Neuronal dynamics direct cerebrospinal fluid perfusion and brain clearance

Neuropathological links between T2DM and LOAD: systematic review and meta-analysis

Recent decades have described parallel neuropathological mechanisms increasing the risk for developing late-onset Alzheimer's dementia (LOAD) in type 2 diabetes mellitus (T2DM); however, still little is known of the role of diabetic encephalopathy and brain atrophy in LOAD. The aim of this systematic review is to provide a comprehensive view on diabetic encephalopathy/cerebral atrophy, taking into account neuroimaging data, neuropathology, metabolic and endocrine mechanisms, amyloid formation, brain perfusion impairments, neuroimmunology, and inflammasome activation. Key switches were identified, to further meta-analyze genomic candidate loci and epigenetic modifications. For the qualitative meta-analysis of genomic bases extracted, human linkage studies were examined; for epigenetic mechanisms, data from both human and animal studies are described. For the systematic review of pathophysiological mechanisms, 1,259 publications were evaluated and 93 gene loci extracted for candidate risk linkages. Sixty-six publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight the insulin signaling system, vascular markers, inflammation and inflammasome pathways, amylin interactions, and glycosylation mechanisms. The protocol was registered with PROSPERO (ID: CRD42023440535).

Targeting Sleep Physiology to Modulate Glymphatic Brain Clearance

Sleep has been postulated to play an important role in the removal of potentially neurotoxic molecules, such as amyloid-β, from the brain via the glymphatic system. Disturbed sleep, on the other hand, may contribute to the accumulation of neurotoxins in brain tissue, eventually leading to neuronal death. A bidirectional relationship has been proposed between impaired sleep and neurodegenerative processes, which start years before the onset of clinical symptoms associated with conditions like Alzheimer's and Parkinson's diseases. Given the heavy burden these conditions place on society, it is imperative to develop interventions that promote efficient brain clearance, thereby potentially aiding in the prevention or slowing of neurodegeneration. In this review, we explore whether the metabolic clearance function of sleep can be enhanced through sensory (e.g., auditory, vestibular) or transcranial (e.g., magnetic, ultrasound, infrared light) stimulation, as well as pharmacological (e.g., antiepileptics) and behavioral (e.g., sleeping position, physical exercise, cognitive intervention) modulation of sleep physiology. A particular focus is placed on strategies to enhance slow-wave activity during nonrapid eye movement sleep as a driver of glymphatic brain clearance. Overall, this review provides a comprehensive overview on the potential preventative and therapeutic applications of sleep interventions in combating neurodegeneration, cognitive decline, and dementia.

Association between sleep and ALS-FTSD: A Prospective Cohort Study based on 396,918 UK biobank participants

Amyotrophic lateral sclerosis-frontotemporal spectrum disorder (ALS-FTSD) is a fatal neurodegenerative condition, and identifying its modifiable risk factors is a critical public health issue. This large-scale prospective cohort study investigated the role of sleep-related factors in ALS-FTSD risk using data from 396,918 UK Biobank participants. Eight sleep-related exposures were assessed, and Cox proportional hazards regression was employed to evaluate their associations with ALS-FTSD incidence. Subgroup and sensitivity analyses were conducted to validate the robustness of our findings. At baseline, participants had a mean age of 56.31 ± 8.12 years, with 47.5% being male. In the fully adjusted Cox model, organic sleep disorders (G47) (HR: 1.81, 95% CI: 1.21, 2.72, P = 0.004), hypersomnia (G47.1) (HR: 36.53, 95% CI: 9.04, 147.55, P < 0.001), and extreme short sleep (<5 h per day) (HR: 2.09, 95% CI: 1.09, 3.99, P = 0.046) were significantly associated with increased ALS-FTSD risk. In conclusions, these findings revealed the relationship between sleep and the risk of ALS-FTSD, identifying new modifiable risk factors and potential preventive possibilities for ALS-FTSD. Further research is warranted to elucidate the mechanistic links between sleep disturbances and ALS-FTSD pathogenesis.

Stress-induced dysfunction of neurovascular astrocytes in the prefrontal cortex contributes to sex-dependent deficits in cognition and behavior

Astrocytes form an integral component of the neurovascular unit, ensheathing brain blood vessels with endfeet high in aquaporin-4 (AQP4) expression. These AQP4-rich endfeet facilitate interaction between the vascular endothelium, astrocytes, and neurons, and help stabilize vascular morphology. Studies using preclinical models of psychological stress and post-mortem tissue from patients with major depressive disorder (MDD) have reported reductions in AQP4, loss of astrocytic structures, and vascular impairment in the prefrontal cortex (PFC). Though compelling, the role of AQP4 in mediating stress-induced alterations in neurovascular function and behavior remains unclear. Here, we address this, alongside potential sex differences in chronic unpredictable stress (CUS) effects on astrocyte phenotype, blood-brain barrier integrity, and behavior. CUS led to more pronounced shifts in stress-coping behavior and working memory deficits in male- as compared to female mice. Following behavioral testing, astrocytes from the frontal cortex were isolated for gene expression analyses. We found that CUS increased transcripts associated with blood vessel maintenance in males, but either had no effect on- or decreased- these transcripts in females. Furthermore, CUS caused a reduction in vascular-localized AQP4 and elevated extravasation of a small fluorescent reporter (Dextran) in the PFC in males but not females. Studies showed that knockdown of AQP4 in the PFC is sufficient to disrupt astrocyte phenotype and increase behavioral susceptibility to a sub-chronic stressor in males yet has little effect on stress susceptibility in females. Our findings provide evidence that sex-specific alterations in astrocyte phenotype and neurovascular integrity in the PFC contribute to cognitive-behavioral consequences following stress.

