Fine structure of the median eminence and the pars nervosa of the bullfrog,Rana catesbeiana

Summary The hypothalamic neurosecretory system of the bullfrog, Rana catesbeiana, was studied with light- and electron microscopy. The median eminence is roughly divided into two portions. The upper portion mostly consists of ependymal cells, glial cells and preoptico-hypophysial nerve tract, whereas in the lower portion, neurosecretory axons, glial cells, processes of glial and ependymal cells, and fine blood vessels of the hypothalamic portal vein are located. A part of the neurosecretory axons of the preoptico-hypophysial tract proceeds to the lower portion of the median eminence. These axons are arranged perpendicularly to the capillaries of the hypothalamic portal vein. The glial cells are densely located in the area of the median eminence where neurosecretory material is abundant. The neurosecretory material in the neurosecretory cells, their axons, the median eminence and the pars nervosa of the bullfrog shows a positive reaction to PAS treatment.The neurohemal area of the median eminence is occupied by many neurosecretory and non-neurosecretory axons, containing neurosecretory granules and/or synaptic vesicles. The axonal portions with the synaptic vesicles which are considered to be the nerve endings abut on the capillaries of the portal system. The size of synaptic vesicles in the axon terminals containing few neurosecretory granules is larger than those in the endings with many neurosecretory granules. Infrequently glial and ependymal processes are interposed between the nerve endings and the capillary wall.In the hilar region of the infundibulum, synapses are frequently observed between the thin fibers with or without neurosecretory granules and dendrites of non-neurosecretory neurons. The probable functions of these synapses are briefly discussed on the basis of our findings. Both in the hilar region of the infundibulum and in the pars nervosa, electron-dense neurosecretory granules of two different sizes were observed. The median eminence contains only one type of granules.The fine structure of the pars nervosa shows similar structures to those of the median eminence. Both in the median eminence and the pars nervosa, the fenestrated endothelium of the capillaries was frequently observed. The thick perivascular connective tissue space containing fibroblasts and collagen fibrils was observed both in the median eminence and the pars nervosa. Vesicles in the cytoplasm of the endothelial cells which appear to take a part in the transendothelial transport were observed.This investigation was supported in part by United States Public Health Service Research Grant, No. A-3678, to Hideshi Kobayashi from the National Institute of Arthritis and Metabolic Diseases and partly by a grant for Fundamental Scientific Research from the Ministry of Education of Japan. The authors wish to express their thanks to Prof. K. Takewaki for his kind encouragement.     

Ultrastructural study of the uptake of peroxidase by the rat median eminence

An active role of the ependymal cells (tanycytes) of the median eminence in the transport of hypothalamic hormones has been recently suggested. In order to investigate the fate of material present in the cerebrospinal fluid, a protein tracer, horse-radish peroxidase (HRP) was injected into the left lateral ventricle of rats. Two minutes after the injection, HRP had largely diffused between tanycytes and hypendymal cells. As soon as 5 min after the injection, HRP had completely penetrated all the layers of the median eminence. A few labelled vesicles and lysosomes were occasionally seen in ependymal and glial cells. At longer time intervals (20 min, 1 and 4 hrs), a reaction was observed in the lumen of fenestrated capillaries of the pituitary portal plexus. In many nerve endings of the external zone, vesicles and lysosomes were seen to contain HRP. An interesting observation was the localization of HRP between nerve endings and cells in both the pars nervosa and the pars intermedia of the pituitary gland. No reaction was recorded in the anterior pituitary and the kidney. Seventeen hours after the injection, the extracellular space was free of reaction but a few positive intracellular structure were still found. These results clearly indicate that some material from the third ventricle can rapidly diffuse between cells and axons of the median eminence to reach the fenestrated capillaries of the pituitary portal plexus and the posterior pituitary without involving an active transport by tanycytes.     

