Dynamic changes in perivascular space morphology predict signs of spaceflight-associated neuro-ocular syndrome in bed rest.

During long-duration spaceflight, astronauts experience headward fluid shifts and expansion of the cerebral perivascular spaces (PVS). A major limitation to our understanding of the changes in brain structure and physiology induced by spaceflight stems from the logistical difficulties of studying astronauts. The current study aimed to determine whether PVS changes also occur on Earth with the spaceflight analog head-down tilt bed rest (HDBR). We examined how the number and morphology of magnetic resonance imaging-visible PVS (MV-PVS) are affected by HDBR with and without elevated carbon dioxide (CO2). These environments mimic the headward fluid shifts, body unloading, and elevated CO2 observed aboard the International Space Station. Additionally, we sought to understand how changes in MV-PVS are associated with signs of Spaceflight Associated Neuro-ocular Syndrome (SANS), ocular structural alterations that can occur with spaceflight. Participants were separated into two bed rest campaigns: HDBR (60 days) and HDBR + CO2 (30 days with elevated ambient CO2). Both groups completed multiple magnetic resonance image acquisitions before, during, and post-bed rest. We found that at the group level, neither spaceflight analog affected MV-PVS quantity or morphology. However, when taking into account SANS status, persons exhibiting signs of SANS showed little or no MV-PVS changes, whereas their No-SANS counterparts showed MV-PVS morphological changes during the HDBR + CO2 campaign. These findings highlight spaceflight analogs as models for inducing changes in MV-PVS and implicate MV-PVS dynamic compliance as a mechanism underlying SANS. These findings may lead to countermeasures to mitigate health risks associated with human spaceflight.

CSF ß-Amyloid and Tau Biomarker Changes in Veterans With Mild Traumatic Brain Injury.

BACKGROUND AND OBJECTIVES: Moderate-to-severe traumatic brain injuries (TBI) have been reported to increase the risk of Alzheimer disease (AD). Whether mild TBI (mTBI) in veterans confers a similar increased risk of AD is less known. This study investigated early AD changes using CSF biomarkers in veterans with blast mTBI. METHODS: This was a cross-sectional case-control study of veterans with mTBI and non-mTBI veterans and civilians from 2 study sources. Blast-mTBI veterans had at least 1 war zone blast or combined blast/impact mTBI meeting Veterans Affairs (VA) and Department of Defense (DoD) criteria for mTBI. Non-mTBI participants had no lifetime history of TBI. All participants underwent standardized clinical and neuropsychological assessments and lumbar puncture for collection of the CSF. CSF biomarkers were measured using MesoScale Discovery assays for Aß40 and Aß42 and INNOTEST ELISAs for phosphorylated tau181 (p-tau181) and total tau (t-tau). RESULTS: Our sample comprised 51 participants with mTBI and 85 non-mTBI participants with mean (SD) ages 34.0 (10.1) and 33.5 years (8.9), respectively. All participants but 1 (99%) were male. Differences in CSF AD biomarkers between mTBI and non-mTBI groups were age dependent and most pronounced at older ages (omnibus test p ≤ 0.08). At age 50 years, the mTBI group had lower mean [95% CI] CSF Aß42 and Aß40 than the non-mTBI group by 154 [-12 to 319] and 1864 [610-3,118] pg/mL, respectively. By contrast, CSF p-tau181 and t-tau mean levels remained relatively constant with age in participants with mTBI, while tending to be higher at older ages for the non-mTBI group. The mTBI group also demonstrated poorer cognitive performance at older ages (omnibus p < 0.08): at age 50 years, the mean TMT-B time was higher by 34 seconds [10-58] and the mean CVLT-II short-delay recall was lower by 4.2 points [1.9-6.6]. Poorer verbal memory and verbal fluency performance were associated with lower CSF Aß42 (p ≤ 0.05) in older participants. DISCUSSION: CSF Aß levels decreased in middle-aged veterans with blast-related mTBI. These data suggest that chronic neuropathologic processes associated with blast mTBI share properties in common with pathogenic processes known to portend AD onset, thus raising concern that veterans with blast-related mTBI may develop a dementing disorder later in life.

