Pathways of cerebrospinal fluid outflow: a deeper understanding of resorption

Anatomy of spinal CSF loss in the American alligator (Alligator mississippiensis)

A variety of anatomical techniques, imaging modalities, dyes and contrast agents, were used to document the mechanisms/routes whereby spinal cerebrospinal fluid (CSF) would move beyond the confines of the spinal dura in the American alligator, Alligator mississippiensis. Three pathways for CSF loss were identified: spinal arachnoid granulations, perineural flow along the spinal nerves, and lymphatic drainage (both along the surface of the dura and at the venous plexus surrounding the spinal ganglion). These same three pathways for spinal CSF loss have been documented in mammals, suggesting that they may be a common feature of (at least) amniotes. Crocodilians, including A. mississippiensis, have the largest epidural venous sinus system of any vertebrate, the present study suggests that, as in mammals, the venous complex of the alligator plays a direct role in regulating the absorption of CSF from the spinal compartment.

Case report: Central venous stenosis-induced intracranial hypertension

Intracranial hypertension due to central venous stenosis (CVS) is an under-recognized but potentially morbid complication of central venous catheters that can have a benign course if recognized and treated early. Here we report a case of a 23-year-old woman requiring hemodialysis via right subclavian catheter who presented with an intracranial hypertension syndrome and sudden visual loss secondary to right innominate vein thrombosis that improved after angioplasty treatment. This case illustrates how CVS can alter the pressure gradient between the subarachnoid space and the cerebral venous sinuses by increasing venous pressure, affecting cerebrospinal fluid drainage. Since CVS is a common finding in patients receiving hemodialysis, intracranial hypertension due to central venous stenosis is a differential diagnosis to consider in patients of this type who present with intracranial hypertension syndrome.

The impact of body position on neurofluid dynamics: present insights and advancements in imaging

The intricate neurofluid dynamics and balance is essential in preserving the structural and functional integrity of the brain. Key among these forces are: hemodynamics, such as heartbeat-driven arterial and venous blood flow, and hydrodynamics, such as cerebrospinal fluid (CSF) circulation. The delicate interplay between these dynamics is crucial for maintaining optimal homeostasis within the brain. Currently, the widely accepted framework for understanding brain functions is the Monro-Kellie's doctrine, which posits a constant sum of intracranial CSF, blood flow and brain tissue volumes. However, in recent decades, there has been a growing interest in exploring the dynamic interplay between these elements and the impact of external factors, such as daily changes in body position. CSF circulation in particular plays a crucial role in the context of neurodegeneration and dementia, since its dysfunction has been associated with impaired clearance mechanisms and accumulation of toxic substances. Despite the implementation of various invasive and non-invasive imaging techniques to investigate the intracranial hemodynamic or hydrodynamic properties, a comprehensive understanding of how all these elements interact and are influenced by body position remains wanted. Establishing a comprehensive overview of this topic is therefore crucial and could pave the way for alternative care approaches. In this review, we aim to summarize the existing understanding of intracranial hemodynamic and hydrodynamic properties, fundamental for brain homeostasis, along with factors known to influence their equilibrium. Special attention will be devoted to elucidating the effects of body position shifts, given their significance and remaining ambiguities. Furthermore, we will explore recent advancements in imaging techniques utilized for real time and non-invasive measurements of dynamic body fluid properties in-vivo.

Cerebrospinal fluid and blood profiles of transfer RNA fragments show age, sex, and Parkinson's disease-related changes

Transfer RNA fragments (tRFs) have recently been shown to be an important family of small regulatory RNAs with diverse functions. Recent reports have revealed modified tRF blood levels in a number of nervous system conditions including epilepsy, ischemic stroke, and neurodegenerative diseases, but little is known about tRF levels in the cerebrospinal fluid (CSF). To address this issue, we studied age, sex, and Parkinson's disease (PD) effects on the distributions of tRFs in the CSF and blood data of healthy controls and PD patients from the NIH and the Parkinson's Progression Markers Initiative (PPMI) small RNA-seq datasets. We discovered that long tRFs are expressed in higher levels in the CSF than in the blood. Furthermore, the CSF showed a pronounced age-associated decline in the level of tRFs cleaved from the 3'-end and anti-codon loop of the parental tRNA (3'-tRFs, i-tRFs), and more pronounced profile differences than the blood profiles between the sexes. In comparison, we observed moderate age-related elevation of blood 3'-tRF levels. In addition, distinct sets of tRFs in the CSF and in the blood segregated PD patients from controls. Finally, we found enrichment of tRFs predicted to target cholinergic mRNAs (Cholino-tRFs) among mitochondrial-originated tRFs, raising the possibility that the neurodegeneration-related mitochondrial impairment in PD patients may lead to deregulation of their cholinergic tone. Our findings demonstrate that the CSF and blood tRF profiles are distinct and that the CSF tRF profiles are modified in a sex-, age-, and disease-related manner, suggesting that they reflect the inter-individual cerebral differences and calling for incorporating this important subset of small RNA regulators into future studies.

Computational fluid dynamics model to predict the dynamical behavior of the cerebrospinal fluid through implementation of physiological boundary conditions

Cerebrospinal fluid (CSF) dynamics play an important role in maintaining a stable central nervous system environment and are influenced by different physiological processes. Multiple studies have investigated these processes but the impact of each of them on CSF flow is not well understood. A deeper insight into the CSF dynamics and the processes impacting them is crucial to better understand neurological disorders such as hydrocephalus, Chiari malformation, and intracranial hypertension. This study presents a 3D computational fluid dynamics (CFD) model which incorporates physiological processes as boundary conditions. CSF production and pulsatile arterial and venous volume changes are implemented as inlet boundary conditions. At the outlets, 2-element windkessel models are imposed to simulate CSF compliance and absorption. The total compliance is first tuned using a 0D model to obtain physiological pressure pulsations. Then, simulation results are compared with in vivo flow measurements in the spinal subarachnoid space (SAS) and cerebral aqueduct, and intracranial pressure values reported in the literature. Finally, the impact of the distribution of and total compliance on CSF pressures and velocities is evaluated. Without respiration effects, compliance of 0.17 ml/mmHg yielded pressure pulsations with an amplitude of 5 mmHg and an average value within the physiological range of 7-15 mmHg. Also, model flow rates were found to be in good agreement with reported values. However, when adding respiration effects, similar pressure amplitudes required an increase of compliance value to 0.51 ml/mmHg, which is within the range of 0.4-1.2 ml/mmHg measured in vivo. Moreover, altering the distribution of compliance over the four different outlets impacted the local flow, including the flow through the foramen magnum. The contribution of compliance to each outlet was directly proportional to the outflow at that outlet. Meanwhile, the value of total compliance impacted intracranial pressure. In conclusion, a computational model of the CSF has been developed that can simulate CSF pressures and velocities by incorporating boundary conditions based on physiological processes. By tuning these boundary conditions, we were able to obtain CSF pressures and flows within the physiological range.

