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

Assessing neonatal brain glymphatic system development using diffusion tensor imaging along the perivascular space and choroid plexus volume

PURPOSE

Neonatal brain development constitutes a critical period of structural and functional maturation underpinning sensory, motor, and cognitive capacities. The glymphatic system-a cerebral waste clearance network-remains poorly understood in neonates. We investigated non-invasive magnetic resonance imaging (MRI) biomarkers of glymphatic system and their developmental correlates in neonates.

METHODS

In 117 neonates undergoing high-resolution T1-weighted and diffusion MRI, we quantified two glymphatic metrics: (1) diffusion tensor imaging along the perivascular space (DTI-ALPS) index, reflecting perivascular fluid dynamics; (2) choroid plexus (CP) volume, a cerebrospinal fluid (CSF) production marker. Associations with postmenstrual age (PMA) at MRI scan, gestational age (GA), birth weight (BW), and sex were analyzed using covariate-adjusted models.

RESULTS

Preterm neonates displayed significantly reduced DTI-ALPS indices versus term neonates (total index: 1.01 vs. 1.05, P = 0.002), with reductions persisting after adjustment (P < 0.05). CP volumes showed right-dominant pre-adjustment differences (preterm: 0.33 vs. term: 0.39, P = 0.039) that attenuated post-adjustment (P = 0.348). DTI-ALPS indices demonstrated transient correlations with PMA/GA/BW in unadjusted analyses (P < 0.05), whereas CP volumes maintained robust PMA associations post-adjustment in all neonates (P = 0.037) and term subgroup (P = 0.013). No significant effects of sex on both metrics were observed.

CONCLUSION

Our findings reveal prematurity-associated delays in glymphatic maturation, rather than biological sex. The persistent PMA-CP volume relationship suggests developmental regulation of CSF production, while attenuated DTI-ALPS correlations highlight covariate-mediated effects. These glymphatic metrics show potential for monitoring neurodevelopmental trajectories, though longitudinal validation is required to establish their clinical utility in neonatal care.

CLINICAL TRIAL NUMBER

Not applicable.

Age-Related Differences in the Choroid Plexus Structural Integrity Are Associated with Changes in Cognition

The choroid plexus (CP) plays a critical role in maintaining central nervous system (CNS) homeostasis, producing cerebrospinal fluid, and regulating the entry of specific substances into the CNS from blood. CP dysfunction has been implicated in various neurological and psychiatric disorders, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. This study investigates the relationship between CP structural integrity and cognitive decline in normative aging, using structural and advanced magnetic resonance imaging techniques, including CP volume, diffusion tensor imaging indices (mean diffusivity, MD, and fractional anisotropy, FA) and relaxometry metrics (longitudinal, T1, and transverse, T2, relaxation times). Our results show that diminished CP microstructural integrity, as reflected by higher T1, T2, and MD values, or lower FA values, is associated with lower cognitive performance in processing speed and fluency. Notably, CP microstructural measures demonstrated greater sensitivity to cognitive decline than macrostructural measures, i.e. CP volume. Longitudinal analysis revealed that individuals with reduced CP structural integrity exhibit steeper cognitive decline over time. Furthermore, structural equation modeling revealed that a latent variable representing CP integrity predicts faster overall cognitive decline, with an effect size comparable to that of age. These findings highlight the importance of CP integrity in maintaining cognitive health and suggest that a holistic approach to assessing CP integrity could serve as a sensitive biomarker for early detection of cognitive decline. Further research is needed to elucidate the mechanisms underlying the relationship between CP structural integrity and cognitive decline and to explore the potential therapeutic implications of targeting CP function to prevent or treat age-related cognitive deficits.

Role of non-human primate models in accelerating research and developing countermeasures against Zika virus infection

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Choroid plexus cysts on 7T MRI: Relationship to aging and neurodegenerative diseases

INTRODUCTION

The choroid plexus (CP) may play a crucial role in brain degeneration. We aim to assess whether CP cysts (CPCs), defined using ultra-high field magnetic resonance imaging (MRI), relate to aging and neurodegeneration.

METHODS

We used multi-sequence 7T MRI to observe CPCs, characterizing their presence and characteristics in healthy younger controls, healthy older controls (OCs), patients with Alzheimer's disease (AD), patients with Parkinson's disease (PD), and patients with uremic encephalopathy. CP volume (CPV) and CPC characteristics were compared across groups, and associations between CPV and CPC features were analyzed across all subjects.

RESULTS

The AD group showed a significantly higher presence and number of CPCs compared to other groups and also had a significantly larger CPV than healthy OCs. The number and size of CPCs were associated with CPV.

DISCUSSION

7T MRI offers a distinct advantage in observing CPCs, and the high prevalence of CPCs in patients with AD warrants further investigation.

HIGHLIGHTS

7T MRI enables visualization of the fine structures of the choroid plexus. Patients with Alzheimer's disease (AD) exhibit a higher number of choroid plexus cysts (CPCs) compared to healthy older adults and other patient groups. CPCs may serve as an auxiliary marker for AD.

Abnormal choroid plexus, hippocampus, and lateral ventricles volumes as markers of treatment-resistant major depressive disorder

AIM

One-third of patients with major depressive disorder (MDD) do not achieve full remission and have high relapse rates even after treatment, leading to increased medical costs and reduced quality of life and health status. The possible specificity of treatment-resistant depression (TRD) neurobiology is still under investigation, with risk factors such as higher inflammatory markers being identified. Given recent findings on the role of choroid plexus (ChP) in neuroinflammation and hippocampus in treatment response, the aim of the present study was to evaluate inflammatory- and trophic-related differences in these regions along with ventricular volumes among patients with treatment-sensitive depression (TSD), TRD, and healthy controls (HCs).

METHODS

ChP, hippocampal, and ventricular volumes were assessed in 197 patients with MDD and 58 age- and sex-matched HCs. Volumes were estimated using FreeSurfer 7.2. Treatment resistance status was defined as failure to respond to at least two separate antidepressant treatments. Region of interest volumes were then compared among groups.

RESULTS

We found higher ChP volumes in patients with TRD compared with patients with TSD and HCs. Our results also showed lower hippocampal volumes and higher lateral ventricular volumes in TRD compared with both patients without TRD and HCs.

CONCLUSIONS

These findings corroborate the link between TRD and neuroinflammation, as ChP volume could be considered a putative marker of central immune activity. The lack of significant differences in all of the region of interest volumes between patients with TSD and HCs may highlight the specificity of these features to TRD, possibly providing new insights into the specific neurobiological underpinnings of this condition.

Choroid Plexus Volume in Rural Chinese Older Adults: Distribution and Association With Cardiovascular Risk Factors and Cerebral Small Vessel Disease

BACKGROUND

The choroid plexus (CP) is involved in neurodegenerative diseases. However, the association of CP with cardiovascular risk factors and cerebral small vessel disease in older adults remains unclear.

