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Biomedical subjects

D G Jones

Publications and source records attributed to D G Jones.

At least 217 records · Page 12Linked to original sources
PubMed1979

Metabolic studies on the uptake of [14C]-histidine and [14C]-histamine and histamine synthesis by guinea-pig basophils, in vitro.

The uptake of [14C]-histidine and [14C]-histamine and the conversion of [14C]-histidine to [14C]-histamine was measured in suspensions of guinea-pig bone marrow cells rich in basophils. When comparable amounts of labelled histidine or histamine were added to equal numbers of basophils, the uptake of histidine was approximately forty-five times greater than that of histamine. Purified eosinophils, neutrophils and mononuclear cells incorporated only a small proportion of [14C]-histidine when compared to the basophil; [14C]-histamine uptake by all these cell types was virtually negligible. Histidine uptake and the amount of histamine formed de novo was directly related to the number of basophils, the time of incubation and the substrate concentration. Histidine uptake was decreased by agents which inhibit glycolysis, oxidative phosphorylation, Na + - K + -dependent ATPase, protein synthesis and RNA synthesis. Inhibition was demonstrable in a dose-dependent fashion and at concentrations which had no apparent effect on cell viability. Inhibitors of DNA synthesis, and of microtubule function, had no influence on histidine uptake. Cytochalasin B, an inhibitor of microfilament function, also decreased histidine uptake but only at concentrations previously showen to affect hexose transport. None of the agents tested affected the uptake of [14C]-histamine or the amounts of new histamine formed from the histidine that had been incorporated. These studies suggest that histidine is preferentially incorporated into the basophil; that the uptake depends on the integrity of a number of metabolic pathways, but that once the histidine is taken up these requirements do not apply to the formation of new histamine. In contrast, histamine appeared to diffuse passively, and in relatively small amounts, into all the cell types tested.

Animals↗
PubMed1978

An ultrastructural study into the effects of pentobarbitone on synaptic organization.

A series of adult male rats was analyzed to test the effects of varying doses of pentobarbitone sodium on the ultrastructure of synapses in the molecular layer of the parietal cortex. The rats were divided into the following categories: unanaesthetized stunned, unanaesthetized cannulated and those subjected to 40, 80, 160, 300, or 400 mg/kg pentobarbitone. All material was examined both qualitatively and quantitatively after aldehyde-OsO4 or ethanolic phosphotungstic acid (E-PTA) treatment. The principal qualitative observations were: the preponderance in the unanaesthetized stunned and 160-400 mg/kg material of a variety of intraterminal profiles including synaptic vesicles, mitochondria, coated vesicles, tubular profiles, vacuoles, cisterns and double membrane profiles; the presence of exocytotic sites along the presynaptic membrane in the unanaesthetized stunned and cannulated material; the presence of endocytotic sites over the limiting membrane of the terminal away from the cleft in the unanaesthetized stunned and 160-400 mg/kg material; the prominence of the presynaptic network in the unanaesthetized and 40 mg/kg E-PTA material; discontinuity of the cleft material in the 40-160 mg/kg material. Findings to emerge from the quantitative aspect of the study show that pentobarbitone influences synaptic curvature, with a marked increase in curvature negativity over the 0-80 mg/kg dose range and a decrease in negativity at higher dose levels. The increase in curvature negativity is accompanied by an increase in synaptic length and dense projection numbers, with a consonant increase in the perimeter and area of the presynaptic terminal. Reversal of the negativity trend at higher dose levels is parallelled by reversal of these accompanying trends. Both sets of findings can be accounted for by membrane recycling within the terminal, supporting a membrane redistribution hypothesis.

Animals↗
PubMed1978

Impact of solid discharges from coal usage in the Southwest.

