), with an average flow velocity of 0.339 ± 0.117 cm / s . The diffusion component was well suppressed by flow-compensated gradients, enabling comprehensive mapping of the rapid CSF flow pattern in the SAS system and ventricles. The flow pattern in the SAS system closely resembles the recently discovered perivascular subarachnoid space (PVSAS) system. CSF flow around the MCA, PCA, and ACA arteries in the SAS exhibited a weak orientation dependency. CSF flow in the ventricles was also measured, with an average flow velocity of 0.309 ± 0.116 cm / s , and the highest velocity observed along the superior-inferior direction. This study underscores the potential of VSSL MRI as a non-invasive tool for investigating CSF dynamics in both SAS and ventricles.

Inferring in vivo murine cerebrospinal fluid flow using artificial intelligence velocimetry with moving boundaries and uncertainty quantification

Cerebrospinal fluid (CSF) flow is crucial for clearing metabolic waste from the brain, a process whose dysregulation is linked to neurodegenerative diseases like Alzheimer's. Traditional approaches like particle tracking velocimetry (PTV) are limited by their reliance on single-plane two-dimensional measurements, which fail to capture the complex dynamics of CSF flow fully. To overcome these limitations, we employ artificial intelligence velocimetry (AIV) to reconstruct three-dimensional velocities, infer pressure and wall shear stress and quantify flow rates. Given the experimental nature of the data and inherent variability in biological systems, robust uncertainty quantification (UQ) is essential. Towards this end, we have modified the baseline AIV architecture to address aleatoric uncertainty caused by noisy experimental data, enhancing our measurement refinement capabilities. We also implement UQ for the model and epistemic uncertainties arising from the governing equations and network representation. Towards this end, we test multiple governing laws, representation models and initializations. Our approach not only advances the accuracy of CSF flow quantification but also can be adapted to other applications that use physics-informed machine learning to reconstruct fields from experimental data, providing a versatile tool for inverse problems.

Advances in Research on Meningeal Lymphatic Vessels in Central Nervous System Diseases

Meningeal lymphatic vessels (mLVs), located around the dural sinuses, are considered significant participants in cerebrospinal fluid (CSF) circulation. Meningeal lymphatic vessels not only drain fluids and metabolic waste from the brain into deep cervical lymph nodes (dCLNs) but also transport immune cells from the brain to dCLNs, thus regulating the interaction between the central and peripheral immune systems. These vessels play a crucial role in maintaining normal physiological functions of the central nervous system (CNS). Meningeal lymphatic vessels are involved in the pathophysiological processes of various CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, and brain tumors. In aging and various CNS diseases, damage and dysfunction of mLVs have been observed, leading to the abnormal accumulation of toxic substances and exacerbating neural damage. By transporting antigen-presenting cells that have taken up antigens within the brain to dCLNs, mLVs modulate the activation of peripheral immune cells and their migration and infiltration into brain lesions. Certain drug interventions or physical therapies can modulate the drainage function of mLVs, effectively improving the prognosis of CNS diseases. This review provides a detailed introduction to the anatomic structure, physiological roles, and research advances of mLVs in CNS diseases. In addition, we propose new strategies for targeting mLVs in the treatment of CNS diseases.

Update on the intriguing roles of AQP4 expression and redistribution in the progression and treatment of glioma

Aquaporin 4 (AQP4) is abundant in the human brain and has an important role in brain homeostasis and diseases. AQP4 expression has been found to be associated with glioma malignancies. However, the complete understanding of the biological processes and curative importance of AQP4 in glioma remains unclear. The impact of AQP4 subcellular mislocalization on glioma progression and the precise mechanisms regarding AQP4 translocation in glioma need further investigation. In this review, we update recent findings about disturbed AQP4 expression in glioma and explore targeting AQP4 to modulate the glioma progression. Thereafter we discuss some possible mechanisms of action of AQP4 translocations in glioma. The present article offers an appropriate introduction to the potential involvement of AQP4 in the emergence and progression of glioma. Both comprehensive research into the mechanisms and systematically intervention studies focusing on AQP4 are essential. By embracing this strategy, we can obtain a new and insightful outlook on managing cancerous glioma. Although the observations summarized in this review should be confirmed with more studies, we believe that they could provide critical information for the design of more focused research that will allow for systematic and definitive evaluation of the role of AQP4 in glioma treatments.

