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

What We Should Know About the Cellular and Tissue Response Causing Catheter Obstruction in the Treatment of Hydrocephalus

The treatment of hydrocephalus by cerebrospinal fluid shunting is plagued by ventricular catheter obstruction. Shunts can become obstructed by cells originating from tissue normal to the brain or by pathological cells in the cerebrospinal fluid for a variety of reasons. In this review, the authors examine ventricular catheter obstruction and identify some of the modifications to the ventricular catheter that may alter the mechanical and chemical cues involved in obstruction, including alterations to the surgical strategy, modifications to the chemical surface of the catheter, and changes to the catheter architecture. It is likely a combination of catheter modifications that will improve the treatment of hydrocephalus by prolonging the life of ventricular catheters to improve patient outcome.

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.

Scanning electron microscopy of central nervous system cerebrospinal-fluid-contacting surfaces: a bibliography (1963-1995)

This bibliography is compiled to assist in locating papers related to the application of scanning electron microscopy (SEM) to cerebrospinal-fluid-contacting surfaces in vertebrates. The use of SEM by neuroscientists has continued apace since the publication of the first bibliography in 1980. SEM studies now include more than 50 species of vertebrates and range from cyclostomes to humans; they encompass development from embryo to senescence and concern both normal and pathologic morphology. Although remarkable strides have been made toward a greater understanding of many aspects of the structure and function of cerebrospinal-fluid-contacting surfaces, many significant problems await the judicious application of scanning electron microscopy.

Origin, nature, and some functional considerations of intraventricular macrophages, with special reference to the epiplexus cells

Intraventricular macrophages encompass the supraependymal, free-floating, and epiplexus (Kolmer) cells; the supraependymal cells lie in close apposition to the ventricular ependyma, the epiplexus cells are closely associated with the choroid plexus epithelium, and the free-floating cells are at a variable distance from the epithelial surface. Although the three cell types are regarded as one cellular entity, the epiplexus cells preponderate. On scanning electron microscopy, the epiplexus cells display diverse morphological forms, ranging from round to bipolar to stellate, and bear a variable number of cytoplasmic processes. Transmission electron microscopy shows the presence of large numbers of lysosomes. The phagocytic nature of epiplexus cells is shown by their intense staining for nonspecific esterase and active uptake of tracers, e.g., horseradish peroxidase and rhodamine isothiocynate, administered intravenously or intraperitoneally. The mode of entry of these tracers in the cerebral ventricles is by way of transepithelial transport. In rats, the population of intraventricular macrophages increases steadily after birth until 17 days of age; thereafter, their cell population remains relatively unchanged. The early upsurge is attributed to proliferation of residential cells and/or influx of circulating monocytes/stromal macrophages through the process of "emperipolesis." The immunophenotypic features of intraventricular macrophages are consistent with other mononuclear phagocytes being immunoreactive for OX-42, OX-18, OX-6, and OX-1 and ED1 for the detection of CR3 receptors, MHC class I and II antigens, leucocyte common antigen, and macrophage antigen, respectively. The expression of these antigens is noticeably enhanced following the injection of lipopolysaccharide (LPS) into postnatal rats. Remarkably, the intraventricular macrophages are induced to express MHC class II (Ia) antigen after LPS or interferon-gamma injections. Furthermore, the expression of transferrin receptors as detected with OX-26 is also upregulated after these treatments. Epiplexus cells are also elicited to display a de novo expression of nitric oxide synthase-like immunoreactivity following intracerebral injection of LPS. They also respond vigorously to a single nonpenetrative blast. Results of our series of studies suggest that, besides their primary function as scavenger cells, the intraventricular macrophages partake in possible immunological responses and iron regulation in the ventricular system or the brain as a whole.

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.

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.

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.

