Electron microscopic study of the epiplexus (Kolmer) cells of the cat choroid plexus

Border-associated macrophages as gatekeepers of brain homeostasis and immunity

The brain's border tissues serve as essential hubs for neuroimmune regulation and the trafficking of biomaterials to and from the brain. These complex tissues-including the meninges, perivascular spaces, choroid plexus, and circumventricular organs-balance the brain's need for immune privilege with immune surveillance and blood-brain communication. Macrophages are integral components of these tissues, taking up key strategic positions within the brain's circulatory system. These border-associated macrophages, or "BAMs," are therefore emerging as pivotal for brain homeostasis and disease. BAMs perform trophic functions that help to support border homeostasis but also act as immune sentinels essential for border defense. In this review, we integrate recent findings on BAM origins, cell states, and functions, aiming to provide global insights and perspectives on the complex relationship between these macrophages and their border niche.

Central Nervous System Macrophages in Health and Disease

The central nervous system (CNS) has a unique set of macrophages that seed the tissue early during embryonic development. Microglia reside in the parenchyma, and border-associated macrophages are present in border regions, including the meninges, perivascular spaces, and choroid plexus. CNS-resident macrophages support brain homeostasis during development and steady state. In the diseased brain, however, the immune landscape is altered, with phenotypic and transcriptional changes in resident macrophages and the invasion of blood-borne monocytes, which differentiate into monocyte-derived macrophages upon entering the CNS. In this review, we focus on the fate and function of the macrophage compartment in health, neurodegenerative conditions such as amyloidosis, and neuroinflammation as observed in multiple sclerosis and infection. We discuss our current understanding that monocyte-derived macrophages contribute to neuropathology whereas native macrophages play a neuroprotective role in disease.

Border-Associated Macrophages: From Embryogenesis to Immune Regulation

Border-associated macrophages (BAMs) play a pivotal role in maintaining brain homeostasis and responding to pathological conditions. Understanding their origins, characteristics, and roles in both healthy and diseased brains is crucial for advancing our knowledge of neuroinflammatory and neurodegenerative diseases. This review addresses the ontogeny, replenishment, microenvironmental regulation, and transcriptomic heterogeneity of BAMs, highlighting recent advancements in lineage tracing and fate-mapping studies. Furthermore, we examine the roles of BAMs in maintaining brain homeostasis, immune surveillance, and responses to injury and neurodegenerative diseases. Further research is crucial to clarify the dynamic interplay between BAMs and the brain's microenvironment in health and disease. This effort will not only resolve existing controversies but also reveal new therapeutic targets for neuroinflammatory and neurodegenerative disorders, pushing the boundaries of neuroscience.

Advances in Intrathecal Nanoparticle Delivery: Targeting the Blood-Cerebrospinal Fluid Barrier for Enhanced CNS Drug Delivery

The blood-cerebrospinal fluid barrier (BCSFB) tightly regulates molecular exchanges between the bloodstream and cerebrospinal fluid (CSF), creating challenges for effective central nervous system (CNS) drug delivery. This review assesses intrathecal (IT) nanoparticle (NP) delivery systems that aim to enhance drug delivery by circumventing the BCSFB, complementing approaches that target the blood-brain barrier (BBB). Active pharmaceutical ingredients (APIs) face hurdles like restricted CNS distribution and rapid clearance, which diminish the efficacy of IT therapies. NPs can be engineered to extend drug circulation times, improve CNS penetration, and facilitate sustained release. This review discusses key pharmacokinetic (PK) parameters essential for the effectiveness of these systems. NPs can quickly traverse the subarachnoid space and remain within the leptomeninges for extended periods, often exceeding three weeks. Some designs enable deeper brain parenchyma penetration. Approximately 80% of NPs in the CSF are cleared through the perivascular glymphatic pathway, with microglia-mediated transport significantly contributing to their paravascular clearance. This review synthesizes recent progress in IT-NP delivery across the BCSFB, highlighting critical findings, ongoing challenges, and the therapeutic potential of surface modifications and targeted delivery strategies.

The evolutionarily conserved choroid plexus contributes to the homeostasis of brain ventricles in zebrafish

The choroid plexus (ChP) produces cerebrospinal fluid (CSF). It also contributes to brain development and serves as the CSF-blood barrier. Prior studies have identified transporters on the epithelial cells that transport water and ions from the blood vasculature to the ventricles and tight junctions involved in the CSF-blood barrier. Yet, how the ChP epithelial cells control brain physiology remains unresolved. We use zebrafish to provide insights into the physiological roles of the ChP. Upon histological and transcriptomic analyses, we identify that the zebrafish ChP is conserved with mammals and expresses transporters involved in CSF secretion. Next, we show that the ChP epithelial cells secrete proteins into CSF. By ablating the ChP epithelial cells, we identify a reduction of the ventricular sizes without alterations of the CSF-blood barrier. Altogether, our findings reveal that the zebrafish ChP is conserved and contributes to the size and homeostasis of the brain ventricles.

The niche matters: origin, function and fate of CNS-associated macrophages during health and disease

There are several cellular and acellular structural barriers associated with the brain interfaces, which include the dura, the leptomeninges, the perivascular space and the choroid plexus epithelium. Each structure is enriched by distinct myeloid populations, which mainly originate from erythromyeloid precursors (EMP) in the embryonic yolk sac and seed the CNS during embryogenesis. However, depending on the precise microanatomical environment, resident myeloid cells differ in their marker profile, turnover and the extent to which they can be replenished by blood-derived cells. While some EMP-derived cells seed the parenchyma to become microglia, others engraft the meninges and become CNS-associated macrophages (CAMs), also referred to as border-associated macrophages (BAMs), e.g., leptomeningeal macrophages (MnMΦ). Recent data revealed that MnMΦ migrate into perivascular spaces postnatally where they differentiate into perivascular macrophages (PvMΦ). Under homeostatic conditions in pathogen-free mice, there is virtually no contribution of bone marrow-derived cells to MnMΦ and PvMΦ, but rather to macrophages of the choroid plexus and dura. In neuropathological conditions in which the blood-brain barrier is compromised, however, an influx of bone marrow-derived cells into the CNS can occur, potentially contributing to the pool of CNS myeloid cells. Simultaneously, resident CAMs may also proliferate and undergo transcriptional and proteomic changes, thereby, contributing to the disease outcome. Thus, both resident and infiltrating myeloid cells together act within their microenvironmental niche, but both populations play crucial roles in the overall disease course. Here, we summarize the current understanding of the sources and fates of resident CAMs in health and disease, and the role of the microenvironment in influencing their maintenance and function.

