Electron microscopy of neurosecretory nerve fibres in the neural lobe of the embryonic mouse

Summary Nerve fibres of the neurosecretory hypothalamo-hypophyseal tract were studied in embryonic C3H mouse neural lobes; at least four glands at each gestational day 15–19 were examined.Single axons and small bundles of fibres are visible at gestational days 15 and 16. By day 17 large fibre bundles penetrate between glial cells. They increase in number during the next two days.Electron-lucent and electron-dense vesicles are seen in the fibres of the 15th and 16th gestational days. In the 17–19 day-old embryos development is characterized by a successive rise in the number of the two types of vesicles. The mean diameter of the electron-lucent vesicles is approximately unchanged in all the stages examined (50 nm). The electron-dense vesicles increase in size from approximately 80–90 nm at days 15–16 to 140 nm at the 19th gestational day.By day 19 contacts between neurosecretory fibre terminals and the outer basement membrane of internal and peripheral capillaries are occasionally observed. The possibly adrenergic nature of a few terminals contacting peripheral vascular structures in 17 and 18 day-old embryos is suggested.This investigation was supported by grant No. 2180-020 from the Swedish Natural Science Research Council. The skilful technical assistance of Mrs. Ulla Wennerberg is gratefully acknowledged.     

Development of cell-to-cell relationships in the thyroid gland of the chick embryo

Summary Thyroid glands of 7 to 21 day-old chick embryos were examined by electron microscopy using freeze-fracture and thin-section preparations. The primitive follicle lumen first appears between two adjacent epithelial cells in 8 day-old embryos, and is formed in the region of a focal tight junction (macula occludens). The focal tight junction develops into the zonula occludens when the primitive follicle lumen first forms.The zonula occludens is, at first, composed of 4.6 ± 2.45 strands, but with increasing embryonic age the number of strands increases to 5.9 ± 1.41 in 13 day-old, and 8.0 ± 1.75 in 19 day-old embryos.Thyroglobulin stored within the embryonic gland lumina is isolated from the mesenchymal tissue even at the first appearance of these follicle cavities.Well developed gap junctions already occur in the thyroid gland of the 7 day-old embryo, so that an intimate relationship and communication between these cells already exists at the time of their functional differentiation.This study was supported by a grant from the Japan Ministry of Education     

Cytodifferentiation of the adenohypophysis of the domestic fowl

Summary In the chick embryo the first membrane-bound secretory granules occur in the cytoplasm of occasional cells in the cephalic lobe of pars distalis at the 7th day of incubation. On the 8th day most of the cells in both the cephalic and caudal lobes contain secretory granules that are variable in size, form and density.On the 9th day at least two types of glandular cells are distinguishable in the cephalic and in the caudal lobes; however, these cells are not comparable with those of the adult gland. Differentiation of acidophils and basophils occurs, apparently simultaneously, in 11-day embryos.The cells of the cephalic and caudal lobes are morphologically distinct from their first appearance. Thus it is concluded that these two lobes develop independently and differently from an early stage of ontogenesis.The secretory granules are formed in the Golgi area of the hypophysial cells after the 8th day of incubation. However, secretory material may be synthesized also by a process not involving the Golgi apparatus.Nerve fibers containing granules first appear in the superficial layer of the median eminence on the 8th embryonic day and by the 12th day three types of granules and two types of clear vesicles are identifiable.The investigation reported herein was supported by grant from Japan-U.S. Cooperative Science Program of Japan Association for Science Promotion to Professor Mikami and by U.S.-Japan Cooperative Science Program Grant No. GF-33334 to Professor Farner.     