Cells resembling intraventricular macrophages are present in the subretinal space of human foetal eyes

The subretinal spaces (SRS) in 17 human foetal eyes were investigated by light microscopy and scanning and transmission electron microscopy. A hitherto undocumented group of pleomorphic cells was detected on the apical surface of the retinal pigment epithelium (RPE) and on the undersurface of the neural retina. These cells formed a regularly spaced array in the peripheral SRS, particularly in the most anterior portion nearest the ciliary body anlage. The morphology of the SRS cells ranged from a small round or ovoid form with a few short basal pseudopodia to an extremely flattened dendritic form. Ultrastructural features, such as large melanophagolysosomes, consistent with a phagocytic function, were observed in some cells. These SRS cells bore remarkable resemblance to epiplexus and supraependymal cells, considered to be the resident population of macrophages on the ventricular surfaces of the brain. This morphological parallelism, together with the anatomically homologous location, is strong evidence that SRS cells represent a normal population of macrophages in the developing human eye. No features consistent with an RPE or neuronal origin were observed. The possible role of these cells as transient phagocytes in the SRS with a possible destiny as retinal microglia is discussed.

Method for the identification of brain macrophages/phagocytic cells in vitro

The use of labelled latex beads, with acute incubation conditions, for the identification of active macrophages in mixed cell cultures based on their phagocytic activity is described. Fluorescent beads provided the best results and selectively labelled active macrophage cells in cultures of blood monocytes. When this technique was applied to primary cultures of rat cerebral cortex, a specific cell type was significantly labelled. This was a small round cell, previously uncharacterized, which in addition to phagocytic activity indicated by the ingestion of beads also possessed macrophage biochemical markers. Thus, the procedure appears useful for phagocytic macrophage identification in vitro, and should be generally applicable to any tissue culture system. Additionally, this procedure can be rendered compatible with cell viability and, therefore, be utilized for long-term monitoring of macrophages.

Immunological reactions induced by intracerebral transplantation: evidence that host microglia but not astroglia are the antigen-presenting cells

The immunological reactions to embryonic cerebellar xenografts (n = 16) and allografts (n = 8) in host rat brain were studied after 2, 4, and 6 weeks of survival and compared to a control group consisting of 10 rats with isografts. Indirect immunofluorescence was performed on fresh frozen brain sections using antibodies against antigen presenting cells (Ia/Ox-6+ cells) and T helper (W3/25+) cells. Massive infiltrations of both cell types were found within xenografts. Ia antigen was present in the walls of small vessels near the transplant as well as in the ventricles on supra- and subependymal cells. In host tissue surrounding the grafts, Ox-6+ immunoreactivity was also observed in a population of cells ranging from an irregular rod-like shape with short branching processes to more rounded cell bodies with retracted processes. The appearance of these cells was characteristic of microglia. These cells were GFAP-negative. These cellular reactions were associated with rejection of the grafts. In contrast, the allografts survived, but nevertheless cells expressing Ox-6+ and to a lesser extent W3/25+ immunoreactivity were found along the injection needle tract and in damaged host tissue surrounding the grafts. No Ox-6+ perivascular infiltrations were seen. Some staining was also found within the allografts, mainly associated with damaged tissue. Ox-6+ ramified cells were also observed. Both Ox-6+ and W3/25+ immunoreactivity decreased with the time of survival. Host and donor GFAP-positive astrocytes did not express Ox-6+ molecules, and therefore probably were not involved in presenting antigen to effector cells. The control isografts also survived very well, but nevertheless Ox-6+ and less widespread W3/25+ cells were present in surrounding injured host tissue. Ox-6+ perivascular infiltration was not found in the host brain of animals with isografts. Ox-6+ and W3/25+ immunoreactivities were present primarily in graft areas that appeared damaged, often closely associated with injured host tissue. These results indicate that the process of implantation of grafts and associated brain injury induces enhanced Ia/Ox-6+ immunoreactivity, primarily on microglia in brain parenchyma surrounding grafts, and suggest that host microglia may substantially contribute to the initiation of immune reactions against intracerebral grafts. Despite this predisposition to an immunological response, only in the case of xenografts did these reactions, with the addition of Ox-6+ perivascular cuffing and cell infiltrations within the grafts, lead ultimately to graft rejection.

