Analysis of the secretions of the subcommissural organs of several vertebrate species by use of fluorescent lectins

Summary The glycoprotein secretions of the subcommissural organ were analyzed with the use of nine fluorescent lectins, specific to different sugar moieties. After exposure to Concanavalin A a bright fluorescence was observed in the ependymal cells of the subcommissural organs of all vertebrates studied (Lampetra planeri, Ameiurus nebulosus, Bufo bufo, Lacerta vivipara, Gallus gallus, Rattus norvegicus, Ovis aries). The fluorescence is abolished by the competitive sugar, -D-mannopyranosyl. The intensity of the lectin fluorescence decreases from the phylogenetically lower to the higher forms, paralleled by a change in polarity of the secretion from a vascular (lower vertebrates) to a ventricular (higher vertebrates) direction. The strong affinity for Concanavalin A suggests the presence of a glycoprotein rich in mannosyl residues in the ependymal cells and a similarity of composition of this glycoprotein among the vertebrates. Lens culinaris agglutinin and wheat germ agglutinin revealed fluorescent rosettes in the hypendymal cells of the sheep. Binding of both these lectins suggests the presence of a glycoprotein rich in N-acetyl-D-glucosamine.In the underlying ventricular cavity, no fluorescence could be observed, suggesting that the Reissner's fiber does not possess the same carbohydrate constitution as the ependymal secretion of the subcommissural organ.     

Electron microscopy of the paraventricular organ in the sparrow (Passer domesticus)

Summary Characteristics of the ependymal cells of the Paraventricular Organ (PVO) in the sparrow are strongly dilated ergastoplasmic cisternae filled with a moderately dense substance, the absence of cilia and a long basal process ending around capillaries. Elongated cells having a pale cytoplasm (light cells) are interposed between the ependymal cells. These cells protrude into the ventricle lumen with a bulbous cytoplasmic swelling; centrioles and several dense-core vesicles occur frequently in them.Two types of nerve cells have been identified in the PVO. The more superficial cells — called type-I neurons have a dendrite-like process which, after passing the ependymal layer reach the ventricle surface and end there freely with a bulbous swelling (club). The whole neuron contains dense-core vesicles of an average diameter of 840 Å; the extensive Golgi region is located in the dendrite.The larger type-II neurons situated in the deeper layers show a folded nuclear membrane, large mitochondria and rarely dense-core vesicles; the Golgi apparatus is enclosed in the perikaryon.The nerve cells are embedded in a feltwork of glial and neural processes the latters showing often synaptic (axodendritic) junctions. The majority of the synapses are supposed to occur between the axon-like processes of the typeI neuron and dendrites of the type-II neuron. Axo-somatic synapses can be found not infrequently on the perikarya of the latters.The nature of the free ventricular endings of the neurons and the possible function of the PVO are discussed in the text.     

Specialized ependyma in the posterior mesencephalon of the chicken: The fine structure of the subtrochlear organ

Summary A formation of specialized ependymal cells in the posterior mesencephalon of the domestic fowl, designated as the subtrochlear organ, was examined with light-,scanning-and transmission electron microscopy. This organ possessing the form of the letter V is located in the ventricular wall of the posterior mesencephalon. Its apex marks the median sulcus, while the arms of the V are directed rostrolaterally. Ependymal cells lining the subtrochlear organ usually project an extremely elongated process into the subependymal region and are classified into three types according to their surface features: (1) cells with a bulbshaped protrusion that projects into the ventricle, (2) single cilium-bearing cells, and (3) cells with a tuft of cilia. The first type of cell is restricted to the median portion of the subtrochlear organ; its bulb-shaped protrusion contains numerous ribosomes. The second type of cell predominates in the arm (rostrolateral) area; in its apical cytoplasm such ciliary structures as basal body are rarely seen. The third type of cell is usually assembled into several small islands on the arm area; it has many basal bodies and other ciliary structures in the apical cytoplasm.     