METHODS AND RESULTS

This population-based study included 1263 participants (60 years and older) from the MIND-China (Multimodal Interventions to Delay Dementia and Disability in Rural China) substudy (2018-2020), of which 111 individuals completed diffusion tensor imaging examination. CP volume was automatically segmented. White matter hyperintensities (WMHs), enlarged perivascular spaces (EPVS), cerebral microbleeds, and lacunes were assessed following the Standards for Reporting Vascular Changes on Neuroimaging 1. Peak width of skeletonized mean diffusivity and free water were derived from diffusion tensor imaging images. We used linear regression models to evaluate the association between CP volume and cardiovascular risk factors, WMH volumes, and diffusion tensor imaging metrics, and logistic regression models to examine the association between CP volume and EPVS, cerebral microbleeds, and lacunes. The CP volume increased with age (P<0.001). Men (β coefficient=0.47 [95% CI, 0.29-0.64]) and participants with diabetes (β coefficient=0.16 [95% CI, 0.01-0.31]) had larger CP volumes than women and individuals without diabetes, respectively (P<0.05). Greater CP volume was significantly associated with larger total and periventricular WMH volumes and moderate to severe EPVS in basal ganglia (P<0.05) but not with deep WMHs, EPVS in centrum semiovale, lacunes, or cerebral microbleeds. In the diffusion tensor imaging subsample, enlarged CP was significantly associated with higher peak width of skeletonized mean diffusivity and free water of periventricular and deep white matter (P<0.05).

CONCLUSIONS

An enlarged CP is associated with larger global and periventricular WMH volume and higher likelihoods of EPVS in basal ganglia and impaired white matter integrity, suggesting that an enlarged CP may represent a precursor of cerebral small vessel disease.

Enhancing spatial memory and pattern separation: Long-term effects of stimulant treatment in individuals with ADHD

This study explores the under-researched domain of long-term stimulant treatment in children and adolescents diagnosed with attention deficit hyperactivity disorder (ADHD). The necessity for extended treatment duration, often accompanied by safety concerns and side effects leading to treatment discontinuation, underscores the significance of this investigation. Concurrently, comparative studies have revealed adverse impacts on vulnerable regions within the hippocampal formation, accompanied by behavioral perturbations. We employed computerized tests and virtual reality to assess spatial memory, pattern separation, and object recognition memory in a cohort of children diagnosed with ADHD receiving stimulant treatment. We compared their performance to a group of neurotypical peers. Our findings indicate that the ADHD group exhibited a lower performance in spatial memory, pattern separation, and object recognition memory than ND group. Intriguingly, a positive relationship emerged between the duration of stimulant treatment and performance in these variables. Notably, this improvement was not immediate to MPH treatment but becomes significant after 24 months of treatment. In contrast to previous comparative investigations, our study did not reveal a detrimental impact on spatial navigation, object recognition memory, or pattern separation, despite the known interplay of these cognitive processes with the hippocampal formation. These results shed new light on the nuanced effects of stimulant treatment in ADHD, underscoring the need for a more comprehensive understanding of long-term treatment outcomes.

Brain development and bioenergetic changes

Bioenergetics describe the biochemical processes responsible for energy supply in organisms. When these changes become dysregulated in brain development, multiple neurodevelopmental diseases can occur, implicating bioenergetics as key regulators of neural development. Historically, the discovery of disease processes affecting individual stages of brain development has revealed critical roles that bioenergetics play in generating the nervous system. Bioenergetic-dependent neurodevelopmental disorders include neural tube closure defects, microcephaly, intellectual disability, autism spectrum disorders, epilepsy, mTORopathies, and oncogenic processes. Developmental timing and cell-type specificity of these changes determine the long-term effects of bioenergetic disease mechanisms on brain form and function. Here, we discuss key metabolic regulators of neural progenitor specification, neuronal differentiation (neurogenesis), and gliogenesis. In general, transitions between glycolysis and oxidative phosphorylation are regulated in early brain development and in oncogenesis, and reactive oxygen species (ROS) and mitochondrial maturity play key roles later in differentiation. We also discuss how bioenergetics interface with the developmental regulation of other key neural elements, including the cerebrospinal fluid brain environment. While questions remain about the interplay between bioenergetics and brain development, this review integrates the current state of known key intersections between these processes in health and disease.

Breaking Barriers: Unveiling Sex-Related Differences in Cerebrospinal Fluid Analysis-A Narrative Review

(1) Background: The recent emphasis on sexual and gender diversity's impact on human health underscores the need for tailored diagnostic and therapeutic approaches in neurology. The aim of this article is to conduct a narrative review of the available scientific literature on sex differences in cerebrospinal fluid analysis. (2) Methods: The literature search encompassed PubMed databases, focusing on cerebrospinal fluid analysis and sex differences, considering parameters like cerebrospinal fluid protein content, cell count, albumin quotient (QAlb) and intrathecal IgG synthesis. (3) Results: Nine articles from the past two decades were identified, revealing limited research in this area. Males consistently exhibited higher cerebrospinal fluid protein content and albumin quotient values across various pathologies and age groups. Consequently, males more frequently manifested blood-cerebrospinal fluid barrier dysfunction than females. No significant sex differences were observed in cerebrospinal fluid leukocyte count or intrathecal IgG synthesis. (4) Conclusions: This review highlights the dearth of research on sex differences in cerebrospinal fluid analysis, despite consistent findings of higher protein content and albumin quotient values in males. Revisiting current diagnostic thresholds based on sex is crucial for accurate prognosis and personalised treatment strategies in neurological disorders. Moving towards sex-specific approaches in clinical practice is imperative for advancing personalised medicine.

The Time Trajectory of Choroid Plexus Enlargement in Multiple Sclerosis

Choroid plexus (CP) can be seen as a watchtower of the central nervous system (CNS) that actively regulates CNS homeostasis. A growing body of literature suggests that CP alterations are involved in the pathogenesis of multiple sclerosis (MS) but the underlying mechanisms remain elusive. CPs are enlarged and inflamed in relapsing-remitting (RRMS) but also in clinically isolated syndrome (CIS) and radiologically isolated syndrome (RIS) stages, far beyond MS diagnosis. Increases in the choroid plexus/total intracranial volume (CP/TIV) ratio have been robustly associated with increased lesion load, higher translocator protein (TSPO) uptake in normal-appearing white matter (NAWM) and thalami, as well as with higher annual relapse rate and disability progression in highly active RRMS individuals, but not in progressive MS. The CP/TIV ratio has only slightly been correlated with magnetic resonance imaging (MRI) findings (cortical or whole brain atrophy) and clinical outcomes (EDSS score) in progressive MS. Therefore, we suggest that plexus volumetric assessments should be mainly applied to the early disease stages of MS, whereas it should be taken into consideration with caution in progressive MS. In this review, we attempt to clarify the pathological significance of the temporal CP volume (CPV) changes in MS and highlight the pitfalls and limitations of CP volumetric analysis.

Transporters, Ion Channels, and Junctional Proteins in Choroid Plexus Epithelial Cells

The choroid plexus (CP) plays significant roles in secreting cerebrospinal fluid (CSF) and forming circadian rhythms. A monolayer of epithelial cells with tight and adherens junctions of CP forms the blood-CSF barrier to control the movement of substances between the blood and ventricles, as microvessels in the stroma of CP have fenestrations in endothelial cells. CP epithelial cells are equipped with several kinds of transporters and ion channels to transport nutrient substances and secrete CSF. In addition, junctional components also contribute to CSF production as well as blood-CSF barrier formation. However, it remains unclear how junctional components as well as transporters and ion channels contribute to the pathogenesis of neurodegenerative disorders. In this manuscript, recent findings regarding the distribution and significance of transporters, ion channels, and junctional proteins in CP epithelial cells are introduced, and how changes in expression of their epithelial proteins contribute to the pathophysiology of brain disorders are reviewed.

