Showing papers in "Cell and Tissue Research in 1974"

Membrane associated particles: distribution in frog urinary bladder epithelium at rest and after oxytocin treatment.

Abstract: The fine structure of the plasmic membrane of the frog urinary bladder epithelium has been studied with a freeze-etching technique. The results reveal that the external face of the cytoplasmic leaflet (A face) of the apical membrane of epithelial cells is characterized by: 1) A markedly reduced number of membrane associated particles compared to the value observed on the A face of the lateral membranes of these cells. 2) The existence after oxytocin treatment of numerous spots of clustered particles.

Kinetics of gametogenesis. I. Comparative histological and autoradiographic studies of oocytes and transitional prospermatogonia during oogenesis and prespermatogenesis.

Abstract: SummaryIn the rat (Wistar-WU) sexual differentiation of the gonads occurs between days 14 and 15 post conception (p.c.). At this time the oogonia and their parallel population — the M-prospermatogonia (I-gonocytes)—divide rapidly. On about day 17 p.c., the last generation of oogonia and M-prospermatogonia, frequently arranged in synchronized clusters, enters mitosis. The postmitotic nuclei of their daughter cells—oocytes and T1-prospermatogonia (II-gonocytes)—are small; coarse flakes of chromatin are associated with the nuclear membrane causing the typical “crustlike” appearance and the similarity with the prophases of oogonia and M-prospermatogonia. After the oocytes have passed a G1-phase of approximately 10 hr, they enter the S-phase at the end of the preleptotene stage. Then they pass the different stages of the meiotic prophase until they enter the dictyate stage from 3 day post partum (p.p.) onwards. The T1-prospermatogonia, on the other hand, spend a long G1-phase of about 10 days without any conspicuous morphological change before entering the S-phase from day 4 p.p. onwards. The duration of the S-pbase (D-S) of both cell types—oocytes and T1-prospermatogonia—as determined by the double labeling method with 14C- and 3H-thymidine is found to be 11.5 hr. The most favourable time for determining the D-S was day 18 p.c. for the oocytes and day 5 p.p. for the T1-prospermatogonia. On these two days the balance was reached between the cells entering and leaving the S-phase. The nuclear volumes of the postmitotic oocytes and T1-prospermatogonia are approximately half the size of those of their precursors. Until day 5 p.p. the nuclear volumes of the oocytes and T1-prospermatogonia increase about fivefold. The degeneration index of the oocytes is considerably higher than that of the T1-prospermatogonia; postnatally it is especially high. T2prospermatogonia arise by mitosis of the T1-prospermatogonia on day 4 and 5 p.p. The nuclei of this cell type are smaller than those of T1-prospermatogonia. T2-prospermatogonia enter mitosis on day 6 p.p and give rise to A-spermatogonia.ZusammenfassungBei der Ratte findet die sexuelle Differenzierung der Gonade zwischen dem 14. und 15. Tag post conceptionem (p.c.) statt. Während dieser Zeit teilen sich die Oogonien und deren Parallelpopulation—die M-prospermatogonien (multiplying prospermatogonia) oder I-Gonocyten—sehr häufig. Um den 17. Tag p.c. tritt die letzte Generation der Oogonien bzw. der M-prospermatogonien in die Mitose. Die Mitosen bilden häufig “synchronisierte Gruppen”. Die postmitotischen Kerne ihrer Tochterzellen—der Oocyten und der T1prospermatogonien (primary transitional prospermatogonia) oder II-Gonocyten—sind klein. Ihr Chromatin ist in Form gröberer Schollen der Kernmembran angelagert. Auf diese Weise kommt das typische “krustenförmige” Aussehen bzw. die Ähnlichkeit mit den Prophasen der Oogonien und M-prospermatogonien zustande. Die Oocyten durchlaufen zunächst die G1-phase (etwa 10 Std Dauer) und treten dann—am Ende des Präleptotänstadiums—in die S-phase. Dann passieren sie die verschiedenen Stadien der meiotischen Prophase und treten vom 3. Tag post partum (p.p.) ab in das Dictyotänstadium. Die T1-prospermatogonien hingegen befinden sich etwa 10 Tage lang in der G1-phase, ohne wesentliche morphologische Veränderungen aufzuweisen. Vom 4. Tag p.p. an durchlaufen sie die S-Phase. Die S-Phasen-Dauer (D-S) beider Zellarten beträgt 11.5 Std und wurde durch Doppelmarkierung mit 14C- und 3H-Thymidin bestimmt. Als am besten geeignete Termine für die Bestimmung der D-S erwiesen sich bei den Oocyten der 18. Tag p.c. und bei den T1-prospermatogonien der 5. Tag p.p. Zu diesen beiden Zeitpunkten war die Anzahl der in die S-phase ein-und austretenden Oocyten bzw. T1-prospermatogonien gleich, die Zellen in S-phase befanden sich im “steady state”. Das Kernvolumen der Oogonien und M-prospermatogonien ist etwa doppelt so groß wie das der postmitotischen Oocyten und T1-prospermatogonien. Bis zum 5. Tage p.p. nimmt das Kernvolumen der Oocyten und T1-prospermatogonien um etwa das Fünffache zu. Der Degenerationsindex der Oocyten liegt wesentlich höher als der der T1-prospermatogonien; er ist postnatal besonders hoch. Aus den T1-prospermatogonien gehen am 4. und 5. Tage p.p. durch Teilung die T2-prospermatogonien (secondary transitional prospermatogonia) hervor. Die Kerne dieses Zelltyps sind etwas kleiner also die der T1-prospermatogonien. Die T2-prospermatogonien treten am 6. Tage p.p. in die Mitose; es entstehen die ersten A-spermatogonien.

