Supraependymal cells and fibers in the third ventricle of the domestic chicken. A scanning electron microscopic study

Supraependymal cells, fibers and what are presumed to be neuronal bulb-like projections were found in the third ventricle of the domestic chicken with a scanning electron microscope. At least two types of supraependymal cells were found: neuron-like cells and phagocyte-like cells. The former were predominantly seen in the area of the paraventricular organ and infundibular recess. The latter were abundant on the ventricular surface of the median eminence and subfornical organ. Bulb or club-like projections thought to be the dendritic terminals of CSF-contacting neurons were observed in the area of the paraventricular organ and infundibular recess. Similar structures were observed at the preoptic recess as well. The supraependymal neuronal components found in the domestic chicken differed from those of mammals in several respects: 1. the wall of the third ventricle was devoid of supraependymal fibrous plexus except for that of the paraventricular organ; 2. bulb-like projections were abundant in the area of the paraventricular organ; 3. supraependymal neuron-like cells were unipolar or bipolar in appearance. These data underline the dissimilarity of the CSF-contacting neuronal system of birds and mammals.     

Correlative scanning-transmission electron microscopic examination of the perinatal rat brain

Summary The ultrastructural organization of the perinatal hypothalamus and the dynamics of neuronal and ependymal growth and plasticity were examined in this investigation. The brains of fetal rats 16, 17 and 18 days in utero and those of postnatal rats 1–16 days post partum were fixed with aldehyde fixatives and prepared for combined SEM/TEM analysis. By day 17 in utero the ventricular (ependymal) surfaces of the fetal thalamic wall, cerebral vesicle and rhomboid fossa were relatively well differentiated with cilia and microvilli. Type II histiocytes were the first supraependymal cell to appear upon the ventricular lumen and were evident by day 17 in utero. In contrast, the apical surfaces of tanycytes of the infundibular recess as well as those of most other circumventricular organs were poorly differentiated and unremarkable. Tanycytes of the infundibular recess exhibited a simple hexagonal mosaic pattern of apposed plasmalemmata and even by day 1 post partum few cilia or microvilli were evident.By day 5–6 post partum Type I supraependymal neurons and axonal processes began to make their appearance with some emerging from the underlying parenchyma of the median eminence. By day 16 post partum the ventricular surface of the infundibular recess was comparable with that of the adult.The Type I supraependymal neurons are remarkably similar in their ultrastructural organization with parvicellular neurosecretory neurons elsewhere in the endocrine hypothalamus. Their emergence at day 5–6 post partum suggests a possible correlation with the critical period of sexual differentiation and a potential receptor role for this cell line. On the contrary this phenomenon may simply be a developmental anomaly. Nonetheless, the mergence of such elements upon the lumen of the third cerebral ventricle underscores a remarkable degree of neuronal plasticity in the perinatal hypothalamus.Supported by USPHS Program Project Grant NS 11642-04 and USPHS-BRSG Grant RR-05403.The authors wish to thank N. Kutryeff for her excellent technical assistance     

Cerebrospinal fluid contacting neurons in the reduced brain ventricular system of the atlantic hagfish,Myxine glutinosa

