The Choroid Plexus‐Cerebrospinal Fluid System: From Development to Aging

Expression Profiling of Solute Carrier Gene Families at the Blood-CSF Barrier

The choroid plexus (CP) is a highly vascularized tissue in the brain ventricles and acts as the blood-cerebrospinal fluid (CSF) barrier (BCSFB). A main function of the CP is to secrete CSF, which is accomplished by active transport of small ions and water from the blood side to the CSF side. The CP also supplies the brain with certain nutrients, hormones, and metal ions, while removing metabolites and xenobiotics from the CSF. Numerous membrane transporters are expressed in the CP in order to facilitate the solute exchange between the blood and the CSF. The solute carrier (SLC) superfamily represents a major class of transporters in the CP that constitutes the molecular mechanisms for CP function. Recently, we systematically and quantitatively examined Slc gene expression in 20 anatomically comprehensive brain areas in the adult mouse brain using high-quality in situ hybridization data generated by the Allen Brain Atlas. Here we focus our analysis on Slc gene expression at the BCSFB using previously obtained data. Of the 252 Slc genes present in the mouse brain, 202 Slc genes were found at detectable levels in the CP. Unsupervised hierarchical cluster analysis showed that the CP Slc gene expression pattern is substantially different from the other 19 analyzed brain regions. The majority of the Slc genes in the CP are expressed at low to moderate levels, whereas 28 Slc genes are present in the CP at the highest levels. These highly expressed Slc genes encode transporters involved in CSF secretion, energy production, and transport of nutrients, hormones, neurotransmitters, sulfate, and metal ions. In this review, the functional characteristics and potential importance of these Slc transporters in the CP are discussed, with particular emphasis on their localization and physiological functions at the BCSFB.

The path from the choroid plexus to the subventricular zone: go with the flow!

In adult mammals, under physiological conditions, neurogenesis, the process of generating new functional neurons from precursor cells, occurs mainly in two brain areas: the subgranular zone in the dentate gyrus of the hippocampus, and the subventricular zone (SVZ) lining the walls of the brain lateral ventricles. Taking into account the location of the SVZ and the cytoarchitecture of this periventricular neural progenitor cell niche, namely the fact that the slow dividing primary progenitor cells (type B cells) of the SVZ extend an apical primary cilium toward the brain ventricular space which is filled with cerebrospinal fluid (CSF), it becomes likely that the composition of the CSF can modulate both self-renewal, proliferation and differentiation of SVZ neural stem cells. The major site of CSF synthesis is the choroid plexus (CP); quite surprisingly, however, it is still largely unknown the contribution of molecules specifically secreted by the adult CP as modulators of the SVZ adult neurogenesis. This is even more relevant in light of recent evidence showing the ability of the CP to adapt its transcriptome and secretome to various physiologic and pathologic stimuli. By giving particular emphasizes to growth factors and axonal guidance molecules we will illustrate how CP-born molecules might play an important role in the SVZ niche cell population dynamics.

In vitro effects of fetal rat cerebrospinal fluid on viability and neuronal differentiation of PC12 cells

Background

Fetal cerebrospinal fluid (CSF) contains many neurotrophic and growth factors and has been shown to be capable of supporting viability, proliferation and differentiation of primary cortical progenitor cells. Rat pheochromocytoma PC12 cells have been widely used as an in vitro model of neuronal differentiation since they differentiate into sympathetic neuron-like cells in response to growth factors. This study aimed to establish whether PC12 cells were responsive to fetal CSF and therefore whether they might be used to investigate CSF physiology in a stable cell line lacking the time-specific response patterns of primary cells previously described.

Methods

In vitro assays of viability, proliferation and differentiation were carried out after incubation of PC12 cells in media with and without addition of fetal rat CSF. An MTT tetrazolium assay was used to assess cell viability and/or cell proliferation. Expression of neural differentiation markers (MAP-2 and β-III tubulin) was determined by immunocytochemistry. Formation and growth of neurites was measured by image analysis.

Results

PC12 cells differentiate into neuronal cell types when exposed to bFGF. Viability and cell proliferation of PC12 cells cultured in CSF-supplemented medium from E18 rat fetuses were significantly elevated relative to the control group. Neuronal-like outgrowths from cells appeared following the application of bFGF or CSF from E17 and E19 fetuses but not E18 or E20 CSF. Beta-III tubulin was expressed in PC12 cells cultured in any media except that supplemented with E18 CSF. MAP-2 expression was found in control cultures and in those with E17 and E19 CSF. MAP2 was located in neurites except in E17 CSF when the whole cell was positive.

Conclusions

Fetal rat CSF supports viability and stimulates proliferation and neurogenic differentiation of PC12 cells in an age-dependent way, suggesting that CSF composition changes with age. This feature may be important in vivo for the promotion of normal brain development. There were significant differences in the effects on PC12 cells compared to primary cortical cells. This suggests there is an interaction in vivo between developmental stage of cells and the composition of CSF. The data presented here support an important, perhaps driving role for CSF composition, specifically neurotrophic factors, in neuronal survival, proliferation and differentiation. The effects of CSF on PC12 cells can thus be used to further investigate the role of CSF in driving development without the confounding issues of using primary cells.

Nonlesions, unusual cell types, and postmortem artifacts in the central nervous system of domestic animals

In the central nervous system (CNS) of domestic animals, numerous specialized normal structures, unusual cell types, findings of uncertain or no significance, artifacts, and various postmortem alterations can be observed. They may cause confusion for inexperienced pathologists and those not specialized in neuropathology, leading to misinterpretations and wrong diagnoses. Alternatively, changes may mask underlying neuropathological processes. "Specialized structures" comprising the hippocampus and the circumventricular organs, including the vascular organ of the lamina terminalis, subfornical organ, subcommissural organ, pineal gland, median eminence/neurohypophyseal complex, choroid plexus, and area postrema, are displayed. Unusual cell types, including cerebellar external germinal cells, CNS progenitor cells, and Kolmer cells, are presented. In addition, some newly recognized cell types as of yet incompletely understood significance and functionality, such as synantocytes and aldynoglia, are introduced and described. Unusual reactive astrocytes in cats, central chromatolysis, neuronal vacuolation, spheroids, spongiosis, satellitosis, melanosis, neuromelanin, lipofuscin, polyglucosan bodies, and psammoma bodies may represent incidental findings of uncertain or no significance and should not be confused with significant microscopic changes. Auto- and heterolysis as well as handling and histotechnological processing may cause postmortem morphological changes of the CNS, including vacuolization, cerebellar conglutination, dark neurons, Buscaino bodies, freezing, and shrinkage artifacts, all of which have to be differentiated from genuine lesions. Postmortem invasion of micro-organisms should not be confused with intravital infections. Awareness of these different changes and their recognition are a prerequisite for identifying genuine lesions and may help to formulate a professional morphological and etiological diagnosis.