The Southwestern region of the United States is extremely wealthy in low sulfur coal resources which must be eventually utilized in response to national energy balance priorities. Fly ash and scrubber sludge can be safely disposed of using properly managed techniques to ensure that any potential impact from elements such as boron, molybdenum, or selenium is rendered insignificant. Alternative methods of solids utilization are presently being developed. Fly ash is presently being marketed commercially as an additive for concrete manufacture. Successful experiments have been completed to demonstrate the manufacture of commercial-grade wallboard from scrubber sludge. Also, greenhouse studies and field experiments have been conducted to demonstrate increased yields of selected crops grown on typical soils amended with fly ash in amounts ranging from 2% to 8%, by weight. These studies also indicate that barium and strontium may be good monitoring indices for determining atmospheric deposition of fly ash, due to their concentration ratios in soil and vegetation samples. Further studies are being conducted to confirm encouraging irrigation and crop-yield data obtained with fly ash amended soils. Finally, the composition of many fly ashes and soils are similar in the Southwest, and there are no anticipated solid discharges from coal usage which cannot be rendered insignificant with proper management of existing and emerging methods of treatment. Compared with the water availability impact of coal usage in the Southwest, the impact of solid waste discharges are insignificant.

Agriculture↗
PubMed1977

The uptake of horseradish peroxidase by cortical synapses in rat brain. An in vivo study.

Horseradish peroxidase (HRP) was introduced directly into the cerebral cortex of adult rats, which were allowed to survive for 60 min before perfusion fixation. After the tissue had been incubated to demonstrate HRP at the LM and EM levels, blocks of cortical tissue were taken at varying distances from the injection site. These eight blocks of tissue constituted a time sequence for HRP diffusion. Qualitative examination of the presynaptic terminals showed that the most commonly encountered profiles are the plain synaptic vesicles, many of which accumulate tracer. In some terminals labelled vesicles are "lined-up" in tubular fashion. Other profiles commonly labelled are coated vesicles, tubular and vacuolar cisternae, and plain and coated pinocytotic vesicles. Quantitative analyses based on the number of terminals containing labelled profiles demonstrate an early rise in the rate of labelling of both plain synaptic vesicles and coated vesicles, after which synaptic vesicle labelling rises slowly towards a plateau. By contrast, there is a late parallel increase in the rate of labelling of coated vesicles and cisternae. A more detailed analysis, based on the actual numbers of labelled and total profiles within each presynaptic terminal, highlight early and late periods of rapid labelling for plain synaptic vesicles, coated vesicles and cisternae. A further aspect of HRP incorporation studied, concerns its uptake into four delineated regions of the presynaptic terminal. Our data indicate that membrane uptake into the presynaptic terminal is accomplished mainly via coated vesicles, although plain synaptic vesicles may also be involved. Coated vesicles, in turn, appear to give rise directly to plain synaptic vesicles, with some coalescing to produce vacuolar cisternae. The latter are involved in a two-way interchange of membrane with tubular cisternae, plain synaptic vesicles and coated vesicles. An additional source of plain synaptic vesicles are the tubular cisternae. Exocytosis of plain synaptic vesicles constitutes the mechanism by which transmitter is released from the presynaptic terminal.

Animals↗
PubMed1977

Neutrophil accumulation in vivo following the administration of chemotactic factors.

Intravenously administered 51Cr-labelled homologous neutrophils accumulated at guinea-pig skin sites prepared by intradermal injection of factors derived from complement-activated serum, possessing in vitro chemotactic activity. There was a strong correlation between the in vitro potency of Sephadex G-100 fractions of the activated serum and their ability to evoke neutrophil accumulation in vivo. These experiments suggest that agents which are chemotactic for neutrophils in vitro also induce the localization of this cell in vivo.

Animals↗
PubMed1977

Chemotactic activity of guinea pig eosinophils for the ECF-A acidic tetrapeptides, histamine, histamine metabolites, and the effect of H1- and H2-receptor antagonists.

Histamine and one of its major metabolites, imidazoleacetic acid, were selectively chemotactic for guinea pig eosinophils, whereas L-histidine, 1,4-methylimidazoleacetic acid, 1,4-methylhistamine and N-acetylhistamine were inactive. The response to histamine was unaffected by concentrations of eosinophils of between 30 and greater than 90% but it was abrogated by preincubation of the cells with histamine prior to assay (self-deactivation). Eosinophilotaxis was also inhibited by H1-(mepyramine-) and H2-)burimamide)-receptor antagonists at high doses (10(-3)m), although at lower concentrations (10(-5) M) inhibition was principally associated with burimamide. The human tetrapeptide, alanine-glycine-serine-glutamic acid, and the analogue, valine-glycine-aspartic acid-glutamic acid, were inactive whereas alanine-glycine-serine-glutamic acid was chemotactic for the guinea pig eosinophil. These results support the concept that the tissue accumulation of eosinophils following anaphylaxis depends on a complex interaction of factors, which in part may be mediated by H2 receptors on the target cells. There may be species differences in the composition of ECF-A.