Remote Regulation of Molecular Diffusion in Extracellular Space of Parkinson's Disease Rat Model by Subthalamic Nucleus Deep Brain Stimulation

Subthalamic nucleus deep brain stimulation (STN-DBS) is an effective therapy for Parkinson's disease (PD). However, the therapeutic mechanisms remain incompletely understood, particularly regarding the extracellular space (ECS), a critical microenvironment where molecular diffusion and interstitial fluid (ISF) dynamics are essential for neural function. This study aims to explore the regulatory mechanisms of the ECS in the substantia nigra (SN) of PD rats following STN-DBS. To evaluate whether STN-DBS can modulate ECS diffusion and drainage, we conducted quantitative measurements using a tracer-based magnetic resonance imaging. Our findings indicated that, compared to the PD group, STN-DBS treatment resulted in a decreased diffusion coefficient (D*), shorted half-life (T 1/2), and increased clearance coefficient (k') in the SN. To investigate the mechanisms underlying these changes in molecular diffusion, we employed enzyme-linked immunosorbent assay (ELISA), Western blotting (WB), and microdialysis techniques. The results revealed that STN-DBS led to an increase in hyaluronic acid content, elevated expression of excitatory amino acid transporter 2 (EAAT2), and a reduction in extracellular glutamate concentration. Additionally, to further elucidate the mechanisms influencing ISF drainage, we employed immunofluorescence and immunohistochemical techniques for staining aquaporin-4 (AQP-4) and α-synuclein. The results demonstrated that STN-DBS restored the expression of AQP-4 while decreasing the expression of α-synuclein. In conclusion, our findings suggest that STN-DBS improves PD symptoms by modifying the ECS and enhancing ISF drainage in the SN regions. These results offer new insights into the mechanisms and long-term outcomes of DBS in ECS, paving the way for precision therapies.

Cognitive reserve linked to network-specific brain-ventricle coupling

Despite showing significant impact in cognitive preservation, the relationship between brain activity captured with functional Magnetic Resonance Imaging (fMRI) in gray matter and ventricular cerebrospinal fluid dynamics remains poorly understood. We analyzed 599 fMRI scans from 163 elderly participants at rest with varying degrees of cognitive impairment employing a unified phase coupling analysis that breaks from convention by incorporating both tissue and ventricular signal fluctuations. This whole-brain approach identified distinct brain-ventricle coupling modes that differentiate between cognitive status groups and correlate with specific cognitive abilities. Beyond the previously reported anti-phase coupling between global brain signals and ventricles-which we confirm occurs more frequently in cognitively normal controls-our analysis method uncovered additional coupling modes where signals in specific brain networks temporarily align with ventricle signals. At the cortical level, these modes reveal patterns corresponding to known resting-state networks: one overlapping with the Default Mode Network occurs significantly less frequently in Alzheimer's Disease patients, while another revealing the Frontoparietal Network correlates positively with memory scores. Our findings demonstrate that different brain-ventricle coupling modes correlate with specific cognitive domains, with particular modes predicting memory, executive function, and visuospatial abilities. The coupling between signals in brain ventricles and established resting-state networks challenges our current understanding of functional network formation, suggesting an integral link with brain fluid motion. This reconceptualization of brain dynamics through the lens of fluid-tissue interactions establishes a fundamental physical basis for cognitive preservation, suggesting that therapeutic interventions targeting these interactions may prove more effective than approaches focused solely on cellular or molecular mechanisms.

Perivascular brain clearance as a therapeutic target in cerebral amyloid angiopathy and Alzheimer's disease

Although distinct diseases, both cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD) are characterized by the aggregation and accumulation of amyloid-β (Aβ). This is thought to be due, in part, to impaired perivascular Aβ clearance from the brain. This shared failure in both diseases presents a common opportunity for therapeutic intervention. In this review we discuss the idea that promoting perivascular brain clearance could be an effective strategy for safely reducing Aβ levels in CAA and AD thereby improving clinical outcomes, most notably hemorrhagic stroke and cognitive decline. We will explore the evidence for the different forces that are thought to drive perivascular brain clearance, review the literature on potential strategies for potentiating these driving forces, and finally we will discuss the substantial translational challenges and considerations that would accompany such an intervention.