Elektronenmikroskopische Untersuchungen am Stirnorgan von Anuren

The ultrastructure of the frontal organ (pineal end-vesicle, Stirnorgan) of Rana temporaria L. and Rana esculenta L. is similar to the submicroscopic organization of the retina and other photosensitive organs. There are five different cell types in the frontal organ: sensory (receptor) cells, ependymal cells, ganglion cells, glial cells and epithelial cells. The ependymal cells may be secretory. There is no evidence for a typical pigment epithelium. The sensory cells have inner and outer segments. The inner segments contain numerous mitochondria, a Golgi complex, filaments, lipid droplets, two centrioles and a fibrillar apparatus (within the connecting piece). The mitochondria are very abundant in the Ellipsoid and Ersatzellipsoid areas (Holmgren) of the inner segment. The outer segment consists of about 60 to 110 discs formed by infoldings of the cell membrane. Most of the sensory cells are cone-like, but there are some elements with rod-like structures. Plexiform areas of the frontal organ contain terminations of the receptor cells, and processes of the nerve cells and glia cells. Synaptic structures have been determined within these areas. Non-medullated and medullated nerve fibers with adjacent glial satellites are observed in the pineal nerve (Nervus pinealis). The anatomical findings are described in detail and discussed in respect to the physiological results of Dodt and Heerd (1962) in Rana temporaria and Rana esculenta.

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Durchgeführt mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Scanning and transmission electron microscopy of the subfornical organ of the grass frog (Rana pipiens)

Summary The ventricular surface of the subfornical organ of the frog is made up of ependymal cells with numerous apical microvilli, occasional cytoplasmic protrusions and many vacuoles projecting into the lumen of the third ventricle. Between these cells dendrites of cerebrospinal fluid-contacting neurons reach the ventricle to terminate in bulbous enlargements. In addition, flask-shaped encephalo-chromaffin cells, containing granulated vesicles and aggregates of filaments in their cytoplasm, project into the cerebrospinal fluid. Surrounding the centrally located capillaries are enlarged dendrites and axons of heterogeneous morphology, some of which appear to originate within the subfornical organ, intermingled with dendrites and axons of normal structure. The glial cells in this region, especially the microglial cells, often contain large lipofuscin inclusions, suggestive of degeneration and subsequent phagocytosis of some of the enlarged dendrites and axons. The normally scarce neurosecretory peptidergic axons become more evident and form typical Herring bodies in stalk-transected animals. Neuronal perikarya of varying morphology are predominantly located peripheral to the region of enlarged dendrites and axons. Supraependymal macrophages are particularly numerous on the subfornical organ.Abbreviations used CSF cerebrospinal fluid - SEM scanning electron microscope, scanning electron microscopy - SFO subfornical organ - TEM transmission electron microscope, transmission electron microscopy Supported, in part, by NIH grant NB 07492The skillful technical assistance of J.G. Linner and the secretarial assistance of Ann Gerdom are gratefully acknowledged. The SEM studies were made possible through a grant from the Graduate College of Iowa State University and the use of the SEM facility in the Department of Botany     

Neuritic growth cone and ependymal gap junctions in the feline subfornical organ during early development

Summary Intercellular contacts in the subfornical organ (SFO) of kittens 3, 16, and 29 days old were studied in thin sections and by the freeze-etch method. Gap junctions appeared between growing nerve processes and target cells. The junctions were interspersed between immature synapses lacking mitochondria as well as full preand postsynaptic membrane specializations. Gap junctions were seen on filopodia as well as on more mature processes. The morphology of these junctions was typical of those described earlier but they were of small size (0.2–0.3 m).Gap junctions of peculiar form were also seen between ependymal elements in the SFO at 16 days. These were of large size (0.5–0.8 m) and were often of segmented character. This segmentation consisted of bands 3–4 particles in width with a center-to-center spacing of 90 nm with particle free corridors between corresponding to the width of about two rows of particles. The margin of the group might be circumscribed by a row of particles. Although gap junctions of large size were seen between ependymal cells in thin section, features corresponding to the particle free corridors have not been observed to date.On leave of absence from the National Institute of Neurological and Communicative Disorders and Stroke, Section of Functional Neurosurgery, Branch of Clinical Neuroscience, Bethesda, Maryland 20014, USAThis work was supported by grants from the Swiss National Foundation for Scientific Research Nos. 3.636.76 and 3.611.0.75, the EMDO Stiftung and the Dr. Eric Slack-Gyr Stiftung     