The structure of fish skin. I. General organization.

Abstract: Both the epidermis and dermis of the anadromous coho salmon, Oncorhynchus kisutch, have a full complement of the protective structures found in fish The living epidermal surface is protected by mucous secretions which are prevented from ablation by the intricately patterned microridges of the surface keratinocytes, as seen by scanning electron microscopy Bundles of filaments are dispersed throughout the keratinocytes but not to the extent that ribosomes, endoplasmic reticulum, and Golgi apparatus are excluded In the yearling salmon, the straight basal lamina of the embryo has changed to a convoluted border invaded by dermal reticular fibers The complex dermis has an upper region of loosely organized collagen fibers, which is interspersed with fibroblasts and pigment cells, and a deeper, highly ordered zone of orthogonally arranged collagen Coho salmon also have overlapping calcified scales that extend at an angle from the upper dermis to the epidermis and push an enclosing sheath of epidermal tissue with them to the skin's surface The other major component of fish skin, the chromatophores, are discussed in an adjacent paper

Development of rat dorsal root ganglion neurones. Studies of cell birthdays and changes in mean cell diameter

Abstract: Pulse labelling with tritiated thymidine was used to determine the time of the final division of the neuroblasts which subsequently form rat lumbar dorsal root ganglion neurones. The final division occurred during a 4 day period, the maximum frequency being on day 12 of gestation. Separation of the ganglion cells into large light neurones and small dark neurones showed that the large light neurones were formed earlier than the small dark neurones. In both cases the final divisions occurred over a period of 3–4 days, but the peak rate of formation of large neurones was on day 12, and that of the small neurones was on day 13.

On the interdigitating cells in the thymus-dependent area of the rat spleen: a relation between the mononuclear phagocyte system and T-lymphocytes.

Abstract: Light- and electron microscopic studies reveal that the peri-arteriolar lymphocytic sheath of the rat spleen can be divided into two areas. The central area contains small lymphocytes, interdigitating cells (IDC, light staining cells with extensive cytoplasmic interdigitations) and some scattered reticulum cells. The peripheral area contains a mixed population of lymphocytes and circumferentially oriented reticulum cells. It is shown that only the central area of the peri-arteriolar lymphocytic sheath is thymus-dependent. In neonatally thymectomized rats, before interdigitating cells appear, monocytes and promonocytes reside in this area. It is suggested that the IDC are part of the mononuclear phagocyte system (Langevoort et al., 1970). They probably form the micro-environment necessary for the differentiation and proliferation of T-cells. The analogies between IDC, epithelioid cells and the macrophages in the migration inhibition test are discussed. The hypothesis is put forward that these cells are similar in ultrastructural and functional aspects because all three are macrophages under the influence of humoral factors from T-cells, such as migration inhibition factor.

Junctions in the central nervous system of the cat. 3. Gap junctions and membrane-associated orthogonal particle complexes (MOPC) in astrocytic membranes.