Effects of Ischemic Stroke on Interstitial Fluid Clearance in Mouse Brain: a Bead Study

The clearance of brain interstitial fluid (ISF) is important in maintaining brain homeostasis. ISF clearance impairment leads to toxic material accumulation in the brain, and ischemic stroke could impair ISF clearance. The present study investigates ISF clearance under normal and ischemic conditions. The carboxylate-modified FluoSpheres beads (0.04 μm in diameter) were injected into the striatum. Sham or transient middle cerebral artery occlusion surgeries were performed on the mice. The brain sections were immunostained with cell markers, and bead distribution at various time points was examined with a confocal microscope. Primary mouse neuronal cultures were incubated with the beads to explore in vitro endocytosis.  Two physiological routes for ISF clearance were identified. The main one was to the lateral ventricle (LV) through the cleft between the striatum and the corpus callosum (CC)/external capsule (EC), where some beads were captured by the ependymal macrophages and choroid plexus. An alternative and minor route was to the subarachnoid space through the CC/EC and the cortex, where some of the beads were endocytosed by neurons. After ischemic stroke, a significant decrease in the main route and an increase in the minor route were observed. Additionally, microglia/macrophages engulfed the beads in the infarction. In conclusion, we report that the physiological clearance of ISF and beads mainly passes through the cleft between the CC/EC and striatum into the LV, or alternatively through the cortex into the subarachnoid space. Stroke delays the main route but enhances the minor route, and microglia/macrophages engulf the beads in the infarction. Ischemic stroke impairs the clearance of brain interstitial fluid/beads. Under physiological conditions, the main route ( ① ) of interstitial fluid clearance is to the lateral ventricle, and the minor one ( ② ) is to the subarachnoid space. Ischemic stroke weakens the main route ( ① ), enhances the minor one ( ② ), and leads to microglial/macrophage phagocytosis within the infarction ( ③ ).

Effect of Systemic Inflammation in the CNS: A Silent History of Neuronal Damage

Central nervous system (CNS) infections including meningitis and encephalitis, resulting from the blood-borne spread of specific microorganisms, provoke nervous tissue damage due to the inflammatory process. Moreover, different pathologies such as sepsis can generate systemic inflammation. Bacterial lipopolysaccharide (LPS) induces the release of inflammatory mediators and damage molecules, which are then released into the bloodstream and can interact with structures such as the CNS, thus modifying the blood-brain barrier's (BBB´s) and blood-cerebrospinal fluid barrier´s (BCSFB´s) function and inducing aseptic neuroinflammation. During neuroinflammation, the participation of glial cells (astrocytes, microglia, and oligodendrocytes) plays an important role. They release cytokines, chemokines, reactive oxygen species, nitrogen species, peptides, and even excitatory amino acids that lead to neuronal damage. The neurons undergo morphological and functional changes that could initiate functional alterations to neurodegenerative processes. The present work aims to explain these processes and the pathophysiological interactions involved in CNS damage in the absence of microbes or inflammatory cells.

Uncovering mechanisms of brain inflammation in Alzheimer's disease with APOE4: Application of single cell-type lipidomics

A chronic state of unresolved inflammation in Alzheimer's disease (AD) is intrinsically involved with the remodeling of brain lipids. This review highlights the effect of carrying the apolipoprotein E ε4 allele (APOE4) on various brain cell types in promoting an unresolved inflammatory state. Among its pleotropic effects on brain lipids, we focus on APOE4's activation of Ca²⁺ -dependent phospholipase A2 (cPLA2) and its effects on arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid signaling cascades in the brain. During the process of neurodegeneration, various brain cell types, such as astrocytes, microglia, and neurons, together with the neurovascular unit, develop distinct inflammatory phenotypes that impact their functions and have characteristic lipidomic fingerprints. We propose that lipidomic phenotyping of single cell-types harvested from brains differing by age, sex, disease severity stage, and dietary and genetic backgrounds can be employed to probe mechanisms of neurodegeneration. A better understanding of the brain cellular inflammatory/lipidomic response promises to guide the development of nutritional and drug interventions for AD dementia.

The choroid plexus and its role in the pathogenesis of neurological infections

The choroid plexus is situated at an anatomically and functionally important interface within the ventricles of the brain, forming the blood-cerebrospinal fluid barrier that separates the periphery from the central nervous system. In contrast to the blood-brain barrier, the choroid plexus and its epithelial barrier have received considerably less attention. As the main producer of cerebrospinal fluid, the secretory functions of the epithelial cells aid in the maintenance of CNS homeostasis and are capable of relaying inflammatory signals to the brain. The choroid plexus acts as an immunological niche where several types of peripheral immune cells can be found within the stroma including dendritic cells, macrophages, and T cells. Including the epithelia cells, these cells perform immunosurveillance, detecting pathogens and changes in the cytokine milieu. As such, their activation leads to the release of homing molecules to induce chemotaxis of circulating immune cells, driving an immune response at the choroid plexus. Research into the barrier properties have shown how inflammation can alter the structural junctions and promote increased bidirectional transmigration of cells and pathogens. The goal of this review is to highlight our foundational knowledge of the choroid plexus and discuss how recent research has shifted our understanding towards viewing the choroid plexus as a highly dynamic and important contributor to the pathogenesis of neurological infections. With the emergence of several high-profile diseases, including ZIKA and SARS-CoV-2, this review provides a pertinent update on the cellular response of the choroid plexus to these diseases. Historically, pharmacological interventions of CNS disorders have proven difficult to develop, however, a greater focus on the role of the choroid plexus in driving these disorders would provide for novel targets and routes for therapeutics.

Cerebrospinal fluid production by the choroid plexus: a century of barrier research revisited

Cerebrospinal fluid (CSF) envelops the brain and fills the central ventricles. This fluid is continuously replenished by net fluid extraction from the vasculature by the secretory action of the choroid plexus epithelium residing in each of the four ventricles. We have known about these processes for more than a century, and yet the molecular mechanisms supporting this fluid secretion remain unresolved. The choroid plexus epithelium secretes its fluid in the absence of a trans-epithelial osmotic gradient, and, in addition, has an inherent ability to secrete CSF against an osmotic gradient. This paradoxical feature is shared with other 'leaky' epithelia. The assumptions underlying the classical standing gradient hypothesis await experimental support and appear to not suffice as an explanation of CSF secretion. Here, we suggest that the elusive local hyperosmotic compartment resides within the membrane transport proteins themselves. In this manner, the battery of plasma membrane transporters expressed in choroid plexus are proposed to sustain the choroidal CSF secretion independently of the prevailing bulk osmotic gradient.

Macrophage compartmentalization in the brain and cerebrospinal fluid system

Macrophages reside within the diverse anatomical compartments of the central nervous system (CNS). Within each compartment, these phagocytes are exposed to unique combinations of niche signals and mechanical stimuli that instruct their tissue-specific identities. Whereas most CNS macrophages are tissue-embedded, the macrophages of the cerebrospinal fluid (CSF) system are bathed in an oscillating liquid. Studies using multiomics technologies have recently uncovered the transcriptomic and proteomic profiles of CSF macrophages, enhancing our understanding of their cellular characteristics in both rodents and humans. Here, we review the relationships between CNS macrophage populations, with a focus on the origins, phenotypes, and functions of CSF macrophages in health and disease.

