Modulating cerebrospinal fluid dynamics using pulsed photobiomodulation.

Animal models of Chiari malformation types 1 and 2: Mechanistic insights and translational challenges.

The glymphatic system is a recently discovered brain clearance pathway that removes metabolic waste, including toxic proteins, via cerebrospinal fluid flow along perivascular spaces. It helps maintain neural homeostasis, and its dysfunction is linked to neurodegenerative diseases like Alzheimer's. Emerging evidence suggests that physical exercise can enhance glymphatic function and promote cerebral clearance, offering a potential nonpharmacological approach to support brain health. In rodent studies, voluntary wheel running has been shown to increase glymphatic flux, likely through improvements in cerebrospinal fluid circulation, vascular pulsatility, and the exchange of interstitial fluid along perivascular routes. Exercise also upregulates the expression and polarization of aquaporin 4 on astrocytic endfeet, which is essential for directing fluid movement and facilitating efficient glymphatic transport, potentially reducing the accumulation of neurotoxic proteins such as β-amyloid and tau. Beyond these direct effects, exercise-induced enhancements in cerebral blood flow, arterial compliance, and sleep quality may indirectly optimize the physiological environment for glymphatic clearance. Together, these mechanisms suggest that regular physical activity is an established, noninvasive intervention to maintain cerebral homeostasis, accelerate metabolic waste removal, and support long-term cognitive function. This review summarizes evidence linking exercise to glymphatic function and its role in brain waste clearance and cognitive function.

The brain-wide glymphatic transport system facilitates cerebrospinal fluid (CSF) circulation and the clearance of metabolic waste, processes largely influenced by sleep and sleep-like anesthesia. Recent research indicates that different anesthetic agents modulate CSF dynamics in distinct ways; however, their effects on CSF efflux pathways remain unclear. This study utilized dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and structural MRI to investigate CSF efflux pathways in mice under three anesthesia protocols (n = 6 per group): isoflurane alone (ISO), isoflurane combined with dexmedetomidine (DEXI), and ketamine/xylazine (K/X). Additionally, blood vessel diameters and CSF volume fractions were quantified. Our results demonstrate that ISO induced vasodilation in the anterior brain, slowing CSF flow to the dorsal brain while substantially accelerating CSF efflux across the cribriform plate and nasal mucosa toward the nasopharyngeal lymphatic plexus compared with DEXI and K/X (p < 0.001). However, ISO reduced CSF outflow through the spinal subarachnoid space primarily due to a decreased spinal subarachnoid CSF volume (ISO vs. DEXI, p = 0.0373; ISO vs. K/X, p = 0.0436). K/X considerably impaired CSF efflux via the cervical ganglia relative to DEXI and ISO, likely resulting from a lower CSF volume fraction within the peri-cranial nerve space (ISO vs. K/X, p = 0.0328, K/X vs. DEXI, p = 0.023). In conclusion, different anesthesia protocols modulate CSF efflux pathways by altering perineural and perivascular CSF spaces. These findings suggest that anesthetic agents influence glymphatic function by modulating distinct CSF efflux routes.

Traditionally, cerebrospinal fluid (CSF) is believed to exit the brain via arachnoid villi, being absorbed into the superior sagittal sinus (SSS), with a net flow towards these exit sites driven by constant CSF turnover. However, measuring these velocities non-invasively in humans is challenging due to their slow nature and the presence of relatively large confounding factors such as physiological CSF pulsations (heartbeat and respiration) and head motion. This study presents a novel magnetic resonance imaging (MRI) method designed to measure the net velocity of CSF whilst accounting for confounding effects, which is called CSF displacement encoding with stimulated echoes (CSF-DENSE). By applying a similar model as used to study sea-level rise, different motion components of CSF were successfully disentangled. Simulations, along with phantom and in vivo experiments, demonstrate the ability of CSF-DENSE combined with time series analysis using unobserved components modeling to detect ultraslow velocities of approximately 1 μm/s, even in the presence of confounding motions that are an order of magnitude larger. Based on CSF flow measurements in the aqueduct, the expected net velocity in the subarachnoid space (SAS) towards the SSS was estimated to be 4.22 ± 0.14 µm/s. However, no significant net velocity toward the SSS was observed (v = −0.18±0.15 µm/s, with positive velocity directed towards the SSS). This questions whether outflow via the SAS towards the SSS is the main exit route of CSF, thereby challenging the classical view of CSF outflow. These findings suggest the need to reconsider traditional models of CSF outflow pathways, with potential implications for understanding and treating neurological disorders. Clinical trial number: Not applicable.Supplementary informationThe online version contains supplementary material available at 10.1186/s12987-025-00735-9.

