Angiotensin II acutely attenuates range of arterial baroreflex control of renal sympathetic nerve activity

Acutely increasing peripheral angiotensin II (ANG II) reduces the maximum renal sympathetic nerve activity (RSNA) observed at low mean arterial blood pressures (MAPs). We postulated that this observation could be explained by the action of ANG II to acutely increase arterial blood pressure or increase circulating arginine vasopressin (AVP). Sustained increases in MAP and increases in circulating AVP have previously been shown to attenuate maximum RSNA at low MAP. In conscious rabbits pretreated with an AVP V1 receptor antagonist, we compared the effect of a 5-min intravenous infusion of ANG II (10 and 20 ng x kg(-1) x min(-1)) on the relationship between MAP and RSNA when the acute pressor action of ANG II was left unopposed with that when the acute pressor action of ANG II was opposed by a simultaneous infusion of sodium nitroprusside (SNP). Intravenous infusion of ANG II resulted in a dose-related attenuation of the maximum RSNA observed at low MAP. When the acute pressor action of ANG II was prevented by SNP, maximum RSNA at low MAP was attenuated, similar to that observed when ANG II acutely increased MAP. In contrast, intravertebral infusion of ANG II attenuated maximum RSNA at low MAP significantly more than when administered intravenously. The results of this study suggest that ANG II may act within the central nervous system to acutely attenuate the maximum RSNA observed at low MAP.     

短期物理应激对云芝菌丝体SOD活性的影响

选取高低温分别胁迫、协同胁迫以及超声波处理等方式研究了短期物理应激对云芝菌丝体超氧化物歧化酶（SOD）活性的影响。与未作胁迫处理的对照相比,在低温处理中,10℃较之15℃处理SOD活性整体水平有明显提高,10℃处理2h可使SOD活性提高36.2%,延长处理时间导致SOD活性下降;高温协迫中30℃处理效果优于40℃、50℃和60℃,30℃处理4h,SOD相对酶活可提高至26.8%,延长处理时间和提高处理温度均导致SOD活性下降。高低温协同作用L16(2×42)正交试验结果分析表明,30℃处理2h后10℃处理     

Diphtheria toxin entry into cells is facilitated by low pH

At neutral pH, NH4Cl and chloroquine protected cells against diphtheria toxin. A brief exposure of the cells to low pH (4.5-5.5) at 37 degrees completely abolished this protection. When, to cells preincubated with diphtheria toxin and NH4Cl, neutralizing amounts of anti-diphtheria toxin were added before the pH was lowered, the toxic effect was considerably reduced, but it was not completely abolished. A much stronger toxic effect was seen when antibodies were added immediately after incubation at low pH. Upon a short incubation with diphtheria toxin at low pH, the rate of protein synthesis in the cells decreased much faster than when the normal pH was maintained. The data suggest that, at low pH, diphtheria toxin (or its A fragment) penetrates directly through the surface membrane of the cell. The possibility is discussed that, when the medium has a neutral pH, the entry of diphtheria toxin involves adsorptive endocytosis and reduction of the pH in the vesicles possibly by fusion with lysosomes. Low pH did not facilitate the entry of the closely related toxins abrin, ricin, and modeccin.     

The effect of energy reserves and food availability on optimal immune defence

In order to avoid both starvation and disease, animals must allocate resources between energy reserves and immune defence. We investigate the optimal allocation. We find that animals with low reserves choose to allocate less to defence than animals with higher reserves because when reserves are low it is more important to increase reserves to reduce the risk of starvation in the future. In general, investment in immune defence increases monotonically with energy reserves. An exception is when the animal can reduce its probability of death from disease by reducing its foraging rate. In this case, allocation to immune defence can peak at intermediate reserves. When food changes over time, the optimal response depends on the frequency of changes. If the environment is relatively stable, animals forage most intensively when the food is scarce and invest more in immune defence when the food is abundant than when it is scarce. If the environment changes quickly, animals forage at low intensity when the food is scarce, but at high intensity when the food is abundant. As the rate of environmental change increases, immune defence becomes less dependent on food availability. We show that the strength of selection on reserve-dependent immune defence depends on how foraging intensity and immune defence determine the probability of death from disease.     

