Brain Interstitial Fluid Research Articles

Minimally Invasive Microelectrode Biosensors Based on Platinized Carbon Fibers for in Vivo Brain Monitoring.

The ability to monitor the chemical composition of brain interstitial fluid remains an important challenge in the field of bioanalytical chemistry. In particular, microelectrode biosensors are a promising resource for the detection of neurochemicals in interstitial fluid in both animals and humans. These biosensors can provide second-by-second temporal resolution and enzymatic recognition of virtually any redox or nonredox molecule. However, despite miniaturization of these sensors to 50–250 μm in diameter to avoid vascular and cellular injury, inflammation and foreign-body reactions still occur following their implantation. Here, we fabricated microelectrodes with platinized carbon fibers to create biosensors that have an external diameter that is less than 15 μm. Platinization was achieved with physical vapor deposition, and increased sensitivity to hydrogen peroxide and improved enzymatic detection were observed for these carbon fiber microelectrodes. When these devices were implanted in the brains of rats, no injuries to the parenchyma or brain blood vessels were detected. In addition, these microelectrodes provided different estimates of basal glucose, lactate, and oxygen concentrations compared to conventional biosensors. Induction of spreading depolarization in the cerebral cortex further demonstrated the greater sensitivity of our microelectrodes to dynamic neurochemical changes. Thus, these minimally invasive devices represent a major advance in our ability to analyze brain interstitial fluid.

In Vivo Quantitative Understanding of PEGylated Liposome's Influence on Brain Delivery of Diphenhydramine.

Despite the promising features of liposomes as brain drug delivery vehicles, it remains uncertain how they influence the brain uptake in vivo. In order to gain a better fundamental understanding of the interaction between liposomes and the blood-brain barrier (BBB), it is indispensable to test if liposomes affect drugs with different BBB transport properties (active influx or efflux) differently. The aim of this study was to quantitatively evaluate how PEGylated (PEG) liposomes influence brain delivery of diphenhydramine (DPH), a drug with active influx at the BBB, in rats. The brain uptake of DPH after 30 min intravenous infusion of free DPH, PEG liposomal DPH, or free DPH + empty PEG liposomes was compared by determining the unbound DPH concentrations in brain interstitial fluid and plasma with microdialysis. Regular blood samples were taken to measure total DPH concentrations in plasma. Free DPH was actively taken up into the brain time-dependently, with higher uptake at early time points followed by an unbound brain-to-plasma exposure ratio ( Kp,uu) of 3.0. The encapsulation in PEG liposomes significantly decreased brain uptake of DPH, with a reduction of Kp,uu to 1.5 ( p < 0.05). When empty PEG liposomes were coadministered with free drug, DPH brain uptake had a tendency to decrease ( Kp,uu 2.3), and DPH was found to bind to the liposomes. This study showed that PEG liposomes decreased the brain delivery of DPH in a complex manner, contributing to the understanding of the intricate interactions between drug, liposomes, and the BBB.

Rapid lymphatic efflux limits cerebrospinal fluid flow to the brain

The relationships between cerebrospinal fluid (CSF) and brain interstitial fluid are still being elucidated. It has been proposed that CSF within the subarachnoid space will enter paravascular spaces along arteries to flush through the parenchyma of the brain. However, CSF also directly exits the subarachnoid space through the cribriform plate and other perineural routes to reach the lymphatic system. In this study, we aimed to elucidate the functional relationship between CSF efflux through lymphatics and the potential influx into the brain by assessment of the distribution of CSF-infused tracers in awake and anesthetized mice. Using near-infrared fluorescence imaging, we showed that tracers quickly exited the subarachnoid space by transport through the lymphatic system to the systemic circulation in awake mice, significantly limiting their spread to the paravascular spaces of the brain. Magnetic resonance imaging and fluorescence microscopy through the skull under anesthetized conditions indicated that tracers remained confined to paravascular spaces on the surface of the brain. Immediately after death, a substantial influx of tracers occurred along paravascular spaces extending into the brain parenchyma. We conclude that under normal conditions a rapid CSF turnover through lymphatics precludes significant bulk flow into the brain.

In Vivo Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes.

