Analysis of developing ependymal and choroidal surfaces in rat brains using scanning electron microscopy

Growth of choroid plexus epithelium vesicles in vitro depends on secretory activity

Although a number of models have been used to study choroid plexus epithelium (CPe) function, analysis in physiological conditions of this polarised epithelium which produces the majority of the cerebrospinal fluid (CSF) and is one of the key barriers between blood and CSF in the brain remains challenging. As CPe cells form polarised CPe vesicles when cultured in Matrigel, we have assessed their behaviour and potential use for pharmacological studies. Like CPe cells in vivo, CPe vesicles express transthyretin, E2f5, Fox-j1 and p73, and contain tight junctions, as indicated by ZO-1 expression and electron microscopy analysis. Time-lapse microscopy shows that CPe cells plated in Matrigel are highly migratory and rapidly form homotypic cell aggregates, which then reorganise to form vesicles whose size increases linearly overtime. Neither aggregate nor vesicle size is affected by AraC treatment, though this inhibitor significantly reduces proliferation in CPe monolayers. Increase in size of vesicles, which have reached a growth plateau is observed following addition of fluorescently-labelled CPe cells, which become incorporated into the vesicle walls. Significantly, treatment with secretion inhibitors blocks vesicle formation and their expansion. These results show that secretion, rather than cell division, controls vesicle growth, consistent with low levels of proliferation and thinning of the CPe observed both in growing vesicles and during CPe development. Therefore, changes in vesicle size can be used to evaluate the effect of putative molecules involved in the regulation of secretion.

Scanning Electron Microscopy of the Choroid Plexus of the Lateral Ventricle of the Horse

The present study examined the ultrastructure of the choroid plexus of the lateral ventricle of the horse. The material was fixed in 2.5% glutaraldehyde in 0.1 m sodium phosphate buffer, pH 7.3, processed and analysed by scanning electron microscopy. The choroid plexus was characterized by regions with a predominance of villi, which resembled finger-like projections or bunches of grapes, and others where straight and uniform folds predominated. Epithelial cells projected into the ventricle and large amounts of cilia and microvilli were observed on their surface. The choroid glomus corresponded to a dilatation of the choroid plexus and was characterized by blood vessels of different calibres surrounded by connective tissue.

Differential expression of fibroblast growth factor receptors in the developing murine choroid plexus

The choroid plexuses (CPs) are specialised secretory organs situated within the ventricles of the brain involved in the production of cerebrospinal fluid (CSF) and the maintenance of the blood-CSF barrier. Abnormal function of the CPs can lead to hydrocephalus and raised intracranial pressure, pathologies frequently observed in certain craniofacial syndromes caused by single point mutations in fibroblast growth factor receptors (FGFRs). At present, relatively little is known about the embryonic CPs in terms of gene or protein expression, function as the brain develops or on the potential role of FGFRs within this context. Given the limited information available on the regulation of FGFRs during development of the CPs and periventricular tissues, we have carried out a detailed analysis of the localisation of FGFR1, 2, 3 and 4 proteins in these regions of the murine embryo from the time of formation of the CP in the third ventricle at E12.5 throughout the second half of gestation, and examined the expression of different FGFR isoforms at E12.5 by RT-PCR. We show here that FGFR1 and FGFR4 are expressed in murine CPs at E12.5 but not at E15.5 or E18.5, suggesting a role for the signaling pathways transduced by these receptors at early stages of CP development. In contrast, FGFR2 expression is maintained throughout CP development, indicating that this receptor may play a role in the function of immature and mature CP. Also FGFR3 is detected at each developmental stage studied, but surprisingly its expression appears confined to the nuclei of CP cells, suggesting that FGFR3 in the CP does not respond to extracellular FGFs but may act in intracrine fashion.

