Glymphatic system disruption as a mediator of brain trauma and chronic traumatic encephalopathy

Cannabidiol Alleviates Neurological Deficits After Traumatic Brain Injury by Improving Intracranial Lymphatic Drainage

Traumatic brain injury (TBI) persists as a substantial clinical dilemma, largely because of the absence of effective treatments. This challenge is exacerbated by the hindered clearance of intracranial metabolic byproducts and the continual accrual of deleterious proteins. The glymphatic system (GS) and meningeal lymphatic vessels (MLVs), key elements of the intracranial lymphatic network, play critical roles in the clearance of harmful substances. Cannabidiol (CBD) has shown promise in reducing metabolite overload and bolstering cognitive performance in various neurodegenerative diseases. The precise mechanisms attributing to its beneficial effects in TBI scenarios, however, are yet to be distinctly understood. Utilizing a fluid percussion injury paradigm, our research adopted a multifaceted approach, encompassing behavioral testing, immunofluorescence and immunohistochemical analyses, laser speckle imaging, western blot techniques, and bilateral cervical efferent lymphatic ligation. This methodology aimed to discern the influence of CBD on both neurological outcomes and intracranial lymphatic clearance in a murine TBI model. We observed that CBD administration notably ameliorated motor, memory, and cognitive functions, concurrently with a significant reduction in the concentration of phosphorylated tau protein and amyloid-β. In addition, CBD expedited the turnover and elimination of intracranial tracers, increased cerebral blood flow, and enhanced the efficacy of fluorescent tracer migration from MLVs to deep cervical lymph nodes (dCLNs). Remarkably, CBD treatment also induced a reversion in aquaporin-4 (AQP-4) polarization and curtailed neuroinflammatory indices. A pivotal discovery was that the surgical interruption of efferent lymphatic conduits in the neck nullified CBD's positive contributions to intracranial waste disposal and cognitive improvement, yet the anti-neuroinflammatory actions remained unaffected. These insights suggest that CBD may enhance intracranial metabolite clearance, potentially via the regulation of the intracranial lymphatic system, thereby offering neurofunctional prognostic improvement in TBI models. Our findings underscore the potential therapeutic applicability of CBD in TBI interventions, necessitating further comprehensive investigations and clinical validations to substantiate these initial conclusions.

Brain Fluid Clearance After Traumatic Brain Injury Measured Using Dynamic Positron Emission Tomography

Brain fluid clearance by pathways including the recently described paravascular glymphatic system is a critical homeostatic mechanism by which metabolic products, toxins, and other wastes are removed from the brain. Brain fluid clearance may be especially important after traumatic brain injury (TBI), when blood, neuronal debris, inflammatory cells, and other substances can be released and/or deposited. Using a non-invasive dynamic positron emission tomography (PET) method that models the rate at which an intravenously injected radiolabeled molecule (in this case 11C-flumazenil) is cleared from ventricular cerebrospinal fluid (CSF), we estimated the overall efficiency of brain fluid clearance in humans who had experienced complicated-mild or moderate TBI 3-6 months before neuroimaging (n = 7) as compared to healthy controls (n = 9). While there was no significant difference in ventricular clearance between TBI subjects and controls, there was a significant group difference in dependence of ventricular clearance upon tracer delivery/blood flow to the ventricles. Specifically, in controls, ventricular clearance was highly, linearly dependent upon blood flow to the ventricle, but this relation was disrupted in TBI subjects. When accounting for blood flow and group-specific alterations in blood flow, ventricular clearance was slightly (non-significantly) increased in TBI subjects as compared to controls. Current results contrast with past studies showing reduced glymphatic function after TBI and are consistent with possible differential effects of TBI on glymphatic versus non-glymphatic clearance mechanisms. Further study using multi-modal methods capable of assessing and disentangling blood flow and different aspects of fluid clearance is needed to clarify clearance alterations after TBI.

Ketamine Improves the Glymphatic Pathway by Reducing the Pyroptosis of Hippocampal Astrocytes in the Chronic Unpredictable Mild Stress Model

Ketamine as a glutamate receptor antagonist has a rapid, potent, and long-lasting antidepressant effect, but its specific mechanism is still not fully understood. Depression is associated with elevated levels of glutamate and astrocyte loss in the brain; the exploration of the relationships between ketamine's antidepressant effect and astrocytes has drawn great attention. Astrocytes and aquaporin 4 (AQP4) are essential components of the glymphatic system, which is a brain-wide perivascular pathway to help transport nutrients to the parenchyma and remove metabolic wastes. In this study, we investigated pyroptosis-associated protein Nlrp3/Caspase-1/Gsdmd-N expression in the hippocampus of mice and the toxic effect of high levels of glutamate on primary astrocytes. On this basis, the protective mechanism of ketamine is explored. A single administration of ketamine (10 mg/kg) remarkably relieved anxious and depressive behaviors in the sucrose preference test, elevated plus maze test, and forced swim test. Meanwhile, ketamine reduced the level of hippocampus Nlrp3 and the expression of its downstream molecules in chronic unpredictable mild stress (CUMS) mice model by western blot and reduced the colocalization of Gfap and Gsdmd by nearly 25% via immunofluorescent staining. Ketamine also increased the Gfap-positive cells and AQP4 expression in the hippocampus of the CUMS mice. More important, ketamine increased the distribution of the fluorescent tracer of CUMS mice. Treatment with 128 mM glutamate in cortical and hippocampus astrocytes increased the level of Nlrp3, and Gsdmd-N, and ketamine alleviated high glutamate-induced pyroptosis-associated proteins. In summary, these results suggest that high glutamate-induced astrocyte pyroptosis through the Nlrp3/Caspase-1/Gsdmd-N pathway which was inhibited by ketamine and ketamine can improve the damaged glymphatic function of the CUMS mice. The present study indicates that inhibiting astrocyte pyroptosis and promoting the glymphatic circulation function are a new mechanism of ketamine's antidepressant effect, and astrocyte pyroptosis may be a new target for other antidepressant medicines.

Mild Traumatic Brain Injury and Career Stage Associate with Visible Perivascular Spaces in Special Operations Forces Soldiers

Mild traumatic brain injury (mTBI) and occupational blast exposure in military Service Members may lead to impaired brain waste clearance which increases neurological disease risk. Perivascular spaces (PVS) are a key part of the glymphatic system which supports brain waste clearance, preferentially during sleep. Visible PVS on clinical magnetic resonance imaging have been previously observed in patients with neurodegenerative diseases and animal neurotrauma models. The purpose of this study was to determine associations between PVS morphological characteristics, military career stage, and mTBI history in Special Operations Forces (SOF) Soldiers. Participants underwent T2-weighed neuroimaging to capture three-dimensional whole brain volumes. Segmentation was performed using a previously validated, multi-scale deep convolutional encoder-decoder neural network. Only PVS clusters within the white matter mask were quantified for analyses. Due to non-normal PVS metric distribution, non-parametric Mann-Whitney U tests were used to determine group differences in PVS outcomes. In total, 223 healthy SOF combat Soldiers (age = 33.1 ± 4.3yrs) were included, 217 reported career stage. Soldiers with mTBI history had greater PVS number (z = 2.51, P = 0.013) and PVS volume (z = 2.42, P = 0.016). In-career SOF combat Soldiers had greater PVS number (z = 2.56, P = 0.01) and PVS volume (z = 2.28, P = 0.02) compared to a baseline cohort. Mild TBI history is associated with increased PVS burden in SOF combat Soldiers that are clinically recovered from mTBI. This may indicate ongoing physiological changes that could lead to impaired waste clearance via the glymphatic system. Future studies should determine if PVS number and volume are meaningful neurobiological outcomes for neurodegenerative disease risk and if clinical interventions such as improving sleep can reduce PVS burden.

Interstitial Fluidopathy of the Central Nervous System: An Umbrella Term for Disorders with Impaired Neurofluid Dynamics

Interest in interstitial fluid dynamics has increased since the proposal of the glymphatic system hypothesis. Abnormal dynamics of the interstitial fluid have been pointed out to be an important factor in various pathological statuses. In this article, we propose the concept of central nervous system interstitial fluidopathy as a disease or condition in which abnormal interstitial fluid dynamics is one of the important factors for the development of a pathological condition. We discuss the aspects of interstitial fluidopathy in various diseases, including Alzheimer's disease, Parkinson's disease, normal pressure hydrocephalus, and cerebral small vessel disease. We also discuss a method called "diffusion tensor image analysis along the perivascular space" using MR diffusion images, which is used to evaluate the degree of interstitial fluidopathy or the activity of the glymphatic system.