In vivo microdialysis is a powerful technique to collect ISF from awake, freely-behaving animals based on a dialysis principle. While microdialysis is an established method that measures relatively small molecules including amino acids or neurotransmitters, it has been recently used to also assess dynamics of larger molecules in ISF using probes with high molecular weight cut off membranes. Upon using such probes, microdialysis has to be run in a push-pull mode to avoid pressure accumulated inside of the probes. This article provides step-by-step protocols including stereotaxic surgery and how to set up microdialysis lines to collect proteins from ISF. During microdialysis, drugs can be administered either systemically or by direct infusion into ISF. Reverse microdialysis is a technique to directly infuse compounds into ISF. Inclusion of drugs in the microdialysis perfusion buffer allows them to diffuse into ISF through the probes while simultaneously collecting ISF. By measuring tau protein as an example, the author shows how its levels are altered upon stimulating neuronal activity by reverse microdialysis of picrotoxin. Advantages and limitations of microdialysis are described along with the extended application by combining other in vivo methods.

&lt;em&gt;In Vivo&lt;/em&gt; Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

&lt;em&gt;In Vivo&lt;/em&gt; Microdialysis Method to Collect Large Extracellular Proteins from Brain Interstitial Fluid with High-molecular Weight Cut-off Probes

Comparison of cerebral Open Flow Microperfusion and Microdialysis when sampling small lipophilic and small hydrophilic substances

BackgroundAssessment of drug concentration in the brain interstitial fluid (ISF) is crucial for development of brain active drugs, which are mainly small, lipophilic substances able to cross the blood-brain barrier (BBB). We aimed to compare the applicability of cerebral Open Flow Microperfusion (cOFM) and Microdialysis (MD) to sample the lipophilic substance amitriptyline (AMI), its metabolites Hydroxyamitriptyline (HYA), Nortriptyline (NOR), Amitriptyline-N-Oxide (ANO), deuterated water (D2O) and the hydrophilic substance sodium fluorescein (Naf) in brain ISF. New methodcOFM has been refined to yield increased spatial resolution and performance. Comparison of cOFM and MD and resultsPerformance of cOFM and MD was assessed by in vivo AUC ratios of probe samples (AUCCOFM/AUCMD) and the in vivo relative recovery of D2O (RRvv,D2O). Adsorption of AMI and Naf to MD and cOFM was assessed by the in vitro relative recovery (RRvt) prior to the in vivo experiments. The in vivo AUC ratio of AMI and RRvv,D2O was about two times higher for cOFM than for MD (AUCOFM/AUCMD = 2.0, RRvv,D2O(cOFM)/RRvv,D2O(MD) = 2.1). cOFM detected all investigated AMI metabolites except NOR. MD did not detect HYA, NOR, ANO and Naf. In vitro adsorption of AMI and Naf to the MD membrane was strong (RRvt,AMI = 4.4%, RRvt,Naf = 1.5%) but unspecific adsorption to cOFM was negligibly small (RRvt,AMI = 98% and RRvt,Naf = 98%). ConclusionscOFM showed better performance when sampling AMI and its metabolites, Naf and D2O, and had an about two times higher RRvv,D2O than MD. MD did not detect HYA, NOR, ANO and Naf, most likely due to membrane adsorption.

Physiology and molecular biology of barrier mechanisms in the fetal and neonatal brain.

Properties of the local internal environment of the adult brain are tightly controlled providing a stable milieu essential for its normal function. The mechanisms involved in this complex control are structural, molecular and physiological (influx and efflux transporters) frequently referred to as the ‘blood–brain barrier’. These mechanisms include regulation of ion levels in brain interstitial fluid essential for normal neuronal function, supply of nutrients, removal of metabolic products, and prevention of entry or elimination of toxic agents. A key feature is cerebrospinal fluid secretion and turnover. This is much less during development, allowing greater accumulation of permeating molecules. The overall effect of these mechanisms is to tightly control the exchange of molecules into and out of the brain. This review presents experimental evidence currently available on the status of these mechanisms in developing brain. It has been frequently stated for over nearly a century that the blood–brain barrier is not present or at least is functionally deficient in the embryo, fetus and newborn. We suggest the alternative hypothesis that the barrier mechanisms in developing brain are likely to be appropriately matched to each stage of its development. The contributions of different barrier mechanisms, such as changes in constituents of cerebrospinal fluid in relation to specific features of brain development, for example neurogenesis, are only beginning to be studied. The evidence on this previously neglected aspect of brain barrier function is outlined. We also suggest future directions this field could follow with special emphasis on potential applications in a clinical setting.