Modulation of iron metabolism in aging and in Alzheimer's disease: relevance of the choroid plexus

Iron is essential for mammalian cellular homeostasis. However, in excess, it promotes free radical formation and is associated with aging-related progressive deterioration and with neurodegenerative disorders such as Alzheimer's disease (AD). There are no mechanisms to excrete iron, which makes iron homeostasis a very tightly regulated process at the level of the intestinal absorption. Iron is believed to reach the brain through receptor-mediated endocytosis of iron-bound transferrin by the brain barriers, the blood-cerebrospinal fluid (CSF) barrier, formed by the choroid plexus (CP) epithelial cells and the blood-brain barrier (BBB) formed by the endothelial cells of the brain capillaries. Importantly, the CP epithelial cells are responsible for producing most of the CSF, the fluid that fills the brain ventricles and the subarachnoid space. Recently, the finding that the CP epithelial cells display all the machinery to locally control iron delivery into the CSF may suggest that the general and progressive senescence of the CP may be at the basis of the impairment of regional iron metabolism, iron-mediated toxicity, and the increase in inflammation and oxidative stress that occurs with aging and, particularly, in AD.

ICV-transplanted human glial precursor cells are short-lived yet exert immunomodulatory effects in mice with EAE

Human glial precursor cells (hGPs) have potential for remyelinating lesions and are an attractive cell source for cell therapy of multiple sclerosis (MS). To investigate whether transplanted hGPs can affect the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of MS, we evaluated the therapeutic effects of transplanted hGPs together with the in vivo fate of these cells using magnetic resonance imaging (MRI) and bioluminescence imaging (BLI). At 14 days post-EAE induction, mice (n = 19) were intracerebroventricularly (ICV) injected with 5 × 10(5) hGPs that were magnetically labeled with superparamagnetic iron oxide (SPIO) particles as MR contrast agent and transduced with firefly luciferase for BLI of cell survival. Control mice (n = 18) received phosphate buffered saline (PBS) vehicle only. The severity of EAE clinical disability in the hGP-transplanted group was significantly suppressed (P < 0.05) with concomitant inhibition of ConA and MOG-specific T cell proliferation in the spleen. Astrogliosis was reduced and a lower activity of macrophages and/or microglia was observed in the spinal cord (P < 0.05). On MRI, SPIO signal was detected within the lateral ventricle from 1 day post-transplantation and remained there for up to 34 days. BLI indicated that most cells did not survive beyond 5-10 days, consistent with the lack of detectable migration into the brain parenchyma and the histological presence of an abundance of apoptotic cells. Transplanted hGPs could not be detected in the spleen. We conclude that ICV transplantation of short-lived hGPs can have a remote therapeutic effect through immunomodulation from within the ventricle, without cells directly participating in remyelination.

The cerebrospinal fluid: regulator of neurogenesis, behavior, and beyond

The cerebrospinal fluid (CSF) has attracted renewed interest as an active signaling milieu that regulates brain development, homeostasis, and disease. Advances in proteomics research have enabled an improved characterization of the CSF from development through adulthood, and key neurogenic signaling pathways that are transmitted via the CSF are now being elucidated. Due to its immediate contact with neural stem cells in the developing and adult brain, the CSF's ability to swiftly distribute signals across vast distances in the central nervous system is opening avenues to novel and exciting therapeutic approaches. In this review, we will discuss the development of the choroid plexus-CSF system, and review the current literature on how the CSF actively regulates mammalian brain development, behavior, and responses to traumatic brain injury.

Neurogenesis at the brain-cerebrospinal fluid interface

Cerebral cortical progenitor cells can be classified into several different types, and each progenitor type integrates cell-intrinsic and cell-extrinsic cues to regulate neurogenesis. On one hand, cell-intrinsic mechanisms that depend upon appropriate apical-basal polarity are established by adherens junctions and apical complex proteins and are particularly important in progenitors with apical processes contacting the lateral ventricle. The apical protein complexes themselves are concentrated at the ventricular surface, and apical complex proteins regulate mitotic spindle orientation and cell fate. On the other hand, remarkably little is known about how cell-extrinsic cues signal to progenitors and couple with cell-intrinsic mechanisms to instruct neurogenesis. Recent research shows that the cerebrospinal fluid, which contacts apical progenitors at the ventricular surface and bathes the apical complex of these cells, provides growth- and survival-promoting cues for neural progenitor cells in developing and adult brain. This review addresses how the apical-basal polarity of progenitor cells regulates cell fate and allows progenitors to sample diffusible signals distributed by the cerebrospinal fluid. We also review several classes of signaling factors that the cerebrospinal fluid distributes to the developing brain to instruct neurogenesis.

Brain homeostasis is maintained by "danger" signals stimulating a supportive immune response within the brain's borders

An organism's behavior is determined by the way it senses and perceives the surrounding environment, and by its responses to these stimuli. The major factors known to affect the behavioral response to an event are genetic background, environmental factors, and past experiences, and their imprinting on the relevant brain circuits. Recently, circulating immune cells were introduced as novel players into this system. It was proposed that the brain and circulating immune cells engage in a continuous dialogue that takes place within the brain's territory, though outside the parenchyma (occurring within the brain's borders - the choroid plexi, the brain meninges and the cerebrospinal fluid (CSF)). The cytokines secreted by activated leukocytes residing at the borders were shown to affect neurotrophic factors production within the parenchyma. Here, we suggest that such a dialogue is stimulated at the brain's borders, upon need, by a "danger" signal that originates in the parenchyma in response to any destabilizing event, and discuss the potential role of reactive oxygen species (ROS) in transmitting this signal. Accordingly, a failure to restore balance is likely to lead to aberrant responses to subsequent events. This view thus supports the contention that circulating immune cells are required to maintain the brain's balanced activity and suggests a novel mechanism whereby the surveying immune cells are sensing the brain's status and needs.