Abstract: SummaryFixed and unfixed astrocytic membranes from the CNS of the cat were studied by means of the freeze-etching technique.A variable number of gap junctions was detected in astrocytic membranes. They are characterized by the well known hexagonal composition of their subunits. Besides this type of highly ordered membrane-bound particles, a second one was found. It is composed of four single particles (diameter 5 nm) which form an orthogonal subunit with a side length of about 10 nm. These membrane-associated orthogonal particle complexes (MOPC) could be observed in different stages of aggregation and expansion. They reveal an accumulation in membranes of the marginal glia layers and in the perivascular astrocytic end-feet. Unfixed, glycerol treated membranes, however, do not show these structures. After glycerol treatment of the unfixed membranes by immersion, the MOPC disintegrate to single particles which form clusters of various extension. The clustering phenomenon is dependent on the length of the time of exposure to glycerol. Shortening of the glycerol treatment by intravasal perfusion of the cryoprotectant agent causes an decrease of the clusters. Fragments and transient forms of the MOPC become visible. By variation of different physico-chemical parameters of the washing solution a similar effect on the MOPC was not achieved. The discussion deals with probable functional aspects of the MOPC. They are considered to act as membrane-bound functional multienzyme complexes which a) might play a role in mediating transmembrane passage of metabolites, or b) are essential for CSF control mechanisms, or c) have a functional relation to the nexus.

Interdigitating reticulum cells in the human thymus.

Abstract: Seven thymuses from children between 1 and 12 years were examined by electron microscopy. Biopsies had been taken during surgical correction of congenital heart defects.

A reappraisal of insect haemocyte classification by the examination of blood from fifteen insect orders.

Abstract: A simplified insect haemocyte classification has been formulated by a light microscopic examination of the haemolymph of insects from fifteen Orders. Six cell types or developmental stages can be distinguished: (1) Prohaemocytes, (2) Plasmatocytes, (3) Granular Cells, (4) Spherule Cells, (5) Cystocytes, and (6) Oenocytoids. The structure and occurrence of these haemocytes are described together with the structural variations which occur in each cell type. Due to considerable overlap in structure and the presence of numerous intermediates the six cell types may represent different developmental and/or functional stages of one basic cell type. The available evidence for this unitarian hypothesis is discussed.

Vital staining of specific monoamine-containing cells in the leech nervous system.

Abstract: Neutral red and several related dyes selectively stain certain cells in the ventral nerve cord of the leech. These cells are identical with those that can be shown by the FalckHillarp fluorescence technique to contain serotonin or a catecholamine; evidence suggests that the catecholamine is dopamine. Although the mechanism of staining remains unknown, it does not depend on active uptake of the dye. Stained cells in ganglia that were incubated for 12 hours in culture medium retained their normal physiological properties. Thus neutral red may be useful for locating specific monoamine-containing neurons in living nervous tissue.

Structure and ultrastructure of the frog motor endplate. A freeze-etching study.

Abstract: The frog motor endplate in its simplest form consists of an elongated, slender nerve ending embedded in a gutter-like depression of the sarcolemma. This nerve terminal contains the usual synaptic organelles. It is covered by a thin coating of Schwann cell cytoplasm which embraces the terminal with thin finger-like processes from both sides, thereby sub-dividing it into 300–1000 regularly spaced compartments. The individual synaptic compartments correspond to the strings of varicosities or grape-like configurations of motor nerve terminals in endplates of other species and in the cerebral neuropil of vertebrates.

The goldfish pituitary. I. Cytology.

Abstract: The innervation of the pituitary gland of Carassius auratus was studied by light and electron microscopy under various physiological and experimental conditions to investigate whether or not neurosecretory fibres play a role in regulating pars distalis function. Two types of neurosecretory fibre (Type A and Type B) were distinguished. Prolactin, ACTH and TSH1 cells were innervated by Type B fibre terminals separated from the endocrine cells by a continuous basal lamina (“indirect contacts”). Gonadotropic, STH and TSH2 cells were innervated by Type A as well as Type B neurosecretory fibres, mostly without an intervening basal lamina (“direct contacts”). The assessment of the amount of neurosecretory granules and microvesicles in nerve terminals during the pre-spawning, spawning and postspawning seasons and following the administration of Oestradiol, Thyroxine, Thiourea and Metopiron respectively revealed convincing evidence for a participation in pars distalis control for Type A and Type B fibres innervating gonadotropic cells and STH cells and Type B fibres innervating TSH2 and ACTH cells. Immediately after spawning both nerve fibre types innervating gonadotropic cells and Type A fibres innervating STH cells showed a striking decrease in the amount of dense core vesicles. During the spawning season nerve fibres innervating somatotropic cells, TSH2 cells and ACTH cells also undergo changes suggesting that prior to spawning major changes in the endocrine system of the goldfish take place.—These results point to a dual control, by peptides and amines, of teleost pars distalis function.

