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Biomedical subjects

E J Sanders

Publications and source records attributed to E J Sanders.

At least 127 records · Page 7Linked to original sources
PubMed1979

The mechanism of sensory transduction in the sensilla of the trochanteral hair plate of the cockroach, Periplaneta americana.

The trochanteral hair plate of the cockroach leg contains approximately 60 hair sensilla that are deflected by a joint membrane during flexion of the leg. Previous work has shown that the organ is a mechanoreceptor which limits leg flexion during walking by reflex connections to flexor and extensor motoneurons. Functional analysis of the largest sensilla has shown that their behaviour may be well approximated by a velocity detector followed by a unidirectional rectifier. We report here the results of an examination of the largest sensilla by scanning and transmission electron microscopy in an attempt to correlate the structure with the known functional elements. Each hair is innervated by a single sensory dendrite which is surrounded by an electron dense dendritic sheath. The dendrite terminates below the hair shaft in a tubular body containing a parallel array of microtubules embedded in an electron dense matrix, while the dendritic sheath extends beyond the tubular body to form the walls of the ecdysial canal. At the proximal end of the tubular body the dendritic sheath and sensory dendrite are anchored to the cuticular socket by a fibrous dome which seems to form a flucrum around which the tubular body can be deflected by movements of the hair. We suggest that the basis for the detection of velocity shealth and the tubular body. The structure is also discussed with relation to the mechanism of sensory transduction and the possible causes of the unidirectional sensitivity.

Animals↗
PubMed1979

Ultrastructural localization of wheat germ agglutinin-binding sites on surfaces of chick embryo cells during early differentiation.

The objective of this work was to examine changes in a surface component of cells from the chick embryo during morphogenetic migrations of gastrulation. Two electron microscope techniques were used to localize cell-bound wheat germ agglutinin (WGA), a lectin which specifically binds N-acetyl glucosamine residues. One technique involved conjugation of peroxidase to WGA before reaction with the cells; the other technique used glucose oxidase to mark WGA which was already cell-bound. In both cases, binding was revealed using diaminobenzidine. Before formation of the primitive streak, all surfaces of the two-layered embryo bound WGA. After migration of cells through the streak, to form the three-layered embryo, not all cell surfaces bound WGA equally. Epiblast cells generally bound WGA lateral to the primitive streak but not during passage through the streak. Mesenchyme cells, after passage through the streak, bound WGA increasingly as they migrated away from the streak. A WGA-binding matrix was observed in the vicinity of the mesenchyme cells and on the dorsal surface of the endoblast. The ventral surface of the endoblast bound the lectin very poorly. In some instances, a peroxidase reaction product was consistently seen on certain surfaces which was not removable by addition of the simple hapten N-acetyl glucosamine. In these cases, the density of the deposit was lessened by use of diacetyl chitobiose as a hapten. This result, together with the reduction of reaction product following certain hyaluronidase treatments, suggests that WGA may be binding to hyaluronic acid as well as membrane glycoproteins.

Animals↗
PubMed1979

Observation of cultured embryonic epithelial cells in side view.

Epithelial cells from the early chick embryo were explanted and grown on a strip of coverglass which was positioned in a culture chamber in such a way that the cells could be filmed in side view. Ruffling of the cells at the leading edge of the sheet (marginal cells) appeared similar to the ruffles at the leading lamella of fibroblasts. The ruffles of the sub-marginal cells showed different characteristics, being longer and not propagated successively as were the marginal ruffles. Superimposition of cells was always the result of the active movement of a non-yolky cytoplasmic process underneath a yolky process (i.e. underlapping). The non-yolky processes appeared to be strongly adherent to the substrate in comparison with the yolky processes, which were easily displaced. Active movement of cells or lamellae on the dorsal surface of the sheet was never observed. Preliminary ultrastructural evidence is presented which suggests that the strongly adherent non-yolky processes possess well-defined microfilament tracts associated with the ventral plasma membrane, while the poorly adherent processes do not possess such tracts.

Animals↗
PubMed1978

The effects of acute and chronic uremia in rats on their hepatic microsomal enzyme activity.

The activity of the hepatic microsomal enzymes hexabarbital oxidase, aminopyrine demethylase, and p-nitrobenzoic acid reductase were determined in the chronically uremic rats, acutely uremic rats and controls. Plasma corticoid levels (corticosterone) were also measured in all groups. A significant reduction in the hepatic microsomal enzyme activity as compared to controls was observed in both groups, with the chronic group showing slightly greater reduction. Furthermore, while plasma corticoid levels were significantly elevated in both groups, the acute uremic group had plasma corticoid levels which were almost twice the levels found in the chronically uremic animals. The significance of these observations are discussed.