Brain Fluid Channels for Metabolite Removal

The adult human brain represents only 2 % of the body's total weight, however it is one of the most metabolically active organs in the mammalian body. Its high metabolic activity necessitates an efficacious waste clearance system. Besides the blood, there are two fluids closely linked to the brain and spinal cord drainage system: interstitial fluid (ISF) and cerebrospinal fluid (CSF). The aim of this review is to summarize the latest research clarifying the channels of metabolite removal by fluids from brain tissue, subarachnoid space (SAS) and brain dura (BD). Special attention is focused on lymphatic vascular structures in the brain dura, their localizations within the meninges, morphological properties and topographic anatomy. The review ends with an account of the consequences of brain lymphatic drainage failure. Knowledge of the physiological state of the clearance system is crucial in order to understand the changes related to impaired brain drainage.

Hyperintense areas in the cisternal segments of the cranial nerves: a magnetic resonance imaging study

PURPOSE

The study aimed to explore hyperintense areas in the cisternal segments of the cranial nerves using magnetic resonance imaging (MRI).

METHODS

Seventy outpatients underwent thin-sliced, coronal constructive interference steady-state (CISS) sequence and sagittal T2-weighted MRI following conventional MRI examination.

RESULTS

With the coronal CISS sequence, hyperintense areas were located in the central parts of the olfactory bulbs in 65.7% of patients. For the intracranial optic nerve and optic chiasm, hyperintense areas were detected in 98.6% of the CISS sequences and 100% of the T2-weighted images. In the optic tract, hyperintense areas were detected in 51.4% of cases. In 35% of the patients who underwent the CISS sequence, the intracranial optic nerves were considerably compressed by the internal carotid and anterior cerebral arteries, with hyperintense areas similar to those in patients without vascular compression. Hyperintense areas of the cisternal segments of the oculomotor nerve and trigeminal root were identified in 52.9% and 87.1% of the patients, respectively.

CONCLUSIONS

The hyperintense areas found within the cisternal segments of the cranial nerves delineated on the coronal CISS sequence and sagittal T2-weighted imaging may indicate the intracranial part of the glymphatic pathway through the cranial nerves. The cranial nerves may function as part of the glymphatic pathway.

A Brief Overview of the Cerebrospinal Fluid System and Its Implications for Brain and Spinal Cord Diseases

A comprehensive understanding of the cerebrospinal fluid (CSF) system is essential for our understanding of health and disease within the central nervous system (CNS). The system of CSF refers to all components involved in CSF production, movement, and absorption. In recent years, extensive research has resulted in vastly improved understanding of the CSF system in health and disease. Yet, several aspects remain to be fully clarified, notably along the spinal cord as the preponderance of research has focused on the brain. This review briefly summarizes the CSF system and its implications for CNS diseases and highlights the knowledge gaps that require further research.

The Brain-Nose Interface: A Potential Cerebrospinal Fluid Clearance Site in Humans

The human brain functions at the center of a network of systems aimed at providing a structural and immunological layer of protection. The cerebrospinal fluid (CSF) maintains a physiological homeostasis that is of paramount importance to proper neurological activity. CSF is largely produced in the choroid plexus where it is continuous with the brain extracellular fluid and circulates through the ventricles. CSF movement through the central nervous system has been extensively explored. Across numerous animal species, the involvement of various drainage pathways in CSF, including arachnoid granulations, cranial nerves, perivascular pathways, and meningeal lymphatics, has been studied. Among these, there is a proposed CSF clearance route spanning the olfactory nerve and exiting the brain at the cribriform plate and entering lymphatics. While this pathway has been demonstrated in multiple animal species, evidence of a similar CSF egress mechanism involving the nasal cavity in humans remains poorly consolidated. This review will synthesize contemporary evidence surrounding CSF clearance at the nose-brain interface, examining across species this anatomical pathway, and its possible significance to human neurodegenerative disease. Our discussion of a bidirectional nasal pathway includes examination of the immune surveillance in the olfactory region protecting the brain. Overall, we expect that an expanded discussion of the brain-nose pathway and interactions with the environment will contribute to an improved understanding of neurodegenerative and infectious diseases, and potentially to novel prevention and treatment considerations.

Craniosynostosis and hydrocephalus: relevance and treatment modalities

INTRODUCTION

Hydrocephalus is variously associated to syndromic craniosynostosis (CS), while it is randomly encountered in monosutural CS. Pathogenesis is still debated and reliable criteria for the diagnosis of overt hydrocephalus are lacking. Additionally, optimal treatment is controversial since it should balance the need to relieve intracranial hypertension and the risk of recurrence favored by lowering intracranial pressure.

METHODS

A thorough review of the literature has been performed. Accordingly, pathogenic theories, diagnostic issues, and treatment options on hydrocephalus presenting in the context of CS are discussed.

RESULTS

The association of hydrocephalus to simple CS is considered a fortuitous event. Its treatment is usually driven by the etiology and clinical relevance of hydrocephalus, favoring treatment before surgical correction to reduce CSF-related complications. On the other side, pathogenesis of hydrocephalus in the context of syndromic CS has been mainly related to factors that are secondary to the synostostic process, such as craniocerebral disproportion and venous hypertension. Hydrocephalus complicates 12-15% of syndromic CS, though its incidence is more relevant in FGFR2-related CS and raises up to 88% in Pfeiffer syndrome. Overt hydrocephalus should be properly differentiated by non-tense ventriculomegaly that is more frequent in Apert syndrome. Since intracranial hypertension is constant in syndromic CS even in the absence of active hydrocephalus, radiological monitoring of ventricular size along with intracranial pressure monitoring is essential. Active hydrocephalus occurs more frequently in infants, though stable ventriculomegaly may evolve into overt hydrocephalus after cranial expansion. If hydrocephalus is not clinically prominent, cranial expansion should be favored as first surgical step. Although posterior cranial expansion may address posterior cranial fossa constriction and stabilize ventricular dilation, effectiveness in long-term control of hydrocephalus is not clear. ETV is an effective treatment option, though success rate is affected by the presence of brain malformations and patient age. Extrathecal CSF shunting should be used as last resource due to the increased risk of complications in this context.

CONCLUSIONS

The pathogenesis of hydrocephalus complicating syndromic CS should be further investigated. Concomitantly, the definition of reliable diagnostic criteria is advocated in order to promptly and properly identify active hydrocephalus. Finally, treatment algorithm should refine the best timing and treatment options aiming to relieve intracranial hypertension on one side and reduce the risk of restenosis on the other side.

Pathogenesis of Thai duck Tembusu virus in BALB/c mice: Descending infection and neuroinvasive virulence

Duck Tembusu virus (DTMUV) is an emerging flavivirus that causes systemic disease in an avian host. The predominant cluster of DTMUV circulating in Thailand was recently classified as cluster 2.1. The pathogenesis of this virus has been extensively studied in avian hosts but not in mammalian hosts. Six-week-old BALB/c mice were intracerebrally or subcutaneously inoculated with Thai DTMUV to examine clinical signs, pathological changes, viral load and virus distribution. Results demonstrated that the virus caused disease in BALB/c mice by the intracerebral inoculation route. Infected mice demonstrated both systemic and neurological symptoms. Pathological changes and virus distribution were observed in all tested organs. Viral load in the brain was significantly higher than in other organs (p < .05), and the virus caused acute death in BALB/c mice. The virus was disseminated in all parts of the body, but no virus shedding was recorded in saliva and faeces. Findings highlighted the potential of Thai DTMUV to transmit disease in mammalian hosts.