Cilia are microtubule-based organelles that protrude from the surface of various eukaryotic cell types. Microtubules are assembled by α/β-tubulin heterodimers, all of which comprise multiple isotypes encoded by distinct genes. However, the composition and function of tubulin isotypes in cilia are largely unclear. Here, we successfully labeled the endogenous α-tubulin and β-tubulin isotypes with HA or GFP tag in cultured mouse ependymal cells (EPCs) via the CRISPR/Cas9 system. TUBA1A, TUBA1B, TUBA1C, TUBB2A, TUBB2B, TUBB4B, and TUBB5 were identified to be incorporated in ependymal cilia, with TUBB4B showing the highest expression. Overexpression assay revealed that the ependymal cilia did not display a preference for the entrance of specific tubulin isotypes. Furthermore, luciferase reporter assay showed that the expression of TUBB4B in EPCs was specifically regulated by the ciliogenesis factor FOXJ1. TUBB4B deficiency disrupted planar polarity of EPCs and impaired cerebrospinal fluid flow, resulting in hydrocephalus. This study reveals the composition of tubulin isotypes in ependymal cilia and the specific role of FOXJ1-promoted TUBB4B in ciliary motility.

Aging is the primary risk factor for chronic neurodegenerative diseases and is associated with alterations to cerebrospinal fluid (CSF) flow and clearance. CSF delivery is currently the most clinically advanced route of administration for oligonucleotide therapeutics, but it remains poorly understood how aging, which is rarely incorporated into clinical trials, impacts biodistribution, gene silencing activity, and potential toxicity of these compounds. Here, we evaluated a lipid-siRNA conjugate (L2-siRNA) for potential age-related changes to CSF-mediated delivery, mRNA silencing, and safety. We found that L2-siRNA exhibited comparable biodistribution and on-target silencing of Huntingtin (Htt) between young and aged mice in all tested regions of the central nervous system (CNS) and across extended time points. Examining transport along CSF efflux routes revealed uptake in deep cervical lymph nodes and dura. Further, L2-siRNA did not generate detectable toxicity in the CNS or periphery of aged mice. A subset of studies benchmarked L2-siRNA against a C16 lipid-siRNA conjugate that recently entered clinical trials. Collectively, these results provide valuable insight into siRNA conjugate biodistribution and activity in the CNS in the context of aging and further establish the performance of L2-siRNA under conditions relevant to the treatment of neurodegenerative diseases.

IntroductionThe glymphatic system is a brain-wide perivascular transport route for fluids and solutes in which cerebrospinal fluid (CSF) serves as a conduit for solute transport and clearance of brain waste. Intrathecal contrast-enhanced magnetic resonance imaging (MRI), where the intrathecal contrast agent serves as a CSF tracer, has been developed to measure glymphatic function in humans. The normalized MRI T1 signal is a semiquantitative measure of CSF flow and exchange with the brain. Objective: To estimate first-time tracer appearance within brain tissue after intrathecal tracer injection.MethodsThis study implemented segmented regression analysis to estimate the first-time tracer appearance of an intrathecal tracer within brain tissues. An increase (breakpoint) in the normalized MRI T1 signal was defined to represent first glymphatic influx of the tracer. The study included 30 reference (REF) subjects with no identified CSF disturbance and 15 patients with a diagnosis of idiopathic intracranial hypertension (IIH). We developed and evaluated the method in REF subjects and further compared it between the two study groups.ResultsThe time to initial glymphatic tracer enrichment in the REF cohort was approximately 1 h in the frontal, temporal, parietal, and occipital cerebral cortex and ranged from two to 4 h in the corresponding white matter regions. In subcortical limbic structures and basal ganglia structures, it was 0.6 and 2.2 h, respectively. Compared with REF subjects, IIH patients presented a non-significant mean difference in the first appearance of ±0.5 h in the cerebral cortex and white matter regions, with somewhat longer estimated delays in the parietal and insular white matter regions. The results are presented as time series plots and estimates with 95% confidence intervals. Additionally, we provide supplementary R code, which can be adapted for use in future studies, and outline a basic assessment of true versus estimated breakpoints using simulated data.ConclusionSegmented regression was found feasible to quantify the time to first glymphatic enrichment, i.e., increase in the normalized MRI T1 signal. Moreover, the method seems reasonable to differentiate first glymphatic influx between the cohorts.