Acute Disease↗
PubMed1978

In vivo and in vitro studies on the hypoblast and definitive endoblast of avian embryos.

An unusual example of the invasion of one tissue by another occurs during gastrulation in the chick embryo when the definitive endoblast becomes inserted into the hypoblast. The two tissues were examined morphologically by SEM and TEM. They resemble each other in being of an epithelial type, though neither possesses a basal lamina. The definitive endoblast cells are flatter than the hypoblast cells and more closely attached to one another. When they were explanted in hanging drop cultures, the two tissues were found to exhibit differences in their behaviour. In comparison with the definitive endoblast, the hypoblast cells attached more readily to the glass, produced larger ruffle membranes, moved more rapidly, showed poorer contact-inhibition of locomotion and showed a greater tendency to break away from the main explant. When a hypoblast explant was confronted with a definitive endoblast explant, the hypoblast cells became displaced by the definitive endoblast. The hypoblast explant tended to fragment into smaller groups of cells, many of which migrated around the definitive endoblast, thus mimicking the situation in vivo. Control experiments comprised confronting hypoblast with hypoblast, hypoblast with somites, definitive endoblast with definitive endoblast, and definitive endoblast with somites. The hypoblast explants behaved in a consistent manner, always fragmenting when coming into contact with cells from a confronting explant. The definitive endoblast explants showed more contact inhibition of locomotion when confronted with definitive endoblast or with somites than when confronted with hypoblast. It is suggested therefore that the ability of the hypoblast cells to separate from one another may play an important role in the penetration of the hypoblast by the definitive endoblast both in vitro and in vivo.

Animals↗
PubMed1978

Cell adhesiveness and embryonic differentiation.

The aim of the investigation was to decide whether changes in cell to cell adhesiveness took place during embryonic differentiation. The technique of Curtis (1969) was used to measure the adhesive behaviour of several types of ectodermal, neural and mesodermal cells of the chick embryo at stages 7 and 12 of differentiation. Cells dissected from segmented mesoderm were found to be more adhesive than cells from unsegmented mesoderm. Cells from the ectoderm were more adhesive than those from the neural tissue, at both stages 7 and 12. Cells from both ectoderm and neural tissue became more adhesive between stages 7 and 12. It is concluded that an increase in adhesiveness may play a role in somite segmentation, but not in neural tube formation.

Animals↗
PubMed1977

Effect of nerve stimulation, denervation, and duct ligation, on kallikrein content and duct cell granules of the cat's submandibular gland.

Various procedures which reduce or deplete the kallikrein content of the cat's submandibular gland correspondingly reduce the number of apical granules in the striated duct cells. The kallikrein content is greatly reduced after chronic parasympathetic but not after sympathetic nerve section which suggests that the parasympathetic innervation is required for synthesis or storage of this enzyme.

Animals↗
PubMed1977

Concanavalin A-binding by cells of the early chick embryo.

The surfaces of cells from the early embryo of the chick were examined using electron microscope techniques for the visualization of concanavalin A-binding sites. Horseradish peroxidase and Ferritin labelled concanavalin A were used to determine the distribution of the binding sites. All surfaces of the epiblast and hypoblast layers which were accessible to concanavalin A showed the presence of binding sites in stage 1 embryos. The ventral surface of the epiblast showed a high lectin affinity which may reflect the development of a basal lamina on this surface. The individual hypoblast cells at this stage showed a non-uniform distribution of binding sites, having a greater affinity on the dorsal surface than the ventral. By the time of primitive streak formation (stage 4-5) the dorsal surface of the epiblast displayed increased binding sites, while the frequency of sites on the ventral surface of the endoblast was reduced. The latter may reflect a change from one cell population to another, which occurs in the lower layer of the embryo at this time. No consistent correlation could be drawn between changes in motility of cells actually invaginating through the primitive streak and changes in affinity for concanavalin A. An overall increase in affinity of the dorsal surface of the epiblast was revealed by Ferritin and may reflect the changes in surface structure occurring in readiness for the morphogenetic migrations of gastrulation.

Animals↗
PubMed1977

A new class of infectious agents detectable by the production of chorioallantoic membrane lesions by human lymphoblastoid cell lines and their culture supernatants.