Aquaporin and vascular diseases

Aquaporins (AQP) are family of water channels found in several epithelial and endothelial cells, whose recent identification has provided insights into water transport in several tissues, including the central nervous system (CNS). Since brain edema continues to be the main cause of death from several CNS diseases, such as stroke, much of the interest in AQPs and their functional contribution to the water balance is due to their possible role in clearing edema water from the brain and in managing hydrocephalus and benign intracranial hypertension, suggesting that they could be targets for future treatments of various brain conditions, particularly vascular diseases. AQPs also seem to be involved in cell migration, and a mechanism of AQP-facilitated cell migration has been proposed where local osmotic gradients created at the tip of the lamellipodium drive water influx, facilitating lamellipodial extension and cell migration. AQP-facilitated cell migration was also detected in tumour cells, suggesting that it may have an important role in tumour angiogenesis and spread, and accounting for AQP expression in many tumour cell types and for correlations found between AQP expression and tumour stage in some tumours.

Growth hormone and prolactin regulate human neural stem cell regenerative activity

We have previously shown that the growth hormone (GH)/prolactin (PRL) axis has a significant role in regulating neuroprotective and/or neurorestorative mechanisms in the brain and that these effects are mediated, at least partly, via actions on neural stem cells (NSCs). Here, using NSCs with properties of neurogenic radial glia derived from fetal human forebrains, we show that exogenously applied GH and PRL promote the proliferation of NSCs in the absence of epidermal growth factor or basic fibroblast growth factor. When applied to differentiating NSCs, they both induce neuronal progenitor proliferation, but only PRL has proliferative effects on glial progenitors. Both GH and PRL also promote NSC migration, particularly at higher concentrations. Since human GH activates both GH and PRL receptors, we hypothesized that at least some of these effects may be mediated via the latter. Migration studies using receptor-specific antagonists confirmed that GH signals via the PRL receptor promote migration. Mechanisms of receptor signaling in NSC proliferation, however, remain to be elucidated. In summary, GH and PRL have complex stimulatory and modulatory effects on NSC activity and as such may have a role in injury-related recovery processes in the brain.

The long adventurous journey of rhombic lip cells in jawed vertebrates: a comparative developmental analysis

This review summarizes vertebrate rhombic lip and early cerebellar development covering classic approaches up to modern developmental genetics which identifies the relevant differential gene expression domains and their progeny. Most of this information is derived from amniotes. However, progress in anamniotes, particularly in the zebrafish, has recently been made. The current picture suggests that rhombic lip and cerebellar development in jawed vertebrates (gnathostomes) share many characteristics. Regarding cerebellar development, these include a ptf1a expressing ventral cerebellar proliferation (VCP) giving rise to Purkinje cells and other inhibitory cerebellar cell types, and an atoh1 expressing upper rhombic lip giving rise to an external granular layer (EGL, i.e., excitatory granule cells) and an early ventral migration into the anterior rhombencephalon (cholinergic nuclei). As for the lower rhombic lip (LRL), gnathostome commonalities likely include the formation of precerebellar nuclei (mossy fiber origins) and partially primary auditory nuclei (likely convergently evolved) from the atoh1 expressing dorsal zone. The fate of the ptf1a expressing ventral LRL zone which gives rise to (excitatory cells of) the inferior olive (climbing fiber origin) and (inhibitory cells of ) cochlear nuclei in amniotes, has not been determined in anamniotes. Special for the zebrafish in comparison to amniotes is the predominant origin of anamniote excitatory deep cerebellar nuclei homologs (i.e., eurydendroid cells) from ptf1a expressing VCP cells, the sequential activity of various atoh1 paralogs and the incomplete coverage of the subpial cerebellar plate with proliferative EGL cells. Nevertheless, the conclusion that a rhombic lip and its major derivatives evolved with gnathostome vertebrates only and are thus not an ancestral craniate character complex is supported by the absence of a cerebellum (and likely absence of its afferent and efferent nuclei) in jawless fishes

Transcriptome signature of the adult mouse choroid plexus

Background

Although the gene expression profile of several tissues in humans and in rodent animal models has been explored, analysis of the complete choroid plexus (CP) transcriptome is still lacking. A better characterization of the CP transcriptome can provide key insights into its functions as one of the barriers that separate the brain from the periphery and in the production of cerebrospinal fluid.

Methods

This work extends further what is known about the mouse CP transcriptome through a microarray analysis of CP tissue from normal mice under physiological conditions.

Results

We found that the genes most highly expressed are those implicated in energy metabolism (oxidative phosphorylation, glycolysis/gluconeogenesis) and in ribosomal function, which is in agreement with the secretory nature of the CP. On the other hand, genes encoding for immune mediators are among those with lower expression in basal conditions. In addition, we found genes known to be relevant during brain development, and not previously identified to be expressed in the CP, including those encoding for various axonal guidance and angiogenesis molecules and for growth factors. Some of these are known to influence the neural stem cell niche in the subventricular zone, highlighting the involvement of the CP as a likely modulator of neurogenesis. Interestingly, our observations confirm that the CP transcriptome is unique, displaying low homology with that of other tissues. Of note, we describe here that the closest similarity is with the transcriptome of the endothelial cells of the blood-brain barrier.

Conclusions

Based on the data presented here, it will now be possible to further explore the function of particular proteins of the CP secretome in health and in disease.

The blood-cerebrospinal fluid barrier: structure and functional significance

The choroid plexus (CP) of the blood-CSF barrier (BCSFB) displays fundamentally different properties than blood-brain barrier (BBB). With brisk blood flow (10 × brain) and highly permeable capillaries, the human CP provides the CNS with a high turnover rate of fluid (∼400,000 μL/day) containing micronutrients, peptides, and hormones for neuronal networks. Renal-like basement membranes in microvessel walls and underneath the epithelium filter large proteins such as ferritin and immunoglobulins. Type IV collagen (α3, α4, and α5) in the subepithelial basement membrane confers kidney-like permselectivity. As in the glomerulus, so also in CP, the basolateral membrane utrophin A and colocalized dystrophin impart structural stability, transmembrane signaling, and ion/water homeostasis. Extensive infoldings of the plasma-facing basal labyrinth together with lush microvilli at the CSF-facing membrane afford surface area, as great as that at BBB, for epithelial solute and water exchange. CSF formation occurs by basolateral carrier-mediated uptake of Na+, Cl-, and HCO3-, followed by apical release via ion channel conductance and osmotic flow of water through AQP1 channels. Transcellular epithelial active transport and secretion are energized and channeled via a highly dense organelle network of mitochondria, endoplasmic reticulum, and Golgi; bleb formation occurs at the CSF surface. Claudin-2 in tight junctions helps to modulate the lower electrical resistance and greater permeability in CP than at BBB. Still, ratio analyses of influx coefficients (Kin) for radiolabeled solutes indicate that paracellular diffusion of small nonelectrolytes (e.g., urea and mannitol) through tight junctions is restricted; molecular sieving is proportional to solute size. Protein/peptide movement across BCSFB is greatly limited, occurring by paracellular leaks through incomplete tight junctions and low-capacity transcellular pinocytosis/exocytosis. Steady-state concentration ratios, CSF/plasma, ranging from 0.003 for IgG to 0.80 for urea, provide insight on plasma solute penetrability, barrier permeability, and CSF sink action to clear substances from CNS.