CNS macrophages differentially rely on an intronic Csf1r enhancer for their development

The central nervous system hosts parenchymal macrophages, known as microglia, and non-parenchymal macrophages, collectively termed border-associated macrophages (BAMs). Microglia, but not BAMs, were reported to be absent in mice lacking a conserved Csf1r enhancer: the fms-intronic regulatory element (FIRE). However, it is unknown whether FIRE deficiency also impacts BAM arrival and/or maintenance. Here, we show that macrophages in the ventricular system of the brain, including Kolmer's epiplexus macrophages, are absent in Csf1r^{ΔFIRE/ΔFIRE} mice. Stromal choroid plexus BAMs are also considerably reduced. During normal development, we demonstrate that intracerebroventricular macrophages arrive from embryonic day 10.5, and can traverse ventricular walls in embryonic slice cultures. In Csf1r^{ΔFIRE/ΔFIRE} embryos, the arrival of both primitive microglia and intracerebroventricular macrophages was eliminated, whereas the arrival of cephalic mesenchyme and stromal choroid plexus BAMs was only partially restricted. Our results provide new insights into the development and regulation of different CNS macrophage populations.

Summary: Deletion of the fms-intronic regulatory element of Csf1r in mouse disrupts the engraftment and maintenance of central nervous system macrophages in a compartment-specific manner.

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.

Hypercholesterolemia negatively influences morphology and molecular markers of epithelial cells within the choroid plexus in rabbits

Background

Choroid plexus (CP) is an important tissue not only to produce cerebrospinal fluid (CSF) but also to regulate substances that are secreted into or absorbed from CSF through blood–cerebrospinal fluid barrier (BCSFB) formed by CP epithelial cells (CPECs). CPECs display signs of deterioration in aged and diseased people. However, whether CPECs in hypercholesterolemic animals develop such damage is not known.

Methods

We used cholesterol-fed wild-type or Watanabe hereditary hyperlipidemic (WHHL) rabbits of identical age to determine CPEC changes in terms of morphology and protein expression/localization.

Results

Compared with non-cholesterol-fed control rabbits, prolonged exposure to cholesterol reduced CPEC height and increased lipofuscin levels in CPECs, indicating cellular damage. Expression of aquaporin 1 on the apical membranes of CPECs was diminished in cholesterol-exposed rabbits, implying a reduced CSF-producing function in the CP. The rabbit macrophage-specific antibody (RAM11) immunoreaction became positive in CPECs adjacent to foam cells, indicating an alteration in this cell type.

Conclusion

Cholesterol insults from the circulation (which is reflected by foam-cell accumulation in the CP) induce CPEC dysfunction, and the latter seems to be enhanced by foam cells in hypercholesterolemic rabbits.

Activation of epiplexus macrophages in hydrocephalus caused by subarachnoid hemorrhage and thrombin

Aims

We have found that hydrocephalus development in spontaneously hypertensive rats was associated with activation of epiplexus cells. The current study examined whether epiplexus cell activation occurs in a rat subarachnoid hemorrhage (SAH), whether activation would be greater in a subset of rats that developed hydrocephalus and the potential role of thrombin in epiplexus cell activation.

Methods

There were two parts in this study. First, an endovascular perforation was performed in rats to induce SAH. Second, rats received an intraventricular infusion of either thrombin or saline. Magnetic resonance imaging was used to measure the ventricular volumes. Immunofluorescence and immunohistochemistry were used to study epiplexus cell activation.

Results

Iba‐1, OX‐6, and CD68 were expressed in the epiplexus cells of the choroid plexus in sham‐operated rats. SAH increased Iba‐1 and CD68 immunoreactivity in epiplexus cells in addition to an increase in Iba‐1‐positive cell soma size. Those effects were greater in rats that developed hydrocephalus. Intraventricular thrombin mimicked the effects of SAH on epiplexus cell activation and hydrocephalus.

Conclusion

This study supports the concept that epiplexus cell activation is associated with hydrocephalus development. Epiplexus cell activation may be in response to thrombin production after hemorrhage, and it may be a therapeutic target.

Cytology of the Normal and Abnormal Choroid Plexi in Selected Domestic Mammals, Wildlife Species, and Man

A cytologic study of the choroid plexi of animals and humans was carried out using impression smears (imprints, imp) to understand better the cellular changes that occur in the cerebrospinal fluid in the case of disease. The samples, totaling 756 imp were from 11 dogs (239 imp), 10 horses (219 imp), 1 mule (23 imp), 3 cattle (69 imp), 1 sheep (19 imp), 2 pigs (39 imp), 1 deer (20 imp), 4 monkeys (22 imp), and 7 humans (106 imp). The samples came from individuals clinically free of neurologic disease, as well as from a few abnormal cases. Six of the 7 humans had no history of neurologic disease and had a complete necropsy with brain histopathology. The seventh human case had mild neurologic signs at the time of death and only a partial necropsy with histopathological examination of the brain, in which a few small leptomeningeal lymphocytic infiltrates and polymicrogyria were found. One of the human brains without neurologic disease had arteriosclerosis. In the 40 individuals studied, several features and some unique cell types were found, for which little or no information is available. Four different morphologic cell types were consistently found in all the species studied. The first 3 types were arbitrarily named alpha (with deeply basophilic cytoplasm), beta (with neutral to weakly acidophilic cytoplasm), and gamma or vesicle-bearing cells. The third type, gamma, was a cell bearing unique inclusions (vesicles) filled with many tiny light tan to pale pink granules. The fourth type was the Kolmer cell found in very low numbers. Immature lymphocytes were found in all of 3 newborn foals, in 1 pig, and in the only stillborn calf and deer studied. The results suggest that the choroid plexi contain more than 1 epithelial cell type and that knowledge of their morphology is far from complete because other unusual cells and structures are also present in small numbers. Imprints are excellent for studying the choroid plexi, especially for tiny changes that are too subtle to be seen in hematoxylin and eosin sections.

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.