Permeability and route of entry for lipid-insoluble molecules across brain barriers in developing Monodelphis domestica

1. We have studied the permeability of blood-brain barriers to small molecules such as [(14)C]sucrose, [(3)H]inulin, [(14)C]L-glucose and [(3)H]glycerol from early stages of development (postnatal day 6, P6) in South American opossums (Monodelphis domestica), using a litter-based method for estimating steady-state cerebrospinal fluid (CSF)/plasma and brain/plasma ratios of markers that were injected I.P. 2. Steady-state ratios for L-glucose, sucrose and inulin all showed progressive decreases during development. The rate of uptake of L-glucose into the brain and CSF, in short time course experiments (7-24 min) when age-related differences in CSF production can be considered negligible also decreased during development. These results indicate that there is a significant decrease in the permeability of brain barriers to small lipid-insoluble molecules during brain development. 3. The steady-state blood/CSF ratio for 3000 Da lysine-fixable biotin-dextran following I.P. injection was shown to be consistent with diffusion from blood to CSF. It was therefore used to visualise the route of penetration for small lipid-insoluble molecules across brain barriers at P0-30. The proportion of biotin-dextran-positive cells in the choroid plexuses declined in parallel with the age-related decline in permeability to the small-molecular-weight markers; the paracellular (tight junction) pathway for biotin-dextran appeared to be blocked, but biotin-dextran was easily detectable in the CSF. A transcellular route from blood to CSF was suggested by the finding that some choroid plexus epithelial cells contained biotin-dextran. 4. Biotin-dextran was also taken up by cerebral endothelial cells in the youngest brains studied (P0), but in contrast to the CSF, could not be detected in the brain extracellular space (i.e. a significant blood-brain barrier to small-sized lipid-insoluble compounds was already present). However, in immature brains (P0-13) biotin-dextran was taken up by some cells in the brain. These cells generally had contact with the CSF, suggesting that it is likely to have been the source of their biotin-dextran. Since the quantitative permeability data suggest that biotin-dextran behaves similarly to the radiolabelled markers used in this study, it is suggested that these markers in the more immature brains were also present intracellularly. Thus, brain/plasma ratios may be a misleading indicator of blood-brain barrier permeability in very immature animals. 5. The immunocytochemical staining for biotin-dextran in the CSF, in contrast to the lack of staining in the brain extracellular space, together with the quantitative permeability data showing that the radiolabelled markers penetrated more rapidly and to a much higher steady-state level in CSF than in the brain, suggests that lipid-insoluble molecules such as sucrose and inulin reach the immature brain predominantly via the CSF rather than directly across the very few blood vessels that are present at that time.

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.

Fetal ependyma in sheep and goat. A scanning electron microscopy study

Morphology of the surface of apical membranes of ependymal cells has been studied in the whole ventricular system of the brain in goat and sheep fetuses using a scanning electron microscope. The surface structure of the ependymal lining surface in fetuses of small ruminants is very similar to that in adult animals. Supraependymal cells were found only in the lower part of the third cerebral ventricle in goat fetuses, but not in sheep fetuses. In small ruminants the ependymal surface is already regionally differentiated within the end of the first half of prenatal development. Fetal ependyma of goats and sheep, unlike the adult ependyma, is characterized by a high secretory activity, which is independent of sex or age of fetuses.

Effects of an 11-day spaceflight on the choroid plexus of developing rats

Cellular distributions of ezrin, a cytoskeletal protein involved in apical cell differentiation in choroid plexus, and carbonic anhydrase II, which is partly involved in the cerebrospinal fluid production, were studied by immunocytochemistry, at the level of choroidal epithelial cells from the lateral, third and fourth ventricles in normal or experimental fetuses, in parallel with the ultrastructure of apical microvilli, observed by transmission electron microscopy. We compared choroid plexuses from developing normal rats (gestational day 15 to birth) with choroid plexuses from 20-day-old rat fetuses, developed for 11 days in space, aboard a space shuttle (NASA STS-66 mission, NIH-R1 experiments), from gestational day 9 to day 20. The main changes observed in fetuses developed in space were demonstrated by immunocytochemistry and concerned the distribution of ezrin and carbonic anhydrase II. Thus, in fetuses developing in space, ezrin was strongly detected in the choroidal cytoplasm and weakly associated to the membrane in the apical domain of the choroid plexus from the fourth ventricle. Such alterations suggested that choroid plexus from rat fetal brain displays a delayed maturation under a micro-gravitational environment. In contrast, intense immunoreactions to anti-carbonic anhydrase II antibodies showed that this enzyme is very abundant in rats developed in space, compared to ground control fetuses.

