A scanning electron microscopic study of the ependymal surface of the third ventricle of the rabbit, rat, mouse and human brain

History of research concerning the ependyma: a view from inside the human brain

The history of research concerning ependymal cells is reviewed. Cilia were identified along the surface of the cerebral ventricles c1835. Numerous anatomical and histopathological studies in the late 1800's showed irregularities in the ependymal surface that were thought to be indicative of specific pathologies such as syphilis; this was subsequently disproven. The evolution of thoughts about functions of cilia, the possible role of ependyma in the brain-cerebrospinal fluid barrier, and the relationship of ependyma to the subventricular zone germinal cells is discussed. How advances in light and electron microscopy and cell culture contributed to our understanding of the ependyma is described. Discoveries of the supraependymal serotoninergic axon network and supraependymal macrophages are recounted. Finally, the consequences of loss of ependymal cells from different regions of the central nervous system are considered.

The Unrestrained Overeating Behavior and Clinical Perspective

Obesity-related co-morbidities decrease life quality, reduce working ability, and lead to early death. In the adult population, eating addiction manifests with excessive food consumption and the unrestrained overeating behavior, which is associated with increased risk of morbidity and mortality and defined as the binge eating disorder (BED). This hedonic intake is correlated with fat preference and the total amount of dietary fat consumption is the most potent risk factor for weight gain. Long-term BED leads to greater sensitivity to the rewarding effects of palatable foods and results in obesity fatefully. Increased plasma concentrations of non-esterified free fatty acids and lipid-overloaded hypertrophic adipocytes may cause insulin resistance. In addition to dietary intake of high-fat diet, sedentary lifestyle leads to increased storage of triglycerides not only in adipose tissue but also ectopically in other tissues. Lipid-induced apoptosis, ceramide accumulation, reactive oxygen species overproduction, endoplasmic reticulum stress, and mitochondrial dysfunction play role in the pathogenesis of lipotoxicity. Food addiction and BED originate from complex action of dopaminergic, opioid, and cannabinoid systems. BED may also be associated with both obesity and major depressive disorder. For preventing morbidity and mortality, as well as decreasing the impact of obesity-related comorbidities in appropriately selected patients, opiate receptor antagonists and antidepressant combination are recommended. Pharmacotherapy alongside behavioral management improves quality of life and reduces the obesity risk; however, the number of licensed drugs is very few. Thus, stereotactic treatment is recommended to break down the refractory obesity and binge eating in obese patient. As recent applications in the field of non-invasive neuromodulation, transcranial magnetic stimulation and transcranial direct current stimulation are thought to be important in image-guided deep brain stimulation in humans. Chronic overnutrition most likely provides repetitive and persistent signals that up-regulate inhibitor of nuclear factor kappa B (NF-κB) kinase beta subunit/NF-κB (IKKβ/NF-κB) in the hypothalamus before the onset of obesity. However, how the mechanisms of high-fat diet-induced peripheral signals affect the hypothalamic arcuate nucleus remain largely unknown.

PCD Genes-From Patients to Model Organisms and Back to Humans

Primary ciliary dyskinesia (PCD) is a hereditary genetic disorder caused by the lack of motile cilia or the assembxly of dysfunctional ones. This rare human disease affects 1 out of 10,000-20,000 individuals and is caused by mutations in at least 50 genes. The past twenty years brought significant progress in the identification of PCD-causative genes and in our understanding of the connections between causative mutations and ciliary defects observed in affected individuals. These scientific advances have been achieved, among others, due to the extensive motile cilia-related research conducted using several model organisms, ranging from protists to mammals. These are unicellular organisms such as the green alga Chlamydomonas, the parasitic protist Trypanosoma, and free-living ciliates, Tetrahymena and Paramecium, the invertebrate Schmidtea, and vertebrates such as zebrafish, Xenopus, and mouse. Establishing such evolutionarily distant experimental models with different levels of cell or body complexity was possible because both basic motile cilia ultrastructure and protein composition are highly conserved throughout evolution. Here, we characterize model organisms commonly used to study PCD-related genes, highlight their pros and cons, and summarize experimental data collected using these models.

Positron emission tomography in multiple sclerosis - straight to the target

Following the impressive progress in the treatment of relapsing-remitting multiple sclerosis (MS), the major challenge ahead is the development of treatments to prevent or delay the irreversible accumulation of clinical disability in progressive forms of the disease. The substrate of clinical progression is neuro-axonal degeneration, and a deep understanding of the mechanisms that underlie this process is a precondition for the development of therapies for progressive MS. PET imaging involves the use of radiolabelled compounds that bind to specific cellular and metabolic targets, thereby enabling direct in vivo measurement of several pathological processes. This approach can provide key insights into the clinical relevance of these processes and their chronological sequence during the disease course. In this Review, we focus on the contribution that PET is making to our understanding of extraneuronal and intraneuronal mechanisms that are involved in the pathogenesis of irreversible neuro-axonal damage in MS. We consider the major challenges with the use of PET in MS and the steps necessary to realize clinical benefits of the technique. In addition, we discuss the potential of emerging PET tracers and future applications of existing compounds to facilitate the identification of effective neuroprotective treatments for patients with MS.