Circadian clock in choroid plexus is resistant to immune challenge but dampens in response to chronodisruption

The choroid plexus (ChP) in the brain ventricles has a major influence on brain homeostasis. In this study, we aimed to determine whether the circadian clock located in ChP is affected by chronodisruption caused by misalignment with the external light/dark cycle and/or inflammation. Adult mPer2Luc mice were maintained in the LD12:12 cycle or exposed to one of two models of chronic chronodisruption - constant light for 22-25 weeks (cLL) or 6-hour phase advances of the LD12:12 cycle repeated weekly for 12 weeks (cLD-shifts). Locomotor activity was monitored before the 4th ventricle ChP and suprachiasmatic nuclei (SCN) explants were recorded in real time for PER2-driven population and single-cell bioluminescence rhythms. In addition, plasma immune marker concentrations and gene expression in ChP, prefrontal cortex, hippocampus and cerebellum were analyzed. cLL dampened the SCN clock but did not shorten the inactivity interval (sleep). cLD-shifts had no effect on the SCN clock, but transiently affected sleep duration and fragmentation. Both chronodisruption protocols dampened the ChP clock. Although immune markers were elevated in plasma and hippocampus, levels in ChP were unaffected, and unlike the liver clock, the ChP clock was resistant to lipopolysaccharide treatment. Importantly, both chronodisruption protocols reduced glucocorticoid signaling in ChP. The data demonstrate the high resistance of the ChP clock to inflammation, highlighting its role in protecting the brain from neuroinflammation, and on the other hand its high sensitivity to chronodisruption. Our results provide a novel link between human lifestyle-induced chronodisruption and the impairment of ChP-dependent brain homeostasis.

Iron-Induced Hydrocephalus: the Role of Choroid Plexus Stromal Macrophages

Evidence indicates that erythrocyte-derived iron and inflammation both play a role in intraventricular hemorrhage-induced brain injury including hydrocephalus. Many immune-associated cells, primarily stromal macrophages, reside at the choroid plexus where they are involved in inflammatory responses and antigen presentation. However, whether intraventricular iron impacts those stromal cells is unknown. The aim of this study was to evaluate the relationship between choroid plexus stromal macrophages and iron-induced hydrocephalus in rats and the impact of minocycline and clodronate liposomes on those changes. Aged (18-month-old) and young (3-month-old) male Fischer 344 rats were used to study choroid plexus stromal macrophages. Rats underwent intraventricular iron injection to induce hydrocephalus and treated with either minocycline, a microglia/macrophage inhibitor, or clodronate liposomes, a macrophage depleting agent. Ventricular volume was measured using magnetic resonance imaging, and stromal macrophages were quantified by immunofluorescence staining. We found that stromal macrophages accounted for about 10% of the total choroid plexus cells with more in aged rats. In both aged and young rats, intraventricular iron injection resulted in hydrocephalus and increased stromal macrophage number. Minocycline or clodronate liposomes ameliorated iron-induced hydrocephalus and the increase in stromal macrophages. In conclusion, stromal macrophages account for ~10% of all choroid plexus cells, with more in aged rats. Treatments targeting macrophages (minocycline and clodronate liposomes) are associated with reduced iron-induced hydrocephalus.

Air Pollution-Related Neurotoxicity Across the Life Span

Air pollution is a complex mixture of gases and particulate matter, with adsorbed organic and inorganic contaminants, to which exposure is lifelong. Epidemiological studies increasingly associate air pollution with multiple neurodevelopmental disorders and neurodegenerative diseases, findings supported by experimental animal models. This breadth of neurotoxicity across these central nervous system diseases and disorders likely reflects shared vulnerability of their inflammatory and oxidative stress-based mechanisms and a corresponding ability to produce brain metal dyshomeo-stasis. Future research to define the responsible contaminants of air pollution underlying this neurotoxicity is critical to understanding mechanisms of these diseases and disorders and protecting public health.

Choroid Plexus Aquaporins in CSF Homeostasis and the Glymphatic System: Their Relevance for Alzheimer's Disease

The glymphatic system, a fluid-clearance pathway involved in brain waste clearance, is known to be impaired in neurological disorders, including Alzheimer's disease (AD). For this reason, it is important to understand the specific mechanisms and factors controlling glymphatic function. This pathway enables the flow of cerebrospinal fluid (CSF) into the brain and subsequently the brain interstitium, supported by aquaporins (AQPs). Continuous CSF transport through the brain parenchyma is critical for the effective transport and drainage of waste solutes, such as toxic proteins, through the glymphatic system. However, a balance between CSF production and secretion from the choroid plexus, through AQP regulation, is also needed. Thus, any condition that affects CSF homeostasis will also interfere with effective waste removal through the clearance glymphatic pathway and the subsequent processes of neurodegeneration. In this review, we highlight the role of AQPs in the choroid plexus in the modulation of CSF homeostasis and, consequently, the glymphatic clearance pathway, with a special focus on AD.

In Vitro Models of the Blood–Cerebrospinal Fluid Barrier and Their Applications in the Development and Research of (Neuro)Pharmaceuticals

The pharmaceutical research sector has been facing the challenge of neurotherapeutics development and its inherited high-risk and high-failure-rate nature for decades. This hurdle is partly attributable to the presence of brain barriers, considered both as obstacles and opportunities for the entry of drug substances. The blood–cerebrospinal fluid (CSF) barrier (BCSFB), an under-studied brain barrier site compared to the blood–brain barrier (BBB), can be considered a potential therapeutic target to improve the delivery of CNS therapeutics and provide brain protection measures. Therefore, leveraging robust and authentic in vitro models of the BCSFB can diminish the time and effort spent on unproductive or redundant development activities by a preliminary assessment of the desired physiochemical behavior of an agent toward this barrier. To this end, the current review summarizes the efforts and progresses made to this research area with a notable focus on the attribution of these models and applied techniques to the pharmaceutical sector and the development of neuropharmacological therapeutics and diagnostics. A survey of available in vitro models, with their advantages and limitations and cell lines in hand will be provided, followed by highlighting the potential applications of such models in the (neuro)therapeutics discovery and development pipelines.

Quantifying cerebrospinal fluid dynamics: A review of human neuroimaging contributions to CSF physiology and neurodegenerative disease

Cerebrospinal fluid (CSF), predominantly produced in the ventricles and circulating throughout the brain and spinal cord, is a key protective mechanism of the central nervous system (CNS). Physical cushioning, nutrient delivery, metabolic waste, including protein clearance, are key functions of the CSF in humans. CSF volume and flow dynamics regulate intracranial pressure and are fundamental to diagnosing disorders including normal pressure hydrocephalus, intracranial hypotension, CSF leaks, and possibly Alzheimer's disease (AD). The ability of CSF to clear normal and pathological proteins, such as amyloid-beta (Aβ), tau, alpha synuclein and others, implicates it production, circulation, and composition, in many neuropathologies. Several neuroimaging modalities have been developed to probe CSF fluid dynamics and better relate CSF volume and flow to anatomy and clinical conditions. Approaches include 2-photon microscopic techniques, MRI (tracer-based, gadolinium contrast, endogenous phase-contrast), and dynamic positron emission tomography (PET) using existing approved radiotracers. Here, we discuss CSF flow neuroimaging, from animal models to recent clinical-research advances, summarizing current endeavors to quantify and map CSF flow with implications towards pathophysiology, new biomarkers, and treatments of neurological diseases.