Inflammatory biomarkers for neurobehavioral dysregulation in former American football players: findings from the DIAGNOSE CTE Research Project.

BACKGROUND: Traumatic encephalopathy syndrome (TES) is defined as the clinical manifestation of the neuropathological entity chronic traumatic encephalopathy (CTE). A core feature of TES is neurobehavioral dysregulation (NBD), a neuropsychiatric syndrome in repetitive head impact (RHI)-exposed individuals, characterized by a poor regulation of emotions/behavior. To discover biological correlates for NBD, we investigated the association between biomarkers of inflammation (interleukin (IL)-1ß, IL-6, IL-8, IL-10, C-reactive protein (CRP), tumor necrosis factor (TNF)-α) in cerebrospinal fluid (CSF) and NBD symptoms in former American football players and unexposed individuals. METHODS: Our cohort consisted of former American football players, with (n = 104) or without (n = 76) NBD diagnosis, as well as asymptomatic unexposed individuals (n = 55) from the DIAGNOSE CTE Research Project. Specific measures for NBD were derived (i.e., explosivity, emotional dyscontrol, impulsivity, affective lability, and a total NBD score) from a factor analysis of multiple self-report neuropsychiatric measures. Analyses of covariance tested differences in biomarker concentrations between the three groups. Within former football players, multivariable linear regression models assessed relationships among log-transformed inflammatory biomarkers, proxies for RHI exposure (total years of football, cumulative head impact index), and NBD factor scores, adjusted for relevant confounding variables. Sensitivity analyses tested (1) differences in age subgroups (< 60, ≥ 60 years); (2) whether associations could be identified with plasma inflammatory biomarkers; (3) associations between neurodegeneration and NBD, using plasma neurofilament light (NfL) chain protein; and (4) associations between biomarkers and cognitive performance to explore broader clinical symptoms related to TES. RESULTS: CSF IL-6 was higher in former American football players with NBD diagnosis compared to players without NBD. Furthermore, elevated levels of CSF IL-6 were significantly associated with higher emotional dyscontrol, affective lability, impulsivity, and total NBD scores. In older football players, plasma NfL was associated with higher emotional dyscontrol and impulsivity, but also with worse executive function and processing speed. Proxies for RHI exposure were not significantly associated with biomarker concentrations. CONCLUSION: Specific NBD symptoms in former American football players may result from multiple factors, including neuroinflammation and neurodegeneration. Future studies need to unravel the exact link between NBD and RHI exposure, including the role of other pathophysiological pathways.

Glymphatic and lymphatic communication with systemic responses during physiological and pathological conditions in the central nervous system.

Crosstalk between central nervous system (CNS) and systemic responses is important in many pathological conditions, including stroke, neurodegeneration, schizophrenia, epilepsy, etc. Accumulating evidence suggest that signals for central-systemic crosstalk may utilize glymphatic and lymphatic pathways. The glymphatic system is functionally connected to the meningeal lymphatic system, and together these pathways may be involved in the distribution of soluble proteins and clearance of metabolites and waste products from the CNS. Lymphatic vessels in the dura and meninges transport cerebrospinal fluid, in part collected from the glymphatic system, to the cervical lymph nodes, where solutes coming from the brain (i.e., VEGFC, oligomeric α-syn, ß-amyloid) might activate a systemic inflammatory response. There is also an element of time since the immune system is strongly regulated by circadian rhythms, and both glymphatic and lymphatic dynamics have been shown to change during the day and night. Understanding the mechanisms regulating the brain-cervical lymph node (CLN) signaling and how it might be affected by diurnal or circadian rhythms is fundamental to find specific targets and timing for therapeutic interventions.

Perivascular Space Burden and Cerebrospinal Fluid Biomarkers in US Veterans With Blast-Related Mild Traumatic Brain Injury.