Multiciliated cells (MCCs) play a crucial role in various physiological processes, including cerebrospinal fluid flow, mucus clearance, and reproductive transport, by coordinating ciliary movement. Their differentiation is regulated by the Notch signaling pathway, along with its downstream targets, Gemc1 and Mcidas transcription factors. This study focuses on Zmynd10, a dynein axonemal assembly factor, to investigate its molecular mechanisms that regulate polycilia differentiation. By constructing a model of Zmynd10-specific knockdown in mouse ependymal cells (mEPCs), we found that Zmynd10 knockdown resulted in a decrease in ciliary density and significantly downregulated the mRNA and protein expression of E2f4 and Deup1. Further experiments demonstrated that E2f4 knockdown inhibited Deup1 expression and reduced cilia numbers, while Zmynd10 regulated the E2f4-Deup1 axis by activating the E2f4 promoter. This study reveals for the first time that Zmynd10 drives centriole amplification through the transcriptional regulation of the E2f4-Deup1 pathway, providing new insights into the molecular mechanisms underlying multicilia differentiation.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-27956-0.

Delirium is a frequent and serious complication in intensive care patients, arising from overlapping vulnerabilities that obscure its primary causes. Using healthy mice, we tested whether mechanical ventilation combined with inhalation anesthetics and opioid sedation is sufficient to induce delirium-like behavior through disruption of cerebrospinal fluid (CSF) glymphatic dynamics. We found that ventilation acutely increased intracranial pressure and induced a long-lasting suppression of glymphatic transport, thereby re-routing and impairing brain waste clearance and promoting cytokine accumulation. These observations establish a mechanistic link between ventilator-associated alterations in brain fluid dynamics and delirium. Our findings identify glymphatic dysfunction and disturbed CSF flow as contributors to acute brain dysfunction following mechanical ventilation and suggest that therapies enhancing glymphatic flux or stabilizing intracranial pressure could reduce delirium incidence and severity in critically ill patients.

Recent studies have uncovered that the calvarial bone marrow (BM), located within the skull, functions as a specialized hematopoietic niche distinct from BM in long bones. This compartment supports a unique repertoire of immune cells, particularly neutrophils, and plays a critical role in neuroimmune surveillance through direct anatomical channels that connect the calvarial BM to the dura mater. These bone marrow-dura mater (BM-DM) channels not only enable immune cell trafficking but may also mediate cerebrospinal fluid (CSF) flow, facilitating bidirectional communication between the central nervous system (CNS) and bone marrow. The vascular and stromal architecture of calvarial BM is notably different, featuring expanded trabecular bone, distinct endothelial subtypes, and perivascular niches that promote hematopoietic stem cell maintenance. Remarkably, the calvarial BM demonstrates resilience to aging-associated hallmarks seen in long bones, such as vascular rarefaction, adipocyte accumulation, and inflammatory signaling. Instead, it continues to expand and maintain vascular and immune integrity well into advanced age, supporting healthy hematopoiesis. This compartment also responds uniquely to physiological and pathological stressors, including pregnancy, stroke, and leukemia, with distinct vascular remodeling and immune cell output compared to femoral BM. The structural and functional heterogeneity of calvarial BM suggests that bone marrow specialization is tightly linked to anatomical location and local physiological demands. These findings underscore the importance of considering site-specific bone marrow microenvironments in both health and disease. Understanding calvarial BM dynamics could open new avenues for modulating neuroimmune interactions and developing targeted therapies for CNS-related pathologies.