H-current modulation of cortical Up and Down states

Understanding the link between cellular processes and brain function remains a key challenge in neuroscience. One crucial aspect is the interplay between specific ion channels and network dynamics. This work reveals a role for h-current, a hyperpolarization-activated cationic current, in shaping cortical slow oscillations. Cortical slow oscillations are generated not only during slow wave sleep and deep anaesthesia, but also in association with disorders of consciousness and brain lesions. Cortical slow oscillations exhibit rhythmic periods of activity (Up states) alternating with silent periods (Down states). By progressively reducing h-current in both cortical slices and in a computational model, we observed Up states transformed into prolonged plateaus of sustained firing, while Down states were also significantly extended. This transformation led to a fivefold reduction in oscillation frequency. In a biophysical recurrent network model, we identified the cellular mechanisms underlying this transformation of network dynamics: an increased neuronal input resistance and membrane time constant, increasing neuronal responsiveness to even weak inputs. A partial block of h-current therefore resulted in a change in brain state. HCN (hyperpolarization-activated cyclic nucleotide-gated) channels, which generate h-current, are known targets for neuromodulation, suggesting potential pathways for dynamic control of brain rhythms. KEY POINTS: We investigated the role of h-current in shaping emergent cortical slow oscillation dynamics, specifically Up and Down states, in cortical slices. Blocking h-current transformed Up states into prolonged plateaus of sustained firing, lasting up to 4 s. Down states were also significantly elongated and the oscillatory frequency decreased. A biophysical model of the cortical network replicated these findings and allowed us to explore the underlying mechanisms. An increase in cellular input resistance and time constant led to a rise in network excitability, synaptic responsiveness and firing rates. Our results highlight the significant role of h-current in controlling cortical slow rhythmic patterns, making it a relevant target for neuromodulators regulating brain states.

Biological Fluid Flows: Signaling Mediums for Circadian Timing

While there is extensive literature on both the neuronal circuitry of rhythms and the intracellular molecular clock, there is a large component of signaling that has been understudied: interstitial fluid (ISF)-fluid that surrounds the cells in the extracellular space of tissue. In this review, we highlight evidence in the circadian literature supporting ISF signaling as key to circadian synchronization and entrainment and propose new mechanisms of how fluid movement between the brain and periphery may act as zeitgebers by examining the main ISF pathways of the body, focusing on circadian regulation of the glymphatic and lymphatic systems. We identify key pieces of circadian research that point to ISF as an important timing medium, expand on the basics of cerebrospinal fluid (CSF) and ISF production, and outline the basic structure and function of the glymphatic and lymphatic systems.

The night's watch: Exploring how sleep protects against neurodegeneration

Sleep loss is often regarded as an early manifestation of neurodegenerative diseases given its common occurrence and link to cognitive dysfunction. However, the precise mechanisms by which sleep disturbances contribute to neurodegeneration are not fully understood, nor is it clear why some individuals are more susceptible to these effects than others. This review addresses critical unanswered questions in the field, including whether sleep disturbances precede or result from neurodegenerative diseases, the functional significance of sleep changes during the preclinical disease phase, and the potential role of sleep homeostasis as an adaptive mechanism enhancing resilience against cognitive decline and neurodegeneration.

Loss of glymphatic homeostasis in heart failure

Heart failure is associated with progressive reduction in cerebral blood flow and neurodegenerative changes leading to cognitive decline. The glymphatic system is crucial for the brain's waste removal, and its dysfunction is linked to neurodegeneration. In this study, we used a mouse model of heart failure, induced by myocardial infarction, to investigate the effects of heart failure with reduced ejection fraction on the brain's glymphatic function. Using dynamic contrast-enhanced MRI and high-resolution fluorescence microscopy, we found increased solute influx from the CSF spaces to the brain, i.e. glymphatic influx, at 12 weeks post-myocardial infarction. Two-photon microscopy revealed that cerebral arterial pulsatility, a major driver of the glymphatic system, was potentiated at this time point, and could explain this increase in glymphatic influx. However, clearance of proteins from the brain parenchyma did not increase proportionately with influx, while a relative increase in brain parenchyma volume was found at 12 weeks post-myocardial infarction, suggesting dysregulation of brain fluid dynamics. Additionally, our results showed a correlation between brain clearance and cerebral blood flow. These findings highlight the role of cerebral blood flow as a key regulator of the glymphatic system, suggesting its involvement in the development of brain disorders associated with reduced cerebral blood flow. This study paves the way for future investigations into the effects of cardiovascular diseases on the brain's clearance mechanisms, which may provide novel insights into the prevention and treatment of cognitive decline.

Assessment of glymphatic function and white matter integrity in children with autism using multi-parametric MRI and machine learning

OBJECTIVES

To assess glymphatic function and white matter integrity in children with autism spectrum disorder (ASD) using multi-parametric MRI, combined with machine learning to evaluate ASD detection performance.

MATERIALS AND METHODS

This retrospective study collected data from 110 children with ASD (80 exploratory, 43 validation) and 68 typically developing children (50 exploratory, 18 validation) from two centers. The automated diffusion tensor imaging along the perivascular space (aDTI-ALPS), fractional anisotropy (FA), cerebrospinal fluid volume, and perivascular space (PVS) volume indices were extracted from DTI, three-dimensional T1-weighted, and T2-weighted images. Intergroup comparisons were conducted using t-tests, Mann-Whitney U-test, and tract-based spatial statistics. Correlation analysis assessed the relationship between glymphatic function, white matter integrity, and clinical scales. Machine learning models based on MRI indices were developed using the AutoGluon framework.

RESULTS

The PVS volume (p < 0.001) was larger, and aDTI-ALPS index (p < 0.001) was lower in children with ASD compared to typically developing children. FA values were reduced in the ASD group and positively correlated with aDTI-ALPS index. The aDTI-ALPS index correlated with ASD severity (r = -0.27, p = 0.02) and developmental delays (r = 0.63, p < 0.001). Mediation analysis indicated the aDTI-ALPS index partially mediated the relationship between white matter integrity and developmental delay. The MRI-based model achieved an area under the curve of 0.84 for ASD diagnosis.

CONCLUSION

Analyzing glymphatic function and white matter integrity enhances understanding of ASD's neurobiological underpinnings. The multi-parametric MRI, combined with machine learning, can facilitate the early detection of ASD.