Der Feinbau des Subfornikalorganes vom Hund

Zusammenfassung Im Subfornikalorgan des jungen Hundes lassen sich mehrere Abschnitte mit unterschiedlichem Aufbau feststellen. Unter dem Ependym befindet sich eine Randzone mit weiten Interzellularspalten. Diese ist wie der Organkern (Zona medialis) von einem Gliaretikulum durchsetzt. In das Retikulum sind zahlreiche kleine Nervenzellen (Typ I) eingelagert. Gegen eine dünne Nervenfaserschicht und den Nucleus triangularis septi gerichtet, schließt sich an das Kerngebiet des Subfornikalorganes eine basale Zone an, die größere Nervenzellen (Typ II) enthält. An der Grenze zur Nervenfaserschicht trifft man auf dünne Ependymkanälchen, die mit Zilien und Mikrozotten ausgekleidet sind. Die Ependymkanälchen haben ihren Ursprung an der Ependymoberflääche. Sie dringen ein Stück weit in das Subfornikalorgan ein und münden schließlich frei im Interzellularspaltraum. Die subependymale Schicht und die Zona medialis sind besonders dicht durch Kapillarsinus vaskularisiert. Die perivaskuläre Bindegewebsscheide ist hier relativ weit. In ihr finden sich Gliazellfortsätze und Nervenzellausläufer, die nur unvollkommen von einer Basalmembran überzogen sind.Die Neuroglia des Subfornikalorganes besteht aus Tanyzyten, satellitären Gliazellen und Mikrogliazellen. An der basalen Grenzzone treten vereinzelt auch Astrozyten und Oligodendrogliazellen auf.Im Neuropil finden sich zahlreiche, meist axodendritische Synapsen, deren präsynaptische Endigungen synaptische Bläschen und 800–1200 Å große, kontrastreiche Granula enthalten. Auf Grund der Mitochondrienstruktur lassen sich zwei Endigungstypen unterscheiden. Hiervon scheint der eine Typ organeigenen Nervenzellen anzugehören. Der andere Typ wird vermutlich von in das Organ eintretenden afferenten Fasern gebildet. Axosomatische Synapsen im Nucleus triangularis septi zeigen den gleichen Aufbau wie Nervenendigungen im Hippocampus.Auf Grund der Organstruktur wird angenommen, daß das Subfornikalorgan ein Chemoreceptor für den Liquor cerebrospinalis ist. Freie Nervenendigungen im Organ geben möglicherweise Neurosekret oder adrenergische Transmittersubstanzen in den Interzellularraum oder in den perivaskulären Bindegewebsspalt ab. Dies dürfte aber nur eine untergeordnete Leistung des Subfornikalorganes sein, da eine Endothelfensterung der Kapillarsinusoide fehlt.

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Summary The subfornical organ of young dogs is subdivided into several parts that show a different structure. Just underneath the ependyma is a marginal zone which exhibits wide intercellular gaps. This region is — as is the case in the zona medialis — interlaced with a glial network. Numerous small nerve cells (type I) are imbedded in this network. The nuclear region of the subfornical organ lies next to a basilar zone that reaches towards a thin layer of nerve fibres and the nucleus triangularis septi. This basilar zone contains larger nerve cells (type II). Thin ependymal caniculi are seen in the region bordering the layer of nerve fibers. The canaliculi are lined with cilia and microvilli. The ependymal canaliculi originate on the surface of the ependyma. They penetrate the subfornical organ and finally end freely in the intercellular space. Subependymal layer and zona medialis are particularly densely vascularized by capillary sinusoids. Here the perivascular connective tissue sheath is relatively wide. In it glia processes and nerve cell processes are found, which are only incompletely covered by a basement membrane.The neuroglia of the subfornical organ consists of tanycytes, satellite cells, and microglia. Astrocytes and oligodendroglia are found sporadically in the region of the basilar border zone.The neuropil exhibits numerous mostly axodendritic synapses, the presynaptic endings of which contain synaptic vesicles and granules of high contrast (800–1200 Å in size). Because of differences in mitochondrial structure two different types of endings can be distinguished. Type one seems to belong to organ specific nerve cells. The other one is presumably formed by afferent fibres which enter the organ. Axosomatic synapses in the nucleus triangularis septi show the same structure as do the nerve endings of the hippocampus.Because of the structure of the organ in question it is postulated that the subfornical organ is a chemoreceptor for the liquor cerebrospinalis. In the organ, free nerve endings possibly secrete neurosecretory material or adrenergic transmitter substances into the intercellular space or into the perivascular connective tissue gap. However, this seems to be a secondary effect of the subfornical organ, as no fenestration of the endothelium is observed in the capillary sinusoids.

