A new look at cerebrospinal fluid circulation

Population Pharmacokinetics of Nusinersen in the Cerebral Spinal Fluid and Plasma of Pediatric Patients With Spinal Muscular Atrophy Following Intrathecal Administrations

Nusinersen is an antisense oligonucleotide intended for the treatment of spinal muscular atrophy. The pharmacokinetics of nusinersen, following intrathecal administrations, in the cerebrospinal fluid (CSF) and plasma of 72 pediatric patients (3 months to 17 years) with spinal muscular atrophy across 5 clinical trials was analyzed via population-based modeling. With sparse data in the CSF and profile data in the plasma, a linear 4-compartment model simultaneously described the time-concentration profiles in both matrices. The typical population parameters were: Q_p = 0.572 L/h, Q_CSF = 0.069 L/h, CL_p = 2.50 L/h, CL_CSF = 0.133 L/hr, V_CSF = 0.441 L, V_p = 32.0 L, V_{systemic_tissue} = 429 L, and V_{CNS_tissue} = 258 L. A full covariate modeling approach identified baseline body weight to be a statistically and clinically relevant covariate on V_CSF , V_p , and CL_p . The model predicted that the CSF volume of distribution increased steadily with age from 0 to 2 years but became relatively steady for children >2 years. Simulations from the final model showed that age-based dosing in children under 2 years ensured a more comparable exposure (peak concentration and area under the concentration-time curve) across subjects in the population relative to a fixed dosing scheme. However, because no dose-limiting toxicity has been reported in any of the trials, a fixed-dose scheme (12 mg across all age groups) was recommended. The median terminal half-life of nusinersen in the CSF was determined from the model to be 163 days, which supported infrequent dosing, once every 4 to 6 months in pediatric patients with spinal muscular atrophy.

Non-Neuronal Cells in the Hypothalamic Adaptation to Metabolic Signals

Although the brain is composed of numerous cell types, neurons have received the vast majority of attention in the attempt to understand how this organ functions. Neurons are indeed fundamental but, in order for them to function correctly, they rely on the surrounding "non-neuronal" cells. These different cell types, which include glia, epithelial cells, pericytes, and endothelia, supply essential substances to neurons, in addition to protecting them from dangerous substances and situations. Moreover, it is now clear that non-neuronal cells can also actively participate in determining neuronal signaling outcomes. Due to the increasing problem of obesity in industrialized countries, investigation of the central control of energy balance has greatly increased in attempts to identify new therapeutic targets. This has led to interesting advances in our understanding of how appetite and systemic metabolism are modulated by non-neuronal cells. For example, not only are nutrients and hormones transported into the brain by non-neuronal cells, but these cells can also metabolize these metabolic factors, thus modifying the signals reaching the neurons. The hypothalamus is the main integrating center of incoming metabolic and hormonal signals and interprets this information in order to control appetite and systemic metabolism. Hence, the factors transported and released from surrounding non-neuronal cells will undoubtedly influence metabolic homeostasis. This review focuses on what is known to date regarding the involvement of different cell types in the transport and metabolism of nutrients and hormones in the hypothalamus. The possible involvement of non-neuronal cells, in particular glial cells, in physiopathological outcomes of poor dietary habits and excess weight gain are also discussed.

The effects of blood and blood products on the arachnoid cell

After traumatic brain injury (TBI), large amounts of red blood cells and hemolytic products are deposited intracranially creating debris in the cerebrospinal fluid (CSF). This debris, which includes heme and bilirubin, is cleared via the arachnoid granulations and lymphatic systems. However, the mechanisms by which erythrocytes and their breakdown products interfere with normal CSF dynamics remain poorly defined. The purpose of this study was to model in vitro how blood breakdown products affect arachnoid cells at the CSF-blood barrier, and the extent to which the resorption of CSF into the venous drainage system is mechanically impaired following TBI. Arachnoid cells were grown to confluency on permeable membranes. Rates of growth and apoptosis were measured in the presence of blood and lysed blood, changes in transepithelial electrical resistance (TEER) was measured in the presence of blood and hemoglobin, and small molecule permeability was determined in the presence of blood, lysed blood, bilirubin, and biliverdin. These results were directly compared with an established rat brain endothelial cell line (RBEC4) co-cultured with rat brain astrocytes. We found that arachnoid cells grown in the presence of whole or lysed erythrocytes had significantly slower growth rates than controls. Bilirubin and biliverdin, despite their low solubilities, altered the paracellular transport of arachnoid cells more than the acute blood breakdown components of whole and lysed blood. Mannitol permeability was up to four times higher in biliverdin treatments than controls, and arachnoid membranes demonstrated significantly decreased small molecule permeabilities in the presence of whole and lysed blood. We conclude that short-term (<24 h) arachnoid cell transport and long-term (>5 days) arachnoid cell viability are affected by blood and blood breakdown products, with important consequences for CSF flow and blood clearance after TBI.

SAMP8 mice as a neuropathological model of accelerated brain aging and dementia: Toshio Takeda's legacy and future directions

Senescence accelerated mice P8 (SAMP8) show significant age-related deteriorations in memory and learning ability in accordance with early onset and rapid advancement of senescence. Brains of SAMP8 mice reveal an age-associated increase of PAS-positive granular structures in the hippocampal formation and astrogliosis in the brain stem and hippocampus. A spongy degeneration in the brain stem appears at 1 month of age and reaches a maximum at 4-8 months. In addition, clusters of activated microglia also appear around the vacuoles in the brain stem. β/A4(Aβ) protein-like immunoreactive granular structures are observed in various regions and increase in number markedly with age. Other age-associated histological changes include cortical atrophy, neuronal cell loss in locus coeruleus and lateral tegmental nuclei, intraneuronal accumulation of lipopigments in Purkinje cells and eosinophilic inclusion bodies in thalamic neurons. A blood-brain barrier dysfunction and astrogliosis are also prominent with advancing age in the hippocampus. These changes are generally similar to the pathomorphology of aging human brains and characterized by their association with some specific glioneuronal reactions. As for the hallmarks of Alzheimer brains, tau morphology has not yet been confirmed regardless of the age-related increase in phosphorylated tau in SAMP8 mice brains, but early age-related Aβ deposition in the hippocampus has recently been published. SAMP8 mice are, therefore, not only a senescence-accelerated model but also a promising model for Alzheimer's disease and other cognitive disorders.

Cerebrospinal fluid hypersecretion in pediatric hydrocephalus

Hydrocephalus, despite its heterogeneous causes, is ultimately a disease of disordered CSF homeostasis that results in pathological expansion of the cerebral ventricles. Our current understanding of the pathophysiology of hydrocephalus is inadequate but evolving. Over this past century, the majority of hydrocephalus cases has been explained by functional or anatomical obstructions to bulk CSF flow. More recently, hydrodynamic models of hydrocephalus have emphasized the role of abnormal intracranial pulsations in disease pathogenesis. Here, the authors review the molecular mechanisms of CSF secretion by the choroid plexus epithelium, the most efficient and actively secreting epithelium in the human body, and provide experimental and clinical evidence for the role of increased CSF production in hydrocephalus. Although the choroid plexus epithelium might have only an indirect influence on the pathogenesis of many types of pediatric hydrocephalus, the ability to modify CSF secretion with drugs newer than acetazolamide or furosemide would be an invaluable component of future therapies to alleviate permanent shunt dependence. Investigation into the human genetics of developmental hydrocephalus and choroid plexus hyperplasia, and the molecular physiology of the ion channels and transporters responsible for CSF secretion, might yield novel targets that could be exploited for pharmacotherapeutic intervention.