Cerebrospinal fluid (CSF)-contacting neurons are sensory-type cells sending ciliated dendritic process into the CSF. Some of the prosencephalic CSF-contacting neurons of higher vertebrates were postulated to be chemoreceptors detecting the chemical composition of the CSF, other cells may percieve light as "deep encephalic photoreceptors". In our earlier works, CSF-contacting neurons of the mechanoreceptor-type were described around the central canal of the hagfish spinal cord. It was supposed that perceiving the flow of the CSF they are involved in vasoregulatory mechanisms of the nervous tissue. In the present work, we examined the brain ventricular system of the Atlantic hagfish with special reference to the presence and fine structure of CSF-contacting neurons. Myxinoids have an ontogenetically reduced brain ventricular system. In the adult hagfish (Myxine glutinosa) the lumen of the lateral ventricle is closed, the third ventricle has a preoptic-, infundibular and subhabenular part that are not connected to each other. The choroid plexus is absent. The infundibular part of the third ventricle has a medial hypophyseal recess and, more caudally, a paired lateral recess. We found CSF-contacting neurons in the lower part of the third ventricle, in the preoptic and infundibular recess as well as in the lateral infundibular recesses. No CSF-contacting neurons were found in the cerebral aqueduct connecting the subhabenular recess to the fourth ventricle. There is a pineal recess and a well-developed subcommissural organ at the rostral end of the aqueduct. Extending from the caudal part of the fourth ventricle in the medulla to the caudal end of the spinal cord, the central canal has a dorsal and ventral part. Dendrites of CSF-contacting neurons are protruding into the ventral lumen. Corroborating the supposed choroid plexus-like function of the wall of the dorsal central canal, segmental vessels reach a thin area on both sides of the ependymal lining. The perikarya of the CSF-contacting neurons found in the brain ventricles are mainly bipolar and contain granular vesicles of various size. The bulb-like terminal of their ventricular dendrites bears several stereocilia and contains basal bodies as well as mitochondria. Basal bodies emit cilia of the 9+0-type. Cilia may arise from the basal body and accessory basal body as well. The axons run ependymofugally and enter--partially cross--the periventricular synaptic zones. No neurohemal terminals similar to those formed by spinal CSF-contacting neurons of higher vertebrates have been found in the hagfish. We suppose that CSF-contacting neurons transform CSF-mediated non-synaptic information taken up by their ventricular dendrites to synaptic one. A light-sensitive role for some (preoptic?) groups of CSF-contacting neurons cannot be excluded.     

Immunohistochemical studies of the serotonergic supraependymal plexus in the mammalian ventricular system, with special reference to the characteristic reticular ramification

Distributional and morphological features, especially characteristics of the ramification of serotonin-containing supraependymal fibers (SEF), were studied in the ventricular systems of mammals (mouse, rat, guinea pig, rabbit, cat, dog, monkey) by means of a modified peroxidase antiperoxidase technique, using antiserotonin antiserum prepared in our laboratory. SEF were present in all ventricular systems, except on the third ventricle floor and in the choroid plexus. The density of SEF was higher in the smaller species. In the rat, light- and scanning electron microscopical SEF were almost completely abolished 1 week after intraventricular administration of 5,6-dihydroxytryptamine. Ramification of SEF was complicated; the SEF formed a true network with frequent anastomosing. In the ventricular system of rats rendered hydrocephalic by kaolin administration, the mode of axonal branching in the supraependymal plexus could best be analyzed by the scanning electron microscope because the meshes of the plexus were spread out.     

A scanning electron microscopic survey of the brain ventricular system of the female armadillo

Summary The scanning electron microscope was used to survey the brain ventricular system of the female armadillo (Dasypus novemcinctus) with emphasis on the third ventricle. The walls of the lateral ventricles, aqueduct, and fourth ventricle are covered by long cilia. In the lateral ventricle, the cilia are arranged in groups; but in the aqueduct and fourth ventricle, they are evenly placed over the cellular surfaces. The ependymal cells of the third ventricle are densely ciliated except for the organum vasculosum and infundibular recess. The non-ciliated luminal surface of these areas has a pebblestone appearance punctuated by numerous microvilli and two types of supraependymal cells.Supported by Edward G. Schlieder Foundation GrantThe authors would like to thank Jacqueline Skaggs for her secretarial assistance and Garbis Kerimian for his photographic work     

The dorso-lateral recess of the hypothalamic ventricle in neonatal rats

Light and electron microscopy of the hypothalamic ventricle in neonatal rats demonstrate morphological specializations of the ventricular wall at the level of the premammillary region of the third ventricle. The morphological features are: (1) A ventricular recess that we have called the "hypothalamic dorso-lateral recess" (HDR). (2) The presence of intraventricular capillaries near the dorso-lateral recess. (3) The HDR possessing a specialized ependymal lining; this consists of non-ciliated cells with short microvilli and bleb-like processes. (4) The existence of cerebrospinal fluid-contacting neurons within the HDR. (5) The presence of numerous phagocytic supraependymal cells. The HDR is not found in adult rats. This indicates that the dorso-lateral recess may play a physiological role during development.     