Fine structure and its functional properties of the ependymal cell in the frog median eminence

Summary Intercellular canaliculi surrounded by several ependymal cells, having numerous microvilli and a few cilia on the apical surface, are present throughout the frog median eminence. The intercellular canaliculi penetrate deeply near the portal vessel from the third ventricle. They are separated from the pericapillary space only by the thin cytoplasm of the ependymal cell.The cytoplasmic protrusions containing a large number of clear vesicles are often found at the apical surface of ependymal cells facing the third ventricle or the lumen of intercellular canaliculus. The ependymal cell shows well developed Golgi apparatus and well developed rough endoplasmic reticulum in its cytoplasm. Dense granules of about 1200–1500 A diameter suggesting secretory materials are found in small number near the Golgi apparatus and abundantly in the ependymal process lying around the portal vessel.Synaptic contacts between the ependymal cell and two different types of the nerve endings, monoaminergic and peptidergic, are frequently observed. A few small flasklike caveolae suggesting micropinocytosis are found in the post-synaptic membrane as well as in the lateral and basal plasma membranes of the ependymal cell. The author consideres that the ependymal cell in this region has secretory and transport (absorption) activities.     

Ultrastructure of the median eminence of the rat

Summary The ependymal cells bordering the median eminence to the third ventricle are characterised by many microvillus-like projections and bulbous cell processes of the luminal plasma membrane. The latter contain many vesicles 500–1,000 Å in diameter. Cilia with 9+2 fibrillar pattern are seen occasionally. Adhesive devices in the from of zonula adhaerens and zonula occludens are found in the apical part of the intercellular junction. Unmyelinated nerve fibres with a mean diameter of 1 and containing many electron dense granules of 830–1,330 Å are often seen between the ependymal cells.Two types of glial cells are found in the median eminence. One is characterised by a nucleus with dense blods of chromatin and dense cytoplasm, and it is associated chiefly with the nerve fibres in the region of the hypothalamo-hypophysial tract. The other type of glial cell is characterised by fine, uniformly distributed chromatin in the nucleus and a relatively pale cytoplasm and branched processes which terminate perivascularly in the base of the median eminence.Myelinated nerve fibres are seen only in the region of the hypothalamo-hypophysial tract. Only a part of them contain electron dense granules 1,330–2,330 Å in diameter.Three types of unmyelinated nerve fibres can be distinguished in the median eminence according to the size of the electron dense granules they contain: 1. Nerve fibres containing granules 1,330–2,330 Å in diameter. They are seen primarily in the hypothalamo-hypophysial tract, but also in the zona externa; 2. those containing granules with a mean diameter of 1,330 Å; and 3. those containing granules with a mean diameter of 1,000 Å. The last two types are both encountered in the hypothalamo-hypophysial tract, the zona externa and the perivascular region of the base of the median eminence. Under high magnification, the membrane of the granules show evidence of a trilaminar structure and the content of the granules with a low electron density appeares to consist of small microvesicles or globular components. Besides granules, these nerve fibres contain vesicles mostly 420 Å in diameter whose relative number increases towards the perivascular nerve endings. 53 per cent of the inclusions in the hypothalamo-hypophysial tract are granules and 47 per cent vesicles, while the corresponding percentages for the zona externa are 40 and 60 and for the perivascular nerve endings 20 and 80.The mean width of the pericapillary space is 1 , but it varies greatly. It containes many collagen fibrils and fibroblasts. The capillary endothelium is frequently fenestrated and contains many vesicles of various sizes.Two types of granules-containing cells are found in the pars tuberalis depending on the size of the electron dense granules: 1. cells containing granules with a mean diameter of 1,330 Å: and 2. cells containing granules with a mean diameter of 2,000 Å. In addition, there are occasional follicular cavities filled with amorphous material, microvilli and cilia of 9+2 fibrillar pattern.Aided by a grant from the Sigrid Jusélius Stifteise.     

Structure of the neurohypophysis and the hypothalamo-hypophysial vascularization in the teleost Channa punctatus Bloch.