Current Concepts in Intracranial Interstitial Fluid Transport and the Glymphatic System: Part I-Anatomy and Physiology

Normal physiologic function of organs requires a circulation of interstitial fluid to deliver nutrients and clear cellular waste products. Lymphatic vessels serve as collectors of this fluid in most organs; however, these vessels are absent in the central nervous system. How the central nervous system maintains tight control of extracellular conditions has been a fundamental question in neuroscience until recent discovery of the glial-lymphatic, or glymphatic, system was made this past decade. Networks of paravascular channels surrounding pial and parenchymal arteries and veins were found that extend into the walls of capillaries to allow fluid transport and exchange between the interstitial and cerebrospinal fluid spaces. The currently understood anatomy and physiology of the glymphatic system is reviewed, with the paravascular space presented as an intrinsic component of healthy pial and parenchymal cerebral blood vessels. Glymphatic system behavior in animal models of health and disease, and its enhanced function during sleep, are discussed. The evolving understanding of glymphatic system characteristics is then used to provide a current interpretation of its physiology that can be helpful for radiologists when interpreting neuroimaging investigations.

CSF-Venous Fistulas: Anatomy and Diagnostic Imaging

CSF-venous fistulas (CVFs), first described in 2014, represent an important cause of spontaneous intracranial hypotension (SIH). CVFs can be challenging to detect on conventional anatomic imaging because, unlike other types of spinal CSF leak, they do not typically result in pooling of fluid in the epidural space, and imaging signs of CVF may be subtle. Specialized myelographic techniques have been developed to help with CVF identification, but these techniques are not yet widely disseminated. This article reviews the current understanding of CVFs, emphasizing correlations between venous anatomy and imaging findings as well as potential mechanisms for pathogenesis, and describes current imaging techniques used for CVF diagnosis and localization. These techniques are broadly classified into fluoroscopy-based methods, including digital subtraction myelography and dynamic myelography, as well as cross-sectional methods, including decubitus CT myelography and MR myelography with intrathecal gadolinium. Knowledge of these various options, including their relative advantages and disadvantages, is critical in the care of patients with SIH. Investigation is ongoing, and continued advances are anticipated in understanding of CVFs as well as in optimal imaging detection.

Central Venous Obstruction-Induced Intracranial Hypertension in Hemodialysis Patients: An Underrecognized Cause of Elevated Intracranial Pressure

BACKGROUND

Central venous obstruction (stenosis or occlusion) is common in patients with renal failure on hemodialysis and may be associated with intracranial hypertension (IH). Causes include vein injury from an endoluminal device, lumen obstruction from a device or thrombus, external vein compression, and high venous flow leading to vein intimal hyperplasia. A combination of high venous flow and central venous obstruction can lead to intracranial venous hypertension, impaired cerebrospinal fluid (CSF) resorption, and subsequent IH.

EVIDENCE ACQUISITION

We conducted a search of the English literature using the Ovid MEDLINE Database and PubMed, with a focus on reports involving IH and central venous obstruction in the setting of hemodialysis. We reviewed CSF flow dynamics, the risk factors and causes of central venous obstruction, and the evaluation, management, and outcomes of central venous obstruction-induced IH.

RESULTS

Twenty-four cases of IH related to central venous obstruction in hemodialysis patients were identified. Twenty patients had headaches (83.3%) and 9 had visual symptoms (37.5%). The brachiocephalic vein was the most common site of stenosis or occlusion (20/24, 83.3%). Twenty-one patients (87.5%) had resolution of IH with treatment. Two patients died from complications of IH (8.3%).

CONCLUSIONS

Central venous obstruction-induced IH is likely underrecognized by clinicians and mimics idiopathic IH. Hemodialysis patients with IH should be screened with computed tomography venography of the chest. Optimal treatment is with vascular intervention or a CSF diversion procedure and can help prevent vision loss from papilledema or nervous system damage. Medical management may be appropriate in mild cases or as a bridge to definitive interventional treatment. Increased awareness among clinicians has potential to facilitate the timely diagnosis of this treatable condition with potential for good neurologic and visual outcomes.

Renal Pelvis Opacification on Postmyelography Computed Tomography as an Indicator for Cerebrospinal Fluid Loss in Spontaneous Intracranial Hypotension

Purpose

To assess early renal pelvis opacification on postmyelography computed tomography (CT) as a marker for cerebrospinal fluid (CSF) loss in patients with spontaneous intracranial hypotension (SIH).

Methods

The SIH patients referred to our hospital between January 2012 and May 2018 were retrospectively reviewed and divided into 2 groups based on the presence of spinal longitudinal extrathecal CSF collection (SLEC): (1) SLEC(+) with, and (2) SLEC(−) without proof of SLEC on multimodal imaging. Non-SIH patients (n = 20) undergoing CT myelography served as controls. The renal pelvis density on postmyelography CT was measured in all patients. Mean difference in renal pelvis density between the groups was calculated.

Results

In total, 111 SIH patients (mean age 48 ± 13 years; 60% female) were included, 71 (64%) SLEC(+) and 40 (36%) SLEC(−). The adjusted renal pelvis density in the SLEC(+), SLEC(−), and the non-SIH group was 108 Hounsfield unit (HU), 83 HU, and 32 HU, respectively, resulting in a significant difference between SLEC(+) vs. control group 1 (75 HU, p < 0.001), SLEC(−) vs. control group 1 (50 HU, p < 0.001), and a tendency for higher density in SLEC(+) than SLEC(−) (25 HU, p = 0.16).

Conclusion

Increased renal pelvis opacification on postmyelography CT was observed in SIH patients, even in the absence of a CSF leak or a CSF venous fistula, when compared to non-SIH patients. Although the provenance of early renal opacification in SLEC (−) SIH patients remains unclear, our results suggest that it may be a surrogate for increased spinal CSF resorption via spinal arachnoid granulations and along spinal nerve sheaths occult to direct imaging.

All Central Nervous System Neuro- and Vascular-Communication Channels Are Surrounded With Cerebrospinal Fluid

Background: Recent emerging evidence has highlighted the potential critical role of cerebrospinal fluid (CSF) in cerebral waste clearance and immunomodulation. It is already very well-established that the central nervous system (CNS) is completely submerged in CSF on a macro-level; but to what extent is this true on a micro-level? Specifically, within the peri-neural and peri-vascular spaces within the CNS parenchyma. Therefore, the objective of this study was to use magnetic resonance imaging (MRI) to simultaneously map the presence of CSF within all peri-neural (cranial and spinal nerves) and peri-vascular spaces in vivo in humans. Four MRI protocols each with five participants were used to image the CSF in the brain and spinal cord. Our findings indicated that all CNS neuro- and vascular-communication channels are surrounded with CSF. In other words, all peri-neural spaces surrounding the cranial and spinal nerves as well as all peri-vascular spaces surrounding MRI-visible vasculature were filled with CSF. These findings suggest that anatomically, substance exchange between the brain parenchyma and outside tissues including lymphatic ones can only occur through CSF pathways and/or vascular pathways, warranting further investigation into its implications in cerebral waste clearance and immunity.

