Ultrastructural changes of the neurohypophysis of the rat after castration

Summary The infundibular processes of the neurohypophysis of male and female rats were studied after different periods of castration. After seven days an increase in neurosecretory granules was observed. Two types of neurosecretory nerve endings were identified: dark ones, with dense neurosecretory elementary granules of 1600 A, and clear ones, with lighter neurosecretory granules of 1800 A. Protoplasmatic pituicytes showed a large increase in lipid granules together with a general hypertrophy. After one week of castration but with hormonal therapy the protoplasmatic pituicytes appeared normal or even showed less lipid granules than in the controls.With one month of castration the changes already mentioned in the nerve endings and pituicytes were more pronounced and after six months even more accentuated. Two types of neurosecretory nerve endings were clearly identified and the protoplasmatic pituicytes were loaded with lipid granules.The probable significance of the two different neurosecretory axons was discussed in relation to recent studies on the isolation of neurosecretory terminals from the neurohypophysis. The changes in the protoplasmatic pituicytes were considered in relation to the possible significance of the lipid granules.Supported by grants from the Consejo Nacional de Investigaciones Cientificas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).We are deeply indebted to Mrs. Defilippi-Novoa and Mr. Alberto Saenz for their skillful assistence.Associated Investigator, Consejo Nacional de Investigaliones Científicas y Técnicas, Argentina.     

FINE STRUCTURE OF THE NEUROHYPOPHYSIS OF THE OPOSSUM (DIDELPHIS VIRGINIANA)

The neurohypophysis of the opossum (Didelphis virginiana) was studied by electron microscopy in order to amplify Bodian''s classic light microscopic observations in which he demonstrated a definite lobular pattern. The lobule of the opossum neurohypophysis is divided into three regions: a hilar, a palisade, and a septal zone. The hilar portion contains bundles of nerve fibers, the extensions of the hypothalamo-hypophyseal tract containing neurofilaments but few neurosecretory granules. In the opossum, pituicytes have a densely fibrillar cytoplasm. Herring bodies are prominent in the hilar region. They are large bodies packed with neurosecretory granules that have been described as end bulb formations of axons. From the hilar region, axons fan out into a palisade zone where the nerve terminals packed with neurosecretory granules, mitochondria, and microvesicles abut upon basement membranes. The neurosecretory granules are similar to those present in the neurohypophysis of other mammals, except for an occasional huge granule of distinctive type. Material morphologically and histochemically resembling glycogen occurs as scattered particles and as aggregates within nerve fibers. The septal zone, containing collagen, fibroblasts, and numerous small capillaries, is separated from the adjacent glandular tissue by a basement membrane.     

Morphological characteristics of pituicytes in different functional stages

Summary Most of the pituicytes of normal rats show relatively few indications of metabolic activity. This situation remains unchanged after two days of dehydration. From the third to the eighth day of dehydration, a considerable hypertrophy of the majority of pituicytes takes place. During this period proliferative and degenerative processes occur. After eight days of dehydration the pituicytes show an increase of degenerative processes and indications of decreased activity. Only one type of pituicytes in three different morphofunctional stages is considered to represent the basic cellular component of the neural lobe. A relationship between these stages and the release of neurosecretory material from the nerve endings is discussed.Partially supported by Unesco and Ibro post-doctoral fellowships.     