Morphological modifications of the choroid plexus in a rodent model of acute ventriculitis induced by gram-negative liquoral sepsis. Possible implications in the pathophysiology of hypersecretory hydrocephalus

Gram-negative bacterial infections of the central nervous system are generally associated with high morbidity and mortality rates. In patients with ventriculitis induced by gram-negative liquoral sepsis, a reduction in cerebrospinal fluid formation has been reported, suggesting that gram-negative ventriculitis is able per se to alter the normal functioning of the choroid plexus. The aim of the present study was to analyse, for the first time in the rat, the effects of acute ventriculitis on the ultrastructure of the choroid plexus. A simple and inexpensive experimental model of acute ventriculitis was developed: we injected into the cisterna magna of rats 10(3) CFU of live Escherichia coli, inducing septic ventriculitis without major neurological deficits. Histological examinations of rodent choroid plexus 24 h after the injection revealed patches of altered epithelium, with swollen and vacuolated ependymal cells associated with leukocyte infiltration. Electron microscopy demonstrated a reduced number of microvilli and flattening of the epithelial surface. These results (a) indicate that gram-negative septic ventriculitis is able to induce visible ultrastructural alterations of the choroid plexus which (b) are consistent with a picture of marked reduction of the functioning epithelial choroid plexus surface, and (c) highlight the potential usefulness of our rodent acute ventriculitis model for developing treatment modalities.

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.

Effects of the extracellular matrix on fetal choroid plexus epithelial cells: changes in morphology and multicellular organization do not affect gene expression

We have developed a primary culture system for fetal mouse choroid plexus epithelial cells which maintains their differentiated phenotype. When grown on a reconstituted basement membrane substrate (Matrigel) epithelial cells formed aggregates which became embedded in the matrix and developed into characteristic and highly reproducible multicellular vesicular structures. These vesicles consisted of a squamous layer of epithelial cells with extensive attachment to the matrix substrate, surrounding a fluid-filled lumen. Electron microscopy showed that cells comprising these vesicles had a high degree of membrane specialization and polarized morphology which in many respects mimicked the in vivo morphology. Biochemical analyses demonstrated that under these culture conditions the tissue-specific pattern of gene expression of fetal choroid plexus epithelium was maintained. After 6 days in culture these cells contained approximately the same amount of transthyretin mRNA as the 12.5-day choroid plexus in vivo, and the level of total RNA per cell, which is proportional to the protein synthetic capability of the cells, was also maintained. The pattern of protein secretion was also very similar to that generated by fetal mouse choroid plexus cells in vivo. In contrast choroid plexus epithelial cells attached poorly to collagen I gels. Heterogeneous aggregates were formed in which cell-cell interactions were more extensive than cell-substrate interactions, and in no cases was a central lumen observed. Cells on the surface of large aggregates showed some evidence of membrane polarization, while the majority of cells in the cultures exhibited little evidence of polarized morphology. Despite the striking difference in morphology and multicellular organization these cells still expressed high levels of transthyretin mRNA and maintained the same pattern of protein synthesis as cells cultured on Matrigel. These results indicate that the basement membrane is important for the organization of choroid plexus epithelial cells into a functional epithelium in vitro and thus presumably the maintenance of the integrity of the blood-brain barrier in vivo. In contrast to several other epithelial systems which have been studied, the type of extracellular matrix does not appear to directly influence tissue-specific gene expression by choroid plexus epithelial cells. Thus the level of gene expression is not dependent on the cytoarchitecture and multicellular organization of this cell type.

A morphometric study on the development of the lateral ventricle choroid plexus, choroid plexus capillaries and ventricular ependyma in the rat

Morphometric changes in the rat lateral ventricle choroid plexus epithelium and endothelium and in the ventricular ependyma were studied between 16 days gestation and 30 days after birth, using stereological techniques. The epithelial apical surface density increased from 0.6 to 3.3 microns 2/microns 3 and the mitochondrial volume fraction from 3.2 to 7.6% during this period. The endothelial fenestrations increased from 0.05 to 0.39 micron-1. These changes may be related to postnatal increases in choroid plexus function. Morphological changes in basolateral surface density, cell height and nucleus and glycogen volume fraction have also been measured. The development of the lateral ventricle choroid plexus was qualitatively similar to the fourth ventricle plexus reported previously, but small quantitative differences occurred. The ventricular ependyma also showed a significant increase in mitochondrial volume fraction after birth, though to a lesser extent than the plexus epithelium. The total apical surface area of the choroid plexuses was estimated at 75 cm2 for 30-day-old rats. This figure, which takes into account the apical microvilli, is much greater than previous estimates and is similar to the surface area of the cerebral capillaries (155 cm2), and suggests that the choroid plexuses may play a more important role in the regulation of the brain microenvironment than previously thought.