Enlarged Perivascular Space and Index for Diffusivity Along the Perivascular Space as Emerging Neuroimaging Biomarkers of Neurological Diseases

The existence of lymphatic vessels or similar clearance systems in the central nervous system (CNS) that transport nutrients and remove cellular waste is a neuroscientific question of great significance. As the brain is the most metabolically active organ in the body, there is likely to be a potential correlation between its clearance system and the pathological state of the CNS. Until recently the successive discoveries of the glymphatic system and the meningeal lymphatics solved this puzzle. This article reviews the basic anatomy and physiology of the glymphatic system. Imaging techniques to visualize the function of the glymphatic system mainly including post-contrast imaging techniques, indirect lymphatic assessment by detecting increased perivascular space, and diffusion tensor image analysis along the perivascular space (DTI-ALPS) are discussed. The pathological link between glymphatic system dysfunction and neurological disorders is the key point, focusing on the enlarged perivascular space (EPVS) and the index of diffusivity along the perivascular space (ALPS index), which may represent the activity of the glymphatic system as possible clinical neuroimaging biomarkers of neurological disorders. The pathological link between glymphatic system dysfunction and neurological disorders is the key point, focusing on the enlarged perivascular space (EPVS) and the index for of diffusivity along the perivascular space (ALPS index), which may represent the activity of the glymphatic system as possible clinical neuroimaging biomarkers of neurological disorders.

Cerebral glucagon-like peptide-1 receptor activation alleviates traumatic brain injury by glymphatic system regulation in mice

AIM

We aimed to assess the effects of cerebral glucagon-like peptide-1 receptor (GLP-1R) activation on the glymphatic system and whether this effect was therapeutic for traumatic brain injury (TBI).

METHODS

Immunofluorescence was employed to evaluate glymphatic system function. The blood-brain barrier (BBB) permeability, microvascular basement membrane, and tight junction expression were assessed using Evans blue extravasation, immunofluorescence, and western blot. Immunohistochemistry was performed to assess axonal damage. Neuronal apoptosis was evaluated using Nissl staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and western blot. Cognitive function was assessed using behavioral tests.

RESULTS

Cerebral GLP-1R activation restored glymphatic transport following TBI, alleviating BBB disruption and neuronal apoptosis, thereby improving cognitive function following TBI. Glymphatic function suppression by treatment using aquaporin 4 inhibitor TGN-020 abolished the protective effect of the GLP-1R agonist against cognitive impairment.

CONCLUSION

Cerebral GLP-1R activation can effectively ameliorate neuropathological changes and cognitive impairment following TBI; the underlying mechanism could involve the repair of the glymphatic system damaged by TBI.

Air pollution, glymphatic impairment, and Alzheimer's disease

Epidemiological evidence demonstrates a link between air pollution exposure and the onset and progression of cognitive impairment and Alzheimer's disease (AD). However, current understanding of the underlying pathophysiological mechanisms is limited. This opinion article examines the hypothesis that air pollution-induced impairment of glymphatic clearance represents a crucial etiological event in the development of AD. Exposure to airborne particulate matter (PM) leads to systemic inflammation and neuroinflammation, increased metal load, respiratory and cardiovascular dysfunction, and sleep abnormalities. All these factors are known to reduce the efficiency of glymphatic clearance. Rescuing glymphatic function by restricting the impact of causative agents, and improving sleep and cardiovascular system health, may increase the efficiency of waste metabolite clearance and subsequently slow the progression of AD. In sum, we introduce air pollution-mediated glymphatic impairment as an important mechanistic factor to be considered when interpreting the etiology and progression of AD as well as its responsiveness to therapeutic interventions.

Assessment of factors influencing glymphatic activity and implications for clinical medicine

The glymphatic system is a highly specialized fluid transport system in the central nervous system. It enables the exchange of the intercellular fluid of the brain, regulation of the movement of this fluid, clearance of unnecessary metabolic products, and, potentially, brain immunity. In this review, based on the latest scientific reports, we present the mechanism of action and function of the glymphatic system and look at the role of factors influencing its activity. Sleep habits, eating patterns, coexisting stress or hypertension, and physical activity can significantly affect glymphatic activity. Modifying them can help to change lives for the better. In the next section of the review, we discuss the connection between the glymphatic system and neurological disorders. Its association with many disease entities suggests that it plays a major role in the physiology of the whole brain, linking many pathophysiological pathways of individual diseases.

Spatiotemporal profile of atrophy in the first year following moderate-severe traumatic brain injury

Traumatic brain injury (TBI) triggers progressive neurodegeneration resulting in brain atrophy that continues months-to-years following injury. However, a comprehensive characterization of the spatial and temporal evolution of TBI-related brain atrophy remains incomplete. Utilizing a sensitive and unbiased morphometry analysis pipeline optimized for detecting longitudinal changes, we analyzed a sample consisting of 37 individuals with moderate-severe TBI who had primarily high-velocity and high-impact injury mechanisms. They were scanned up to three times during the first year after injury (3 months, 6 months, and 12 months post-injury) and compared with 33 demographically matched controls who were scanned once. Individuals with TBI already showed cortical thinning in frontal and temporal regions and reduced volume in the bilateral thalami at 3 months post-injury. Longitudinally, only a subset of cortical regions in the parietal and occipital lobes showed continued atrophy from 3 to 12 months post-injury. Additionally, cortical white matter volume and nearly all deep gray matter structures exhibited progressive atrophy over this period. Finally, we found that disproportionate atrophy of cortex along sulci relative to gyri, an emerging morphometric marker of chronic TBI, was present as early as 3 month post-injury. In parallel, neurocognitive functioning largely recovered during this period despite this pervasive atrophy. Our findings demonstrate msTBI results in characteristic progressive neurodegeneration patterns that are divergent across regions and scale with the severity of injury. Future clinical research using atrophy during the first year of TBI as a biomarker of neurodegeneration should consider the spatiotemporal profile of atrophy described in this study.

Circadian therapy interventions for glymphatic dysfunction in concussions injuries: A narrative review

There are two primary threats to the brain after concussion. The first is a buildup of neurotoxic proteins in the brain. The second, a partial consequence of the first, is a sustained neuroinflammatory response that may lead to central sensitization and the development of persistent post-concussive symptoms. These threats make neurotoxin clearance a high clinical priority in the acute period after injury. The glymphatic system is the brain's primary mechanism for clearing neurotoxic waste. The glymphatic system is intimately tied to the sleep cycle and circadian dynamics. However, glymphatic dysfunction and sleep disturbances are nearly ubiquitous in the acute period after concussion injury. Because of this, sleep optimization via circadian therapy is a time-sensitive and critical tool in acute concussion management.

The Correlation of Sleep Disturbance and Location of Glioma Tumors: A Narrative Review

Sleep disturbance can occur when sleep centers of the brain, regions that are responsible for coordinating and generating healthy amounts of sleep, are disrupted by glioma growth or surgical resection. Several disorders cause disruptions to the average duration, quality, or patterns of sleep, resulting in sleep disturbance. It is unknown whether specific sleep disorders can be reliably correlated with glioma growth, but there are sufficient numbers of case reports to suggest that a connection is possible. In this manuscript, these case reports and retrospective chart reviews are considered in the context of the current primary literature on sleep disturbance and glioma diagnosis to identify a new and useful connection which warrants further systematic and scientific examination in preclinical animal models. Confirmation of the relationship between disruption of the sleep centers in the brain and glioma location could have significant implications for diagnostics, treatment, monitoring of metastasis/recurrence, and end-of-life considerations.

Glymphatic clearance estimated using diffusion tensor imaging along perivascular spaces is reduced after traumatic brain injury and correlates with plasma neurofilament light, a biomarker of injury severity

The glymphatic system is a perivascular fluid clearance system, most active during sleep, considered important for clearing the brain of waste products and toxins. Glymphatic failure is hypothesized to underlie brain protein deposition in neurodegenerative disorders like Alzheimer's disease. Preclinical evidence suggests that a functioning glymphatic system is also essential for recovery from traumatic brain injury, which involves release of debris and toxic proteins that need to be cleared from the brain. In a cross-sectional observational study, we estimated glymphatic clearance using diffusion tensor imaging along perivascular spaces, an MRI-derived measure of water diffusivity surrounding veins in the periventricular region, in 13 non-injured controls and 37 subjects who had experienced traumatic brain injury ∼5 months previously. We additionally measured the volume of the perivascular space using T2-weighted MRI. We measured plasma concentrations of neurofilament light chain, a biomarker of injury severity, in a subset of subjects. Diffusion tensor imaging along perivascular spaces index was modestly though significantly lower in subjects with traumatic brain injury compared with controls when covarying for age. Diffusion tensor imaging along perivascular spaces index was significantly, negatively correlated with blood levels of neurofilament light chain. Perivascular space volume did not differ in subjects with traumatic brain injury as compared with controls and did not correlate with blood levels of neurofilament light chain, suggesting it may be a less sensitive measure for injury-related perivascular clearance changes. Glymphatic impairment after traumatic brain injury could be due to mechanisms such as mislocalization of glymphatic water channels, inflammation, proteinopathy and/or sleep disruption. Diffusion tensor imaging along perivascular spaces is a promising method for estimating glymphatic clearance, though additional work is needed to confirm results and assess associations with outcome. Understanding changes in glymphatic functioning following traumatic brain injury could inform novel therapies to improve short-term recovery and reduce later risk of neurodegeneration.