Ventricular system and choroid plexuses of the human brain during the embryonic period proper

This morphological study, based on serial sections and graphic reconstructions at 4-8 postovulatory weeks (stages 11-23), is believed to be the first account of the ventricular system in staged human embryos. Closure of the caudal neuropore at stage 12 heralds the onset of the ventricular system and separates the ependymal from the amniotic fluid. After the appearance of the optic ventricle at stage 11, the cavity of the telencephalon medium is discernible at stage 13. At stage 14 the future cerebral hemispheres and lateral ventricles begin, and the rhomboid fossa becomes apparent. The medial and lateral ventricular eminences cause indentations in the lateral ventricle by stage 15. The hypothalamic sulcus is evident at stage 16. At stages 17-18 the interventricular foramina are becoming relatively smaller, and cellular accumulations indicate the future choroid villi of the fourth and lateral ventricles. The areae membranaceae rostralis and caudalis are visible in the roof of the fourth ventricle at stage 18, and the paraphysis is appearing. At stage 19 choroid villi are seen in the fourth ventricle, and a mesencephalic evagination (Blindsack) is detectable. Choroid villi are noticeable in the lateral ventricle at stage 20. An olfactory ventricle is present by stage 21. At about stages 21-23 the lateral ventricle has become C-shaped, so that anterior and inferior horns are visible. Several recesses, e.g., the optic, infundibular, and pineal, develop in the third ventricle during the embryonic period. Features of the ventricular system that do not become apparent until the fetal period include the posterior horn of the lateral ventricle, choroid plexus of the third ventricle, suprapineal recess, interthalamic adhesion, aqueduct, and apertures in the roof of the fourth ventricle.     

Supraependymal cells occurrence in ventricular system of small ruminants. Scanning electron microscopy study

The third cerebral ventricle ependymal lining including eminentia medians was studied by means of SEM in 20 sheep, 13 goats and one goat hermaphrodite. Supraependymal cells in addition to the usual supraependymal structures were observed. In sheep, they occurred in the infundibular low part only in females during oestrus. In goats, they were present in almost every case with the exception of male animals during the "rest" period (April). The number, topography and-to some extent--the appearance of the goat supraependymal cells were in relation to the animal's sex, and the females to the ovarian cycle phase. The supraependymal cells were found on the eminentia mediana surface only in the goats. In small ruminants, the processes of most supraependymal cells formed the ruffled membranes and only the eminentia mediana supraependymal cells--and in hermaphrodite also in the infundibular rostral part--resembled more neurons.     

Localization of immunoreactive prolactin in ependyma and circumventricular organs of rat brain

Summary Immunoreactive prolactin (IMP) has been localized in the male rat brain using the soluble peroxidase-anti-peroxidase (PAP) technique. In normal untreated animals, reaction product was seen in choroid plexus (CP) and in ependymal cells of the ventricular lining with heaviest concentrations of positively staining cells in the 3rd ventricle near the subcommisural organ (SCO), in the lateral ventricles near the subfornical organ (SFO), and in the 4th ventricle near the area postrema (AP). IMP was also present in numerous ependymal cells resembling tanycytes in the cerebral aqueduct, central canal of the spinal cord at the level of the AP, the organum vasculosum of the lamina terminalis (OVLT) and the floor of the infundibular recess. Immunoreactive cells resembling neurons were localized within the substance of the AP, SCO, and OVLT. IMP was also present in fibers of the zona externa of the median eminence and infundibular stalk; a few cells of the pars tuberalis contained reaction product. Hypophysectomized rats and bromocriptine-treated rats exhibited a similar staining pattern except that bromocriptine treatment eliminated IMP from most CP cells. Hypophysectomy, bromocriptine or estrogen treatment enhanced staining for IMP in cells of the pars tuberalis; estrogen treatment or hypophysectomy produced an increase in the number and distribution of immunoreactive cells as well as increased density of reaction product in cells of the medial habenular nucleus. The functional relevance of prolactin in these locations in the brain, the possible routes of transport of prolactin from the pituitary gland to the central nervous system, and the strong suggestion of extra-pituitary sites of synthesis of a prolactin-like hormone are discussed.     