Periarterial cerebrospinal fluid (CSF) flow has been hypothesized to contribute to brain waste clearance but is poorly understood. Animal studies suggest arterial pulsatility drives perivascular CSF in the direction of cerebral arterial blood flow (CBF), but human validation has relied on MRI approaches that do not inform on flow-directionality. Here, we use a high-performance gradient system enabling low velocity encoding (Venc) 4D flow MRI, to characterize cardiac-driven periarterial CSF flow and CBF-to-CSF flow coupling. Healthy participants (N = 10) underwent high resolution (0.8mm isotropic) 4D flow MRI of blood (Venc = 120cm/s) and CSF (Venc = 1.0cm/s) on a 3.0T head-only system (MAGNUS, GE Healthcare; Gmax = 300mT/m, Smax = 750T/m/s). Images were reconstructed using local low rank (LLR) constrained parallel imaging and background field corrected using iterative, complex domain fitting. Luminal blood and associated periarterial CSF waveforms were extracted along the left and right anterior (ACA A1), middle (MCA M1 and M2), and posterior (PCA P2) cerebral arteries using a centerline approach, and characterized individually by amplitude and stroke volume and jointly by coupling coefficients from maximum cross-correlation ([Formula: see text]) and time-lags. For low Venc 4D flow MRI, MAGNUS dramatically reduced the echo time and temporal resolution compared to whole-body systems. CBF and CSF measurements were successful in 61/80 locations (up to 8 per participant) with 19 measurements excluded due to velocity aliasing and/or poor local quality of the flow data. Inverse (anti-correlated) CBF-to-CSF coupling ([Formula: see text]) was observed for most segments (56/61), with strong coupling observed for all vessels, including M1 (-0.85 ± 0.06), A1 (-0.80 ± 0.12), P2 (-0.79 ± 0.08), and M2 (-0.78 ± 0.08). Further, CBF preceded CSF for most (43/56) segments, with short CBF-to-CSF lags in A1 (5.30 ± 64 ms) and P2 (4.13 ± 63 ms), higher in M1 (43 ± 39 ms), and highest in M2 (115 ± 39 ms). CBF and CSF flow metrics were also correlated in terms of flow rate amplitude (r = 0.40, p = 0.015) and stroke volume (r = 0.56, p < 0.001). High-performance gradient systems facilitate 4D flow imaging of very slow CSF. Joint analysis of CBF and periarterial CSF allowed assessment of CBF-to-CSF dynamics coupling. For most vessels, an inverse coupling and a positive time-lag was found from CBF to periarterial CSF, suggesting that the systolic arterial expansion drives CSF backwards and inwards again during diastolic relaxation. The proposed approach can be used to improve our understanding of CBF and CSF dynamics in aging and dementia. Not applicable.

In the assessment of cerebrospinal fluid flow disorders such as aqueductal stenosis, Chiari malformation, and post-operative complications, conventional imaging often falls short in resolving subtle anatomical and dynamic nuances. This case series explores the value of integrating high-resolution flow-sensitive and flow-compensated magnetic resonance imaging sequences to enhance diagnostic precision in challenging scenarios. Across five diverse cases, the combined approach revealed subtle aetiologies like prepontine adhesions, fourth ventricle outlet obstruction, aqueductal stenosis and minute dural breaches - all which were undetectable with routine conventional imaging.

Central nervous system (CNS) involvement in acute myeloid leukemia (AML) is uncommon, reported in < 3% of patients, and confers poor prognosis. We present a 71‐year‐old Korean woman with prior myeloid sarcoma who progressed to AML and later developed isolated CNS leukemia. Her course included pancytopenia, extramedullary skin lesions, hyperleukocytosis, transfusion‐dependent anemia, and elevated LDH. Neurologic decline revealed dural lesions on imaging; cerebrospinal fluid flow cytometry confirmed CNS disease despite negative cytology. She responded to intrathecal methotrexate and high‐dose cytarabine, underscoring the need for CNS‐directed therapy. Myeloid sarcoma precedes AML in 2%–8% of cases, yet CNS relapse remains rare. Diagnostic challenges arise from nonspecific neuroimaging and overlap with infectious or inflammatory etiologies, highlighting the role of flow cytometry and molecular studies. Median survival after CNS relapse is reported at 3–6 months. This case also illustrates how language barriers may delay diagnosis and complicate management, emphasizing the need for accessible care frameworks.