Eye changes in space : New insights into clinical aspects, pathogenesis, and prevention

BACKGROUND

More than ever research into changes in the eye caused by long-term space flight is becoming the focus of the international and national space agencies National Aeronautics and Space Administration (NASA), European Space Agency (ESA) and German Aerospace Center (DLR). In addition to space radiation-induced cataract formation considerable eye changes, summarized under space flight-associated neuro-ocular syndrome (SANS), can occur.

OBJECTIVE

This article gives an overview of the current state of research and future directions in the field of research concerned with ocular alterations in SANS and presents the relevance for terrestrial ophthalmological research.

MATERIAL AND METHODS

An analysis of existing publications on SANS in PubMed and reports on the risk of SANS published by the NASA of the USA was carried out.

RESULTS

The reasons for the development of the eye changes in space have not been clarified. Factors such as the increase in intracranial pressure, fluid shifts, hypercapnia and genetic factors are the subject of intensive research efforts. A terrestrial model for the induction of papilledema could be established (bed rest studies with -6° head-down tilt as a space analogue). Countermeasures for the development of eye changes, such as intermittent artificial gravity, are the subject of current research studies.

CONCLUSION

Research into SANS as part of bed rest studies will provide further important insights in the future for space research and also for terrestrial research. Clinical research projects can be derived from space research.

Dural venous sinus anatomy in children with external hydrocephalus: analysis of a series of 97 patients

PURPOSE

To evaluate the anatomical variations of dural venous sinuses in children with external hydrocephalus, proposing a radiological grading of progressive anatomic restriction to venous outflow based on brain phase-contrast magnetic resonance venography (PC-MRV); to evaluate the correlation between positional plagiocephaly and dural sinuses patency; and to compare these findings with a control group to ascertain the role of anatomical restriction to venous outflow in the pathophysiology of external hydrocephalus.

METHODS

Brain MRI and PC MRV were performed in 97 children (76 males, 21 females) diagnosed with external hydrocephalus at an average age of 8.22 months. Reduction of patency of the dural sinuses was graded as 1 (stenosis), 2 (complete stop) and 3 (complete agenesis) for each transverse/sigmoid sinus and sagittal sinus. Anatomical restriction was graded for each patient from 0 (symmetric anatomy of patent dural sinuses) through 6 (bilateral agenesis of both transverse sinuses). Ventricular and subarachnoid spaces were measured above the intercommissural plane using segmentation software. Positional plagiocephaly (PP) and/or asymmetric tentorial insertion (ATI) was correlated with the presence and grading of venous sinus obstruction. These results were compared with a retrospective control group of 75 patients (35 males, 40 females).

RESULTS

Both the rate (84.53% vs 25.33%) and the grading (mean 2.59 vs mean 0.45) of anomalies of dural sinuses were significantly higher in case group than in control group. In the case group, sinus anomalies were asymmetric in 59 cases (right-left ratio 1/1) and symmetric in 22. A significant association was detected between the grading of venous drainage alterations and diagnosis of disease and between the severity of vascular anomalies and the widening of subarachnoid space (SAS). Postural plagiocephaly (39.1% vs 21.3%) and asymmetric tentorial insertion (35.4% vs 17.3%) were significantly more frequent in the case group than in the control group. When sinus anomalies occurred in plagiocephalic children, the obstruction grading was significantly higher on the flattened side (p ≤ 0.001).

CONCLUSION

Decreased patency of the dural sinuses and consequent increased venous outflow resistance may play a role in the pathophysiology of external hydrocephalus in the first 3 years of life. In plagiocephalic children, calvarial flattening may impact on the homolateral dural sinus patency, with a possible effect on the anatomy of dural sinuses and venous drainage in the first months of life.

High-resolution Micro-CT Myelography to Assess Spinal Subarachnoid Space Changes After Spinal Cord Injury in Rats

BACKGROUND AND PURPOSE

The spinal subarachnoid space (SSAS) is vital for neurologic function. Although SSAS alterations are known to occur after spinal cord injury (SCI), there is a lack of high-resolution imaging studies of the SSAS after SCI in rodents. Therefore, the aim here was to assess changes in the SSAS of rats subjected to graded SCI, using high-resolution micro-CT myelography.

METHODS

Long-Evans adult rats were subjected to mild or severe spinal cord contusion at T9. Imaging studies of SSAS features were carried out in injured rats at acute (day 1) and subacute (day 15) stages postinjury, as well as in control rats, using high-resolution micro-CT myelography with a contrast-enhanced digital subtraction protocol. We studied a total of 33 rats randomly allocated into five experimental groups. Micro-CT myelograms were assessed by expert observers using both qualitative and quantitative criteria.

RESULTS

Qualitative and quantitative analyses showed that SCI induces changes in the SSAS that vary as a function of both injury severity and time elapsed after injury. SSAS blockage was the main alteration detected. Moreover, the method used here allowed fine details to be observed in small animals, such as variations in the preferential pathways for contrast medium flow, neuroimaging nerve root enhancement, and leakage of contrast medium due to tearing of the dural sac.

CONCLUSION

Micro-CT myelography provides high-resolution images of changes in the SSAS after SCI in rats and is a useful tool for further experimental studies involving rat SCI in vivo.

Transient enlargement of brain ventricles during relapsing-remitting multiple sclerosis and experimental autoimmune encephalomyelitis

The brain ventricles are part of the fluid compartments bridging the CNS with the periphery. Using MRI, we previously observed a pronounced increase in ventricle volume (VV) in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS). Here, we examined VV changes in EAE and MS patients in longitudinal studies with frequent serial MRI scans. EAE mice underwent serial MRI for up to 2 months, with gadolinium contrast as a proxy of inflammation, confirmed by histopathology. We performed a time-series analysis of clinical and MRI data from a prior clinical trial in which RRMS patients underwent monthly MRI scans over 1 year. VV increased dramatically during preonset EAE, resolving upon clinical remission. VV changes coincided with blood-brain barrier disruption and inflammation. VV was normal at the termination of the experiment, when mice were still symptomatic. The majority of relapsing-remitting MS (RRMS) patients showed dynamic VV fluctuations. Patients with contracting VV had lower disease severity and a shorter duration. These changes demonstrate that VV does not necessarily expand irreversibly in MS but, over short time scales, can expand and contract. Frequent monitoring of VV in patients will be essential to disentangle the disease-related processes driving short-term VV oscillations from persistent expansion resulting from atrophy.

Brain ventricle volumes expand and contract during experimental autoimmune encephalomyelitis and relapsing-remitting multiple sclerosis, suggesting that short-term inflammatory processes are interlaced with gradual brain atrophy.