Traumatic brain injury and recovery mechanisms: peptide modulation of periventricular neurogenic regions by the choroid plexus-CSF nexus

In traumatic brain injury (TBI), severe disruptions occur in the choroid plexus (CP)-cerebrospinal fluid (CSF) nexus that destabilize the nearby hippocampal and subventricular neurogenic regions. Following invasive and non-invasive injuries to cortex, several adverse sequelae harm the brain interior: (i) structural damage to CP epithelium that opens the blood-CSF barrier (BCSFB) to protein, (ii) altered CSF dynamics and intracranial pressure (ICP), (iii) augmentation of leukocyte traffic across CP into the CSF-brain, (iv) reduction in CSF sink action and clearance of debris from ventricles, and (v) less efficient provision of micronutritional and hormonal support for the CNS. However, gradual post-TBI restitution of the injured CP epithelium and ependyma, and CSF homeostatic mechanisms, help to restore subventricular/subgranular neurogenesis and the cognitive abilities diminished by CNS damage. Recovery from TBI is facilitated by upregulated choroidal/ependymal growth factors and neurotrophins, and their secretion into ventricular CSF. There, by an endocrine-like mechanism, CSF bulk flow convects the neuropeptides to target cells in injured cortex for aiding repair processes; and to neurogenic niches for enhancing conversion of stem cells to new neurons. In the recovery from TBI and associated ischemia, the modulating neuropeptides include FGF2, EGF, VEGF, NGF, IGF, GDNF, BDNF, and PACAP. Homeostatic correction of TBI-induced neuropathology can be accelerated or amplified by exogenously boosting the CSF concentration of these growth factors and neurotrophins. Such intraventricular supplementation via the CSF route promotes neural restoration through enhanced neurogenesis, angiogenesis, and neuroprotective effects. CSF translational research presents opportunities that involve CP and ependymal manipulations to expedite recovery from TBI.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.

Vascular basis for brain degeneration: faltering controls and risk factors for dementia

The integrity of the vascular system is essential for the efficient functioning of the brain. Aging-related structural and functional disturbances in the macro- or microcirculation of the brain make it vulnerable to cognitive dysfunction, leading to brain degeneration and dementing illness. Several faltering controls, including impairment in autoregulation, neurovascular coupling, blood-brain barrier leakage, decreased cerebrospinal fluid, and reduced vascular tone, appear to be responsible for varying degrees of neurodegeneration in old age. There is ample evidence to indicate vascular risk factors are also linked to neurodegenerative processes preceding cognitive decline and dementia. The strongest risk factor for brain degeneration, whether it results from vascular or neurodegenerative mechanisms or both, is age. However, several modifiable risks such as cardiovascular disease, hypertension, dyslipidemia, diabetes, and obesity enhance the rate of cognitive decline and increase the risk of Alzheimer's disease in particular. The ultimate accumulation of brain pathological lesions may be modified by genetic influences, such as the apolipoprotein E ε4 allele and the environment. Lifestyle measures that maintain or improve cardiovascular health, including consumption of healthy diets, moderate use of alcohol, and implementation of regular physical exercise are important factors for brain protection.

Collection of biological samples in forensic toxicology

Forensic toxicology is the study and practice of the application of toxicology to the purposes of the law. The relevance of any finding is determined, in the first instance, by the nature and integrity of the specimen(s) submitted for analysis. This means that there are several specific challenges to select and collect specimens for ante-mortem and post-mortem toxicology investigation. Post-mortem specimens may be numerous and can endow some special difficulties compared to clinical specimens, namely those resulting from autolytic and putrefactive changes. Storage stability is also an important issue to be considered during the pre-analytic phase, since its consideration should facilitate the assessment of sample quality and the analytical result obtained from that sample. The knowledge on degradation mechanisms and methods to increase storage stability may enable the forensic toxicologist to circumvent possible difficulties. Therefore, advantages and limitations of specimen preservation procedures are thoroughfully discussed in this review. Presently, harmonized protocols for sampling in suspected intoxications would have obvious utility. In the present article an overview is given on sampling procedures for routinely collected specimens as well as on alternative specimens that may provide additional information on the route and timing of exposure to a specific xenobiotic. Last, but not least, a discussion on possible bias that can influence the interpretation of toxicological results is provided. This comprehensive review article is intented as a significant help for forensic toxicologists to accomplish their frequently overwhelming mission.

Systemic treatment with liver X receptor agonists raises apolipoprotein E, cholesterol, and amyloid-β peptides in the cerebral spinal fluid of rats

Background

Apolipoprotein E (apoE) is a major cholesterol transport protein found in association with brain amyloid from Alzheimer's disease (AD) patients and the ε4 allele of apoE is a genetic risk factor for AD. Previous studies have shown that apoE forms a stable complex with amyloid β (Aβ) peptides in vitro and that the state of apoE lipidation influences the fate of brain Aβ, i.e., lipid poor apoE promotes Aβ aggregation/deposition while fully lipidated apoE favors Aβ degradation/clearance. In the brain, apoE levels and apoE lipidation are regulated by the liver X receptors (LXRs).

Results

We investigated the hypothesis that increased apoE levels and lipidation induced by LXR agonists facilitates Aβ efflux from the brain to the cerebral spinal fluid (CSF). We also examined if the brain expression of major apoE receptors potentially involved in apoE-mediated Aβ clearance was altered by LXR agonists. ApoE, cholesterol, Aβ40, and Aβ42 levels were all significantly elevated in the CSF of rats after only 3 days of treatment with LXR agonists. A significant reduction in soluble brain Aβ40 levels was also detected after 6 days of LXR agonist treatment.

Conclusions

Our novel findings suggest that central Aβ lowering caused by LXR agonists appears to involve an apoE/cholesterol-mediated transport of Aβ to the CSF and that differences between the apoE isoforms in mediating this clearance pathway may explain why individuals carrying one or two copies of APOE ε4 have increased risk for AD.