On degeneration of peptidergic neurosecretory fibres in the albino rat

Three types of degenerating peptidergic neurosecretory fibres have been found in the posterior pituitary of chronically dehydrated albino rats. "Dark" neurosecretory fibres and their swellings contain neurosecretory granules, neurotubules, shrunken mitochondria and diffusely distributed fine dense material. Some swellings are filled with synaptic vesicles and/or conglomerations of dense membranes. The transitional forms exist between these fibres and extracellular accumulations of electron dense material. Synaptic vesicles, single neurosecretory granules, lipid-like droplets and lamellar bodies occur in the latter. Some neurosecretory fibres and swellings have numerous polymorphous inclusions arising due to degradation of secretory inclusions and organelles, mitochondria and neurotubules in particular. "Dark" neurosecretory elements and those with numerous polymorphous inclusions are enveloped by pituicyte cytoplasm. Sometimes the plasma membranes both of the pituicytes and neurosecretory fibres are destroyed or transformed into a multi-membrane complex. It is assumed that pituicytes may phagocytize degenerating neurosecretory elements. N urosecretory fibres with a locally dissolved neuroplasm and/or large lucent vacuoles seem to be due to axonal degeneration by the "light" type. These neurosecretory elements, the largest of them in particular, may transform into large cavities bordered by a membrane and containing flake-like material and single-membrane vacuoles. Degeneration of neurosecretory elements seems to occur mainly due to hyperfunction of the hypothalamo-hypophysial neurosecretory system.     

Ultrastructure of the rabbit neurohypophysis with special reference to the release of hormones

Summary The ultrastructure of normal neural lobes of adult rabbits is described. The major part consists of non-myelinated fibres containing neural swellings at intervals. These enclose the neurosecretory granules, mitochondria and a few microtubules. The swellings are connected by narrow nerve fibres with parallel neurotubules but no granules. The Herring bodies resemble large neural swellings and may contain many neurotubules. They are sometimes enclosed by multilamellate sheaths. True myelinated nerve fibres full of granules also occur. The relationship between the neural swellings and pituicytes is discussed. The pituicyte cytoplasm contains many delicate fibrils but it does not resemble an active secretory cell.The blood vessels are characterised by an unusually wide perivascular space containing two condensed layers of basement membrane. These layers can be traced into channels which extend from the perivascular spaces and break up the tissue into lobules. It is suggested that these channels form a mucopolysaccharide spongework that may be important in relation to the release of hormones.The common feature of ether-treated, dehydrated and immature animals is the absence of electron-dense cores from the neurosecretory granules. Such glands are not completely depleted of hormones and much of the hormonal activity is still associated with a sedimentable fraction. Loss of electron density may be due to diffusion of the neurophysin carrier or to a change in configuration of the neurophysin molecules resulting in inaccessibility of both osmiophilic and hormone binding sites. The unbound hormone may be stored in the mucopolysaccharide sponge-work and released gradually into the blood stream.This work is offered as a tribute to Dr. Berta Scharrer on the occasion of her 60th birthday and in appreciation of her leading contribution over many years towards the understanding of the concept of neurosecretion.We are grateful to the Wellcome Trust for providing the Siemens Elmiskop 1 electron microscope used at the Dept. of Human Anatomy, Oxford, and to the D.S.I.R. for other assistance. We also acknowledge valuable discussions with our colleagues, especially Professors H. Heller and W. Bartley.     

Alterations in the neurohypophysis of rats treated with chlorphentermine or tricyclic antidepressants

Summary Rats were treated with several amphiphilic, cationic compounds that are known to cause generalized lipidosis (chlorphentermine, iprindole, 1-chloro-amitriptyline, clomipramine). After prolonged drug treatment the neurohypophysis showed severe morphologic alterations particularly in Herring bodies (HB), perivascular cells, and pituicytes. HBs displayed the following abnormalities: (a) great accumulation of autophagic vacuoles that contained neurosecretory granules (NSG); (b) numerous coarse osmiophilic conglomerates; (c) masses of multilamellated material; (d) reduced numbers of intact NSGs. Perivascular cells accumulated large lamellated inclusion bodies. Pituicytes contained membrane-bound crystalloid inclusion bodies. The noxious effect of chlorphentermine and 1-chloro-amitriptyline was more pronounced than that of iprindole and clomipramine.The alterations in perivascular cells and in pituicytes are typical of drug-induced lipidosis. The lesions in HBs are tentatively explained as follows: HBs were previously proposed to be the sites of normally occurring intraaxonal disposal of excess neurosecretory material. The present experimental conditions interfere with this catabolic process. Incomplete digestion of the axoplasmic constituents due for disposal might result in abnormal accumulation of NSG-containing autophagic vacuoles, osmiophilic conglomerates, and multilamellated material. This eventually leads to degeneration of HBs.The functional implications of the neurohypophysial lesions remain to be elucidated by functional experiments.This work was supported by the Deutsche Forschungsgemeinschaft (Lu 172/2) and the Stiftung Volkswagenwerk. The skilful technical assistance of Mrs. R. Worm is thankfully acknowledged     