Developmental patterns of gene expression of secreted proteins in brain and choroid plexus

The proteins secreted by the choroid plexus throughout rat brain development were analyzed by two-dimensional polyacrylamide gel electrophoresis following biosynthetic labeling of choroid plexus pieces with [14C]leucine in vitro. Approximately 20 major protein species were resolved which, with the exception of transferrin, transthyretin, and alpha 2-macroglobulin, appear to be unrelated to proteins found in high concentrations in plasma. Several patterns of developmental regulation were observed. At least two of the proteins were synthesized and secreted at high levels only by fetal choroid plexus, whereas the secretion of several other proteins including transferrin and proteins comigrating with cystatin C and alpha 2-macroglobulin increased only after birth. The levels of mRNA coding for transferrin, ceruloplasmin, cystatin C, alpha 2-macroglobulin, beta 2-microglobulin, and transthyretin were measured in the brain during development by dot hybridization and northern gel analysis. No mRNA was detected coding for the proteins alpha-fetoprotein, alpha 1-antitrypsin, haptoglobin, and thiostatin in the brain at any stage. For those proteins, which are produced in other parts of the brain as well as by the choroid plexus, the changes in their corresponding mRNA levels measured in whole brain paralleled the changes in their secretion by the choroid plexus. The results presented in this paper show that the choroid plexus is active in protein secretion at all stages studied. The changing pattern of protein secretion by the choroid plexus, combined with its early development compared with other tissues in the brain, suggests that it is active in providing the appropriate extracellular environment for the growth and differentiation of the brain.

The expression of transthyretin mRNA in the developing rat brain

Specific cDNA and oligonucleotide probes were used to study the appearance of transthyretin mRNA in developing rat brain using Northern gel analysis, cytoplasmic dot hybridization, and in situ hybridization. Transthyretin mRNA in embryonic rat brain was found to be confined to the epithelial layer of the choroid plexus primordia appearing first in the fourth ventricle, followed by appearance in the lateral ventricles, and subsequently in the third ventricle. Transthyretin mRNA was localized in these cells from early stages of neuroepithelium differentiation, showing that it is a sensitive marker for the differentiation of the choroid plexus within the fetal brain.

Development of the choroid plexus anlage and supraependymal structures in the fourth ventricular roof plate of human embryos: scanning electron microscopic observations

The developing anlage of the choroid plexus and supraependymal structures in the fourth ventricular roof plates of nine normal human embryos ranging from Carnegie stages 14 to 19 were investigated with scanning electron microscopy. In the human embryos at stage 18, the first semimacroscopic choroidal anlage developed in the form of bilateral evaginations that ran dorsomedially and caudally from the bilateral corners of the rhombencephalon. The anlage became evident with even smaller and parallel ridges in the embryo at stage 19. Embryos at earlier stages exhibited surface membrane modifications such as convexity, microvilli, cilia, and spherical protrusions at the middle one-third of the rhombencephalon, which corresponded to the future choroidal anlage region. Two morphologically different groups of supraependymal cells (SE cells) were elucidated throughout the stages examined. Type 1 SE cells has spindle or tear-drop-like bodies, frequently with one or more long cytoplasmic processes. Type 2 SE cells were globular, with numerous fine pseudopodial processes. Type 1 SE cells were distributed mainly at the future choroidal anlage regions or on the anlage itself and were less frequently located at the rostral end of the roof. We found no general pattern in the distribution of type 2 SE cells. Supraependymal fibers (SE fibers) were seen as fine processes that were distributed similarly to type 1 SE cells and extended transversely for a long distance.