Traumatic Brain Injury, Sleep, and Melatonin-Intrinsic Changes with Therapeutic Potential

Traumatic brain injury (TBI) is one of the most prevalent causes of morbidity in the United States and is associated with numerous chronic sequelae long after the point of injury. One of the most common long-term complaints in patients with TBI is sleep dysfunction. It is reported that alterations in melatonin follow TBI and may be linked with various sleep and circadian disorders directly (via cellular signaling) or indirectly (via free radicals and inflammatory signaling). Work over the past two decades has contributed to our understanding of the role of melatonin as a sleep regulator and neuroprotective anti-inflammatory agent. Although there is increasing interest in the treatment of insomnia following TBI, a lack of standardization and rigor in melatonin research has left behind a trail of non-generalizable data and ambiguous treatment recommendations. This narrative review describes the underlying biochemical properties of melatonin as they are relevant to TBI. We also discuss potential benefits and a path forward regarding the therapeutic management of TBI with melatonin treatment, including its role as a neuroprotectant, a somnogen, and a modulator of the circadian rhythm.

Neuroinflammation with increased glymphatic flow in a murine model of decompression sickness

This project investigated glial-based lymphatic (glymphatic) function and its role in a murine model of decompression sickness (DCS). DCS pathophysiology is traditionally viewed as being related to gas bubble formation from insoluble gas on decompression. However, a body of work implicates a role for a subset of inflammatory extracellular vesicles, 0.1 to 1 µm microparticles (MPs) that are elevated in human and rodent models in response to high gas pressure and rise further after decompression. Herein, we describe immunohistochemical and Western blot evidence showing that following high air pressure exposure, there are elevations of astrocyte NF-κB and microglial-ionized calcium-binding adaptor protein-1 (IBA-1) along with fluorescence contrast and MRI findings of an increase in glymphatic flow. Concomitant elevations of central nervous system-derived MPs coexpressing thrombospondin-1 (TSP) drain to deep cervical nodes and then to blood where they cause neutrophil activation. A new set of blood-borne MPs are generated that express filamentous actin at the surface that exacerbate neutrophil activation. Blood-brain barrier integrity is disrupted due to activated neutrophil sequestration that causes further astrocyte and microglial perturbation. When postdecompression node or blood MPs are injected into naïve mice, the same spectrum of abnormalities occur and they are blocked with coadministration of antibody to TSP. We conclude that high pressure/decompression causes neuroinflammation with an increased glymphatic flow. The resulting systemic liberation of TSP-expressing MPs sustains the neuroinflammatory cycle lasting for days.NEW & NOTEWORTHY A murine model of central nervous system (CNS) decompression sickness demonstrates that high gas pressure activates astrocytes and microglia triggering inflammatory microparticle (MP) production. Thrombospondin-expressing MPs are released from the CNS via enhanced glymphatic flow to the systemic circulation where they activate neutrophils. Secondary production of neutrophil-derived MPs causes further cell activation and neutrophil adherence to the brain microvasculature establishing a feed-forward neuroinflammatory cycle.

Glymphatic system evaluation using diffusion tensor imaging in patients with traumatic brain injury

PURPOSE

Glymphatic system dysfunction has been reported in animal models of traumatic brain injury (TBI). This study aimed to evaluate the activity of the human glymphatic system using the non-invasive Diffusion Tensor Image-Analysis aLong the Perivascular Space (DTI-ALPS) method in patients with TBI.

METHODS

A total of 89 patients with TBI (June 2018 to May 2020) were retrospectively enrolled, and 34 healthy volunteers were included who had no previous medical or neurological disease. Magnetic resonance imaging (MRI) with DTI was performed, and the ALPS index was calculated to evaluate the glymphatic system's activity. Wilcoxon rank-sum test was used to compare the ALPS index between patients with TBI and healthy controls. ANOVA was done to compare the ALPS index among controls and patients with mild/moderate-to-severe TBI. Multivariate logistic regression analyses were used to identify independent clinical and radiological factors associated with the ALPS index. The correlation between Glasgow Coma Scale (GCS) score and the ALPS index was also assessed.

RESULTS

The ALPS index was significantly lower in patients with TBI than in healthy controls (median, 1.317 vs. 1.456, P < 0.0001). There were significant differences in the ALPS index between healthy controls and patients with mild/moderate-to-severe TBI (ANOVA, P < 0.001). The presence of subarachnoid hemorrhage (P = 0.004) and diffuse axonal injury (P = 0.001) was correlated with a lower ALPS index in the multivariate analysis. There was a weak positive correlation between the ALPS index and GCS scores (r = 0.242, P = 0.023).

CONCLUSIONS

The DTI-ALPS method is useful for evaluating glymphatic system impairment and quantifying its activity in patients with TBI.

Lack of difference between amyloid-beta burden at gyral crests and sulcal depths in diverse neurodegenerative diseases

AIMS

The aim of this study is to clarify whether there is a difference in amyloid-beta burden between gyral crests (GCs) and sulcal depths (SDs) in different neurodegenerative proteinopathies.

METHODS

We analysed the burden and distribution of amyloid-beta deposition in post-mortem brain samples from 138 autopsies, including Alzheimer's disease (n = 30), Down's syndrome (n = 11), Lewy body disease (LBD; n = 53), multiple system atrophy (n = 8) and progressive supranuclear palsy (n = 36). We applied quantitative amyloid-beta burden analysis to compare amyloid-beta deposition in both GCs and SDs. We also evaluated the prevalence of amyloid-beta plaques in both regions in samples exhibiting high or low amounts of amyloid-beta pathology.

RESULTS

Amyloid-beta burden was evaluated in 67 and 84 samples of the frontal and temporal cortices, respectively. We did not find significant differences in the amyloid-beta burden between GCs and SDs in these regions in any examined disease. In addition, amyloid-beta plaques were almost evenly distributed in both regions in cases with low amounts of amyloid-beta pathology. Females in the LBD group showed significantly higher amyloid-beta burden than males (temporal cortex, p < 0.01). Furthermore, only one LBD case showed SD-predominant deposition associated with the coarse-grained plaques.

CONCLUSIONS

We have shown that amyloid-beta is almost evenly distributed in both GCs and SDs in the frontal and temporal lobes from the early stage, in diverse neurodegenerative diseases. Sex may contribute to differences in the amyloid-beta burden. The coarse-grained plaque may show SD-predominant neuritic tau deposition that must be carefully distinguished from chronic traumatic encephalopathy-related SD tau pathology.

Nanodelivery of Histamine H3/H4 Receptor Modulators BF-2649 and Clobenpropit with Antibodies to Amyloid Beta Peptide in Combination with Alpha Synuclein Reduces Brain Pathology in Parkinson's Disease

Parkinson's disease (PD) in military personnel engaged in combat operations is likely to develop in their later lives. In order to enhance the quality of lives of PD patients, exploration of novel therapy based on new research strategies is highly warranted. The hallmarks of PD include increased alpha synuclein (ASNC) and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) leading to brain pathology. In addition, there are evidences showing increased histaminergic nerve fibers in substantia niagra pars compacta (SNpc), striatum (STr), and caudate putamen (CP) associated with upregulation of histamine H3 receptors and downregulation of H4 receptors in human brain. Previous studies from our group showed that modulation of potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist induces neuroprotection in PD brain pathology. Recent studies show that PD also enhances amyloid beta peptide (AβP) depositions in brain. Keeping these views in consideration in this review, nanowired delivery of monoclonal antibodies to AβP together with ASNC and H3/H4 modulator drugs on PD brain pathology is discussed based on our own observations. Our investigation shows that TiO₂ nanowired BF-2649 (1 mg/kg, i.p.) or CLBPT (1 mg/kg, i.p.) once daily for 1 week together with nanowired delivery of monoclonal antibodies (mAb) to AβP and ASNC induced superior neuroprotection in PD-induced brain pathology. These observations are the first to show the modulation of histaminergic receptors together with antibodies to AβP and ASNC induces superior neuroprotection in PD. These observations open new avenues for the development of novel drug therapies for clinical strategies in PD.