Reduced subarachnoid fluid diffusion in enlarged subarachnoid spaces of infancy

Background and purpose Enlargement of the subarachnoid spaces in infancy (ESSI) is a common cause of macrocephaly without proven explanation. We have observed subarachnoid diffusion to be decreased in these patients. We aim to quantify the diffusivity of ventricular and subarachnoid cerebrospinal fluid in ESSI patients, to determine if diffusion characteristics deviate from normocephalic infants, and to propose a unique mechanism for ESSI. Materials and methods 227 consecutive brain magnetic resonance exams from different macrocephalic children were retrospectively reviewed after institutional review board waiver. Patients with noncommunicating hydrocephalus, substantial ventriculomegaly, atrophy, structural bone and/parenchymal abnormalities, abnormal brain signal, hemorrhages, meningitis, and normal imaging were excluded. A total of 53 exams from macrocephalic patients and 21 normocephalic subjects were analyzed. Mean quantitative apparent diffusion coefficient (ADC) values were obtained from the ventricular frontal horn and frontal subarachnoid spaces. The subarachnoid:ventricular ADC ratios were compared using a Mann-Whitney U-test. Results The mean age was 13 +/-8 months (macrocephalic cohort) and 13 +/- 6 months (normocephalic cohort). The subarachnoid fluid mean ADC was 2.50+/-0.26 × 10^-3 mm²/s in the macrocephalic group and 2.84+/-0.29 × 10^-3 mm²/s in the normocephalic group. The ventricular fluid mean ADC was 2.97+/-0.37 × 10^-3 mm²/s and 2.74 +/-0.32 × 10^-6 mm²/s, respectively. The mean quantitative ADC ratios in the macrocephalic group were 0.85, significantly smaller than the normocephalic group (1) ( z = -6.3; p = 0). Conclusion Subarachnoid space fluid diffusivity is reduced in patients with enlarged subarachnoid spaces of infancy. We propose insufficient frontotemporal capillary protein resorption to be the initiating factor in ESSI, leading to unbalanced osmotic/hydrostatic pressures, and secondary congestion.

Role of endothelial nitric oxide synthase and endothelin-1 polymorphism genes with the pathogenesis of intraventricular hemorrhage in preterm infants

In the pathogenesis of neonatal intraventricular hemorrhage (IVH) in preterm infants, an important role is played by changes in venous and arterial cerebral flows. It has been shown that the ability of autoregulation of cerebral flows in response to variations in arterial blood pressure in preterm infants is impaired. This impaired autoregulation causes an increased risk of germinal matrix rupture and IVH occurrence. We examined three polymorphisms of genes, related to regulation of blood flow, for an association with IVH in 100 preterm infants born from singleton pregnancy, before 32 + 0 weeks of gestation, exposed to antenatal steroids therapy, and without congenital abnormalities. These polymorphisms include: eNOS (894G > T and -786T > C) and EDN1 (5665G > T ) gene. We found that infants with genotype GT eNOS 894G > T have 3.4-fold higher risk developing of IVH born before 28 + 6 weeks of gestation. Our investigation did not confirm any significant prevalence for IVH development according to eNOS -786T > C genes polymorphism. Our novel investigations in EDN1 5665G > T polymorphism did not show any link between alleles or genotypes and IVH. Future investigations of polymorphisms in blood-flow associated genes may provide valuable insight into the pathogenetic mechanisms underlying the development of IVH.

Homeostasis and the concept of 'interstitial fluids hierarchy': Relevance of cerebrospinal fluid sodium concentrations and brain temperature control (Review)

In this review, the aspects and further developments of the concept of homeostasis are discussed also in the perspective of their possible impact in the clinical practice, particularly as far as psychic homeostasis is concerned. A brief historical survey and comments on the concept of homeostasis and allostasis are presented to introduce our proposal that is based on the classical assumption of the interstitial fluid (ISF) as the internal medium for multicellular organisms. However, the new concept of a hierarchic role of ISF of the various organs is introduced. Additionally, it is suggested that particularly for some chemico‑physical parameters, oscillatory rhythms within their proper set‑ranges should be considered a fundamental component of homeostasis. Against this background, we propose that the brain ISF has the highest hierarchic role in human beings, providing the optimal environment, not simply for brain cell survival, but also for brain complex functions and the oscillatory rhythms of some parameters, such as cerebrospinal fluid sodium and brain ISF pressure waves, which may play a crucial role in brain physio‑pathological states. Thus, according to this proposal, the brain ISF represents the real internal medium since the maintenance of its dynamic intra-set-range homeostasis is the main factor for a free and independent life of higher vertebrates. Furthermore, the evolutionary links between brain and kidney and their synergistic role in H2O/Na balance and brain temperature control are discussed. Finally, it is surmised that these two interrelated parameters have deep effects on the Central Nervous System (CNS) higher integrative actions such those linked to psychic homeostasis.

The Glymphatic Pathway: Waste Removal from the CNS via Cerebrospinal Fluid Transport

The overall premise of this review is that cerebrospinal fluid (CSF) is transported within a dedicated peri-vascular network facilitating metabolic waste clearance from the central nervous system while we sleep. The anatomical profile of the network is complex and has been defined as a peri-arterial CSF influx pathway and peri-venous clearance routes, which are functionally coupled by interstitial bulk flow supported by astrocytic aquaporin 4 water channels. The role of the newly discovered system in the brain is equivalent to the lymphatic system present in other body organs and has been termed the "glymphatic pathway" or "(g)lymphatics" because of its dependence on glial cells. We will discuss and review the general anatomy and physiology of CSF from the perspective of the glymphatic pathway, a discovery which has greatly improved our understanding of key factors that control removal of metabolic waste products from the central nervous system in health and disease and identifies an additional purpose for sleep. A brief historical and factual description of CSF production and transport will precede the ensuing discussion of the glymphatic system along with a discussion of its clinical implications.

Brain barriers and brain fluid research in 2016: advances, challenges and controversies

This editorial highlights some of the advances that occurred in relation to brain barriers and brain fluid research in 2016. It also aims to raise some of the attendant controversies and challenges in such research.

A journey into the brain: insight into how bacterial pathogens cross blood-brain barriers

The blood-brain barrier, which is one of the tightest barriers in the body, protects the brain from insults, such as infections. Indeed, only a few of the numerous blood-borne bacteria can cross the blood-brain barrier to cause meningitis. In this Review, we focus on invasive extracellular pathogens, such as Neisseria meningitidis, Streptococcus pneumoniae, group B Streptococcus and Escherichia coli, to review the obstacles that bacteria have to overcome in order to invade the meninges from the bloodstream, and the specific skills they have developed to bypass the blood-brain barrier. The medical importance of understanding how these barriers can be circumvented is underlined by the fact that we need to improve drug delivery into the brain.

Orchestration of dynamic copper navigation – new and missing pieces

A general principle in all cells in the body is that an essential metal – here copper – is taken up at the plasma membrane, directed through cellular compartments for use in specific enzymes and pathways, stored in specific scavenging molecules if in surplus, and finally expelled from the cells.

The choroid plexus as a sex hormone target: Functional implications

The choroid plexuses (CPs) are highly vascularized branched structures that protrude into the ventricles of the brain, and form a unique interface between the blood and the cerebrospinal fluid (CSF). In recent years, novel functions have been attributed to this tissue such as in immune and chemical surveillance of the central nervous system, brain development, adult neurogenesis and circadian rhythm regulation. Sex hormones (SH) are widely recognized as modulators in several neurodegenerative diseases, and there is evidence that estrogens and androgens regulate several fundamental biological functions in the CPs. Therefore, SH are likely to affect the composition of the CSF impacting on brain homeostasis. This review will look at implications of the CPs' sex-related specificities.