Targeting the Choroid Plexuses for Protein Drug Delivery

Delivery of therapeutic agents to the central nervous system is challenged by the barriers in place to regulate brain homeostasis. This is especially true for protein therapeutics. Targeting the barrier formed by the choroid plexuses at the interfaces of the systemic circulation and ventricular system may be a surrogate brain delivery strategy to circumvent the blood-brain barrier. Heterogenous cell populations located at the choroid plexuses provide diverse functions in regulating the exchange of material within the ventricular space. Receptor-mediated transcytosis may be a promising mechanism to deliver protein therapeutics across the tight junctions formed by choroid plexus epithelial cells. However, cerebrospinal fluid flow and other barriers formed by ependymal cells and perivascular spaces should also be considered for evaluation of protein therapeutic disposition. Various preclinical methods have been applied to delineate protein transport across the choroid plexuses, including imaging strategies, ventriculocisternal perfusions, and primary choroid plexus epithelial cell models. When used in combination with simultaneous measures of cerebrospinal fluid dynamics, they can yield important insight into pharmacokinetic properties within the brain. This review aims to provide an overview of the choroid plexuses and ventricular system to address their function as a barrier to pharmaceutical interventions and relevance for central nervous system drug delivery of protein therapeutics. Protein therapeutics targeting the ventricular system may provide new approaches in treating central nervous system diseases.

Intracisternal injection of beta-amyloid seeds promotes cerebral amyloid angiopathy

Beta amyloid (Aβ) is a key component of parenchymal Aβ plaques and vascular Aβ fibrils, which lead to cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD). Recent studies have revealed that Aβ contained in the cerebrospinal fluid (CSF) can re-enter into brain through paravascular spaces. However, whether Aβ in CSF may act as a constant source of pathogenic Aβ in AD is still unclear. This study aimed to examine whether Aβ pathology could be worsened when CSF Aβ level was enhanced by intra-cisternal infusion of aged brain extract containing abundant Aβ in TgCRND8 host mice. TgCRND8 mouse is an AD animal model which develops predominant parenchymal Aβ plaques in the brain at as early as 3 months of age. Here, we showed that single intracisternal injection of Aβ seeds into TgCRND8 mice before the presence of Aβ pathology induced robust prion-like propagation of CAA within 90 days. The induced CAA is mainly distributed in the cerebral cortex, hippocampus and thalamus of TgCRND8 mice. Surprisingly, despite the robust increase in CAA levels, the TgCRND8 mice had a marked decrease in parenchymal Aβ plaques and the plaques related neuroinflammation in the brains compared with the control mice. These results amply indicate that Aβ in CSF may act as a source of Aβ contributing to the growth of vascular Aβ deposits in CAA. Our findings provide experimental evidence to unravel the mechanisms of CAA formation and the potential of targeting CSF Aβ for CAA.

[Eye changes in space : New insights into clinical aspects, pathogenesis and prevention]

BACKGROUND

More than ever research into changes in the eye caused by long-term space flight is becoming the focus of the international and national space agencies National Aeronautics and Space Administration (NASA), European Space Agency (ESA) and German Aerospace Center (DLR). In addition to space radiation-induced cataract formation considerable eye changes, summarized under space flight-associated neuro-ocular syndrome (SANS), can occur.

OBJECTIVE

This article gives an overview of the current state of research and future directions in the field of research concerned with ocular alterations in SANS and presents the relevance for terrestrial ophthalmological research.

MATERIAL AND METHODS

An analysis of existing publications on SANS in PubMed and reports on the risk of SANS published by the NASA of the USA was carried out.

RESULTS

The reasons for the development of the eye changes in space have not been clarified. Factors such as the increase in intracranial pressure, fluid shifts, hypercapnia and genetic factors are the subject of intensive research efforts. A terrestrial model for the induction of papilledema could be established (bed rest studies with -6° head-down tilt as a space analogue). Countermeasures for the development of eye changes, such as intermittent artificial gravity, are the subject of current research studies.

CONCLUSION

Research into SANS as part of bed rest studies will provide further important insights in the future for space research and also for terrestrial research. Clinical research projects can be derived from space research.

Glycan changes in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis

Glycans are components of glycoconjugates and function in odorant recognition and cell signaling in the olfactory mucosa. However, little is known about glycan expression in the olfactory mucosa in the presence of neuroinflammatory disorders, which can influence olfaction. We evaluated the changes in glycan in the olfactory mucosa of rats with experimental autoimmune encephalomyelitis (EAE) by histochemical analyses of 21 lectins. In the olfactory mucosa of normal control rats, 16 lectins bound to olfactory sensory neurons, supporting cells, basal cells, nerve and Bowman's glands, and their expression did not significantly change during the course of EAE. In rats with paralytic-stage EAE, five lectins showed different reactivities with the olfactory mucosa compared to those of normal control rats. Of them, Bandeiraea simplicifolia lectin (BSL)-II and BSL-I showed transiently downregulated binding to olfactory sensory neurons and supporting cells in rats with EAE. The reactivities of Lens culinaris agglutinin for the basement membrane, Vicia villosa agglutinin for Bowman's glands and Dolichos biflorus agglutinin for all nuclei were upregulated in the olfactory mucosa of EAE rats. These results suggest that BSL-II-binding N-acetyl-glucosamine and BSL-I-binding N-acetyl-galactose are involved in transient olfactory dysfunction in EAE, which may hamper odor perception and/or signal processing in olfactory sensory neurons.

Hydrocephalus associated with multiple Tarlov cysts

Tarlov cysts (TCs) consist of dilated nerve root sheaths filled with cerebrospinal fluid (CSF) and are most frequently found in the sacrum. It is estimated that 25% of detected TCs cause chronic pain and intestinal and urogenital symptoms due to compression of the sacral nerve root fibers inside the TC. Unfortunately, symptomatic TCs are frequently overlooked. It is assumed that TCs result from pathologically increased hydrostatic pressure (HP) in the dural sac that forces CSF into the nerve root sheaths. We hypothesize that in patients with TCs, increased spinal hydrostatic pressure is always associated with increased intracranial pressure. This hypothesis of increased cerebrospinal pressure might explain why patients with sacral TCs frequently report distant symptoms, such as headaches and pain in the neck and arms. In this paper, we describe a case report that provides evidence for this hypothesis. A 30-year-old man presented for the first time in our clinic complaining of lower back, leg, thoracic, neck, and arm pain; headaches; and bladder, bowel, and sphincter symptoms. He was born prematurely and suffered cerebral intraventricular bleeding followed by progressive hydrocephalus. Progression was stabilized with acetazolamide and lumbar punctures. At 19 years of age, his head circumference had further increased and he reported back pain and headaches. Fundoscopy showed no papilledema, and lumbar puncture for CSF evacuation improved the headaches and back pain. The former medical team chose not to insert a ventriculo-external shunt. Brain magnetic resonance imaging (MRI) showed significant dilation of all the ventricles. No CSF flow obstruction between the ventricles was observed. Surprisingly, MRI of the lumbar and sacral spine showed multiple large TCs. This case report indicates that hydrocephalus with a patent aqueduct may be associated with TCs because the increased intracranial pressure is transferred to the spinal canal. While increased intracranial pressure causes dilation of the ventricles, the associated increased spinal pressure may cause dilation of multiple spinal nerve root sheaths to form TCs. Furthermore, while the increased volume of the ventricles gradually compresses the neurons and axons of the brain against the bony skull, simultaneously, the increased pressure inside the nerve sheaths may also gradually compress the neurons and axons located inside the dorsal root ganglia and spinal nerves, resulting in neuropathic pain, sensory abnormalities, and neurogenic bladder and bowel symptoms. Hydrocephalus patients reporting neuropathic pain should be screened for the presence of TCs.