Identification of neurophysin producing cells. I. The origin of the neurophysin-like substance-containing nerve fibres of the external region of the median eminence of the rat.

Abstract: Immuno-histochemical investigations on the brain of the rat showed: (1) the presence of neurophysins in the whole magnocellular neurosecretory hypothalamo-hypophysial system, the extra-hypothalamic neurosecretory tracts included; (2) the presence, in the external region of the median eminence, of neurophysin-like substance-containing nerve fibres which accumulate around the blood-capillaries and of which the number of detectable fibres is strongly influenced by adrenalectomy and by colchicine treatment; (3) that the suprachiasmatic nuclei produce neurophysin-like substances, the amount of which is also influenced by adrenalectomy and by colchicine treatment.

Ovulation and the mechanism of follicle rupture. III. Transmission electron microscopy of rabbit germinal epithelium prior to induced ovulation.

Abstract: The rabbit Graafian follicles are encircled by a capillary network between the theca interna and the avascular membrana granulosa. After injection of an ovulatory dose of human chorionic gonadotrophin (HCG) the theca interna cells showed an increase in the amount of smooth endoplasmic reticulum, lipid droplets and mitochondria with tubular cristae. In addition, considerably more junctions, similar to the abutment nexuses of granulosa cells were found; annular nexuses also appeared. At 4 hours after injection of HCG a prominent oedema was evident in the theca interna layer, particularly in the apical region.

Structure and development of the auditory system in the prothoracic leg of the cricket Teleogryllus commodus (walker)

Abstract: The anatomical development of the tympanal organ, the tracheal system and the tympana of Teleogryllus commodus is described. The tympanal organ is undifferentiated until instar 3 when the first scolopales appear. The organ develops in a proximo-distal direction but the more distal groups begin to form before the proximal groups are complete. All groups of scolopidia are represented in instar 7 but numbers of scolopidia continue to increase until the adult stage. Scolopales and scolopale cells are first formed at less than adult size and increase in size during subsequent instars. The subgenual organ is present in instar 1 and is complete in instar 4. The posterior and anterior tympanal trachease develop respectively from the tracheal trunk and tracheal branch, which are present from instar 2. These remain as simple, unconnected tubes until instar 7 and begin to show the adult form during instars 8 and 9, finally enlarging in conjunction with the tympana at the last two moults. The tympana first appear as hairless areas of cuticle in the larval stages: the posterior tympanum in instar 8 and anterior tympanum in instar 10, but the translucent appearance of the adult tympana is not present before the final moult.

Structure of rat liver sinusoids and associated tissue spaces as revealed by scanning electron microscopy.

Abstract: The inner surface of sinusoids and adjacent hepatocytes have been examined by scanning electron microscopy. The endothelial cells lining the sinusoids show large numbers of fenestrations which vary greatly in size and arrangement. Some are very small (0.1 μm) and arranged in clusters; others that are much larger (∼1.0 μm) are subdivided by slender strands of cytoplasm. At sites where the larger fenestrae are present it is evident that the endothelial lining of the sinusoid is double. This may represent a kind of structural assurance against complete breakdown of what seems to be a very thin and fragile endothelial wall. Junctions between adjacent endothelial cells have not been found in these preparations.

Taste bud types in fishes. II. Scanning electron microscopical investigations on Xiphophorus helleri Heckel (Poeciliidae, Cyprinodontiformes, Teleostei).