Elektronenmikroskopische Untersuchungen über die Reaktion der Pituizyten nach Hypophysenstieldurchtrennung bei Rana esculenta

Zusammenfassung Etwa 2 Tage nach Durchtrennung des Hypophysenstiels beginnen die Pituizyten der Froschhypophyse (Rana) die degenerierenden sekrethaltigen Axone zu phagozy tieren. Nach 3–4 Tagen werden die Neurosekretgranula in den Einschlußkörpern immer mehr zusammengedrängt und verlieren schließlich ihren elektronendichten Inhalt. Die Hüllen der Elementargranula verwandeln sich mit eingelagerten Lysosomen zu membranösen, sehr stark osmiophilen Körpern, die sich schließlich langsam auflösen.Die mitotische Aktivität der Pituizyten ist während des Abbaues gesteigert. Zwischen Gefäßen und Pituizyten bestehen enge räumliche Beziehungen. Die Fähigkeit zur Phagozytose wird als Grundfunktion der Pituizyten angesehen.

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Electron microscopical investigation on the reaction of the pituicytes after stalk section in Rana esculenta

Summary About 2 days after transsection of the pituitary stalk the pituicytes of the frog neurohypophysis (Rana) start to phagocytate the degenerating neurosecretory axons. After 3–4 days the neurosecretory granules inside the inclusion bodies are compressed more and more and finally their electron-dense contents disappear. The membranes of the elementary granules together with lysosomes alter into membranous highly osmiophilic bodies slowly dissolving at last.During the desintegration of nerve endings the mitotic activity of the pituicytes increases. Blood vessels and pituicytes are closely connected.It is supposed that the ability of phagocytosis represents a basic function of the pituicytes.

     

ISOLATION OF NERVE ENDINGS FROM THE POSTERIOR PITUITARY GLAND : Electron Microscopy of Fractions Obtained by Centrifugation

Bovine posterior pituitary glands were homogenized in 10 per cent sucrose and fractionated by differential centrifugation. The following centrifugation procedure resulted in the most satisfactory separation: 1000 g for 15 minutes—nuclei, connective tissue, basement membranes with associated endothelium, giant nerve endings, and whole pituicytes; 4200 g for 15 minutes—free nerve endings, including Herring bodies; 17,000 g for 15 minutes—mitochondria; 68,000 g for 15 minutes—neurosecretory granules. Electron microscopic examination was carried out on whole tissue and on the isolated fractions. Isolated nerve endings were examined also by negative staining techniques. Isolated nerve endings retain an apparently normal complement of mitochondria, neurosecretory granules, and microvesicles ("synaptic" vesicles). The free nerve endings closely resemble those observed in sections of intact posterior pituitary tissue. Free microvesicles were not observed in any of the fractions isolated and apparently sediment at centrifugal forces higher than those employed in this study.     

