Cyclic Nucleotides and the Release of Vasopressin from the Rat Posterior Pituitary Gland

Abstract: The effect of ATP, Mg²⁺, or MgATP on the release of luteinizing hormone-releasing hormone (LH-RH) from hypothalamic granules was examined under in vitro conditions. Granules, isolated from adult male hypothalami, were incubated at 37°C in a buffered (pH 7.8) medium containing 0.15 m -KCl. The addition of ATP to the incubation mixture did not stimulate the release of LH-RH. In contrast, the addition of MgATP stimulated the release of LH-RH, the release being 62% greater than control. The addition of Mg²⁺ to the incubated granules also stimulated the release of LH-RH. However, the magnitude of this Mg²⁺-stimulated release of LH–RH was significantly ( P < 0.01) lower than that of the MgATP-stimulated release, indicating that ATP stimulates LH-RH release in a Mg²⁺-dependent manner. As both MgATP and Mg²⁺ alone stimulated LH-RH release, we characterized further these two release processes by incubating the granules under one of the following conditions: incubation at 4°C in a buffered medium containing 0.15 m -KCl or incubation at 37°C in a medium that does not contain KCl. Under these two incubation conditions, the MgATP-stimulated release of LH-RH was not manifested, whereas the Mg²⁺-stimulated release of LH-RH was manifested. On the basis of these differences, we propose that two different processes can lead to the release of LH-RH from isolated hypothalamic granules: one process involves ATP and Mg²⁺ (MgATP) and another process involves Mg²⁺ alone.     

The physical characteristics of anaerobic granular sludges in relation to their internal architecture

A range of granular sludges was taken from industrial anaerobic sludge blanket reactors treating a wide variety of wastewaters and a comparison was made between the polymers which were extractable from the granules and their internal structures. The study of the internal structure, using sequential staining of ultra-thin sections, showed the complexity of granular sludges. Much of the area was occupied by Gram-negative cells and the area which stained positive for protein was found to increase nearer the centre of the granules. This was accompanied by a decrease in the carbohydrate positive areas. Positive areas for lipid were widespread throughout the granules. Changes in the internal structure were observed when the type of wastewater treated by the granules was changed and a comparison between sludges treating the same type of wastewater showed that factors other than the nature of the substrate must be considered as parameters which will affect the structure of the granules. Although an appreciable variation in the granule strengths was noted, it was not possible to relate these differences, on an overall basis, to either the internal structure or the chemical composition of the extracted polymers. However, an examination of data for granules produced during the treatment of nominally similar wastes did suggest that there would be a relationship between polymer composition and granule strength in these cases.     

The Fine Structure of the Scopula-Stalk Region of Vorticella convallaria

ABSTRACT. We examined by SEM and TEM the stalk-scopular junction, the stalk, and stalk formation in Vorticella convallaria Linnaeus, 1767. The stalk sheath is anchored to the walls of the scopular lip and to the scopular cilia by thin fibrils. Experimental extraction of these fibrils weakens this junction enough to separate the stalk from the cell body. Telotrochs escape from the stalk by means of violent contractions of the cell body, accelerated beating of the trochal band cilia, and twisting of the cell body against the stalk. The edges of the scopular lip spread over the scopular cilia after escape and, in some cases, fuse to enclose the entire, aboral scopular surface in a cupola-like structure. The sessile cells contain fewer and smaller scopular granules than telotrochs. The presence of disintegrating scopular granules in the stalk matrix of some sessile cells suggests that they contain material which is secreted over a period of time to form the stalk. Eruptive formation of the initial adhesive pad and quick elongation of the distal part of the stalk suggests a rapid exocytosis of the larger, more numerous granules of the telotroch. The stalk sheath is formed of fibrils making up complete and incomplete compartments peripherally arranged along the major stalk axis.     