Intravenous injection of cells and their tissue culture supernatants (CS) from human lymphoblastoid cell lines (LCL) induced the formation of lesions on the chorioallantoic membrane (CAM) of the chicken embryo. Injection of cells and CS from non-LCL and normal human lymphocytes induced few or no lesions. Irradiated chick embryos were more sensitive to lesion formation than were nonirradiated embryos. The log10 CAM lesions induced in irradiated (500 rads) embryos were a linear function of the log10 cells (from LCL) in the inoculum; the slope was 1.0, within experimental error. The formation of CAM lesions did not depend on the presence of Epstein-Barr virus (EBV) since lesions were also induced by cells and extracts derived from EBV genome-free LCL. Lesion-inducing activity associated with CS was filterable through 0.22-mu filters, sedimented at 78,000 x g, and sensitive to inactivation by heat (56 degrees C for 30 min), UV irradiation, chloroform, sera from chickens immunized against CS, and certain human sera. Lesion-inducing activity associated with cells and extracts was resistant to 5,000 rads of gamma-radiation. B2/B2 embryos (the B locus is the major histocompatibility locus of chickens) were more sensitive to lesion formation than were B15/B21 and outbred embryos; this suggested a genetic influence on lesion formation. Our data suggest that the irradiated chicken embryo may be a highly sensitive and useful means for the detection of an unidentified or unknown agent or agents that may play an important role in human oncogenic lymphocyte transformation or might interact with transforming viruses.

Allantois↗
PubMed1976

A freeze-fracture and concanavalin A-binding study of the membrane of cleaving Xenopus embryos.

The freeze-fracture appearance and concanavalin A-binding capacity of the plasma membrane of cells of the cleaving Xenopus embryo have been examined up to the 16-cell stage. It was found that membrane on the outer surface of the embryo, which faces the vitelline membrane and is remote from cleavage furrows, and membrane in the shallow regions of the furrow possessed a high population of intramembranous particles on the PF-face (1171 per mum2). The EF-face of these membranes showed a lower particle population (245 per mum2). By contrast, membrane deep in the furrow and bounding the blastocoel did not display a face with high particle numbers. Both faces of this membrane, which is newly exposed as the furrow grows, were relatively poorly supplied with particles (93 per mum2). Therefore it appears that, in this tissue, newly added membrane possesses fewer intramembranous particles than the pre-existing membrane. Concanavalin A, as detected cytochemically using peroxidase and haemocyanin techniques, bound extensively to both particle-rich and particle-poor membrane. Thus there was no correlation between intramembranous particle frequency and degree of concanavalin A binding.

Animals↗
PubMed1976

On the mechanism of electrical coupling between cells of early Xenopus embryos.

The mechanism of electrical coupling between cells of early Xenopus embryos has been studied by examination of the nonjunctional membrane resistances and capacitances as a function of cleavage stage, the junctional and nonjunctional membrane resistances as functions of time during the first cleavage, and the electrical properties of the primitive blastocoel. The changes in membrane resistances and capacitances during the first two cleavages may be completely explained by the addition of new membrane, identical in specific resistance and capacitance to the original membrane, at a constant rate to furrows which are electrically connected to the perivitelline space. Microelectrode recording from the primitive blastocoel indicates that there is no electrical difference detectable between it and the perivitelline space. These results are discussed in the context of current theories of the mechanism of intercellular electrotonic coupling.

Animals↗
PubMed1976

Aggregation of cells from early chick blastoderms.

The aggregation of dissociated cells from chick blastoderms at Hamburger and Hamilton stages 1-5 was studied. Aggregation was measured during the first 4 h of culture by determination of the proportion of single cells in the medium. No difference in aggregation was found when cells dissociated by either trypsin or EDTA were studied. Similarly the presence or absence of serum in the medium had no appreciable effect on early phases of aggregation, although at 24 h and thereafter, aggregate size was reduced in serum-free cultures. It was found that at all of the stages studied, cells aggregate and sort out into two groups. One group forms a continuous phase of loosely associated cells while the other segregates into several localised areas of closely associated cells within the aggregate. Examination of aggregates up to 7 days in culture showed progressive differentiation within each phase and several identifiable cell types were observed. Basal laminae were present at the boundary between the compact phase and the loose phase.

Animals↗
PubMed1976

Intercellular junctions in the Xenopus embryo prior to gastrulation.