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Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.     

The cellular organization and nervous supply of the basilar papilla in the lizard,Calotes versicolor

Summary The basilar papilla of the lizard Calotes versicolor contains about 225 sensory cells. These are of two types: the short-haired type A cells in the ventral (apical) part of the organ, and the type B cells with long hair bundles, in the dorsal (basal) part of the organ. The type A cells are unidirectionally oriented and are covered by a tectorial membrane while the type B cells lack a covering structure and their hair bundles are oriented bidirectionally. Apart from those differences, the type A and type B cells are similar. They are columnar, and display the features common to most sensory cells in inner ear epithelia. The sensory cells are separated by supporting cells, which have long slender processes that keep the sensory cells apart. Close to the surface of the basilar papilla a terminal bar of specialized junctions interlocks adjacent cells. Below this, adjacent supporting cells are linked by an occluding junction.The cochlear nerve enters from the medial (neural) aspect. The fibres of the nerve lose their myelin sheaths as they enter the basilar papilla. Each sensory cell is associated with several nerve endings. All the nerves identified were afferent. Marked variations were seen between nerve endings in the basilar papilla, but no morphological equivalents of any functional differences were observed.This work is supported by grant no. B76-12X-00720-11A from the Swedish Medical Research Council, and by funds from the Karolinska Institute, Stockholm, Sweden.     

Concanavalin A-binding glycoproteins in the subcommissural and the pineal organ of the sheep (Ovis aries)

Summary Glycoproteins rich in mannosyl or glucosyl residues were analyzed in the subcommissural organ (SCO) and the pineal organ of the sheep (Ovis aries). By use of concanavalin A labelled with fluorescein isothiocyanate, fluorescent material was found both in ependymal and hypendymal cells of the SCO. In the pineal organ, either isolated or grouped parenchymal cells showed a marked fluorescence. These cells may correspond to ependymal elements also called interstitial cells or supporting cells. In addition, scarce slender, fluorescent processes were observed in the pineal parenchyma. The techniques of electrophoresis and electrotransfer on nitrocellulose paper have been applied to analyze the glycopeptide content of the SCO and the pineal organ in comparison to cerebellar and cerebral fractions solubilized by use of Triton X 100. Approximately 30 different concanavalin A-reactive glycopeptides were revealed in each fraction. In the SCO extract four glycopeptides (30, 54, 72, 100 kd) might correspond to subunits of the glycoprotein(s) characteristically stored in the ependymal cells of the SCO. In addition, two glycopeptides (32/33, 115 kd) are specific to the pineal organ extract. The possible similarity of the concanavalin A-reactive material in both organs is discussed and a putative secretory activity of the pineal ependymal cells is postulated.     

Ultrastructure of epidermal sensory receptors in Amphibolurus barbatus (Lacertilis: Agamidae)

Summary The histological and ultrastructural organisation of the epidermal sensory organs in Amphibolurus barbatus has been described with respect to their position and possible functions. The sensory organs, located at the scale's edge, are most numerous in scales of the dorsal surface of the head. Most other scales of the body surface have two receptors located laterally to the spine or keel of the scale. In the imbricate scales of the ventral body region, the receptors lie just beneath the reinforced scale lip. Scanning electron microscopy has revealed the surface of the organ to be a crater lacking any surface projections. These sensory organs have a dermal papilla consisting of a nerve plexus and loose connective tissue. The nerve fibres arising from the plexus, pass to the epidermal columnar cells, where some form nerve terminals at the base of the cells, while others pass between them to form nerve terminals embedded in a superficial layer of cuboidal cells. The superficial terminals are held against the overlying keratin by masses of tonofilaments. The keratin is thickened to form a collar around the periphery of the organ but is only about 0.5 m thick immediately above it. Mechanical deformation of the scale's spine or reinforced scale lip may initiate stimulation of the nerve terminals described.     