Reimagining the meninges from a neuroimmune perspective: a boundary, but not peripheral

Recent advances in neuroscience have transformed our understanding of the meninges, the layers surrounding the central nervous system (CNS). Two key findings have advanced our understanding: researchers identified cranial bone marrow as a reservoir for meningeal immune cells, and rediscovered a brain lymphatic system. Once viewed merely as a protective barrier, the meninges are now recognized as a dynamic interface crucial for neuroimmune interactions. This shift in perspective highlights their unique role in maintaining CNS balance, shaping brain development, and regulating responses to injury and disease. This review synthesizes the latest insights into meningeal anatomy and function, with a focus on newly identified structures such as dural-associated lymphoid tissues (DALT) and arachnoid cuff exit (ACE) points. We also examine the diverse immune cell populations within the meninges and their interactions with the CNS, underscoring the emerging view of the meninges as active participants in brain immunity. Finally, we outline critical unanswered questions about meningeal immunity, proposing directions for future research. By addressing these knowledge gaps, we aim to deepen our understanding of the meninges' role in brain health and disease, potentially paving the way for novel therapeutic approaches.

Transport of β-amyloid from brain to eye causes retinal degeneration in Alzheimer's disease

The eye is closely connected to the brain, providing a unique window to detect pathological changes in the brain. In this study, we discovered β-amyloid (Aβ) deposits along the ocular glymphatic system in patients with Alzheimer's disease (AD) and 5×FAD transgenic mouse model. Interestingly, Aβ from the brain can flow into the eyes along the optic nerve through cerebrospinal fluid (CSF), causing retinal degeneration. Aβ is mainly observed in the optic nerve sheath, the neural axon, and the perivascular space, which might represent the critical steps of the Aβ transportation from the brain to the eyes. Aquaporin-4 facilitates the influx of Aβ in brain-eye transport and out-excretion of the retina, and its absence or loss of polarity exacerbates brain-derived Aβ induced damage and visual impairment. These results revealed brain-to-eye Aβ transport as a major contributor to AD retinopathy, highlighting a new therapeutic avenue in ocular and neurodegenerative disease.

Research Trends and Visualization of Cerebrospinal Fluid Dynamics (2013-2023)

OBJECTIVE

This study aims to analyze cerebrospinal fluid (CSF) dynamics using VOSviewer, CiteSpace, and the Bibliometrix R-package software to identify research hotspots and future directions.

METHODS

Search by Web of Science Core Collection Database for related literature on CSF dynamics from 2013 to 2023. Bibliometric and visual analysis of data on number of citations, number of publications, most productive countries and institutions, important authors and journals, time of publication, popular topics, and keywords were performed by CiteSpace and VOSviewer.

RESULTS

In the field of CSF dynamics, there is a clear upward trend in annual publications. The United States, Japan, and China are among the top three countries in publishing output. The University of Copenhagen, the University of Idaho, and the University of Zurich are leading institutions in research publications. The most prolific writers in this field are Bryn A. Martin, and Olivier Baledent. Active authors and institutions in the field form multiple structurally stable research teams with each other, but the collaboration between different authors and institutional teams needs to be further strengthened. The literature with the highest citation rates in the past decade is "Blood-Brain Barrier Breakdown in the Aging Human Hippocampus," "Blood-Brain Barrier Breakdown Is an Early Biomarker of Human Cognitive Dysfunction," "Serum Neurofilament Dynamics Predicts Neurodegeneration and Clinical Progression in Presymptomatic Alzheimer's Disease," and Coupled Electrophysiological, Hemodynamic, and Cerebrospinal Fluid Oscillations in Human Sleep." Key research keywords such as CSF, hydrocephalus, dynamics, brain, blood flow, CSF, pressure, CSF flow, and MRI highlight focal areas for CSF dynamics studies. These keywords represent current research priorities and research frontiers in this field.

CONCLUSIONS

This bibliometric analysis reveals hot and future research issues in the field of CSF fluid dynamics, demonstrating the need for enhanced international collaboration and interdisciplinary research to deepen the field. Keyword analysis further clarified the research focus and provided useful guidance for subsequent studies.