The efficiency of C(4) photosynthesis under low light conditions: assumptions and calculations with CO(2) isotope discrimination

Leakiness (Φ), the proportion of carbon fixed by phosphoenolpyruvate carboxylation that leaks out of the bundle-sheath cells, determines C(4) photosynthetic efficiency. Large increases in Φ have been described at low irradiance. The underlying mechanisms for this increase remain uncertain, but changes in photorespiration or the energy partitioning between the C(4) and C(3) cycles have been suggested. Additionally, values of Φ at low light could be magnified from assumptions made when comparing measured photosynthetic discrimination against (13)C (Δ) with the theoretical formulation for Δ. For example, several simplifications are often made when modelling Δ to predict Φ including: (i) negligible fractionation during photorespiration and dark respiration; (ii) infinite mesophyll conductance; and (iii) CO(2) inside bundle-sheath cells (C(s)) is much larger than values in mesophyll cells (C(m)). Theoretical models for C(4) photosynthesis and C(4) Δ were combined to evaluate how these simplifications affect calculations of Δ and Φ at different light intensities. It was demonstrated that the effects of photorespiratory fractionations and mesophyll conductance were negligible at low light. Respiratory fractionation was relevant only when the magnitude of the fractionation factor was artificially increased during measurements. The largest error in estimating Φ occurred when assuming C(s) was much larger than C(m) at low light levels, when bundle-sheath conductance was large (g(s)), or at low O(2) concentrations. Under these conditions, the simplified equation for Δ overestimated Φ, and compromised comparisons between species with different g(s), and comparisons across O(2) concentrations.     

Sibling cannibalism in the ladybird beetleHarmonia axyridis: Fitness consequences for mother and offspring

The adaptive significance of sibling cannibalism was analyzed in the ladybird beetle Harmonia axyridis at two prey densities. Possible costs and benefits were considered from three points of view: the mother, the cannibal and the victim. Cannibals ate both infertile and fertile eggs, thereby increasing in body length and survival rate with the intensity of sibling cannibalism. The cannibalistic trait was clearly beneficial to the cannibal when aphid density was low. However, it was not always beneficial when aphid density was high and the victims were full siblings. The altruistic behavior of being a victim was beneficial only when the victim was cannibalized by full siblings at low aphid density. The mother attained almost equal fitness at low aphid density, regardless of the intensity of sibling cannibalism. This suggests that sibling cannibalism is not maladaptive for the mother. At high aphid density, however, mother's fitness decreased with the intensity of sibling cannibalism, indicating that sibling cannibalism is maladaptive for the mother when larval food availability is high.     

Chorusing Behaviour in the Lusitanian Toadfish: Should I Match My Neighbours' Calling Rate?

Choruses have been described mostly in birds, anurans and insects but have been poorly studied in fish. Research in batrachoidid (toadfishes) species suggest vocal facilitation among neighbouring males, but whether chorusing fish present more complex interactions is unknown. In this study, we test the hypothesis that chorusing fish males compete actively to increase attractiveness to females. We first describe vocal interactions in natural choruses of Lusitanian toadfish males. Our analysis found positive correlations between the calling rates of neighbouring males in several occasions. However, we also found that males that showed an overall low vocal activity throughout the observation period exhibited peaks of increased calling activity when neighbours decreased their calling rate, suggesting an opportunistic maximisation of attractiveness. We further test with playback experiments how toadfish males adjust calling activity relative to their neighbours'. We observed that males silent at the time of the playbacks but who had an overall high vocal performance tended to start calling when exposed to playbacks in contrast to low‐activity males. Playback experiments further showed that males initially calling at a high rate adjust their calling rate according to the neighbour's vocal activity level, that is, they increased calling rate when exposed to a high calling rate and decreased it when confronted with a low calling rate. However, males calling at a low rate did not significantly alter their calling rate when presented with a low (similar) or higher calling rate, probably due to temporary physiological and/or ecological constraints. We argue that Lusitanian toadfish males tend to optimise calling effort in relation to their neighbours when they are actively advertising. Further studies are necessary to better understand vocal behaviour with increased chorus size.     

Evidence for a ferryl Fea3 in oxygenated cytochrome c oxidase

Evidence is reported which shows that a reactive ferryl Fea3/cupric CuB binuclear couple is present at the dioxygen reduction site in "oxygenated" cytochrome c oxidase; when the fully reduced enzyme is reoxidized at low temperatures; and when partially reduced cytochrome c oxidase is reoxidized with dioxygen at room temperature.     