Aging differentially affects male and female neural stem cell neurogenic properties

Purpose

Neural stem cell transplantation as a brain repair strategy is a very promising technology. However, despite many attempts, the clinical success remains very deceiving. Despite clear evidence that sexual dimorphism rules many aspects of human biology, the occurrence of a sex difference in neural stem cell biology is largely understudied. Herein, we propose to determine whether gender is a dimension that drives the fate of neural stem cells through aging. Should it occur, we believe that neural stem cell sexual dimorphism and its variation during aging should be taken into account to refine clinical approaches of brain repair strategies.

Methods

Neural stem cells were isolated from the subventricular zone of three- and 20-month-old male and female Long-Evans rats. Expression of the estrogen receptors, ERα and ERβ, progesterone receptor, androgen receptor, and glucocorticoid receptor was analyzed and quantified by Western blotting on undifferentiated neural stem cells. A second set of neural stem cells was treated with retinoic acid to trigger differentiation, and the expression of neuronal, astroglial, and oligodendroglial markers was determined using Western blotting.

Conclusion

We provided in vitro evidence that the fate of neural stem cells is affected by sex and aging. Indeed, young male neural stem cells mainly expressed markers of neuronal and oligodendroglial fate, whereas young female neural stem cells underwent differentiation towards an astroglial phenotype. Aging resulted in a lessened capacity to express neuron and astrocyte markers. Undifferentiated neural stem cells displayed sexual dimorphism in the expression of steroid receptors, in particular ERα and ERβ, and the expression level of several steroid receptors increased during aging. Such sexual dimorphism might explain, at least in part, the sex difference in neural fate we observed in young and old neural stem cells. These results suggest that sex and aging are two factors to be taken into consideration for future neural stem cell transplantation protocols in brain repair strategies.

The expression of twisted gastrulation in postnatal mouse brain and functional implications

Twisted gastrulation (TWSG1), an extracellular regulator of bone morphogenetic protein (BMP) signaling, is critical for embryonic brain development. Mice deficient in TWSG1 have abnormal forebrain development manifesting as holoprosencephaly. The expression and potential roles of TWSG1 in postnatal brain development are less well understood. We show that Twsg1 is expressed in the adult mouse brain in the choroid plexus (CP), hippocampus, and other regions, with the strongest expression observed in CP. TWSG1 was also detected in a human fetal brain at mid-gestation, with highest levels in the epithelium of CP. Bmp1, Bmp2, Bmp4-Bmp7 as well as BmprIA and BmprII, but not BmprIB, were expressed in CP. BMP antagonists Chordin (Chrd) and Noggin were not detected in CP, however Chrd-like 1 and brain-specific Chrd-like (Brorin) were expressed. Electrophysiological study of synaptic plasticity revealed normal paired-pulse facilitation and long-term potentiation in the CA1 region of hippocampus in Twsg1(-/-) mice. Among the homozygous mutants that survive beyond the first 2 weeks, the prevalence of hydrocephalus was 4.3%, compared to 1.5% in a wild type colony (P=0.0133) between 3 and 10 weeks of life. We detected a high level of BMP signaling in CP in wild type adult mice that was 17-fold higher than in the hippocampus (P=0.005). In contrast, transforming growth factor beta (TGFbeta) signaling was predominant in the hippocampus. Both BMP signaling and the expression of BMP downstream targets Msx1 and Msx2 were reduced in CP in Twsg1(-/-) mice. In summary, we show that Twsg1 is expressed in the adult mouse and human fetal CP. We also show that BMP is a branch of TGFbeta superfamily that is dominant in CP. This presents an interesting avenue for future research in light of the novel roles of CP in neural progenitor differentiation and neuronal repair, especially since TWSG1 appears to be the main regulator of BMP present in CP.

Cerebellopontine angle arachnoid cyst containing ectopic choroid plexus--case report

We present a rare and interesting case of a cerebellopontine angle cyst containing ectopic choroid plexus tissue in a 26 year-old female. Surgical resection was performed, and histological examination confirmed the presence of choroid plexus in the cyst wall. This is the first reported case of ectopic choroid plexus at the cerebellopontine angle in an adult. We present the case and review the literature.

Transventricular delivery of Sonic hedgehog is essential to cerebellar ventricular zone development

Cerebellar neurons are generated from two germinal neuroepithelia: the ventricular zone (VZ) and rhombic lip. Signaling mechanisms that maintain the proliferative capacity of VZ resident progenitors remain elusive. We reveal that Sonic hedgehog (Shh) signaling is active in the cerebellar VZ and essential to radial glial cell proliferation and expansion of GABAergic interneurons. We demonstrate that the cerebellum is not the source of Shh that signals to the early VZ, and suggest a transventricular path for Shh ligand delivery. In agreement, we detected the presence of Shh protein in the circulating embryonic cerebrospinal fluid. This study identifies Shh as an essential proliferative signal for the cerebellar ventricular germinal zone, underscoring the potential contribution of VZ progenitors in the pathogenesis of cerebellar diseases associated with deregulated Shh signaling, and reveals a transventricular source of Shh in regulating neural development.

Cerebrospinal fluid promotes survival and astroglial differentiation of adult human neural progenitor cells but inhibits proliferation and neuronal differentiation

BACKGROUND

Neural stem cells (NSCs) are a promising source for cell replacement therapies for neurological diseases. Growing evidence suggests an important role of cerebrospinal fluid (CSF) not only on neuroectodermal cells during brain development but also on the survival, proliferation and fate specification of NSCs in the adult brain. Existing in vitro studies focused on embryonic cell lines and embryonic CSF. We therefore studied the effects of adult human leptomeningeal CSF on the behaviour of adult human NSCs (ahNSCs).

RESULTS

Adult CSF increased the survival rate of adult human NSCs compared to standard serum free culture media during both stem cell maintenance and differentiation. The presence of CSF promoted differentiation of NSCs leading to a faster loss of their self-renewal capacity as it is measured by the proliferation markers Ki67 and BrdU and stronger cell extension outgrowth with longer and more cell extensions per cell. After differentiation in CSF, we found a larger number of GFAP+ astroglial cells compared to differentiation in standard culture media and a lower number of beta-tubulin III+ neuronal cells.

CONCLUSIONS

Our data demonstrate that adult human leptomeningeal CSF creates a beneficial environment for the survival and differentiation of adult human NSCs. Adult CSF is in vitro a strong glial differentiation stimulus and leads to a rapid loss of stem cell potential.