Advances and controversies in meningeal biology

The dura, arachnoid and pia mater, as the constituent layers of the meninges, along with cerebrospinal fluid in the subarachnoid space and ventricles, are essential protectors of the brain and spinal cord. Complemented by immune cells, blood vessels, lymphatic vessels and nerves, these connective tissue layers have held many secrets that have only recently begun to be revealed. Each meningeal layer is now known to have molecularly distinct types of fibroblasts. Cerebrospinal fluid clearance through peripheral lymphatics and lymph nodes is well documented, but its routes and flow dynamics are debated. Advances made in meningeal immune functions are also debated. This Review considers the cellular and molecular structure and function of the dura, arachnoid and pia mater in the context of conventional views, recent progress, and what is uncertain or unknown. The hallmarks of meningeal pathophysiology are identified toward developing a more complete understanding of the meninges in health and disease.

Formaldehyde initiates memory and motor impairments under weightlessness condition

During space flight, prolonged weightlessness stress exerts a range of detrimental impacts on the physiology and psychology of astronauts. These manifestations encompass depressive symptoms, anxiety, and impairments in both short-term memory and motor functions, albeit the precise underlying mechanisms remain elusive. Recent studies have revealed that hindlimb unloading (HU) animal models, which simulate space weightlessness, exhibited a disorder in memory and motor function associated with endogenous formaldehyde (FA) accumulation in the hippocampus and cerebellum, disruption of brain extracellular space (ECS), and blockage of interstitial fluid (ISF) drainage. Notably, the impairment of the blood-brain barrier (BBB) caused by space weightlessness elicits the infiltration of albumin and hemoglobin from the blood vessels into the brain ECS. However, excessive FA has the potential to form cross-links between these two proteins and amyloid-beta (Aβ), thereby obstructing ECS and inducing neuron death. Moreover, FA can inhibit N-methyl-D-aspartate (NMDA) currents by crosslinking NR1 and NR2B subunits, thus impairing memory. Additionally, FA has the ability to modulate the levels of certain microRNAs (miRNAs) such as miRNA-29b, which can affect the expression of aquaporin-4 (AQP4) so as to regulate ECS structure and ISF drainage. Especially, the accumulation of FA may inactivate the ataxia telangiectasia-mutated (ATM) protein kinase by forming cross-linking, a process that is associated with ataxia. Hence, this review presents that weightlessness stress-derived FA may potentially serve as a crucial catalyst in the deterioration of memory and motor abilities in the context of microgravity.

Revisiting Virchow's triad: exploring the cellular and molecular alterations in cerebral venous congestion

BACKGROUND

Cerebral venous thrombosis (CVT) is a rare but serious condition that can lead to significant morbidity and mortality. Virchow's triad elucidates the role of blood hypercoagulability, blood flow dynamics, and endothelial damage in the pathogenesis of CVT. Cerebral venous congestion (CVC) increases the risk of cerebral venous sinus thrombosis and can lead to recurrent episodes and residual symptoms. However, the precise mechanism by which blood congestion leads to thrombosis remains unclear. Our objective was to investigate the cellular and molecular alterations linked to CVC through analysis of the pathological morphology of venous sinus endothelial cells and transcriptomic profiling.

RESULTS

This study demonstrated a remarkable correlation between CVC and the phenotypic transformation of endothelial cells from an anticoagulant to a procoagulant state. The findings revealed that cerebral venous stasis results in tortuous dilatation of the venous sinuses, with slow blood flow and elevated pressure in the sinuses and damaged endothelial cells of the retroglenoid and internal jugular vein ligation (JVL) rat model. Mechanistically, analysis of transcriptomic results of cerebral venous sinus endothelial cells showed significant activation of platelet activation, complement and coagulation cascades pathway in the JVL rats. Furthermore, the expression of von Willebrand factor (vWF) and coagulation factor VIII (F8) in the complement and coagulation cascades and Fgg and F2 in the platelet activation was increased in the cerebral venous sinuses of JVL rats than in sham rats, suggesting that endothelial cell injury in the venous sinus induced by CVC has a prothrombotic effect. In addition, endothelial cell damage accelerates coagulation and promotes platelet activation. Significantly, the concentrations of vWF, F2 and F8 in venous sinus blood of patients with internal jugular vein stenosis were higher than in their peripheral blood.