Abstract: Within the epithelium of the head gut of the sword-tail (Xiphophorus helleri Heckel) there are three types of taste buds that can be identified with certainty in the scanning electron microscope. The breathing valves, which are situated behind the mouth region, bear relatively high epidermal papillae in which type I taste buds can be found. The middle region of the head gut is mostly occupied by low epidermal papillae containing type II taste buds. Type III taste buds are present within the metabranchial head gut; they never rise above the normal level of the epithelium. Taste buds of each type show two kinds of receptor villi within their receptor areas: tall villi (about 1,5×0,5 μm) and small villi (about 0.5×0.2 μm). A few tall villi belonging to solitary chemosensory cells are situated between the superficial epithelial cells of the tongue. In addition, the surface of the epidermal cells shows a delicate microridge system.—It is postulated that the taste buds of different types serve different functions: Taste buds within epidermal papillae may act both as chemoreceptors, and mechanoreceptors. Taste buds that never rise above the normal level of the epithelium perhaps act predominantly as chemoreceptors.

The structure of fish skin. II. The chromatophore unit.

Abstract: SummaryThe chromatophore unit concept is applicable to the variety of chromatophore associations in the coho salmon, Oncorhynchus kisutch. Individual pigment cells of three general types—melanophores, xanthophores, and iridophores—vary structurally according to skin location, age, and physiological state. In growing fish, melanophores have a bimodal size distribution; in adults, they have a normal size distribution. Both melanophores and xanthophores are dendritic cells which respond to potassium and sodium ions by respectively aggregating and dispersing pigment granules. The third cell, the iridophore, is characterized by reflecting platelets of birefringent crystals of guanine of hypoxanthine and has at least two distinct shapes. In the upper dermis of the dark-colored skin, globular iridophores are encompassed by the dendritic arms of subjacent melanophores. In relation to this melanophoreiridopbore unit, the xanthophores appear to be randomly distributed and to afford an effective filter by virtue of their quantity and shape as well as their pigment granules. In deeper locations in the dermis, particularly below the stratum compactum in the shiny ventral skin, layers of dendritic iridophores are only partially shielded by the few melanophores and thus represent the nadir of chromatophore unit organization in the salmon.

Distribution of heavy metals in the hippocampal region of the guinea pig. A light microscope study with Timm's sulfide silver method.

Abstract: With the present modification of Timm's sulfide silver method all parts of the hippocampal region show a distinctly stratified staining pattern, suggesting large regional differences in the content of heavy metals. The stain is largely confined to distinct grains, partly associated with neuronal somata and partly dispersed in the neuropil. Work in progress supports the idea that the grains in the neuropil are synaptic boutons, as has been shown previously for the mossy fibre layer. The staining pattern has been compared in detail with the fields and layers of the hippocampal region as delineated by cyto- and fibroarchitectonics. Previous concepts of the subdivision of this cortical region are confirmed and supplemented. The sulfide silver pattern of the guinea pig hippocampal region is fundamentally similar to that of the rat. However, the entorhinal area, the regio inferior hippocampi, and the dentate area show notable differences in the staining pattern between the two species.

Reconstitution of the thymus dependent area in the spleen of lethally irradiated mice. A light and electron microscopical study of the T-cell microenvironment.

Abstract: To study the submicroscopical morphology of the microenvironment for T-lymphocytes in the spleen, mice were lethally X-irradiated and injected intravenously with syngeneic thymocytes. 24 hours after cell transfer, small lymphocytes occurred in the thymus dependent area of the spleen: the periarteriolar lymphatic sheath (PALS). They localized preferentially around a special type of mononuclear phagocyte, the Interdigitating Cell (IDC), which is considered to be characteristic for thymus-dependent areas in peripheral lymphoid organs. A close cell contact between both cell types was observed: small lymphocytes protruded into the cytoplasm of the IDC by means of fingerlike protrusions. This type of cell contact seems to induce blast transformation of the lymphoid cells which resulted in the formation of medium sized T-cells. In a control experiment, spleen cells from thymectomized, X-irradiated and bone marrow reconstituted mice were injected intravenously into lethally X-irradiated recipients. These B-lymphocytes, however, were not found to be localized around IDC. They preferentially formed primary follicles at the periphery of lymphocyte-depleted thymus dependent areas.

Estrogen-induced transformation of somatotrophs into mammotrophs in the rat.

Abstract: In the normal male rat pituitary tritiated thymidine labeled mainly STH cells (somatotrophs), no labeled prolactin cell was found. Following estradiol treatment for 21 days tritiated thymidine labeled mainly prolactin cells (mammotrophs). To determine the origin of these mammotrophs tritiated thymidine was given before the estradiol treatment started, thus labeling many somatotrophs. After 21 days of estradiol, out of 42 labeled cells, 14 were mammotrophs and 13 were somatotrophs; these results suggest that there might be a true transformation of somatotrophs into mammotrophs under the influence of estradiol or that there exist two types of somatotrophs: 1) a committed somatotroph which is not transformed by estrogen treatment, and 2) an uncommitted mammosomatotroph, which under normal conditions bears the features of a somatotroph, but which transforms into a mammotroph under the influence of estradiol.