The impact of sleep components, quality and patterns on glymphatic system functioning in healthy adults: A systematic review

OBJECTIVE

The glymphatic system is thought to be responsible for waste clearance in the brain. As it is primarily active during sleep, different components of sleep, subjective sleep quality, and sleep patterns may contribute to glymphatic functioning. This systematic review aimed at exploring the effect of sleep components, sleep quality, and sleep patterns on outcomes associated with the glymphatic system in healthy adults.

METHODS

PubMed®, Scopus, and Web of Science were searched for studies published in English until December 2021. Articles subjectively or objectively investigating sleep components (total sleep time, time in bed, sleep efficiency, sleep onset latency, wake-up after sleep onset, sleep stage, awakenings), sleep quality, or sleep pattern in healthy individuals, on outcomes associated with glymphatic system (levels of amyloid-β, tau, α-synuclein; cerebrospinal fluid, perivascular spaces; apolipoprotein E) were selected.

RESULTS

Out of 8359 records screened, 51 studies were included. Overall, contradictory findings were observed according to different sleep assessment method. The most frequently assessed sleep parameters were total sleep time, sleep quality, and sleep efficiency. No association was found between sleep efficiency and amyloid-β, and between slow-wave activity and tau. Most of the studies did not find any correlation between total sleep time and amyloid-β nor tau level. Opposing results correlated sleep quality with amyloid-β and tau.

CONCLUSIONS

This review highlighted inconsistent results across the studies; as such, the specific association between the glymphatic system and sleep parameters in healthy adults remains poorly understood. Due to the heterogeneity of sleep assessment methods and the self-reported data representing the majority of the observations, future studies with universal study design and sleep methodology in healthy individuals are advocated.

Associations between early sleep-disordered breathing following moderate-to-severe traumatic brain injury and long-term chronic pain status: a Traumatic Brain Injury Model Systems study

STUDY OBJECTIVES

To explore the relationship between polysomnography-derived respiratory indices and chronic pain status among individuals following traumatic brain injury (TBI).

METHODS

Participants (n = 66) with moderate to severe TBI underwent polysomnography during inpatient acute rehabilitation and their chronic pain status was assessed at 1- to 2-year follow-up as part of the TBI Model Systems Pain Collaborative Study. Pairwise comparisons across pain cohorts (ie, chronic pain, no history of pain) were made to explore differences on polysomnography indices.

RESULTS

Among our total sample, approximately three-quarters (74.2%) received sleep apnea diagnoses utilizing American Academy of Sleep Medicine criteria, with 61.9% of those endorsing a history of chronic pain. Of those endorsing chronic pain, the average pain score was 4.8 (standard deviation = 2.1), with a mean interference score of 5.3 (2.7). Pairwise comparisons revealed that those endorsing a chronic pain experience at follow-up experienced categorically worse indicators of sleep-related breathing disorders during acute rehabilitation relative to those who did not endorse chronic pain. Important differences were observed with elevations on central (chronic pain: 2.6; no pain: 0.8 per hour) and obstructive apnea (chronic pain: 15.7; no pain: 11.1 per hour) events, as well as oxygen desaturation indices (chronic pain: 19.6; no pain: 7.9 per hour).

CONCLUSIONS

Sleep-disordered breathing appears worse among those who endorse chronic pain following moderate-to-severe TBI, but additional research is needed to understand its relation to postinjury pain. Prospective investigation is necessary to determine how clinical decisions (eg, opioid therapy) and intervention (eg, positive airway pressure) may mutually influence outcomes.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Name: Comparison of Sleep Apnea Assessment Strategies to Maximize TBI Rehabilitation Participation and Outcome (C-SAS); URL: https://clinicaltrials.gov/ct2/show/NCT03033901; Identifier: NCT03033901.

CITATION

Martin AM, Pinto SM, Tang X, et al. Associations between early sleep-disordered breathing following moderate-to-severe traumatic brain injury and long-term chronic pain status: a Traumatic Brain Injury Model Systems study. J Clin Sleep Med. 2023;19(1):135-143.

Emerging Materials, Wearables, and Diagnostic Advancements in Therapeutic Treatment of Brain Diseases

Among the most critical health issues, brain illnesses, such as neurodegenerative conditions and tumors, lower quality of life and have a significant economic impact. Implantable technology and nano-drug carriers have enormous promise for cerebral brain activity sensing and regulated therapeutic application in the treatment and detection of brain illnesses. Flexible materials are chosen for implantable devices because they help reduce biomechanical mismatch between the implanted device and brain tissue. Additionally, implanted biodegradable devices might lessen any autoimmune negative effects. The onerous subsequent operation for removing the implanted device is further lessened with biodegradability. This review expands on current developments in diagnostic technologies such as magnetic resonance imaging, computed tomography, mass spectroscopy, infrared spectroscopy, angiography, and electroencephalogram while providing an overview of prevalent brain diseases. As far as we are aware, there hasn't been a single review article that addresses all the prevalent brain illnesses. The reviewer also looks into the prospects for the future and offers suggestions for the direction of future developments in the treatment of brain diseases.

Research Evidence of the Role of the Glymphatic System and Its Potential Pharmacological Modulation in Neurodegenerative Diseases

The glymphatic system is a unique pathway that utilises end-feet Aquaporin 4 (AQP4) channels within perivascular astrocytes, which is believed to cause cerebrospinal fluid (CSF) inflow into perivascular space (PVS), providing nutrients and waste disposal of the brain parenchyma. It is theorised that the bulk flow of CSF within the PVS removes waste products, soluble proteins, and products of metabolic activity, such as amyloid-β (Aβ). In the experimental model, the glymphatic system is selectively active during slow-wave sleep, and its activity is affected by both sleep dysfunction and deprivation. Dysfunction of the glymphatic system has been proposed as a potential key driver of neurodegeneration. This hypothesis is indirectly supported by the close relationship between neurodegenerative diseases and sleep alterations, frequently occurring years before the clinical diagnosis. Therefore, a detailed characterisation of the function of the glymphatic system in human physiology and disease would shed light on its early stage pathophysiology. The study of the glymphatic system is also critical to identifying means for its pharmacological modulation, which may have the potential for disease modification. This review will critically outline the primary evidence from literature about the dysfunction of the glymphatic system in neurodegeneration and discuss the rationale and current knowledge about pharmacological modulation of the glymphatic system in the animal model and its potential clinical applications in human clinical trials.

Systematic Review of the Diagnostic and Clinical Utility of Salivary microRNAs in Traumatic Brain Injury (TBI)

Research in traumatic brain injury (TBI) is an urgent priority, as there are currently no TBI biomarkers to assess the severity of injury, to predict outcomes, and to monitor recovery. Small non-coding RNAs (sncRNAs) including microRNAs can be measured in saliva following TBI and have been investigated as potential diagnostic markers. The aim of this systematic review was to investigate the diagnostic or prognostic ability of microRNAs extracted from saliva in human subjects. PubMed, Embase, Scopus, PsycINFO and Web of Science were searched for studies that examined the association of saliva microRNAs in TBI. Original studies of any design involving diagnostic capacity of salivary microRNAs for TBI were selected for data extraction. Nine studies met inclusion criteria, with a heterogeneous population involving athletes and hospital patients, children and adults. The studies identified a total of 188 differentially expressed microRNAs, with 30 detected in multiple studies. MicroRNAs in multiple studies involved expression change bidirectionality. The study design and methods involved significant heterogeneity that precluded meta-analysis. Early data indicates salivary microRNAs may assist with TBI diagnosis. Further research with consistent methods and larger patient populations is required to evaluate the diagnostic and prognostic potential of saliva microRNAs.

Technical feasibility of using auditory phase-targeted stimulation after pediatric severe traumatic brain injury in an intensive care setting

Background

Supplementary treatment options after pediatric severe traumatic brain injury (TBI) are needed to improve neurodevelopmental outcome. Evidence suggests enhancement of brain delta waves via auditory phase-targeted stimulation might support neuronal reorganization, however, this method has never been applied in analgosedated patients on the pediatric intensive care unit (PICU). Therefore, we conducted a feasibility study to investigate this approach: In a first recording phase, we examined feasibility of recording over time and in a second stimulation phase, we applied stimulation to address tolerability and efficacy.

Methods

Pediatric patients (> 12 months of age) with severe TBI were included between May 2019 and August 2021. An electroencephalography (EEG) device capable of automatic delta wave detection and sound delivery through headphones was used to record brain activity and for stimulation (MHSL-SleepBand version 2). Stimulation tolerability was evaluated based on report of nurses, visual inspection of EEG data and clinical signals (heart rate, intracranial pressure), and whether escalation of therapy to reduce intracranial pressure was needed. Stimulation efficacy was investigated by comparing EEG power spectra of active stimulation versus muted stimulation (unpaired t-tests).