The control of potassium concentration in the cerebrospinal fluid and brain interstitial fluid of developing rats

1. In situ measurements of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid (ISF) K+ concentrations have been made in anaesthetized rats aged between 19 days gestation and 30 days after birth using K+-selective micro-electrodes. 2. Under control conditions, plasma, CSF and ISF [K+] did not vary significantly with age, the over-all mean concentrations being 3.8, 3.1 and 3.2 mM respectively. The CSF and ISF [K+] were significantly lower than plasma [K+] at all ages. 3. It is concluded that young rats, from the age of 19 days gestation, can normally maintain plasma-to-CSF and plasma-to-ISF gradients similar to those in the adult, presumably by action of the blood-CSF and blood-brain barriers. 4. During acute plasma hyperkalaemia there was very little regulation of CSF [K+] at 21 days gestation, but after birth there was a gradual improvement in CSF K+ homeostasis until by 30 days after birth a normal CSF [K+] could be maintained. 4. There was no regulation of ISF [K+] during hyperkalaemia at 21 days gestation, although after birth there was a rapid improvement in ISF K+ homeostasis. 1-day-old neonates were able to maintain a normal forebrain ISF [K+] during hyperkalaemia. 6. It is concluded that the onset of both CSF and ISF K+ homeostasis takes place at around birth in rats. However, K+ homeostasis matures more rapidly in the ISF than in the CSF. This suggests that, at least in the neonatal period, the CSF is not essential for ISF [K+] regulation.

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.

A morphometric analysis of the development of the fourth ventricle choroid plexus in the rat

The choroid plexus from the rat fourth ventricle was investigated at ages from 16 days of gestation to 30 days after birth. Choroid plexus weights were measured and light and electron micrographs were analysed by quantitative stereological techniques at 4 levels of magnification. There was a 10-fold increase in plexus weight between 19 days of gestation and 30 days after birth which was largely due to an increase in epithelial weight, with little change occurring in the connective tissue core. Before birth, epithelial cell height decreased whereas between 10 and 30 days after birth cross-sectional area increased, both events being accompanied by corresponding changes in cell volume. Large intracellular stores of glycogen were present around birth, when they occupied up to 20% of the cell volume. After birth there were significant increases in apical microvillus height, the number of microvilli per cell and in the size of the mitochondria, suggesting that a large increase in choroid plexus secretory function, or the commencement of a new function, occurs after birth in the rat.

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.

Sodium, phosphorus, sulphur, chlorine and potassium shifts in rat brain during embryonic development

Concentrations of sodium (Na), phosphorus (P), sulphur (S), chlorine (Cl) and potassium (K) and their variations during brain development were measured in freeze-dried thick sections from rat brain (16-20 micron). Sprague-Dawley rats were bred and the day of finding vaginal spermatozoa was considered as day zero of pregnancy. On days 12E, 13E, 14E, 16E, 19E, 21E (embryonic) and postnatal day one whole embryos or fetal heads were rapidly frozen in liquid Freon 22 cooled with liquid nitrogen (-180 degrees C), sectioned in a cryostat (-20 to -40 degrees C), and processed for X-ray microanalysis on pure carbon plates. Concentrations of Na and Cl differed in the cells of the cerebral cortex, ependyma, choroid plexus and cerebral spinal fluid (CSF). During cerebral development, Na and Cl concentrations appeared to be correlated, while K was more related to P. S was low and unchanged in all compartments during development and was thus considered as an internal control. K was inversely related to Na and Cl fluctuations within the choroid plexus epithelia. Sharp phase changes of elemental composition appeared in all tissues at specific growth stages, e.g. days 14E and 19E. These results demonstrate rhythmic changes in the inorganic components of developing rat brain cells and fluid environment presumably reflecting physiological fluctuations and cell cycle phenomena. Such changes may also be related directly or indirectly to known 'growth phase changes' in the developing rat.

X-ray induced dysplasia in the developing telencephalic choroid plexus of mice exposed in utero

Pregnant NMRI-mice were X-irradiated with single doses of 0.95 Gy (100 R) and 1.9 Gy (200 R) on day of gestation (dg) 12. For sampling, anesthetized animals were perfused with buffered glutaraldehyde solution or fixed by immersion in Karnovsky solution. LM, SEM, and TEM studies were carried out on brains prenatally and up to the age of 20 months to follow the radiation effects on the developing lateral choroid plexus. Radiation-induced changes were found using all three methods and at all stages studied. The normally sickle-shaped and stretched choroid plexus is shortened and irregular, and the dome-shaped plexus cells are flattened. Their superficial fine structures, i.e., the microvilli and cilia, are altered. Three stages of severity can be distinguished and the internal hydromicrocephalus increases from stage I to III. Intercellular spaces of the treated plexus epithelium are often dilated, but the tight junctions at the ventricular surface seem to be intact. The interstitium shows large dilations in comparison with the controls. Thus, gross changes and alterations in the fine structure can be induced in the choroid plexus by doses of 0.95 Gy and 1.9 Gy, which persist throughout postnatal life.