Eat and Death: Chronic Over-Eating

Obesity-related co-morbidities decrease life quality, reduce working ability and lead to early death. The total amount of dietary fat consumption may be the most potent food-related risk factor for weight gain. In this respect, dietary intake of high-caloric, high-fat diets due to chronic over-eating and sedentary lifestyle lead to increased storage of triglycerides not only in adipose tissue but also ectopically in other tissues . Increased plasma concentrations of non-esterified free fatty acids and lipid-overloaded hypertrophic adipocytes may cause insulin resistance in an inflammation-independent manner. Even in the absence of metabolic disorders, mismatch between fatty acid uptake and utilization leads to the accumulation of toxic lipid species resulting in organ dysfunction. Lipid-induced apoptosis, ceramide accumulation, reactive oxygen species overproduction, endoplasmic reticulum stress, and mitochondrial dysfunction may play role in the pathogenesis of lipotoxicity. The hypothalamus senses availability of circulating levels of glucose, lipids and amino acids, thereby modifies feeding according to the levels of those molecules. However, the hypothalamus is also similarly vulnerable to lipotoxicity as the other ectopic lipid accumulated tissues. Chronic overnutrition most likely provides repetitive and persistent signals that up-regulate inhibitor of nuclear factor kappa B kinase beta subunit/nuclear factor kappa B (IKKβ/NF-κB) in the hypothalamus before the onset of obesity. However, the mechanisms by which high-fat diet induced peripheral signals affect the hypothalamic arcuate nucleus remain largely unknown. In this chapter, besides lipids and leptin, the role of glucose and insulin on specialized fuel-sensing neurons of hypothalamic neuronal circuits has been debated.

Scanning and Transmission Electron Microscopy of the Ependymal Lining of the Third Ventricle

In its simplest form, the ependyma of the third ventricle consists of a single layer of cuboidal cells. Although these typical mural cells constitute the greater part of the lining of the ventricle, a specialized variety of ependymal cell (the tanycyte) can also be distinguished within circumscribed areas of the ventricular wall. Although such cells are found scattered throughout the dorsoventral extent of the third ventricle, they are particularly numerous along the ventrolateral walls and floor. The regional variation in the surface morphology of the ventricle walls as evident with the scanning electron microscope is consistent with this pattern of tanycyte distribution. Ultrastructural studies have established that the tanycyte is a fundamentally distinct cell with a long basal process extending into the subjacent neuropil and frequently directed toward a capillary wall. This unique morphology conforms closely to its three-dimensional appearance as demonstrated with the scanning electron microscope. The significance of ependymal tanycytes particularly of the third ventricle derives largely from the connections they establish between the ventricular lumen and vasculature of the median eminence. This intriguing structural relationship has led to the suggestion that ependymal cells and cerebrospinal fluid of the third ventricle may be involved in the regulation of adenohypophysial activity. Evidence indicating the functional involvement of specialized ependymal cells in the neuroendocrine control of pituitary activity is reviewed.

Co-localization of serine/threonine kinase 33 (Stk33) and vimentin in the hypothalamus

We investigate the immunoreactivity of serine/threonine kinase 33 (Stk33) and of vimentin in the brain of mouse, rat and hamster. Using a Stk33-specific polyclonal antibody, we show by immunofluorescence staining that Stk33 is present in a variety of brain regions. We found a strong staining in the ependymal lining of all cerebral ventricles and the central canal of the spinal cord as well as in hypothalamic tanycytes. Stk33 immunoreactivity was also found in circumventricular organs such as the area postrema, subfornical organ and pituitary and pineal glands. Double-immunostaining experiments with antibodies against Stk33 and vimentin showed a striking colocalization of Stk33 and vimentin. As shown previously, Stk33 phosphorylates recombinant vimentin in vitro. Co-immunoprecipitation experiments and co-sedimentation assays indicate that Stk33 and vimentin are associated in vivo and that this association does not depend on further interacting partners (Brauksiepe et al. in BMC Biochem 9:25, 2008). This indicates that Stk33 is involved in the dynamics of vimentin polymerization/depolymerization. Since in tanycytes the vimentin expression is regulated by the photoperiod (Kameda et al. in Cell Tissue Res 314:251-262, 2003), we determine whether this also holds true for Stk33. We study hypothalamic sections from adult Djungarian hamsters (Phodopus sungorus) held under either long photoperiods (L:D 16:8 h) or short photoperiods (L:D 8:16 h) for 2 months. In addition, we examine whether age-dependent changes in Stk33 protein content exist. Our results show that Stk33 in tanycytes is regulated by the photoperiod as is the case for vimentin. Stk33 may participate in photoperiodic regulation of the endocrine system.

Photoperiodic expression of two RALDH enzymes and the regulation of cell proliferation by retinoic acid in the rat hypothalamus

Retinoic acid (RA) has been found to regulate hypothalamic function, but precisely where it acts is unknown. This study shows expression of retinaldehyde dehydrogenase (RALDH) enzymes in tanycytes that line the third ventricle in an area overlapping with the site of hypothalamic neural stem cells. The influence of RA was examined on the proliferation of progenitors lining the third ventricle using organotypic slice cultures. As has been shown in other regions of neurogenesis, RA was found to inhibit proliferation. Investigations of the dynamics of RALDH1 expression in the rat hypothalamus have shown that this enzyme is in tanycytes under photoperiodic control with highest levels during long versus short days. In parallel to this shift in RA synthesis, cell proliferation in the third ventricle was found to be lowest during long days when RA was highest, implying that RALDH1 synthesized RA may regulate neural stem cell proliferation. A second RA synthesizing enzyme, RALDH2 was also present in tanycytes lining the third ventricle. In contrast to RALDH1, RALDH2 showed little change with photoperiodicity, but surprisingly the protein was present in the apparent absence of mRNA transcript and it is hypothesized that the endocytic tanycytes may take this enzyme up from the cerebrospinal fluid (CSF).