Fine structure of ependymal cells in the median eminence of the frog and mouse revealed by freeze-etching

Summary Freeze-etched preparations of the ventricular surfaces of ependymal cells clearly reveal the presence of pinocytotic vesicles opening into the third ventricle and large vacuoles formed by broad cell projections. The density of the vesicular openings is approximately 20 per m². The ependymal cells in the median eminence of the frog are adjoined by tight junctions comprised of five to eight interconnected junctional strands, whereas near the median eminence in the mouse only one to two such strands form the tight junction of the ependymal cells. Gap junctions between the adjacent ependymal cells are detected near the median eminence in the mouse but not in the frog.This study was supported in part by a grant from the Japanese Ministry of Education (No. 067670)     

Ependymal and neuronal specializations in the lateral ventricle of the Pekin duck,Anas platyrhynchos

Summary The lateral ventricles of the Pekin duck, Anas platyrhynchos, display characteristic ependymal and hypendymal specializations. Adjacent to the nucleus accumbens and the basal pole of the lateral septum the ventricular surface shows a highly folded pattern either with protrusions into the ventricular lumen or deep invaginations into the brain tissue. These medial and basal ependymal folds are found exclusively in a circumscribed region extending over a range of 600 m in the rostrocaudal direction. Ependymal folds occurring in the lateral wall of the ventricles were traced up to the level of the interventricular foramen. Numerous capillaries are observed in the subependymal layer of these folds.By means of immunocytochemistry with antibodies against chicken vasoactive intestinal polypeptide (VIP) an aggregation of classical cerebrospinal fluid-contacting neurons is shown in the region of the nucleus accumbens and the lateral septum. These neurons are closely related to the ependymal folds. Additional VIP-immunoreactive neurons are scattered in deeper layers of the lateral septum and the nucleus accumbens. The latter are richly innervated by VIP-immunoreactive nerve fibers.The results of the present study are discussed with particular reference to the hypothesis of Kuenzel and van Tienhoven (1982) that ependymal specializations demonstrated in the lateral ventricles of the domestic fowl might represent a new circumventricular organ (lateral septal organ).The authors are greatly indebted to Professor A. Oksche for stimulating discussionsSupported by the Deutsche Forschungsgemeinschaft (Ko 758/2-2; 2-3) and the P. Carl Petersen Foundation     

Cells capable of uptake of horseradish peroxidase in some circumventricular organs of the cat and rat

Summary The structure of mesenchymal cells distributed in some of the hypendymal organs of the circumventricular system in the cat and rat was demonstrated after intravenous injection of high doses of horseradish peroxidase. These cellular elements were observed in the vicinity of blood vessels of the organon vasculosum laminae terminalis, subfornical organ and area postrema. Electron-microscopically, these cells located between the basal laminae of the brain parenchyma and the blood capillaries show long cellular processes encircling fenestrated capillaries. Light and electron-microscopic examination revealed that this cell type is identical with the horseradish peroxidase-uptake cells, previously reported in the vicinity of the hypophysial portal system. Such phagocytic cells may be considered as a cellular component intervening between the brain parenchyma and the blood stream, playing a role in selective barrier functions in the above-mentioned circumventricular organs where a blood-brain barrier in the classical sense of the definition is lacking.This work was supported by grant No. 437002 from the Ministry of Education, Science and Culture, Japan     

The ultrastructure of the human fetal pineal gland

Summary The innervation of the pineal gland, the cell junctions in this organ and junctions between ependymal cells in the pineal recess were investigated in 27 human fetuses (crown-rump length 30–190 mm).Free nerve boutons containing clear and a few dense core vesicles were present in the pineal parenchyma and in the perivascular spaces. The boutons did not make synaptic contacts with the pinealocytes. No evidence for the presence of noradrenaline in the vesicles of nerve boutons was found.Gap junctions, intermediate-like junctions and desmosomes were frequently seen between the pinealocytes. Ruthenium red was used in three fetuses as an extracellular marker.The continuous endothelial cells surrounding the capillary lumen were connected by tight junctions. This indicates the presence of a blood-brain barrier.Tight junctions were present between the ependymal cells in the pineal recess. These junctions constitute an extracellular barrier between the pineal and the cerebrospinal fluid. Acknowledgements: The author wishes to thank Inger Ægidius and Jb Machen for their technical, Ruth Fatum for her linguistic and Karsten Bundgaard for his photographical assistance     

Estrogen-dependent changes in the functional interrelationships among neurons,ependymal cells and glial cells of the arcuate nucleus