Coupling between hydrodynamic forces and planar cell polarity orients mammalian motile cilia

In mammals, motile cilia cover many organs, such as fallopian tubes, respiratory tracts and brain ventricles. The development and function of these organs critically depend on efficient directional fluid flow ensured by the alignment of ciliary beating. To identify the mechanisms involved in this process, we analysed motile cilia of mouse brain ventricles, using biophysical and molecular approaches. Our results highlight an original orientation mechanism for ependymal cilia whereby basal bodies first dock apically with random orientations, and then reorient in a common direction through a coupling between hydrodynamic forces and the planar cell polarity (PCP) protein Vangl2, within a limited time-frame. This identifies a direct link between external hydrodynamic cues and intracellular PCP signalling. Our findings extend known PCP mechanisms by integrating hydrodynamic forces as long-range polarity signals, argue for a possible sensory role of ependymal cilia, and will be of interest for the study of fluid flow-mediated morphogenesis.

A lifespan MRI evaluation of ventricular enlargement in normal aging mice

Ventricular enlargement has been proposed as a structural biomarker for the progression of Alzheimer's disease (AD). This biomarker, established in human patients, needs to be translated to animals to facilitate drug development for the disease. However, ventricular enlargement is not exclusive to AD, since the ventricle size increases during normal aging. A longitudinal characterization of ventricular enlargement in normal aging in mice is therefore crucial before further evaluations of mouse models or neurodegenerative diseases associated to brain atrophy. To this end, ventricular enlargement in normal aging mice was characterized over the lifespan (i.e., 2 years). The results showed that the overall ventricle size increased with age, with the expansion beginning during the early life stages and continuing to old age. The reported data represent a biomarker benchmark for normal aging mice under unmodified conditions. This provides a foundation for evaluating the validity of AD mouse models or the effects of potential drugs. The considerable physiological ventricular enlargement during normal aging must be considered in related experiments.

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

The cerebrospinal fluid (CSF) system provides nutrients to and removes waste products from the brain. Recent findings suggest, however, that in addition, the CSF contains message molecules in the form of actively released neuroactive substances. The concentrations of these vary between locations, suggesting they are important for the changes in brain activity that underlie different brain states, and induce different sensory input and behavioral output relationships.The cranial CSF displays a rapid caudally-directed ventricular flow followed by a slower rostrally-directed subarachnoid flow (mainly towards the cribriform plate and from there into the nasal lymphatics). Thus, many brain areas are exposed to and can be influenced by substances contained in the CSF. In this review we discuss the production and flow of the CSF, including the mechanisms involved in the regulation of its composition. In addition, the available evidence for the release of neuropeptides and other neuroactive substances into the CSF is reviewed, with particular attention to the selective effects of these on distant downstream receptive brain areas. As a conclusion we suggest that (1) the flowing CSF is involved in more than just nutrient and waste control, but is also used as a broadcasting system consisting of coordinated messages to a variety of nearby and distant brain areas; (2) this special form of volume transmission underlies changes in behavioral states.

Regulation of cytokine signaling and T-cell recruitment in the aging mouse brain in response to central inflammatory challenge

Aging is often accompanied by increased levels of inflammatory molecules in the organism, but age-related changes in the brain response to inflammatory challenges still require clarification. We here investigated in mice whether cytokine signaling and T-cell neuroinvasion undergo age-related changes. We first analyzed the expression of molecules involved in T-cell infiltration and cytokine signaling regulation in the septum and hippocampus of 2-3 months and 20- to 24-month-old mice at 4h after intracerebroventricular injections of tumor necrosis factor (TNF)-alpha or interferon-gammaversus saline injections. Transcripts of the chemokine CXCL9, intercellular adhesion molecule (ICAM)-1 and suppressor of cytokine signaling molecules (SOCS) 1 and 3 were increased in both age groups after cytokine injection; microglia-derived matrix metalloproteinase (MMP) 12 mRNA was induced in old mice also after control saline injections. Age-related changes in ICAM-1 protein expression and T-cell infiltration were then analyzed in mice of 3-4, 8-9 and 15-16 months at 48h after TNF-alpha injections. ICAM-1 immunoreactivity, and Western blotting in striatum, septum, hippocampus and hypothalamus showed progressive age-related enhancement of TNF-alpha-elicited ICAM-1 upregulation. Double immunofluorescence revealed ICAM-1 expression in microglia and astrocytic processes. CD3(+), CD4(+) and CD8(+) T-cells exhibited progressive age-related increases in brain parenchyma and choroid plexus after cytokine exposure. The findings indicate that the brain responses to inflammatory challenges are not only preserved with advancing age, but also include gradual amplification of ICAM-1 expression and T-cell recruitment. The data highlight molecular and cellular correlates of age-related increase of brain sensitivity to inflammatory stimuli, which could be involved in altered brain vulnerability during aging.

What is the clinical importance of echogenic material in the fetal frontal horns?

OBJECTIVE

The purpose of this study was to evaluate the importance of echogenic material in the fetal frontal horns.

METHODS

This was a Health Insurance Portability and Accountability Act-compliant, Institutional Review Board-approved retrospective study. In part 1 of the study, prenatal sonography, prenatal magnetic resonance imaging (MRI), and birth outcomes of 17 fetuses (mean gestational age, 19 weeks; range, 15-34 weeks) with prospective echogenic material in the frontal horns were assessed. In part 2, 400 consecutive sonographic fetal surveys (mean gestational age, 19 weeks; range, 15-38 weeks) were reviewed to determine the incidence. In part 3, 2 independent reviewers assessed the appearance of the frontal horns in 40 fetuses (20 with suspected intraventricular hemorrhage from parts 1 and 2 and 20 who were interpreted to have normal findings in part 2).

RESULTS

Part 1 of the study showed that suspected hemorrhage was unilateral in 13 fetuses and bilateral in 4. Additional findings by sonography were grade 4 intraventricular hemorrhage (n = 2), ventriculomegaly (n = 2), and porencephaly (n = 1). An additional finding by MRI was porencephaly in 1 fetus. In part 2, echogenic material in the frontal horns was identified in 3 of 400 fetuses (0.8%). In part 3, hemorrhage was probably or definitely present in 11 of the 20 fetuses with abnormalities; material looked like a cyst in 6; and normal choroid was in an abnormal position in 2 and a normal position 1. Of 19 fetuses with abnormalities, 14 had a posteriorly symmetric choroid; 9 had material of different echogenicity compared with the choroid; and 17 had an expanded frontal horn. Birth outcomes were abnormal in 7, including platelet abnormalities (n = 2), hemorrhage on imaging or pathologic examination (n = 2), extraventricular hemorrhage (n = 3), and ventriculomegaly (n = 3).