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.

The lateral, third, and fourth ventricle choroid plexus of the dog: a structural and ultrastructural study

The morphology of the choroid plexuses of the lateral, third, and fourth ventricles in dogs was studied by histological and ultrastructural techniques after in situ fixation. Most portions of the plexus in the lateral ventricle showed a parallel arrangement of capillaries, producing a fine corrugation of the overlying layer of epithelial cells. Relatively large amounts of connective tissue separated the capillaries from the epithelium. The fourth ventricle choroid plexus showed short capillary loops projecting into the ventricle and more intimately covered by epithelium. Smaller amounts of connective tissue separated the capillaries from the epithelium. The choroid plexus of the third ventricle showed characteristics seen in the plexuses of both the lateral and fourth ventricles. The total surface of the choroid plexuses in the dog averaged 10.7 cm2, of which 55% was fourth ventricle choroid plexus.

The development of the diencephalic choroid plexus in the chick. A scanning electron-microscopic study

The surface morphology of the diencephalic choroid plexus (Pl. ch. v. III) was investigated by light microscopy and scanning electron microscopy in chicks from the 7th embryonic day (ED) to the 8th week after hatching. Pl. ch. v. III develops on the anterior ventricular roof from a sagittally oriented fold and a few posteriorly located transverse folds. On the 7th ED no significant differences in the cell surface morphology between Pl. ch. v. III and the surrounding ependyma are observed: both are covered with cilia. During the next four days, long cell prolongations (one per cell) covered with microvilli develop first on the surface of the posterior ventricular roof and then on the posterior part of Pl. ch. v. III. These structures are transitory. On the 11th ED, round cell prolongations (one per cell) appear progressively on the entire plexus, also replacing the long ones. Now the plexus surface is distinct from the surface of the surrounding ependyma. During the last week before hatching and also after hatching, the round cell prolongations become less prominent. Simultaneously, the number of cilia per unit surface area diminishes. With consideration of earlier reports, this study suggests that the following factors are involved in the increase of the surface area of Pl. ch. v. III: (1) The pseudostratified epithelium changes into columnar epithelium. (2) Ependymal elements of the posterior roof of the 3rd ventricle contribute to the anlage of Pl. ch. v. III. In later stages, however, Pl. ch. v. III grows only by mitoses.

The pathology of experimental obstructive hydrocephalus. A scanning electron microscopic study

Obstructive hydrocephalus was produced in 14-day old rabbits by injection of kaolin into the cisterna magna. The ependymal lining was studied by scanning electron microscopy. Marked hydrocephalus was present 1 or 2 weeks after the kaolin injection. The ependymal lining adapted remarkably well to the rapid expansion by increasing the surface area of the ependymal cells. No breaks or denudement of the ependymal lining was observed except at the sites of ruptured ventricular synechiae. Generally, these findings confirm previous light and electron microscopic observations on the same model (Torvik et al. 1976; Torvik and Stenwig 1977). The results are discussed in relation to current theories concerning the pathophysiology of acute hydrocephalus.

The choroid plexus of the mature and aging rat: the choroidal epithelium

The choroid plexus of mature and old rats has been examined by both scanning and transmission electron microscopy. It has been shown that the macrophages lying upon the ventricular surface of the choroid plexus have a close association with burr-like protrusions that extend from the apical surfaces of the choroidal epithelial cells. These protrusions have a dark cytoplasm filled with vesicles and tubules, and projecting from them are thin, shrunken microvilli. It is suggested that these protrusions are phagocytosed by the macrophages and that they are the source of some of the inclusions which become increasingly common within the cytoplasm of macrophages in older rats. The lateral surfaces of the choroidal epithelial cells have also been examined in the scanning electron microscope after exposure of the surfaces by dissection. In such preparations it is apparent that the elaborate interdigitations between adjacent cells are effected by irregular and vertically arranged folds confined to the basal portions of the lateral cell surfaces. Lastly, it has been shown that at the junction between the choroid plexus and the ependyma in the lateral ventricle, there are two modes of transition between the choroidal and ependymal epithelia. In one, typical choroidal and ependymal epithelial cells lie next to each other to produce a distinct and continuous bondary. In the other mode the boundary is also continuous, but there are modified ependymal cells present. These modified cells have short, relatively sparsely distributed microvilli and not more than one or two cilia.