TRANSLATIONAL QUANTITATIVE SYSTEMS PHARMACOLOGY MODEL OF TAUOPATHIES

Quantitative systems pharmacology modelling can be valuable tool for understanding such a multifaceted process as tau protein accumulation. For prediction of the results of tau targeted therapy we propose a mechanistic model describing such tauopathies as Alzheimer's disease (AD), and frontotemporal degeneration (FTD) in human and tau accumulation in preclinical tauopathy model, mice carrying P301S(L) tau mutation. The model describes tau production, tau-microtubules interaction, tau modification, aggregation and propagation through different brain compartments. Tau oligomers serve as the key intermediates for fibril growth and as mediators of tau pathology connectivity-driven propagation mediators from entorhinal cortex through limbic system to neocortex. The driver of londitudinal disease progression in AD model is the decrease of autophagic degradation of tau fibrils. For FTD case we use assumption about tau mutation influence on polymerization and microtubule binding confirmed by in vitro data. The human model versions were calibrated across published biochemical data for soluble, insoluble tau, CSF tau and PET (18F-AV-1451 SUVR) data. The mouse model was calibrated across biochemical data for soluble (RAB, RIPA soluble fractions), insoluble tau (FA soluble fraction) in several brain structures, interstitial fluid and CSF of mouse. Model satisfactorily describes consecutive appearance of insoluble tau in different regions corresponding to Braak stages of AD. FTD data verification revealed that tau propagation parameters differ from AD situation. Mouse model version satisfactorily describes reduction of soluble tau in brain and accumulation of insoluble tau in the mouse P301S(L). Tau pathology propagation and gradual appearance of polymerized tau starting from entorhinal cortex through the limbic system to neocortex is also predicted correctly and follows the experimentally observed trend. Data on immunotherapy by antibodies HJ8.5 in mouse are described satisfactorily only if significant (10 times) increase of insoluble tau degradation is assumed, while blocking tau propagation only does not allow for describing the mouse data. Analogous degradation activation in humans, would lead to complete disappearance of tau in AD, but cause moderate effect in FTD according to the model. The proposed QSP model could be considered as platform for investigation of therapeutic impact on tau pathology and translational analysis.

Sleep Disorders Associated With Alzheimer's Disease: A Perspective.

Sleep disturbances, as well as sleep-wake rhythm disturbances, are typical symptoms of Alzheimer's disease (AD) that may precede the other clinical signs of this neurodegenerative disease. Here, we describe clinical features of sleep disorders in AD and the relation between sleep disorders and both cognitive impairment and poor prognosis of the disease. There are difficulties of the diagnosis of sleep disorders based on sleep questionnaires, polysomnography or actigraphy in the AD patients. Typical disturbances of the neurophysiological sleep architecture in the course of the AD include deep sleep and paradoxical sleep deprivation. Among sleep disorders occurring in patients with AD, the most frequent disorders are sleep breathing disorders and restless legs syndrome. Sleep disorders may influence circadian fluctuations of the concentrations of amyloid-β in the interstitial brain fluid and in the cerebrovascular fluid related to the glymphatic brain system and production of the amyloid-β. There is accumulating evidence suggesting that disordered sleep contributes to cognitive decline and the development of AD pathology. In this mini-review, we highlight and discuss the association between sleep disorders and AD.

Insulin transport into the brain.

While there is a growing consensus that insulin has diverse and important regulatory actions on the brain, seemingly important aspects of brain insulin physiology are poorly understood. Examples include: what is the insulin concentration within brain interstitial fluid under normal physiologic conditions; whether insulin is made in the brain and acts locally; does insulin from the circulation cross the blood-brain barrier or the blood-CSF barrier in a fashion that facilitates its signaling in brain; is insulin degraded within the brain; do privileged areas with a "leaky" blood-brain barrier serve as signaling nodes for transmitting peripheral insulin signaling; does insulin action in the brain include regulation of amyloid peptides; whether insulin resistance is a cause or consequence of processes involved in cognitive decline. Heretofore, nearly all of the studies examining brain insulin physiology have employed techniques and methodologies that do not appreciate the complex fluid compartmentation and flow throughout the brain. This review attempts to provide a status report on historical and recent work that begins to address some of these issues. It is undertaken in an effort to suggest a framework for studies going forward. Such studies are inevitably influenced by recent physiologic and genetic studies of insulin accessing and acting in brain, discoveries relating to brain fluid dynamics and the interplay of cerebrospinal fluid, brain interstitial fluid, and brain lymphatics, and advances in clinical neuroimaging that underscore the dynamic role of neurovascular coupling.