CONCLUSIONS

The incidence of echogenic material in the frontal horns is less than 1%. This does not represent the normal location of the choroid plexus and may represent hemorrhage, which may resolve without sequelae or result in ventriculomegaly and porencephaly.

Disruption of the neurogenic niche in the subventricular zone of postnatal hydrocephalic hyh mice

Neural stem cells persist after embryonic development in the subventricular zone (SVZ) niche and produce new neural cells during postnatal life; ependymal cells are a key component associated with this neurogenic niche. In the animal model of human hydrocephalus, the hyh mouse, the ependyma of the lateral ventricles is progressively lost during late embryonic and early postnatal life and disappears from most of the ventricular surface throughout its life span. To determine the potential consequences of this loss on the SVZ, we characterized the abnormalities in this neurogenic niche in hyh mice. There was overall disorganization and a marked reduction of proliferative cells in the SVZ of both newborn and adult hyh hydrocephalic mice in vivo; neuroblasts were displaced to the ventricular surface, and their migration through the rostral migratory stream was reduced. The numbers of resident neural progenitor cells in hyh mice were also markedly reduced, but they were capable of proliferating, forming neurospheres, and differentiating into neurons and glia in vitro in a manner indistinguishable from that of wild-type progenitor cells. These findings suggest that the reduction of proliferative activity observed in vivo is not caused by a cell autonomous defect of SVZ progenitors but is a consequence of a reduced number of these cells. Furthermore, the overall tissue disorganization of the SVZ and displacement of neuroblasts imply alterations in the neurogenic niche of postnatal hyh mice.

The blood-brain barrier in neurodegenerative disease: a rhetorical perspective

Recent studies suggest that the function of the blood-brain barrier (BBB) is not static under normal physiologic conditions and is likely altered in neurodegenerative disease. Prevailing thinking about CNS function, and neurodegenerative disease in particular, is neurocentric excluding the impact of factors outside the CNS. This review challenges this perspective and discusses recent reports suggesting the involvement of peripheral factors including toxins and elements of adaptive immunity that may not only play a role in pathogenesis, but also progression of neurodegenerative diseases. Central to this view is neuroinflammation. Several studies indicate that the neuroinflammatory changes that accompany neurodegeneration affect the BBB or its function by altering transport systems, enhancing immune cell entry, or influencing the BBB's role as a signaling interface. Such changes impair the BBB's normal homeostatic function and affect neural activity. Moreover, recent studies reveal that alterations in BBB and its transporters affect the entry of drugs used to treat neurodegenerative diseases. Incorporating BBB compromise and dysfunction into our view of neurodegenerative disease leads to the inclusion of peripheral mediators in its pathogenesis and progression. In addition, this changing view of the BBB raises interesting new therapeutic possibilities for drug delivery as well as treatment strategies designed to reinstate normal barrier function.

The role of the choroid plexus in neutrophil invasion after traumatic brain injury

Traumatic brain injury (TBI) frequently results in neuroinflammation, which includes the invasion of neutrophils. After TBI, neutrophils infiltrate the choroid plexus (CP), a site of the blood-cerebrospinal fluid (CSF) barrier (BCSFB), and accumulate in the CSF space near the injury, from where these inflammatory cells may migrate to brain parenchyma. We have hypothesized that the CP functions as an entry point for neutrophils to invade the injured brain. Using the controlled cortical impact model of TBI in rats and an in vitro model of the BCSFB, we show that the CP produces CXC chemokines, such as cytokine-induced neutrophil chemoattractant (CINC)-1 or CXCL1, CINC-2alpha or CXCL3, and CINC-3 or CXCL2. These chemokines are secreted both apically and basolaterally from the choroidal epithelium, a prerequisite for neutrophil migration across epithelial barriers. Consistent with these findings, we also provide electron microscopic evidence that neutrophils infiltrate the choroidal stroma and subsequently reach the intercellular space between choroidal epithelial cells. This is the first detailed analysis of the BCSFB function related to neutrophil trafficking. Our observations support the role of this barrier in posttraumatic neutrophil invasion.

Changes in cerebrospinal fluid nerve growth factor levels during chick embryonic development

In the early stages of brain development, cells within the ependymal lining of the neural tube are thought to secrete cerebrospinal fluid (CSF), the so-called neural tube fluid (NTF), whereas before fusion of the neural folds, the neuroepithelium that lines the inside of the neural tube is in contact with amniotic fluid. As the neural tube closes, a membrane formed from these cells invaginates to form the specialized choroid plexus. The choroid plexus is a highly vascularized epithelial cell structure that secretes proteins, including growth factors, into the CSF. Embryonic CSF (e-CSF) contains high concentrations of proteins compared to adult CSF. CSF has been reported to contain nerve growth factor (NGF) and other neurotrophic factors. In this study, total protein concentration and NGF level in e-CSF samples from chick embryos were measured using a dye-based protein assay, enzyme-linked immunosorbent assay (ELISA) and Western blot. The total protein concentration and NGF levels in the CSF decreased from days E10 to E16. There was a rapid increase in total protein content on days E17 and E18, and thereafter the levels decreased from day E19 to day E21. Days E17 and E18 coincide with the onset of neuron migration, proliferation and organization of the cytoarchitecture of the developing cerebral cortex. After that time the total protein concentration and NGF levels decrease until hatching. Since CSF is in contact with the cerebral cortical germinal epithelium, changes in the protein concentration in the CSF could affect neuroepithelial cell proliferation, survival and migration. It is concluded that NGF is not only a constant component of CSF during chick embryogenesis but it might also be involved in cerebral cortical development.

Sonic hedgehog signaling regulates a novel epithelial progenitor domain of the hindbrain choroid plexus

Choroid plexuses (ChPs) are vascularized secretory organs involved in the regulation of brain homeostasis, and function as the blood-cerebrospinal fluid (CSF) barrier. Despite their crucial roles, there is limited understanding of the regulatory mechanism driving ChP development. Sonic hedgehog (Shh), a secreted signal crucial for embryonic development and cancer, is strongly expressed in the differentiated hindbrain ChP epithelium (hChPe). However, we identify a distinct epithelial domain in the hChP that does not express Shh, but displays Shh signaling. We find that this distinct Shh target field that adjoins a germinal zone, the lower rhombic lip (LRL), functions as a progenitor domain by contributing directly to the hChPe. By conditional Shh mutant analysis, we show that Shh signaling regulates hChPe progenitor proliferation and hChPe expansion through late embryonic development, starting around E12.5. Whereas previous studies show that direct contribution to the hChPe by the LRL ceases around E14, our findings reveal a novel tissue-autonomous role for Shh production and signaling in driving the continual growth and expansion of the hindbrain choroid plexus throughout development.