Immunohistochemical and in situ hybridization study of urate transporters GLUT9/URATv1, ABCG2, and URAT1 in the murine brain

BACKGROUND

Uric acid (UA) is known to exert neuroprotective effects in the brain. However, the mechanism of UA regulation in the brain is not well characterized. In our previous study, we described that the mouse urate transporter URAT1 is localized to the cilia and apical surface of ventricular ependymal cells. To further strengthen the hypothesis that UA is transported transcellularly at the ependymal cells, we aimed to assess the distribution of other UA transporters in the murine brain.

METHODS

Immunostaining and highly-sensitive in situ hybridization was used to assess the distribution of UA transporters: GLUT9/URATv1, ABCG2, and URAT1.

RESULTS

Immunostaining for GLUT9 was observed in ependymal cells, neurons, and brain capillaries. Immunostaining for ABCG2 was observed in the choroid plexus epithelium and brain capillaries, but not in ependymal cells. These results were validated by in situ hybridization.

CONCLUSIONS

We propose that given their specific expression patterns in ependymal, choroid plexus epithelial, and brain capillary endothelial cells in this study, UA may be transported by these UA transporters in the murine brain. This may provide a novel strategy for targeted neuroprotection.

Choroidal fissure acts as an overflow device in cerebrospinal fluid drainage: morphological comparison between idiopathic and secondary normal-pressure hydrocephalus

To clarify the pathogenesis of two different types of adult-onset normal-pressure hydrocephalus (NPH), we investigated cerebrospinal fluid distribution on the high-field three-dimensional MRI. The subarachnoid spaces in secondary NPH were smaller than those in the controls, whereas those in idiopathic NPH were of similar size to the controls. In idiopathic NPH, however, the basal cistern and Sylvian fissure were enlarged in concurrence with ventricular enlargement towards the z-direction, but the convexity subarachnoid space was severely diminished. In this article, we provide evidence that the key cause of the disproportionate cerebrospinal fluid distribution in idiopathic NPH is the compensatory direct CSF communication between the inferior horn of the lateral ventricles and the ambient cistern at the choroidal fissure. In contrast, all parts of the subarachnoid spaces were equally and severely decreased in secondary NPH. Blockage of CSF drainage from the subarachnoid spaces could cause the omnidirectional ventricular enlargement in secondary NPH.

Glymphatic distribution of CSF-derived apoE into brain is isoform specific and suppressed during sleep deprivation

Background

Apolipoprotein E (apoE) is a major carrier of cholesterol and essential for synaptic plasticity. In brain, it’s expressed by many cells but highly expressed by the choroid plexus and the predominant apolipoprotein in cerebrospinal fluid (CSF). The role of apoE in the CSF is unclear. Recently, the glymphatic system was described as a clearance system whereby CSF and ISF (interstitial fluid) is exchanged via the peri-arterial space and convective flow of ISF clearance is mediated by aquaporin 4 (AQP4), a water channel. We reasoned that this system also serves to distribute essential molecules in CSF into brain. The aim was to establish whether apoE in CSF, secreted by the choroid plexus, is distributed into brain, and whether this distribution pattern was altered by sleep deprivation.

Methods

We used fluorescently labeled lipidated apoE isoforms, lenti-apoE3 delivered to the choroid plexus, immunohistochemistry to map apoE brain distribution, immunolabeled cells and proteins in brain, Western blot analysis and ELISA to determine apoE levels and radiolabeled molecules to quantify CSF inflow into brain and brain clearance in mice. Data were statistically analyzed using ANOVA or Student’s t- test.

Results

We show that the glymphatic fluid transporting system contributes to the delivery of choroid plexus/CSF-derived human apoE to neurons. CSF-delivered human apoE entered brain via the perivascular space of penetrating arteries and flows radially around arteries, but not veins, in an isoform specific manner (apoE2 > apoE3 > apoE4). Flow of apoE around arteries was facilitated by AQP4, a characteristic feature of the glymphatic system. ApoE3, delivered by lentivirus to the choroid plexus and ependymal layer but not to the parenchymal cells, was present in the CSF, penetrating arteries and neurons. The inflow of CSF, which contains apoE, into brain and its clearance from the interstitium were severely suppressed by sleep deprivation compared to the sleep state.

Conclusions

Thus, choroid plexus/CSF provides an additional source of apoE and the glymphatic fluid transporting system delivers it to brain via the periarterial space. By implication, failure in this essential physiological role of the glymphatic fluid flow and ISF clearance may also contribute to apoE isoform-specific disorders in the long term.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0138-8) contains supplementary material, which is available to authorized users.

Perivascular macrophages mediate the neurovascular and cognitive dysfunction associated with hypertension

Hypertension is a leading risk factor for dementia, but the mechanisms underlying its damaging effects on the brain are poorly understood. Due to a lack of energy reserves, the brain relies on continuous delivery of blood flow to its active regions in accordance with their dynamic metabolic needs. Hypertension disrupts these vital regulatory mechanisms, leading to the neuronal dysfunction and damage underlying cognitive impairment. Elucidating the cellular bases of these impairments is essential for developing new therapies. Perivascular macrophages (PVMs) represent a distinct population of resident brain macrophages that serves key homeostatic roles but also has the potential to generate large amounts of reactive oxygen species (ROS). Here, we report that PVMs are critical in driving the alterations in neurovascular regulation and attendant cognitive impairment in mouse models of hypertension. This effect was mediated by an increase in blood-brain barrier permeability that allowed angiotensin II to enter the perivascular space and activate angiotensin type 1 receptors in PVMs, leading to production of ROS through the superoxide-producing enzyme NOX2. These findings unveil a pathogenic role of PVMs in the neurovascular and cognitive dysfunction associated with hypertension and identify these cells as a putative therapeutic target for diseases associated with cerebrovascular oxidative stress.

Role of vitamin A metabolism in IIH: Results from the idiopathic intracranial hypertension treatment trial

INTRODUCTION

Vitamin A and its metabolites (called retinoids) have been thought to play a role in the development of idiopathic intracranial hypertension (IIH). The IIH Treatment Trial (IIHTT) showed the efficacy of acetazolamide (ACZ) in improving visual field function, papilledema grade, quality of life and cerebrospinal fluid (CSF) pressure. We postulated that IIH patients would demonstrate elevated measures of vitamin A metabolites in the serum and CSF.

METHODS

Comprehensive measures of serum vitamin A and its metabolites were obtained from 96 IIHTT subjects, randomly assigned to treatment with ACZ or placebo, and 25 controls with similar gender, age and body mass index (BMI). These included retinol, retinol binding protein, all-trans retinoic acid (ATRA), alpha- and beta-carotenes, and beta-cryptoxanthin. The IIHTT subjects also had CSF and serum vitamin A and metabolite measurements obtained at study entry and at six months.

RESULTS

At study entry, of the vitamin A metabolites only serum ATRA was significantly different in IIHTT subjects (median 4.33nM) and controls (median 5.04nM, p=0.02). The BMI of IIHTT subjects showed mild significant negative correlations with serum ATRA, alpha- and beta-carotene, and beta-cryptoxanthin. In contrast, the control subject BMI correlated only with serum ATRA. At six months, the serum retinol, alpha-carotene, beta-carotene, and CSF retinol were increased from baseline in the ACZ treated group, but only increases in alpha-carotene (p=0.02) and CSF ATRA (p=0.04) were significantly greater in the ACZ group compared with the placebo group. No other vitamin A measures were significantly altered over the six months in either treatment group. Weight loss correlated with only with the change in serum beta-carotene (r=-0.44, p=0.006) and the change in CSF retinol (r=-0.61, p=0.02).