Ultrastructural changes and proliferation of pituicytes in mouse posterior lobe during water deprivation and rehydration

Ultrastructural changes and proliferation of pituicytes during water deprivation and rehydration were studied in the posterior lobe of C57BL/Tw mice. Deprivation for 3 days brought about a significant increase in the number of electron-dense bodies (lysosomes) in pituicyte perikarya and their processes. The frequency of pituicytes enclosing neurosecretory axons in their cytoplasm significantly decreased as compared with that of the controls. 12-hour rehydration following deprivation for 3 days induced extensive development of rough endoplasmic reticulum and Golgi apparatus and an increase in frequency of neurosecretory axons enwrapped by pituicyte cytoplasm. However, at 2 days of rehydration the morphology of pituicytes was no more different from that of the controls. Mitotic figures of pituicytes were not encountered throughout the deprivation period of 6 days, but rehydration for 12 h and 1, 2, or 3 days following deprivation for 3 or 6 days was effective in eliciting an increase in mitotic activity. The present results indicate that pituicytes in the mouse posterior lobe are intimately related with the secretory mechanism of neurosecretory material from the neurosecretory axons and that the proliferation of pituicytes is stimulated in conditions of reaccumulation of neurosecretory material.     

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.     

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.     

Glycogen in the neurohypophysis of toads

Summary Studies with the electron microscope revealed the presence of glycogen granules in the neurohypophysis of toads (Bufo arenarum Hensel). The glycogen appeared as scattered particles or as clusters formed by these particles within the nerve fibers. The scattered granules were intermingled with the neurosecretory granules and with the microvesicles. Chemical assays showed the presence of glycogen in the neurointermediate lobe of the toad's hypophysis.This work was supported by research grants from the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and The Rockefeller Foundation.The authors wish to express their appreciation to Prof. Bernardo A. Houssay and to Dr. Luis F. Leloir for their encouragement during the preparation of this paper; to Miss Susana Camocardi for her technical assistance and to Mr. Luis Millara for the photographic work.     

Ultrastructure of the peptidergic and monoaminergic neurons in the hypothalamic neurosecretory system of Anuran Batracians

Summary In the toad Bufo arenarum Hensel the following regions of the hypothalamic — neurohypophyseal system were studied under the electronmicroscope: preoptic and paraventricular nuclei, median eminence and infundibular process of the neurohypophysis.Neuronal perikarya of the preoptic nucleus are loaded with typical neurosecretory granules of peptidergic nature having a mean diameter of 1660 Å. While most neurons of the winter toad are in a storage stage a few show signs of a more active synthetic activity. A distinctive feature of preoptic neurons is the presence of large lipid droplets. The paraventricular nucleus contains small neurons containing granulated vesicles with a mean diameter of 800-1000 Å. In the region extending between these two nuclei and the median eminence axons containing either neurosecretory elementary granules or granulated vesicles are observed.The inner zone of the median eminence is occupied by axons of the preoptic neurohypophyseal tract; two types of axons, according to the size and density of the neurosecretory granules, may be recognized. The outer zone of the median eminence contains mainly axons and nerve terminals containing granulated vesicles of probable monoaminergic nature and only a few with granules of peptidergic type.The neurohypophysis contains two kinds of axons: one with more dense granules of 1800 Å and the other with granules of lesser electron density and 2100 Å. At the ending proper small clear vesicles of synaptic type are found.A progressive increase in volume of the peptidergic granules along the axon is demonstrated. This is of the order of 218% from the preoptic perikarya down to the infundibular process. The physiological significance of the two neurosecretory systems — i.e. the monoaminergic and the peptidergic — and the probable nature of the two types of peptidergic axons is discussed.Supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).The authors want to express their gratitude to Mrs. Defilippi-Novoa and Mr. Alberto Sáenz for their skillful assistance.     

Electron microscopic histochemistry of lysosomes in neurosecretory nerve endings and pituicytes of rat posterior pituitary

Summary Electron microscopic localization of acid phosphatase (AcPase) was carried out on posterior pituitary glands from rats. An estimated 5% of the neurosecretory nerve terminals contained structures which showed reaction product. Most of the lysosomes were small dense bodies, often with a membranous substructure. Other lysosomes were larger in size or were found within vacuoles. AcPase was also localized to lysosomes and the Golgi apparatus of pituicytes. Evidence is presented which would associate the large lipid droplets characteristic of pituicytes with AcPase-positive dense bodies. The present study indicates that hydrolytic activity by lysosomes occurs within the terminals of neurosecretory cells, and adds further support to the concept that this process represents a normal phenomenon of cells and their extensions in general.Supported by the Medical Research Council of Canada.Medical Research Associate of the Medical Research Council of Canada.     