A freeze-fracture study of Xenopus embryos at the eight-cell stage revealed the presence of tight junctions and small aggregations of 120 A diameter intramembranous particles. These aggregations consisted of up to ten particles and resembled forming gap junctions. Examination of early blastulae showed that fully developed gap junctions were present, apparently occurring very infrequently. These results support the contention that specialized junctions mediate electrical coupling during early amphibian development.

Animals↗
PubMed1975

Aspects of furrow membrane formation in the cleaving Drosophila embryo.

During blastoderm formation, the Drosophila embryo produces a large area of new membrane to accommodate the simultaneous demands of approximately four thousand newly cleaved cells. The embryo was examined with the electron microscope at various stages during cleavage in order to investigate the high membrane forming capacity of these cells. Embryos were subjected to the histochemical procedure for the demonstration of thiamine pyrophosphatase. The enzyme was present in the cisternae of the endoplasmic reticulum, Golgi bodies and the nuclear envelope. No activity could be demonstrated on the furrow surface or at the furrow tip despite closely adjacent reactive cisternae. It is concluded that the endoplasmic reticulum and Golgi bodies are not major contributors to the new surface. Lamellar bodies were frequently observed in the cytoplasm of all stages examined. The bodies showed a lamellar periodicity of approximately 3.5 nm, and were ultrastructurally similar in appearance after a variety of fixation procedures. The distribution of these bodies was markedly related to the stage of blastoderm formation. Before the commencement of cleavage, lamellar bodies were very prominent within a region 4--5 mum below the cell surface. As cleavage progressed, the bodies became sparse or absent from this region but were apparent at the base of the blastoderm cells or in the sub-blastoderm region, where they were not previously present. Lamellar bodies with leaflets closely associated with, or in apparent continuity with, the cleavage furrow membrane were frequently observed. In these regions the lamellar periodicity was the same as the thickness of the membrane laminae. It is suggested that these bodies play a role in the synthesis of new membrane in the furrow. Intercellular contact specializations between the developing membranes of the furrow were restricted to incipient desmosones and point contacts where the intercellular gap was reduced to 3 nm or less.

Animals↗
PubMed1975

Intercellular connectivity in the eight-cell Xenopus embryomcorrelation of electrical and morphological investigations.

The distribution of individual intercellular electrical junctions has been examined in eight-cell Xenopus embryos using linear systems analysis. Morphological evidence for corresponding intercellular contacts has been sought by light microscopy and scanning electron microscopy. The electrical investigation indicated that each cell is directly coupled to each of the other seven cells by identical resistive junctions. Scanning electron microscopy of the cell surfaces of cleaved embryos revealed protrusions from the surfaces of the cells which could mediate such intercellular connections. Light microscopy of serial sections through the embryos also showed fine processes of the cell surfaces which come into contact with several other cells. The complete intercellular connectivity suggested by these results appears to be an extension of similarly close connectivity in the two- and four-cell embryos. The possible significance of this high connectivity to morphogenesis is discussed.

Animals↗
PubMed1975

The influence of chronic uremia on hepatic glycogen in the rat.

Long term maintenance of male Wistar rats following sub-total nephrectomy has been shown to alter carbohydrate metabolism. These rats frequently became hypoglycemic and concurrently demonstrated increased hepatic glycogen stores. Chemical analysis of glycogen revealed a significant increase in branching, with a concomitant decrease in glucose residues per segment. The influence of food intake and glycosuria are discussed. Decreased glycogen autolysis is attributed to increased glycogen branching in the uremic liver.

Animals↗
PubMed1975

Autonomic nerve stimulation, kallikrein content anc acinar cell granules of the cat's submandibular gland.

The parasympathetic and sympathetic nerves to the submandibular gland of the anaesthetized cat were stimulated under specific conditions. 1. It was possible to decrease the kallikrein (kininogenase) content of the gland by as much as 90-95% by sympathetic nerve stimulation. In such a gland the appearance and concentration of secretory granules in the acinar cells were indistinguishable from an unstimulated gland. 2. Parasympathetic nerve stimulation, in contrast to sympathetic nerve stimulation, whilst having no significant effect on the kininogenase content of the gland, resulted in the disappearance of a great majority of the acinar granules. 3. These results demonstrate that the acinar granules in the submandibular gland of the cat are not a significant source of kallikrein. 4. Our experiments also failed to indicate any obvious correlation between the granules of the demilune cells and the kallikrein content of the gland. 5. The possibility is raised that kallikrein is located in the cells of the striated ducts.

Animals↗