Penetration of Organophosphate Triesters and Diesters across the Blood-Cerebrospinal Fluid Barrier: Efficiencies, Impact Factors, and Mechanisms

The penetration of organophosphate triesters (tri-OPEs) and diesters (di-OPEs) across the blood-brain barrier and their influencing factors remain unclear in humans. In this study, 21 tri-OPEs and 8 di-OPEs were measured in 288 paired serum and cerebrospinal fluid (CSF) samples collected in Jinan, China. Six tri-OPEs were frequently detected in both serum and CSF, with median concentrations ranging from 0.062 to 1.62 and 0.042-1.11 ng/mL, respectively. Their penetration efficiencies across the blood-CSF barrier (BCSFB) (R_CSF/serum, C_CSF/C_serum) were calculated at 0.667-2.80, and these efficiencies first increased and then decreased with their log K_ow values. The reduced penetration efficiencies of triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) may be attributed to their strong binding affinities for human serum albumin and p-glycoprotein due to their high hydrophobicity and aryl structure, as indicated by molecular docking. This suggests that active efflux transport may be involved in the penetration of TPHP and EHDPP in addition to passive diffusion similar to the other four tri-OPEs. Di-OPEs were found in few serum samples and even fewer CSF samples, indicating their limited BCSFB permeability. This may be due to their high polarity, low hydrophobicity, and ionic state in blood. This study has important implications for understanding the neurotoxicity of tri-OPEs and di-OPEs and the underlying mechanisms.

Live Tissue Imaging Reveals Distinct Transcellular Pathways for Organic Cations and Anions at the Blood-Cerebrospinal Fluid Barrier

Formed by the choroid plexus epithelial (CPE) cells, the blood-cerebrospinal fluid barrier (BCSFB) plays an active role in removing drugs, toxins, and metabolic wastes from the brain. Several organic cation and anion transporters are expressed in the CPE cells, but how they functionally mediate transepithelial transport of organic cations and anions remain unclear. In this study, we visualized the transcellular transport of fluorescent organic cation and organic anion probes using live tissue imaging in freshly isolated mouse choroid plexuses (CPs). The cationic probe, 4-[4-(dimethylamino)phenyl]-1-methylpyridinium iodide (IDT307) was transported into CPE cells at the apical membrane and highly accumulated in mitochondria. Consistent with the lack of expression of organic cation efflux transporters, there was little efflux of IDT307 into the blood capillary space. Furthermore, IDT307 uptake and intracellular accumulation was attenuated by approximately 70% in CP tissues from mice with targeted deletion of the plasma membrane monoamine transporter (Pmat). In contrast, the anionic probe fluorescein-methotrexate (FL-MTX) was rapidly transported across the CPE cells into the capillary space with little intracellular accumulation. Rifampicin, an inhibitor of organic anion transporting polypeptides (OATPs), completely blocked FL-MTX uptake into the CPE cells whereas MK-571, a pan-inhibitor of multidrug resistance associated proteins (MRPs), abolished basolateral efflux of FL-MTX. In summary, our results suggest distinct transcellular transport pathways for organic cations and anions at the BCSFB and reveal a pivotal role of PMAT, OATP and MRP transporters in organic cation and anion transport at the blood-cerebrospinal fluid interface. SIGNIFICANCE STATEMENT: Live tissue imaging revealed that while organic cations are transported from the cerebrospinal fluid (CSF) into the choroid plexus epithelial cells by plasma membrane monoamine transporter without efflux into the blood, amphipathic anions in the CSF are efficiently transported across the BCSFB through the collaborated function of apical organic anion transporting polypeptides and basolateral multidrug resistance associated proteins. These findings contribute to a mechanistic understanding of the molecular and cellular pathways for choroid plexus clearance of solutes from the brain.

Role of Dendritic Cells in Viral Brain Infections

To gain access to the brain, a so-called immune-privileged organ due to its physical separation from the blood stream, pathogens and particularly viruses have been selected throughout evolution for their use of specific mechanisms. They can enter the central nervous system through direct infection of nerves or cerebral barriers or through cell-mediated transport. Indeed, peripheral lymphoid and myeloid immune cells can interact with the blood-brain and the blood-cerebrospinal fluid barriers and allow viral brain access using the "Trojan horse" mechanism. Among immune cells, at the frontier between innate and adaptive immune responses, dendritic cells (DCs) can be pathogen carriers, regulate or exacerbate antiviral responses and neuroinflammation, and therefore be involved in viral transmission and spread. In this review, we highlight an important contribution of DCs in the development and the consequences of viral brain infections.

Metabolites and Biomarker Compounds of Neurodegenerative Diseases in Cerebrospinal Fluid

Despite recent advances in diagnostic procedures for neurological disorders, it is still difficult to definitively diagnose some neurodegenerative diseases without neuropathological examination of autopsied brain tissue. As pathological processes in the brain are frequently reflected in the components of cerebrospinal fluid (CSF), CSF samples are sometimes useful for diagnosis. After CSF is secreted from the choroid plexus epithelial cells in the ventricles, some flows in the brain, some is mixed with intracerebral interstitial fluid, and some is excreted through two major drainage pathways, i.e., the intravascular periarterial drainage pathway and the glymphatic system. Accordingly, substances produced by metabolic and pathological processes in the brain may be detectable in CSF. Many papers have reported changes in the concentration of substances in the CSF of patients with metabolic and neurological disorders, some of which can be useful biomarkers of the disorders. In this paper, we show the significance of glucose- and neurotransmitter-related CSF metabolites, considering their transporters in the choroid plexus; summarize the reported candidates of CSF biomarkers for neurodegenerative diseases, including amyloid-β, tau, α-synuclein, microRNAs, and mitochondrial DNA; and evaluate their potential as efficient diagnostic tools.

New Paradigm in Cell Therapy Using Sperm Head to Restore Brain Function and Structure in Animal Model of Alzheimer’s Disease: Support for Boosting Constructive Inflammation vs. Anti-Inflammatory Approach

Alzheimer’s is characterized by accumulation of amyloid-β (Aβ) associated with insufficient clearance of toxicants from the brain establishing a chronic inflammation and other abnormalities in the brain. Inflammatory microglia and astrocytes along with abnormal lymphatics associated with insufficient clearance of Aβ and other toxicants from the brain establish a chronic inflammation. This causes abnormal choroid plexus, leukocyte trafficking, and hypoxic condition along with high levels of regulatory T cells (Tregs). There is no consensus among researchers regarding decreasing or increasing Tregs to achieve therapeutic effects. Different opposing studies tried to suppress or boost inflammation to treat AD. Based on reproductive immunology, sperm induces constructive inflammatory response and seminal-vesicle-fluid (SVF) suppresses inflammation leading to uterus remodeling. It prompted us to compare therapeutic efficiency of inflammatory or anti-inflammatory approaches in AD model based on reproductive immunology. To do so, SVF, sperm, or sperm head (from Wistar rat) was administered via intra-cerebro-ventricular route to Sprague Dawley rat AD model. Behavioral and histological examination were made and treatment groups were compared with control AD model and normal groups. Therapeutic efficacy was in the order of sperm head>sperm>SVF. Sperm head returned learning memory, Aβ, lymphatics, neural growth factors, choroid plexus function, Iba-1/GFAP, MHC II/CD86/CD40, CD38/IL-10, and hypoxia levels back to normal level. However, SVF just partially ameliorated the disease. Immunologic properties of sperm/sperm head to elicit constructive inflammation can be extended to organs other than reproductive. This nature-based approach overcomes genetic difference as an important obstacle and limitation in cell therapy, and is expected to be safe or with least side effects.