CONCLUSION

Collectively, our data suggest that CVC can induce endothelial cell damage, which then exhibits a procoagulant phenotype and ultimately increases the risk of CVT. This research contributes to our understanding of the pathophysiology of CVC associated with procoagulant factors and reexamines the components of Virchow's triad in the context of CVC.

Impairment of spinal CSF flow precedes immune cell infiltration in an active EAE model

Accumulation of immune cells and proteins in the subarachnoid space (SAS) is found during multiple sclerosis and in the animal model experimental autoimmune encephalomyelitis (EAE). Whether the flow of cerebrospinal fluid (CSF) along the SAS of the spinal cord is impacted is yet unknown. Combining intravital near-infrared (NIR) imaging with histopathological analyses, we observed a significantly impaired bulk flow of CSF tracers within the SAS of the spinal cord prior to EAE onset, which persisted until peak stage and was only partially recovered during chronic disease. The impairment of spinal CSF flow coincided with the appearance of fibrin aggregates in the SAS, however, it preceded immune cell infiltration and breakdown of the glia limitans superficialis. Conversely, cranial CSF efflux to cervical lymph nodes was not altered during the disease course. Our study highlights an early and persistent impairment of spinal CSF flow and suggests it as a sensitive imaging biomarker for pathological changes within the leptomeninges.

Nasal lymphatic obstruction of CSF drainage as a possible cause of Alzheimer's disease and dementia

Alzheimer's disease, the most common form of dementia among older adults, slowly destroys memory and thinking skills. In recent years, scientists have made tremendous progress in understanding Alzheimer's disease, still, they do not yet fully understand what causes the disease. This article proposes a novel etiology for Alzheimer's disease. Our hypothesis developed from a review of nuclear medicine scans, in which the authors observed a significant increase in nasal turbinate vasodilation and blood pooling in patients with hypertension, sleep apnea, diabetes and/or obesity, all risk factors for Alzheimer's disease. The authors propose that nasal turbinate vasodilation and resultant blood pooling lead to the obstruction of normal nasal lymphatic clearance of cerebrospinal fluid and its waste products from the brain. The nasal turbinate vasodilation, due to increased parasympathetic activity, occurs alongside the well-established increased sympathetic activity of the cardiovascular system as seen in patients with hypertension. The increased parasympathetic activity is likely due to an autonomic imbalance secondary to the increase in worldwide consumption of highly processed food associated with dysregulation of the glucose regulatory system. The authors' hypothesis offers a novel mechanism and a new paradigm for the etiology of Alzheimer's disease and helps explain the rapid worldwide rise in the disease and other dementias which are expected to double in the next 20 years. This new paradigm provides compelling evidence for the modulation of the parasympathetic nervous system as a novel treatment strategy for Alzheimer's disease and other degenerative brain diseases, specifically targeting nasal turbinate lymphatic flow.

Neuroimmune and neuroinflammation response for traumatic brain injury

Traumatic brain injury (TBI) is one of the major diseases leading to mortality and disability, causing a serious disease burden on individuals' ordinary lives as well as socioeconomics. In primary injury, neuroimmune and neuroinflammation are both responsible for the TBI. Besides, extensive and sustained injury induced by neuroimmune and neuroinflammation also prolongs the course and worsens prognosis of TBI. Therefore, this review aims to explore the role of neuroimmune, neuroinflammation and factors associated them in TBI as well as the therapies for TBI. Thus, we conducted by searching PubMed, Scopus, and Web of Science databases for articles published between 2010 and 2023. Keywords included "traumatic brain injury," "neuroimmune response," "neuroinflammation," "astrocytes," "microglia," and "NLRP3." Articles were selected based on relevance and quality of evidence. On this basis, we provide the cellular and molecular mechanisms of TBI-induced both neuroimmune and neuroinflammation response, as well as the different factors affecting them, are introduced based on physiology of TBI, which supply a clear overview in TBI-induced chain-reacting, for a better understanding of TBI and to offer more thoughts on the future therapies for TBI.