The relationships among spinal CSF flows, spinal cord geometry, and vascular correlations: evidence of intrathecal sources and sinks

We studied relationships of cerebral spinal fluid (CSF) pulsatile flow at cervical, thoracic, and lumbar levels using phase-contrast cine MRI (PCCMRI) to determine the following: 1) instantaneous and average net flows at cervical, thoracic, and lumbar levels, 2) stochastic correlations of CSF flow with major arterial supplies and major draining veins, and 3) whether adjustments of cord-flow curves-using cord cross-sectional areas, caudal lengths, and caudal volumes-would normalize flow curves from different levels. We scanned 15 healthy volunteers without anesthesia, ages 23-46 yr, using external, retrocardiac-gated, two-dimensional PCCMRI at 3T. Transverse scans of the subarachnoid space, arteries, and veins were acquired and analyzed at cervical, thoracic, and lumbar levels. Instantaneous CSF flow decreased craniocaudally along the full time course of a cardiac cycle. Downward net flow generally increased craniocaudally. During diastole, instantaneous CSF flow decreased proportionally to cross-sectional area, caudal residual length, and caudal residual volume of the cord. The proportionalities were less consistent during systole. CSF, internal carotid artery (ICA), vertebral artery, and lower aorta temporal correlations were highest in systole and decreased craniocaudally. CSF flow temporally correlated better with lower aorta flow than with the ICA at T7 and L2 during systole but not diastole. Inferior vena cava temporal correlation increased craniocaudally. We conclude that whereas instantaneous flow is attenuated cranial caudally, net downward flow, per cardiac cycle, increases caudally, becoming statistically significant at T7 and below the conus medullaris. We can explain the results with the assumption of cord CSF production and peripheral-dominated CSF absorption.

Upward movement of cerebrospinal fluid in obstructive hydrocephalus-revision of an old concept

PURPOSE

The specific pathophysiological processes in many forms of obstructive hydrocephalus (HC) are still unclear. Current concepts of cerebrospinal fluid (CSF) dynamics presume a constant downward flow from the lateral ventricles towards subarachnoid spaces, which are in contrast to neurosurgical observations and findings of MRI flow studies. The aim of our study was to analyze CSF movements in patients with obstructive HC by neuroendoscopic video recordings, X-ray studies, and MRI.

METHODS

One hundred seventeen pediatric patients with obstructive HC who underwent neuroendoscopy in our center were included. Video recordings were analyzed in 85 patients. Contrast-enhanced X-rays were conducted during surgery prior to intervention in 75 patients, and flow void signals on pre-operative MRI could be evaluated in 110 patients.

RESULTS

In 83.5% of the video recordings, CSF moved upwards synchronous to inspiration superimposed by cardiac pulsation. Application of contrast medium revealed a flow delay in 52% of the X-ray studies prior to neurosurgery, indicating hindered CSF circulation. The appearances and shapes of flow void signals in 88.2% of the pre-operative MRI studies suggested valve-like mechanisms and entrapment of CSF.

CONCLUSIONS

Neuroendoscopic observations in patients with obstructive HC revealed upward CSF movements and the corresponding MRI signs of trapped CSF in brain cavities. These observations are in contrast to the current pathophysiological concept of obstructive HC. However, recent real-time flow MRI studies demonstrated upward movement of CSF, hence support our clinical findings. The knowledge of cranial-directed CSF flow expands our understanding of pathophysiological mechanisms in HC and is the key to effective treatment.

Dynamic 11C-PiB PET Shows Cerebrospinal Fluid Flow Alterations in Alzheimer Disease and Multiple Sclerosis

Cerebrospinal fluid (CSF) plays an important role in solute clearance and maintenance of brain homeostasis. ¹¹C-Pittsburgh compound B (PiB) PET was recently proposed as a tool for detection of CSF clearance alterations in Alzheimer disease. The current study investigates the magnitude of ¹¹C-PiB PET signal in the lateral ventricles of an independent group of Alzheimer and mild cognitive impairment subjects. We have also evaluated multiple sclerosis as a model of disease with CSF clearance alterations without amyloid-β tissue accumulation. Methods: A set of 11 Alzheimer and 12 mild cognitive impairment subjects and a set of 20 multiple sclerosis subjects with matched controls underwent MRI and dynamic ¹¹C-PiB PET. Lateral ventricle regions of interest were generated manually from MRI data. PET data were analyzed using cerebellum or a supervised reference region for the Alzheimer and multiple sclerosis data sets, respectively. The magnitude of ¹¹C-PiB signal in the lateral ventricles was calculated as area under the curve from 35 to 80 min and SUV ratio (SUVR) from 50 to 70 min. Compartmental modeling analysis was performed on a separate data set containing 11 Alzheimer and matched control subjects; this analysis included an arterial input function, to further understand the kinetics of the lateral ventricular ¹¹C-PiB signal. Results: ANOVA revealed significant group differences in lateral ventricular SUVR across the Alzheimer, mild cognitive impairment, and healthy control groups (P = 0.004). Pairwise comparisons revealed significantly lower lateral ventricular SUVR in Alzheimer subjects than in healthy controls (P < 0.001) or mild cognitive impairment subjects (P = 0.029). Lateral ventricular SUVR was significantly lower in multiple sclerosis subjects than in healthy controls (P = 0.008). Compartmental modeling analysis revealed significantly lower uptake rates of ¹¹C-PiB signal from blood (P = 0.005) and brain tissue (P = 0.004) to the lateral ventricles and significantly lower ¹¹C-PiB signal clearance out of the lateral ventricles (P = 0.002) in Alzheimer subjects than in healthy controls. Conclusion: These results indicate that dynamic ¹¹C-PiB PET can be used to observe pathologic changes in CSF dynamics. We have replicated previous work demonstrating CSF clearance deficits in Alzheimer disease associated with amyloid-β deposits and have extended the observations to include ventricular CSF clearance deficits in mild cognitive impairment and multiple sclerosis.

The link between idiopathic intracranial hypertension, fibromyalgia, and chronic fatigue syndrome: exploration of a shared pathophysiology

PURPOSE

Idiopathic intracranial hypertension (IICH) is a condition characterized by raised intracranial pressure (ICP), and its diagnosis is established when the opening pressure measured during a lumbar puncture is elevated >20 cm H2O in nonobese patients or >25 cm H2O in obese patients. Papilledema is caused by forced filling of the optic nerve sheath with cerebrospinal fluid (CSF). Other common but underappreciated symptoms of IICH are neck pain, back pain, and radicular pain in the arms and legs resulting from associated increased spinal pressure and forced filling of the spinal nerves with CSF. Widespread pain and also several other characteristics of IICH share notable similarities with characteristics of fibromyalgia (FM) and chronic fatigue syndrome (CFS), two overlapping chronic pain conditions. The aim of this review was to compare literature data regarding the characteristics of IICH, FM, and CFS and to link the shared data to an apparent underlying physiopathology, that is, increased ICP.

METHODS

Data in the literature regarding these three conditions were compared and linked to the hypothesis of the shared underlying physiopathology of increased cerebrospinal pressure.