Results

In total, 4 out of 32 TBI patients admitted to the PICU (12.5%) between 4 and 15 years of age were enrolled in the study. All patients were enrolled in the recording phase and the last one also to the stimulation phase. Recordings started within 5 days after insult and lasted for 1–4 days. Overall, 23–88 h of EEG data per patient were collected. In patient 4, stimulation was enabled for 50 min: No signs of patient stress reactions were observed. Power spectrums between active and muted stimulation were not statistically different (all P > .05).

Conclusion

Results suggests good feasibility of continuously applying devices needed for auditory stimulation over multiple days in pediatric patients with TBI on PICU. Very preliminary evidence suggests good tolerability of auditory stimuli, but efficacy of auditory stimuli to enhance delta waves remains unclear and requires further investigation. However, only low numbers of severe TBI patients could be enrolled in the study and, thus, future studies should consider an international multicentre approach.

The lymphatic system: a therapeutic target for central nervous system disorders

The lymphatic vasculature forms an organized network that covers the whole body and is involved in fluid homeostasis, metabolite clearance, and immune surveillance. The recent identification of functional lymphatic vessels in the meninges of the brain and the spinal cord has provided novel insights into neurophysiology. They emerge as major pathways for fluid exchange. The abundance of immune cells in lymphatic vessels and meninges also suggests that lymphatic vessels are actively involved in neuroimmunity. The lymphatic system, through its role in the clearance of neurotoxic proteins, autoimmune cell infiltration, and the transmission of pro-inflammatory signals, participates in the pathogenesis of a variety of neurological disorders, including neurodegenerative and neuroinflammatory diseases and traumatic injury. Vascular endothelial growth factor C is the master regulator of lymphangiogenesis, a process that is critical for the maintenance of central nervous system homeostasis. In this review, we summarize current knowledge and recent advances relating to the anatomical features and immunological functions of the lymphatic system of the central nervous system and highlight its potential as a therapeutic target for neurological disorders and central nervous system repair.

Basal cisternostomy for traumatic brain injury: A case report of unexpected good recovery

In subarachnoid hemorrhage following traumatic brain injury (TBI), the high intracisternal pressure drives the cerebrospinal fluid into the brain parenchyma, causing cerebral edema. Basal cisternostomy involves opening the basal cisterns to atmospheric pressure and draining cerebrospinal fluid in an attempt to reverse the edema. We describe a case of basal cisternostomy combined with decompressive craniectomy. A 35-year-old man with severe TBI following a road vehicle accident presented with acute subdural hematoma, Glasgow coma scale score of 6, fixed pupils and no corneal response. Opening of the basal cisterns and placement of a temporary cisternal drain led to immediate relaxation of the brain. The patient had a Glasgow coma scale score of 15 on postoperative day 6 and was discharged on day 10. We think basal cisternostomy is a feasible and effective procedure that should be considered in the management of TBI.

Glymphatic System a Window on TBI Pathophysiology: A Systematic Review

Background: In recent years, the attention of the scientific world has focused on a clearance system of brain waste metabolites, called the glymphatic system, based on its similarity to the lymphatic system in peripheral tissue and the relevant role of the AQP4 glial channels and described for the first time in 2012. Consequently, numerous studies focused on its role in organ damage in cases of neuropathologies, including TBI. Methods: To evaluate the role that the glymphatic system has in the pathogenesis of TBI, on 23 March 2022, a systematic review of the literature according to PRISMA guidelines was carried out using the SCOPUS and Medline (via PubMed) databases, resulting in 12 articles after the selection process. Discussion and conclusion: The present review demonstrated that an alteration of AQP4 is associated with the accumulation of substances S100b, GFAP, and NSE, known markers of TBI in the forensic field. In addition, the alteration of the functionality of AQP4 favors edema, which, as already described, constitutes alterations of secondary brain injuries. Moreover, specific areas of the brain were demonstrated to be prone to alterations of the glymphatic pathway, suggesting their involvement in post-TBI damage. Therefore, further studies are mandatory. In this regard, a study protocol on cadavers is also proposed, based on the analyzed evidence.

Glymphatic System: Emerging Therapeutic Target for Neurological Diseases

The newly discovered glymphatic system acts as pseudolymphatic vessels subserving brain waste clearance and is functionally dependent on astrocytic aquaporin-4 channels. The glymphatic system primarily functions during sleep as an interchange between cerebrospinal fluid and interstitial fluid, with cerebrospinal fluid flowing into the parenchyma via the perivascular spaces and then exchanging with interstitial fluid. The discovery of meningeal lymphatics helps refine the conceptual framework of glymphatic pathway, as certain waste products collected alongside perivascular spaces ultimately drain into the cervical lymph nodes via meningeal lymphatics, whose function regulates the functioning of the glymphatic system. The glymphatic and meningeal lymphatic systems are critical for the homeostasis of central nervous system, and their malfunctions complicate cerebral dysfunction and diseases. The present review will shed light on the structure, regulation, functions, and interrelationships of the glymphatic system and meningeal lymphatics. We will also expound on their impairments and corresponding targeted intervention in neurodegenerative diseases, traumatic brain injury, stroke, and infectious/autoimmune diseases, offering valuable references for future research.

Association between Sleep Disturbances at Subacute Stage of Mild Traumatic Brain Injury and Long-Term Outcomes

Mild (mTBI) traumatic brain injury (TBI) accounts for the majority of all TBI cases. Evidence has suggested that patients with mTBI can suffer from long-lasting cognitive deficits, persistent symptoms, and decreased quality of life. Sleep disorders are commonly observed after TBI, with the prevalence rate of sleep disturbances in persons with TBI being much higher than that in the general population. Poor sleep quality can impair cognitive functions in the general population. This effect of sleep disturbances may impede the recovery processes in the population with TBI. The objective of this study is to add to our understanding of the relationship between self-reported sleep problems and other post-concussion symptoms and look at the association between early sleep problems and long-term outcomes in mTBI. Post-concussion symptoms, neurocognitive functions, level of global outcomes, and rating of satisfaction of life were assessed in 64 patients with mTBI. The results revealed that the presence of sleep disturbances co-occur with an increased level of overall post-concussion symptoms at the subacute stage of mTBI, particularly with symptoms including poor concentration, memory problems, and irritability. In addition, sleep disturbance at the subacute stage is associated with persistent poor concentration and memory problems, as well as worse neurocognitive function, slower overall recovery, and lower satisfactory of life at the long term. Our findings suggest that sleep disturbance can be a prognostic factor of long-term outcomes after mTBI. Early interventions to improve sleep quality can have potential benefits to facilitate the recovery process from mTBI.

A network model of glymphatic flow under different experimentally-motivated parametric scenarios

Flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) in the brain delivers nutrients, clears metabolic waste, and causes edema formation. Brain-wide imaging cannot resolve PVSs, and high-resolution methods cannot access deep tissue. However, theoretical models provide valuable insight. We model the CSF pathway as a network of hydraulic resistances, using published parameter values. A few parameters (permeability of PVSs and the parenchyma, and dimensions of PVSs and astrocyte endfoot gaps) have wide uncertainties, so we focus on the limits of their ranges by analyzing different parametric scenarios. We identify low-resistance PVSs and high-resistance parenchyma as the only scenario that satisfies three essential criteria: that the flow be driven by a small pressure drop, exhibit good CSF perfusion throughout the cortex, and exhibit a substantial increase in flow during sleep. Our results point to the most important parameters, such as astrocyte endfoot gap dimensions, to be measured in future experiments.

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We model the CSF pathway as a network of hydraulic resistances

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Predictions are bracketed by analyzing parametric scenarios for unknown parameters

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Low-resistance PVSs and high-resistance parenchyma produce realistic flows

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Astrocyte endfoot gap size is among the important parameters to be measured

The association of enlarged perivascular space with microglia-related inflammation and Alzheimer's pathology in cognitively normal elderly

BACKGROUND

Glymphatic dysfunction may contribute to the accumulation of Alzheimer's disease (AD) pathologies. Conversely, AD pathologic change might also cause neuroinflammation and aggravate glymphatic dysfunction, forming a loop that accelerates AD progression. In vivo validations are needed to confirm their relationships.