Differential distribution of tight junction proteins suggests a role for tanycytes in blood-hypothalamus barrier regulation in the adult mouse brain

The median eminence is one of the seven so-called circumventricular organs. It is located in the basal hypothalamus, ventral to the third ventricle and adjacent to the arcuate nucleus. This structure characteristically contains a rich capillary plexus and features a fenestrated endothelium, making it a direct target of blood-borne molecules. The median eminence also contains highly specialized ependymal cells called tanycytes, which line the floor of the third ventricle. It has been hypothesized that one of the functions of these cells is to create a barrier that prevents substances in the portal capillary spaces from entering the brain. In this paper, we utilize immunohistochemistry to study the expression of tight junction proteins in the cells that compose the median eminence in adult mice. Our results indicate that tanycytes of the median eminence express occludin, ZO-1, and claudin 1 and 5, but not claudin 3. Remarkably, these molecules are organized as a continuous belt around the cell bodies of the tanycytes that line the ventral part of the third ventricle. In contrast, the tanycytes at the periphery of the arcuate nucleus do not express claudin 1 and instead exhibit a disorganized expression pattern of occludin, ZO-1, and claudin 5. Consistent with these observations, permeability studies using peripheral or central injections of Evans blue dye show that only the tanycytes of the median eminence are joined at their apices by functional tight junctions, whereas tanycytes located at the level of the arcuate nucleus form a permeable layer. In conclusion, this study reveals a unique expression pattern of tight junction proteins in hypothalamic tanycytes, which yields new insights into their barrier properties.

Evidence supporting a role for corticotropin-releasing factor type 2 (CRF2) receptors in the regulation of subpopulations of serotonergic neurons

Corticotropin-releasing factor (CRF)-related peptides can modulate stress-related physiology and behavior. Some of these effects may be mediated via the CRF type 2 (CRF2) receptor on serotonergic neurons in the dorsal raphe nucleus (DR). To determine if the CRF2 receptor agonist urocortin 2 (Ucn 2) increases c-Fos expression in rat DR serotonergic neurons via actions on CRF2 receptors, we gave intracerebroventricular (icv) injections of mouse Ucn 2 after icv injections of either saline or the CRF2 receptor antagonist antisauvagine-30 (ASV-30). Double immunostaining methods for c-Fos and tryptophan hydroxylase revealed that, consistent with previous studies, mouse Ucn 2 increased c-Fos expression in tryptophan hydroxylase immunostained neurons in the middle and caudal parts (-8.18, -8.54, and -9.16 mm bregma) of the dorsal subdivision of the dorsal raphe nucleus 2 h after drug treatment. Pre-treatment with ASV-30 blocked these effects. Mouse Ucn 2 had no effect on c-Fos expression within the median raphe nucleus, consistent with the hypothesis that Ucn 2 has specific actions on an anatomically and functionally distinct subset of serotonergic neurons via activation of CRF2 receptors. These findings are also consistent with the hypothesis that Ucn 2, or another CRF-related neuropeptide acting at CRF2 receptors, modulates physiological and behavioral responses to stress-related stimuli via actions on a specific subset of serotonergic neurons within the dorsal raphe nucleus.

Circadian and light regulation of oxytocin and parvalbumin protein levels in the ciliated ependymal layer of the third ventricle in the C57 mouse

The walls of the third ventricle have been proposed to serve as a bidirectional conduit for exchanges between the neural parenchyma and the cerebrospinal fluid. In immunohistochemical studies of mice, we observed that light exposure and circadian phase affected peptide staining surrounding the third ventricle at the level of the suprachiasmatic nuclei. Under high magnification, we observed robust staining for the neurohormone oxytocin and the calcium-binding protein parvalbumin associated with cilia extending into the third ventricle from the surrounding ventricular wall; no similar staining was observed for vasopressin or calbindin. Retinal illumination had opposite effects on levels of parvalbumin and oxytocin in the cilia: light exposure during late subjective night increased oxytocin staining, but decreased parvalbumin staining in the cilia. Preventing cellular transport with colchicine eliminated immunohistochemical staining for oxytocin in the cilia. There was also a significant daily rhythm of oxytocin immunostaining in the third ventricle wall, and in magnocellular neurons in the anterior hypothalamus. The results suggest that environmental lighting and circadian rhythms regulate levels of oxytocin in the cerebrospinal fluid, possibly by regulating movement of oxytocin through the third ventricle wall.

Fatty acid amide hydrolase in brain ventricular epithelium: mutually exclusive patterns of expression in mouse and rat

Fatty acid amides and fatty acid ethanolamides are novel signalling molecules exemplified by the sleep-inducing lipid oleamide and the endocannabinoid anandamide, respectively. These substances are inactivated by fatty acid amide hydrolase (FAAH), an enzyme that is expressed by neurons and non-neuronal cells in the brain. In the rat, FAAH-immunoreactivity has been detected in epithelial cells of the choroid plexus and, in accordance with this finding, here we report FAAH mRNA expression in rat choroid plexus epithelium using in situ hybridisation methods. Surprisingly, a comparative analysis of mouse brain did not reveal FAAH mRNA expression or FAAH-immunoreactivity in the choroid plexus of this species. FAAH-immunoreactivity was, however, detected in non-choroidal ventricular ependymal cells in the mouse brain and the specificity of this immunostaining was confirmed by analysis of FAAH-knockout mice. FAAH-immunoreactivity was detected in ependymal cells throughout the ventricles of the mouse brain but with regional variation in the intensity of immunostaining. Intriguingly, in rat brain, although FAAH expression is observed in choroid plexus epithelial cells, little or no FAAH-immunoreactivity is present in the ventricular ependyma. Thus, there are mutually exclusive patterns of FAAH expression in the ventricular epithelium of rat and mouse brain. Our observations provide the basis for an experimental analysis that exploits differences in FAAH expression in rat and mouse to investigate FAAH function in ventricular epithelial cells and, in particular, the role of FAAH in regulating the sleep-inducing agent oleamide in cerebrospinal fluid.