Summary The synchronizing effect of ethinylestradiol (4 g/g b.w.) on neurons of the arcuate nucleus 700–950 m caudal to the posterior edge of the optic chiasma was studied by karyometry in 6-week-old albino mice during proestrus.The caudal portion of the arcuate nucleus was identified as the most estrogen-sensitive subdivision; all neurons showed an increase in their nuclear area (mean transect, profile area of the nucleus) 1 h following administration of ethinylestradiol. This hypothalamic region was selected for the subsequent electron-microscopic cytometric study to analyze functional interrelationships among neurons, ependymal cells and glial cells. Six and 12 days after ovariectomy no significant change in the nuclear area of neurons and ependymal cells was found 850–950 m behind the posterior slope of the optic chiasma, but the neurons exhibited a decrease in the number of polyribosomes, the volume fraction (V_Vmi) and the surface density of the inner membrane of mitochondria (S_Vmi). A similar decrease in V_Vmi and S_Vmi was measured in the apical part of ependymal cells and in the pericapillary profiles of ependymal and glial cells, which was accompanied by a reduction in the surface density of ependymal processes extending into the ventricular lumen. In addition, no change of V_Vmi and S_Vmi was seen in the basal subnuclear part of ependymal cells.This bipolar functional reaction of ependymal cells after ovariectomy is discussed as an indicator of ependymal control of neuronal activity by sequestering biologically active agents, e.g., transmitters of neurohormones, in their apical and basal extensions facing the ventricular surface or the pericapillary space.     

The neurohypophysis of the crested newt

Summary In the crested newt, the ultrastructural organization of the pars nervosa is analogous to that already known in non-mammal tetrapods. An orderly array of ependymal cells makes up the inner limiting layer while less abundant pituicytes are irregularly distributed within this organ. Light and dark pituicytes can be distinguished on the basis of the relative density of the cytoplasmic matrix and the distribution of the cell organelles.Both the ependymal cells and pituicytes are rich in dense bodies and possess extensive processes which ramify among the nerve fibers, often reaching the pericapillary space which they can line for long distances.The main components of the pars nervosa are nerve fibers and nerve terminals (type A), containing electron dense granules 1200–2000 Å in diameter together with clear vesicles averaging 250–400 Å. These fibers are likely to correspond to the aldehyde fuchsin positive neurosecretory fibers revealed by light microscopy. Differences in the granule size within the fibers and terminals lead to further recognition of two subgroups (A₁ and A₂).Other fibers and terminals (type B) containing clear vesicles and granular vesicles 600 to 1000 Å in diameter, possibly of aminergic type, are also encountered. These fibers are rare and can be seen only in the portion of the pars nervosa near the pars intermedia of the adenohypophysis.Lastly, fibers and terminals containing only clear vesicles ranging from 250 to 400 Å (type C) are occasionally found.Nerve endings are often formed by type A fibers on the perivascular space and on the perivascular processes of the ependymal cells and pituicytes. In agreement with recent findings available in the literature, the occurrence of synaptoid contacts between these terminals and both pituicytes and ependymal cells may confirm the active role of these cells in transport and release of neurosecretion.Work supported by a grant from the Consiglio Nazionale delle Ricerche.We are gratefully indebted to Dr. G. Gendusa and P. Balbi for technical assistance, dr. G. E. Andreoletti for statistical analysis.     

Development of the subfornical organ and area postrema of the male albino mouse. Karyometric effect of neonatal and prepuberal castration

We have studied the karyometric development of the nuclei of the ependymal cells and neurons of the subfornical organ and the area postrema in the male albino mouse from the 5th to the 190th postnatal day. We have found similar patterns of development in both although the area postrema showed more significant postnatal oscillations than those of the subfornical organ, suggesting a more intimate chronological relationship to gonadal development. We have furthermore analyzed the development in two experimental groups: in the one animals were castrated at birth, in the other, castration was made on the 20th postnatal day. We have found that neonatal castration produced a significant decrease of nuclear sizes; this was more evident in the subfornical organ than in the area postrema in earlier stages of development while the response was similar in both at peripuberal ages. The response to prepuberal castration was similar in both organs.     