METHODS

In this study, we included 144 cognitively normal participants with AD pathological biomarker data (baseline CSF Aβ_1-42, T-Tau, P-Tau₁₈₁; plasma P-Tau₁₈₁ at baseline and at least one follow-up) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Each subject had completed structural MRI scans. Among them, 117 subjects have available neuroinflammatory biomarker (soluble triggering receptor expressed on myeloid cells 2 (sTREM2), and 123 subjects have completed two times [18F]-florbetapir PET. The enlarged PVS (EPVS) visual rating scores in basal ganglia (BG) and centrum semiovale (CS) were assessed on T1-weighted images to reflect glymphatic dysfunction. Intracranial volume and white matter hyperintensities (WMH) volume were also calculated for further analysis. We performed stepwise linear regression models and mediation analyses to estimate the association between EPVS severity, sTREM2, and AD biomarkers.

RESULTS

CS-EPVS degree was associated with CSF sTREM2, annual change of plasma P-tau₁₈₁ and total WMH volume, whereas BG-EPVS severity was associated with age, gender and intracranial volume. The sTREM2 mediated the association between CSF P-tau₁₈₁ and CS-EPVS.

CONCLUSION

Impaired glymphatic dysfunction could contribute to the accumulation of pathological tau protein. The association between tauopathy and glymphatic dysfunction was mediated by the microglia inflammatory process. These findings may provide evidence for novel treatment strategies of anti-neuroinflammation therapy in the early stage.

A Review of Glymphatics and the Impact of Osteopathic Manipulative Treatment in Alzheimer's Disease, Concussions, and Beyond

Glymph is a fluid that circulates in the brain interstitium and, under pathological conditions, unusually accumulates and enhances the buildup of other noxious molecules. The study of this process of circulation, accumulation, and clearance is called glymphatics. We review the physiology of glymphatics and then dive into recent innovative research surrounding this neurological field of study and how it has applied to mainstream pathological processes, including Alzheimer's disease and spectrums of traumatic brain injury that range from a concussion to chronic traumatic encephalopathy (CTE). Furthermore, we explore the implications of glymphatics and a new and developing frontier of healthcare in space travel; with the advent of a Space Force and the introduction of space travel to consumer markets, this is an exciting time to develop novel techniques in enhancing its safety and optimizing human physiology for best outcomes. Therefore, we also propose that osteopathic manipulative treatment (OMT) plays an intuitive role in the treatment of abnormal glymphatics, as adjunctive therapy in Alzheimer's and CTE, and as a future staple before, during, and after space travel for the benefit of both enhancing healthcare in chronic conditions and advancing the capabilities of the human race in its shining new endeavor.

The Bidirectional Link Between Sleep Disturbances and Traumatic Brain Injury Symptoms: A Role for Glymphatic Dysfunction?

Mild traumatic brain injury (mTBI), often referred to as concussion, is a major cause of morbidity and mortality worldwide. Sleep disturbances are common after mTBI. Moreover, subjects who develop subjective sleep complaints after mTBI also report more severe somatic, mental health, and cognitive impairment and take longer to recover from mTBI sequelae. Despite many previous studies addressing the role of sleep in post-mTBI morbidity, the mechanisms linking sleep to recovery after mTBI remain poorly understood. The glymphatic system is a brainwide network that supports fluid movement through the cerebral parenchyma and the clearance of interstitial solutes and wastes from the brain. Notably, the glymphatic system is active primarily during sleep. Clearance of cellular byproducts related to somatic, mental health, and neurodegenerative processes (e.g., amyloid-β and tau, among others) depends in part on intact glymphatic function, which becomes impaired after mTBI. In this viewpoint, we review the current knowledge regarding the association between sleep disturbances and post-mTBI symptoms. We also discuss the role of glymphatic dysfunction as a potential link between mTBI, sleep disruption, and posttraumatic morbidity. We outline a model where glymphatic dysfunction and sleep disruption caused by mTBI may have an additive effect on waste clearance, leading to cerebral dysfunction and impaired recovery. Finally, we review the novel techniques being developed to examine glymphatic function in humans and explore potential interventions to alter glymphatic exchange that may offer a novel therapeutic approach to those experiencing poor sleep and prolonged symptoms after mTBI.

Lower cortical volume is associated with poor sleep quality after traumatic brain injury

Traumatic brain injury (TBI) is known to be associated with poor sleep. In this report, we aimed to identify associations between differences in cortical volume and sleep quality post-TBI. MRI anatomical scans from 88 cases with TBI were analyzed in this report. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Voxel Based Morphometry (VBM), was used to obtain statistical maps of the association between PSQI and cortical volume in gray matter and white matter voxels. Higher PSQI total scores (poor sleep quality) were strongly associated with smaller gray matter volume in the cerebellum. White matter volume was not associated with total PSQI. The sleep disturbance subcomponent showed a significant association with gray and white matter volumes in the cerebellum. Although not significant, cortical areas such as the cingulate and medial frontal regions were associated with sleep quality. The cerebellum with higher contribution to motor and autonomic systems was associated strongly with poor sleep quality. Additionally, regions that play critical roles in inhibitory brain function and suppress mind wandering (i.e., default mode network including medial frontal and cingulate regions) were associated (although to a lesser extent) with sleep. Our findings suggest that poor sleep quality following TBI is significantly associated with lower cerebellar volume, with trending relationships in regions associated with inhibitory function.

A clinical primer for the glymphatic system

The complex and dynamic system of fluid flow through the perivascular and interstitial spaces of the central nervous system has new-found implications for neurological diseases. Cerebrospinal fluid movement throughout the CNS parenchyma is more dynamic than could be explained via passive diffusion mechanisms alone. Indeed, a semi-structured glial-lymphatic (glymphatic) system of astrocyte-supported extracellular perivascular channels serves to directionally channel extracellular fluid, clearing metabolites and peptides to optimize neurologic function. Clinical studies of the glymphatic network has to date proven challenging, with most data gleaned from rodent models and post-mortem investigations. However, increasing evidence suggests that disordered glymphatic function contributes to the pathophysiology of CNS aging, neurodegenerative disease, and CNS injuries, as well as normal pressure hydrocephalus. Unlocking such pathophysiology could provide important avenues toward novel therapeutics. We here provide a multidisciplinary overview of glymphatics and critically review accumulating evidence regarding its structure, function, and hypothesized relevance to neurological disease. We highlight emerging technologies of relevance to the longitudinal evaluation of glymphatic function in health and disease. Finally, we discuss the translational opportunities and challenges of studying glymphatic science.

Post-injury ventricular enlargement associates with iron in choroid plexus but not with seizure susceptibility nor lesion atrophy-6-month MRI follow-up after experimental traumatic brain injury

Ventricular enlargement is one long-term consequence of a traumatic brain injury, and a risk factor for memory disorders and epilepsy. One underlying mechanisms of the chronic ventricular enlargement is disturbed cerebrospinal-fluid secretion or absorption by choroid plexus. We set out to characterize the different aspects of ventricular enlargement in lateral fluid percussion injury (FPI) rat model by magnetic resonance imaging (MRI) and discovered choroid plexus injury in rats that later developed hydrocephalus. We followed the brain pathology progression for 6 months and studied how the ventricular growth was associated with the choroid plexus injury, cortical lesion expansion, hemorrhagic load or blood perfusion deficits. We correlated MRI findings with the seizure susceptibility in pentylenetetrazol challenge and memory function in Morris water-maze. Choroid plexus injury was validated by ferric iron (Prussian blue) and cytoarchitecture (Nissl) stainings. We discovered choroid plexus injury that accumulates iron in 90% of FPI rats by MRI. The amount of the choroid plexus iron remained unaltered 1-, 3- and 6-month post-injury. During this time, the ventricles kept on growing bilaterally. Ventricular growth did not depend on the cortical lesion severity or the cortical hemorrhagic load suggesting a separate pathology. Instead, the results indicate choroidal injury as one driver of the post-traumatic hydrocephalus, since the higher the choroid plexus iron load the larger were the ventricles at 6 months. The ventricle size or the choroid plexus iron load did not associate with seizure susceptibility. Cortical hypoperfusion and memory deficits were worse in rats with greater ventricular growth.

Mild repetitive head impacts alter perivascular flow in the midbrain dopaminergic system in awake rats

Head injury is a known risk factor for Parkinson's disease. Disruption in the perivascular clearance of metabolic waste and unwanted proteins is thought to be a contributing factor to disease progression. We hypothesized that repetitive mild head impacts, without evidence of structural brain damage, would increase microgliosis and AQP4 expression and depolarization and alter perivascular flow in the midbrain dopaminergic system. Adult male rats were subjected to sham, or two mild head impacts separated by 48 h. Three weeks later, fully awake rats were imaged using dynamic, contrast-enhanced MRI to follow the distribution of intraventricular gadobenate dimeglumine contrast agent. Images were registered to and analysed using a 3D MRI rat atlas providing site-specific data on 171 different brain areas. Following imaging, rats were tested for cognitive function using the Barnes maze assay. Histological analyses of tyrosine hydroxylase, microglia activation and AQP4 expression and polarization were performed on a parallel cohort of head impacted rats at 20 days post insult to coordinate with the time of imaging. There was no change in the global flux of contrast agent between sham and head impacted rats. The midbrain dopaminergic system showed a significant decrease in the influx of contrast agent as compared to sham controls together with a significant increase in microgliosis, AQP4 expression and depolarization. There were no deficits in cognitive function. The histology showed a significant level of neuroinflammation in the midbrain dopaminergic system 3 weeks post mild repetitive head impact but no loss in tyrosine hydroxylase. MRI revealed no structural brain damage emphasizing the potential serious consequences of mild head impacts on sustained brain neuroinflammation in this area critical to the pathophysiology of Parkinson's.