The distributions and signaling directions of the cerebrospinal fluid contacting neurons in the parenchyma of a rat brain

Many studies have been made on the distributions of CSF contacting neurons (CSF-CNs) in the parenchyma of the brain with horseradish peroxidase (HRP) or autoradiographics. A significant amount of data has shown that both HRP and autoradiographical substances could pass freely through the spaces of ependyma into the parenchyma of the brain. It is therefore possible that the results were not exact. We found that CB-HRP was a dependable tracer to CSF-CNs and studied the distributions and the signaling directions of cerebrospinal fluid contacting neurons (CSF-CNs) in the parenchyma of the brain with the cholera toxin subunit B with horseradish peroxidase (CB-HRP) tracing combined with transmission electron microscopy. The results were as follows: (1) CSF contacting tanycytes existed not only in the wall of the third ventricle (3V), but also in the walls of the lateral ventricle (LV), the fourth ventricle (4V) and the central canal (CC) of the spinal cord. (2) Some CSF contacting glia cells were observed in the lateral septal nucleus (LS). (3)The distal CSF-CNs in the parenchyma were found in LS, the anterodorsal thalamic nucleus (AD), the supramammillary nucleus (SuM), the dorsal raphe nucleus (DR), the floor of 4V and the lateral superior olive (LSO), but they were mainly found in DR and divided into groups A and B. (4) Axon terminals labeled by CB-HRP were found in the cavity of the brain ventricle. (5) The synaptic relationships between the neurons were labeled by CB-HRP in DR and no-labeled by CB-HRP in the parenchyma. Both synapses Gray I and II were found. It was significant that the presynaptic elements were formed by the neurons no-labeled CB-HRP and the postsynaptic elements labeled CB-HRP. Our results suggested firstly that the signaling directions of CSF-CNs in DR were only from the parenchyma to CSF.

Localization of glucokinase-like immunoreactivity in the rat lower brain stem: for possible location of brain glucose-sensing mechanisms

Pancreatic glucokinase (GK) is considered an important element of the glucose-sensing unit in pancreatic beta-cells. It is possible that the brain uses similar glucose-sensing units, and we employed GK immunohistochemistry and confocal microscopy to examine the anatomical distribution of GK-like immunoreactivities in the rat brain. We found strong GK-like immunoreactivities in the ependymocytes, endothelial cells, and many serotonergic neurons. In the ependymocytes, the GK-like immunoreactivity was located in the cytoplasmic area, but not in the nucleus. The GK-positive ependymocytes were found to have glucose transporter-2 (GLUT2)-like immunoreactivities on the cilia. In addition, the ependymocytes had GLUT1-like immunoreactivity on the cilia and GLUT4-like immunoreactivity densely in the cytoplasmic area and slightly in the plasma membrane. In serotonergic neurons, GK-like immunoreactivity was found in the cytoplasm and their processes. The present results raise the possibility that these GK-like immunopositive cells comprise a part of a vast glucose-sensing mechanism in the brain.

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.

[The microvascularization of the choroid plexus of the lateral ventricles in the goat (Capra hircus)]

The goat choroid plexus angioarchitecture of the lateral ventricles was studied under the SEM using the method of "microvascular corrosion casts". The whole plexus is semilunar shaped and directed in an antero-posterior, latero-median fashion. In the plexus the lateral extremity is larger than the median one. All the components of the vascular bed (arteries, veins and capillaries) of the choroid plexus have interesting morpho-structural features. In particular, the capillaries are more developed than the other components and they are variously located on both sides of the plexus. The capillary network has a various organization in different zones of each side of the plexus.

Differentiation of ependymal surface of lateral ventricles in fetus and newborn rabbits: observations by SEM

The ultrastructural modifications that occur on the ependymal surface of the lateral ventricles of prenatal rabbit brains at 25, 27, 29 days of pregnancy, of term fetuses (30-31 days) and of 5, 10, 15 day old newborn rabbits, were studied by a SEM. On the ependymal surface the cilia, usually associated in tufts and the microvilli, variable in size and number, that surround them, show a rate of development correlated to the age. The results show the early differentiation of the surface features commensurated with early cerebrospinal fluid (CSF) functioning.