The fine structure of the collar cells in the optic tentacles of Helix aspersa

Summary At the base of the optic tentacular ganglion there is a group of large monopolar cells containing numerous secretory inclusions. These are the collar cells. Secretory material can be seen accumulating in swollen portions of the granular endoplasmic reticulum. It is postulated that this material is transported to the Golgi bodies and thus the limiting membrane of the inclusions is derived from the Golgi membranes. The Golgi bodies appear to be polarized and small vesicles resembling secretory inclusions are associated with one face of these organelles. The secretory inclusions fuse together to form large membrane-bound secretory pools in the perikaryon. The collar-cell processes are packed with secretory inclusions. These processes traverse the digital extensions of the tentacular ganglion and pass into the epithelium covering the tip of the tentacle. The secretory inclusions do not resemble neurosecretory inclusions in other situations. The collar cell processes receive a nerve supply from single axons containing granular and agranular vesicles. The evidence that these cells may be modified neurons is only minimal.This work was supported by the Australian Research Grants Committee.     

Mode de formation des inclusions lamellaires dans le poumon embryonnaire de poulet

Résumé Les pneumocytes granuleux, qui constituent l'un des principaux types cellulaires de l'épithélium pulmonaire, sont caractérisés par la présence de volumineuses inclusions osmiophiles lamellaires.Nous avons étudié l'apparition et l'origine de ces inclusions dans l'épithélium du poumon embryonnaire de Poulet, en l'examinant à différents stades du développement.Les premières inclusions lamellaires apparaissent dans le poumon de l'embryon de 16 jours. A ce stade, quelques lamelles concentriques entourent une zône centrale amorphe étendue; la périphérie des inclusions contient toujours de petites structures granulaires. Les jours suivants le nombre de cellules contenant des inclusions lamellaires augmente rapidement; en même temps, les lamelles deviennent plus nombreuses. A 19 jours, les inclusions lamellaires ont un aspect semblable à celui qu'elles ont dans les poumons d'animaux adultes.Dès l'apparition des ébauches pulmonaires, à 2 1/2 jours d'incubation, les cellules épithéliales contiennent des inclusions typiques: les inclusions granulaires. Ces organites sont caractérisés par un centre granulaire, qu'entouré un système membranaire. Ce système, simple chez le jeune embryon, évolue ensuite en se compliquant; chez l'embryon de 16 jours, il s'enroule en plusieurs couches autour de la masse centrale. Au moment où les premières inclusions lamellaires apparaissent, le nombre des inclusions granulaires augmente rapidement; on les trouve souvent étroitement associées à des vacuoles lipidiques.L'analyse des relations entre inclusions lamellaires, inclusions granulaires et vacuoles lipidiques suggère que l'inclusion lamellaire résulte de la collaboration entre une vacuole lipidique et plusieurs inclusions granulaires.

---

Differentiation of lamellar inclusions in the chick embryonic lung

Summary The granular pneumocytes, one of the main cellular types of the lung epithelium, are characterized by the presence of large osmiophilic lamellar inclusions. The appearance and origin of these inclusions has been studied in the epithelium of chick embryonic lung at different developmental stages.Lamellar inclusions are first seen in the lung of 16 day old embryos. At this stage, few concentric lamellae surround a large amorphous center; the periphery of the inclusions always contains small granular structures. In the following days, the number of cells containing these lamellar inclusions increases rapidly, while their lamellae progressively become more numerous. In 19 day old embryos, the lamellar inclusions are similar to those in the lungs of adult animals.From the earliest formation of the bronchial primordia, their epithelial cells contain a number of typical granular inclusions. These organelles are characterized by a granular center, enclosed in a membranous system. This structure becomes more complex as the embryo develops; in the 16 day old embryo, the multilayered membranous system coils around the granular center. At the time when lamellar inclusions first appear, granular inclusions increase rapidly in number and are often found in close association with lipidic vacuoles.The relationships between lamellar inclusions, granular inclusions and lipidic vacuoles are discussed. The evidence suggests that a lamellar inclusion arises from the cooperation of several granular inclusions and a lipidic vacuole.

     

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.     