Acute infusion of chemotactic or enkephalin-analog peptides into rat cerebral ventricles: scanning and transmission electron microscopy of leukocyte immigration in vivo

Acute infusions of the formylated chemotactic peptide formyl-methionyl-leucyl-phenylalanine-lysine (FMLPL) or enkephalin analogue (Sandoz peptide) were made to the lateral cerebral ventricle of adult male rats to examine potential cellular responses within the central nervous system (CNS). Ependymal regions lining the third ventricle atop the hypothalamus were examined using scanning and transmission electron microscopy. The formylated peptide induced a significant, primarily neutrophilic cellular response in animals sacrificed 1 h after infusion. Cells were observed within and external to neuropil blood capillaries, suggestive of emigration from vasculature in response to the peptide. In contrast, the enkephalin analogue did not induce any leukocyte cellular response within the same time frame. Earlier studies have shown a monocyte/macrophage response in the same setting to the opioid peptides beta-endorphin, and to a lesser extent, methionine enkephalin. The present findings suggest that a formylated peptide is a potent stimulus for neutrophil migration within a CNS site, while opioid peptides may be variable with respect to effectiveness on cells of the immune system within the CNS, depending upon chemical configuration.

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.

Fourth ventricular floor in human embryos: scanning electron microscopic observations

The ultrastructural surface features of the normal fourth ventricular floor of seven human embryos ranging from Carnegie stage 14 to stage 19 (crown-rump length: 7.6-16.2 mm) were examined by using scanning electron microscopy (SEM). Low-power SEM views showed the median sulcus, sulcus limitans, and neuromeres, transient structures characteristic of the earlier embryonic period. High-power SEM observation revealed supraependymal cells (SE cells) and supraependymal fibers (SE fibers) which exhibited a characteristic localization, as well as generalized surface-membrane modifications such as microvilli and cilia. SE cells could be classified into two major groups. The type 1 SE cells seem to possess neuronal functions, as deduced from morphological similarities to their counterparts in adults and the specialized distribution closely related to neuromeres. The type 2 SE cell morphologically resembled the phagocytic SE cell described in related literature. SE fibers ran a course either rostrocaudally in the median sulcus or mediolaterally on the neuromeres, most frequently near the interneuromeric cleft; they made contact with type 1 SE cells and ependymal surface modifications and then penetrated the ependymal layer.

Intraventricular neuronal complex of the lamina terminalis of the mouse

An intraventricular neuronal complex has been identified with scanning and transmission electron microscopy at the base of the lamina terminalis of the mouse. The raspberry-shaped complex protrudes from a thickened bulge on the ependymal surface of the lamina terminalis or adjacent rostral floor of the third ventricle. Neurons and occasional ependymal cells cover the surface of the complex. Its core is made up of neurons, ependymal cells, and neuronal processes, which are usually compactly arranged. The core is continuous, through a breach in the ependymal layers, with the subependymal neuropil of the lamina terminalis. Within the core of the complex are large numbers of axodendritic synapses. Axonal varicosities and synaptic terminals are filled with vesicles and mitochondria. Synaptic endings have one of two populations of vesicles: exclusively clear, small, round or flattened vesicles. In view of the known structural and functional characteristics of the lamina terminalis, it is possible that the neuronal complex may participate in neurohormonal regulatory systems of the hypothalamus and hypophysis or in the network of circumventricular organs mediating angiotensin effects.

Pathomorphology and pathogenesis of bacterial meningoventriculitis of neonatal ungulates

Bacterial meningoventriculitis was studied in 26 neonatal ungulates. Preceded by a substantial bacteremia, usually due to Escherichia coli, the fibrinopurulent inflammation involved leptomeninges, choroid plexuses, and ventricle walls, but largely spared the neuraxial parenchyma. It is proposed that this surface-relatedness results from the transport of bacteria by monocytes of low bactericidal power, migrating by normal pathways to maintain significant surface populations of macrophages. The neuraxial parenchyma is spared because of its normal lack of a macrophage population. A similar pathogenesis would hold for the frequent concurrent appearance of serositis and synovitis.