A glioependymal cyst of the cerebellopontine angle. Immunohistochemical and ultrastructural studies

Epithelial cysts in the subarachnoid space are infrequently reported and appear to be histogenetically heterogenous. This report describes the gross, immunohistochemical and ultrastructural findings of an asymptomatic isolated 3-cm epithelial cyst in the cerebellopontine angle. The cyst wall was composed of an inner glial layer with a luminal ependymal lining and an outer fibrous layer with no external lining cells. The lining ependymal cells had vacuoles, bleb-like protrusions, normal and abnormal cilia, and microvilli, the later were sometimes distended and detached into the lumen. They possessed neither pinocytic vesicles nor a basement membrane. The glial layer contained astrocytes, glial bundles and ependymal cells, often in pairs and forming intercellular lumina with cilia and microvilli. Some single and paired ependymal cells contained abnormal cilia and intracytoplasmic lumina. The blood vessels within the glial layer had elongated tight junctions and were fenestrated. The glial layer was demarcated from the outer fibrous layer by a continuous basement membrane. This cyst appears to have originated from a leptomeningeal neuroglial heterotopia and may represent a continued proliferative growth rather than degenerative change of the heterotopia.

Ependyma formation in adult rat spinal cord after transplantation of fetal cerebral cortex homografts

The ependymal cells in rat host spinal cord were studied after transplantation of fetal cerebral cortex homografts. Adult Sprague-Dawley male rats had pieces of E14 fetal rat cortex pressure-injected into the spinal cord at T6. The tissue was prepared for light and electron microscopy and studied for over 2 months postimplantation. At 7 and 14 days postimplantation (DPI), there were dividing ventricular-ependymal cells lining cysts in the host spinal cord. After 21 days, cell division was no longer observed in these cells, and only mature ependymal cells lined these cysts. Mature ependymal cells were either: columnar, pseudocolumnar, cuboidal, squamous, or pseudomorphic; had cilia and villi on only one surface of the cell and shared tight junctions when contiguous. These data show that ependymal cells were mature cellular components of adult spinal cord after transplantation of fetal CNS grafts. In addition, ventricular-ependymal cells continued to divide within the parenchyma of the graft, indicating continued growth of transplanted fetal cerebral cortex in host spinal cord.

Abnormal cilia in a fourth ventricular ependymoma

Although the luminal surface of the ependymal cells of the human ventricular system is characterized by the presence of cilia with a typical 9 + 2 arrangement of microtubules, cilia are usually described as sparse or absent in ependymal cells of ependymomas. The incidence of aberrant cilia and structurally abnormal cilia in normal ependymal cells and ependymomal cells has not been documented. This report describes detailed ultrastructural and quantitative studies of cilia of the ependymal cells of a fourth ventricular ependymoma in a 5-year-old boy. Of a total of 267 cilia studied, 50% were located in the extracellular microrosettes, 30% in the intracytoplasmic lumina and 20% in the cytoplasm. Thirty precent of all cilia studied showed structural abnormalities. Those present in the aberrant locations, e.g., intracytoplasmic lumina and in the cytoplasm, had a higher incidence of abnormality. Ciliary abnormalities fell into four majors categories: (1) cilia with abnormal axial microtubules, (2) compound cilia, (3) swollen cilia, and (4) cilia with dynein arm defect. Of these, addition, deletion and disorganization of axonemal microtubules were most common. The present study suggested that ciliary abnormality is common in ependymoma and may represent another example of oncogenetic effect on the ciliogenesis of ciliated epithelium.

Colloid cyst of the third ventricle. A scanning and transmission electron microscopic study

Three colloid cysts of the third ventricle were examined by both transmission (TEM) and scanning electron microscopy (SEM). There was morphological diversity of the cyst surface on SEM, with ciliated and non-ciliated cells present. In some areas, the non-ciliated cells were more numerous and extended above the surface. Individual non-ciliated cells show a wrinkled cell surface and bleb-like structures. The TEM findings correlated well with SEM, revealing two cell types. The non-ciliated cells appeared to have both exocrine and apocrine activity. In ciliated cells, abnormal cilia were related to abnormal centrioles; also present were highly abnormal microvilli. The appearance of the surface was similar to a normal ventricular surface. By allowing a greater assessment of cell types and their distribution, SEM has added one additional dimension in the evaluation of colloid cysts and their possible derivation.

Ventricular ependyma of normal and hydrocephalic subjects: a scanning electronmicroscopic study

Recent scanning electronmicroscopic studies of the ependymal surfaces of the lateral, third and fourth ventricles of a variety of animals have shown that most areas are covered by numerous cilia. In this paper, the density of the ciliary population in each of the ventricles is illustrated with material taken from human and rat brains. The authors' examination of Hy3 mice with hydrocephalus, and a number of other reports of examinations of animals with genetic and artificially induced hydrocephalus, have shown that the cilia are lost only from the ependymal surfaces covering those parts of the ventricular wall which are stretched and thinned by the raised intraventricular pressure. Thus the loss of the cilia is most probably the result of the hydrocephalus, and not its cause. Theories concerning the functions of the cilia are reviewed, and a new one accounting for why they are present in such large numbers is suggested. It is proposed that the cilia, together with the ventricular system and the cerebrospinal fluid, provide a cooling system for the brain.

The morphology of extrachoroidal ependyma overlying gray and white matter in the rabbit lateral ventricle

A morphologic investigation of ependyma over gray matter (caudate nucleus) and over periventricular white matter (tapetum) of the rabbit lateral ventricle was undertaken prior to evaluation of morphological changes which occur with experimental hydrocephalus. Ependymal cells over the caudate nucleus are cuboidal and heavily ciliated. Numerous microvilli cover the cell surface. The lateral margins are straight and interdigitations between adjacent ependymal cells are absent. Ependymal cells over white matter are squamous. Nonciliated as well as ciliated cells contribute to the epithelial lining. Microvilli are present at the cell surface but tend to aggregate near the cellular borders. The lateral margins are convoluted and complex interdigitations are present between adjacent cells. Morphologic differences between ependymal cells over the caudate nucleus and those over periventricular white matter may help to explain the differential response to hydrocephalus observed in these two regions of the lateral ventricle.