In C. punctatus the median eminence includes the subterminal region of the hypothalamus and the anterior neurohypophysis. It is formed of ependymal, fibrous and reticular layers as in the tetrapods. Primary capillary plexus extends from the subterminal region to the extremity of the anterior neurohypophysis. Only few portal vessels from the hypothalamus enter in the pars distalis. All the components of pituitary including the pars intermedia are irrigated by the secondary plexus formed from the portal vessels emerging out of the anterior neurohypophysis. The neurosecretory axons and the ependymal cells are in close morphological contact with the primary plexus. Several axons have perivascular endings at the median eminence. Some axons were found to be only silver or aldehyde fuchsin positive whereas some others take up both. The silver positive axons were abundant in the pars distalis and the AF positive ones were more concentrated in the pars intermedia with greater accumulation of neurosecretory material.     

Tanycyte and vascular patterns in the basal hypothalamus of Coturnix quail with reference to their possible neuroendocrine significance

Summary A well developed system of ependymal glial cells with long basilar processes stretching to the surface of the brain (tanycytes, Horstmann, 1954) has been described in the basal hypothalamus of Coturnix quail. The tanycytes both in the median eminence and the ventro-lateral hypothalamus form a link between the third ventricle and the hypophysial circulation. The processes of the ventro-lateral tanycytes terminate in the region of the infundibular sulcus in apposition to a loose network of vessels which are continuous with the primary plexus of the hypophysial portal system.Within the median eminence, the subependymal capillary network connects the vasculature of the contra-lateral sides of hypothalamus. There are no direct connections with the hypophysial portal vessels.With the aid of the light and electron microscope the ventricular ependyma was divided into a dorsal typical region and two glandular regions (ventro-lateral and ventral). Each region contains different forms of tanycyte. One of the two forms of tanycyte (designated type 3) associated with the ventro-lateral glandular ependyma has no contact with the third ventricle.Ultrastructural studies on the glandular ependyma failed to show any obvious differences between castrated, oestrogen or testosterone implanted, and sexually mature or immature quail.The possibility that the tanycyte-vascular system may have a neuroendocrine role is discussed.I am indebted to Professor A. Oksche, Dept. of Anatomy, University of Giessen for providing research facilities and to The Royal Society for additional financial support.     

Quantitative radioautographic light and electron microscopic analysis of the localization of monoamines in the median eminence of the rat

Summary By means of light and electron microscopic radioautography a quantitative study of the regional distribution of catecholamines in the median eminence of the rat was carried out. One hour after intraventricular injection of ³H-dopamine the highest radioautographic reaction was recorded in the external zone, especially in the lateral palisade zone where many neurosecretory terminals are separated from the basal lamina of the portal pericapillary space by a glial cuff. This area showed the highest percentage (52%) of labelled catecholamine containing neurosecretory terminals as well as the maximal silver grain density per one terminal. In the medial palisade zone where direct neurovascular contacts with the capillary loops prevail, only 27 per cent of neurosecretory terminals were found to harbour tritiated dopamine. On the average 35 per cent of neurosecretory terminals in the median eminence of the rat contain catecholamines (both dopamine and noradrenaline). Pretreatment of animals with reserpine strongly reduced the binding of the label. Per cent of labelled neurosecretory terminals as well as grain density over terminals were decreased in both the medial and lateral palisade zones, although to a lesser degree in the latter. The site of origin of catecholamine fibers as well as the mode of catecholamine action at the level of the median eminence are discussed.This work was presented at the joint session of the Society of Anatomists, Histologists and Embryologists, the Society of Physiologists, and the Society of Neuroendocrinologists dedicated to the memory of Professor Wolfgang Bargmann, held in Leningrad, January 17, 1979It is a pleasure to express our deep gratitude to Prof. P.P. Rumyantzev and Dr. N.V. Seina of the Institute of Cytology of the USSR Academy of Sciences, Leningrad, for their valuable advice on electron microscopic radioautography     