The aim of this study was to evaluate the long-term visual outcomes following optic nerve decompression in patients with CSF flow disturbances and to propose a mechanistic framework for surgical qualification based on infusion testing and orbital MRI, independent of idiopathic intracranial hypertension (IIH) diagnostic criteria. This retrospective study analyzed 30 eyes in 26 patients with progressive visual impairment and evidence of CSF flow abnormalities. All patients underwent standardized lumbar infusion testing to quantify CSF outflow resistance, pressure-volume index, and opening pressure. Orbital MRI was used to assess perioptic CSF collections or optic canal narrowing. On the basis of these data, patients underwent either optic nerve sheath fenestration (ONSF) or endoscopic optic nerve sheath decompression (EONSD). Visual function was evaluated using mean deviation of the visual field, visual evoked potentials, and optical coherence tomography of the retinal nerve fiber layer (RNFL) thickness at baseline and 6 and 24 months. Mean deviation of the visual field improved by a median of +1.89 dB (p < 0.05), and P100 latency (i.e., the time between a visual stimulus and the visual cortex's response) decreased by -5 msec at 24 months. Papilledema resolved in 87.5% of affected eyes. RNFL thickness remained stable or modestly increased across the cohort, with a trend toward greater thickening following EONSD (+9 µm at both 6 and 24 months) compared with ONSF (minimal change at 6 months [+1 µm] and slight thinning at 24 months [-2 µm]), although the differences were not statistically significant. No significant differences in functional outcomes were observed between the procedures. Patients were stratified into 3 CSF pathophysiological subgroups: 1) IIH with elevated intracranial pressure (ICP), 2) abnormal hydrodynamics without raised ICP, and 3) normal ICP and hydrodynamics with MRI-confirmed perioptic CSF collection. Visual improvement occurred across all subgroups, including groups 2 and 3. The authors found that optic nerve decompression guided by CSF infusion testing and orbital MRI effectively stabilizes or improves visual function in patients with CSF-related optic neuropathy, including those without elevated ICP. A mechanism-based classification into three surgical phenotypes enables individualized treatment beyond syndromic definitions. This approach may redefine surgical eligibility and expand access to vision-preserving interventions in CSF-mediated optic nerve dysfunction.

BackgroundSporadic cerebral small vessel disease (SVD) has a heterogeneous underlying pathology, and current SVD magnetic resonance imaging (MRI) markers do not accurately capture this heterogeneity. Novel ultrahigh-field (7T) brain MRI markers provide a window of opportunity to study early changes and potential determinants of SVD. White matter hyperintensity (WMH) shape is a relatively novel MRI marker of SVD and has shown prognostic potential. However, the exact microstructural changes within or surrounding WMHs or potential causes related to WMH shape variations are unknown. Furthermore, impaired brain clearance via the recently discovered brain clearance system may be another early change or potential cause of SVD.ObjectiveIn the White Matter Hyperintensity Shape and Brain Clearance (WHIMAS) study, we aim to assess the link between WMHs—their shape in particular—and brain clearance and other MRI markers on ultrahigh-field (7T) brain MRI and show whether these markers are associated with cognitive functioning in older adults with memory complaints.MethodsThis is a cross-sectional study conducted at the Leiden University Medical Center. A total of 50 outpatients from the memory or geriatric clinic aged ≥65 years will be recruited for a 3T and 7T MRI scan (including clinical structural scans, eg, 3D T1-weighted, 3D fluid-attenuated inversion recovery), and experimental scans such as cerebrospinal fluid (CSF)–selective T2-prepared readout with acceleration and mobility encoding (CSF-STREAM) and the relationship between blood oxygen level–dependent [BOLD] signals and CSF flow) and magnetic resonance fingerprinting, as well as a standardized neuropsychological test battery (domains: memory, executive function, visuoconstruction, and processing speed). We will assess WMH shape markers (solidity, convexity, concavity index, fractal dimension, and eccentricity) and brain clearance markers (CSF mobility and the relationship between blood oxygen level–dependent signals and CSF flow) and study their relationship to other MRI markers and cognitive functioning using multivariable regression analyses.ResultsPatient inclusion started in January 2023, and study enrollment of patients is expected to finish in the second quarter of 2027, whereas the main results are expected to be published in the first quarter of 2028.ConclusionsWe aim to understand variations in WMH shape and find their relationship to cerebral SVD and markers of brain clearance and cognitive functioning. WMH shape and brain clearance markers early in the disease process of SVD are extremely important as they may represent a basis for future patient selection for lifestyle interventions or for treatment trials aimed at the prevention of dementia.Trial RegistrationClinicalTrials.gov NCT06010511; https://clinicaltrials.gov/study/NCT06010511International Registered Report Identifier (IRRID)DERR1-10.2196/77681