RESULTS

The shared characteristics of IICH, FM, and CFS that can be caused by increased ICP include headaches, fatigue, cognitive impairment, loss of gray matter, involvement of cranial nerves, and overload of the lymphatic olfactory pathway. Increased pressure in the spinal canal and in peripheral nerve root sheaths causes widespread pain, weakness in the arms and legs, walking difficulties (ataxia), and bladder, bowel, and sphincter symptoms. Additionally, IICH, FM, and CFS are frequently associated with sympathetic overactivity symptoms and obesity. These conditions share a strong female predominance and are frequently associated with Ehlers-Danlos syndrome.

CONCLUSION

IICH, FM, and CFS share a large variety of symptoms that might all be explained by the same pathophysiology of increased cerebrospinal pressure.

Military-related risk factors for dementia

INTRODUCTION

In recent years, there has been growing discussion to better understand the pathophysiological mechanisms of traumatic brain injury and post-traumatic stress disorder and how they may be linked to an increased risk of neurodegenerative diseases including Alzheimer's disease in veterans.

METHODS

Building on that discussion, and subsequent to a special issue of Alzheimer's & Dementia published in June 2014, which focused on military risk factors, the Alzheimer's Association convened a continued discussion of the scientific community on December 1, 2016.

RESULTS

During this meeting, participants presented and evaluated progress made since 2012 and identified outstanding knowledge gaps regarding factors that may impact veterans' risk for later life dementia.

DISCUSSION

The following is a summary of the invited presentations and moderated discussions of both the review of scientific understanding and identification of gaps to inform further investigations.

The efficacy of intracerebroventricular idursulfase-beta enzyme replacement therapy in mucopolysaccharidosis II murine model: heparan sulfate in cerebrospinal fluid as a clinical biomarker of neuropathology

Mucopolysaccharidosis II (MPS II) is caused by a deficiency of iduronate-2-sulfatase that results in accumulation of glycosaminoglycans (GAG), including heparan sulfate (HS), which is considered to contribute to neuropathology. We examined the efficacy of intracerebroventricular (ICV) enzyme replacement therapy (ERT) of idursulfase-beta (IDS-β) and evaluated the usefulness of HS as a biomarker for neuropathology in MPS II mice. We first examined the efficacy of three different doses (3, 10, and 30 μg) of single ICV injections of IDS-β in MPS II mice. After the single-injection study, its long-term efficacy was elucidated with 30 μg of IDS-β ICV injections repeated every 4 weeks for 24 weeks. The efficacy was assessed by the HS content in the cerebrospinal fluid (CSF) and the brain of the animals along with histologic examinations and behavioral tests. In the single-injection study, the 30 μg of IDS-β ICV injection showed significant reductions of HS content in brain and CSF that were maintained for 28 days. Furthermore, HS content in CSF was significantly correlated with HS content in brain. In the long-term repeated-injection study, the HS content in the brain and CSF was also significantly reduced and correlated. The histologic examinations showed a reduction in lysosomal storage. A significant improvement in memory/learning function was observed in open-field and fear-conditioning tests. ICV ERT with 30 μg of IDS-β produced significant improvements in biochemical, histological, and functional parameters in MPS II mice. Furthermore, we demonstrate for the first time that the HS in the CSF had significant positive correlation with brain tissue HS and GAG levels, suggesting HS in CSF as a useful clinical biomarker for neuropathology.

Neuroimmunological Implications of Subclinical Lipopolysaccharide from Salmonella Enteritidis

Mounting evidence has indicated that lipopolysaccharide (LPS) is implicated in neuroimmunological responses, but the body’s response to subclinical doses of bacterial endotoxin remains poorly understood. The influence of a low single dose of LPS from Salmonella Enteritidis, which does not result in any clinical symptoms of intoxication (subclinical lipopolysaccharide), on selected cells and signal molecules of the neuroimmune system was tested. Five juvenile crossbred female pigs were intravenously injected with LPS from S. Enteritidis (5 μg/kg body weight (b.w.)), while five pigs from the control group received sodium chloride in the same way. Our data demonstrated that subclinical LPS from S. Enteritidis increased levels of dopamine in the brain and neuropeptides such as substance P (SP), galanin (GAL), neuropeptide Y (NPY), and active intestinal peptide (VIP) in the cervical lymph nodes with serum hyperhaptoglobinaemia and reduction of plasma CD4 and CD8 T-lymphocytes seven days after lipopolysaccharide administration. CD4 and CD8 T-lymphocytes from the cervical lymph node and serum interleukin-6 and tumour necrosis factor α showed no significant differences between the control and lipopolysaccharide groups. Subclinical lipopolysaccharide from S. Enteritidis can affect cells and signal molecules of the neuroimmune system. The presence of subclinical lipopolysaccharide from S. Enteritidis is associated with unknown prolonged consequences and may require eradication and a deeper search into the asymptomatic carrier state of Salmonella spp.

The Route by Which Intranasally Delivered Stem Cells Enter the Central Nervous System

Intranasal administration is a promising route of delivery of stem cells to the central nervous system (CNS). Reports on this mode of stem cell delivery have not yet focused on the route across the cribriform plate by which cells move from the nasal cavity into the CNS. In the current experiments, human mesenchymal stem cells (MSCs) were isolated from Wharton’s jelly of umbilical cords and were labeled with extremely bright quantum dots (QDs) in order to track the cells efficiently. At 2 h after intranasal delivery in immunodeficient mice, the labeled cells were found under the olfactory epithelium, crossing the cribriform plate adjacent to the fila olfactoria, and associated with the meninges of the olfactory bulb. At all times, the cells were separate from actual nerve tracts; this location is consistent with them being in the subarachnoid space (SAS) and its extensions through the cribriform plate into the nasal mucosa. In their location under the olfactory epithelium, they appear to be within an expansion of a potential space adjacent to the turbinate bone periosteum. Therefore, intranasally administered stem cells appear to cross the olfactory epithelium, enter a space adjacent to the periosteum of the turbinate bones, and then enter the SAS via its extensions adjacent to the fila olfactoria as they cross the cribriform plate. These observations should enhance understanding of the mode by which stem cells can reach the CNS from the nasal cavity and may guide future experiments on making intranasal delivery of stem cells efficient and reproducible.

Characterizing the glymphatic influx by utilizing intracisternal infusion of fluorescently conjugated cadaverine

AIMS

Accumulating evidence supports that cerebrospinal fluid (CSF) in the subarachnoid space (SAS) could reenter the brain parenchyma via the glymphatic influx. The present study was designed to characterize the detailed pathway of subarachnoid CSF influx by using a novel CSF tracer.

MAIN METHODS

Fluorescently conjugated cadaverine (A488-ca), for the first time, was employed to investigate CSF movement in the brain. Following intracisternal infusion of CSF tracers, mice brain was sliced and prepared for fluorescence imaging. Some brain sections were immunostained in order to observe tracer distribution and cellular uptake.

KEY FINDINGS

A488-ca moved into the brain parenchyma rapidly, and the influx was time and region dependent. A488-ca entered the mice brain more readily and spread more widely than another commonly used CSF tracer-fluorescently conjugated ovalbumin (OA-45). Furthermore, A488-ca could enter the brain parenchyma either along the paravascular space or across the pial surface. Suppression of glymphatic transport by administration with acetazolamide strikingly reduced the influx of A488-ca. More importantly, relative to OA-45 largely remained in the extracellular space, A488-ca exhibited obvious cellular uptake by astrocytes surrounding the blood vessels and neurons in the cerebral cortex.