Expression of EAAT-1 distinguishes choroid plexus tumors from normal and reactive choroid plexus epithelium

Microscopic distinction of normal choroid plexus (CP) from choroid plexus tumors (CPT) may be difficult, especially in small samples of well-differentiated CP papillomas. So far, there are no established markers that reliably distinguish normal and neoplastic CP epithelium. Recently, a correlation between expression/function of glial glutamate transporters EAAT-1 (GLAST) and EAAT-2 (Glt-1) and tumor proliferation has been reported. Furthermore, we previously found that CPTs frequently express EAAT-1, but not EAAT-2. We now compared expression of EAAT-1, EAAT-2 and GFAP in non-neoplastic CP (n = 68) and CPT (n = 79) by immunohistochemistry. Tissue of normal CP was obtained from 50 autopsy cases (20 normal and 30 pathologic brains) and 18 neurosurgical specimens that included 17 fetal, 21 pediatric and 30 adult cases. In non-neoplastic postnatal CP (n = 51), focal expression of EAAT-1 was found in only two pediatric cases (4%). In CPT, expression of EAAT-1 was found in 64 of 79 (81%) tumor samples and was significantly age-dependent (P < 0.0001). Hence, EAAT-1 expression distinguishes neoplastic from normal CP, both in children (P = 0.0032) and in adults (P < 0.0001). Immunostaining for EAAT-2 in selected samples from cases of different ages showed that normal CP (n = 15) or CPT (n = 16) lacked EAAT-2 expression. GFAP expression was found in 3 of 32 (10%) normal CP and in 28 of 73 (38%) tumor samples. In conclusion, in contrast to neoplastic CP samples, expression of EAAT-1 is exceptionally rare in non-neoplastic CP. Thus, EAAT-1 is superior to GFAP as a helpful diagnostic tool in CP samples.

Addressing a folate imbalance in fetal cerebrospinal fluid can decrease the incidence of congenital hydrocephalus

Fetal-onset hydrocephalus (HC), which affects between 1:500 and 1:5000 live human births, results from unequal production and drainage of cerebrospinal fluid (CSF) and is associated with abnormal development of the cerebral cortex leading to severe neurological deficits. We previously found that in the hydrocephalic Texas rat, the CSF of affected fetuses induced a cell cycle arrest in neural progenitor cells. Here, we show that alterations in folate metabolism in the CSF of the developing cerebrum are likely responsible for this effect. We identified 3 folate enzymes in the CSF and demonstrate that low levels of one of these, 10-formyltetrahydrofolate dehydrogenase, are associated with HC in the hydrocephalic Texas rat. Therefore, we tested whether supplementation with specific folate species would improve developmental outcome. After daily administration of a combination of tetrahydrofolic and 5-formyltetrahydrofolic acids to pregnant dams, there was a significant reduction in the incidence of HC and improved brain development. By contrast, supplementation with folic acid increased the incidence of congenital HC in this model. These results indicate the complexities of folate metabolism in the developing brain and suggest that folate imbalance leading to HC in the hydrocephalic Texas rat fetuses can be treated with maternal folate supplementation using specific folate metabolites and combinations thereof.

Fgf2 is expressed in human and murine embryonic choroid plexus and affects choroid plexus epithelial cell behaviour

Background

Although fibroblast growth factor (Fgf) signalling plays crucial roles in several developing and mature tissues, little information is currently available on expression of Fgf2 during early choroid plexus development and whether Fgf2 directly affects the behaviour of the choroid plexus epithelium (CPe). The purpose of this study was to investigate expression of Fgf2 in rodent and human developing CPe and possible function of Fgf2, using in vitro models. The application of Fgf2 to brain in vivo can affect the whole tissue, making it difficult to assess specific responses of the CPe.

Methods

Expression of Fgf2 was studied by immunohistochemistry in rodent and human embryonic choroid plexus. Effects of Fgf2 on growth, secretion, aggregation and gene expression was investigated using rodent CPe vesicles, a three-dimensional polarized culture model that closely mimics CPe properties in vivo, and rodent CPe monolayer cultures.

Results

Fgf2 was present early in development of the choroid plexus both in mouse and human, suggesting the importance of this ligand in Fgf signalling in the developing choroid plexus. Parallel analysis of Fgf2 expression and cell proliferation during CP development suggests that Fgf2 is not involved in CPe proliferation in vivo. Consistent with this observation is the failure of Fgf2 to increase proliferation in the tri-dimensional vesicle culture model. The CPe however, can respond to Fgf2 treatment, as the diameter of CPe vesicles is significantly increased by treatment with this growth factor. We show that this is due to an increase in cell aggregation during vesicle formation rather than increased secretion into the vesicle lumen. Finally, Fgf2 regulates expression of the CPe-associated transcription factors, Foxj1 and E2f5, whereas transthyretin, a marker of secretory activity, is not affected by Fgf2 treatment.

Conclusion

Fgf2 expression early in the development of both human and rodent choroid plexus, and its ability to modulate behaviour and gene expression in CPe, supports the view that Fgf signalling plays a role in the maintenance of integrity and function of this specialized epithelium, and that this role is conserved between rodents and humans.

In vivo analysis of choroid plexus morphogenesis in zebrafish

Background

The choroid plexus (ChP), a component of the blood-brain barrier (BBB), produces the cerebrospinal fluid (CSF) and as a result plays a role in (i) protecting and nurturing the brain as well as (ii) in coordinating neuronal migration during neurodevelopment. Until now ChP development was not analyzed in living vertebrates due to technical problems.

Methodology/Principal Findings

We have analyzed the formation of the fourth ventricle ChP of zebrafish in the GFP-tagged enhancer trap transgenic line SqET33-E20 (Gateways) by a combination of in vivo imaging, histology and mutant analysis. This process includes the formation of the tela choroidea (TC), the recruitment of cells from rhombic lips and, finally, the coalescence of TC resulting in formation of ChP. In Notch-deficient mib mutants the first phase of this process is affected with premature GFP expression, deficient cell recruitment into TC and abnormal patterning of ChP. In Hedgehog-deficient smu mutants the second phase of the ChP morphogenesis lacks cell recruitment and TC cells undergo apoptosis.

Conclusions/Significance

This study is the first to demonstrate the formation of ChP in vivo revealing a role of Notch and Hedgehog signalling pathways during different developmental phases of this process.