Recent Review of Germinal Matrix Hemorrhage-Intraventricular Hemorrhage in Preterm Infants

Germinal matrix hemorrhage-intraventricular hemorrhage (GMH-IVH) is a particular type of intracranial hemorrhage that affects the preterm population. GMH-IVH originates from bleeding within the highly vascular area near the center of the brain known as the germinal matrix. The pathogenesis of GMH-IVH is unclear; it is likely related to hemodynamic changes and fluctuations in cerebral blood flow within a fragile developing brain. Cranial ultrasound is the primary diagnostic test and reveals the degree of GMH-IVH based on a grading system. Management includes prevention of preterm delivery with meticulous antenatal and postnatal preventative strategies. This article discusses current evidence specific to the pathogenesis, risk factors, diagnosis, grading scales, and management approaches with GMH-IVH in preterm infants.

Clearance Systems in the Brain, From Structure to Function

As the most metabolically active organ in the body, there is a recognized need for pathways that remove waste proteins and neurotoxins from the brain. Previous research has indicated potential associations between the clearance system in the brain and the pathological conditions of the central nervous system (CNS), due to its importance, which has attracted considerable attention recently. In the last decade, studies of the clearance system have been restricted to the glymphatic system. However, removal of toxic and catabolic waste by-products cannot be completed independently by the glymphatic system, while no known research or article has focused on a comprehensive overview of the structure and function of the clearance system. This thesis addresses a neglected aspect of linkage between the structural composition and main components as well as the role of neural cells throughout the clearance system, which found evidence that the components of CNS including the glymphatic system and the meningeal lymphatic system interact with a neural cell, such as astrocytes and microglia, to carry out vital clearance functions. As a result of this evidence that can contribute to a better understanding of the clearance system, suggestions were identified for further clinical intervention development of severe conditions caused by the accumulation of metabolic waste products and neurotoxins in the brain, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD).

The brain as a source and a target of prolactin in mammals

Prolactin is a polypeptide hormone associated with an extensive variety of biological functions. Among the roles of prolactin in vertebrates, some were preserved throughout evolution. This is the case of its function in the brain, where prolactin receptors, are expressed in different structures of the central nervous system. In the brain, prolactin actions are principally associated with reproduction and parental behavior, and involves the modulation of adult neurogenesis, neuroprotection, and neuroplasticity, especially during pregnancy, thereby preparing the brain to parenthood. Prolactin is mainly produced by specialized cells in the anterior pituitary gland. However, during vertebrate evolution many other extrapituitary tissues do also produce prolactin, like the immune system, endothelial cells, reproductive structures and in several regions of the brain. This review summarizes the relevance of prolactin for brain function, the sources of prolactin in the central nervous system, as well as its local production and secretion. A highlight on the impact of prolactin in human neurological diseases is also provided.

Inflammatory hydrocephalus

Reparative inflammation is an important protective response that eliminates foreign organisms, damaged cells, and physical irritants. However, inappropriately triggered or sustained inflammation can respectively initiate, propagate, or prolong disease. Post-hemorrhagic (PHH) and post-infectious hydrocephalus (PIH) are the most common forms of hydrocephalus worldwide. They are treated using neurosurgical cerebrospinal fluid (CSF) diversion techniques with high complication and failure rates. Despite their distinct etiologies, clinical studies in human patients have shown PHH and PIH share similar CSF cytokine and immune cell profiles. Here, in light of recent work in model systems, we discuss the concept of "inflammatory hydrocephalus" to emphasize potential shared mechanisms and potential therapeutic vulnerabilities of these disorders. We propose that this change of emphasis could shift our thinking of PHH and PIH from a framework of life-long neurosurgical disorders to that of preventable conditions amenable to immunomodulation.

Translational value of choroid plexus imaging for tracking neuroinflammation in mice and humans

Neuroinflammation is a pathophysiological hallmark of multiple sclerosis and has a close mechanistic link to neurodegeneration. Although this link is potentially targetable, robust translatable models to reliably quantify and track neuroinflammation in both mice and humans are lacking. The choroid plexus (ChP) plays a pivotal role in regulating the trafficking of immune cells from the brain parenchyma into the cerebrospinal fluid (CSF) and has recently attracted attention as a key structure in the initiation of inflammatory brain responses. In a translational framework, we here address the integrity and multidimensional characteristics of the ChP under inflammatory conditions and question whether ChP volumes could act as an interspecies marker of neuroinflammation that closely interrelates with functional impairment. Therefore, we explore ChP characteristics in neuroinflammation in patients with multiple sclerosis and in two experimental mouse models, cuprizone diet-related demyelination and experimental autoimmune encephalomyelitis. We demonstrate that ChP enlargement-reconstructed from MRI-is highly associated with acute disease activity, both in the studied mouse models and in humans. A close dependency of ChP integrity and molecular signatures of neuroinflammation is shown in the performed transcriptomic analyses. Moreover, pharmacological modulation of the blood-CSF barrier with natalizumab prevents an increase of the ChP volume. ChP enlargement is strongly linked to emerging functional impairment as depicted in the mouse models and in multiple sclerosis patients. Our findings identify ChP characteristics as robust and translatable hallmarks of acute and ongoing neuroinflammatory activity in mice and humans that could serve as a promising interspecies marker for translational and reverse-translational approaches.

The epithelial potassium channel Kir7.1 is stimulated by progesterone

The choroid plexus (CP) epithelium secretes cerebrospinal fluid and plays an important role in healthy homeostasis of the brain. CP function can be influenced by sex steroid hormones; however, the precise molecular mechanism of such regulation is not well understood. Here, using whole-cell patch-clamp recordings from male and female murine CP cells, we show that application of progesterone resulted in specific and strong potentiation of the inwardly rectifying potassium channel Kir7.1, an essential protein that is expressed in CP and is required for survival. The potentiation was progesterone specific and independent of other known progesterone receptors expressed in CP. This effect was recapitulated with recombinant Kir7.1, as well as with endogenous Kir7.1 expressed in the retinal pigment epithelium. Current-clamp studies further showed a progesterone-induced hyperpolarization of CP cells. Our results provide evidence of a progesterone-driven control of tissues in which Kir7.1 is present.

Oxidized/deamidated-ceruloplasmin dysregulates choroid plexus epithelial cells functionality and barrier properties via RGD-recognizing integrin binding

Choroid plexus epithelial cells (CPEpiCs) determine the composition of cerebrospinal fluid (CSF) and constitute the blood-CSF barrier (BCSFB), functions that are altered in neurodegenerative diseases. In Parkinson's disease (PD) the pathological environment oxidizes and deamidates the ceruloplasmin, a CSF-resident ferroxidase, which undergoes a gain of RGD-recognizing integrin binding property, that may result in signal transduction. We investigated the effects that oxidized/deamidated ceruloplasmin (Cp-ox/de) may exert on CPEpiCs functions. Through RGD-recognizing integrins binding, Cp-ox/de mediates CPEpiCs adhesion and intracellular signaling, resulting in cell proliferation inhibition and alteration of the secretome profile in terms of proteins related to cell-extracellular matrix interaction. Oxidative conditions, comparable to those found in the CSF of PD patients, induced CPEpiCs barrier leakage, allowing Cp-ox/de to cross it, transducing integrins-mediated signal that further worsens BCSFB integrity. This mechanism might contribute to PD pathological processes altering CSF composition and aggravating the already compromised BCSFB function.