Diversity in the surface morphology of adjacent epithelial cells of the choroid plexus: an ultrastructural analysis

It is generally known that the luminal surface of the choroidal epithelial cells is covered with a luxuriant coat of slender microvilli and cilia. However, extensive ultrastructural studies on the surface morphology of choroidal epithelial cells are lacking. This study, therefore, is focused on the detailed surface morphology of the choroid plexus of the lateral ventricle of adult Wistar rats using transmission and scanning electron microscopy. The animals were anesthetized, perfused with 0.9% oxygenated saline followed by 3% gluteraldehyde and the choroid plexus was processed for routine electron microscopy. The results of the ultrastructural observations presented in this study show that even the neighboring choroidal epithelial cells may express distinct morphology. In addition to the usually described morphology of choroidal epithelial cells, in this study, the presence of cells with uniform small blebs, crenulated or doughnut shaped structures, large mature blebs, or cells with an extensive network of fibers were observed. Although, dissimilar surface morphology of adjacent choroidal epithelial cells may indicate their distinct functional status, further studies are necessary to understand the physiological relevance of the varied surface morphology of choroidal epithelial cells.

[The choroid plexuses: a dynamic interface between the blood and the cerebrospinal fluid]

The choroid plexuses form one of the interfaces that control the brain microenvironment by regulating the exchanges between the blood and the central nervous system. They appear early during brain development. Originating from four different areas of the neural tube, they protrude into the ventricular system of the brain. The choroidal mechanisms involved in the control of brain homeostasis include the structural properties of the epithelial cells that restrict diffusional processes, as well as specific exchange and secretion mechanisms. In addition to the anatomical and histological organization of the choroidal tissue, this review describes the mechanism of cerebrospinal fluid secretion which is the most studied function of the choroid plexus. Experimental evidence for an implication of the choroid plexuses in neuroprotective mechanisms and in the supply of biologically active polypeptides to the brain are also reviewed.

Scanning electron microscopy study of the choroid plexus in the monkey (Cebus apella apella)

The cells of the choroid plexus of the lateral ventricles of the monkey Cebus apella apella were examined through scanning electron microscopy at contributing to the description of such structures in primates. The animals were anesthetized previously with 3% hypnol intraperitoneally and after perfusion with 2.5% glutaraldehyde, samples of the choroid plexus were collected after exhibition of the central portion and inferior horn of the lateral ventricles. The ventricular surface of those cells presents globose form as well as fine interlaced protrusions named microvilli. Among those, it is observed the presence of some cilia. Resting on the choroid epithelial cells there is a variable number of free cells, with fine prolongations which extend from them. They are probably macrophages and have been compared to Kolmer cells or epiplexus cells, located on choroid epithelium. The choroid plexus of the encephalic lateral ventricles of the monkey Cebus apella apella at scanning electron microscopy is similar to that of other primates, as well as to that of other species of mammals mainly cats and rats, and also humans.

Histochemical demonstration of nitric oxide synthase-like immunoreactivity in epiplexus cells and choroid epithelia in the lateral ventricles of postnatal rat brain induced by an intracerebral injection of lipopolysaccharide

The present in vivo study showed the expression of nitric oxide synthase-like immunoreactivity in epiplexus cells in the lateral ventricles induced by intracerebral injection of lipopolysaccharide into postnatal rats. Nitric oxide synthase-like immunoreactivity was vigorously expressed in epiplexus cells 1 and 3 days after the lipopolysaccharide injection, but by 7 days post-injection, it became undetectable. The expression of nitric oxide synthase-like immunoreactivity was also observed in some of the choroid epithelial cells. The nitric oxide synthase-like immunoreactivity in these cells appeared to be more intense in the ventricle ipsilateral to the LPS injection than that on the contralateral side. The immunostaining patterns of OX-42 and OX-6 for the detection of complement type 3 receptors and major histocompatibility complex class II antigens respectively paralleled that of anti-nitric oxide synthase, indicating that lipopolysaccharide-induced nitric oxide synthase-like immunoreactivity was primarily in epiplexus cells. Immunoelectron microscopy revealed that the nitric oxide synthase-like immunoprecipitate in epiplexus cells and choroid epithelial cells filled the entire cytoplasm and in some areas associated with the membranes of some of the organelles especially the mitochondria, suggesting that the enzyme is mainly cytosolic. It is speculated that nitric oxide synthase in these cells is involved in the synthesis of nitric oxide. The nitric oxide production, if any, through the enzymatic activity of nitric oxide synthase in epiplexus cells as well as the choroid epithelial cells may be involved in host defense against bacterial endotoxin in the ventricular system of postnatal rat brain.

Effects of dexamethasone on the epiplexus cells in postnatal rats

The epiplexus cells in postnatal rats were markedly reduced in number and immunoreactivity for OX-42, OX-18 and ED1 following subcutaneous injections of dexamethasone. This was especially evident in rats receiving two or three successive injections of dexamethasone and killed at the age of 4 or 7 days. At 14 and 21 days, the cells did not exhibit any striking difference from their corresponding controls in terms of cell number and immunoreactivity for the above antibodies. Occasional epiplexus cells were labelled with the antibody OX-6 in both groups of rats sacrificed at different time points. In rats receiving dexamethasone coupled with rhodamine isothiocyanate (RhIc), the epiplexus cells, though fewer in number than the corresponding controls, emitted bright fluorescence. It is concluded that the reduction of epiplexus cells following dexamethasone injections is due to the suppression of their precursor cells, i.e. monocytes. The phagocytic activity of the persisting epiplexus cells did not appear to be abolished by dexamethasone as evidenced by their uptake of RhIc. Our results suggest that the effects of dexamethasone are reversible.

Macrophage-lymphocyte cell clusters in the hypothalamic ventricle of some elasmobranch fish: ultrastructural analysis and possible functional significance

BACKGROUND

Previous studies have demonstrated the existence of lympho-haemopoietic tissue in the meninges and choroid plexuses of various primitive vertebrates, including the stingray Dasyatis akajei and in early human embryos. In the present study, we extend these results analyzing macrophage-lymphocyte cell clusters found in the floor of the hypothalamic ventricle of several specimens of elasmobranchs.

METHODS

After aseptical isolation of the brain from several specimens of smooth dogfish Triakis scyllia, cloudy dogfish Scyliorhinus torazame, gummy shark Mustelus manazo, and stingray Dasyatis akajei their hypothalamic regions were processed routinely by light, scanning, and transmission electron microscopy.

RESULTS

The study of serial histological sections demonstrated that the macrophage-lymphocyte cell clusters proceeded from the meningeal lymphohaemopoietic tissue, reaching the ventricular lumen along large blood vessels. In this tissue, macrophages, different sized lymphocytes, lymphoblasts, granulocytes, monocytes, and developing and mature plasma cells were closely packed among a meshwork of fibroblastic reticular cell processes. It never invaded the brain parenchyma. A cell layer of glial elements and a continuous basement membrane interposed between the lymphoid tissue and the neural elements although some macrophages had migrated across the ependymal cell layer. In the ventricular lumen very irregular macrophages with long cell processes and containing abundant engulfed material of unknown origin formed big cell clusters with neighboring lymphocytes, lymphoblasts, and plasma cells, similar to those described during the immune response. Moreover, electron lucent cells which resembled the antigen-presenting cells of higher vertebrates established intimate surface cell contacts with the surrounding lymphocytes. In the third ventricle of several specimens of gummy shark, Mustelus manazo, morphologically similar cell clusters appeared but these were not connected to the meningeal lympho-haemopoietic tissue. No intraventricular cell aggregates were found in the stingray brain.