The Known Unknowns: An Overview of the State of Blood-Based Protein Biomarkers of Mild Traumatic Brain Injury

Blood-based protein biomarkers have revolutionized several fields of medicine by enabling molecular level diagnosis, as well as monitoring disease progression and treatment efficacy. Traumatic brain injury (TBI) so far has benefitted only moderately from using protein biomarkers to improve injury outcome. Because of its complexity and dynamic nature, TBI, especially its most prevalent mild form (mild TBI; mTBI), presents unique challenges toward protein biomarker discovery and validation given that blood is frequently obtained and processed outside of the clinical laboratory (e.g., athletic fields, battlefield) under variable conditions. As it stands, the field of mTBI blood biomarkers faces a number of outstanding questions. Do elevated blood levels of currently used biomarkers-ubiquitin carboxy-terminal hydrolase L1, glial fibrillary acidic protein, neurofilament light chain, and tau/p-tau-truly mirror the extent of parenchymal damage? Do these different proteins represent distinct injury mechanisms? Is the blood-brain barrier a "brick wall"? What is the relationship between intra- versus extracranial values? Does prolonged elevation of blood levels reflect de novo release or extended protein half-lives? Does biological sex affect the pathobiological responses after mTBI and thus blood levels of protein biomarkers? At the practical level, it is unknown how pre-analytical variables-sample collection, preparation, handling, and stability-affect the quality and reliability of biomarker data. The ever-increasing sensitivity of assay systems and lack of quality control of samples, combined with the almost complete reliance on antibody-based assay platforms, represent important unsolved issues given that false-negative results can lead to false clinical decision making and adverse outcomes. This article serves as a commentary on the state of mTBI biomarkers and the landscape of significant challenges. We highlight and discusses several biological and methodological "known unknowns" and close with some practical recommendations.

Repetitive low-level blast exposure improves behavioral deficits and chronically lowers Aβ42 in an Alzheimer's disease transgenic mouse model

Public awareness of traumatic brain injury (TBI) in the military increased recently because of the conflicts in Iraq and Afghanistan where blast injury was the most common mechanism of injury. Besides overt injuries, concerns also exist over the potential adverse consequences of subclinical blast exposures, which are common for many service members. TBI is a risk factor for the later development of neurodegenerative diseases, including Alzheimer's disease (AD)-like disorders. Studies of acute TBI in humans and animals have suggested that increased processing of the amyloid precursor protein (APP) towards the amyloid beta protein (Aβ) may explain the epidemiological associations with AD. However, in a prior study we found in both rat and mouse models of blast overpressure exposure (BOP), that rather than increasing, rodent brain Aβ42 levels were decreased following acute blast exposure. Here we subjected APP/presenilin 1 transgenic mice (APP/PS1 Tg) to an extended sequence of repetitive low-level blast exposures (34.5 kPa) administered three times per week over 8 weeks. If initiated at 20 weeks of age, these repetitive exposures, which were designed to mimic human subclinical blast exposures, reduced anxiety and improved cognition as well as social interactions in APP/PS1 Tg mice, returning many behavioral parameters in APP/PS1 Tg mice to levels of non-transgenic wild type mice. Repetitive low-level blast exposure was less effective at improving behavioral deficits in APP/PS1 Tg mice when begun at 36 weeks of age. While amyloid plaque loads were unchanged, Aβ42 levels and Aβ oligomers were reduced in brain of mice exposed to repetitive low-level blast exposures initiated at 20 weeks of age, although levels did not directly correlate with behavioral parameters in individual animals. These results have implications for understanding the nature of blast effects on the brain and their relationship to human neurodegenerative diseases.

Current Understanding of Central Nervous System Drainage Systems: Implications in the Context of Neurodegenerative Diseases

Until recently, it was thought that there were no lymphatic vessels in the central nervous system (CNS). Therefore, all metabolic processes were assumed to take place only in the circulation of the cerebrospinal fluid (CSF) and through the blood-brain barrier's (BBB), which regulate ion transport and ensure the functioning of the CNS. However, recent findings yield a new perspective: There is an exchange of CSF with interstitial fluid (ISF), which is drained to the paravenous space and reaches lymphatic nodes at the end. This circulation is known as the glymphatic system. The glymphatic system is an extensive network of meningeal lymphatic vessels (MLV) in the basal area of the skull that provides another path for waste products from CNS to reach the bloodstream. MLV develop postnatally, initially appearing around the foramina in the basal part of the skull and the spinal cord, thereafter sprouting along the skull's blood vessels and spinal nerves in various areas of the meninges. VEGF-C protein (vascular endothelial growth factor), expressed mainly by vascular smooth cells, plays an important role in the development of the MLV. The regenerative potential and plasticity of MLV and the novel discoveries related to CNS drainage offer potential for the treatment of neurodegenerative diseases such as dementia, hydrocephalus, stroke, multiple sclerosis, and Alzheimer disease (AD). Herein, we present an overview of the structure and function of the glymphatic system and MLV, and their potential involvement in the pathology and progression of neurodegenerative diseases.

The impact of exercise, sleep, and diet on neurocognitive recovery from mild traumatic brain injury in older adults: A narrative review

Mild traumatic brain injury (mTBI) accounts for a large majority of traumatic brain injuries sustained globally each year. Older adults, who are already susceptible to age-related declines to neurocognitive health, appear to be at an increased risk of both sustaining an mTBI and experiencing slower or impaired recovery. There is also growing evidence that mTBI is a potential risk factor for accelerated cognitive decline and neurodegeneration. Lifestyle-based interventions are gaining prominence as a cost-effective means of maintaining cognition and brain health with age. Consequently, inter-individual variations in exercise, sleep, and dietary patterns could influence the trajectory of post-mTBI neurocognitive recovery, particularly in older adults. This review synthesises the current animal and human literature centred on the mechanisms through which lifestyle-related habits and behaviours could influence acute and longer-term neurocognitive functioning following mTBI. Numerous neuroprotective processes which are impacted by lifestyle factors have been established in animal models of TBI. However, the literature is characterised by a lack of translation to human samples and limited appraisal of the interaction between ageing and brain injury. Further research is needed to better establish the therapeutic utility of applying lifestyle-based modifications to improve post-mTBI neurocognitive outcomes in older adults.

Spectral analysis of physiological brain pulsations affecting the BOLD signal

Physiological pulsations have been shown to affect the global blood oxygen level dependent (BOLD) signal in human brain. While these pulsations have previously been regarded as noise, recent studies show their potential as biomarkers of brain pathology. We used the extended 5 Hz spectral range of magnetic resonance encephalography (MREG) data to investigate spatial and frequency distributions of physiological BOLD signal sources. Amplitude spectra of the global image signals revealed cardiorespiratory envelope modulation (CREM) peaks, in addition to the previously known very low frequency (VLF) and cardiorespiratory pulsations. We then proceeded to extend the amplitude of low frequency fluctuations (ALFF) method to each of these pulsations. The respiratory pulsations were spatially dominating over most brain structures. The VLF pulsations overcame the respiratory pulsations in frontal and parietal gray matter, whereas cardiac and CREM pulsations had this effect in central cerebrospinal fluid (CSF) spaces and major blood vessels. A quasi‐periodic pattern (QPP) analysis showed that the CREM pulsations propagated as waves, with a spatiotemporal pattern differing from that of respiratory pulsations, indicating them to be distinct intracranial physiological phenomenon. In conclusion, the respiration has a dominant effect on the global BOLD signal and directly modulates cardiovascular brain pulsations.