Improving Choroid Plexus Segmentation in the Healthy and Diseased Brain: Relevance for Tau-PET Imaging in Dementia

Recent studies have revealed the possible role of choroid plexus (ChP) in Alzheimer's disease (AD). T1-weighted MRI is the modality of choice for the segmentation of ChP in humans. Manual segmentation is considered the gold-standard technique, but given its time-consuming nature, large-scale neuroimaging studies of ChP would be impossible. In this study, we introduce a lightweight segmentation algorithm based on the Gaussian Mixture Model (GMM). We compared its performance against manual segmentation as well as automated segmentation by Freesurfer in three separate datasets: 1) patients with structural MRIs enhanced with contrast (n = 19), 2) young healthy subjects (n = 20), and 3) patients with AD (n = 20). GMM outperformed Freesurfer and showed high similarity with manual segmentation. To further assess the algorithm's performance in large scale studies, we performed GMM segmentations in young healthy subjects from the Human Connectome Project (n = 1,067), as well as healthy controls, mild cognitive impairment (MCI), and AD patients from the Alzheimer's Disease Neuroimaging Initiative (n = 509). In both datasets, GMM segmented ChP more accurately than Freesurfer. To show the clinical importance of accurate ChP segmentation, total AV1451 (tau) PET binding to ChP was measured in 108 MCI and 32 AD patients. GMM was able to reveal the higher AV1451 binding to ChP in AD compared with MCI. Our results provide evidence for the utility of the GMM in accurately segmenting ChP and show its clinical relevance in AD. Future structural and functional studies of ChP will benefit from GMM's accurate segmentation.

The blood cerebrospinal fluid barrier orchestrates immunosurveillance, immunoprotection, and immunopathology in the central nervous system

Once characterized as an immune privileged area, recent scientific advances have demonstrated that the central nervous system (CNS) is both immunologically active and a specialized site. The anatomical and cellular features of the brain barriers, the glia limitans, and other superficial coverings of the CNS endow the brain with specificity for immune cell entry and other macro- and micro-elements to the brain. Cellular trafficking via barriers comprised of tightly junctioned non-fenestrated endothelium or tightly regulated fenestrated epithelium results in different phenotypic and cellular changes in the brain, that is, inflammatory versus regulatory changes. Based on emerging evidence, we described the unique ability of the blood cerebrospinal fluid barrier (BCSFB) to recruit, skew, and suppress immune cells. Additionally, we sum up the current knowledge on both cellular and molecular mechanisms governed by the choroid plexus and the cerebrospinal fluid at the BCSFB for immunosurveillance, immunoprotection, and immunopathology.

Cost-reducing traits for agonistic head collisions: a case for neurophysiology

Many animal species have evolved extreme behaviors requiring them to engage in repeated high-impact collisions. These behaviors include mating displays like headbutting in sheep and drumming in woodpeckers. To our knowledge, these taxa do not experience any notable acute head trauma, even though the deceleration forces would cause traumatic brain injury in most animals. Previous research has focused on skeletomuscular morphology, biomechanics, and material properties in an attempt to explain how animals moderate these high-impact forces. However, many of these behaviors are understudied, and most morphological or computational studies make assumptions about the behavior without accounting for the physiology of an organism. Studying neurophysiological and immune adaptations that co-vary with these behaviors can highlight unique or synergistic solutions to seemingly deleterious behavioral displays. Here, we argue that selection for repeated, high-impact head collisions may rely on a suite of coadaptations in intracranial physiology as a cost-reducing mechanism. We propose that there are three physiological systems that could mitigate the effects of repeated head trauma: (i) the innate neuroimmune response, (ii) the glymphatic system, and (iii) the choroid plexus. These systems are interconnected yet can evolve in an independent manner. We then briefly describe the function of these systems, their role in head trauma, and research that has examined how these systems may evolve to help reduce the cost of repeated, forceful head impacts. Ultimately, we note that little is known about cost-reducing intracranial mechanisms making it a novel field of comparative study that is ripe for exploration.

The Choroid Plexus Is an Alternative Source of Prolactin to the Rat Brain

Among the more than 300 functions attributed to prolactin (PRL), this hormone has been associated with the induction of neurogenesis and differentiation of olfactory neurons especially during pregnancy, which are essential for maternal behavior. Despite the original hypothesis that PRL enters the central nervous system through a process mediated by PRL receptors (PRLR) at the choroid plexus (CP), recent data suggested that PRL transport into the brain is independent of its receptors. Based on transcriptomic data suggesting that PRL could be expressed in the CP, this work aimed to confirm PRL synthesis and secretion by CP epithelial cells (CPEC). The secretion of PRL and the distribution of PRLR in CPEC were further characterized using an in vitro model of the rat blood-cerebrospinal fluid barrier. RT-PCR analysis of PRL transcripts showed its presence in pregnant rat CP, in CPEC, and in the rat immortalized CP cell line, Z310. These observations were reinforced by immunocytochemistry staining of PRL in CPEC and Z310 cell cytoplasm. A 63-kDa immunoreactive PRL protein was detected by Western blot in CP protein extracts as well as in culture medium incubated with rat pituitary and samples of rat cerebrospinal fluid and serum. Positive immunocytochemistry staining of PRLR was present throughout the CPEC cytoplasm and in the apical and basal membrane of these cells. Altogether, our evidences suggest that CP is an alternative source of PRL to the brain, which might impact neurogenesis of olfactory neurons at the subventricular zone, given its proximity to the CP.

Dwellers and Trespassers: Mononuclear Phagocytes at the Borders of the Central Nervous System

The central nervous system (CNS) parenchyma is enclosed and protected by a multilayered system of cellular and acellular barriers, functionally separating glia and neurons from peripheral circulation and blood-borne immune cells. Populating these borders as dynamic observers, CNS-resident macrophages contribute to organ homeostasis. Upon autoimmune, traumatic or neurodegenerative inflammation, these phagocytes start playing additional roles as immune regulators contributing to disease evolution. At the same time, pathological CNS conditions drive the migration and recruitment of blood-borne monocyte-derived cells across distinct local gateways. This invasion process drastically increases border complexity and can lead to parenchymal infiltration of blood-borne phagocytes playing a direct role both in damage and in tissue repair. While recent studies and technical advancements have highlighted the extreme heterogeneity of these resident and CNS-invading cells, both the compartment-specific mechanism of invasion and the functional specification of intruding and resident cells remain unclear. This review illustrates the complexity of mononuclear phagocytes at CNS interfaces, indicating how further studies of CNS border dynamics are crucially needed to shed light on local and systemic regulation of CNS functions and dysfunctions.

Cardiac glycosides target barrier inflammation of the vasculature, meninges and choroid plexus

Neuroinflammation is a key component of virtually all neurodegenerative diseases, preceding neuronal loss and associating directly with cognitive impairment. Neuroinflammatory signals can originate and be amplified at barrier tissues such as brain vasculature, surrounding meninges and the choroid plexus. We designed a high content screening system to target inflammation in human brain-derived cells of the blood-brain barrier (pericytes and endothelial cells) to identify inflammatory modifiers. Screening an FDA-approved drug library we identify digoxin and lanatoside C, members of the cardiac glycoside family, as inflammatory-modulating drugs that work in blood-brain barrier cells. An ex vivo assay of leptomeningeal and choroid plexus explants confirm that these drugs maintain their function in 3D cultures of brain border tissues. These results suggest that cardiac glycosides may be useful in targeting inflammation at border regions of the brain and offer new options for drug discovery approaches for neuroinflammatory driven degeneration.