CONCLUSION

Vitamin A toxicity is unlikely a contributory factor in the causation of IIH. Our findings differ from those of prior reports in part because of our use of more accurate quantitative methods and measuring vitamin A metabolites in both serum and CSF. ACZ may alter retinoid metabolism in IIH patients.

Understanding the continuum of radionecrosis and vascular disorders in the brain following gamma knife irradiation: An MRI study

PURPOSE

The radiation dose delivered to brain tumors is limited by the possibility to induce vascular damage and necrosis in surrounding healthy tissue. In the present study, we assessed the ability of MRI to monitor the cascade of events occurring in the healthy rat brain after stereotactic radiosurgery, which could be used to optimize the radiation treatment planning.

METHODS

The primary somatosensory forelimb area (S1FL) and the primary motor cortex in the right hemisphere of Fischer rats (n = 6) were irradiated with a single dose of Gamma Knife radiation (Leksell Perfexion, Elekta AG, Stockholm, Sweden). Rats were scanned with a small-animal 7 Tesla MRI scanner before treatment and 16, 21, 54, 82, and 110 days following irradiation. At every imaging session, T₂ -weighted (T₂ w), Gd-DTPA dynamic contrast-enhanced MRI (DCE-MRI), and T2*-weighted ( T2* w) images were acquired to measure changes in fluid content, blood vessel permeability, and structure, respectively. At days 10, 110, and 140, histopathology was performed on brain sections. Locomotion and spatial memory ability were assessed longitudinally by behavioral tests.

RESULTS

No vascular changes were initially observed. After 54 days, a small necrotic volume in the white matter below the S1FL, surrounded by an area presenting significant vascular permeability, was revealed. Between 54 and 110 days, the necrotic volume increased and was accompanied by the formation of a ring-like region, where a mixture of necrosis and permeable blood vessels were observed, as confirmed by histology. Behavioral changes were only observed after day 82.

CONCLUSION

Together, DCE-MRI and T2* w images supported by histology provided a coherent picture of the phenomena involved in the formation of new, leaky blood vessels, which was followed by the detection of radionecrosis in a preclinical model of brain irradiation. Magn Reson Med 78:1420-1431, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Experimental Spinal Stenosis in Cats: New Insight in Mechanisms of Hydrocephalus Development

In our new experimental model of cervical stenosis without inflammation we have tested hypothesis that cranio-spinal communication impairment could lead to hydrocephalus development. Spinal and cranial cerebrospinal fluid (CSF) space separation was obtained with positioning of plastic semiring in epidural space at C2 level in cats. Brain ventricles planimetry, and CSF pressure recording in lateral ventricle (LV) and lumbar subarachnoid space (LSS) were performed in acute and subchronic experiments. In all experiments opening CSF pressures were normal. However, in acute experiments, an infusion of artificial CSF into the LV led to increase of CSF pressure and significant gradient pressure development between LV and LSS due to limited pressure transmission. After 3 or 6 weeks spinal cord atrophy was observed at the site of cervical stenosis, and pressure transmission from LV to LSS was improved as a consequence of spinal tissue atrophy. Planimetry of both the coronal brain slices and the ventricles' surface showed that control ventricular surface was 0.6 ± 0.1% (n = 5), and 1.6 ± 0.2% (n = 4) in animals with subchronic cervical stenosis (P < 0.002). These results support the mentioned hypothesis claiming that CSF volume cranio-spinal displacement impairment could start pathophysiological processes leading to development of hydrocephalus.

Fluid and ion transfer across the blood-brain and blood-cerebrospinal fluid barriers; a comparative account of mechanisms and roles

The two major interfaces separating brain and blood have different primary roles. The choroid plexuses secrete cerebrospinal fluid into the ventricles, accounting for most net fluid entry to the brain. Aquaporin, AQP1, allows water transfer across the apical surface of the choroid epithelium; another protein, perhaps GLUT1, is important on the basolateral surface. Fluid secretion is driven by apical Na+-pumps. K+ secretion occurs via net paracellular influx through relatively leaky tight junctions partially offset by transcellular efflux. The blood-brain barrier lining brain microvasculature, allows passage of O2, CO2, and glucose as required for brain cell metabolism. Because of high resistance tight junctions between microvascular endothelial cells transport of most polar solutes is greatly restricted. Because solute permeability is low, hydrostatic pressure differences cannot account for net fluid movement; however, water permeability is sufficient for fluid secretion with water following net solute transport. The endothelial cells have ion transporters that, if appropriately arranged, could support fluid secretion. Evidence favours a rate smaller than, but not much smaller than, that of the choroid plexuses. At the blood-brain barrier Na+ tracer influx into the brain substantially exceeds any possible net flux. The tracer flux may occur primarily by a paracellular route. The blood-brain barrier is the most important interface for maintaining interstitial fluid (ISF) K+ concentration within tight limits. This is most likely because Na+-pumps vary the rate at which K+ is transported out of ISF in response to small changes in K+ concentration. There is also evidence for functional regulation of K+ transporters with chronic changes in plasma concentration. The blood-brain barrier is also important in regulating HCO3- and pH in ISF: the principles of this regulation are reviewed. Whether the rate of blood-brain barrier HCO3- transport is slow or fast is discussed critically: a slow transport rate comparable to those of other ions is favoured. In metabolic acidosis and alkalosis variations in HCO3- concentration and pH are much smaller in ISF than in plasma whereas in respiratory acidosis variations in pHISF and pHplasma are similar. The key similarities and differences of the two interfaces are summarized.

Translating the Low Translaminar Cribrosa Pressure Gradient Hypothesis into the Clinical Care of Glaucoma

Glaucoma is an optic neuropathy with multiple known risk factors, including age, race, family history, and intraocular pressure. Unfortunately, the only currently modifiable risk factor in treating the disease is intraocular pressure (IOP). Recent studies have investigated intracranial pressure (ICP) and the translaminar cribrosa pressure gradient as a potential explanation for glaucomatous optic nerve vulnerability across a range of IOP values. The difference between these two pressures across the lamina cribrosa may have an effect on the optic nerve, which could provide another modifiable parameter in the battle against glaucoma. In order for modification of the translaminar pressure gradient to be considered in the treatment of glaucoma, noninvasive methods to accurately measure ICP need to be developed. The translaminar pressure gradient could be therapeutically adjusted by either further lowering the IOP or raising the ICP when it is pathologically low, if possible.

Diffusion tensor imaging detects early brain microstructure changes before and after ventriculoperitoneal shunt in children with high intracranial pressure hydrocephalus

To explore the use of diffusion tensor imaging (DTI) parameters in the quantitative assessment of early brain microstructure changes before and after ventriculoperitoneal shunt in children with high intracranial pressure hydrocephalus.Ten patients with communicating hydrocephalus (age: 2-36 months) and 14 age-/gender-matched controls (age: 2-36 months) were enrolled in this study. All patients underwent the ventriculoperitoneal shunt procedure. The imaging data were collected before and 3 months after the operation. Regions of interests (ROIs) included the white matter near the frontal horn of the lateral ventricles (FHLV), the occipital horn of the lateral ventricles (OHLV), occipital subcortical (OS) area, frontal subcortical (FS) area, and thalamus. Fractional anisotropies (FA) and apparent diffusion coefficients (ADC) of the ROIs before and after ventriculoperitoneal shunt were compared between the patients and the controls.Three months after surgery, the patients recovered from the surgery with ameliorated intracranial pressure and slight improvement of clinical intelligence scale and motor scale. Before ventriculoperitoneal shunt, the FA values (except the right FHLV) were significantly decreased and the ADC values were significantly increased in the patients with hydrocephalus, compared with the controls. After the ventriculoperitoneal shunt, the FA values in the FHLV and OHLV of the patients were similar to the controls, but the FA values in other ROIs were still significantly lower than controls. The ADC values in the FS and OS white matter areas of the patients were similar to the controls; however, the ADC values in other ROIs were still significantly higher in patients.The increase of FA and the reduction in ADC in the ROIs preceded the clinical function improvement in patients with high intracranial pressure hydrocephalus and reflected the early changes in brain tissue microstructure, such as the compression of the white matter areas in the ROIs.