KEY POINTS

Question How can multi-parametric MRI based on the glymphatic system improve early diagnosis of autism spectrum disorder (ASD) beyond the limitations of current behavioral assessments? Findings Glymphatic dysfunction and disruptions in white matter integrity were associated with clinical symptoms of ASD. Multi-parametric MRI with machine learning can improve early ASD detection. Clinical relevance Multi-parametric MRI, focusing on glymphatic function and white matter integrity, enhances the diagnostic accuracy of ASD by serving as an objective complement to clinical scales.

Rest and rinse: sleeping rhythms drive brain detox

Sleep is a major driver of waste clearance from the brain, but the mechanisms underpinning brain cleansing during sleep, which are also important for immunological functions, are poorly understood. Recent mouse work by Hauglund et al. shows how oscillatory surges in norepinephrine (NE) during sleep drive vascular pulsation and cerebrospinal fluid (CSF) movement to cleanse the brain.

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

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

Norepinephrine-mediated slow vasomotion drives glymphatic clearance during sleep

As the brain transitions from wakefulness to sleep, processing of external information diminishes while restorative processes, such as glymphatic removal of waste products, are activated. Yet, it is not known what drives brain clearance during sleep. We here employed an array of technologies and identified tightly synchronized oscillations in norepinephrine, cerebral blood volume, and cerebrospinal fluid (CSF) as the strongest predictors of glymphatic clearance during NREM sleep. Optogenetic stimulation of the locus coeruleus induced anti-correlated changes in vasomotion and CSF signal. Furthermore, stimulation of arterial oscillations enhanced CSF inflow, demonstrating that vasomotion acts as a pump driving CSF into the brain. On the contrary, the sleep aid zolpidem suppressed norepinephrine oscillations and glymphatic flow, highlighting the critical role of norepinephrine-driven vascular dynamics in brain clearance. Thus, the micro-architectural organization of NREM sleep, driven by norepinephrine fluctuations and vascular dynamics, is a key determinant for glymphatic clearance.

The role of sleep in Alzheimer's disease: a mini review

Sleep is a stereotyped and well-preserved series of neurophysiological states that are essential for overall health and brain functioning. Emerging research suggests that sleep disturbances are not only associated with but also causally contribute to neurodegenerative disease onset and progression. This mini-review examines some of the current knowledge and evidence for relationships between sleep abnormalities and Alzheimer's disease within context of possible uses and limitations of sleep biomarkers for evaluation of Alzheimer's disease. Understanding these relationships could lead to readily accessible and easily quantifiable biomarkers of Alzheimer's dementia.

Cell-type specific profiling of human entorhinal cortex at the onset of Alzheimer's disease neuropathology

Neurons located in layer II of the entorhinal cortex (ECII) are the primary site of pathological tau accumulation and neurodegeneration at preclinical stages of Alzheimer's disease (AD). Exploring the alterations that underlie the early degeneration of these cells is essential to develop therapies that curb the disease before symptom onset. Here we performed cell-type specific profiling of human EC at the onset of AD neuropathology. We identify an early response to amyloid pathology by microglia and oligodendrocytes. Importantly, we provide the first insight into neuronal alterations that coincide with incipient tau pathology: the signaling pathway for Reelin, recently shown to be a major AD resilience gene is dysregulated in ECII neurons, while the secreted synaptic organizer molecules NPTX2 and CBLN4, emerging AD biomarkers, are downregulated in surrounding neurons. By uncovering the complex multicellular landscape of EC at these early AD stages, this study paves the way for detailed characterization of the mechanisms governing NFT formation and opens long-needed novel therapeutic avenues.

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

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

Immune control of brain physiology

The peripheral immune system communicates with the brain through complex anatomical routes involving the skull, the brain borders, circumventricular organs and peripheral nerves. These immune-brain communication pathways were classically considered to be dormant under physiological conditions and active only in cases of infection or damage. Yet, peripheral immune cells and signals are key in brain development, function and maintenance. In this Perspective, we propose an alternative framework for understanding the mechanisms of immune-brain communication. During brain development and in homeostasis, these anatomical structures allow selected elements of the peripheral immune system to affect the brain directly or indirectly, within physiological limits. By contrast, in ageing and pathological settings, detrimental peripheral immune signals hijack the existing communication routes or alter their structure. We discuss why a diversity of communication channels is needed and how they work in relation to one another to maintain homeostasis of the brain.

Mechanisms by which microbiome-derived metabolites exert their impacts on neurodegeneration

Recent developments in microbiome research suggest that the gut microbiome may remotely modulate central and peripheral neuronal processes, ranging from early brain development to age-related changes. Dysbiotic microbiome configurations have been increasingly associated with neurological disorders, such as neurodegeneration, but causal understanding of these associations remains limited. Most mechanisms explaining how the microbiome may induce such remote neuronal effects involve microbially modulated metabolites that influx into the 'sterile' host. Some metabolites are able to cross the blood-brain barrier (BBB) to reach the central nervous system, where they can impact a variety of cells and processes. Alternatively, metabolites may directly signal to peripheral nerves to act as neurotransmitters or exert modulatory functions, or impact immune responses, which, in turn, modulate neuronal function and associated disease propensity. Herein, we review the current knowledge highlighting microbiome-modulated metabolite impacts on neuronal disease, while discussing unknowns, controversies and prospects impacting this rapidly evolving research field.