Use of Subcutaneous and Intraperitoneal Administration Methods to Facilitate Cassette Dosing in Microdialysis Studies in Rats.

Microdialysis is a powerful technique allowing for real-time measurement of unbound drug concentrations in brain interstitial fluid in conscious animals. Use of microdialysis in drug discovery is limited by high resource requirement and low throughput, but this may be improved by cassette dosing. Administering multiple compounds intravenously of diverse physiochemical properties, it is often very challenging and time consuming to identify a vehicle that can dissolve all of the compounds. To overcome this limitation, the present study explores the possibility of administering a cassette dose of nine diverse compounds (carbamazepine, citalopram, desmethylclozapine, diphenhydramine, gabapentin, metoclopramide, naltrexone, quinidine, and risperidone) in suspension, rather than in solution, by intraperitoneal and subcutaneous routes, and determining if this is a viable option for assessing blood-brain barrier penetration in microdialysis studies. Repeated hourly subcutaneous dosing during the 6-hour microdialysis study allowed for the best attainment of distributional equilibrium between brain and plasma, resulting in less than a 2-fold difference in the unbound brain to unbound plasma concentration ratio for the cassette dosing method versus discrete dosing. Both subcutaneous and intraperitoneal repeated dosing can provide a more practical substitute for intravenous dosing in determining brain penetration of a cassette of diverse compounds in brain microdialysis studies. The results from the present study demonstrate that dosing compounds in suspension represents a practical approach to eliminating the technical challenge and labor-intensive step of preparation of solutions of a mixture of compounds and will enable the use of the cassette brain microdialysis method in a central nervous system drug discovery setting.

Microelectrode Biosensors for in vivo Analysis of Brain Interstitial Fluid

AbstractChemical analyses of brain interstitial fluid can reveal important information about local brain metabolism and neurochemistry, and can enhance our understanding of how neuronal networks respond to physiological or pathological stimuli. Among brain monitoring methods currently available, microelectrode biosensors provide real‐time analyses with high temporal resolution and minimal perturbation to living tissue by using oxidase enzymes for biological recognition. Two types of microelectrodes are used: cylindrically shaped wire electrodes provide the smallest implantable devices to date, and microfabricated multi‐electrode needles can monitor several molecules simultaneously. They have already contributed significantly to our understanding of brain energy metabolism with glucose and lactate detection, and to neurotransmitter systems with glutamate, D‐serine, acetylcholine, and purine detection. They have the potential to undergo further technological developments in future studies.

The insulin receptor is expressed and functional in cultured blood-brain barrier endothelial cells but does not mediate insulin entry from blood to brain.

Insulin and its receptor are known to be present and functional in the brain. Insulin cerebrospinal fluid concentrations have been shown to correlate with plasma levels of insulin in a nonlinear fashion, indicative of a saturable transport pathway from the blood to the brain interstitial fluid. The aim of the present study was to investigate whether insulin was transported across brain endothelial cells in vitro via an insulin receptor-dependent pathway. The study showed that the insulin receptor was expressed at both the mRNA and protein levels in bovine brain endothelial cells. Luminally applied radiolabeled insulin showed insulin receptor-mediated binding to the endothelial cells. This caused a dose-dependent increase in Akt-phosphorylation, which was inhibited by coapplication of an insulin receptor inhibitor, s961, demonstrating activation of insulin receptor signaling pathways. Transport of insulin across the blood-brain barrier in vitro was low and comparable to that of a similarly sized paracellular marker. Furthermore, insulin transport was not inhibited by coapplication of an excess of unlabeled insulin or an insulin receptor inhibitor. The insulin transport and uptake studies were repeated in mouse brain endothelial cells demonstrating similar results. Although it cannot be ruled out that culture-induced changes in the cell model could have impaired a potential insulin transport mechanism, these in vitro data indicate that peripheral insulin must reach the brain parenchyma through alternative pathways rather than crossing the blood-brain barrier via receptor mediated transcytosis.

Serum calcium levels and neuropsychological performance in depression and matched healthy controls: Reversal of correlation a marker of the aging cognitive clock?