Blast-related mild traumatic brain injury (mTBI) is recognized as the "signature injury" of the Iraq and Afghanistan wars. Sleep disruption, mTBI, and neuroinflammation have been individually linked to cerebral perivascular space (PVS) dilatation. Dilated PVSs are putative markers of impaired cerebrospinal fluid (CSF) and interstitial fluid exchange, which plays an important role in removing cerebral waste. The aim of this cross-sectional, retrospective study was to define associations between biomarkers of inflammation and MRI-visible PVS (MV-PVS) burden in Veterans after blast-related mTBI (blast-mTBI) and controls. The CSF and plasma inflammatory biomarker concentrations were compared between blast-mTBI and control groups and correlated with MV-PVS volume and number per white matter cm3. Multiple regression analyses were performed with inflammatory biomarkers as predictors and MV-PVS burden as the outcome. Correction for multiple comparisons was performed using the Banjamini-Hochberg method with a false discovery rate of 0.05. There were no group-wise differences in MV-PVS burden between Veterans with blast-mTBI and controls. Greater MV-PVS burden was significantly associated with higher concentrations of several proinflammatory biomarkers from CSF (i.e., eotaxin, MCP-1, IL-6, IL-8) and plasma (i.e., MCP-4, IL-13) in the blast-mTBI group only. After controlling for sleep time and symptoms of post-traumatic stress disorder, temporal MV-PVS burden remained significantly associated with higher CSF markers of inflammation in the blast-mTBI group only. These data support an association between central, rather than peripheral, neuroinflammation and MV-PVS burden in Veterans with blast-mTBI independent of sleep. Future studies should continue to explore the role of blast-mTBI related central inflammation in MV-PVS development, as well as investigate the impact of subclinical exposures on MV-PVS burden.

A case of prazosin in treatment of rapid eye movement sleep behavior disorder.

Rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by dream-enactment behaviors that emerge during a loss of REM sleep atonia. Untreated RBD carries risks for physical injury from falls or other traumatic events during dream enactment as well as risk of injury to the bed partner. Currently, melatonin and clonazepam are the mainstay pharmacological therapies for RBD. However, therapeutic response to these medications is variable. While older adults are most vulnerable to RBD, they are also particularly vulnerable to the adverse effects of benzodiazepines, including increased risk of falls, cognitive impairment, and increased risk of Alzheimer disease. Prazosin is a centrally active alpha-1 adrenergic receptor antagonist often prescribed for trauma nightmares characterized by REM sleep without atonia in patients with posttraumatic stress disorder. We report a case of successful RBD management with prazosin in a patient in whom high-dose melatonin was ineffective. Although there was no observable reduction in dream-enactment behaviors with high-dose melatonin, the possibility of a synergistic effect of prazosin combined with melatonin cannot be ruled out. This case report supports further evaluation of prazosin as a potential therapeutic for RBD. CITATION: Cho Y, Iliff JJ, Lim MM, Raskind M, Peskind E. A case of prazosin in treatment of rapid eye movement sleep behavior disorder. J Clin Sleep Med. 2024;20(2):319-321.

Longitudinal Sleep Patterns and Cognitive Impairment in Older Adults.

Importance: Sleep disturbances and clinical sleep disorders are associated with all-cause dementia and neurodegenerative conditions, but it remains unclear how longitudinal changes in sleep impact the incidence of cognitive impairment. Objective: To evaluate the association of longitudinal sleep patterns with age-related changes in cognitive function in healthy older adults. Design, Setting, and Participants: This cross-sectional study is a retrospective longitudinal analyses of the Seattle Longitudinal Study (SLS), which evaluated self-reported sleep duration (1993-2012) and cognitive performance (1997-2020) in older adults. Participants within the SLS were enrolled as part of a community-based cohort from the Group Health Cooperative of Puget Sound and Health Maintenance Organization of Washington between 1956 and 2020. Data analysis was performed from September 2020 to May 2023. Main Outcomes and Measures: The main outcome for this study was cognitive impairment, as defined by subthreshold performance on both the Mini-Mental State Examination and the Mattis Dementia Rating Scale. Sleep duration was defined by self-report of median nightly sleep duration over the last week and was assessed longitudinally over multiple time points. Median sleep duration, sleep phenotype (short sleep, median ≤7 hours; medium sleep, median = 7 hour; long sleep, median ≥7 hours), change in sleep duration (slope), and variability in sleep duration (SD of median sleep duration, or sleep variability) were evaluated. Results: Of the participants enrolled in SLS, only 1104 participants who were administered both the Health Behavior Questionnaire and the neuropsychologic battery were included for analysis in this study. A total of 826 individuals (mean [SD] age, 76.3 [11.8] years; 468 women [56.7%]; 217 apolipoprotein E ε4 allele carriers [26.3%]) had complete demographic information and were included in the study. Analysis using a Cox proportional hazard regression model (concordance, 0.76) showed that status as a short sleeper (hazard ratio, 3.67; 95% CI, 1.59-8.50) and higher sleep variability (hazard ratio, 3.06; 95% CI, 1.14-5.49) were significantly associated with the incidence of cognitive impairment. Conclusions and Relevance: In this community-based longitudinal study of the association between sleep patterns and cognitive performance, the short sleep phenotype was significantly associated with impaired cognitive performance. Furthermore, high sleep variability in longitudinal sleep duration was significantly associated with the incidence of cognitive impairment, highlighting the possibility that instability in sleep duration over long periods of time may impact cognitive decline in older adults.