Waste clearance shapes aging brain health

Brain health is intimately connected to fluid flow dynamics that cleanse the brain of potentially harmful waste material. This system is regulated by vascular dynamics, the maintenance of perivascular spaces, neural activity during sleep, and lymphatic drainage in the meningeal layers. However, aging can impinge on each of these layers of regulation, leading to impaired brain cleansing and the emergence of various age-associated neurological disorders, including Alzheimer's and Parkinson's diseases. Understanding the intricacies of fluid flow regulation in the brain and how this becomes altered with age could reveal new targets and therapeutic strategies to tackle age-associated neurological decline.

Repetitive Transcranial Magnetic Stimulation and Tai Chi Chuan for Older Adults With Sleep Disorders and Mild Cognitive Impairment: A Randomized Clinical Trial

Importance

Sleep disorders and mild cognitive impairment (MCI) commonly coexist in older adults, increasing their risk of developing dementia. Long-term tai chi chuan has been proven to improve sleep quality in older adults. However, their adherence to extended training regimens can be challenging. Repetitive transcranial magnetic stimulation (rTMS) is a neuromodulation technique that may enhance the benefits of exercise.

Objective

To investigate whether 1-Hz rTMS of the right dorsolateral prefrontal cortex could enhance the clinical benefits of tai chi chuan in improving sleep quality and cognitive function among older adults with sleep disorders and MCI.

Design, Setting, and Participants

This 2-arm, sham-controlled, assessor-masked randomized clinical trial was conducted at a university hospital in China between October 2022 and February 2024. Adults aged 60 to 75 years with sleep disorders and MCI were eligible. Data analysis was performed from February to May 2024.

Intervention

Participants were randomized in a 1:1 ratio to an experimental group (tai chi chuan and 1-Hz rTMS) or a sham group (tai chi chuan and sham rTMS). Each participant received 30 sessions of personalized rTMS targeting the right dorsolateral prefrontal cortex, and the sham group underwent the same procedure. The 2 groups received 30 sessions of 60 minutes of the 24-form simplified tai chi chuan, 5 times per week for 6 weeks.

Main Outcomes and Measures

The primary outcomes were subjective sleep quality assessed by the Pittsburgh Sleep Quality Index (PSQI), in which scores range from 0 to 21, with lower scores indicating a healthier sleep quality, and global cognitive function assessed by the Montreal Cognitive Assessment (MoCA), in which scores range from 0 to 30, with higher scores indicating less cognitive impairment. The secondary outcomes included measures of objective sleep actigraphy, anxiety and depression scales, and other cognitive subdomains. Assessments were performed at baseline, 6 weeks after the intervention, and at the 12-week follow-up.

Results

A total of 110 participants (mean [SD] age, 67.9 [4.6] years; 68 female [61.8%]) were randomized to the experimental group (n = 55) and the sham group (n = 55) and included in the intention-to-treat analysis. At 6 weeks after the intervention, compared with the sham group, the experimental group showed a lower PSQI score (between-group mean difference, -3.1 [95% CI, -4.2 to -2.1]; P < .001) and a higher MoCA score (between-group mean difference, 1.4 [95% CI, 0.7-2.1]; P < .001). The per-protocol dataset analyses and 12-week follow-up showed similar results. The generalized estimated equation model revealed an interaction effect between the PSQI score (mean difference, -2.1 [95% CI, -3.1 to -0.1]; P < .001) and the MoCA total score (mean difference, 0.9 [95% CI, 0.1-1.6]; P = .01). There were 7 nonserious, unrelated adverse events (experimental group: 2; sham group: 5) with no significant difference between the 2 groups.

Conclusions and Relevance

In this randomized clinical trial, the findings suggest that 1-Hz rTMS enhanced the clinical benefits of tai chi chuan in improving sleep quality and cognitive function among older adults with sleep disorders and MCI, which may be related to alterations in neural plasticity. These findings provide novel data on nonpharmacologic strategies for the rehabilitation of sleep disorders and may delay or even prevent MCI.

Trial Registration

Chinese Clinical Trial Registry Identifier: ChiCTR2200063274.

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.

Depleting parenchymal border macrophages alleviates cerebral edema and neuroinflammation following status epilepticus

BACKGROUND

Status epilepticus (SE) is a common severe neurological emergency. Cerebral edema caused by SE is unavoidable and may exacerbate epilepsy. Recent studies have identified cerebrospinal fluid (CSF) as a crucial fluid source of initial cerebral edema following ischemic stroke and cardiac arrest. Moreover, synchronized neuronal firings drive CSF influx into interstitial fluid (ISF). Parenchymal border macrophages (PBMs) have been found to play a role in regulating CSF flow dynamics. However, the involvement of CSF and PBMs in cerebral edema during SE remains unclear. Here, we investigated the fluid source of cerebral edema in the initial phase of SE with the role of PBMs involved.

METHODS

Lithium chloride-pilocarpine was used to induce SE in C57BL/6 J mice. Electroencephalogram (EEG) was acquired to assess changes in relative EEG power pre- and post-seizure onset. Apparent diffusion coefficient (ADC) maps reconstructed from diffusion-weighted imaging (DWI) were utilized to evaluate cytotoxic edema. Blood-brain barrier (BBB) permeability was examined using sodium fluorescein (NaFl). CSF tracer influx into the brain was assessed by transcranial imaging and brain slices. PBMs were depleted using clodronate liposomes. Immunohistochemistry was used to evaluate PBM depletion, severity of vasogenic edema, inflammation, and neuronal damage.