Some scanning electron microscopic observations of the ependymal surface of the ventricles of hydrocephalic Hy3 mice and a human infant

Two hydrocephalic Hy 3 mice and an infant with hydrocephalus and the Arnold-Chiari malformation were examined with the scanning electron microscope. Both mice had advanced hydrocephalus but had normal appearances in the basal regions of the ventricles. However, as the ventricular walls were ascended first the cilia gradually disappeared, then the microvilli, and finally on the roof of the ventricle the ependymal cells disappeared leaving the subependymal layers exposed. The infant had mild hydrocephalus and normal ependymal appearances. The most likely explanation of these findings is that they are a consequence of raised intracranial pressure, and are not the cause of hydrocephalus.

Development of the diencephalon in the rat. III. Ontogeny of the specialized ventricular linings of the hypothalamic third ventricle

The development of the specialized linings of the hypothalamic third ventricle was examined autoradiographically in mature rats that were labelled with 3H-thymidine during the developmental period, and in a closely spaced series of embryonic and infant rats. We distinguished in mature rats, apart from the typical ependymal wall, three specialized linings: the convoluted ependyma, the laminated epithelium, and the tanycytic epithelium. The ventricular wall of most of the anterior hypothalamus, and of the dorsal portion of the posterior hypothalamus, is composed of ciliated ependymal cells and most of them are generated several days before birth, soon after the cessation of neurogenesis in the adjacent hypothalamic nuclei. The cells of the rostral convoluted ependyma adjacent to the paraventricular nucleus are produced at about the same time as the neighboring cells of the smooth ependyma. Its cells come from the same germinal region that we have assumed to generate the neurons of the magnocellular neurohypophysial secretory system. The structural differentiation of the convoluted ependyma starts after birth and is completed by the beginning of the second week. Many of the ependymal cells of the laminated epithelium are produced postnatally, and the production of the specialized cells that form a parallel subependymal row extends into the third week. These cells appear to arise from the same matrix that generates earlier the neurons of the dorsomedial and ventromedial hypothalamic nuclei; their structural differentiation begins during the second week. Also the cells of the tanycytic epithelium are produced mostly postnatally, predominantly during the first week. They appear to arise from the same matrix that generated earlier the neurons of the hypophysiotropic tuberomammillary and arcuate nuclei. It is postulated that these three specialized ventricular linings are specifically related to the three cpmponents of the endocrine hypothalamus with which they have shared neuroepithelial sites of origin.

Supraependymal neurons overlying the periventricular region of the third ventricle of the guinea pig: a correlative scanning--transmission electron microscopic study

The frequency of occurrence, distribution and morphology of supraependymal neurons associated with the third ventricular wall of the guinea pig were investigated by correlative scanning and transmission electron microscopy. Each of the specimens was located on the ciliated ventricular wall between the inferior border of the thalamus and the non-ciliated ependyma associated with the median eminence. Prominent clusters of neuronal perikaria in association with massive process bundles were observed in 7 of the 31 specimens examined. In those specimens lacking prominent neuronal networks a more diffuse array of independent nerve fibers was sometimes seen on the ependymal surface. Neuronal perikaria exhibited numerous surface protrusions and were covered by a rich meshwork of crisscrossing, varicosed fibers. Many of these cells were associated with multiple processes of varying diameters and lengths which either coursed independently over the ventricular surface or formed fasciculated bundles. As process bundles traversed the ependymal surface, individual processes branched off and either terminated within the ventricular lumen or penetrated the subjacent ependymal lining. Fibers also made contact with adjacent supraependymal neuronal elements. Correlative transmission electron microscopic observations indicate that both the perikaria and processes of such supraependymal networks possess ultrastructural features characteristic of neurons. The morphological characteristics of the intraventricular neuronal networks suggest that they may be engaged in functional interactions with the cerebrospinal fluid, with adjacent supraependymal neuronal elements and with the subjacent neuropil.

Surface ultrastructure of tissues occluding ventricular catheters

Specimens of material occluding ventricular catheters removed at shunt revision operations were studied by scanning electron microscopy. Immediate fixation allowed examination of human choroid plexus and ependyma which resembled living tissue.

Early postnatal development of ependyma in the third ventricle of male and female rats

Ependyma in the third ventricle of developing male and female rats (0, 5, and 10 days postpartum) were compared with those of sexually mature male rats by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). No sexual dimorphism appeared in the developmental group. At all ages the dorsolateral ventricular wall was composed of ciliated ependymal cells, while ependymal cells of the ventrolateral wall exhibited apical microvilli and bleb-like irregularities. While SEM revealed similarities in apical morphology between ependymal cells adult and developing animals, TEM revealed marked differences between these cells. Many ciliated ependymal cells in developing animals resembled those of the adult while other neonatal cell profiles suggested ciliogenesis. Adult male rats exhibited two distinct tanycyte populations. One population, characterized by elaborate intercellular interdigitations and basal processes containing predominantly fine filaments, occurred adjacent to the ventromedial nucleus (VMN). The second population, characterized by less extensive intercellular interdigitations and basal processes containing, primarily microtubules, lined the roof of the lateral recess adjacent to the arcuate nucleus. Many tanycytes at the level of the arcuate nucleus in developing rats resembled closely those of the adult. In contrast, developing ependymal cells at the level of the VMN differed differed from their adult counterparts in that they exhibited little intercellular interdigitation and projected basal processes characterized by an internal framework of microtubules. Similarities in cytology between developing and adult tanycytes of the arcuate region suggest that the adult function of this population may be operative in the early postnatal period. In contrast, the differing cytology between adult and developing tanycytes of the VMN region suggests that the function of these cells is age-dependent.