Alanine↗
PubMed1976

Some observations on the ultrastructure of developing rat cerebral capillaries.

Developing blood vessels in rat cerebral cortex were studied at a number of stages between 3 and 28 days postnatal, in an attempt to obtain data on the mechanisms by which the lumen is established within cords of mesodermal cells. A combination of techniques was utilized in an attempt to elucidate these mechanisms. These were: (a) aldehyde fixation and block staining with phosphotungstic acid; (b) aldehyde perfusion followed by perfusion of a lead solution and post-fixation in osmium tetroxide; (c) conventional preparation of tissue with aldehyde and osmium fixation. Support for interendothelial lumen formation was readily forthcoming, including vessels with junctions between two or more endothelial cells cut transversely. There was some support for intraendothelial lumen formation, in the form of "seamless" endothelial cells. Other features noted included the presence of free ribosomes and vacuoles in the endothelial cells, endothelial flaps, sprouts and tendrils, intraluminal debris, endothelial degeneration and a junction with a nonendothelial cell. Large numbers of endothelial vacuoles were noted, many of them occurring at the abluminal edge of the cells. These vacuoles may be involved in the formation of intraendothelial lumina and also in the enlargement of both types of lumina. This study provides evidence that besides the well-established interendothelial lumen formation, intraendothelial mechanisms may also be operative in rat cerebral cortex. The techniques employed in this study offer the potential for clarifying these and related issues.

Animals↗
PubMed1976

Some effects of undernutrition on synaptic development -- a quantitative ultrastructural study.

The development of synaptic junctions in rat occipital cortex has been studied at 7 and 20 days postnatal in control and undernourished animals. In addition, adult control cortex has been compared with cortex derived from animals undernourished until 35 days postnatal and then nutritionally rehabilitated. Emphasis has been placed on material stained with phosphotungstic acid (E-PTA technique) although osmicated material has been examined. The body weights of the undernourished animals were lower than those of their age-matched controls, the deficit at 20 days being 55%. The number of synaptic junctions per unit area of the molecular layer was lower in the undernourished animals at 7 and 20 days, the most prominent deficit being at 20 days. In an attempt to detect ultrastructural correlates of undernutrition, E-PTA stained synaptic junctions were divided into 5 types (A-E), based upon their presynaptic characteristics are reflecting varying degrees of maturity. During normal development the immature synaptic types, particularly type E, are predominant, giving way to the more mature types (A-C) as development proceeds. Undernutrition however, appears to disrupt this developmental sequence, with a higher than normal percentage of immature synaptic types present at the age studied. Nutritional rehabilitation rectifies the imbalance to a degree, the adult rehabilitated pattern resembling the 20-day control pattern. Preliminary examination of the 20-day osmicated material confirmed the deficit of synapses per area of tissue in the undernourished cortex. It also revealed decreases in the number of vesicles per terminal unit area and in the internal area of the synaptic vesicles in the undernourished tissue.

Age Factors↗
PubMed1976

A critical evaluation of the relationship between the presynaptic network, synaptic vesicles and dense projections in central synapses.