Ovulation and the mechanism of follicle rupture. VI. Ultrastructure of theca interna and the inner vascular network surrounding rabbit graafian follicles prior to induced ovulation.

Abstract: SummaryThe rabbit Graafian follicles are encircled by a capillary network between the theca interna and the avascular membrana granulosa. After injection of an ovulatory dose of human chorionic gonadotrophin (HCG) the theca interna cells showed an increase in the amount of smooth endoplasmic reticulum, lipid droplets and mitochondria with tubular cristae. In addition, considerably more junctions, similar to the abutment nexuses of granulosa cells were found; annular nexuses also appeared. At 4 hours after injection of HCG a prominent oedema was evident in the theca interna layer, particularly in the apical region.Small fenestrations in the endothelium of the blood capillaries increased in amount after HCG injection, and close to the time of ovulation, large gaps or perforations, 1–3 μ in diameter, were found in the thin, distended part of the endothelial cells. The surrounding basement membrane became fragmented and partly lost, so that a seemingly free passage from the capillary lumen to the interstitium was eventually established. Leakage of fluid, causing interstitial oedema, presumably proceeds until the pressure in the pericapillary interstitium has risen to the pressure in the capillaries. Some hours before and up to ovulation the pericapillary interstitium has also broad communications with the cavity of the follicles. Therefore, both pressure and fluid can be passed from the capillaries-via the interstitium-to the follicle antrum. However, influx of fluid with subsequent follicle expansion and ovulation-at constant pressure-does not occur until the tensile strength of the follicle wall has decreased.

On the structure of the human archicortex. I. The cornu ammonis. A Golgi and pigmentarchitectonic study.

Abstract: By means of a method for the stereomicroscopical demonstration of neurolipofuscines in sections ranging from 400 up to 800 μm in thickness (Braak, 1970), the distribution pattern of these pigments all over the various layers and sectors of the cornu ammonis of man is described. Additionally Golgi studies were made for an improved interpretation of the pigment picture. Our new technique utilizing the successive examination of both the Golgi and the pigment picture of individual neurons allows a clear determination of the cell types by distinguishing characteristics of the pigment deposits. Thus, the pigment preparations allow to separate unequivocally the pyramids from the various types of stellate cells. Hence, the qualitative results of the Golgi studies are translated into the language of the pigment preparations, giving quantitative information about the distribution pattern and packing density of pyramids and the various types of interneurons. Pigmentarchitectonic studies are therefore of great value, if deciphering of the bewildering maze of the human cerebral cortex is attempted.

Monoaminergic tracts of the diencephalon and innervation of the pars intermedia in Rana temporaria. A fluorescence and microspectrofluorimetric study.

Abstract: With the fluorescence technique of Falck-Hillarp two monoaminergic tracts having independent nuclear sources, and extending towards the hypophysis, were identified in the diencephalon of Rana temporaria. The nature of the fluorophore in the diencephalic nuclei which give rise to the tracts, and also that of the nerve fibers innervating the pars intermedia (PI), were analyzed microspectrofluorimetrically.

The ultrastructure of the human fetal pineal gland. I. Cell types and blood vessels.

Abstract: The ultrastructure of the pineal gland of 18 human fetuses (crown-rump lengths 30–178 mm) was investigated. The pineal gland exhibits a pyramidal shape and consists of an anterior and posterior lobe. Only one parenchymal cell type, the pinealocyte, was observed. Few neuroblasts were seen between the pinealocytes and in the extended perivascular space. The pinealocytes possess all the organelles necessary for hormone synthesis. No specific secretory granule could be observed. The organ is abundantly vascularized and richly innervated. The morphology of the capillaries indicates the existence of a blood-brain barrier. The ultrastructure of the human fetal pineal gland suggests that the gland has a secretory function in early intrauterine life.

Ultrastructural distribution of calcium in smooth muscle cells of guinea-pig taenia coli. A correlated electron microscopic and quantitative study.

