Continuous intracellular recording from mammalian neurons exposed to hyperbaric helium, oxygen, or air.

We developed a hyperbaric chamber for intracellular recording in rat brain stem slices during continuous compression and decompression of the tissue bath with the inert gas helium. Air, rather than helium, was also used as the compression medium in some cases to increase tissue nitrogen levels. An important feature is the chamber door, which opens or closes rapidly at 1 atmosphere absolute (ATA) for increased accessibility of the microelectrode. The door also closes and seals smoothly without disrupting the intracellular recording. Hyperbaric oxygen was administered during helium compression using a separate pressure cylinder filled with perfusate equilibrated with 2. 3-3.3 ATA oxygen. Measurements of tissue/bath PO(2) and pH confirmed that the effects of compression using helium or air could be differentiated from those due to increased PO(2). One hundred and thirteen neurons were studied during 375 compression cycles ranging from 1 to 20 ATA (mode 3.0 ATA). We conclude that it is technically feasible to record intracellularly from the same mammalian neuron while changing ambient pressure over a physiologically important range. These techniques will be useful for studying how various hyperbaric environments affect neurophysiological mechanisms.     

iRFP is a sensitive marker for cell number and tumor growth in high-throughput systems

GFP and luciferase are used extensively as markers both in vitro and in vivo although both have limitations. The utility of GFP fluorescence is restricted by high background signal and poor tissue penetrance. Luciferase throughput is limited in vitro by the requirement for cell lysis, while in vivo, luciferase readout is complicated by the need for substrate injection and the dependence on endogenous ATP. Here we show that near-infrared fluorescent protein in combination with widely available near-infrared scanners overcomes these obstacles and allows for the accurate determination of cell number in vitro and tumor growth in vivo in a high-throughput manner and at negligible per-well costs. This system represents a significant advance in tracking cell proliferation in tissue culture as well as in animals, with widespread applications in cell biology.     

Neuronal sensitivity to hyperoxia, hypercapnia, and inert gases at hyperbaric pressures.

As ambient pressure increases, hydrostatic compression of the central nervous system, combined with increasing levels of inspired Po2, Pco2, and N2 partial pressure, has deleterious effects on neuronal function, resulting in O2 toxicity, CO2 toxicity, N2 narcosis, and high-pressure nervous syndrome. The cellular mechanisms responsible for each disorder have been difficult to study by using classic in vitro electrophysiological methods, due to the physical barrier imposed by the sealed pressure chamber and mechanical disturbances during tissue compression. Improved chamber designs and methods have made such experiments feasible in mammalian neurons, especially at ambient pressures <5 atmospheres absolute (ATA). Here we summarize these methods, the physiologically relevant test pressures, potential research applications, and results of previous research, focusing on the significance of electrophysiological studies at <5 ATA. Intracellular recordings and tissue Po2 measurements in slices of rat brain demonstrate how to differentiate the neuronal effects of increased gas pressures from pressure per se. Examples also highlight the use of hyperoxia (相似文献   

THE OCCURRENCE OF CHLOROPHYLLS C1 AND C2 IN THE CHRYSOPHYCEAE1

We analyzed 34 strains representing 25 species of Chrysophyceae for chlorophylls c₁ and c₂ using thin-layer chromatography. Most organisms had both chlorophylls c₁ and c₂ in addition to chlorophyll a but 17 strains of 9 species of Synura and Mallomonas possessed only chlorophylls a and c₁. These are the first chlorophyll c-bearing algae which lack chlorophyll c₂. We postulate that at least some of the silica-scaled algae including Mallomonas and Synura may be distinct from other Chrysophyceae based upon pigmentation and other characters described in the literature.     

Plant physiological ecology of tropical forest canopies

Mechanistic information about tropical canopy function is emerging at the leaf, tree, stand and landscape levels. With improved canopy access, comprehensive data are accumulating about seasonal and spatial variation in light, temperature and humidity, and corresponding variation in leaf carbon gain and water loss. At the whole-plant level, simultaneous measurements at different spatial scales have revealed the role of boundary layer dynamics in regulating transpiration. Emergent properties of canopy function are being explored through models that integrate leaf and landscape-level exchange processes. Integration of exchange processes that include functional diversity at different scales has the potential to validate regional estimates of gas exchange, which are critical to our understanding of the role of tropical forests in global atmospheric carbon balance.     