Neuronal Ndst1 depletion accelerates prion protein clearance and slows neurodegeneration in prion infection.

Select prion diseases are characterized by widespread cerebral plaque-like deposits of amyloid fibrils enriched in heparan sulfate (HS), a abundant extracellular matrix component. HS facilitates fibril formation in vitro, yet how HS impacts fibrillar plaque growth within the brain is unclear. Here we found that prion-bound HS chains are highly sulfated, and that the sulfation is essential for accelerating prion conversion in vitro. Using conditional knockout mice to deplete the HS sulfation enzyme, Ndst1 (N-deacetylase / N-sulfotransferase) from neurons or astrocytes, we investigated how reducing HS sulfation impacts survival and prion aggregate distribution during a prion infection. Neuronal Ndst1-depleted mice survived longer and showed fewer and smaller parenchymal plaques, shorter fibrils, and increased vascular amyloid, consistent with enhanced aggregate transit toward perivascular drainage channels. The prolonged survival was strain-dependent, affecting mice infected with extracellular, plaque-forming, but not membrane bound, prions. Live PET imaging revealed rapid clearance of recombinant prion protein monomers into the CSF of neuronal Ndst1- deficient mice, neuronal, further suggesting that HS sulfate groups hinder transit of extracellular prion protein monomers. Our results directly show how a host cofactor slows the spread of prion protein through the extracellular space and identify an enzyme to target to facilitate aggregate clearance.

Preliminary cross-sectional investigations into the human glymphatic system using multiple novel non-contrast MRI methods.

We discuss two potential non-invasive MRI methods to cross-sectionally study two distinct facets of the glymphatic system and its association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D*, or cerebrospinal fluid (CSF) movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded multi-delay arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and transendothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N=9, 6F, 23±3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults, (6F, 67±3 years old) were imaged after a night of normal sleep only and compared with the young adults. D* in SAS was significantly (p<0.05) lesser after sleep deprivation (0.014±0.001 mm2/s) than after normal sleep (0.016±0.001 mm2/s), but was unchanged with aging. Cortical CBF and Tex on the other hand, were unchanged after sleep deprivation but were significantly lower in older adults (37±3 ml/100g/min, 476±66 ms) than young adults (42±2 ml/100g/min, 624±66 ms). IVIM was thus, sensitive to sleep physiology and multi-echo, multi-delay ASL was sensitive to aging.

Instability in longitudinal sleep duration predicts cognitive impairment in aged participants of the Seattle Longitudinal Study.