The neurohypophysis of the crested newt

Summary In the median eminence of the newt a medial region and two lateral regions are described.In cross section, the medial region appears to be made up of 1) an outer or glandular zone (Zone I) containing aldehyde-thionine-positive and negative nerve fibres and blood capillaries. Nerve fibres appear aligned in palisade array along the capillaries. 2) An inner zone (Zone II) made up of a) a layer of aldehyde-thionine-positive nerve fibres (fibrous layer) belonging to the preoptic hypophyseal tract and b) a layer of ependymal cells lining the infundibular lumen and reaching the blood vessels with their long processes.The lateral regions display a less pronounced stratification and aldehyde-thionine positive nerve fibres are nearly absent.A slender lamina (ependymal border) containing mainly aldehyde-thionine-positive nerve fibres and ependymal cells connects the median eminence to the pars nervosa.At the ultrastructural level, in the outer zone of the medial region at least 4 types of nerve fibres and nerve endings are identified:Type I nerve fibres containing granular vesicles of 700–1000 Å and clear vesicles (250–400 Å).Type II nerve fibres containing granular vesicles and polymorphous granules of 900–1300 Å and clear vesicles (250–400 Å).Type III nerve fibres containing dense granules of 1200–2000 Å and clear vesicles of 250–400 Å.Type IV nerve fibres containing only clear vesicles of 250–400 Å. In the inner zone too, all these nerve fiber types are found among ependymal cells, while the fibrous layer consists of nerve fibres containing granules of 1200–2000 Å in diameter.In the lateral regions Type I, Type II and Type IV nerve fibres and their respective perivascular terminals are found; axons containing dense granules (1200–2000 Å) are scanty. In these regions typical synapses between Type I nerve fibres and processes rich in microtubules are visible.The classification and functional significance of nerve fibres in the median eminence are still unsolved, but it may be assumed that nerve fibres of the medial region belong to both the preoptic hypophyseal and tubero hypophyseal tract, while the lateral regions are characterized by nerve fibres of the tubero hypophyseal tract. Peculiar specializations of the ependymal cells in the median eminence of the newt are also discussed.Work supported by a grant from the Consiglio Nazionale delle Ricerche.The authors are indebted to Mr. G. Gendusa and P. Balbi for technical assistance.     

Ultrastructural study of neurovascular contacts in the median eminence of the rat

Summary In the median eminence of the rat axons of the supraoptic-paraventricular-hypophyseal tract with elementary neurosecretory granules (150–200 m) traverse the internal zone. Terminals containing dense core vesicles 60–120 m in diameter end on the portal capillaries of the median eminence. A unique organisation of the primary portal capillaries is shown. Endothelial cells have many fenestrae. The pericapillary space has numerous extensions all of which represent a special zone around the endothelial tube. The fine structural organisation and function of the neurovascular contacts in the median eminence are discussed.     

Cellular organization of the lateral and postinfundibular regions of the median eminence in the rat

Summary The structural organization of the rostral, lateral and postinfundibular regions of the median eminence (ME) of 5-day cyclic diestrous rats was studied with light and electron microscopic methods. The ependymal cells lining (i) the floor of the infundibular recess (IR) at rostral levels, (ii) the lateral extensions of the IR, and (iii) the floor of the premammillary recess appear to represent the same type of tanycyte ependyma (1 tanycytes). In the entire width of the rostral and postinfundibular palisade regions, as well as in the lateral palisade region of the preinfundibular ME, the processes of the 1 tanycytes form a continuous cuff. This cuff separates the nerve endings from the blood vessels and the pars tuberalis. At this level, synaptoid contacts between neurosecretory axons and the ependymal cuff can be observed. The ultrastructural characteristics of the 1 tanycytes are described and their ependymal endings tentatively classified into three types. In the lateral regions of the ME, the Golgi study revealed the presence of two fiber systems: (i) one possessing a latero-medial trajectory and distributed in the subependymal region; (ii) the other formed by a loose longitudinal tract originating from neurons of the arcuate nucleus. Some functional implications of the cellular organization of the rat ME are discussed.Supported by Grants from PLAMIRH (92.171.2.77) and from the Dirección de Investigaciones, Universidad Austral (S-77-28)The authors wish to thank Miss Rosario Andrade, Mrs. Elizabeth Santibáñez and Mr. Armando Bilbao for their assistance     