BackgroundMajor depressive disorder (MDD) is associated with cognitive impairment, that might be related to disturbed calcium homeostasis. Calcium-related processes have also been implicated in age related cognitive decline. Since serum calcium and brain interstitial fluids maintain long-term equilibrium under normal physiological states, serum calcium levels could affect neuronal and hence cognitive function. High serum calcium has been associated with cognitive decline in geriatric populations, whereas evidence for MDD and healthy populations is less consistent. MethodsDifferences in neuropsychological (NPS) performance and their relationship with serum calcium (total, ionized, total to ionized ratio) in (partially) remitted MDD patients (n = 59) and healthy controls (HC) (n = 59) individually matched for age, gender and education (age-range 19–60 years) were examined. Modulation of study parameters and their interaction by the factor age was investigated, with subgroups young and old divided at median = 37 years. Participants provided blood samples and completed an extensive NPS test battery. ResultsMDD showed significantly poorer NPS performance compared to HC. Serum calcium associated positively with NPS performance in HC and negatively in MDD for entire age-range samples. While younger MDD and HC showed positive NPS-calcium correlations, older MDD and HC exhibited negative NPS-calcium correlations (‘correlation reversal'). Age had a significant effect on cognition and ionized calcium and interacted with illness-status, with an exaggerated influence on cognition in MDD compared to HC. ConclusionsThe results place calcium ‘correlation reversal’ to early middle-age time window, which may be accelerated for MDD and highlight the central role of calcium pathways in normal and pathological cognitive aging.

Functional Polarity of Microvascular Brain Endothelial Cells Supported by Neurovascular Unit Computational Model of Large Neutral Amino Acid Homeostasis.

The homeostatic regulation of large neutral amino acid (LNAA) concentration in the brain interstitial fluid (ISF) is essential for proper brain function. LNAA passage into the brain is primarily mediated by the complex and dynamic interactions between various solute carrier (SLC) transporters expressed in the neurovascular unit (NVU), among which SLC7A5/LAT1 is considered to be the major contributor in microvascular brain endothelial cells (MBEC). The LAT1-mediated trans-endothelial transport of LNAAs, however, could not be characterized precisely by available in vitro and in vivo standard methods so far. To circumvent these limitations, we have incorporated published in vivo data of rat brain into a robust computational model of NVU-LNAA homeostasis, allowing us to evaluate hypotheses concerning LAT1-mediated trans-endothelial transport of LNAAs across the blood brain barrier (BBB). We show that accounting for functional polarity of MBECs with either asymmetric LAT1 distribution between membranes and/or intrinsic LAT1 asymmetry with low intraendothelial binding affinity is required to reproduce the experimentally measured brain ISF response to intraperitoneal (IP) L-tyrosine and L-phenylalanine injection. On the basis of these findings, we have also investigated the effect of IP administrated L-tyrosine and L-phenylalanine on the dynamics of LNAAs in MBECs, astrocytes and neurons. Finally, the computational model was shown to explain the trans-stimulation of LNAA uptake across the BBB observed upon ISF perfusion with a competitive LAT1 inhibitor.

Clinical Pharmacokinetics and Pharmacodynamics of Drugs in the Central Nervous System.

Despite contributing significantly to the burden of global disease, the translation of new treatment strategies for diseases of the central nervous system (CNS) from animals to humans remains challenging, with a high attrition rate in the development of CNS drugs. The failure of clinical trials for CNS therapies can be partially explained by factors related to pharmacokinetics/pharmacodynamics (PK/PD), such as lack of efficacy or improper selection of the initial dosage. A focused assessment is needed for CNS-acting drugs in first-in-human studies to identify the differences in PK/PD from animal models, as well as to choose the appropriate dose. In this review, we summarize the available literature from human studies on the PK and PD in brain tissue, cerebrospinal fluid, and interstitial fluid for drugs used in the treatment of psychosis, Alzheimer's disease and neuro-HIV, and address critical questions in the field. We also explore newer methods to characterize PK/PD relationships that may lead to more efficient dose selection in CNS drug development.

Assembly of Taurine Transporter (Slc6a6) with Na+-H+ Exchanger Regulatory Factor 1 (Slc9a3r1) Improves GABA Transport Activity by Increasing the Maximum Transport Velocity.