Effect of ethylene antagonists on auxin-induced inhibition of intact primary root elongation in maize (Zeamays L.)

We tested that the hypothesis that root elongation might be controlled by altering the level of ethylene in intact primary roots of maize(Zea mays L.). We measured root elongation in a short period using a computerized root auxanometer. Compounds which regulate ethylene production were applied to intact primary roots in different time periods. Root elongation was stimulated by the treatment with ethylene antagonists such as Co²⁺, aminoethoxyvinylglycine (AVG) and L-canaline. This result suggested that root elongation was closely related to ethylene level of intact primary roots. Furthermore, IAA- and 1-aminocyclopropane-1-carboxylic acid (ACC)-induced inhibition of root elongation was reversed by treatment with Co²⁺. The application of ACC to roots which have been exposed to IAA and Co²⁺ have no significant effect on root elongation. However, the inhibition of root elongation by ACC in roots previously treated with IAA and AVG became manifest when the applied IAA concentrations were lower. These results were consistent with the hypothesis that the level of ethylene in intact roots functions to moderate root elongation, and suggested that auxin-induced inhibition of root elongation results from auxin induced promotion of ethylene production.     

Management of warm-season grass mixtures for biomass production in South Dakota USA

Switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), and indiangrass (Sorghastrum nutans (L.) Nash) are native warm-season grasses commonly used for pasture, hay, and conservation. More recently switchgrass has also been identified as a potential biomass energy crop, but management of mixtures of these species for biomass is not well documented. Therefore, the objectives of our study were to: (1) determine the effects of harvest timing and N rate on yield and biomass characteristics of established warm-season grass stands containing a mixture of switchgrass, big bluestem, and indiangrass, and (2) evaluate the impact of harvest management on species composition. Five N rates (0, 56, 112, and 224 kg ha(-1) applied annually in spring and 224 kg ha(-1) evenly split between spring and fall) and two harvest timings (anthesis and killing frost) were applied to plots at two South Dakota USA locations from 2001 to 2003. Harvesting once a year shortly after a killing frost produced the greatest yields with high concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) along with lower concentrations of total nitrogen (TN) and ash. This harvest timing also allowed for the greatest percentage of desirable species while maintaining low grass weed percentages. While N rates of 56 and 112 kg ha(-1) tended to increase total biomass without promoting severe invasion of grass and broadleaf weed species, N application did not always result in significant increases in biomass production. Based on these results, mixtures of switchgrass and big bluestem were well suited for sustainable biomass energy production. Furthermore, N requirements of these mixtures were relatively low thus reducing production input costs.     

Decline of photosynthetic capacity with leaf age and position in two tropical pioneer tree species

The effect of leaf age on photosynthetic capacity, a critical parameter in the theory of optimal leaf longevity, was studied for two tropical pioneer tree species, Cecropia longipes and Urera caracasana, in a seasonally dry forest in Panama. These species continuously produce short-lived leaves (74 and 93 d, respectively) during the rainy season (May-December) on orthotropic branches. However, they differ in leaf production rate, maximum number of leaves per branch, light environment experienced by the leaves, leaf mass per unit area, and nitrogen content. Light-saturated photosynthetic rates for marked leaves of known ages (±1 wk) were measured with two contrasting schemes (repeated measurements vs. chronosequence within branch), which overall produced similar results. In both species, photosynthetic rates and nitrogen use efficiency were negatively correlated with leaf age and positively correlated with light availability. Photosynthetic rates declined faster with leaf age in Cecropia than in Urera as predicted by the theory. The rate of decline was faster for leaves on branches with faster leaf turnover rates. Nitrogen per unit leaf area decreased with leaf age only for Urera. Leaf mass per unit area increased with leaf age, either partly (in Cecropia) or entirely (in Urera) due to ash accumulation.