Die Feinstruktur des Subfornikalorgans beim Kaninchen

Zusammenfassung Im Subfornikalorgan des Kaninchens zeigen dieParenchymzellen sämtliche Feinstrukturmerkmale von Nervenzellen; an ihren Mitochondrion sind longitudinale Cristae und eine zentrale Aufhellung charakteristisch. Ein beträchtlicher Teil der Parenchymzellen unterliegt einervakuolären Umwandlung: die Cisternen des endoplasmatischen Reticulum erweitern sich; kleine Vakuolen, deren Inhalt als eine Art Neurosekret aufzufassen ist, konfluieren zu größeren; schließlich enthält die Zelle eine einzige Riesenvakuole, die nur noch von einem äußerst schmalen Cytoplasmasaum umgeben ist; ein Kern ist auf den Schnitten nicht mehr zu sehen. Auch Parenchymzellfortsätze werden vakuolisiert. Die Riesenvakuolen sind im Ependymbereich gehäuft zu beobachten. Zwischen ihnen und dem Ventrikellumen wird stets eine, oft aus extrem abgeplatteten Zellelementen bestehende, Trennwand festgestellt. — Der überwiegende Teil derneuronalen Fortsätze entstammt den Parenchymzellen; andere gehören vermutlich zu außerhalb des Subfornikalorgans gelegenen Neuronen. Vereinzelt werden Axone mit Myelinscheide gefunden. Untereinander und mit Perikarya von Parenchymzellen sind neuronale Fortsätze durch axo-dendritische und axo-somatische Synapsen verbunden. Einige Fortsätze enthalten elektronendichte Granula; außer Katecholamingranula kommt eine Population von größeren Elementargranula (Durchmesser 1050–1350 Å) vor. Aufweitungen neuronaler Fortsätze, die in dichter Packung granulaartige Einschlüsse enthalten, werden als Herring-Körper aufgefaßt.Am Ependym fällt eine bemerkenswerte Variabilität auf. Zwischen hochprismatischen Zellen mit basalen Fortsätzen, die geradlinig ins Organinnere ziehen oder umbiegen, und extrem abgeflachten, kommen mannigfache, z.T. bizarre Formen vor. Ähnlich unregelmäßig ist die Ependymoberfläche, an der glatte Bereiche abrupt mit tiefen Einsenkungen oder Ausstülpungen wechseln; auf freie Strecken folgen Abschnitte, die Cilien oder Büschel von Mikrovilli tragen. Ausnahmsweise werden im Ventrikel neuronale Fortsätze gefunden. Eine Besonderheit der Ependymzellen sind fingerförmige laterale Ausläufer, die in benachbarte Zellen einwachsen. Das Cytoplasma hat sehr unterschiedliche Dichte; es enthält 0,3–0,45 große dichte Granula.— Dassubependymale Geflecht besteht überwiegend aus umgebogenen Fortsätzen von Ependymzellen; zusammen mit anderen glialen und einigen neuronalen Fortsätzen bilden sie oberflächenparallel angeordnete Bündel. — Im Organinneren finden sich in großer Zahlprotoplasmatische Astrocyten, filamentäre Astrocyten sowie Übergangsformen zwischen beiden. Oligodendrocyten werden selten gesehen. Als dichte Gliazellen werden Elemente beschrieben, die sich keinem der bekannten Gliazelltypen zuordnen lassen; ihr dichtes Cytoplasma enthält viel endoplasmatisches Reticulum.Satellitenzellen liegen Parenchymzellen halbmondartig an.

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The fine structure of the subfornical organ in the rabbitII. Neurons and glia