Regulating γ-aminobutyric acid (GABA) uptake transport on the plasma membranes is required for its efficient clearance from the brain interstitial fluid. The purpose of this study was to clarify the assembly of taurine transporter (TauT/Slc6a6) and PSD-95/Disc-large/Zo-1 (PDZ) domain of Na+-H+ exchanger regulatory factor 1 (NHERF1) as a regulatory mechanism of TauT-mediated GABA transport activity. In vitro glutathione S-transferase (GST)-pull down assay and immunoblotting with anti-NHERF1 antibody revealed that NHERF1 protein was present in rat brain lysates as the binding protein of the GST-fusion TauT C-terminal protein with the PDZ-binding ETMM motif but not its corresponding deletion mutant lacking the motif. [3H]GABA uptake by TauT-NHERF1-coexpressing oocytes and TauT-singly expressing oocytes exhibited saturable kinetics with Michaelis-Menten constant values of 0.835±0.288 and 0.982±0.569 mM and a maximal transport velocity of 206±37 and 283±28 pmol/(h·oocyte), respectively. These results suggest that the assembly of TauT PDZ-binding motif and NHERF1 increases the maximal transport velocity of GABA rather than changes the affinity.

The Effect of Aquaporin-4 Knockout on Interstitial Fluid Flow and the Structure of the Extracellular Space in the Deep Brain.

It has been reported that aquaporin-4 (AQP4) deficiency impairs transportation between the cerebrospinal fluid and interstitial fluid (ISF) as well as the clearance of interstitial solutes in the superficial brain. However, the effect of AQP4 on ISF flow in the deep brain remains unclear. This study compared the brain ISF flow in the caudate nucleus and thalamus of normal rats (NO) and AQP4 knockout rats (KO) using tracer-based magnetic resonance imaging. The rate of brain ISF flow slowed to different degrees in the two regions of KO rats’ brains. Compared with NO rats, the half-life of ISF in the thalamus of KO rats was significantly prolonged, with a corresponding decrease in the clearance coefficient. The tortuosity of the brain extracellular space (ECS) was unchanged in the thalamus of KO rats. In the caudate nucleus of KO rats, the volume fraction of the ECS and the diffusion coefficient were increased, with significantly decreased tortuosity; no significant changes in brain ISF flow were demonstrated. Combined with a change in the expression of glial fibrillary acidic protein and AQP4 in two brain regions, we found that the effect of AQP4 knockout on ISF flow and ECS structure in these two regions differed. This difference may be related to the distribution of astrocytes and the extent of AQP4 decline. This study provides evidence for the involvement of AQP4 in ISF transportation in the deep brain and provides a basis for the establishment of a pharmacokinetic model of the brain’s interstitial pathway.

Metabolic mechanisms of development and compensation of osmotic stress in the brain

Extracellular fluid of the brain, consisting of cerebrospinal fluid and interstitial fluid, is normally isotonic to blood plasma. Problems arise with a rapid change in osmolality of circulating blood or interstitial brain fluid. The permeability of the blood-brain barrier is lower than in the peripheral capillaries, but this permeability is still several times greater than the passive permeability for electrolytes or glucose. Because of this difference, it is believed that the brain is like an osmometer: it swells with reduced plasma osmolality and contracts (dehydrated) when the plasma becomes hypertonic. Osmotic stress has a direct effect on the functioning of the brain and triggers physiological compensatory mechanisms, in the absence of which due to the intensity or duration of stress, irreversible serious complications may develop. Knowledge and understanding of these processes are the basis for preventing their development and treatment.

Understanding the functions and relationships of the glymphatic system and meningeal lymphatics.

Recent discoveries of the glymphatic system and of meningeal lymphatic vessels have generated a lot of excitement, along with some degree of skepticism. Here, we summarize the state of the field and point out the gaps of knowledge that should be filled through further research. We discuss the glymphatic system as a system that allows CNS perfusion by the cerebrospinal fluid (CSF) and interstitial fluid (ISF). We also describe the recently characterized meningeal lymphatic vessels and their role in drainage of the brain ISF, CSF, CNS-derived molecules, and immune cells from the CNS and meninges to the peripheral (CNS-draining) lymph nodes. We speculate on the relationship between the two systems and their malfunction that may underlie some neurological diseases. Although much remains to be investigated, these new discoveries have changed our understanding of mechanisms underlying CNS immune privilege and CNS drainage. Future studies should explore the communications between the glymphatic system and meningeal lymphatics in CNS disorders and develop new therapeutic modalities targeting these systems.