Stability of aerobic granules during long-term bioreactor operation

Aerobic granular sludge technology has been extensively studied over the past 20 years and is regarded as the upcoming new standard for biological treatment of domestic and industrial wastewaters. Aerobic granules (AG) are dense, compact, self-immobilized microbial aggregates that allow better sludge-water separation and thereby higher biomass concentrations in the bioreactor than conventional activated sludge aggregates. This brings potential practical advantages in terms of investment cost, energy consumption and footprint. Yet, despite the relevant advances regarding the process of AG formation, instability of AG during long-term operation is still seen as a major barrier for a broad practical application of this technology. This paper presents an up-to-date review of the literature focusing on AG stability, aiming to contribute to the identification of key factors for promoting long-term stability of AG and to a better understanding of the underlying mechanisms. Operational conditions leading to AG disintegration are described, including high organic loads, particulate substrates in the influent, toxic feed components, aerobic feeding and too short famine periods. These operational and influent wastewater composition conditions were shown to influence the micro-environment of AG, consequently affecting their stability. Granule stability is generally favored by the presence of a dense core, with microbial growth throughout the AG depth being a crucial intrinsic factor determining its structural integrity. Accordingly, possible practical solutions to improve granule long-term stability are described, namely through the promotion of minimal substrate concentration gradients and control of microbial growth rates within AG, including anaerobic, plug-flow feeding and specific sludge removal strategies.     

Stress granules counteract senescence by sequestration of PAI‐1

Cellular senescence is a physiological response by which an organism halts the proliferation of potentially harmful and damaged cells. However, the accumulation of senescent cells over time can become deleterious leading to diseases and physiological decline. Our data reveal a novel interplay between senescence and the stress response that affects both the progression of senescence and the behavior of senescent cells. We show that constitutive exposure to stress induces the formation of stress granules (SGs) in proliferative and presenescent cells, but not in fully senescent cells. Stress granule assembly alone is sufficient to decrease the number of senescent cells without affecting the expression of bona fide senescence markers. SG‐mediated inhibition of senescence is associated with the recruitment of the plasminogen activator inhibitor‐1 (PAI‐1), a known promoter of senescence, to these entities. PAI‐1 localization to SGs increases the translocation of cyclin D1 to the nucleus, promotes RB phosphorylation, and maintains a proliferative, non‐senescent state. Together, our data indicate that SGs may be targets of intervention to modulate senescence in order to impair or prevent its deleterious effects.     

Changes in the ultrastructure of Nematospiroides dubius (Nematoda) intestinal cells during development from fourth stage to adult

Summary The general fine structure of intestinal cells and changes which occur in ultrastructure during development from fourth-stage to adult N. dubius are reported. In fourth-stage worms pigment granules are prominent in intestinal cells. In adults the number of pigment granules appears to be reduced and phagolysosomes containing membranous profiles and pigment material increase in number. Another reorganization of cell structure involves mitochondria which are randomly distributed in the cytoplasm of cells in fourth-stage worms, concentrated in the apical cytoplasm in worms in the molting process, and confined to the base of cells in adult worms. Other changes involved structure of the nucleus, rough endoplasmic reticulum and glycogen content of cells.This investigation was supported, in part, by NIH Fellowships I-FI-GM-32750 and 5-F02-AI-32750.     

Ultrastructural study of the neurosecretory granules in the sinus gland of the blue crab,Callinectes sapidus

Summary Seven morphologically different types of neurosecretory granules have been found in the axon terminals of the sinus gland of the blue crab, Callinectes sapidus. They differ from each other in size, shape, staining characteristics, solubility characteristics, core matrix characteristics, axon terminal matrix characteristics, presence or absence of space between the granule membrane and granule core matrix, and frequency of occurrence. Five of the types are segregated in different axon terminals and are believed to represent different hormone-protein complexes. Two of the types, which have lost part or all of their granular contents, are thought to be variants of the other five types. The differences in granular morphology are better revealed by some fixation procedures than others. Palade's acetate-veronal buffered osmium tetroxide, in particular, reveals striking differences. The following observations suggest that different hormone-protein complexes are segregated in different axon terminals and that these complexes may be morphologically distinguished at the level of the electron microscope.Supported by USPHS-NIH Training Grant GM-00669 and Grant GB-7595X from the National Science Foundation.