SIGNIFICANCE

Subarachnoid CSF could flow into the brain parenchyma via the glymphatic influx, in which the transcellular pathway was faithfully traced by intracisternal infusion with fluorescently conjugated cadaverine. These observations extend our comprehension on the glymphatic influx pathway.

Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures

Visual impairment intracranial pressure (VIIP) syndrome is considered an unexplained major risk for future long-duration spaceflight. NASA recently redefined this syndrome as Spaceflight-Associated Neuro-ocular Syndrome (SANS). Evidence thus reviewed supports that chronic, mildly elevated intracranial pressure (ICP) in space (as opposed to more variable ICP with posture and activity on Earth) is largely accounted for by loss of hydrostatic pressures and altered hemodynamics in the intracranial circulation and the cerebrospinal fluid system. In space, an elevated pressure gradient across the lamina cribrosa, caused by a chronic but mildly elevated ICP, likely elicits adaptations of multiple structures and fluid systems in the eye which manifest themselves as the VIIP syndrome. A chronic mismatch between ICP and intraocular pressure (IOP) in space may acclimate the optic nerve head, lamina cribrosa, and optic nerve subarachnoid space to a condition that is maladaptive to Earth, all contributing to the pathogenesis of space VIIP syndrome. Relevant findings help to evaluate whether artificial gravity is an appropriate countermeasure to prevent this seemingly adverse effect of long-duration spaceflight.

Traumatic Transient Herniation Concomitant with Tonsillar Hemorrhagic Contusion in a Child

Downward displacement of cerebellar tonsils more than 5 mm below the foramen magnum is named as Chiari type I malformation and named benign tonsillar ectopia if herniation is less than 3 mm. It does not just depend on congenital causes. There are also some reasons for acquired Chiari Type 1 and benign tonsillar ectopia/herniation. Trauma is one of them. Trauma may increase tonsillar ectopia or may be the cause of new-onset Chiari type 1. The relationship between the tonsil contusion and its position is unclear. We present a case of pediatric age group with tonsillar herniation with a hemorrhagic contusion. Only 1 case has been presented so far in the literature. A case with unilateral tonsil contusion has not been presented to date. We will discuss the possible reasons for taking the place of the tonsils to the above level of the foramen magnum in the follow-up period, by looking at the literature.

The pathway of subarachnoid CSF moving into the spinal parenchyma and the role of astrocytic aquaporin-4 in this process

AIMS

It has been proved that cerebrospinal fluid (CSF) in the subarachnoid space could reenter the brain parenchyma via the perivascular space. The present study was designed to explore the pathway of subarachnoid CSF flux into the spinal cord and the potential role of aquaporin-4 (AQP4) in this process.

MAIN METHODS

Fluorescently tagged cadaverine, for the first time, was used to study CSF movement in mice. Following intracisternal infusion of CSF tracers, the cervical spinal cord was sliced and prepared for fluorescence imaging. Some sections were subject with immunostaining in order to observe tracer distribution and AQP4 expression.

KEY FINDINGS

Fluorescently tagged cadaverine rapidly entered the spinal cord. Tracer influx into the spinal parenchyma was time dependent. At 10min post-infusion, cadaverine was largely distributed in the superficial tissue adjacent to the pial surface. At 70min post-infusion, cadaverine was distributed in the whole cord and especially concentrated in the gray matter. Furthermore, fluorescent tracer could enter the spinal parenchyma either along the perivascular space or across the pial surface. AQP4 was observed highly expressed in the astrocytic endfeet surrounding blood vessels and the pial surface. Blocking AQP4 by its specific inhibitor TGN-020 strikingly reduced the inflow of CSF tracers into the spinal cord.

SIGNIFICANCE

Subarachnoid CSF could flow into the spinal cord along the perivascular space or across the pial surface, in which AQP4 is involved. Our observation provides a basis for the study on CSF movement in the spinal cord when some neurological diseases occur.

The choroid plexus in health and in disease: dialogues into and out of the brain

This article brings the choroid plexus into the context of health and disease. It is remarkable that the choroid plexus, composed by a monolayer of epithelial cells that lie in a highly vascularized stroma, floating within the brain ventricles, gets so little attention in major physiology and medicine text books and in the scientific literature in general. Consider that it is responsible for producing most of the about 150mL of cerebrospinal fluid that fills the brain ventricles and the subarachnoid space and surrounds the spinal cord in the adult human central nervous system, which is renewed approximately 2-3 times daily. As such, its activity influences brain metabolism and function, which will be addressed. Reflect that it contains an impressive number of receptors and transporters, both in the apical and basolateral sides of the epithelial cells, and as such is a key structure for the communication between the brain and the periphery. This will be highlighted in the context of neonatal jaundice, multiple sclerosis and Alzheimer's disease. Realize that the capillaries that irrigate the choroid plexus stroma do not possess tight junctions and that the blood flow to the choroid plexus is five times higher than that in the brain parenchyma, allowing for a rapid sensing system and delivery of molecules such as nutrients and metals as will be revised. Recognize that certain drugs reach the brain parenchyma solely through the choroid plexus epithelia, which has potential to be manipulated in diseases such as neonatal jaundice and Alzheimer's disease as will be discussed. Without further notice, it must be now clear that understanding the choroid plexus is necessary for comprehending the brain and how the brain is modulated and modulates all other systems, in health and in disease. This review article intends to address current knowledge on the choroid plexus, and to motivate the scientific community to consider it when studying normal brain physiology and diseases of the central nervous system. It will guide the reader through several aspects of the choroid plexus in normal physiology, in diseases characteristic of various periods of life (newborns-kernicterus, young adults-multiple sclerosis and the elder-Alzheimer's disease), and how sex-differences may relate to disease susceptibility.

Research into the Physiology of Cerebrospinal Fluid Reaches a New Horizon: Intimate Exchange between Cerebrospinal Fluid and Interstitial Fluid May Contribute to Maintenance of Homeostasis in the Central Nervous System

Cerebrospinal fluid (CSF) plays an essential role in maintaining the homeostasis of the central nervous system. The functions of CSF include: (1) buoyancy of the brain, spinal cord, and nerves; (2) volume adjustment in the cranial cavity; (3) nutrient transport; (4) protein or peptide transport; (5) brain volume regulation through osmoregulation; (6) buffering effect against external forces; (7) signal transduction; (8) drug transport; (9) immune system control; (10) elimination of metabolites and unnecessary substances; and finally (11) cooling of heat generated by neural activity. For CSF to fully mediate these functions, fluid-like movement in the ventricles and subarachnoid space is necessary. Furthermore, the relationship between the behaviors of CSF and interstitial fluid in the brain and spinal cord is important. In this review, we will present classical studies on CSF circulation from its discovery over 2,000 years ago, and will subsequently introduce functions that were recently discovered such as CSF production and absorption, water molecule movement in the interstitial space, exchange between interstitial fluid and CSF, and drainage of CSF and interstitial fluid into both the venous and the lymphatic systems. Finally, we will summarize future challenges in research. This review includes articles published up to February 2016.