Morphological aspects of the hypothalamic-hypophyseal system

Summary The reaction of neural structures of the medial basal hypothalamus (MBH) to its complete deafferentation was studied in male rats by means of enzyme-histochemical and histoautoradiographic methods. Particular attention was paid to nerve cells of the arcuate nucleus and to the tanycytes. The metabolic activity of these cells increased upon the whole.According to the indices of metabolic activity in normal conditions and following deafferentation, the authors distinguish among the ependymal cells of the recessus infundibularis in rats, -tanycytes, which correspond to the ependymal lining at the level of the arcuate nucleus, and -tanycytes, which correspond to the ependyma of the median eminence. In normal conditions both were marked by a sufficiently high level of metabolism, which did not exclude the possibility of protein synthesis. Following deafferentation, -tanycytes seemed most reactive. The most active elements among the -tanycytes were the ependymal cells of the lateral part of the median eminence (¹-tanycytes).The metabolic peculiarities of the nerve cells of the arcuate nuclei and the tanycytes, revealed in normal conditions and after deafferentation, are discussed in connection with the modern concepts of the role of these cells in hypothalamic-hypophyseal transmission.     

Kapillaren und perikapilläre Räume im Hypothalamus-Hypophysen-System und ihre Beziehungen zum Nervengewebe

Zusammenfassung Elektronenmikroskopische Beobachtungen an den Kapillarsystemen der Neurohypophyse des Meerschweinchens bestätigen, daß diese Gefäße eine Sonderstellung unter den Hirnkapillaren einnehmen. Ein Porenendothel zeichnet die Kapillaren des Portalplexus der Zona externa, des Hinterlappens und des Vorderlappens aus. Weite perikapilläre Räume umgeben die Kapillaren der Neurohypophyse im Gegensatz zu den übrigen Hirnkapillaren, die von einer Gliascheide dicht umschlossen sind. Die Baueigentümlichkeiten der neurohypophysären Kapillarsysteme weisen auf einen gesteigerten Austausch zwischen dem Blut und dem benachbarten inkretorisch tätigen Gewebe hin.Eine Besonderheit stellt das Vorkommen von Axonen und Axonendigungen in den perivaskulären Räumen um die Kapillaren der neurohämalen Kontaktzonen im Hinterlappen und der Zona externa dar. Die Nervenelemente unterschiedlichen Kalibers enthalten dort neben großen und kleinen Elementargranula auch synaptische Vesikel. Drei Axontypen lassen sich feststellen.Die Möglichkeit regeneratorischer Wachstumsvorgänge an neurosekretorisch tätigen Nerven wird diskutiert. Andererseits kommt der in der Neurohypophyse spezifisch differenzierten Glia (Tanyzyten, Pituizyten) auf Grund ihrer elektronenoptischen Struktur und ihrer engen Beziehung zu Nerven und Gefäßen eine besondere Bedeutung zu. Die lichtmikroskopisch bei Tieren beobachtete Zona granulosa (Hagen [1955]) zwischen Zona externa und Pars tuberalis der Adenohypophyse läßt sich in diesem Sinne deuten.

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Summary EM observations of the capillary system of the neurohypophysis of the guinea pig confirm that these vessels are unique among the capillaries of the brain. The capillaries of the portal plexus, the median eminence, the neural lobe and the pars anterior all possess a fenestrated endothelium. In contrast to the other brain capillaries, provided with a thick glial sheath, those of the neurohypophysis are surrounded by wide perivascular spaces. The structural peculiarities of the neurohypophysial capillary system point to an enhanced interchangeactivity between blood and surrounding endocrinous tissue.Especially noteworthy is the presence of axons and axon-endings in the perivascular space round the capillaries of the neurohaemal contact areas in the neural lobe and in the median eminence. These neural elements are of varying calibre and they contain synaptic vesicles in addition to large and small elementary granules. Three types of axon are observable.The possibility of regenerative growth-processes taking place on neurosecretory-active nerves is considered. On the other hand, specially differentiated glial cells (tanycytes, pituicytes) in the hypophysis are of particular significance on account of their EM structure and their close relation to nerves and blood vessels. The lightmicroscopically observed zona granulosa in animals (Hagen [1955]), observed between the median eminence and the pars tuberalis of the adenohypophysis, could be explainable on this basis.