Harmony of T cell profile in brain, nasal, spleen, and cervical lymph nodes tissues in Alzheimer's: A systemic disease with local manifestations

The brain has special importance and is known as immune privileged site to and from which trafficking of immune cells is tightly regulated. However, in Alzheimer's disease (AD) the balance of the immune system is disturbed and damages the brain. Given the anatomical and immunological barriers in the brain, we attempted to evaluate if the neuroinflammation occurred in AD is limited to the brain or is expanded to the periphery. Hence, rat model of AD was induced by intra-hippocampal injection of beta-amyloid1-42. Then, nasal, brain, cervical lymph nodes, and spleen were isolated. Then, profile of T-helper (Th)1, Th2, and Th17, represented by IFN-γ, IL-4, and IL-17, respectively, was determined. The results were compared between the organs and with the corresponding tissue in normal animals. IFN-γ and IL-17 levels in the brain, nasal tissue, and cervical lymph nodes of AD model were higher than IL-4, comparing with normal animals. Similar profile was observed in the spleen. The results suggest Alzheimer's as a systemic disease whose complication are observed locally. The possibility of epitope spreading and autoimmune nature of AD is raised again. Interestingly, although AD model was induced by injection of beta-amyloid in the brain, the cellular responses in the brain and nasal tissue were similar indicating that the nasal-brain axis is two-sided. In addition, both of IFN-γ/IL-17 and IL-4/IL-17 ratios, just in nasal tissue were markedly decreased in AD model comparing with normal animals. This suggests development of future nasal-based diagnostic approaches.

A combination of lycopene and human amniotic epithelial cells can ameliorate cognitive deficits and suppress neuroinflammatory signaling by choroid plexus in Alzheimer's disease rat

Neuroinflammation characterized by glial activation and release of proinflammatory mediators is considered to be correlated with cognitive deficits in Alzheimer's disease (AD). Previously, some studies have demonstrated that lycopene (LYCO) or human amniotic epithelial cells (HAECs) could attenuate inflammation in AD. Specifically, the choroid plexus (CP), an epithelial layer that forms the blood-cerebrospinal fluid barrier, is able to modulate the cognitive function, through changes in the neuroinflammatory response and in brain immune surveillance. However, it is unclear if LYCO can interact with HAECs to improve neuroinflammation at the CP. Thus, this study chose the region of interest, considered the feasibility of using a combination of LYCO and HAECs, as a therapeutic agent for immunomodulatory effects at the CP in an acutely induced AD rat model. Results showed that oral administration of LYCO, HAECs transplantation, and their combination significantly improved cognitive deficits in water maze test, decreased the level of proinflammatory mediators (TNF-α and IL-1β), increased the level of anti-inflammatory mediators (IL-10 and TGF-β1) in the cerebro-spinal fluid, and hippocampal tissue. Interestingly, LYCO administration, HAECs transplantation and their combination reversed the Aβ_1-42 induced up-regulation of Toll like receptor 4 and nuclear factor-κB p65 mRNA and protein expressions at the CP. This study provided the novel experimental evidence for the influence of co-treatment with LYCO and HAECs on immunomodulatory capabilities of CP. It could also warrant therapeutic window for the pathophysiology of AD and the associated underlying mechanisms at the CP.

Cannabinoids, Inner Ear, Hearing, and Tinnitus: A Neuroimmunological Perspective

Cannabis has been used for centuries for recreational and therapeutic purposes. Whereas, the recreative uses are based on the psychotropic effect of some of its compounds, its therapeutic effects range over a wide spectrum of actions, most of which target the brain or the immune system. Several studies have found cannabinoid receptors in the auditory system, both at peripheral and central levels, thus raising the interest in cannabinoid signaling in hearing, and especially in tinnitus, which is affected also by anxiety, memory, and attention circuits where cannabinoid effects are well described. Available studies on animal models of tinnitus suggest that cannabinoids are not likely to be helpful in tinnitus treatment and could even be harmful. However, the pharmacology of cannabinoids is very complex, and most studies focused on neural CB1R-based responses. Cannabinoid effects on the immune system (where CB2Rs predominate) are increasingly recognized as essential in understanding nervous system pathological responses, and data on immune cannabinoid targets have emerged in the auditory system as well. In addition, nonclassical cannabinoid targets (such as TRP channels) appear to play an important role in the auditory system as well. This review will focus on neuroimmunological mechanisms for cannabinoid effects and their possible use as protective and therapeutic agents in the ear and auditory system, especially in tinnitus.

The blood-brain barrier in health and disease: Important unanswered questions

The blood vessels vascularizing the central nervous system exhibit a series of distinct properties that tightly control the movement of ions, molecules, and cells between the blood and the parenchyma. This "blood-brain barrier" is initiated during angiogenesis via signals from the surrounding neural environment, and its integrity remains vital for homeostasis and neural protection throughout life. Blood-brain barrier dysfunction contributes to pathology in a range of neurological conditions including multiple sclerosis, stroke, and epilepsy, and has also been implicated in neurodegenerative diseases such as Alzheimer's disease. This review will discuss current knowledge and key unanswered questions regarding the blood-brain barrier in health and disease.

Purinergic signaling orchestrating neuron-glia communication

This review discusses the evidence supporting a role for ATP signaling (operated by P₂X and P₂Y receptors) and adenosine signaling (mainly operated by A₁ and A_2A receptors) in the crosstalk between neurons, astrocytes, microglia and oligodendrocytes. An initial emphasis will be given to the cooperation between adenosine receptors to sharpen information salience encoding across synapses. The interplay between ATP and adenosine signaling in the communication between astrocytes and neurons will then be presented in context of the integrative properties of the astrocytic syncytium, allowing to implement heterosynaptic depression processes in neuronal networks. The process of microglia 'activation' and its control by astrocytes and neurons will then be analyzed under the perspective of an interplay between different P₂ receptors and adenosine A_2A receptors. In spite of these indications of a prominent role of purinergic signaling in the bidirectional communication between neurons and glia, its therapeutical exploitation still awaits obtaining an integrated view of the spatio-temporal action of ATP signaling and adenosine signaling, clearly distinguishing the involvement of both purinergic signaling systems in the regulation of physiological processes and in the control of pathogenic-like responses upon brain dysfunction or damage.

Photoperiod Affects Leptin Action on the Choroid Plexus in Ewes Challenged with Lipopolysaccharide-Study on the mRNA Level

The ovine choroid plexus (ChP) expresses the long isoform of the leptin receptor, which makes this structure a potential target for leptin action. In sheep, leptin concentration in plasma is higher during long days (LD) than short days (SD). This study evaluates the influence a of photoperiod on leptin impact on the gene expression of Toll-like receptor 4 (TLR4), proinflammatory cytokines (IL1B, IL6), their receptors (IL1R1, IL1R2, ILRN, IL6R, IL6ST) and inflammasome components necessary for pro-IL-1β activation (NLRP3, PYCARD, CASP1), chemokine (CCL2), leptin receptor isoforms (LEPRa, LEPRb) and a suppressor of cytokine signalling (SOCS3) in the ChP of ewes treated or not with lipopolysaccharide (LPS). Studies were conducted on adult female sheep divided into four groups (n = 6 in each): control, leptin (20 μg/kg), LPS (400 ng/kg), and LPS and leptin injected under SD and LD photoperiods. The leptin alone did not affect the gene expression but in co-treatment with LPS increased (p < 0.05) IL1B but only during SD, and SOCS3, IL1R2, IL1RN, IL6ST and CCL2 only during LD, and decreased (p < 0.05) the IL1R1 expression only during SD photoperiod. This indicates that the immunomodulatory action of leptin on the ChP is manifested only under the LPS challenge and is photoperiodically dependent.