Blood-brain barrier disruption during spontaneous canine visceral leishmaniasis

Visceral leishmaniasis is a complex disease caused by Leishmania infantum, and in dogs, besides the classical symptoms, there are descriptions of inflammatory alterations in the brain. Brain inflammation is a strictly controlled process, and as the brain counts on the efficiency of the blood-brain barrier (BBB), we aimed to assess BBB integrity in dogs with spontaneous visceral leishmaniasis. Therefore, we evaluated markers in the cerebrospinal fluid (CSF) and in brain tissue related to BBB disruption and brain inflammation. Elevated albumin quota revealed BBB breakdown, corroborated by increased concentrations of anti-Leishmania antibodies in the CSF. In the brain, albumin and IgG staining formed halos around blood vessels, a classical indicator of BBB leakage. Soluble IgG was also detected in the choroid plexus and ependyma, and in these structures, IgG stained random resident cells. IgG(+) cells and Fcγ-RI(+) cells were identified in the choroid plexus, ependyma and perivascular in the brain parenchyma. The data support the occurrence of BBB disruption in dogs with spontaneous visceral leishmaniasis, and IgG as a key molecule that is capable of initiating and/or maintaining the inflammatory stimuli in the nervous milieu and the CSF as an important disseminator of inflammatory stimuli within the CNS.

Shear-Induced Amyloid Formation in the Brain: I. Potential Vascular and Parenchymal Processes

Shear distortion of amyloid-beta (Aβ) solutions accelerates amyloid cascade reactions that may yield different toxic oligomers than those formed in quiescent solutions. Recent experiments indicate that cerebrospinal fluid (CSF) and interstitial fluid (ISF) containing Aβ flow through narrow brain perivascular pathways and brain parenchyma. This paper suggests that such flow causes shear distortion of Aβ molecules involving conformation changes that may be one of the initiating events in the etiology of Alzheimer's disease. Aβ shearing can occur in or around brain arteries and arterioles and is suggested as the origin of cerebral amyloid angiopathy deposits in cerebrovascular walls. Comparatively low flow rates of ISF within the narrow extracellular spaces (ECS) of the brain parenchyma are suggested as a possible initiating factor in both the formation of neurotoxic Aβ42 oligomers and amyloid fibrils. Aβ42 in slow-flowing ISF can gain significant shear energy at or near the walls of tortuous brain ECS flow paths, promoting the formation of a shear-distorted, excited state hydrophobic Aβ42* conformation. This Aβ42* molecule could possibly be involved in one of two paths, one involving rapid adsorption to a brain membrane surface, ultimately forming neurotoxic oligomers on membranes, and the other ultimately forming plaque within the ECS flow pathways. Rising Aβ concentrations combined with shear at or near critical brain membranes are proposed as contributing factors to Alzheimer's disease neurotoxicity. These hypotheses may be applicable in other neurodegenerative diseases, including tauopathies and alpha-synucleinopathies, in which shear-distorted proteins also may form in the brain ECS.

How Do Meningeal Lymphatic Vessels Drain the CNS?

The many interactions between the nervous and the immune systems, which are active in both physiological and pathological states, have recently become more clearly delineated with the discovery of a meningeal lymphatic system capable of carrying fluid, immune cells, and macromolecules from the central nervous system (CNS) to the draining deep cervical lymph nodes. However, the exact localization of the meningeal lymphatic vasculature and the path of drainage from the cerebrospinal fluid (CSF) to the lymphatics remain poorly understood. Here, we discuss the potential differences between peripheral and CNS lymphatic vessels and examine the purported mechanisms of CNS lymphatic drainage, along with how these may fit into established patterns of CSF flow.

Preventive effects of cilostazol against the development of shunt-dependent hydrocephalus after subarachnoid hemorrhage

OBJECTIVE Chronic hydrocephalus develops in association with the induction of tenascin-C (TNC), a matricellular protein, after aneurysmal subarachnoid hemorrhage (SAH). The aim of this study was to examine if cilostazol, a selective inhibitor of phosphodiesterase Type III, suppresses the development of chronic hydrocephalus by inhibiting TNC induction in aneurysmal SAH patients. METHODS The authors retrospectively reviewed the factors influencing the development of chronic shunt-dependent hydrocephalus in 87 patients with Fisher Grade 3 SAH using multivariate logistic regression analyses. Cilostazol (50 or 100 mg administered 2 or 3 times per day) was administered from the day following aneurysmal obliteration according to the preference of the attending neurosurgeon. As a separate study, the effects of different dosages of cilostazol on the serum TNC levels were chronologically examined from Days 1 to 12 in 38 SAH patients with Fisher Grade 3 SAH. RESULTS Chronic hydrocephalus occurred in 12 of 36 (33.3%), 5 of 39 (12.8%), and 1 of 12 (8.3%) patients in the 0 mg/day, 100 to 200 mg/day, and 300 mg/day cilostazol groups, respectively. The multivariate analyses showed that older age (OR 1.10, 95% CI 1.13-1.24; p = 0.012), acute hydrocephalus (OR 23.28, 95% CI 1.75-729.83; p = 0.016), and cilostazol (OR 0.23, 95% CI 0.05-0.93; p = 0.038) independently affected the development of chronic hydrocephalus. Higher dosages of cilostazol more effectively suppressed the serum TNC levels through Days 1 to 12 post-SAH. CONCLUSIONS Cilostazol may prevent the development of chronic hydrocephalus and reduce shunt surgery, possibly by the inhibition of TNC induction after SAH.

Current Evidence for a Role of the Kynurenine Pathway of Tryptophan Metabolism in Multiple Sclerosis

The kynurenine pathway (KP) is the major metabolic pathway of the essential amino acid tryptophan (TRP). Stimulation by inflammatory molecules, such as interferon-γ (IFN-γ), is the trigger for induction of the KP, driving a complex cascade of production of both neuroprotective and neurotoxic metabolites, and in turn, regulation of the immune response and responses of brain cells to the KP metabolites. Consequently, substantial evidence has accumulated over the past couple of decades that dysregulation of the KP and the production of neurotoxic metabolites are associated with many neuroinflammatory and neurodegenerative diseases, including Parkinson’s disease, AIDS-related dementia, motor neurone disease, schizophrenia, Huntington’s disease, and brain cancers. In the past decade, evidence of the link between the KP and multiple sclerosis (MS) has rapidly grown and has implicated the KP in MS pathogenesis. KP enzymes, indoleamine 2,3-dioxygenase (IDO-1) and tryptophan dioxygenase (highest expression in hepatic cells), are the principal enzymes triggering activation of the KP to produce kynurenine from TRP. This is in preference to other routes such as serotonin and melatonin production. In neurological disease, degradation of the blood–brain barrier, even if transient, allows the entry of blood monocytes into the brain parenchyma. Similar to microglia and macrophages, these cells are highly responsive to IFN-γ, which upregulates the expression of enzymes, including IDO-1, producing neurotoxic KP metabolites such as quinolinic acid. These metabolites circulate systemically or are released locally in the brain and can contribute to the excitotoxic death of oligodendrocytes and neurons in neurological disease principally by virtue of their agonist activity at N-methyl-d-aspartic acid receptors. The latest evidence is presented and discussed. The enzymes that control the checkpoints in the KP represent an attractive therapeutic target, and consequently several KP inhibitors are currently in clinical trials for other neurological diseases, and hence may make suitable candidates for MS patients. Underpinning these drug discovery endeavors, in recent years, several advances have been made in how KP metabolites are assayed in various biological fluids, and tremendous advancements have been made in how specimens are imaged to determine disease progression and involvement of various cell types and molecules in MS.