Granulated ‘marginal cell layer’ in the rat anterior pituitary gland

A granulated ‘marginal layer cell’ was observed in the lining of Rathke's residual pouch of 5 and 10 day-old rat anterior pituitary glands. Immunohistochemistry was not employed to identify the precise function of these cells. However, the cytological characteristics of nearly all of the cells indicated that they resembled GH-secreting cells, with a few displaying morphological features of corticotrophs. In pituitary glands of 5–20 day-old rats, both ends of Rathke's residual pouch extended into the pars distalis at the site of transitional zone of this lobe and of the pars intermedia. The cells within the ‘invading’ residual pouch contained numerous microvilli. In the middle portion of the residual pouch, cavities lined by ‘marginal layer cells’ had numerous microvilli and were adjoined by junctional complexes. In the adult rat pituitary gland, there were no granulated cells in the ‘marginal cell layer’ and no invasion of the residual pouch into the anterior lobe. From these data the possible source of the follicle and of the folliculo-stellate cells in the anterior pituitary of the rat is proposed.     

Immunocytochemical localization of vimentin in the posterior lobe of the cat, rabbit and rat pituitary glands

The presence and distribution of vimentin, a subunit of intermediate filaments, in the neural lobe and in the pars intermedia of the cat, rabbit and rat pituitary glands were investigated immunocytochemically. In the pars intermedia, our study revealed the presence of vimentin in glial-like cells located between glandular secretory cells of the three species and in the cells of the marginal layer of the cat and rat hypophyseal cleft. In the neural lobe of the cat and rabbit pituitary glands, there was a large amount of cell processes and immunoreactive pituicytes. In contrast, in the rat neural lobe, few pituicytes exhibited immunoreactivity, and these were located principally in the posterior region near the pituitary stalk. The significance of immunoreactive vimentin in these cells is discussed.     

Morphogenesis and ultrastructure of the peripolar cells in the mouse kidney.

Peripolar cells are located in the outer layer of the Bowman's capsule. They surround the vascular pole of the renal corpuscle and project into the urinary space. Morphologically they are characterized by the presence of secretory granules within their cytoplasm. In order to study their embryological development, we used 60 C57bl mice embryos (15th to 19th gestational day), 10 newborn mice (2 hours to 6 days old), 10 preadult mice (8-30 days old) and 4 adults (4 months old). Some granular cells, dispersed at the outer and inner layer of the Bowman's capsule, appear on the 17th gestational day. Later, these cells are found around the vascular pole of the renal corpuscle, located exclusively at the outer layer of the Bowman's capsule. Their granules are spherical and variously dense, they are surrounded by a membrane and their number increases progressively with time and reaches a maximum on the 4th postnatal day. Following that, there is a diminution and then their population stabilizes. By the end of the first month, there are only a few such cells (mean number 1 to 2). They become smaller and they always project into the urinary space.     

Control of the pars intermedia of the lizard,Anolis carolinensis

Summary The distribution of the tracer substance horseradish peroxidase (HRP, Mw 40,000) in the neuro-intermediate lobe of the lizard, Anolis carolinensis, was studied at various time intervals (13 min to 24 h) after vascular injection. HRP rapidly entered the extracellular lumen of the neural lobe, but did not penetrate into the third ventricle. The tracer was found in micropinocytotic vesicles (MPVs) of ependymal cells within 13 min after injection. The number of cellular inclusions containing HRP increased during the period of observation (24 h). The tracer was sparsely taken up by aminergic and peptidergic nerve terminals of the external layer. After transection of the hypophysial stalk, numerous dense, labelled droplets were found in the peptidergic terminals, and the number of labelled inclusions in ependymal cells increased.MPVs were frequently found in extensions of stellate cells of the intermediate lobe, and endocytotic vacuoles (EVs) developed especially in the perikaryon. HRP was also found in large cisternae of the secretory cells, appearing predominantly towards the perivascular septum (PVS). These cisternae were found to communicate with the extracellular lumen, probably representing a system of the extracellular space extending into the secretory cell. After transection of the hypophysial stalk, there was an increase in the number of small EVs in secretory cells of the intermediate lobe.The results are discussed in terms of MSH-release regulation and possible participation of the extracellular lumen, glial and stellate cells in the transport of regulating factors and secretory material.Supported by grants from the Swedish Natural Science Research Council (to Dr. Patrick Meurling) and the Royal Physiographic Society of LundThe author is indebted to Mrs. Lena Sandell and Miss Inger Norling for excellent technical assistance and photographic aid; and to Dr. Rolf Libelius and Dr. Ingmar Lundquist for generous advice and stimulating discussions concerning the tracer technique     

Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.     

Embryonic malformations in a case of intrauterine parvovirus B19 infection

An incomplete embryo of 9 weeks development from a woman infected by human parvovirus B19 during early pregnancy was histologically examined. B19-DNA was detected in both embryonic and placental tissue by dot-blot hybridization. Focal vascular endothelial damage was found throughout the entire embryo and placenta together with mononuclear infiltrations around the vessels. In the placenta these mononuclear cells belonged for the greater part to the cytotoxic and/or suppressor T-cell group. One eye showed lens abnormalities and retinal folds. The other eye was microphthalmic and aphakic and showed dysplasia of the sclera, anterior segment, and retina. The skeletal muscle cells displayed a general eosinophilic degeneration. Focally, similar changes were found in heart muscle and smooth muscle tissue. In several tissues pathologic effects at a cellular level were noted, as intranuclear vacuole-like inclusions and nuclear ballooning. On the basis of this study it is concluded that human parvovirus B19 may affect several fetal tissues and may even have teratological effects on a developing human embryo.     

Antioxidant systems of the developing quail embryo are compromised by mycotoxin aurofusarin

The effects of aurofusarin in the quail diet on the antioxidant systems of the developing embryo are investigated. Thirty eight 45-day-old Japanese quails (Coturnix japonica) were divided into two groups and were fed on a corn-soya diet or the same diet supplemented with aurofusarin at the level of 26.4 mg/kg feed in the form of Fusarium graminearum culture enriched with aurofusarin. Eggs obtained after 7 weeks of feeding were incubated. Samples of quail tissues were collected at day 17 of embryonic development and from day old hatchlings. Antioxidants and malondialdehyde were analysed by HPLC-based methods. Inclusion of aurofusarin in the maternal diet was associated with decreased concentrations of alpha- and gamma-tocopherols, alpha- and gamma-tocotrienols, retinol, lutein and zeaxanthin in egg yolk. The vitamin E (tocopherols and tocotrienols) concentration in the liver and yolk sac membrane (YSM) of the day 17 embryos and the hatchlings from aurofusarin-fed group was significantly decreased. Alpha-tocopherol concentration was also reduced in kidney, lung, heart, muscle and brain of day-old quails. In the liver of day-old quails, concentrations of lutein, zeaxanthin, retinol, retinyl linoleate, retinyl oleate, retinyl palmitate and retinyl stearate were also reduced. As a result of these diminished antioxidant concentrations, tissue susceptibility to lipid peroxidation was significantly increased. It is suggested that a compromised antioxidant system of the egg yolk and embryonic tissues could predispose quails to increased mortality at late stages of their embryonic development.     

Embryonic development and secretory differentiation in the pars tuberalis of the mouse hypophysis