Synapses of the oculomotor nucleus of Echidna have been examined ultrastructurally with the aim of integrating data obtained from osmicated and nonosmicated PTA stained material. Particular emphasis has been laid on the relationship between the synaptic vesicles of the osmicated material and the presynaptic network and vesicular grid of the PTA material. This relationship has been explored qualitatively by examining osmicated material of varying qualities of fixation. Such material contains dense projections in addition to synaptic vesicles, and various vesicular network appearances. A variety of measurement techniques have shown that the PTA network is characterised by reticular strands, spaces, and regular hexagonal units smaller than vesicles, these observations prompting the formulation of a "vesicle-network coincidence" model of the presynaptic terminal. This model has been tested by tracing the profiles of vesicles within the PTA network and comparing their size and shape frequency distributions with those of osmicated synaptic vesicles. The distributions have been found to be essentially similar, suggesting that vesicles can be located within the network, and that the hexagonal network units are formed only in the presence of an underlying vesicular matrix. Additionally, the following points have emerged: 1) the dense projections in the two types of material appear to be quivalent; 2) a loose correlation exists between dense projections and vesicles in osmicated terminals, increase in the area of the dense projections being associated with a decrease in the area of the vesicles; 3) network and dense projection units are similar. In view of the similarity between network and dense projection units, the demonstrated vesicular basis of the network raises the question of whether dense projections are entirely independent structures, or whether they depend in part for their existence on the nearby presence of synaptic vesicles.

Animals↗
PubMed1976

The morphological categorization of developing synaptic junctions.

The molecular layer of rat occipital cortex was studied at a number of ages throughout postnatal development in an attempt to a formulate a quantitative morphogenetic scheme of synaptic development. As previous work had pointed to the potential usefulness of E-PTA stained material in synaptogenic studies, this technique was employed. Synaptic junctions were assigned to five categories, A-E, on the basis of variations in the organization of their presynaptic densities. Of these categories, Type A represented a mature junctional form with well-defined and discrete dense projections. Type E, by contrast, represented the immature end of the spectrum, its presynaptic apposition generally lacking recognizable densities. Types B-D represented intermediate forms. As development proceeded, the percentage of A type junctions increased from 0.3% at 7 days to 25% in the adult. Type E junctions showed the opposite trend falling from 42% at 7 days to 5% in the adult. On the basis of these results, and those relating to types B-D, possible morphogenetic schemes involving the five synaptic categories are put forward. These schemes incorporate and extend those previously suggested by other workers. By placing observations on a quantitative footing, the schemes proposed here lend themselves to use in experimental investigations.

Animals↗
PubMed1976

Effect of "restricted ovulator" gene on uptake of yolk-precursor protein.

The bulk of the yolk proteins and lipoproteins constituting the yolks of mature oocytes in birds are synthesized by the liver and transported via the plasma to the oocytes where they are incorporated by micropinocytosis. Evidence is presented indicating that oocytes of hens possessing a mutation identified by Jones, Briles, and Schjeide as a "restricted ovulator gene" fail to incorporate normal amounts and proportions of low density lipoproteins, lipovitellin and possible other proteins making up the bulk of the yolk material. Plasma albumin is taken into the yolks but the other proteins synthesized by the liver for deposition within the oocytes accumulate in the plasma, attaining very high levels. The possible nature of the "lock" preventing normal deposition of the excluded yolk proteins is discussed.

Animals↗
PubMed1976

Further observations of the ultrastructure of synaptosomes separated from spinal cord and medulla, with especial emphasis on the postsynaptic membrane.

Synaptosomes from rat medulla and spinal cord have been examined in an attempt to formulate morphological criteria for distinguishing between those found in two subfractions of P1 (nuclear fraction). The mean diameter of those in the lighter of the subfractions (P1C) is 0.6 mum, with a preponderance in the range 0.4-0.6 mum and a minor peak at 0.7-0.8 mum. Subjunctional bodies are associated with 60.2% of the junctional regions in this subfraction. By contrast, those in the heavy subfraction (P1D) have a larger overall diameter (0.7 mum), a greater percentage of them have visible junctional regions (68.1% opposed to 51.6%), but of the junctional regions a lower percentage have associated subjunctional bodies (36.2%). The subjunctional bodies consist of a central core with five spokes radiating from it. The tips of the spokes are connected by fine strands which connect individual bodies to neighboring ones, as well as to the postsynaptic thickening. The persistence of subjunctional bodies in synaptosomes highlights the strength of the attachment between them and the postsynaptic thickening, and suggests that these bodies may be integral components of the "postsynaptic thickening complex." They may also help in the formulation of criteria by which different populations of these synaptosomes may be separated from each other.

Animals↗