The fine structure of the ependymal surface of the recessus infundibularis in the rat

The surface of the recessus infundibularis of the third ventricle has been studied with the scanning and transmission technique in normal and experimental material. Surface specializations such as microvilli, craters and areas of discontinuous lining are described. Supraependymal cells and fibres have been found; some of these cells form wide-meshed networks. The supraependymal fibres may be regular or varicose; the former seem to perforate the ependyma. With the transmission electron microscope the supraependymal cells are divided into three categories; nerve cells, lymphocytes and "dense cells". Two fibre populations are distinguished: thin profiles (nerve fibres) and thick profiles (nerve terminals). Axosomatic and axoaxonic synapses are described. Synapses between supraependymal fibres and ependyma cells have also been found.

Scanning electron microscopy of the third ventricular floor of the rat

By utilizing a horizontal dissection technique the entire floor of the third ventricle has been examined. When viewed in toto the ventricular floor was seen to have an hourglass shape with the supraoptic and infundibular recesses equalling the widened portions. Consistent regional differnces were also noted. The rostral half of the floor was densely ciliated while the caudal portion, containing ependymal elements of the underlying median emience, possessed few cilia. The ciliated cells ended in an abrupt transition zone located about halfway along the floor. The rostral portion of the infundibular recess had many more apical blebs and microvilli than did the caudal areas. Supraepen dymal cells of both the phagocyte-like and neuron-like variety were observed in all of the animals examined. In some animals, complex, branching, interconnecting networks of fine calibered fibers interconnected neuron-like cells that occurred singly and occasionally in clusters. Female rats examined at all phases of the estrus cycle demonstrated no cyclic alterations of the ependymal surface.

The third ventricle of monkeys; Scanning electron microscopy of surface features in mature males and females

Surface features of the ependymal lining of the third ventricle in mature male and female monkeys have been investigated with scanning electron microscopy (SEM); Broad aspects of third ventricular morphology from three species of monkey are similar regardless of sex. The lateral walls are heavily ciliated whereas the ventral floor and most ventral parts of the lateral walls are not. Clumps of cilia on the lateral walls are so dense that underlying surface details are usually obscured. There is a transition zone between the ciliated lateral wall and nonciliated ventral floor. The floor and lower part of the lateral walls of the third ventricule exhibit a characteristic polygonal pattern upon which surface specializations such as microvilli, blebs and polymorphous membrane protrusions are superimposed. Ependyma of the choroid plexus of the third ventricle also display membrane specializations. Supraependymal cells are more visible in nonciliated regions.

Supratentorial intracerebral epithelial (ependymal) cysts: review, case reports, and fine structure

The paper concerns the rare supratentorial, intracerebral or convexity cysts in adults having a wall lined with an epithelium resembling ependyma. The clincopathological aspects of such cysts are reviewed from 15 published cases and two specimens of the authors which could be examined with the electronmicroscope. These cysts manifest at a median age of 46 years as progressive, space occupying lesions with a fairly rapid clinical course of about one to two years. Twelve of 17 cysts were located in the frontal lobes, most were unequivocally intracerebral and none communicated with the lateral ventricle. Microscopic examination of the cyst wall disclosed some variance in structure, the most common feature being a monolayer of ciliated cells sitting on a very thin collagen membrane. One of the present cases was unique in that the compression by the cyst had caused a shell of infarction in the encompassing tissue. The fine structure of the cysts is described and compared with that of potential host tissues from which such cysts may originate. It is concluded that the cysts arise from displaced segments of the wall of the neural tube which correspond to the sites from which the tela chorioidea forms.

The structure of the hypothalamic inferior lobes of the blacktip reef shark: scanning and transmission electron microscopic observations

The inferior lobes of the shark hypothalamus were examined with light, transmission and scanning electron microscopy. The cells bordering the floor of the lateral recess appear to be typical liquor-contacting neurons. With scanning electron microscopy (SEM) the apical ends of these cells are seen to bulge into the ventricular lumen. In contrast, the roof is lined by a more typical ependymal cell characterized by numerous cilia and microvilli. In addition, SEM reveals several kinds of supraependymal cells with processes that appear to penetrate the ventricular lining. A periventricular nucleus underlies the ependymal cells. Neurons of the periventricular nucleus contain numerous lipofuchsin granules. The rest of the inferior lobe consists of many neuronal fibers. The morphology of the hypothalamic inferior lobe is discussed in relation to its possible role in feeding and aggressive behavior in both elasmobranchs and teleosts.

Surface ultrastructure of human ependyma

Specimens of human ependyma obtained immediately after death were immersion-fixed and studied with a scanning electron microscope. Human ependyma is nearly identical in its surface ultrastructural features to the ependyma of other mammals.