Transcriptomic Analysis of Mouse Brain After Traumatic Brain Injury Reveals That the Angiotensin Receptor Blocker Candesartan Acts Through Novel Pathways

Traumatic brain injury (TBI) results in complex pathological reactions, where the initial lesion is followed by secondary inflammation and edema. Our laboratory and others have reported that angiotensin receptor blockers (ARBs) have efficacy in improving recovery from traumatic brain injury in mice. Treatment of mice with a subhypotensive dose of the ARB candesartan results in improved functional recovery, and reduced pathology (lesion volume, inflammation and gliosis). In order to gain a better understanding of the molecular mechanisms through which candesartan improves recovery after controlled cortical impact injury (CCI), we performed transcriptomic profiling on brain regions after injury and drug treatment. We examined RNA expression in the ipsilateral hippocampus, thalamus and hypothalamus at 3 or 29 days post injury (dpi) treated with either candesartan (0.1 mg/kg) or vehicle. RNA was isolated and analyzed by bulk mRNA-seq. Gene expression in injured and/or candesartan treated brain region was compared to that in sham vehicle treated mice in the same brain region to identify genes that were differentially expressed (DEGs) between groups. The most DEGs were expressed in the hippocampus at 3 dpi, and the number of DEGs reduced with distance and time from the lesion. Among pathways that were differentially expressed at 3 dpi after CCI, candesartan treatment altered genes involved in angiogenesis, interferon signaling, extracellular matrix regulation including integrins and chromosome maintenance and DNA replication. At 29 dpi, candesartan treatment reduced the expression of genes involved in the inflammatory response. Some changes in gene expression were confirmed in a separate cohort of animals by qPCR. Fewer DEGs were found in the thalamus, and only one in the hypothalamus at 3 dpi. Additionally, in the hippocampi of sham injured mice, 3 days of candesartan treatment led to the differential expression of 384 genes showing that candesartan in the absence of injury had a powerful impact on gene expression specifically in the hippocampus. Our results suggest that candesartan has broad actions in the brain after injury and affects different processes at acute and chronic times after injury. These data should assist in elucidating the beneficial effect of candesartan on recovery from TBI.

Osteopathic Manipulative Treatment to Optimize the Glymphatic Environment in Severe Traumatic Brain Injury Measured With Optic Nerve Sheath Diameter, Intracranial Pressure Monitoring, and Neurological Pupil Index

Background

Traumatic brain injury (TBI) has a complex pathophysiology that has historically been poorly understood. New evidence on the pathophysiology, molecular biology, and diagnostic studies involved in TBI have shed new light on optimizing rehabilitation and recovery. The goal of this study was to assess the effect of osteopathic manipulative treatment (OMT) on peripheral and central glial lymphatics in patients with severe TBI, brain edema, and elevated intracranial pressure (ICP) by measuring changes in several parameters regularly used in management.

Methodology

This was a retrospective study at a level II trauma center that occurred in 2018. The study enrolled patients with TBI, increased ICP, or brain edema who had an external ventricular drain placed. Patients previously underwent a 51-minute treatment with OMT with an established protocol. Patients received 51 minutes of OMT to the head, neck, and peripheral lymphatics. The ICP, cerebrospinal fluid (CSF) drainage, optic nerve sheath diameter (ONSD) measured by ultrasonography, and Neurological Pupil Index (NPi) measured by pupillometer were recorded before, during, and after receiving OMT.

Results

A total of 11 patients were included in the study, and 21 points of data were collected from the patients meeting inclusion criteria who received OMT. There was a mean decrease in the ONSD of 0.62 mm from 6.24 mm to 5.62 mm (P = 0.0001). The mean increase in NPi was 0.18 (P = 0.01). The mean decrease in ICP was 3.33 mmHg (P= 0.0001). There was a significant decrease in CSF output after treatment (P = 0.0001). Each measurement of ICP, ONSD, and NPi demonstrated a decrease in overall CSF volume and pressure after OMT compared to CSF output and ICP prior to OMT.

Conclusions

This study demonstrates that OMT may help optimize glial lymphatic clearance of CSF and improve brain edema, interstitial waste product removal, NPi, ICP, CSF volume, and ONSD. A holistic approach including OMT may be considered to enhance management in TBI patients. As TBI is a spectrum of disease, utilizing similar techniques may be considered for all forms of TBI including concussions and other diseases with brain edema. The results of this study can better inform future trials to specifically study the effectiveness of OMT in post-concussive treatment and in those with mild-to-moderate TBI.

Case report: Manual therapies promote resolution of persistent post-concussion symptoms in a 24-year-old athlete

This case report illustrates the treatment outcomes of a collegiate athlete presenting with an 18-month history of post-concussion syndrome who received a series of mixed manual therapies in isolation of other therapy. Persistent symptoms were self-reported as debilitating, contributing to self-removal from participation in school, work, and leisure activities. Patient and parent interviews captured the history of multiple concussions and other sports-related injuries. Neurological screening and activities of daily living were baseline measured. Post-Concussion Symptom Checklist and Headache Impact Test-6™ were utilized to track symptom severity. Treatments applied included craniosacral therapy, manual lymphatic drainage, and glymphatic techniques. Eleven treatment sessions were administered over 3 months. Results indicated restoration of oxygen saturation, normalized pupil reactivity, and satisfactory sleep. Post-concussion syndrome symptom severity was reduced by 87% as reflected by accumulative Post-Concussion Symptom Checklist scores. Relief from chronic headaches was achieved, reflected by Headache Impact Test-6 scores. Restoration of mood and quality of life were reported. A 6-month follow-up revealed symptoms remained abated with full re-engagement of daily activities. The author hypothesized that post-concussion syndrome symptoms were related to compression of craniosacral system structures and lymphatic fluid stagnation that contributed to head pressure pain, severe sleep deprivation, and multiple neurological and psychological symptoms. Positive outcomes over a relatively short period of time without adverse effects suggest these therapies may offer viable options for the treatment of post-concussion syndrome.

The Rise of Inflow Cisternostomy in Resource-Limited Settings: Rationale, Limitations, and Future Challenges

Low- and middle-income countries (LMICs) bear most of the global burden of traumatic brain injury (TBI), but they lack the resources to address this public health crisis. For TBI guidelines and innovations to be effective, they must consider the context in LMICs; keeping this in mind, this article will focus on the history, pathophysiology, practice, evidence, and implications of cisternostomy. In this narrative review, the author discusses the history, pathophysiology, practice, evidence, and implications of cisternostomy. Cisternostomy for the management of TBI is an innovation developed in LMICs, primarily for LMICs. Its practice is based on the cerebrospinal fluid shift edema theory that attributes injury to increased pressure within the subarachnoid space due to subarachnoid hemorrhage and subsequent dysfunction of glymphatic drainage. Early reports of the technique report significant improvements in the Glasgow Outcome Scale, lower mortality rates, and shorter intensive care unit durations. Most reports are single-center studies with small sample sizes, and the technique requires experience and skill. These limitations have led to criticisms and slow adoption of the technique. Further research is needed to establish the effect of cisternostomy on TBI outcomes.

Part 2: Bypassing TBI-Metabolic Surgery and the Link Between Obesity and Traumatic Brain Injury-A Review

Obesity is a common outcome of traumatic brain injury (TBI) that exacerbates principal TBI symptom domains identified as common areas of post-TBI long-term dysfunction. Obesity is also associated with increased risk of later-life dementia and Alzheimer's disease. Patients with obesity and chronic TBI may be more vulnerable to long-term mental abnormalities. This review explores the question of whether weight loss induced by bariatric surgery could delay or perhaps even reverse the progression of mental deterioration. Bariatric surgery, with its induction of weight loss, remission of type 2 diabetes, and other expressions of the metabolic syndrome, improves metabolic efficiency, leads to reversal of brain lesions seen on imaging studies, and improves function. These observations suggest that metabolic/bariatric surgery may be the most effective therapy for TBI.

Association of enlarged perivascular spaces with Aβ and tau deposition in cognitively normal older population

The relationship between magnetic resonance imaging (MRI)-visible enlarged perivascular spaces (EPVS) and Aβ and tau deposition is poorly investigated in cognitively normal older population. In our study, a total of 106 cognitively normal older subjects from the Alzheimer's Disease Neuroimaging Initiative database were included. All the subjects underwent brain MRI, florbetapir positron emission tomography (PET), and flortaucipir PET examinations. EPVS were rated on MRI using a 5-point scale in the basal ganglia (BG-EPVS) and the centrum semiovale (CSO-EPVS). Our study revealed that 43 subjects had high-degree BG-EPVS (degree >1) and 58 subjects had high-degree CSO-EPVS (degree >1). In logistic regression, high degree of BG-EPVS was associated with age (odds ratio [OR]: 1.08, 95% confidence interval [CI]: 1.01-1.16) and severe deep white matter hyperintensity (OR: 2.67, 95% CI: 1.12-6.35). High degree of CSO-EPVS was associated with flortaucipir PET positivity (OR: 2.24, 95% CI: 1.02-4.93). In conclusion, high degree of CSO-EPVS was associated with tau deposition in the brain, whereas high degree of BG-EPVS was associated with age and severe deep white matter hyperintensity, a marker of small vessel disease.