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.

The effects of hydrocephalus upon the developing brain. Histological and quantitative studies of the ependyma and subependyma in hydrocephalic rats

A suspension of kaolin was injected into the cisterna magna of 44 rats at 2 weeks of age. Animals killed at intervals from 5--19 weeks of age showed varying degrees of hydrocephalus. Light microscopy, scanning and transmission electron microscopy revealed stretching and flattening of the ependymal cells but no significant loss of cilia. Histological evidence of periventricular tissue damage in these chronically hydrocephalic animals was only present when the ventricular dilatation was extensive. A quantitative assessment was made of the ependymal and subependymal cell reactions around the lateral ventricles of the hydrocephalic animals. Although the ependymal cells were clearly stretched around the ventricles, there was no apparent proliferation of these cells. An increase in the total number of subependymal cells was observed in hydrocephalic animals when compared with a series of 39 aged-matched controls. The greatest proliferation was in the dorsal and lateral walls of the ventricles which were the regions most severely stretched by the ventricular dilatation. There is evidence that subependymal cells differentiate into astrocytes and microglia so that proliferation of these cells may be interpreted as a response to continuing and progressive brain damage in chronic hydrocephalus. Such progressive tissue damage could adversely affect the developing brain.

Specializations of the ependyma in the third ventricle of the developing hamster

Ependymal cells in the region of the hypothalamic sulcus, hypothalamus, infundibular recess and supraoptic recess exhibit large apical protrusions between day 12 and day 14 post coitus. The ependyma was examined using light microscopy and transmission and scanning electron microscopy. The protrusions contain ribosomes and cytoplasmic matrix. Occasionally other cytoplasmic organelles were found within the protrusions. The protrusions range in shape from a rounded elevation of the apical surface of the ependymal cell to spherical bodies attached to cell surface by a slender stalk. The unique transitory specialization of the ependyma may represent either a neurosecretory or mechanical folding mechanism.

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.

Pathogenesis of aqueductal occlusion in congenital murine hydrocephalus

In a study of congenital hydrocephalus in the murine mutant (hy-3/hy-3), the authors found that aqueductal stenosis develops during the progression of hydrocephalus. In Stage 1 hydrocephalus (ventricular dilation and open aqueduct), a block in the subarachnoid space over the cerebral convexities causes the lateral and third ventricles to enlarge. The ependyma becomes stretched and a collection of edematous fluid forms in the subependymal layer. In Stage 2 hydrocephalus (edema in white matter around lateral ventricles and compression of quadrigeminal plate), edema develops peripheral to ependyma in the aqueduct and compresses the lateral surfaces of the aqueductal wall to obstruct the lumen. While periaqueductal edema is spreading, the forces of the expanding midline structures and the cystic occiital horns alter the relationship of brain structures. There is no proliferation of glia, but, rather, a "simple stenosis" which results from a combination of ventricular dilation, cerebral edema, brain shift, brain-stem compression, and brain-stem edema. In this study, normal ependymal specializations were observed that indicate a more active functional role for aqueductal ependyma than previously recognized.

Scanning electron microscopy of epiplexus macrophages (Kolmer cells) in the dog

Young dogs (6-14 weeks) were perfused with buffered aldehydes by standard techniques. The inferior medullary velum and tela choroidea were removed intact from the fourth ventricle, post-osmicated, dehydrated, critical point dried, coated with palladium-gold and examined in a Cambridge Stereoscan S4 scanning electron microscope. Selected samples after thorough scanning were routinely prepared for transmission electron microscopy (TEM). This study depicts numerous epiplexus (Kolmer cell) macrophages that exhibit extreme polymorphism. Because of the pleomorphic nature of these cells and their processes, classification based on external morphology is not practical. TEM shows their internal structure to be that of a macrophage. Bleb-like structures and bulbous projections appear to emerge from certain ependymal cell surfaces which seem to be completely or partially devoid of cilia.

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.