RESULTS

During the initial stage of SE, relative EEG power sharply increased and ADC values significantly decreased. Concurrently, CSF tracer influx into the cortex significantly elevated, though NaFl leakage from blood to brain parenchyma did not evidently alter. Following depletion of PBM, CSF influx declined but AQP4 expression and polarization remained unaffected. Post-PBM depletion, there was no significant alteration in relative EEG power, yet CSF influx decreased substantially during the initial stage of SE. The degree of ADC decline lessened, IgG extravasation after SE decreased, activated microglia and proliferating astrocytes count fell, and neuronal damage post-SE alleviated.

CONCLUSIONS

CSF appeared to contribute to cerebral edema in SE. Depletion of PBM alleviated cytotoxic edema in the initial phase of SE, and subsequent vasogenic edema, inflammatory response and neurological damage were reduced. These findings may provide potential novel strategies for treating cerebral edema following SE.

Modified rat pup cerebrospinal fluid collection method

BACKGROUND

Cerebrospinal fluid (CSF) reflects biochemical changes in the brain due to its direct contact with brain interstitial fluid, making it a valuable tool for diagnosing and monitoring disease progression and therapeutic effectiveness in clinical practice. However, collecting CSF in animal studies, particularly from small animals like rat pups or mice, poses significant challenges.

NEW METHOD

After attempting various reported protocols, we encountered difficulties in consistently obtaining sufficient CSF from rat pups (P7-P42). Consequently, we modified these methods and developed a protocol with controllable and precise parameters for each step, enhancing reproducibility across different researchers.

RESULTS

The newly developed method enables rapid, single-operator, and reproducible CSF extraction while ensuring high-quality (the absorbance of the "quality control solution" at 415 nm < 0.05 AU, an indicator of oxyhemoglobin contamination for the collected CSF samples) and high-yield samples (33 ± 2.128 μL for P7 pups, 34.10 ± 2.747 μL for P8 pups, 36.67 ± 3.997 μL for P9 pups, 36.90 ± 1.946 μL for P10 pups, 35.11 ± 3.285 μL for P10 hypoxic-ischemic brain damage (HIBD) pups and 51.70 ± 5.256 μL for P42 pups, respectively).

COMPARISON WITH EXISTING METHODS

Unlike existing methods of CSF extraction in rat pups, our protocol has reproducible capillary pipette pulling parameters, controllable CSF quality indexes, and can be operated by a single person with high yield in a short time.

CONCLUSIONS

This paper provides a step-by-step comparison and discussion of the CSF collection process, establishing a method that enables a single operator to collect CSF rapidly, consistently, sufficiently, and with controlled quality.

The role and mechanism of Aβ clearance dysfunction in the glymphatic system in Alzheimer's disease comorbidity

Alzheimer's disease (AD) is the leading type of dementia globally, characterized by a complex pathogenesis that involves various comorbidities. An imbalance in the production and clearance of amyloid β-protein (Aβ) peptides in the brain is a key pathological mechanism of AD, with the glymphatic system playing a crucial role in Aβ clearance. Comorbidities associated with AD, such as diabetes, depression, and hypertension, not only affect Aβ production but also impair the brain's lymphatic system. Abnormalities in the structure and function of this system further weaken Aβ clearance capabilities, and the presence of comorbidities may exacerbate this process. This paper aims to review the role and specific mechanisms of impaired Aβ clearance via the glymphatic system in the context of AD comorbidities, providing new insights for the prevention and treatment of AD. Overall, the damage to the glymphatic system primarily focuses on aquaporin-4 (AQP4) and perivascular spaces (PVS), suggesting that maintaining the health of the glymphatic system may help slow the progression of AD and its comorbidities. Additionally, given the ongoing controversies regarding the structure of the glymphatic system, this paper revisits this structure and discusses the principles and characteristics of current detection methods for the glymphatic system.

Blood osmolytes such as sugar can drive brain fluid flows in a poroelastic model

The glymphatic system of fluid flow through brain tissue may clear amyloid-β during sleep and as such underlie the need for sleep. Dysfunctional glymphatic transport has been implicated in pathological conditions ranging from stroke and dementia to psychiatric illnesses. To date, the fastest observed in-vivo brain flows have been reported after the manipulation of blood osmotic pressures. Surprisingly, the brain seems to shrink while receiving more influx. Though influx of an incompressible fluid might expand the tissue, no physical theory for these observations has been proposed. We here present a minimal mathematical model of brain pressure, deformation, and fluid flows due to vascular osmotic pressures. The model is based on Darcy flow, linear poroelasticity theory and conservation of mass. We propose that a screened Poisson equation holds for interstitial pressure because vascular filtration corresponds to fluid divergence. The model resolves the apparent paradox of combined fluid influx with tissue shrinkage by showing that fluid absorption into the blood can drive both. In this model, small glucose concentration differences between plasma and brain can drive brain flow velocities observed in recent in-vivo assays. Osmosis may therefore drive brain fluid flow under physiological conditions and provide an explanation for the known correlations between diabetes and dementia.