CONCLUSIONS

Although we cannot rule out that these macrophage-lymphocyte cell clusters represent a permanent structure in the elasmobranch brain they rather seem to be only established after specific stimulation for preventing the entrance of noxious, foreign materials into the elasmobranch brain parenchyma.

Up-regulation of surface antigens on epiplexus cells in postnatal rats following intraperitoneal injections of lipopolysaccharide

Epiplexus cells in postnatal rats exhibited a remarkable up-regulation of major histocompatibility complex class I and II antigen expression after intraperitoneal administration of bacterial lipopolysaccharide; other surface antigens, i.e. complement type 3 receptors and leukocyte common antigens, were also vigorously elevated when compared with those of the corresponding control rats. The immunostaining of epiplexus cells with OX-42, OX-18 and OX-1 for the detection of complement type 3 receptors, major histocompatibility class I and leukocyte common antigens, respectively, was noticeably enhanced with a drastic increase in their numbers. The most significant finding was the upsurge of OX-6-positive epiplexus cells exhibiting major histocompatibility class II antigens, especially in rats receiving two intraperitoneal injections of lipopolysaccharide and killed at the age of 14 days. Immunoelectron microscopy confirmed the above findings and added the fact that the immunoreactive site was confined to the plasma membrane. An interesting feature was the occurrence of OX-6-positive macrophage-like cells in transit across the choroid epithelium. It is concluded from this study that the upsurge of immunopositive epiplexus cells after lipopolysaccharide injections was partly attributed to the infiltration of stromal macrophages which migrated across the epithelium. The up-regulation of major histocompatibility complex class I and II antigen expression on epiplexus cells by lipopolysaccharide would enable them to carry out self-recognizing and antigen-presenting function in the ventricular system.

Transitory disappearance of microglia during the regeneration of the lizard medial cortex

In normal lizards, microglial cells populate the medial cortex (a zone homologous to the hippocampal fascia dentata), with a preferential distribution along the border between the granular cell layer and the plexiform layers. Intraperitoneal injection of the neurotoxin 3-acetylpyridine (3AP) induces a selective lesion in the medial cortex with a rapid degeneration of the granular layer and its zinc-enriched axonal projection. Within 6-8 weeks, the granular layer is, however, repopulated by a new set of neurons generated in the subjacent ependyma and the cell debris is removed. The aim of this study was to determine to what extent microglia were involved in the scavenging processes during the regeneration process. To this end we studied the brains of regenerating lizards at different times after 3AP lesion, visualising microglial cells by the nucleoside diphosphatase (NDPase) histochemical reaction. Surprisingly, we found that stained microglial cells disappeared 6-8 hours after 3AP injection and remained absent until 10-15 days after injection. One month postlesion an increased population of microglial cells was found scattered throughout all plexiform layers of the cortex. Thorough examination of semithin and ultrathin sections confirmed the absence of microglia in the medial cortex of recent lesioned animals but the presence of an exuberant population after 1 month postlesion. In the tissue, phagocytotic scavenging was carried out by radial ependymocytes, not by microglia.

A scanning and transmission electron microscopic analysis of the cerebral aqueduct in the rabbit

An examination of the surface of the cerebral aqueduct with the scanning electron microscope revealed that the walls of the cerebral aqueduct were so heavily ciliated that most of the ependymal surface was obscured, yet certain specialized supraependymal structures could be discerned lying on (or embedded within) this matt of cilia. These structures were determined by transmission electron microscopy and Golgi analysis to be either macrophages, supraependymal neurons, dendrites from medial periaqueductal gray neurons, or axons of unknown origin. Some axons, which were found to contain vesicles, appeared to make synaptic contacts with ependymal cells. Using the transmission electron microscope, the ependymal lining was found to consist of two different cell types: normal ependymal cells and tanycytes which have a long tapering basal process that was observed to contact blood vessels or, more rarely, seemed to terminate in relation to neuronal elements. While there have been previous reports on the structure of the third and lateral ventricles in other species, there are limited reports in the rabbit. The present report is not only the first description for the rabbit, but it is the first complete scanning and transmission electron microscopic analysis of the cerebral aqueduct in any species.

Cellular components of the immune barrier in the spinal meninges and dorsal root ganglia of the normal rat: immunohistochemical (MHC class II) and electron-microscopic observations

This report deals with the distribution, morphology and specific topical relationships of bone-marrow-derived cells (free cells) in the spinal meninges and dorsal root ganglia of the normal rat. The morphology of these cells has been studied by transmission and scanning electron microscopy. Cells expressing the major histocompatibility complex (MHC) class II gene product have been recognized by immunofluorescence. At the level of the transmission electron microscope, free cells are found in all layers of the meninges. Many of them display characteristic ultrastructural features of macrophages, whereas others show a highly vacuolated cytoplasm and are endowed with many processes. These elements lack a conspicuous lysosomal system and might represent dendritic cells. Scanning electron microscopy has revealed that free cells contact the cerebrospinal fluid via abundant cytoplasmic processes that cross the cell layers of the pia mater and of the arachnoid. Cells expressing the MHC class II antigen are also found in all layers of the meninges. They are particularly abundant in the layers immediately adjacent to the subarachnoid space, in the neighbourhood of dural vessels, along the spinal roots and in the dural funnels. In addition to the meninges, strong immunoreactivity for MHC class II antigen is observed in the dorsal root ganglia. The ultrastructural and immunohistochemical findings of this study suggest the existence of a well-developed system of immunological surveillance of the subarachnoid space and of the dorsal root ganglia.

Stromal macrophages of the choroid plexus situated at an interface between the brain and peripheral immune system constitutively express major histocompatibility class II antigens

Using immunocytochemistry we have shown that there is a population of macrophages within the stroma of the choroid plexus of rats and mice which expresses high levels of major histocompatibility complex Class II antigens. In whole mount preparations of the choroid plexus, the morphology and regular distribution of these cells is similar to the Langerhans cells of the skin. These cells reside at an important interface between the central nervous system and the peripheral immune system and their possible role in immune-mediated diseases of the central nervous system is discussed.