Abstract: In order to demonstrate the ultrastructural distribution of calcium in smooth muscle cells of the guinea pig taenia coli a precipitation method with potassium oxalate has been used. In addition, morphometric assessment (“stereology”) of cell components and direct quantitative estimation of calcium content in isolated subcellular fractions by atomic absorbtion analyses were carried out. After oxalate treatment smooth muscle cells show four major and distinct sites of calcium oxalate deposition: sarcoplasmic reticulum, mitochondria, cell boundaries (sarcolemma, surface microvesicles) and nucleus. Calcium oxalate deposits were frequently found at the level of close associations formed by different cell organelles. Correlating the morphometric analysis of electron micrographs with microchemical measurements of calcium in isolated subcellular fractions an estimation of calcium content in each cell component of one smooth muscle cell was performed. The nucleus has a significantly higher calcium content than that of any other cellular compartment, but the mitochondria are the main calcium-storage sites of smooth muscle cytoplasm. The highest calcium concentration was found in mitochondria. Although the amount of calcium stored in the sarcoplasmic reticulum represents only about a quarter of that accumulated in mitochondria, around 20% might be enough to produce contraction. On the other hand, the surface microvesicles may accommodate the entire amount of calcium translocated during activity. Functional implications of these findings in relation to the contraction-relaxation cycle are considered and the possible role of the surface microvesicles is discussed.

The differentiation of intrafusal fibre types in rat muscle spindles after motor denervation.

Abstract: Hind limb muscles were de-efferented in 19 new-born rats by removal of the lumbosacral spinal cord, with preservation of spinal ganglia and their peripheral branches. The juxtaequatorial and polar zones of muscle spindles were studied in different leg muscles 3 to 9 weeks after the operation in order to establish whether intrafusal fibre types would become differentiated after permanent motor denervation.

Ultrastructure of mucosal mast cells in normal and compound 48-80-treated rats.

Abstract: Mast cells in the tongue and lamina propria of the duodenal mucosa, representing two cell types with different morphological, histochemical and functional properties have been studied under the electron microscope. Both cell types were found to contain similar moderately electron dense and homogeneous granules surrounded by a tight membrane constituting the basic ultrastructural characteristics of mast cells. The mucosal mast cells, however, contained fewer granules per cell and the individual granules often exhibited considerable variation in size. In addition the mucosal mast cells, unlike those of the tongue, peritoneum and skin, had a smooth plasma membrane lacking microvilli and possessed irregularly shaped or lobulated nuclei. In the tongue mast cells, administration of Compound 48/80 caused the formation of vacuoles around the granules, expulsion of granules from the cells and disintegration of the granular matrix, but no changes that could be attributed to 48/80 could be found in the mucosal mast cells.

Studies on central projections of the pineal nerve tract in rainbow trout, Salmo gairdneri Richardson, using cobalt chloride iontophoresis.

Abstract: The central projections and terminations of the pineal nerve tract in rainbow trout, Salmo gairdneri, were studied using the cobalt chloride method developed for selectively staining nerve fibres by Pitman et al. (1972). A modification of the method is described for the first time making its use possible in the study of central pathways of the pineal nerve tract.

Ultrastructure of immature, developing, and secretory rodlet cells in fish.

Abstract: Rodlet cells from many species of fresh water fish were examined with the electron microscope. Observations of these cells in the epithelia of intestine, gill, and other organs favor the interpretation that rodlet cells are secretory cells rather than protozoan parasites (Rhabdospora thelohani). Evidence is presented that rodlet cells develop from undifferentiated cells near the epithelial basement membranes and migrate“upward” to secrete their contents in a holocrine manner at the epithelial surface. The major secretory product is packaged in unique club-shaped sacs which contain a central core of highly electron dense material with less dense material surrounding it. Secretion often appears to be accomplished by active contraction of a 0.5 μm fibrillar border resembling smooth muscle which lies just inside of the plasma membrane. Some rodlet cells, however, merely break apart and release their contents.

Fat absorption by the enterocytes of the carp (Cyprinus carpio L.).

Abstract: In the carp, the absorption of fat from the food occurs at the level of the enterocytes of the proximal region of the intestine. The absorbed fat gives rise to the presence of two forms of inclusions: lipid particles and lipid droplets. These two forms, whose precise significance is unknown, definitely play different roles in fat absorption. Only lipid particles are involved in direct transport of absorbed fatty acids into the blood circulation. Lipid droplets seem to be involved in the temporary storage of fatty acids.