Magnetic Resonance Imaging Technique for Visualization of Irregular Cerebrospinal Fluid Motion in the Ventricular System and Subarachnoid Space

BACKGROUND

Many studies have shown that cerebrospinal fluid (CSF) behaves irregularly, rather than with laminar flow, in the various CSF spaces. We adapted a modified previously known magnetic resonance imaging technique to visualize irregular CSF motion. Subsequently, we assessed the usefulness and clinical significance of the present method.

MATERIALS AND METHODS

Normal CSF motion in 10 healthy volunteers was visualized with the dynamic improved, motion-sensitized, driven-equilibrium steady-state free precession technique. Subsequently, CSF motion visualization with a modified sequence was applied to 3 patients.

RESULTS

In healthy volunteers, we achieved visualization of the irregularity of CSF flow in the ventricles and spinal canal, whereas CSF motion was diminished in the peripheral part of the intracranial subarachnoid space. In one case, we confirmed the patency of the patient's third ventriculostomy fenestration site. In the other, we verified the usefulness of the proposed sequence for determining the communication between the ventricle or subarachnoid space and the cyst.

CONCLUSIONS

Using the present sequence, we obtained images that accentuated CSF motion, which is largely composed of irregular motion. This method does not require pulse triggering or complex post-processing of images and allows visualization of CSF motion in a short period of time in selected whole imaging planes. It can therefore be applied clinically to diagnose various diseases that cause abnormalities in the CSF space.

The prevalence of cardiovascular disease in non-communicating hydrocephalus

OBJECTIVE

Hydrocephalus (HC) caused by blockade of ventricular cerebrospinal fluid (CSF) pathways is denoted non-communicating HC. One issue not previously addressed is how the prevalence of cardiovascular disease compares between patients with non-communicating HC and the general population.

METHODS

We examined whether the prevalence of cardiovascular disease (arterial hypertension, angina pectoris, cardiac infarction, and diabetes) differed between cases with non-communicating HC and a general control population, represented by participants of the North-Trøndelag Health 3 Survey (The HUNT3 Survey). A second control group consisted of patients with communicating hydrocephalus (idiopathic normal pressure hydrocephalus, iNPH).

RESULTS

The study included 50 cases with non-communicating HC (53.4+10.5years), and two control cohorts: 35,413 participants of the HUNT3 Survey (52.8+9.6years), and 176 iNPH patients (61.2+8.3years). All individuals were aged 35-70 years. Among the non-communicating HC patients, the results showed increased prevalence for arterial hypertension (males), cardiac infarction (females), and diabetes (females), as compared with the HUNT3 control group with significant odds ratio estimates. However, the prevalence of cardiovascular disease did not significantly differ between patients with non-communicating HC or iNPH. In patients with either non-communicating HC or iNPH and elevated pulsatile intracranial pressure (ICP) during overnight monitoring, the prevalence of diabetes was increased.

CONCLUSION

This study showed significantly increased prevalence of cardiovascular disease in non-communicating HC, indicating an association between cardiovascular disease and the development of non-communicating HC. Further, diabetes was associated with abnormal pulsatile ICP in both non-communicating HC and iNPH patients.

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.

Col1a1+ perivascular cells in the brain are a source of retinoic acid following stroke

Background

Perivascular stromal cells (PSCs) are a recently identified cell type that comprises a small percentage of the platelet derived growth factor receptor-β+ cells within the CNS perivascular space. PSCs are activated following injury to the brain or spinal cord, expand in number and contribute to fibrotic scar formation within the injury site. Beyond fibrosis, their high density in the lesion core makes them a potential significant source of signals that act on neural cells adjacent to the lesion site.

Results

Our developmental analysis of PSCs, defined by expression of Collagen1a1 in the maturing brain, revealed that PSCs first appear postnatally and may originate from the meninges. PSCs express many of the same markers as meningeal fibroblasts, including expression of the retinoic acid (RA) synthesis proteins Raldh1 and Raldh2. Using a focal brain ischemia injury model to induce PSC activation and expansion, we show a substantial increase in Raldh1+/Raldh2+ PSCs and Raldh1+ activated macrophages in the lesion core. We find that RA levels are significantly elevated in the ischemic hemisphere and induce signaling in astrocytes and neurons in the peri-infarct region.

Conclusions

This study highlights a dual role for activated, non-neural cells where PSCs deposit fibrotic ECM proteins and, along with macrophages, act as a potentially important source of RA, a potent signaling molecule that could influence recovery events in a neuroprotective fashion following brain injury.

Increased CSF aquaporin-4, and interleukin-6 levels in dogs with idiopathic communicating internal hydrocephalus and a decrease after ventriculo-peritoneal shunting

Background

Studies in animal models, in which internal hydrocephalus has been induced by obstructing the cerebrospinal fluid pathways, have documented an up-regulation of the concentrations of aquaporin-4 (AQP4) in the brain. In this study, the concentrations of aquaporin-1 (AQP1), AQP1, AQP4 and interleukin-6 (IL-6) were determined in the CSF of dogs with idiopathic communicating hydrocephalus before and after the reduction of intraventricular volume following ventriculo-peritoneal shunt (VP-shunt) treatment.

Results

The concentrations of AQP4 and IL-6 were increased in the cerebrospinal fluid of dogs with hydrocephalus compared to controls. Both parameters significantly decreased after surgical treatment, accompanied by decrease of ventricular size and the clinical recovery of the dogs. AQP1 was not detectable in CSF.

Conclusions

Brain AQP4 up-regulation might be a compensatory response in dogs with hydrocephalus. Future determination of AQP4 at the mRNA and protein level in brain tissue is warranted to substantiate this hypothesis.

Selective Detection of the D-enantiomer of 2-Hydroxyglutarate in the CSF of Glioma Patients with Mutated Isocitrate Dehydrogenase

PURPOSE

Elevation in D-2-Hydroxyglutarate (D-2HG) has recently emerged as a mandatory byproduct of mutated Isocitrate Dehydrogenase (IDH) genes 1 and 2 in glioma patients. The goal of the present study was to demonstrate the feasibility of detection of elevated levels of D-2HG in the cerebrospinal fluid (CSF) of glioma patients that carry point substitutions in the IDH gene.

EXPERIMENTAL DESIGN

We developed a mass spectrometry (MS)-based platform to detect and quantify the D- and L-forms of 2HG in the CSF of glioma patients. Three independent cohorts of patients were analyzed, comprising a total of 176 samples derived from 84 patients. The levels of D- and L-2HG were used to stratify patients into IDH wild-type or IDH-mutated groups using an empirically obtained threshold of 0.69 μmol/L.

RESULTS

Using this platform, a greater than 17-fold mean increase in D-2HG was observed in the CSF of patients with IDH mutant versus wild-type gliomas. The means for the D-2HG levels in CSF were 0.427 μmol/L in wild-type and 7.439 μmol/L in mutant groups. The C statistic for the receiver operator curve was 0.938, with 84% sensitivity, 90% specificity, and 89% accuracy to detect D-2HG. The levels of D- and L-2HG in CSF from wild-type patients varied by location of CSF draw (cisternal > ventricular > lumbar).