Changes in the choroid plexus, responses by intrinsic epiplexus cells and recruitment from monocytes after experimental head acceleration injury in the non-human primate

We have examined, by scanning and transmission electron microscopy, morphological changes in the choroid plexus of the lateral ventricles of the non-human primate brain after lateral head acceleration. We demonstrate passage of plasma and blood cells either through tears in blood vessels and the choroidal epithelium, or through the cells of the choroidal epithelium, 20 min after injury, together with morphological changes in that epithelium. At 3 and 4 h small cells with a reniform nucleus accumulate in the connective tissue core of the choroid plexus. We suggest that these are monocytes. At 6 and 12 h cells can be seen in enlarged intercellular spaces within the choroidal epithelium. These cells possess surface ruffles and we suggest that they are monocytes differentiating into macrophages and epiplexus cells. Further evidence for transepithelial migration of monocytes/macrophages is obtained at 7 days. However, at 28 days all blood has been removed from the surface of the choroid plexus and epiplexus cells possess an appearance typical of that in uninjured animals. The possible sources of epiplexus cells are discussed with reference to studies of responses after brain insult and of development. We have obtained no evidence in support of emperipolesis by monocytes through the choroidal epithelium. We suggest that monocytes/macrophages migrate, via an intercellular route, to differentiate into epiplexus cells, thus providing additional numbers of epiplexus cells after head injury.

Monocyte-mediated entry of pathogens into the central nervous system

The origin of the microglia has long been a subject of debate. However it is now clear that monocytes enter the normal central nervous system and follow a series of morphological transformations as they differentiate into microglia. Thus, microglia are of monocytic origin. Since monocytes migrate into the normal CNS, they represent potential vehicles for the entry of pathogens into the nervous system and indeed may carry particulate matter into the CNS. Both viruses and bacteria use this 'Trojan horse' mechanism of entry in the pathogenesis of CNS disease.

Pathomorphological changes in rat brain choroid plexus due to administration of the amine-curing agent, bis(4-amino-3-methylcyclohexyl)methane

Repeated oral administration of an amine-curing agent for epoxy resin, bis(4-amino-3-methylcyclohexyl)methane, gave rise to severe damage in the choroid plexus of rat brain. The damaged epithelium presented varying degrees of swelling and hydropic vacuolation on light microscopy, and varying numbers of vacuoles and inclusion bodies, frequently with lamellar structure, on transmission electron microscopy. Scanning electron microscopy of the choroid plexus disclosed some irregularity in the size of epithelial cells and occasional loss of microvilli. These changes in the choroid plexus were closely correlated with the dosage of the agent administered and the period of administration. In spite of the severe changes in the choroid plexus, no neurological abnormalities were observed in the animals during the experimental period.

An experimental and ultrastructural study on the development of the avian choroid plexus

The choroid plexus consists of the choroidal epithelium, a derivative of the neural tube, and the choroidal stroma, which originates from the embryonic head mesenchyme. This study deals with epithelio-mesenchymal interactions of these two components leading to the formation of the organ. Grafting experiments of the prospective components have been performed using the quail-chicken marker technique. Prospective choroidal epithelium of quail embryos, forced to interact with mesenchyme of the body wall of chicken embryos, gives rise to a choroid plexus showing normal morphogenesis and differentiation. The choroidal epithelium induces the differentiation of organ-typical fenestrated capillaries, which are highly permeable to intravenously injected horseradish peroxidase. The choroidal epithelium of the grafts constitutes a blood-cerebrospinal fluid barrier. On top of the choroidal epithelium, there are epiplexus cells displaying a typical ultrastructure. The experimental results show that these cells do not originate from the transplanted neural epithelium. Prospective choroidal stroma of chicken embryos does not exert a choroid plexus-inducing influence upon a quail embryo's neural epithelium isolated from parts of the brain that normally do not develop a choroid plexus. The experiments show that the choroidal epithelial cells are determined at least three days before the first organ anlage is detectable.

Brain macrophages: questions of origin and interrelationship

Brain tissue appears to contain several distinct types of macrophages. An effort is made here to present a description of the complete cohort of macrophages and sources of phagocytic activity in this tissue. Initially, the criteria and methods used for the identification of tissue macrophages in general are considered. These include some morphological and ultrastructural features, assessment of phagocytic activity, and histochemistry for intracellular and surface components. Each of these methods or criteria has certain advantages but also associated problems and limitations; all have been applied in various instances to brain tissue. In a final analysis, the most reliable means of identification of tissue macrophages involves a combination of all of these approaches. The identification and characterization of macrophages have been rendered extremely confusing in the brain because of so many different sources of these cells, both intrinsic and blood-derived. The classes of macrophages or phagocytic cells in brain tissue are microglia, supraependymal cells, epiplexus cells, meningeal macrophages, pericytes, and direct blood-derived macrophages. The morphology, location, and functional properties of each of these classes is described. In an overall view, brain tissue is very well protected by intrinsic macrophages, and the locations and distribution of these cells are consistent with other tissues. Finally, in a consideration of origin and interrelationship, the idea is presented that the most likely source for all or most brain macrophages is monocytic blood cells. The latter cells appear to migrate into the tissue from several sites during embryogenesis and may continue to enter, at least from blood vessels, in the adult state.

A scanning electron-microscopic study of "supramarginal cells" in the pituitary cleft of the rat

Unusual cells lying above the marginal cellular layer of the rat pituitary cleft were studied by SEM and TEM. These cells - from their location termed supramarginal cells - have a characteristically irregular cell body from which arise a number of long and thin branched processes ending among the microvilli and cilia of the marginal cells delimiting the anterior and posterior walls of the cleft. Some supramarginal cells are star-shaped elements with thin extensions, others have a triangular or spindle-shaped body from which emerge long ameboid processes with fibril-like projections. Miniblebs, miniruffles, occasional veils and short microvilli extend over the surface of these elements. Supramarginal cells are very similar to the "Kolmer epiplexus cells" originally found on the choroid plexus or other areas of the third ventricular wall where they are known as "supraependymal cells". Present evidence suggests that supramarginal cells of pituitary cleft might have phagocytic properties and an hematogenous origin as monocytes and, as such, closely resemble Kolmer epiplexus cells of brain ventricles. Others might arise from "folliculo-stellate cells" or closely related marginal cells once they become free into the pituitary cleft. Supramarginal cells are recognized as motile phagocytes acting as scavengers and possibly regulating the extracellular environment of the cleft and associated adenohypophysial tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Scanning electron microscopy of the subarachnoid space in the dog: inflammatory response after injection of defibrinated chicken erythrocytes

The leptomeningeal reaction and the cerebrospinal fluid reaction of the canine inflammatory response were investigated concurrently. One-half milliliter cerebrospinal fluid (CSF) was withdrawn from the cisterna magna of 17 anesthetized mongrel dogs and analyzed. Using this same spinal tap, control and experimental animals were injected with 0.5 ml sterile saline and 0.5 ml defibrinated chicken erythrocytes, respectively. A second spinal tap was performed 2 to 168 hr later. The CSF from the first spinal tap contained less than 1 WBC/mm3. The cell population was unchanged in the second spinal tap of control animals. In experimental animals, the WBC population increased more than 100-fold by 24 hr. Polymorphonuclear cells (PMNs) appeared in the CSF first, followed by lymphocytes and monocytes. Injected erythrocytes seemed trapped in the subarachnoid space (SAS), especially in the inner sheet of the arachnoid mater. The leptomeninges had a substantial increase in free cells without fibrosis. Pial and leptomeningeal cells of the arachnoid trabeculae appeared swollen. Two hours after injection, chicken erythrocytes were phagocytosed by pial cells, macrophages, and free cells adherent to the leptomeninges. The epiplexus cell populations for saline-control and erythrocyte-experimental animals were similar, suggesting that the choroid plexuses were not a gateway for PMN, lymphocyte, or monocyte infusion into the SAS.