     

The tanycyte of the rat median eminence

Summary The present ultrastructural study proves the existence of nerve terminals closely apposed to the plasmalemmata of tanycytes in the rat median eminence. Several of these axo-tanycytic endings display remarkable accumulations of agranular endoplasmic reticulum in the form of pleomorphic vesicles which are closely apposed on either side of the plasma membrane of each cell compartment. Some of these vesicular profiles give the impression of structural continuity across both membrane systems. This phenomenon is discussed in the context of being a potential substratum for communication between both cell compartments.Supported by NIH Grant NS13717 and NSF Grant BNS 78-11820     

Ultrastructure of the neurohaemal region of the toad median eminence

Summary According to the internal structure and size of the granules, six types of nerve endings can be distinguished in the toad median eminence: 1. Endings containing mostly dense granules of 600 Å in diameter; 2. Endings containing dense granules of about 800 Å in diameter; 3. Endings which contain dense granules 1,000–2,000 Å in diameter, with the peak at 1,200–1,400 Å; 4. Endings containing granules with a characteristic structure, which differentiate them from the other three types; 5. Scarce endings containing granules 2,000 to 3,800 Å in diameter; and 6. Endings containing only vesicles 400–500 Å in diameter. Types 3 and 4 endings are mainly found in the outer pericapillary zone, and are probably responsible for the strong Gomori-positive reaction observed in this zone. The other four types of endings occur mainly in the inner pericapillary zone, and appear to be Gomori-negative.The probable origins of the different types of endings, and their possible relations with the different releasing factors is discussed.The subendothelial basement membrane has numerous long processes which form a complicated network in contact with all the nerve endings, some nerve fibres and glial cells.Two types of glial cells are described. Pinocytotic vesicles are frequently seen at the points where these cells contact the basement membrane. All the ultrastructural features suggest that these cells are carrying out transport functions.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.The author is very grateful to Professor H. Heller for his continued encouragement and criticism and to Mr. J. Lane and Mr. P. Heap for their valuable help.     

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)     

Electron microscope studies on the development of the external zone of the mouse median eminence

Summary The development of the external zone of the median eminence of the mouse was studied in the electron microscope. The examination follows the development of the embryo from the 15th day of the gestation period and the juvenile growth until 24 days of age.Single terminals of the tubero-infundibular neurons of the external zone were found to extend to the outer basement membrane of the perivascular space of the portal primary capillary plexus in the 16 day-old embryo. In the 18 day-old embryo a narrow external zone has developed. Organization of the external zone into the adult pattern is accomplished at the age of three to four weeks. Small agranular as well as large granular vesicles are present in the tubero-infundibular nerve terminals even in the 16 day-old embryo.Changes in the organization of the nerve endings along the outer perivascular basement membrane in relation to the ependymal vascular feet were considered.     

Ultrastructural development of the neurohemal organ joined to the ecdysial gland after imaginal moulting in the male isopod Sphaeroma serratum fab. (Crustacea Flabellifera)

Summary The present ultrastructural study deals with the lateral cephalic nerve plexus of Sphaeroma serratum, a neurohemal organ joined to the Y organ (ecdysial gland). This plexus acts as a storage centre for neurosecretory products from two sources: the two autochtonous cells (plexus cells) within the plexus itself, and the neurosecretory cells in various parts of the central nervous system, particulary the mandibular ganglion (A-cells).In prepuberal animals, plexus cells and subesophageal A-cells produce neurosecretory granules of two types measuring 1550±50Å and 1570±40Å respectively. Five categories of axon terminals were distinguished in the plexus. The granules found in two of these terminal types are believed to come from the plexus cells and from the mandibular ganglion A-cells.Cessation of production of neurosecretory granules in these A cells and plexus cells was observed in puberal animals, in the plexus with concomitant depletion and disappearance of different granule categories. The first axon terminals affected by this process are the two categories containing granules originating in the plexus and mandibular ganglion A-cells. Degeneration of the ecdysial gland in male Sphaeroma serratum might be connected with the cessation of granule formation in these two types of cell.