鳗鲡繁殖生物学研究 Ⅱ.下海雌鳗脑垂体超显微构造的研究

神经垂体主要由神经分泌纤维、脑垂体细胞和微血管组成。神经分泌纤维主要是无髓鞘神经纤维,也有一些是有髓鞘神经纤维。神经垂体中还有一些多层体构造。神经分泌纤维有两个基本类型:A型纤维含有直径为1250—1750Å的神经分泌颗粒;B型纤维含有直径为450—1000Å的颗粒状囊泡。腺垂体的分泌细胞按其超显微构造的特点和所含的分泌颗粒大小不同可以区分为六个类型:催乳激素分泌细胞、促甲状腺激素分泌细胞,促肾上腺皮质激素分泌细胞、促生长激素分泌细胞、促性腺激素分泌细胞和后腺垂体的分泌细胞。       

Occurrence of large hyaline bodies in the preoptic nerve cells of Zoarces Viviparus L.

Summary Specially in stress conditoin, some hyaline droplets occur in the perikarya of the neurosecretory hypothalamic cell of Zoarces viviparus. They first appear as filamentous macromolecular material in the intracisternal space, then tend to accumulate in the form of irregular electron dense rods or reticulum. The neurosecretory cells containing such hyaline bodies have usually few elementary neurosecretory granules and dilated endoplasmic reticulum.Aided by a Grant from NATO and the Deutsche Forschungsgemeinschaft.My thanks are due to Prof. Dr. E. Lindner and Doz. Dr. K. H. Andres for their kind help in the explanation of electronmicrographs.     

The structure of the hypothalamic neurosecretory cells of Zoarces viviparus L. under the conditions of constant dark and light during the reproductive cycle

Summary The Structure of the hypothalamic neurosecretory cells during their activity in continuous light and dark conditions and depending on the seasonal alteration has been investigated in Zoarces viviparus L. in the level of light and electron microscopy.The depletion of AF- or AT-stainable material, of the elementary neurosecretory granules and the disappearance of smooth-surfaced vesicles occur during April and June. The accumulation of the stanable material as well as the elementary neurosecretory granules and the smooth-surfaced vesicles has been observed in the cell body in late September.An excess increase in number of the smooth-surfaced vesicles of dark-induced animals and light-induced animals kept in a black stained tank is apparent. On the other hand, the disappearance of the elementary granules and the smooth-surfaced vesicles and an enlargement in the reletive nuclear surface of the neurosecretory cells of light-induced animals which were kept in a gray stained tank in April is also evident.Taking into consideration the responsiveness of both the elementary neurosecretory granules and the smooth-surfaced vesicles in relation to the external environment as well as their topographical arrangement in the cell body the possible differences in their origin and function are discussed.Numerous studies indicate that the physical environment is in part responsible for the functional properties of the hypothalamic neurosecretory centers of various vertebrates. In the level of light microscope, it has been repeatedly shown that the neurosecretory cells are activated in the animals subjected to continuous illumination, and in those subjected to long daily photo period (Oksche et al., 1958; Fiske and Greep, 1959; Öztan and Gorbman, 1960; Satyanesan, 1965). The enlargement of the nuclei and the amount of Gomori — or aldehyde fuchsin — stainable material, as well as the enzymatic activity, were used as the criteria of cellular activity in the histological preparation. In the level of electronmicroscope it has been shown that Gomori positive material (Bargmann, 1949) is represented as aggregated elementary neurosecretory granules in the ultrathin sections of neurohypophysis (Bargmann et al,. 1957). Although the fine structure of the hypothalamic neurosecretory cells of various fishes and higher vertebrates have been studied in normal and experimental conditions (Palay, 1960; Lederis, 1962, 1964; Follenius et Porte, 1962; Follenius, 1963; Murakami, 1961–1964; Gansler, 1965; Holmes, 1965) the type of granules and their function still remains as an open question (see Bargmann, 1963; Knowles, 1965).This work was aided by a grant from Nato and the Deutsche Forschungsgemeinschaft.This paper was written as a tribute in honor of the 60th birthday of Prof. Dr. Berta Scharrer.     