Immunohistochemical localization of macrophages and microglia in the adult and developing mouse brain

Macrophages and microglia in the developing and adult mouse brain have been identified by immunohistochemical localization of the macrophage-specific antigen F4/80 and monoclonal antibodies to the FcIgG1/2b (2.4G2) and type-three complement (Mac-1) receptors. In the adult mouse there are two classes of F4/80-positive cells; those associated with the choroid plexus, ventricles and leptomeninges and the microglia. The cells bearing Fc and complement receptors are indistinguishable, by their morphology and distribution, from those revealed by F4/80. During development macrophages invade the brain and can be followed through a series of transitional forms as they differentiate to become microglia. Macrophage invasion occurs when naturally dying cells are observed in large numbers and this is consistent with the idea that dying neurons and axons provide a stimulus for macrophage infiltration. Our results provide strong support for the hypothesis that the microglia are derived from monocytes and show that microglia possess receptors which would allow them to play a part in the immune defence of the nervous system.

Supramarginal cells in the rat pituitary cleft revealed by scanning electron microscopy

An unusual cell type consisting of free elements widely scattered over the marginal epithelium of the rat pituitary cleft is revealed by SEM. Most of these supramarginal cells characteristically have irregularly shaped cell bodies from which thin branched processes extend. Supramarginal cells bear resemblances to Kolmer (epiplexus) cells and to supraependymal cells of the brain ventricles. Their ultrastructural features make it probable that supramarginal cells are phagocytes, and can be regarded as scavengers of the cleft. Considering the close topographical association between the hypophysial cleft and the floor or the 3rd ventricle, supramarginal cells may be members of the motile macrophagic Kolmer cells populating the ventricular surfaces of the brain.

The mononuclear phagocyte system of the mouse defined by immunohistochemical localisation of antigen F4/80: macrophages associated with epithelia

The tissue distribution of the murine macrophage-specific antigen F4/80 has been analysed using an immunohistochemical technique. The antigen is observed on all known macrophage populations (including Kupffer cells and bronchoalveolar macrophages) and is absent from any cell types that are definitely not mononuclear phagocytes. Microglial cells from brain express F4/80. F4/80+ macrophages observed associated with epithelia can be divided into two categories, intraepithelial and periepithelial. The former includes epidermal Langerhans cells and cells with similar morphology in other stratified squamous epithelia (cervix, oesophagus), pseudostratified epithelium (trachea), transitional epithelium of urinary bladder, and simple epithelia lining various ducts (salivary gland, common bile duct, tracheobronchial gland). Periepithelial F4/80+ cells, apparently spread immediately below the basal lamina, are associated with simple epithelia throughout the gastrointestinal, respiratory, and male and female reproductive tract as well as the brain ependyma. A major class of periepithelial F4/80+ cells is associated with capillaries throughout the microcirulation. The role of these macrophage populations in control of epithelial function is discussed.

Supraependymal cell clusters in the rat hypothalamus

The fine structure of supraependymal cell clusters of the median eminence was studied with TEM. The cluster cells were identified on the basis of ultrastructure and histochemical determination of glial fibrillar acidic protein (GFA). The phagocytic properties were also studied by means of intraventricular injections of HRP. Neurons, neuroglia cells and degenerating ependyma- and glial cells were found. The extrusion of degenerating infundibular elements into the ventricle is a constant phenomenon but its precise localization and intensity are variable. The close proximity of the clusters to capillary loops is stressed. Because of the broken ependyma at the neck of the cluster, the permeability of the infundibular lining for HRP is increased. Clusters may be seen as sites lacking a brain--CSF barrier.

Regional surface changes during the development of the telencephalic choroid plexus in the chick. A scanning-electron microscopic study

The surface morphology of the developing chick telencephalic choroid plexus (TCP) was examined by scanning electron and light microscopy. A blunt evagination develops rostro-cranially to the foramen of Monro on the medial telencephalic septum. The pseudostratified TCP epithelium differs in its surface morphology from that of the surrounding ependyma. Subsequently the TCP becomes elongated and branches. On the 9th embryonic day (ED) the pseudostratified epithelium progressively becomes high columnar epithelium in a distal to proximal direction along the branches of the TCP. The apical poles of the high columnar epithelial cells protrude into the ventricular lumen. Later, additional branches sprout at the base of the TCP, which then resembles a tree with a bush growing at its roots. Before the time of hatching, the high columnar epithelium changes to low columnar epithelium again in a distal to proximal direction. The surface of the TCP becomes flatter, in the process of which the number of cilia per unit surface area is reduced. On the developing TCP the epiplexus cells vary in shape, depending upon their functional state. It is proposed that not only the morphological but also the functional differentiation of the TCP proceeds in a distal to proximal direction along the branches of the choroid plexus. The surface differentiation of the TCP has a more regular character than that of the diencephalic CP (DCP), described previously, which seems to be influenced in its development by other anatomical structures.

Morphological changes in the hypothalamic arcuate nucleus and median eminence in the golden hamster during the neonatal period

The purpose of the present investigation was to study the ultrastructure of the arcuate nucleus (ARC) and median eminence of hamsters on days 1-15 of the neonatal period. From days 1-6, the neurons of the ARC had large nuclei and a small amount of cytoplasm which contained polysomes, mitochondria, RER, lysosomes and Golgi complexes. From days 7-15 there was an increase in the amount of cytoplasm as well as more extensive Golgi complexes and RER. Astrocytes were the predominant glial component in both the ARC and median eminence. Astrocytic processes were in juxtaposition to unmyelinated axons, dendrites, and synapses. Axodendritic and axosomatic synapses containing clear vesicles were observed in the neuropil on day 1. There was an increase in the number of dense-core vesicles in the axonal endings beginning on day 4. Concomitantly, there were increasing numbers of clear and dense-core vesicles (64-70 nm) in terminals of the external layer of the median eminence, whereas larger dense-core vesicles (105-140 nm) were distinguishable by day 10 immediately dorsal to the external layer. The capillaries of the median eminence were composed of nonfenestrated endothelium from days 1-9. Fenestrae began to appear about day 10. Ependymal cells lining the third ventricle had pinocytotic vesicles, microvilli, and bleb-like protrusions on their apical surfaces. Ependymal processes were adjacent to nerve processes in the neuropil of the ARC and in the external layer of the median eminence, where they contacted the perivascular space. Two types of supraependymal cells were seen in animals throughout the neonatal period. One resembled a neuron which sent processes along the ependymal surface and often between cells. The second type was similar to a macrophage. The results of this study demonstrate the maturation of the neural elements in the ARC/median eminence area of the neonatal hamster.

