去甲肾上腺素、甘氨酸、γ-氨基丁酸和L-谷氨酸对节段性与下行性脊髓场电位的影响

在麻醉的大鼠脊髓背部表面,记录刺激腓神经引起的节段性脊髓场电位(SP)与刺激C_2背索引起的下行性脊髓场电位(DP),观察在脊髓表面局部施加去甲肾上腺素(NE),甘氨酸(GLY),γ-氨基丁酸(GABA)和L-谷氨酸(L-GLU)时SP与DP的变化。结果表明,NE使SP与DP的N、P波波幅均明显降低,GLY、GABA、L-GLU明显降低SP与DP的N波波幅同时使SP与DP的P波明显增大。本文讨论了可能的作用机制。     

Decreased hydraulic conductance in plants at elevated carbon dioxide

Previous work indicated that long-term exposure to elevated carbon dioxide levels can reduce hydraulic conductance in some species, but the basis of the response was not determined. In this study, hydraulic conductance was measured at concentrations of both 350 and 700 cm³ m^–3 carbon dioxide for plants grown at both concentrations, to determine the reversibility of the response. In Zea mays and Amaranthus hypochondriacus , exposure to the higher carbon dioxide concentration for several hours reduced whole-plant transpiration rate by 22–40%, without any consistent change in leaf water potential, indicating reversible reductions in hydraulic conductance at elevated carbon dioxide levels. Hydraulic conductance in these species grown at both carbon dioxide concentrations responded similarly to measurement concentration of carbon dioxide, indicating that the response was reversible. In Glycine max , which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide levels, and in Abutilon theophrasti , no short-term changes in hydraulic conductance with measurement concentration of carbon dioxide were found, despite lower transpiration rates at elevated carbon dioxide. In G. max and Medicago sativa , growth at high dew-point temperature reduced transpiration rate and decreased hydraulic conductance. The results indicate that both reversible and irreversible decreases in hydraulic conductance can occur at elevated carbon dioxide concentrations, and that both could be responses to reduced transpiration rate, rather than to carbon dioxide concentration itself.     

Inclusion of phytosociological data in an index of vegetation fire danger: application and mapping on the Karst area around Trieste (Italy)

In this paper we propose a method to produce maps of fire danger index (FDI). The index includes in the formula a vegetation pyrogenic potential index (VPPI) based on floristic phytosociological data. The map of FDI is produced by integrating available phytosociological maps of vegetation, geomorphology and climate, using the Geographic Information System technology. The method is applied to an area of the coastal Classical Karst (NE-Italy). While fire risk maps based on the incidence of previous fires are useful for facilitating emergency operations, e.g. the allocation of fire fighting resources, we conclude that the proposed index offers an effective tool to plan actions for fire prevention.     

Plasmalemmal interface for calcium signaling in osteoclast differentiation

There are three hot topics for research on calcium (Ca) signaling in osteoclast differentiation. First, Transient receptor potential (TRP) vanilloid channel 4 is important for late differentiation. In addition, TRP canonical channels and Ca release-activated Ca channels cooperatively inhibit differentiation. Second, antioxidants against reactive oxygen species inhibit osteoclastogenesis and bone loss. Mechanical stress in osteoclasts is also a focus of investigation. Third, immunoreceptor tyrosine-based activation motif (ITAM) adaptor–receptor complexes evoke costimulatory signals for osteoclastogenesis. ITAM molecules like cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) for Fc receptor gamma and Siglec-15 for DNAX-activating protein of 12 kD (DAP12) are potential targets for modification in osteoclast inhibition. Detection and analysis methods need to be objective and interdisciplinary to clarify the integrative mechanism for Ca oscillations induced by many factors including Ca channels and transporters.     

Ridge crest versus swale: contrasting plant–water relations and performance indexes in two understory plant species in a coastal maritime forest

Coastal-ridge plains are progradational landforms composed of elevated ridges and low-lying swales. The transitions between ridges and swales are steep, promoting dynamic shifts between xeric and mesic systems. Two understory plants that co-occur in ridge plains of North American mid-Atlantic maritime forests are Sabal minor and Ilex vomitoria. As coastal-ridge plains foster varying amounts of surface and sub-surface water driven largely by topography, the purpose of this study was to evaluate plant–water relations and chlorophyll a fluorescence in these two species. Ridge plants had lower leaf- and xylem-water potentials, lower osmotic potential (I. vomitoria), and lower symplastic water content (S. minor). Although there were no differences in potential- and effective-quantum yields, there were decreases in fluorescence performance index for ridge I. vomitoria and swale S. minor. While the data support potential water-stress conditions in ridge plants of both species, the data also suggest that I. vomitoria and S. minor use different physiological processes to tolerate hydrologically dynamic ridge–swale maritime forests.     