Summary In the subfornical organ of the rabbit the parenchymal cells show all structural features of nervous cells. Most of their mitochondria are characterized by longitudinally arranged cristae and a central less dense area. Numerous parenchymal cells become vacuolated: The cisternae of the endoplasmic reticulum dilate; small vacuoles filled with a kind of neurosecretory substance confluate into larger vacuoles. Finally the cell contains one giant vacuole lined only by a very thin rim of cytoplasm; a nucleus cannot be found. The processes of parenchymal cells may be vacuolated as well. The giant vacuoles accumulate in the ependymal zone. Between these vacuoles and the ventricular lumen a cellular layer consisting of extremely flattened elements is always observed. — Most of the neuronal processes originate from parenchymal cells; others seem to be part of neurons outside of the subfornical organ. Sometimes myelinated axons are found. Neuronal processes are connected with one another and with the perikarya of parenchymal cells by axo-dendritic and axo-somatic synapses. Some processes contain dense granules; apart from catecholamine granules a population with larger elementary granules is found (diameter 1050–1350 Å). Extensions of neuronal processes containing tightly packed granule-like inclusions are supposed to be Herring bodies.The ependymal cells show great variations. Besides prismatic cells with basal processes running into the interior of the organ or curving, and extremely flattened cells many other bizarre cell shapes are found. The surface of the ependymal cells is also irregular: smooth areas alternate abruptly with deep invaginations or protrusions or with areas bearing cilia or tufts of microvilli. Occasionally, in the ventricular lumen neuronal processes are found. The ependymal cells possess peculiar finger-like lateral processes penetrating into neighbouring cells. The density of the cytoplasm varies considerably; the cells contain dense granules with a diameter of 0.3–0.45 . — The subependymal texture is built up mainly of curving processes of ependymal cells. Together with other glial and some neuronal processes they form bundles running in a plane parallel to the surface. — In the interior of the organ many protoplasmic astrocytes, filamentous astrocytes and cells transitional between the former are found. Oligodendrocytes are rarely seen. Cells with a dense cytoplasm containing numerous cisternae of the endoplasmic reticulum cannot be ascribed to one of the conventional types of glial cells; they are termed dense glial cells. Parenchymal cells are surrounded by satellite cells which are shaped like a half-moon.

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Herrn Professor Dr.Benno Romeis zum 80. Geburtstag gewidmet.

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Die Arbeit wurde mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft ausgeführt. — FrauH. Asam danken wir für ihre hervorragende Mitarbeit bei der Präparation und für die Anfertigung der Abbildungen; bei photographischen Arbeiten halfen außerdem Frl.R. Beck, Frl.C. Degen und FrauB. Rottmann. Herrn Dr.A. Weindl danken wir für wertvolle Diskussionen.     

Acetylcholinesterase-containing nerve cells in the pineal complex and subcommissural area of the frogs,Rana ridibunda and Rana esculenta

Summary In Rana esculenta and Rana ridibunda the frontal organ and the pineal organ (epiphysis cerebri) form a pineal complex. Approximately 60 nerve cells of the frontal organ and 220–320 nerve cells of the pineal organ display a positive acetylcholinesterase reaction (Karnovsky and Roots, 1964). The dorsal wall of the pineal organ is considerably richer in acetylcholinesterase-positive neurons than the ventral wall (ratio 31); a group of unusually large-sized nerve cells occurs in the rostral portion of the frog pineal. Two different types of nerve cells were observed in the pineal complex: multipolar and pseudounipolar elements. The former are embedded in the pineal parenchyma and their processes penetrate radially into the plexiform layer, whereas the latter are distributed along the roots of the pineal tract near the basal lamina. The ratio of the multipolar to pseudounipolar neurons is 14 for the frontal organ and 35 for the pineal organ. The multipolar elements may be interneurons; the pseudouni-polar cells send one of their processes into the pineal tract. At the caudal end of the pineal organ 30–50 unipolar nerve cells are clustered in juxtaposition with the pineal tract, and other 30–50 unipolar neurons are scattered along the basis of the subcommissural organ. Some of these nerve cells emit their processes toward the mesencephalon and others toward the pineal organ via the pineal tract. The results are discussed with respect to previous physiological and morphological findings on the pineal complex of Anura.Supported by a fellowship from the Alexander von Humboldt Foundation, Federal Republic of Germany, to K. Wake. Completed November 22, 1973.Supported by the Deutsche Forschungsgemeinschaft.     

The secretory ependymal cells of the subcommissural organ: Which role in hydrocephalus?

Ependyma in the central nervous system gives rise to several specialized cell types, including the secretory ependymal cells located in the subcommissural organ. These elongated cells show large cisternae in their cytoplasm, which are filled with material secreted into the cerebrospinal fluid and toward the leptomeningeal spaces. A specific secretion of the subcommissural organ was named SCO-spondin, regarding its marked homology with developmental proteins of the thrombospondin superfamily (presence of thrombospondin type 1 repeats). The ependymal cells of the subcommissural organ and SCO-spondin secretion are suspected to play a crucial role in cerebrospinal fluid flow and/or homeostasis. There is a close correlation between absence of the subcommissural organ and hydrocephalus in rat and mouse strains exhibiting congenital hydrocephalus, and in a number of mice transgenic for developmental genes. The ependymal cells of the subcommissural organ are under research as a key factor in several developmental processes of the central nervous system.