Importance: Sleep disturbances and clinical sleep disorders are associated with all-cause dementia and neurodegenerative conditions. It remains unclear how longitudinal changes in sleep impact the incidence of cognitive impairment. Objective: To evaluate how longitudinal sleep patterns contribute to age-related changes in cognitive function in healthy adults. Design Setting Participants: This study utilizes retrospective longitudinal analyses of a community-based study within Seattle, evaluating self-reported sleep (1993-2012) and cognitive performance (1997-2020) in aged adults. Main Outcomes and Measures: The main outcome is cognitive impairment as defined by sub-threshold performance on 2 of 4 neuropsychological batteries: Mini-Mental State Examination (MMSE), Mattis Dementia Rating Scale, Trail Making Test, and Wechsler Adult Intelligent Scale (Revised). Sleep duration was defined through self-report of 'average nightly sleep duration over the last week' and assessed longitudinally. Median sleep duration, change in sleep duration (slope), variability in sleep duration (standard deviation, Sleep Variability), and sleep phenotype ("Short Sleep" median ≤7hrs.; "Medium Sleep" median = 7hrs; "Long Sleep" median ≥7hrs.). Results: A total of 822 individuals (mean age of 76.2 years [11.8]; 466 women [56.7%]; 216 APOE allele positive [26.3%]) were included in the study. Analysis using a Cox Proportional Hazard Regression model (concordance 0.70) showed that increased Sleep Variability (95% CI [1.27,3.86]) was significantly associated with the incidence of cognitive impairment. Further analysis using linear regression prediction analysis (R2=0.201, F (10, 168)=6.010, p=2.67E-07) showed that high Sleep Variability (ß=0.3491; p=0.048) was a significant predictor of cognitive impairment over a 10-year period. Conclusions and Relevance: High variability in longitudinal sleep duration was significantly associated with the incidence of cognitive impairment and predictive of decline in cognitive performance ten years later. These data highlight that instability in longitudinal sleep duration may contribute to age-related cognitive decline.

Emerging Perspectives on MRI Application in Multiple Sclerosis: Moving from Pathophysiology to Clinical Practice.

MRI plays a central role in the diagnosis of multiple sclerosis (MS) and in the monitoring of disease course and treatment response. Advanced MRI techniques have shed light on MS biology and facilitated the search for neuroimaging markers that may be applicable in clinical practice. MRI has led to improvements in the accuracy of MS diagnosis and a deeper understanding of disease progression. This has also resulted in a plethora of potential MRI markers, the importance and validity of which remain to be proven. Here, five recent emerging perspectives arising from the use of MRI in MS, from pathophysiology to clinical application, will be discussed. These are the feasibility of noninvasive MRI-based approaches to measure glymphatic function and its impairment; T1-weighted to T2-weighted intensity ratio to quantify myelin content; classification of MS phenotypes based on their MRI features rather than on their clinical features; clinical relevance of gray matter atrophy versus white matter atrophy; and time-varying versus static resting-state functional connectivity in evaluating brain functional organization. These topics are critically discussed, which may guide future applications in the field.

Interrogation of dynamic glucose-enhanced MRI and fluorescence-based imaging reveals a perturbed glymphatic network in Huntington's disease.

Huntington's disease (HD) is a neurodegenerative disorder that presents with progressive motor, mental, and cognitive impairment leading to early disability and mortality. The accumulation of mutant huntingtin protein aggregates in neurons is a pathological hallmark of HD. The glymphatic system, a brain-wide perivascular network, facilitates the exchange of interstitial fluid (ISF) and cerebrospinal fluid (CSF), supporting interstitial solute clearance including abnormal proteins from mammalian brains. In this study, we employed dynamic glucose-enhanced (DGE) MRI to measure D-glucose clearance from CSF as a tool to assess CSF clearance capacity to predict glymphatic function in a mouse model of HD. Our results demonstrate significantly diminished CSF clearance efficiency in premanifest zQ175 HD mice. The impairment of CSF clearance of D-glucose, measured by DGE MRI, worsened with disease progression. These DGE MRI findings in compromised glymphatic function in HD mice were further confirmed with fluorescence-based imaging of glymphatic CSF tracer influx, suggesting an impaired glymphatic function in premanifest stage of HD. Moreover, expression of the astroglial water channel aquaporin-4 (AQP4) in the perivascular compartment, a key mediator of glymphatic function, was significantly diminished in both HD mouse brain as well as postmortem human HD brain. Our data, acquired using a clinically translatable MRI approach, indicate a perturbed glymphatic network in the HD brain as early as in the premanifest stage. Further validation of these findings in clinical studies should provide insights into potential of glymphatic clearance as a HD biomarker and for glymphatic functioning as a disease-modifying therapeutic target for HD.

Quantification approaches for magnetic resonance imaging following intravenous gadolinium injection: A window into brain-wide glymphatic function.