Changes of ventricular ependyma and choroid plexus in experimental hydrocephalus, as observed by scanning electron microscopy

Hydrocephalus was induced in rats by the injection of silicone oil or kaolin suspension into the cisterna magna. One to 5 weeks later the walls of the lateral ventricles were studied with the scanning electron microscope after killing the animals by perfusion fixation. In contrast to controls, the hydrocephalic animals killed 1 or 2 weeks after injection showed degeneration of ependymal cilia and infestation of the ependymal and choroid plexus surface with reactive cells, which presumably may be identified as Kolmer phagocytic cells by their ultrastructural features as studied by the transmission electron microscope. A coating of debris on the surface of the choroid plexus in the hydrocephalic animals possibly bears upon the ciliary degeneration with consequent deficiency of the clearing effect of ciliary movement. In the longer surviving hydrocephalic animals regeneration of cilia seemed to have occurred.

Human nervous system tumors. Observations by high voltages electron microscopy

Thick sections (0.5--2 mu) of biopsies from human nervous system tumors (Schwannoma, ependymoma, medulloblastoma), fixed in aldehydes followed by osmium, and stained with uranyl acetate and lead, have been studied at 2.5 MV, and compared to thin sections of the same material observed by ordinary low voltage electron microscopy. High voltage electron microscopy permits direct observation of cell fine structure in three dimensions, including the spatial relations of organelles. Details of contours of nuclear envelopes, shapes of mitochondria, fine aspects of the structure of cell surfaces and processes, such as the flat sheet-like and irregular cylindrical processes of Schwannoma cells, the small projections and ridges on their surfaces, and microvilli and cilia of ependymoma cells, and other features have been observed. These initial observations demonstrate the applicability of high voltage electron microscopy to further study of neural neoplasms.

Surface fine structure of supraependymal elements and ependyma of hypothalamic third ventricle of mouse

The ependymal surface of the hypothalamic third ventricle of the adult female and male mouse was examined with the scanning electron microscope. The material was dried with the critical point method. Supraependymal cells, exhibiting a variety of forms, lie among the cilia of the rostrodorsal two-thirds of the ventricle. The cell bodies are usually between 8 and 10 mu in diameter and have dividing pseudopodial processes which may be broad or narrow, flat or stout, smooth or varicosed. The textured surfaces of the cells seen in this material appear to have no cilia, microvilli or membraneous folds though they may have small bleb-like protrusions. Some cells and adjacent cilia bear clusters of friable-looking material that may be secretory. In several female mice, mounds of debris, that could be degenerating cells or secretory material, were seen in intimate association with clusters of cells. The cells' processes extend over and through the surface of the mound. While some supraependymal cells may be neurons or glia, it is suggested that many of the cells seen may be morphological variants of one cell line, mononuclear phagocytes. Sausage-shaped structures at the end of long cilia-like stalks are described and their possible identity discussed.

Scanning electron microscopy of the ventricular system in normal and hydrocephalic rabbits. Preliminary report and atlas

The author used the scanning electron microscope to study the ependyma in six control rabbits and six rabbits made hydrocephalic by infusion of silicone oil into the cisterna magna. The ependymal lining of the third ventricle, head of the caudate nucleus, superior angle of the caudate, and atrium of the lateral ventricle was examined. In the hydrocephalic animals, clusters of cilia emanating from the ependyma over periventricular white matter become separated; the author believes this is secondary to ingrowth of new ependymal cell processes covered with microvilli. The addition of these cells to the ependymal surface permits ventricular dilatation without ependymal disruption and provides more surface containing microvilli, presumably capable of increased transventricular fluid transfer. No such changes occur over gray matter masses since their surfaces are not deformed by moderate ventricular dilatation. The morphological alterations in the ependyma that occur in moderate hydrocephalus do not appear to be simply manifestations of ependymal destruction but rather suggest a modification in its function from that of a surface capable of propelling cerebrospinal fluid to one capable of increased transfer of transventricular fluid. As hydrocephalus progresses, compensation may fail because of the relative decrease in microvilli so that the cell surface provides a less efficient mechanism for absorption.

Surface defects in ventricular cells of brains of mouse embryos homozygous for the Loop-tail gene: scanning electron microscopic study

Luminal surfaces in the mesencephalon and rhombencephalon in normal mouse embryos and those homozygous for Lopp-tail were studied by means of scanning electron microscopy. Ventricular cells in the ventrolateral regions of normal day-10 and -11 brains showed single apical cilia and microvilli, whereas those in ventromedial regions showed a dense network of microvilli and bulbous projections which tended to obscure the apical cilia and cellular outlines. Similar regional differences occurred in the Loop-tail brains, although there was a marked decrease in the number and density of microvilli and bulbous projections. At days 12-14 of gestation the latter brains also showed a flattening of cell surfaces, shallow depressions, and craterlike ruptures in the plasma membranes.

The distribution, activity, and function of the cilia in the frog brain

1. The distribution, activity, and function of the cilia in the brain was studied using in vitro preparations of the frog choroid plexuses and ependyma.2. Scanning electron microscopy revealed that twenty to forty cilia, about 20 mum long, project from the cells of the choroidal epithelium and ependyma into the ventricular system of the brain.3. These cilia beat at a constant frequency which ranged from 5 to 20 c/s. Ciliary activity was enhanced by ATP, cyclic AMP, theophylline, and acetylcholine, and was depressed by DNP, IAA, Ni(2+), La(3+), and Co(2+).4. Ciliary motion produced a flow of c.s.f. over the surface of the cells lining the ventricles, and in the choroid plexus this flow reduced the effective thickness of the unstirred layer adjacent to the epithelium by about 100 mum.5. These results are discussed in relation to the factors that control the frequency of ciliary beating, and the role of the cilia in the circulation of the c.s.f.