Neurofluids, including cerebrospinal fluid (CSF) and interstitial fluid, circulate through regulated central nervous system pathways to clear cerebral waste and support brain health, with elevated CSF flow hyperdynamicity and regurgitation through the cerebral aqueduct associating with aging and neurodegeneration. Sleep exerts state-dependent effects on neurofluid circulation, yet similar modulation during unique waking states, such as meditation, remains underexplored. Notably, mindfulness meditation shares several regulatory features with sleep, with core meditation practices representing distinct arousal states. We investigated whether the focused attention (FA) style of mindfulness meditation modulates neurofluid dynamics directionally opposite to aging and consistent with sleep. Using phase-contrast MRI, we assessed absolute CSF flow and velocity through the aqueduct, and using blood oxygenation level-dependent (BOLD) MRI, we assessed CSF fluctuations near the cervicomedullary junction together with total supratentorial gray matter fluctuations. Assessments were repeated in meditation-naïve adults during mind wandering (MW) without (n = 13; repeatability controls) and with (n = 14; breath controls) respiration rate modulation and in adept meditators (n = 23) during MW and FA meditation. No aqueduct CSF flow changes were observed in control groups. In meditators, aqueduct absolute CSF flow motion decreased from MW to FA meditation (4.60 ± 2.27 mL/min to 4.17 ± 2.10 mL/min, P = 0.005) owing to reduced regurgitant cranially directed CSF flow velocity. On BOLD, this paralleled increased low-frequency (0.0614 to 0.0887 Hz) CSF fluctuations (P = 0.0138), which were inversely correlated with gray matter fluctuations during FA meditation. Findings suggest that mindfulness meditation may represent a nonpharmacological, waking state capable of modulating neurofluid dynamics in a directionally similar manner to sleep and opposite to aging and neurodegeneration.

Alzheimer's disease (AD) is characterized by the accumulation of extracellular aggregated amyloid beta, resulting from impaired waste clearance. We recently identified new cerebrospinal fluid (CSF) efflux structures termed arachnoid cuff exit (ACE) points and speculated that these may be impacted in AD, leading to impaired waste clearance function. Using 5XFAD mice, we found progressive amyloidosis of bridging veins at ACE points. Indeed, in 5XFAD mice, there is impaired CSF efflux to the dura mater, impaired CSF flow along bridging veins, and impaired blood flow through bridging veins. These observations suggest that ACE point amyloidosis plays a role in waste clearance dysfunction in AD. In postmortem human samples, we also found striking amyloidosis of the bridging veins of individuals with AD. Moreover, in human AD specimens, there was prominent bridging vein structural degeneration, indicating advanced pathology and stronger deficits in humans. We propose that bridging vein amyloidosis is an underrecognized pathophysiological correlate of AD that may impair CSF efflux, intracranial pressure, vascular reactivity, and vascular integrity.

Reduced coupling between global signal and cerebrospinal fluid inflow in patients with generalized anxiety disorder: A resting state functional MRI study.

How volume changes in the epidural space drives respiratory cerebrospinal fluid flow.