Histology and ultrastructure of the neural lobe of the lizard,Klauberina riversiana

Summary The pars nervosa of Klauberina riversiana belongs to a primitive tetrapod type which is characterized by the deep penetration of the infundibular recess, a thin-walled structure, and the virtual absence of pituicytes. The differential response of this gland to aldehyde fuchsin and periodic acid Schiff suggests the presence of two types of neurosecretory nerve endings. Ultrastructurally four kinds of nerve endings are distinguishable. Type I, probably a cholinergic nerve ending, contains only small clear vesicles ca. 400 Å in diameter. The relative abundance of cholinergic nerve endings in this pars nervosa may be related to the necessity of transporting hormone through the ependymal cell. Type II, containing granulated vesicles about 1,000 Å in diameter and probably aminergic, is very rare. The two remaining types apparently secrete neurohypophysial hormones. They are Type III, containing dense granules ca. 1,500 Å in diameter and Type IV containing pale granules ca. 1,500 Å in diameter. Evidence is reviewed which suggests that Type III nerve endings may secrete arginine vasotocin while Type IV endings may secrete (an)other hormone(s).All these axons end only on the ependymal cells, the vascular processes of which form a continuous cuff over the basement membranes of the blood vessels. Hence the ependymal cells link the cerebrospinal fluid, the nerve endings and the blood vessels. Particles resolvable with the electron microscope are traced through a possible transport pathway from the granules, through the ependymal cells to the basement membrane. It is suggested that pituicytes replace ependymal cells and assume their transport functions in animals with massive neural lobes containing large numbers of nerve endings and blood vessels.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.This investigation was supported in part by a Public Health Service fellowship 1 FZ HD 32,949-01 REP from the national Institute of Child Health and Human Development.The authors wish to thank Professor H. Heller for his constant interest and constructive criticism.     

Ultrastructural features of rat pituicytes in organotypic culture

Summary Neural lobes of adult rats have been explanted and organ-cultured for 5–10 days. While perivascular cells and neurosecretory fibers undergo a progressive degeneration, scattered pituicyte-like cells are observed mostly associated with each other in number of two or three cells for group. Cultured pituicytes are quite similar to in vivo pituicytes except for some particular features as the shape of the nucleus and the number of dense bodies. Furthermore they share with the in vivo pituicytes the phagocytic capacity which appears even increased as far as neurosecretory fibers are concerned. Finally, degenerating pituicytes and free lipid droplets are observed in the intercellular spaces: the significance of these facts is discussed and tentatively interpreted. The organotypic culture of the neural lobe seems to represent an experimental model useful to obtain a relatively pure population of pituicytes.With the technical assistance of Vincenzo Panetta.     

Myelinated Herring bodies in the posterior part of the median eminence of the mouse

Summary The posterior part of the median eminence of the albino mouse (CF # 1-JCL) contains a cluster of myelinated axons beneath the tanycyte layer. Among them, small Herring bodies surrounded by myelin sheaths are revealed by electron microscopy. These structures contain electron-dense bodies, lamellar bodies, autophagic bodies, autophagic vacuoles, and neurofilaments. A few neurosecretory granules and mitochondria are also present. Some myelinated axons contain mostly accumulated neurosecretory granules.