Enhancing glymphatic fluid transport by pan-adrenergic inhibition suppresses epileptogenesis in male mice

Epileptogenesis is the process whereby the previously normally functioning brain begins to generate spontaneous, unprovoked seizures. Status epilepticus (SE), which entails a massive release of neuronal glutamate and other neuroactive substances, is one of the best-known triggers of epileptogenesis. We here asked whether pharmacologically promoting glymphatic clearance during or after SE is beneficial and able to attenuate the subsequent epileptogenesis. We induced SE in adult male mice by intrahippocampal kainic acid (KA) infusion. Acute administration of a cocktail of adrenergic receptor antagonists (propranolol, prazosin, and atipamezole: PPA), enhanced glymphatic flow and effectively reduced the severity of spontaneous seizures in the chronic phase. The PPA treatment also reduced reactive gliosis and inhibited the loss of polarized expression of AQP4 water channels in the vascular endfeet of astrocytes. Administration of PPA after cessation of SE (30 hours post KA) also effectively suppressed epileptogenesis and improved outcome. Conversely, mice with constitutively low glymphatic transport due to genetic deletion of the aquaporin 4 (AQP4) water channel showed exacerbation of KA-induced epileptogenesis. We conclude that the pharmacological modulation of glymphatic fluid transport may represent a potential strategy to dampen epileptogenesis and the occurrence of spontaneous seizures following KA-induced SE.

KETAMINE: Neural- and network-level changes

Ketamine is a widely used clinical drug that has several functional and clinical applications, including its use as an anaesthetic, analgesic, anti-depressive, anti-suicidal agent, among others. Among its diverse behavioral effects, it influences short-term memory and induces psychedelic effects. At the neural level across different brain areas, it modulates neural firing rates, neural tuning, brain oscillations, and modularity, while promoting hypersynchrony and random connectivity between neurons. In our recent studies we demonstrated that topical application of ketamine on the visual cortex alters neural tuning and promotes vigorous connectivity between neurons by decreasing their firing variability. Here, we begin with a brief review of the literature, followed by results from our lab, where we synthesize a dendritic model of neural tuning and network changes following ketamine application. This model has potential implications for focused modulation of cortical networks in clinical settings. Finally, we identify current gaps in research and suggest directions for future studies, particularly emphasizing the need for more animal experiments to establish a platform for effective translation and synergistic therapies combining ketamine with other protocols such as training and adaptation. In summary, investigating ketamine's broader systemic effects, not only provides deeper insight into cognitive functions and consciousness but also paves the way to advance therapies for neuropsychiatric disorders.

Can Neuromodulation Improve Sleep and Psychiatric Symptoms?

PURPOSE OF REVIEW

In this review, we evaluate recent studies that employ neuromodulation, in the form of non-invasive brain stimulation, to improve sleep in both healthy participants, and patients with psychiatric disorders. We review studies using transcranial electrical stimulation, transcranial magnetic stimulation, and closed-loop auditory stimulation, and consider both subjective and objective measures of sleep improvement.

RECENT FINDINGS

Neuromodulation can alter neuronal activity underlying sleep. However, few studies utilizing neuromodulation report improvements in objective measures of sleep. Enhancements in subjective measures of sleep quality are replicable, however, many studies conducted in this field suffer from methodological limitations, and the placebo effect is robust. Currently, evidence that neuromodulation can effectively enhance sleep is lacking. For the field to advance, methodological issues must be resolved, and the full range of objective measures of sleep architecture, alongside subjective measures of sleep quality, must be reported. Additionally, validation of effective modulation of neuronal activity should be done with neuroimaging.

Glymphatic clearance is enhanced during sleep

We here revisited the concept that glymphatic clearance is enhanced by sleep and anesthesia. Utilizing dynamic magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and fluorescent fiber photometry, we report brain glymphatic clearance is enhanced by both sleep and anesthesia, and sharply suppressed by wakefulness. Another key finding was that less tracer enters the brains of awake animals and that brain clearance across different brain states can only be compared after adjusting for the injected tracer dose.

Clearance and transport of amyloid β by peripheral monocytes correlate with Alzheimer's disease progression

Impaired clearance of amyloid β (Aβ) in late-onset Alzheimer's disease (AD) affects disease progression. The role of peripheral monocytes in Aβ clearance from the central nervous system (CNS) is unclear. We use a flow cytometry assay to identify Aβ-binding monocytes in blood, validated by confocal microscopy, Western blotting, and mass spectrometry. Flow cytometry immunophenotyping and correlation with AD biomarkers are studied in 150 participants from the AIBL study. We also examine monocytes in human cerebrospinal fluid (CSF) and their migration in an APP/PS1 mouse model. The assay reveals macrophage-like Aβ-binding monocytes with high phagocytic potential in both the periphery and CNS. We find lower surface Aβ levels in mild cognitive impairment (MCI) and AD-dementia patients compared to cognitively unimpaired individuals. Monocyte infiltration from blood to CSF and migration from CNS to peripheral lymph nodes and blood are observed. Here we show that Aβ-binding monocytes may play a role in CNS Aβ clearance, suggesting their potential as a biomarker for AD diagnosis and monitoring.

The anatomy of brainwashing

Glymphatic-lymphatic brain cleansing may reveal new therapeutic strategies.