Chronic infusion of opiate peptides to rat cerebrospinal fluid with osmotic minipumps

Beta-endorphin-related opiate peptides or the opiate antagonist naloxone were chronically infused for periods of 24 to 48 hours to the lateral cerebral ventricle of adult male rats using Alza osmotic minipumps. Previous studies have suggested a "chemotactic"-like effect of opiate peptides for supraependymal macrophages in the region of the third ventricle of the brain. The present study demonstrates a stimulatory effect of beta-endorphin infusion on the appearance of lymphocyte and neutrophil-like cells, in addition to macrophages, in the region of the third ventricle, suggestive of an intracerebral inflammatory response. None of the other molecules, including alpha-endorphin, methionine-enkephalin, naloxone, or sterile saline produced similar cellular responses after infusion, although some of the latter substances may have induced the appearance of supraependymal neuron-like cells in the area. Observations suggest that the chronic presence of beta-endorphin, a biologically active opiate peptide, will interact with cells of the immune system, which have the ability to gain access to the cerebrospinal fluid.

Acute injections of opiate peptides into the rat cerebral ventricle: a macrophage-like cellular response

Opiate peptides (beta-endorphin, alpha-endorphin or met-enkephalin) were administered to the lateral cerebral ventricle of adult male rats via single injection into implanted cannulas. Scanning EM of the third ventricle above the median eminence of animals sacrificed approximately one hour after peptide injection revealed numerous free cells above the ependyma. Beta-endorphin induced a significantly greater cellular response than other peptides or control injections. Transmission EM demonstrated that the cells had morphologic characteristics of macrophages. Opiate peptides in cerebrospinal fluid may act as "chemotactic" factors to induce the migration of macrophage-like supraependymal cells.

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.

The immune system and the nervous system

The immune system may interfere with brain function. The central nervous system may also influence the activity of the immune system. The central nervous system is functionally protected by the blood-brain barrier. The central nervous system is functionally protected by the blood-brain barrier. The endothelial cells of the brain capillaries are linked by tight junctions, resulting in an almost continuous interior wall which restricts the transfer of plasma proteins. The barrier function is modified by inflammatory meningeal lesions, stroke and epileptic seizures. Antigenic material may penetrate the barrier and enter the nerve tissue. The phagocytic cells in the central nervous system are mainly of haematogenous origin. The number of such cells in the brain is very low. There are also few lymphocytes under normal circumstances. These cells circulate from the blood, through the vessel walls and into the perivascular spaces, along the perivascular channels and to the CSF and back to the blood. This circulation may increase enormously during inflammatory conditions. In multiple sclerosis, the number of T-lymphocytes in the CSF is increased, corresponding to a preponderance of T-lymphocytes in the perivascular cell infiltrates in and around the lesions. Thus, the individual elements of the immune system are all present in the brain, which is only partially immunologically privileged. The mechanisms underlying the brain's immunological privilege may be of a non-immunological nature. As yet there are only few data which indicate that auto-immunity is a prominent feature in diseases of the human brain. The central nervous system also exerts a modulating influence upon the immune response. This may take place both by secretion of hormones and by a nervous/neurotransmitter influence upon the immune system.

Third ventricle suprachoroidal cells

Using transmission electron microscopy two types of cells on the choroid plexus of the third ventricle of the frog Rana esculenta have been located. They lie on the microvilli and cilia of the choroid epithelium. Their free surface is in contact with the cerebrospinal fluid. One type, Kolmer-like, has large, dense bodies in its cytoplasm. The cytoplasm of the other type is completely filled by large, ovoidal structures which have a limiting membrane and a polymorphic filamentous content. Their functional significance is unknown.

Emergence of supraependymal cells in rat third ventricle after administration of p-chloroamphetamine

Administration of single or multiple 10 mg/kg doses of parachloroamphetamine hydrochloride, a serotonin-neurotoxic drug, to adult male rats, leads to emergence of clusters of supraependymal cells in the third ventricle above the median eminence. Transmission EM of specimens previously examined with scanning electron optics reveals that the cell clusters have characteristics of neurons. Two weeks after the initial drug injection, the ventricular surfaces of some animals lack the cell clusters, suggesting a "transience" in their appearance. The neuron-like elements may appear in response to alterations in brain serotonin levels, and their presence suggests an ability of adult nerve cells to migrate in response to chemical changes in neural tissue or cerebrospinal fluid.