CONCLUSIONS

Our findings demonstrate that the CSF of patients harboring IDH mutant gliomas contain increased levels of D-2HG, which can be reliably detected with a MS-based platform. Clin Cancer Res; 22(24); 6256-65. ©2016 AACR.

Directional cerebrospinal fluid movement between brain ventricles in larval zebrafish

BACKGROUND

Cerebrospinal fluid (CSF) contained within the brain ventricles contacts neuroepithelial progenitor cells during brain development. Dynamic properties of CSF movement may limit locally produced factors to specific regions of the developing brain. However, there is no study of in vivo CSF dynamics between ventricles in the embryonic brain. We address CSF movement using the zebrafish larva, during the major period of developmental neurogenesis.

METHODS

CSF movement was monitored at two stages of zebrafish development: early larva [pharyngula stage; 27-30 h post-fertilization (hpf)] and late larva (hatching period; 51-54 hpf) using photoactivatable Kaede protein to calculate average maximum CSF velocity between ventricles. Potential roles for heartbeat in early CSF movement were investigated using tnnt2a mutant fish (tnnt2a (-/-)) and chemical [2,3 butanedione monoxime (BDM)] treatment. Cilia motility was monitored at these stages using the Tg(βact:Arl13b-GFP) transgenic fish line.

RESULTS

In wild-type early larva there is net CSF movement from the telencephalon to the combined diencephalic/mesencephalic superventricle. This movement directionality reverses at late larval stage. CSF moves directionally from diencephalic to rhombencephalic ventricles at both stages examined, with minimal movement from rhombencephalon to diencephalon. Directional movement is partially dependent on heartbeat, as indicated in assays of tnnt2a (-/-) fish and after BDM treatment. Brain cilia are immotile at the early larval stage.

CONCLUSION

These data demonstrate directional movement of the embryonic CSF in the zebrafish model during the major period of developmental neurogenesis. A key conclusion is that CSF moves preferentially from the diencephalic into the rhombencephalic ventricle. In addition, the direction of CSF movement between telencephalic and diencephalic ventricles reverses between the early and late larval stages. CSF movement is partially dependent on heartbeat. At early larval stage, the absence of motile cilia indicates that cilia likely do not direct CSF movement. These data suggest that CSF components may be compartmentalized and could contribute to specialization of the early brain. In addition, CSF movement may also provide directional mechanical signaling.

Vascular basement membranes as pathways for the passage of fluid into and out of the brain

In the absence of conventional lymphatics, drainage of interstitial fluid and solutes from the brain parenchyma to cervical lymph nodes is along basement membranes in the walls of cerebral capillaries and tunica media of arteries. Perivascular pathways are also involved in the entry of CSF into the brain by the convective influx/glymphatic system. The objective of this study is to differentiate the cerebral vascular basement membrane pathways by which fluid passes out of the brain from the pathway by which CSF enters the brain. Experiment 1: 0.5 µl of soluble biotinylated or fluorescent Aβ, or 1 µl 15 nm gold nanoparticles was injected into the mouse hippocampus and their distributions determined at 5 min by transmission electron microscopy. Aβ was distributed within the extracellular spaces of the hippocampus and within basement membranes of capillaries and tunica media of arteries. Nanoparticles did not enter capillary basement membranes from the extracellular spaces. Experiment 2: 2 µl of 15 nm nanoparticles were injected into mouse CSF. Within 5min, groups of nanoparticles were present in the pial-glial basement membrane on the outer aspect of cortical arteries between the investing layer of pia mater and the glia limitans. The results of this study and previous research suggest that cerebral vascular basement membranes form the pathways by which fluid passes into and out of the brain but that different basement membrane layers are involved. The significance of these findings for neuroimmunology, Alzheimer’s disease, drug delivery to the brain and the concept of the Virchow–Robin space are discussed.

PBPK model of methotrexate in cerebrospinal fluid ventricles using a combined microdialysis and MRI acquisition

The objective of the study was to evaluate the distribution of methotrexate (MTX) in cerebrospinal fluid (CSF) lateral ventricles and in cisterna magna after 3rd intraventricular CSF administration in a rabbit model. MTX or gadolinium chelate (Gd-DOTA) was administered in the 3rd ventricle with a local microdialysis to study the pharmacokinetics at the site of administration and with a simultaneous magnetic resonance imaging (MRI) acquisition in the 3rd ventricle, the lateral ventricles and in the cisterna magna. A specific CSF Physiologically Based Pharmacokinetic (PBPK) model was then extrapolated for MTX from Gd-DOTA data. The relative contribution of elimination and distribution processes to the overall disposition of MTX and Gd-DOTA in the 3rd ventricle was similar (i.e., around 60% for CLE and 40% for CLI) suggesting that Gd-DOTA was a suitable surrogate marker for MTX disposition in ventricular CSF. The PBPK predictions for MTX both in CSF of the 3rd ventricle and in plasma were in accordance with the in vivo results. The present study showed that the combination of local CSF microdialysis with MRI acquisition of the brain ventricles and a PBPK model could be a useful methodology to estimate the drug diffusion within CSF ventricles after direct brain CSF administration. Such a methodology would be of interest to clinicians for a rationale determination and optimization of drug dosing parameters in the treatment of leptomeningeal metastases.

Idiopathic Normal Pressure Hydrocephalus: A Review for General Practitioners

Idiopathic normal pressure hydrocephalus (iNPH) is a potentially reversible neurodegenerative disease commonly characterized by a triad of dementia, gait, and urinary disturbance. Advancements in diagnosis and treatment have aided in properly identifying and improving symptoms in patients. However, a large proportion of iNPH patients remain either undiagnosed or misdiagnosed. Using PubMed search engine of keywords "normal pressure hydrocephalus," "diagnosis," "shunt treatment," "biomarkers," "gait disturbances," "cognitive function," "neuropsychology," "imaging," and "pathogenesis," articles were obtained for this review. The majority of the articles were retrieved from the past 10 years. The purpose of this review article is to aid general practitioners in further understanding current findings on the pathogenesis, diagnosis, and treatment of iNPH.

Longitudinal Metabolite Profiling of Cerebrospinal Fluid in Normal Pressure Hydrocephalus Links Brain Metabolism with Exercise-Induced VEGF Production and Clinical Outcome

Idiopathic normal pressure hydrocephalus is a neurological disease caused by abnormal cerebrospinal fluid flow and presents with symptoms such as dementia. Current therapy involves the removal of excess cerebrospinal fluid by shunting. Not all patients respond to this therapy and biomarkers are needed that could facilitate the characterization of patients likely to benefit from this treatment. Here, we measure brain metabolism in normal pressure hydrocephalus patients by performing a novel longitudinal metabolomic profiling study of cerebrospinal fluid. We find that the levels of brain metabolites correlate with clinical parameters, the amount of vascular endothelial growth factor in the cerebrospinal fluid, and environmental stimuli such as exercise. Metabolomic analysis of normal pressure hydrocephalus patients provides insight into changes in brain metabolism that accompany cerebrospinal fluid disorders and may facilitate the development of new biomarkers for this condition.