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Résumé Chez Sphaeroma serratum, la mue de puberté est suivie d'une dégénérescence de l'organe Y (glands de mue). Le plexus nerveux céphalique latéral, organe neurohémal accolé à cette glande a été l'objet de la présente étude ultrastructurale. Cet organe représente un centre de stockage de neurosécrétions qui proviennent d'une part, de deux cellules autochtones (cellules plexales) situées au sein même de ce plexus, d'autre part, de cellules neurosécrétrices situées dans le ganglion mandibulaire (cellules de type A).Chez les individus pubères, les cellules plexales et les cellules A du ganglion sous-oesophagien synthétisent des granules de neurosécrétion dont la taille est respectivement 1550±50Å et 1570±40Å. Il a été reconnu au sein du plexus 5 catégories de terminaisons dont les granules proviendraient pour deux d'entre elles des cellules plexales et des cellules A du ganglion mandibulaire. Chez les animaux pubères on observe un arrêt de la synthèse des granules de neurosécrétion au sein des cellules plexales et des cellules A du ganglion mandibulaire. Simultanément on enregistre dans le plexus la raréfaction puis la disparition des divers types de granules. Ce processus atteint en premier les terminaisons correspondant aux cellules plexales et aux cellules A du ganglion mandibulaire. La dégénérescence de la glande de mue chez les mâles pourrait être en relation avec l'arrêt de synthèse de ces cellules.

     

Small intensely fluorescent (SIF) cells and sympathetic nerves in the adult rabbit portal vein and during perinatal development

Summary The ontogenesis of small intensely fluorescent (SIF) cells and the adrenergic nerve plexus is described in stretch preparations of the rabbit portal vein. On the 25 to 26th days of gestation there was a predominance of SIF cells (8 to 30 m in diameter), but a few nerve fibres in bundles were also present. Each portal vein preparation contained 6 to 9 groups of cells. The distribution and number of SIF cells and nerve bundles remained constant until the 31st day of gestation at which stage the number of SIF cells had decreased, while the density of the nerve plexus had increased approximately 4-fold. The adult portal vein exhibited a dense adrenergic plexus, but SIF cells were absent from nine out of ten preparations.     

Immunohistochemical identification of supportive cell types in the enteric nervous system of the rat colon and rectum

Summary The non-neuronal, supportive cells of the enteric nerve plexus were investigated in the colon and rectum of adult and developing rats by means of immunohistochemistry, utilizing antisera against GFA protein and S-100 protein. Immunoreactivity to GFA protein was almost exclusively found in cells associated with the myenteric plexus and a small number of cells within the submucous ganglia. On the other hand, the use of S-100 protein antiserum resulted in the visualization of all supportive elements in the enteric nervous system. However, two types of supportive cells could be tentatively differentiated in the enteric nerve plexus during the second week of postnatal development, using GFA protein and S-100 protein antisera; GFA protein-positive cells were clearly discernible from S-100 protein-positive cells in terms of both the morphological profiles and immunohistochemical properties. It was assumed that at least two different types of supportive cells are contained in the enteric nerve plexus. We suggest that in the enteric nervous system the terms glial cells and Schwann cells should be employed to designate the supportive cells containing GFA and S-100 proteins, and cells containing S-100 protein, respectively. We discuss the possibility that glial cells are associated with the parasympathetic preganglionic fibres directly derived from the central nervous system, while Schwann cells originate from the neural crest.     

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.