The glymphatic system is a brain-wide network of perivascular pathways along which cerebrospinal fluid and interstitial fluid rapidly exchange, facilitating solute and waste clearance from the brain parenchyma. The characterization of this exchange process in humans has relied primarily upon serial magnetic resonance imaging following intrathecal gadolinium-based contrast agent injection. However, less invasive approaches are needed. Here, we administered a gadolinium-based contrast agent intravenously in eight healthy participants and acquired magnetic resonance imaging scans prior to and 30, 90, 180, and 360 min post contrast injection. Using a region-of-interest approach, we observed that peripheral tissues and blood vessels exhibited high enhancement at 30 min after contrast administration, likely reflecting vascular and peripheral interstitial distribution of the gadolinium-based contrast agent. Ventricular, grey matter and white matter enhancement peaked at 90 min, declining thereafter. Using k-means clustering, we identify distinct distribution volumes reflecting the leptomeningeal perivascular network, superficial grey matter and deep grey/white matter that exhibit a sequential enhancement pattern consistent with parenchymal contrast enhancement via the subarachnoid cerebrospinal fluid compartment. We also outline the importance of correcting for (otherwise automatic) autoscaling of signal intensities, which could potentially lead to misinterpretation of gadolinium-based contrast agent distribution kinetics. In summary, we visualize and quantify delayed tissue enhancement following intravenous administration of gadolinium-based contrast agent in healthy human participants.

The effect of aquaporin-4 mis-localization on Aß deposition in mice.

The reduced clearance of amyloid-ß (Aß) is thought to contribute to the development of the pathology associated with Alzheimer's disease (AD), which is characterized by the deposition of Aß plaques. Previous studies have shown that Aß is cleared via the glymphatic system, a brain-wide network of perivascular pathways that supports the exchange between cerebrospinal fluid and interstitial fluid within the brain. Such exchange is dependent upon the water channel aquaporin-4 (AQP4), localized at astrocytic endfeet. While prior studies have shown that both the loss and mislocalization of AQP4 slow Aß clearance and promote Aß plaque formation, the relative impact of the loss or mislocalization of AQP4 on Aß deposition has never been directly compared. In this study, we evaluated how the deposition of Aß plaques within the 5XFAD mouse line is impacted by either Aqp4 gene deletion or the loss of AQP4 localization in the α-syntrophin (Snta1) knockout mouse. We observed that both the absence (Aqp4 KO) and mislocalization (Snta1 KO) of AQP4 significantly increases the parenchymal Aß plaque and microvascular Aß deposition across the brain, when compared with 5XFAD littermate controls. Further, the mislocalization of AQP4 had a more pronounced impact on Aß plaque deposition than did global Aqp4 gene deletion, perhaps pointing to a key role that mislocalization of perivascular AQP4 plays in AD pathogenesis.

Mapping the lymphatic system across body scales and expertise domains: A report from the 2021 National Heart, Lung, and Blood Institute workshop at the Boston Lymphatic Symposium.

Enhancing our understanding of lymphatic anatomy from the microscopic to the anatomical scale is essential to discern how the structure and function of the lymphatic system interacts with different tissues and organs within the body and contributes to health and disease. The knowledge of molecular aspects of the lymphatic network is fundamental to understand the mechanisms of disease progression and prevention. Recent advances in mapping components of the lymphatic system using state of the art single cell technologies, the identification of novel biomarkers, new clinical imaging efforts, and computational tools which attempt to identify connections between these diverse technologies hold the potential to catalyze new strategies to address lymphatic diseases such as lymphedema and lipedema. This manuscript summarizes current knowledge of the lymphatic system and identifies prevailing challenges and opportunities to advance the field of lymphatic research as discussed by the experts in the workshop.

Locoregional CAR T cells for children with CNS tumors: Clinical procedure and catheter safety.

Central nervous system (CNS) tumors are the most common solid malignancy in the pediatric population. Based on adoptive cellular therapy's clinical success against childhood leukemia and the preclinical efficacy against pediatric CNS tumors, chimeric antigen receptor (CAR) T cells offer hope of improving outcomes for recurrent tumors and universally fatal diseases such as diffuse intrinsic pontine glioma (DIPG). However, a major obstacle for tumors of the brain and spine is ineffective T cell chemotaxis to disease sites. Locoregional CAR T cell delivery via infusion through an intracranial catheter is currently under study in multiple early phase clinical trials. Here, we describe the Seattle Children's single-institution experience including the multidisciplinary process for the preparation of successful, repetitive intracranial T cell infusion for children and the catheter-related safety of our 307 intracranial CAR T cell doses.