The cerebral venous system and the postural regulation of intracranial pressure: implications in the management of patients with cerebrospinal fluid diversion

Loss of cerebrospinal fluid (CSF) occurs commonly in daily neurosurgical practice. Understanding the altered physiology following CSF loss is important for optimization of patient care and avoidance of complications. There is overwhelming evidence now that the cerebral venous system plays a major role in intracranial pressure (ICP) dynamics especially when one takes into account the effects of postural changes, atmospheric pressure, and gravity on the craniospinal axis as a whole. The CSF and cerebral venous compartments are tightly coupled in two important ways. CSF is resorbed into the venous system, and there is also an evolved mechanism that prevents overdrainage of venous blood with upright positioning known as the Starling resistor. With loss of CSF pressure, this protective mechanism could become nonfunctional which may result in posture-related venous overdrainage through the cranial venous outflow tracts leading to pathologic states. This review article summarizes the relevant anatomic and physiologic basis of the relationship between the craniospinal venous and CSF compartments in the setting of CSF diversion. It is hoped that this article improves our understanding of ICP dynamics after CSF loss, adds a new dimension to our therapeutic methods, stimulates further research into this field, and ultimately improves our care of these patients.

Lymphatic Clearance of the Brain: Perivascular, Paravascular and Significance for Neurodegenerative Diseases

The lymphatic clearance pathways of the brain are different compared to the other organs of the body and have been the subject of heated debates. Drainage of brain extracellular fluids, particularly interstitial fluid (ISF) and cerebrospinal fluid (CSF), is not only important for volume regulation, but also for removal of waste products such as amyloid beta (Aβ). CSF plays a special role in clinical medicine, as it is available for analysis of biomarkers for Alzheimer's disease. Despite the lack of a complete anatomical and physiological picture of the communications between the subarachnoid space (SAS) and the brain parenchyma, it is often assumed that Aβ is cleared from the cerebral ISF into the CSF. Recent work suggests that clearance of the brain mainly occurs during sleep, with a specific role for peri- and para-vascular spaces as drainage pathways from the brain parenchyma. However, the direction of flow, the anatomical structures involved and the driving forces remain elusive, with partially conflicting data in literature. The presence of Aβ in the glia limitans in Alzheimer's disease suggests a direct communication of ISF with CSF. Nonetheless, there is also the well-described pathology of cerebral amyloid angiopathy associated with the failure of perivascular drainage of Aβ. Herein, we review the role of the vasculature and the impact of vascular pathology on the peri- and para-vascular clearance pathways of the brain. The different views on the possible routes for ISF drainage of the brain are discussed in the context of pathological significance.

Molecular pathophysiology of cerebral edema

Advancements in molecular biology have led to a greater understanding of the individual proteins responsible for generating cerebral edema. In large part, the study of cerebral edema is the study of maladaptive ion transport. Following acute CNS injury, cells of the neurovascular unit, particularly brain endothelial cells and astrocytes, undergo a program of pre- and post-transcriptional changes in the activity of ion channels and transporters. These changes can result in maladaptive ion transport and the generation of abnormal osmotic forces that, ultimately, manifest as cerebral edema. This review discusses past models and current knowledge regarding the molecular and cellular pathophysiology of cerebral edema.

Dynamic dual-isotope molecular imaging elucidates principles for optimizing intrathecal drug delivery

The intrathecal (IT) dosing route offers a seemingly obvious solution for delivering drugs directly to the central nervous system. However, gaps in understanding drug molecule behavior within the anatomically and kinetically unique environment of the mammalian IT space have impeded the establishment of pharmacokinetic principles for optimizing regional drug exposure along the neuraxis. Here, we have utilized high-resolution single-photon emission tomography with X-ray computed tomography to study the behavior of multiple molecular imaging tracers following an IT bolus injection, with supporting histology, autoradiography, block-face tomography, and MRI. Using simultaneous dual-isotope imaging, we demonstrate that the regional CNS tissue exposure of molecules with varying chemical properties is affected by IT space anatomy, cerebrospinal fluid (CSF) dynamics, CSF clearance routes, and the location and volume of the injected bolus. These imaging approaches can be used across species to optimize the safety and efficacy of IT drug therapy for neurological disorders.

Nonsurgical therapy for hydrocephalus: a comprehensive and critical review

Pharmacological interventions have been tested experimentally and clinically to prevent hydrocephalus and avoid the need for shunting beginning in the 1950s. Clinical trials of varied quality have not demonstrated lasting and convincing protective effects through manipulation of cerebrospinal fluid production, diuresis, blood clot fibrinolysis, or manipulation of fibrosis in the subarachnoid compartment, although there remains some promise in the latter areas. Acetazolamide bolus seems to be useful for predicting shunt response in adults with hydrocephalus. Neuroprotection in the situation of established hydrocephalus has been tested experimentally beginning more recently. Therapies designed to modify blood flow or pulsation, reduce inflammation, reduce oxidative damage, or protect neurons are so far of limited success; more experimental work is needed in these areas. As has been recommended for preclinical studies in stroke and brain trauma, stringent conditions should be met for preclinical studies in hydrocephalus.

Signal Increase on Unenhanced T1-Weighted Images in the Rat Brain After Repeated, Extended Doses of Gadolinium-Based Contrast Agents: Comparison of Linear and Macrocyclic Agents

OBJECTIVES

In this prospective preclinical study, we evaluated T1-weighted signal intensity in the deep cerebellar nuclei (CN) and globus pallidus (GP) up to 24 days after repeated administration of linear and macrocyclic gadolinium-based contrast agents (GBCAs) using homologous imaging and evaluation methods as in the recently published retrospective clinical studies. In a second part of the study, cerebrospinal fluid (CSF) spaces were evaluated for contrast enhancement by fluid-attenuated magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Sixty adult male Wistar-Han rats were randomly divided into a control and 5 GBCA groups (n = 10 per group). The administered GBCAs were gadodiamide, gadopentetate dimeglumine, and gadobenate dimeglumine (linear GBCAs) as well as gadobutrol and gadoterate meglumine (macrocyclic GBCAs) and saline (control). Over a period of 2 weeks, the animals received 10 intravenous injections at a dose of 2.5 mmol Gd/kg body weight, each on 5 consecutive days per week. Before GBCA administration, as well as 3 and 24 days after the last injection, a whole-brain MRI was performed using a standard T1-weighted 3-dimensional turbo spin echo sequence on a clinical 1.5 T scanner. The ratios of signal intensities in deep CN to pons (CN/Po) and GP to thalamus (GP/Th) were determined. For the evaluation of the CSF spaces, 18 additional rats were randomly divided into 6 groups (n = 3 per group) that received the same GBCAs as in the first part of the study. After MR cisternography for anatomical reference, a fluid-attenuated inversion recovery sequence was performed before and 1 minute after intravenous injection of a dose of 1 mmol Gd/kg body weight GBCA or saline.

RESULTS

A significantly increased signal intensity ratio of CN/Po was observed 3 and 24 days after the last injection of gadodiamide and gadobenate dimeglumine. No significant changes were observed between the 2 time points. Gadopentetate dimeglumine injection led to a moderately elevated but statistically not significant CN/Po signal intensity ratio. No increased CN/Po signal intensity ratios were determined in the MRI scans of rats that received macrocyclic GBCAs gadobutrol and gadoterate meglumine or saline. The ratio of signal intensity in GP/Th was not elevated in any group injected with GBCAs or saline. Enhanced signal intensities of CSF spaces were observed in the postcontrast fluid-attenuated inversion recovery images of all animals receiving GBCAs but not for saline.

CONCLUSIONS

In this animal study in rats, increased signal intensity in the CN was found up to 24 days after multiple, extended doses of linear GBCAs. However, in contrast to clinical reports, the signal enhancement in the GP was not reproduced, demonstrating the limitations of this animal experiment. The elevated signal intensities remained persistent over the entire observation period. In contrast, no changes of signal intensities in either the CN or the GP were observed for macrocyclic GBCAs. However, all GBCAs investigated were able to pass the blood-CSF barrier in rats to a certain, not yet quantified extent.