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.     

Morphology and distribution of tanycytes in the third ventricle of the adult rat. A study using semithin methacrylate sections

Light microscopy and semithin methacrylate sections were used to study the tanycytic projections and morphology in the floor of the third ventricle of the rat. The tanycytic cell soma was located in the ependyma. The luminal surface showed minute protrusions into the ventricular space and their basal processes projected across the width of the parenchyma of the infundibular region. During their course, tanycytic processes made contact with capillaries in the parenchyma and pial surface, suggesting that they might be involved in uptake and/or delivery mechanisms between the cerebrospinal fluid, hypothalamic cells and blood vessels.     

The ventricular system in neuroendocrine mechanisms

Summary This investigation has utilized a correlative scanning-transmission electron microscopic technique in the analysis of the primate cerebral ventricular system. This approach has demonstrated a complex network of supraependymal cellular elements upon the walls of the third cerebral ventricle in direct contact with the ventricular lumen. Type I neuronal-like cells and type II histiocytic-like cells with potential phagocytic capabilities have been observed in large numbers throughout the third ventricle. Type I neuron-like cells are discussed in the context that they may represent a population of receptor-cells which serve to assess ambient changes in the composition of bioactive peptides in the cerebrospinal fluid and may serve as a supraependymal network that integrates the endocrine hypothalamus with other circumventricular organs which may also be sites of neuroendocrine transduction.Supported by USPHS Program Project Grant NS-11642Career Development Awardee GM K04 70001     

大白鼠第三脑室室管膜的超微结构

本文用扫描和透射电镜证实在成年大白鼠的第三脑室存在室管膜上神经元样细胞、神经胶质细胞和类组织细胞。神经纤维发自神经元样细胞或自脑室外穿入室腔而来,其末梢内含有清亮囊泡或兼有大颗粒囊泡。室腔內尚有膨大的树突末梢和室管膜细胞的球状小体。上述各种结构与感受、分泌和调节功能有关,并为下丘脑控制垂体机能的另一新途径(经脑脊液和室管膜)提供了形态学依据。     

Scanning electron microscopy of the third ventricle of sheep

Summary Scanning electron microscopy of the third ventricle of sheep demonstrates areas of ciliated ependymal cells at the dorsal and middle third. The cilia of the dorsal portion of the ventricle have biconcave discs that are attached to each cilium by a slender stalk. The lower third and floor of the ventricular wall, as well as the pineal recess, are largely covered by ependymal cells that possess numerous microvilli with only a few isolated cilia scattered along cell surfaces. The infundibular recess is papillated with apical blebs of the ependymal cells that project into the lumen of the recess. Measurements of these surface elements indicate an average diameter of 0.28 for cilia, 0.10 for microvilli and 0.50 for the apical blebs of the infundibular recess. The functional significance of the regional differences in surface structures is discussed in relation to cerebrospinal fluid movement, ependymoabsorption and ependymosecretion.Supported by U.S.P.H.S. Grant NS 08171.Career Development Awardee KO4 GM 70001.     

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.     