Prepontine epithelium-lined cyst. Case report

A 30-year-old woman presented with recurrent episodes of severe headache associated with visual disturbances. Neurological examination showed minimal neurological defects. Angiography, computerized tomography, and radioisotope cisternography revealed a large cyst in the prepontine region, which did not communicate with either the subarachnoid space or the ventricular system. Histologically, the cyst was lined by columnar and/or cuboidal cells, which contained materials positive on periodic acid-Schiff staining. Ultrastructurally, there were two types of cells, ciliated and noncillated. Characteristic findings were continuous basement membrane, microvilli covered with electron-dense material, several intercellular junctional devices, and an open intercellular space which was occasionally filled with a migrating cell. These findings would support the view that the epithelial cyst with such features was derived from endodermal tissues rather than from neuroepithelium. Electron microscopic examination is indispensable in making a correct diagnosis of intracranial cysts.

The disposition of intraventricularly injected 14C-5,6-DHT-melanin in, and possible routes of elimination from the rat CNS. An autoradiographic study

14C-5,6-DHT-Melanin was injected into the left lateral ventricle of adult rats and its fate followed by light and EM autoradiography and by TEM of structures identified as labeled in preceding light micrographs. Shortly after injection, melanin particles were seen ingested by supraependymal and epiplexus cells, by cells residing in the pia-arachnoid, i.e. free subarachnoidal cells and perivascular cells, and by subependymally located microglia-like cells with intraventricular processes. Up to day four, an increase in the number of labelled phagocytes in the CSF was noted which transformed into typical reactive macrophages. After this time, many intraventricular melanin-laden phagocytes formed rounded clusters; cells of such clusters were subsequently found to invade the brain parenchyma by penetrating the ependymal lining and to accumulate in the perivascular space of brain vessels. 14C-Melanin-storing macrophages were found in the marginal sinus of the deep jugular lymph nodes suggesting emigration of CNS-derived phagocytes via lymphatics or pre-lymphatics that contact the subarachnoidal space compartment. This does not exclude the possibility that some of the macrophages leave the brain via the systemic circulation by penetrating the vascular endothelium; these may be disposed of in peripheral organs other than the lymph nodes. The ability of supraependymal, epiplexus, free subarachnoidal and perivascular cells in the pia and of subependymal microglia cells to accumulate synthetic melanin by phagocytosis suggests that these cells are local variants of the same type of resting potential phagocytes of the mammalian brain. The present study shows that 14C-5,6-DHT-melanin is an ideal phagocytic stimulant and marker for phagocytosis.

Prenatal and early postnatal development of the glial cells in the median eminence of the rat

The development of the glial cells of the rat median eminence (ME), including the supraependymal cells, was investigated from embryonic day (ED) 14 through postnatal day (PD) 7, and pituicyte development from ED 12 through ED 17. The anlage of the ME and neurohypophysis shows a neuroepithelial-like structure at ED 12. From ED 13 to 15, the cells of both regions start to differentiate. At the ultrastructural level, only one cell type appears. At the beginning of ED 16, glioblasts of the oligodendrocyte and astrocyte series migrate laterally (from the region of the arcuate nucleus) into the ME. Also at this time the first distinctive structural features appear in the neurohypophysial anlage, the cells of which later develop into pituicytes. Starting at ED 18, tanycytes and astrocytic tanycytes arise in the ME from local glial cells, and somewhat later oligodendroblasts and astroblasts are formed from immigrant glioblasts. Due to their common features, the pituicytes, tanycytes and astrocytic tanycytes apparently represent different forms of the same parent cell type. Microglial and supraependymal cells are first seen at ED 12. Initially, they resemble the prenatal phagocytic connective tissue cells and mature in fetus into typical electron-dense microglia and macrophage-like supraependymal cells. Both cell types are apparently of mesodermal origin. The microglial elements of the ME probably migrate from the mesenchyma through the basement into the nervous tissue. The intraventricular macrophages of the infundibular region may originate from microglia, epiplexal cells and subarachnoid macrophages.

Proliferation of epithelial cells in the adult primate choroid plexus

An adult rhesus monkey was injected intraperitoneally with [H3] thymidine (2.3 microCi/gram body weight) and perfused 90 minutes later with a mixture of aldehydes. One and a half micrometer plastic sections were then cut and dipped into liquid emulsion for radioautography. Labeled cells were observed in the choroid plexus of the anterior lateral ventricle; cell identification was evaluated using electron micrographs taken from serial thin sections of re-embedded. radioautographic 1.5-micron sections. The ultrastructure and location of both mitotic figures and labeled cells confirmed the presence of undifferentiated basal choroid plexus epithelial cells in the adult primate central nervous system.

Supraependymal macrophages of third ventricle of hamster: morphological, functional and histochemical characterization in situ and in culture

Supraependymal cells (SECs) of the young hamster's third ventricle have been examined by scanning and transmission electron microscopy. Of special interest were cells with the surface morphology and ultrastructure of macrophages, which were found in largest numbers in 12--15-day-old females and males. In the ciliated areas SECs are generally smooth and rounded; in nonciliated areas, they frequently have surface ruffles, blebs and microprocesses. SECs were frequently seen to be dividing or fusing. The macrophage-like cells are characterized by prominent Golgi zones and numerous large vacuoles, and frequently contain inclusions in their cytoplasm which resemble intraventricular cell processes, cytoplasmic protrusions from ependymal cells and cellular debris. We have demonstrated that supraependymal macrophage-like cells phagocytose latex beads injected into the ventricles of the brain. Supraependymal cells from 12-day-old hamsters were grown in tissue culture. Phagocytic, cytochemical and surface ultrastructural studies were then done sequentially on the same population of cells. These studies revealed the cells to be actively phagocytic as well as strongly esterase positive and peroxidase negative, consistent with their classification in the macrophage/monocyte category. The surface ruffles, ridges and microprocesses were also characteristic of the SECs seen in situ with scanning electron microscopy and of the macrophages cultured from the peritoneum and peripheral blood of the same hamsters. On the basis of cellular morphology, cytochemical staining characteristics and functional response to exposure to foreign particles both in situ and in cell culture, we have demonstrated that supraependymal cells of the third ventricle of the hamster are phagocytes that resemble cells of the macrophage/monocyte line. It is suggested that they constitute a resident macrophage system of the ventricles of the brain.