Summary The pars tuberalis (PT) of the mouse, like that of other mammals, consists mainly of glandular cells rich in glycogen and peculiar to this lobe. In the mouse, the glandular cells are characterized by large, dense secretory vesicles (up to 300 nm in diameter), the abundance of which indicates a marked secretory activity. The PT develops from a distinct antero-ventral area of Rathke's pouch. The border between the anlagen of the PT and the pars distalis is formed by Atwell's recessus which represents the access for the vessels afferent to the pars distalis. The pedicle of Rathke's pouch is incorporated into the PT anlage, thus contributing to its formation. The entire PT anlage is characterized by glycogen accumulation from the commencement of its formation and persisting in the adult tuberal lobe. Secretory differentiation of the glandular cells of the PT occurs at day 12 of gestation, preceding that of all other adenohypophysial cell types. The secretory features of these cells (development of ergastoplasm and Golgi apparatus, abundance of dense secretory vesicles) appear at an early stage of the embryonic life (14 days) comparable to those of mature cells. These results confirm earlier observations in the foetal rat where hypophysial secretion also begins in the PT. The existence of peculiar glandular cells speaks in favour of a specific but still unknown function of the PT during foetal and adult life.This work is dedicated to Professor F. Stutinsky     

Cuticle formation in the embryo of Drosophila melanogaster

In Drosophila melanogaster embryos cuticle formation occurs between 12 and 16 hours of development at 25°C. The formation of the cuticulin and the protein epicuticular layers is simultaneous in the hypoderm, the tracheoblasts, and the fore- and hindgut cells. The cuticulin forms as a dual lamina, aggregating from granules secreted by the hypodermal cells. This is followed by the formation of a granular protein epicuticle and finally by the secretion of a mixed fibrous and granular endocuticle. All secretory cells are relatively simple in their ultrastructure. The secretory process is a membrane phenomenon, occurring at the tips of hypodermal microvillae on cells at the surface of the embryo and on those hypodermal cells lining the lumen of the fore- and hindgut. It also occurs along the entire surface of the tracheoblast lumen as well as on the outer surface of those cells which form exoskeletal chitinous setae. The process involves a specialization of the plasma membrane with the formation of secretory granules intracellularly beneath the membrane and the extrusion of these granules through the membrane to the outside where final cuticle formation occurs.     

The secretory cells of the submaxillary gland in the perinatal period of development in the rat

Summary Secretory cell differentiation in the submaxillary gland of the rat was investigated electron microscopically within the period of the 19th–22nd embryonic and the 1st–6th postnatal days.Within this period three types of secretory cells were identified which differed mainly in the morphological appearance of their secretory granules. In addition to the previously described cells of the terminal tubules and the glandular cells of the acini, we observed secretory cells with polymorphic granules, characterized by the presence of small osmiophilic bodies in the matrix of the granules, both after simple and double fixation. The chronological occurrence as well as the quantitative representation of these three types of secretory cells changes in the course of the period investigated. The cells of the terminal tubules are differentiated at the 19th embryonic day; the secretory cells with polymorphic granules by the 21st embryonic day; the glandular cells of the acini do not appear until after birth. It is presumed that the cells of the terminal tubules are precursors of the glandular cells of the acini and that the cells containing polymorphic granules represent an intermediate stage between them.

---

Zusammenfassung Die Differenzierung der Drüsenzellen der Glandula submaxillaris bei Ratten in der Periode vom 19.–22. Tage pränatal und vom 1.–6. Tage postnatal wurde elektronenmikroskopisch studiert.In dieser Periode haben wir in dieser Drüse drei Typen von sezernierenden Zellen festgestellt, welche sich morphologisch hauptsächlich bezüglich verschiedenartiger Sekretionsgranula voneinander unterscheiden. Zu den schon früher beschriebenen Zellen der terminalen Tubuli und den Drüsenzellen der Azini haben wir neu die sezernierenden Zellen mit polymorphen Granula, welche sich durch das Vorhandensein osmiophiler Körperchen in der Matrix der Granula nach einfacher sowohl als auch zweifacher Fixation auszeichnen, angereiht. Das zeitliche Erscheinen und die quantitative Verteilung der erwähnten drei Typen von Sekretionszellen änderten sich während der Beobachtungsperiode dahin, daß die Zellen der terminalen Tubuli am 19. Tage, die Sekretionszellen mit polymorphen Granula am 21. Tage der pränatalen Periode sich differenzieren und die Drüsenzellen der Azini erst nach der Geburt erscheinen.Unserer Ansicht nach sind die Zellen der terminalen Tubuli die Mutterzellen der Drüsenzellen der Azini und die sezernierenden Zellen mit polymorphen Granula das Übergangsstadium zwischen ihnen beiden.