The third ventricle of monkeys

Summary 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 ventricle 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.Supported by USPHS Grants RR-05432, GM-16598 and HD-10010 from the National Institutes of Health and GSRF 171 funds from the University of Washington Graduate School. Portions of this work have been reported previously in abstract form in Anat. Rec. 175, 294 (1973) (before the 86th annual session of the American Association of Anatomists, New York, N.Y., April, 1973)     

Serotonin axons of the ependyma and circumventricular organs in the forebrain of the guinea pig

Summary The distribution of supraependymal nerve fibers (SEF) containing serotonin (5-HT) was investigated immunohistochemically in the forebrain of the guinea pig. The highest densities of immunoreactive axons were found in the pars centralis and the inferior horn of the lateral ventricle and also in the superior part of the third ventricle. Because of the special development of the choroid plexus in these ventricular regions, it is suggested that 5-HT SEF might be involved in the regulation of the composition of the cerebrospinal fluid. The ependyma lining the circumventricular organs located in the forebrain, was not observed to receive a significant 5-HT-SEF innervation. In the pituitary gland, a loose but constant network of 5-HT axons, resembling those which course in the anterobasal hypothalamus, arcuate nucleus and internal layer of the median eminence, was observed in the neural lobe. In the epiphysis, immunoreactive 5-HT was detected in all pinealocytes (the entire cell was filled with reaction product) and in fibers running between them.     

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.     

Permeability of the csf-brain barrier in the median eminence of rats in the perinatal period

The ultrastructure and permeability of the CSF-brain barrier in the median eminence were studied during the perinatal period in rats with electron microscopy, electron-microscopic radioautography and electron-dense markers. It was shown that the ependymal cells forming the ventral portion of the 3rd ventricle (infundibular recess) are joined by the specialized junctions. The specialized junctions are similar in ultrastructure in different parts of infundibular recess all through the perinatal period. They consist of the tight junctions which are sometimes in series with the gap junctions and adhesion zones. An electron-dense marker, La3+, injected into the cerebral ventricles, penetrates through the foetal ependymal linins both via the ependymal cells and intercellularly in all parts of the infundibular recess. In neonatal rats La3+ penetrates in the same way in the rostral part of infundibular recess only, while in the caudal part its permeability is markedly limited, apparently by the tight junctions formed de novo around the cells. 3H-dopamine, introduced into the ventricles, crosses over the ependymal linins apparently in the same way as La3+. Then the labeled dopamine is transported into the pericapillary space of the primary portal plexus and, finally, into the capillary lumen. Thus, the results obtained point to the permeability of the CSF-brain barrier in the foetal median eminence for the markers including neurohormones. In the postnatal period the permeability of the ependyma becomes limited due to the formation of the tight junctions surrounding the ependymal cells.     

Monoamines in the liquor-contacting nerve cells in the hypothalamus of the lamprey,Lampetra fluviatilis L.

Summary The hypothalamus of adult lampreys (Lampetra fluviatilis L.) was studied by means of light and fluorescence microscopy (Falck's technique). Some single liquorcontacting nerve cells (LCNC) showing a weak green fluorescence were demonstrated in the ventral part of the third ventricle, above the preoptic recess. Caudally numerous fluorescent LCNC occur in the ventral part of the third ventricle, in the infundibular and in the posterior recess. The LCNC are to be observed between or below the ependymal cells lining the ventricular wall. These cells appear to be of the bipolar type. One process with a club-like protrusion is directed into the ventricular lumen, the other one into the opposite direction. Two types of fluorescent LCNC were distinguished: yellowish green cells, containing catecholamines, and yellowish orange cells, containing 5-hydroxytryptamine. Some similarity between the hypothalamic monoaminergic LCNC in lampreys and LCNC of the paraventricular organ of the other vertebrates was found. The localization, structure and monoaminergic nature of the hypothalamic LCNC in lampreys suggest the possibility, that their monoamines are released into the cerebrospinal fluid.I am very obliged to Prof. A.L. Polenov for his continuous help and advice. The skilful technical assistance of Mrs. G.N. Yakshina is gratefully acknowledged.