Glucose, Fructose, and Urate Transporters in the Choroid Plexus Epithelium

The choroid plexus plays a central role in the regulation of the microenvironment of the central nervous system by secreting the majority of the cerebrospinal fluid and controlling its composition, despite that it only represents approximately 1% of the total brain weight. In addition to a variety of transporter and channel proteins for solutes and water, the choroid plexus epithelial cells are equipped with glucose, fructose, and urate transporters that are used as energy sources or antioxidative neuroprotective substrates. This review focuses on the recent advances in the understanding of the transporters of the SLC2A and SLC5A families (GLUT1, SGLT2, GLUT5, GLUT8, and GLUT9), as well as on the urate-transporting URAT1 and BCRP/ABCG2, which are expressed in choroid plexus epithelial cells. The glucose, fructose, and urate transporters repertoire in the choroid plexus epithelium share similar features with the renal proximal tubular epithelium, although some of these transporters exhibit inversely polarized submembrane localization. Since choroid plexus epithelial cells have high energy demands for proper functioning, a decline in the expression and function of these transporters can contribute to the process of age-associated brain impairment and pathophysiology of neurodegenerative diseases.

Ceruloplasmin oxidized and deamidated by Parkinson's disease cerebrospinal fluid induces epithelial cells proliferation arrest and apoptosis

In Parkinson's disease, the ferroxidase ceruloplasmin (Cp) is oxidized and deamidated by the pathological cerebrospinal fluid (CSF) environment. These modifications promote the gain of integrin binding properties, fostered by the deamidation of two NGR-motifs present in the Cp sequence that convert into the isoDGR-motif. Through isoDGR/integrin binding, the oxidized/deamidated-Cp (Cp-ox/de) mediates cell adhesion and transduces an intracellular signal in epithelial cells that seems to be addressed to regulate cell cycle, proliferation and cytoskeletal re-arrangement. However, the effect fostered on cells by integrins engagement via Cp-ox/de is not known. We found that in HaCaT epithelial cells, the incubation with Cp-ox/de resulted in proliferation inhibition mediated by isoDGR, cell cycle arrest and apoptosis induction. Similar proliferation inhibition was induced by treatment with purified Cp previously incubated in the CSF from Parkinson's disease patients, but not by Cp incubated in the CSF from healthy subjects. In human primary choroid plexus epithelial cells, a possible in vivo target of Cp-ox/de generated in pathological CSFs, we found that Cp-ox/de mediated cell adhesion via isoDGR/integrins binding and transduced an intracellular signal, which resulted in cell proliferation inhibition. Thus, the generation of Cp-ox/de in pathological CSFs and the consequent apoptosis induction of epithelial cells facing the liquor, might represent a novel mechanism that contributes to neurodegeneration.

The molecular anatomy and functions of the choroid plexus in healthy and diseased brain

The choroid plexus (CP) is located in the ventricular system of the brain (one in each ventricle), and the CP epithelial cells form an important barrier between the blood and the cerebrospinal fluid (CSF). Their main function comprises CSF secretion, maintenance of brain homeostasis, signalling, and forming a neuroprotective barrier against harmful external and internal compounds. The CPs mature early and demonstrate expressional changes of barrier-specific genes and proteins related to location and developmental stage of the CP. Important proteins for the barrier function include tight junction proteins, numerous transporters and enzymes. Natural senescence leads to structural changes in the CP cells and reduced or loss of function, while further loss of CP function and changes in immune status may be relevant in neurodegenerative diseases such as Alzheimer's disease and Multiple Sclerosis. Neuroprotective genes expressed at CPs may be unexplored targets for new therapies for neurodegenerative diseases.

Choroidal Differences between Spectral and Swept-source Domain Technologies

PURPOSE OF THE STUDY

To assess differences in healthy eyes in volume (CV) and choroidal thicknesses (CT) across all macular Early Treatment Diabetic Retinopathy Study (ETDRS) areas measured by swept source (SS)-OCT and spectral domain (SD)-OCT with enhanced depth imaging (EDI).

MATERIALS AND METHODS

One hundred and fifty healthy eyes were studied in patients aged between 21-68 years. All of these patients underwent an ophthalmic examination that included axial length (AL), a fast macula protocol with EDI by Spectralis SD-OCT, and a 3D macular cube by DRI-Triton SS-OCT. CT and CV values were measured after a manual segmentation with SD-OCT and automatically with SS-OCT.

RESULTS

The values obtained by SD-OCT were statistically higher than the values obtained by SS-OCT in all ETDRS areas. To determine the differences that were related to total CV or AL, the eyes were divided depending on their total CV and AL values into two groups. There were persistent differences between the two devices that were not related to the total CV. In subjects with a higher AL, these differences were not present in either the total CV or the subfoveal CT. In longer eyes, the differences diminished, and there were no statistical differences between the devices in the subfoveal area, temporal quadrants, inferior inner ring, or CV.

CONCLUSIONS

The choroidal values obtained with the SD-OCT are statistically higher than those measured by SS-OCT. Both techniques are able to clearly visualize the choroidoscleral interface and provide different values that are highly correlated. These differences are smaller in eyes with a longer AL and are not related to the total CV.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.

Proliferation of endothelial cells in the choroid plexus of normal and hydrocephalic mice

The choroid plexus (CP), located at the walls of the brain ventricles, produces and secretes cerebrospinal fluid (CSF). Hydrocephalus is a neurological disorder in which the CP abnormally secretes excess amounts of CSF into the ventricles. There is currently no information on the vascular dynamics of the CP in adult brains under normal and hydrocephalic conditions. In the present study, we reported the continuous proliferation of endothelial cells in the CP of normal mice, which depended on vascular endothelial cell growth factor (VEGF). The proliferation of endothelial cells increased in mice with intraventricular hemorrhage, which was attenuated by a pretreatment with the toll-like receptor 4 (TLR4) inhibitor VIPER. Moreover, the intracerebroventricular infusion of the TLR4 agonist, lipopolysaccharide, increased endothelial cell proliferation in the CP and induced ventriculomegaly. The present results provide insights into the importance of the TLR4-initiated and VEGF-dependent proliferation of endothelial cells in the pathogenesis of hydrocephalus.

Choroid Plexus Enlargement and Allostatic Load in Schizophrenia

Although schizophrenia is a brain disorder, increasing evidence suggests that there may be body-wide involvement in this illness. However, direct evidence of brain structures involved in the presumed peripheral-central interaction in schizophrenia is still unclear. Seventy-nine previously treatment-naïve first-episode schizophrenia patients who were within 2-week antipsychotics initial stabilization, and 41 age- and sex-matched healthy controls were enrolled in the study. Group differences in subcortical brain regional structures measured by MRI and the subclinical cardiovascular, metabolic, immune, and neuroendocrine biomarkers as indexed by allostatic load, and their associations were explored. Compared with controls, patients with schizophrenia had significantly higher allostatic load (P = .001). Lateral ventricle (P < .001), choroid plexus (P < .001), and thalamus volumes (P < .001) were significantly larger, whereas amygdala volume (P = .001) was significantly smaller in patients. The choroid plexus alone was significantly correlated with higher allostatic load after age, sex, education level, and the total intracranial volume were taken into account (t = 3.60, P < .001). Allostatic load was also significantly correlated with PANSS positive (r = 0.28, P = .016) and negative (r = -0.31, P = .008) symptoms, but in opposite directions. The peripheral multisystemic and central nervous system abnormalities in schizophrenia may interact through the choroid plexus during the early stage of the illness. The choroid plexus might provide a sensitive structural biomarker to study the treatment and prevention of brain-periphery interaction abnormalities in schizophrenia.