     

Cytologic features of secretory meningioma

OBJECTIVE: To describe the cytologic features of secretory meningioma on crush preparations. STUDY DESIGN: In five cases, the diagnosis of secretory meningioma was made and crush preparations were available. In each case, crush preparations were made at the time of intraoperative consultation from an open biopsy specimen or stereotactic biopsy. RESULTS: Hematoxylin and eosin-stained crushes showed the presence of clusters of cohesive cells containing variable numbers of inclusions among less cohesive typical meningothelial cells. In two cases, the inclusions were especially prominent. Inclusions varied in size from 3 to 40 microns, had a well-defined rim and contained finely granular or hyaline material and a central core. CONCLUSION: Secretory meningiomas demonstrate distinct cytologic features on crush preparations. Recognition of these inclusions is important since their prominence in some stereotactic smear preparations may lead to diagnostic problems.     

Subcellular localization of thyrotropin-releasing hormone (TRH)- and Neuropeptide Y (NPY)-like immunoreactivity in the neurointermediate lobe of the frog pituitary

The presence of thyrotropin-releasing hormone (TRH) and neuropeptide Y (NPY) has been demonstrated in the neural lobe and in the intermediate lobe of the frog pituitary by immunocytochemistry on ultrathin sections of neurointermediate lobes obtained by cryoultramicrotomy. In the neural lobe, separate populations of TRH- or NPY-immunoreactive nerve fibers were observed. Both neuropeptides were contained in dense-core secretory vesicles about 200 nm in diameter. In intermediate lobe cells, TRH- and NPY-like immunoreactivities were observed in the cytoplasmic matrix and more sparsely in secretory granules. Occasionally, immunoreactive TRH could be visualized at the plasma membrane level. In the nucleus, both peptides were detected in the euchromatin, in the vicinity of the heterochromatin and in the nucleolus. Conversely, gonadotropin-releasing hormone-like immunoreactivity could not be detected. These results provide immunocytological evidence for the presence of endogenous TRH and NPY in frog melanotrophs indicating that these peptides may participate in the regulation of intermediate lobe secretion.     

Acetylcholinesterase activity in the myotome of the early chick embryo

Summary The myotome of early chick embryos was investigated histochemically by means of the acetylcholinesterase (AChE) reaction.Light-microscopically, at the cervical level, the myotome was first recognized and AChE activity demonstrated at stage 13 (2 day-old embryo). Subsequently, the myotome elongated ventro-laterally along the inner surface of the dermomyotome and reached the ventro-lateral end of the dermomyotome at stage 17 to 18 (3 day-old embryo). AChE activity in the myotome showed subsequent increase in intensity during the course of development. The myotome consisted mainly of AChE-positive cells displaying enzymatic activity along the nuclear membrane and within the cytoplasm. In contrast, almost all cells of the dermomyotome and the interstitial cells were AChE-negative.Electron-microscopically, the myotome cells of the 2 day-old embryo and the cells in the dorso-medial portion of the myotome of the 3 day-old embryo were morphologically undifferentiated; AChE activity was detected in the nuclear envelope and in single short profiles of the endoplasmic reticulum (ER). On the other hand, in the 3 day-old embryo the cells in the ventro-lateral portion of the myotome showed AChE activity in the nuclear envelope, numerous profiles of the ER and some Golgi complexes. These AChE-positive cells were regarded as developing myogenic cells based on their morphological characteristics.The present findings indicate (i) that the appearance of AChE activity in the cytoplasm is the first sign of the differentiation of myogenic cells, and (ii) that in these myogenic cells the increase in AChE activity is based on the development of the ER.