Recommended gas transport properties of argon at low density using ab initio potential

The most important transport properties of argon have been calculated using classical kinetic theory expressions in conjunction with high-quality ab initio potential energy values computed by Patkowski and Szalewicz. Dilute gas transport properties have been calculated for the viscosity, thermal conductivity, self-diffusion coefficient and thermal diffusion factor from 83 to 10,000 K. Comparisons between experimental transport property data and values presently calculated indicate that the present theoretical predictions may be employed as recommended values for this set of transport properties over a wide temperature range.     

Water movement through Quercus rubra I. Leaf water potential and conductance during polycyclic growth

Two experiments examined simultaneous changes in leaf area (A_L), root length (L_r), stomatal conductance (g_s), leaf water potential (Ψ_L), transpiration and hydraulic plant conductance per unit leaf area (G) during the first three shoot cycles of northern red oak (Quercus rubra L.) grown under favourable and controlled conditions. Each shoot cycle consisted of bud swell, stem elongation, leaf expansion and rest; roots grew almost continuously. The g_s of all leaves decreased substantially while leaves of the newest flush were expanding and increased modestly when seedling leaf area remained constant. Overall, g_s decreased. The Ψ_L of mature leaves decreased during leaf expansion and increased by an equivalent amount during intervening periods. Possible explanations for the paired changes in g_s and Ψ_L are considered. Changes in G closely paralleled those of canopy g_s. These parallel changes during polycyclic seedling growth should act to keep seedling Ψ_L relatively constant as plant size increases and thereby help prevent Ψ_L from dropping to levels that would cause runaway embolism.     

Depolarization-induced release of l-glutamic acid from isolated-resealed synaptic membrane vesicles

l-Glutamic acid actively loaded into resealed brain synaptic membrane vesicles was rapidly released into the incubation medium following the introduction of KCl and CaCl₂, or nigericin, or veratridine into the external medium. The KCl-induced release was enhanced by the presence of low (0.1 mM), extravesicular [Ca²⁺]. Neither the KCl-induced nor the veratridine-stimulated l-glutamate efflux were carrier-mediated processes. Finally, the KCl-stimulated l-glutamate efflux was dependent on the ratio of intra- to extravesicular [K⁺]. The observations described in this study were indicative of depolarization-induced l-glutamate release from isolated synaptic plasma membrane vesicles.     

Integration of hydraulic and chemical signalling in the control of stomatal conductance and water status of droughted plants

We describe here an integration of hydraulic and chemical signals which control stomatal conductance of plants in drying soil, and suggest that such a system is more likely than control based on chemical signals or water relations alone. The determination of xylem [ABA] and the stomatal response to xylem [ABA] are likely to involve the water flux through the plant. (1) If, as seems likely, the production of a chemical message depends on the root water status (Ψ_r), it will not depend solely on the soil water potential (Ψ_s) but also on the flux of water through the soil-plant-atmosphere continuum, to which are linked the difference between Ψ_r and Ψ_s. (2) The water flux will also dilute the concentration of the message in the xylem sap. (3) The stomatal sensitivity to the message is increased as leaf water potential falls. Stomatal conductance, which controls the water flux, therefore would be controlled by a water-flux-dependent message, with a water-flux-dependent sensitivity. In such a system, we have to consider a common regulation for stomatal conductance, leaf and root water potentials, water flux and concentration of ABA in the xylem. In order to test this possibility, we have combined equations which describe the generation and effects of chemical signals and classical equations of water flux. When the simulation was run for a variety of conditions, the solution suggested that such common regulation can operate. Simulations suggest that, as well as providing control of stomatal conductance, integration of chemical and hydraulic signalling may also provide a control of leaf water potential and of xylem [ABA], features which are apparent from our experimental data. We conclude that the root message would provide the plant with a means to sense the conditions of water extraction (soil water status and resisance to water flux) on a daily timescale, while the short-term plant response to this message would depend on the evaporative demand.     

Location and functional characterization of the right atrioventricular pacemaker ring in the adult avian heart

Previous histological studies showed that in addition to a sinus node, an atrioventricular (AV) node, an AV bundle, left and right bundle branches, birds also possess a right AV‐Purkinje ring that is located in the atrial sheet of the right muscular AV‐valve along all its base length. The functionality of the AV‐Purkinje ring is unknown. In this work, we studied the topology of pacemaker myocytes in the atrial side of the isolated chicken spontaneously contracting right muscular AV‐valve using the method of microelectrode mapping of action potentials. We show that AV‐cells having the ability to show pacemaking reside in the right muscular AV‐valve. Pacemaker action potentials were exclusively recorded close to the base of the valve along its whole length from dorsal to the ventral attachment to the interventricular septum. These action potentials have much slower rate of depolarization, lower amplitude, and higher diastolic depolarization than action potentials of Purkinje (conducting) cells. We conclude the right AV‐valve has a ring bundle of pacemaker cells (but not Purkinje cells) in the adult chicken heart. J. Morphol. 277:363–369, 2016. © 2015 Wiley Periodicals, Inc.