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Electron microscopical neurohistochemical studies of the choledocho-duodenal junction of the cat revealed acetylcholinesterase-positve nerve terminals closely abutting on ("ectopic"), mono-amine(s)-containing alpha-cells (of the islets of Langerhans) scattered in small clusters between bundles of the sphincteric smooth muscle (of Oddi). The cell membrane of the alpha-cells at and near the site of the neuro-effector contacts was reactive, too. This finding may be considered as some evidence for cholinergic innervation of cholinoceptive neuro-endocrine cells, and obviously represents one of the neuro-endocrine links involved in the regulation of the extra-hepatic biliary dynamics, demonstrated earlier in physiological and pharmacological studies. 相似文献
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Takehiko Saito Kyōsuke Tenma 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1976,111(1):39-53
1. | Stimulation to left and right vagi caused an almost equal amount of inhibitory, and occasionally excitatory, effects on pacemaker activity. Both inhibitory and excitatory effects were abolished by atropine. Vagal stimulation hyperpolarized the resting membrane potential of pacemaker fibers in the sino-atrial valve, but did not change their action potential profile. |
2. | The atrial action potential showed a prominent decrease in the action potential amplitude and duration in response to vagal stimulation. The atrial region surrounding the sino-atrial valve was more sensitive to right vagal stimulation. |
3. | The fibers in the atrio-ventricular ring muscle were less sensitive to vagal stimulation than the atrial fibers. Some fibers showed a decrease in the action potential amplitude and duration by vagal stimulation, and other fibers showed a decrease in the amplitude, but a prolongation of the duration as the result of a slowing of the rate of upstroke. The atrial-ventricular conduction delay or block by vagal stimulation may depend on these properties of the action potential of the atrio-ventricular ring muscle. |
4. | The sino-atrial conduction block is explained by the fact that the atrial fibers are more sensitive to vagal stimulation than pacemaker fibers. |
5. | The possible pathways for the sino-ventricular conduction during vagal stimulation are discussed. |
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From geochemical background determination to pollution assessment of heavy metals in sediments and soils 总被引:5,自引:0,他引:5
Tran Thi Thu Dung Valérie Cappuyns Rudy Swennen Nguyen Ky Phung 《Reviews in Environmental Science and Biotechnology》2013,12(4):335-353
Establishing geochemical background concentrations to distinguish the natural background from anthropogenic concentrations of heavy metals in sediments and soils is necessary to develop guidelines for environmental legislation. Due to the fact that the background concentrations strongly depend on geological characteristics such as mineral composition, grain size distribution and organic matter content, several normalization methods have been developed. Empirical (geochemical), theoretical (statistical) and integrated methods (combining both empirical and theoretical methods) are the main approaches described in literature for determination of geochemical background concentrations. In this review paper, the different approaches as well as the main normalization methods for heavy metal concentrations in sediments and soils will be discussed. Both geochemical background concentrations and added risk level (maximum permissible addition) should be taken into account for setting up legal threshold limits. Moreover, different approaches to evaluate the pollution status of heavy metals in sediments and soils, from Sediment/Soil Quality Guidelines to quantitative indices (Geo-accumulation Index-Igeo, Enrichment Factor-EF, Pollution Load Index-PLI and Risk assessment Code-RAC) will be presented. Although guidelines to establish whether a sediment or soil is polluted or not are generally only related to total metal concentrations, the available/reactive pool i.e., availability/reactivity of metals should be taken into account for sediment/soil pollution assessment. 相似文献
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Journal of Mathematical Biology - We study an ecosystem of interacting species that are influenced by random environmental fluctuations. At any point in time, we can either harvest or seed... 相似文献
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The Gram‐negative periodontal pathogen Porphyromonas gingivalis produces a family of outer membrane‐anchored proteases, the gingipains, shown to play an essential role in virulence of the organism. The C‐terminal domain (CTD) of gingipains and other secreted proteins is known to be the targeting signal for maturation and translocation of the protein through the outer membrane. The CTD is subsequently cleaved during the secretion process. Multiple alignment of various CTDs failed to define a consensus sequence at the putative CTD processing site. Using mutagenesis, we were able to show that cleavage at the site is not dependent on a specific residue and that recognition of the site is independent of local sequence. Interestingly, length of the junction between the CTD and adjacent Ig‐like subdomain has a critical influence on post‐translational glycan modification of the protein, whereby insertion of additional residues immediately N‐terminal to the cleavage site results in failure of glycan modification and release of soluble protease into the culture medium. Various hypotheses are presented to explain these phenomena. Knowledge of the role CTDs play in maturation of gingipains has broader application for understanding maturation of CTD homologues expressed by bacteria of the Bacteriodetes phylum. 相似文献
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Dendrites show remarkable diversity in morphology and function, but the mechanisms that produce the characteristic forms is poorly understood. Insect systems offer a unique opportunity to manipulate and study identified neurons in otherwise undisturbed environments. Recent studies in Drosophila show that dendritic targeting, branching patterns, territories, and metamorphic remodeling are controlled in specific ways, by intrinsic genetic programs and extrinsic cues, with important implications for function. Here, we review some recent advances in our understanding of dendritic development in insects, focusing primarily on insights that have been gained from studies of Drosophila. 相似文献
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Much attention has focused on dendritic translational regulation of neuronal signaling and plasticity. For example, long-term memory in adult Drosophila requires Pumilio (Pum), an RNA binding protein that interacts with the RNA binding protein Nanos (Nos) to form a localized translation repression complex essential for anterior-posterior body patterning in early embryogenesis. Whether dendrite morphogenesis requires similar translational regulation is unknown. Here we report that nos and pum control the elaboration of high-order dendritic branches of class III and IV, but not class I and II, dendritic arborization (da) neurons. Analogous to their function in body patterning, nos and pum require each other to control dendrite morphogenesis, a process likely to involve translational regulation of nos itself. The control of dendrite morphogenesis by Nos/Pum, however, does not require hunchback, which is essential for body patterning. Interestingly, Nos protein is localized to RNA granules in the dendrites of da neurons, raising the possibility that the Nos/Pum translation repression complex operates in dendrites. This work serves as an entry point for future studies of dendritic translational control of dendrite morphogenesis. 相似文献
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