The glymphatic system: Current understanding and modeling.

We review theoretical and numerical models of the glymphatic system, which circulates cerebrospinal fluid and interstitial fluid around the brain, facilitating solute transport. Models enable hypothesis development and predictions of transport, with clinical applications including drug delivery, stroke, cardiac arrest, and neurodegenerative disorders like Alzheimer's disease. We sort existing models into broad categories by anatomical function: Perivascular flow, transport in brain parenchyma, interfaces to perivascular spaces, efflux routes, and links to neuronal activity. Needs and opportunities for future work are highlighted wherever possible; new models, expanded models, and novel experiments to inform models could all have tremendous value for advancing the field.

Dynamic infrared imaging of cerebrospinal fluid tracer influx into the brain.

Significance: The glymphatic system has been described recently as a series of perivascular channels that facilitate fluid exchange and solute clearance in the brain. Glymphatic dysfunction has been implicated in numerous pathological conditions, including Alzheimer's disease, traumatic brain injury, and stroke. Existing methods for assessing glymphatic function have been challenging: dynamic methods, such as two-photon microscopy and contrast-enhanced magnetic resonance imaging require expensive instrumentation and specific technical skills; slice-based fluorescent imaging is more readily implemented but lacks temporal resolution. Aim: To develop a straightforward and adaptable dynamic imaging approach for assessing glymphatic function in vivo in mice. Approach: Using a widely available small animal infrared (IR) imaging system (LICOR Pearl), visualization of IR cerebrospinal fluid tracer distribution over the cortical surface enables time-resolved measurement of the dynamics of glymphatic exchange. Using co-injection of IR and conventional fixable fluorescent tracers, dynamic imaging can be paired with whole-slice fluorescence imaging, permitting the quantification of glymphatic function throughout the brain as well as subsequent histological assessment. Results: These techniques were validated against one another, comparing differences between animals anesthetized with ketamine/xylazine and isoflurane. Conclusions: This technique permits sensitive dynamic imaging of glymphatic function, with the concurrent visualization of resolution of deeper structures.

Longitudinal MRI-visible perivascular space (PVS) changes with long-duration spaceflight.

Humans are exposed to extreme environmental stressors during spaceflight and return with alterations in brain structure and shifts in intracranial fluids. To date, no studies have evaluated the effects of spaceflight on perivascular spaces (PVSs) within the brain, which are believed to facilitate fluid drainage and brain homeostasis. Here, we examined how the number and morphology of magnetic resonance imaging (MRI)-visible PVSs are affected by spaceflight, including prior spaceflight experience. Fifteen astronauts underwent six T1-weighted 3 T MRI scans, twice prior to launch and four times following their return to Earth after ~ 6-month missions to the International Space Station. White matter MRI-visible PVS number and morphology were calculated using an established, automated segmentation algorithm. We validated our automated segmentation algorithm by comparing algorithm PVS counts with those identified by two trained raters in 50 randomly selected slices from this cohort; the automated algorithm performed similarly to visual ratings (r(48) = 0.77, p < 0.001). In addition, we found high reliability for four of five PVS metrics across the two pre-flight time points and across the four control time points (ICC(3,k) > 0.50). Among the astronaut cohort, we found that novice astronauts showed an increase in total PVS volume from pre- to post-flight, whereas experienced crewmembers did not (p = 0.020), suggesting that experienced astronauts may exhibit holdover effects from prior spaceflight(s). Greater pre-flight PVS load was associated with more prior flight experience (r = 0.60-0.71), though these relationships did not reach statistical significance (p > 0.05). Pre- to post-flight changes in ventricular volume were not significantly associated with changes in PVS characteristics, and the presence of spaceflight associated neuro-ocular syndrome (SANS) was not associated with PVS number or morphology. Together, these findings demonstrate that PVSs can be consistently identified on T1-weighted MRI scans, and that spaceflight is associated with PVS changes. Specifically, prior spaceflight experience may be an important factor in determining PVS characteristics.