Long-wavelength traveling waves of vasomotion modulate the perfusion of cortex

Brain arterioles are active, multicellular complexes whose diameters oscillate at ∼ 0.1 Hz. We assess the physiological impact and spatiotemporal dynamics of vaso-oscillations in the awake mouse. First, vaso-oscillations in penetrating arterioles, which source blood from pial arterioles to the capillary bed, profoundly impact perfusion throughout neocortex. The modulation in flux during resting-state activity exceeds that of stimulus-induced activity. Second, the change in perfusion through arterioles relative to the change in their diameter is weak. This implies that the capillary bed dominates the hydrodynamic resistance of brain vasculature. Lastly, the phase of vaso-oscillations evolves slowly along arterioles, with a wavelength that exceeds the span of the cortical mantle and sufficient variability to establish functional cortical areas as parcels of uniform phase. The phase-gradient supports traveling waves in either direction along both pial and penetrating arterioles. This implies that waves along penetrating arterioles can mix, but not directionally transport, interstitial fluids.

Modal Analysis of Cerebrovascular Effects for Digital Health Integration of Neurostimulation Therapies-A Review of Technology Concepts

Transcranial electrical stimulation (tES) is increasingly recognized for its potential to modulate cerebral blood flow (CBF) and evoke cerebrovascular reactivity (CVR), which are crucial in conditions like mild cognitive impairment (MCI) and dementia. This study explores the impact of tES on the neurovascular unit (NVU), employing a physiological modeling approach to simulate the vascular response to electric fields generated by tES. Utilizing the FitzHugh-Nagumo model for neuroelectrical activity, we demonstrate how tES can initiate vascular responses such as vasoconstriction followed by delayed vasodilation in cerebral arterioles, potentially modulated by a combination of local metabolic demands and autonomic regulation (pivotal locus coeruleus). Here, four distinct pathways within the NVU were modeled to reflect the complex interplay between synaptic activity, astrocytic influences, perivascular potassium dynamics, and smooth muscle cell responses. Modal analysis revealed characteristic dynamics of these pathways, suggesting that oscillatory tES may finely tune the vascular tone by modulating the stiffness and elasticity of blood vessel walls, possibly by also impacting endothelial glycocalyx function. The findings underscore the therapeutic potential vis-à-vis blood-brain barrier safety of tES in modulating neurovascular coupling and cognitive function needing the precise modulation of NVU dynamics. This technology review supports the human-in-the-loop integration of tES leveraging digital health technologies for the personalized management of cerebral blood flow, offering new avenues for treating vascular cognitive disorders. Future studies should aim to optimize tES parameters using computational modeling and validate these models in clinical settings, enhancing the understanding of tES in neurovascular health.

Ultrasonic cerebrospinal fluid clearance improves outcomes in hemorrhagic brain injury models

Impaired clearance of the byproducts of aging and neurologic disease from the brain exacerbates disease progression and severity. We have developed a noninvasive, low intensity transcranial focused ultrasound protocol that facilitates the removal of pathogenic substances from the cerebrospinal fluid (CSF) and the brain interstitium. This protocol clears neurofilament light chain (NfL) - an aging byproduct - in aged mice and clears red blood cells (RBCs) from the central nervous system in two mouse models of hemorrhagic brain injury. Cleared RBCs accumulate in the cervical lymph nodes from both the CSF and interstitial compartments, indicating clearance through meningeal lymphatics. Treating these hemorrhagic brain injury models with this ultrasound protocol reduced neuroinflammatory and neurocytotoxic profiles, improved behavioral outcomes, decreased morbidity and, importantly, increased survival. RBC clearance efficacy was blocked by mechanosensitive channel antagonism and was effective when applied in anesthetized subjects, indicating a mechanosensitive channel mediated mechanism that does not depend on sensory stimulation or a specific neural activity pattern. Notably, this protocol qualifies for an FDA non-significant risk designation given its low intensity, making it readily clinically translatable. Overall, our results demonstrate that this low-intensity transcranial focused ultrasound protocol clears hemorrhage and other harmful substances from the brain via the meningeal lymphatic system, potentially offering a novel therapeutic tool for varied neurologic disorders.

Stress-induced dysfunction of neurovascular astrocytes contributes to sex-specific behavioral deficits

Astrocytes form an integral component of the neurovascular unit, ensheathing brain blood vessels with projections high in aquaporin-4 (AQP4) expression. These AQP4-rich projections facilitate interaction between the vascular endothelium, astrocytes, and neurons, and help stabilize vascular morphology. Studies using preclinical models of psychological stress and post-mortem tissue from patients with major depressive disorder (MDD) have reported reductions in AQP4, loss of astrocytic structures, and vascular impairment in the prefrontal cortex (PFC). Though compelling, the role of AQP4 in mediating stress-induced alterations in blood vessel function and behavior remains unclear. Here, we address this, alongside potential sex differences in chronic unpredictable stress (CUS) effects on astrocyte phenotype, blood-brain barrier integrity, and behavior. CUS led to pronounced shifts in stress-coping behavior and working memory deficits in male -but not female- mice. Following behavioral testing, astrocytes from the frontal cortex were isolated for gene expression analyses. We found that CUS increased various transcripts associated with blood vessel maintenance in astrocytes from males, but either had no effect on- or decreased- these genes in females. Furthermore, CUS caused a reduction in vascular-localized AQP4 and elevated extravasation of a small molecule fluorescent reporter (Dextran) in the PFC in males but not females. Studies showed that knockdown of AQP4 in the PFC in males is sufficient to disrupt astrocyte phenotype and increase behavioral susceptibility to a sub-chronic stressor. Collectively, these findings provide initial evidence that sex-specific alterations in astrocyte phenotype and neurovascular integrity in the PFC contribute to behavioral and cognitive consequences following chronic stress.