Diurnal periodicity of uridine uptake by Hymenolepis diminuta

A diurnal pattern in the uptake of uridine was displayed by the rat cestode Hymenolepis diminuta. No periodicity in the uptake of uracil was observed over a 48-hr period. A high level of uridine uptake occurred at 6 PM. when 10-day-old worms were in a posterior location in the intestine of rats maintained on a 6 PM.-6 AM. dark cycle-feeding regime, while low levels of uptake were correlated with an anteriad location at 6 AM. The lowest levels of uridine uptake were recorded at noon. Coincubation with thymine caused a stimulation of uridine uptake at midnight, 6 AM., and noon when uridine's transport rate in the absence of thymine was low. Stimulation was not demonstrable when uridine's transport rate was at its highest at 6 PM. Preincubation with uridine did not alter the diurnal uridine uptake pattern. This diurnal phenomenon is an important consideration essential to future studies on transport in parasitic and other organisms.     

The role of abscisic acid and low temperature in chickpea (Cicer arietinum) cold tolerance. II. Effects on plasma membrane structure and function

The frost hardiness of many plants such as chickpea can be increased by exposure to low non-freezing temperatures and/or the application of abscisic acid (ABA), a process known as frost acclimation. Experiments were conducted to study the response over a 14 d period of enriched plasma membrane fractions isolated from chickpea plants exposed to low temperature and sprayed with exogenous ABA. Measurement of the temperatures inducing 50% foliar cell death (LT50), and subsequent statistical analysis suggest that, like many plants, exposure to low temperatures (5/-2 degrees C; day/night) induces a significant level (P <0.05) of frost acclimation in chickpea when compared with control plants (20/7 degrees C; day/night). Spraying plants with exogenous ABA also increased frost tolerance (P <0.05), but was not as effective as low temperature-induced frost acclimation. Both pre-exposure to low temperatures and pre-treatment with ABA increased the levels of fatty acid desaturation in the plasma membrane (measured as the double bond index, DBI). Exposure of chickpea plants to low temperatures increased the DBI by 15% at day 4 and 19% at day 14 when compared with untreated control plants. Application of ABA alone did not increase the DBI by more than 6% at any time; the effects of both treatments applied together was more than additive, inducing a DBI increase of 27% at day 14 when compared with controls. There was a good correlation (P <0.05) between the DBI and LT50, suggesting that the presence of more unsaturated lipid in the plasma membrane may prevent cell lysis at low temperatures. Both pre-exposure to low, non-freezing temperatures and pre-treatment with ABA induced measurable changes in membrane fluidity, but these changes did not correlate with changes in LT50, suggesting that physical properties of the plasma membrane other than fluidity are involved in frost acclimation in chickpea.     

SUN-SHADE ECOTYPES OF A BLUEGREEN ALGA IN A HOT SPRING1,2

Clone cultures of the thermophilic alga Plectonema notatum Schmidle were established from cells collected from the high and low light intensity regions of the algal mat which developed in Jerry Johnson Hot Spring, Idaho. Clones isolated from cither high, or low light intensify zones were grown at light intensities of 8000 and 400 ft-c. The existence of specialized and genetically fixed sun or shade ecotypes was evidenced, by the ability of low light intensity clones to synthesize more light harvesting chlorophyll a when grown under low light conditions than the high light clones. High light clones showed light saturation of photosynthesis at higher light intensities with higher carboxylating enzyme activities and less chlorophyll a than low light clones when both were cultured at 8000 ft-c. These clones displayed infraspecific variation along the light intensity gradient and therefore exist as a mosaic of light, intensity ecotypes.     

Group-specific quantification of methanotrophs in landfill gas-purged laboratory biofilters by tyramide signal amplification-fluorescence in situ hybridization

The aim of this study was to quantitatively analyse methanotrophs in two laboratory landfill biofilters at different biofilter depths and at temperatures which mimicked the boreal climatic conditions. Both biofilters were dominated by type I methanotrophs. The biofilter depth profiles showed that type I methanotrophs occurred in the upper layer, where relatively high O(2) and low CH(4) concentrations were present, whereas type II methanotrophs were mostly distributed in the zone with high CH(4) and low O(2) concentrations. The number of type I methanotrophic cells declined when the temperature was raised from 15 degrees C to 23 degrees C, but increased when lowered to 5 degrees C. A slight decrease in type II methanotrophs was also observed when the temperature was raised from 15 degrees C to 23 degrees C, whereas cell numbers remained constant when lowered to 5 degrees C. The results indicated that low temperature conditions favored both type I and type II methanotrophs in the biofilters.     

Coding the differently directed behavioral actions by the putamen neurons of the monkey brain

Spike activity related to the problem of alternative choice of behavioral actions was recorded in the putamen of the monkey brain. The patterns of low and high activities were identified. Each neuron during different behaviour actions could generate any kind of patterns. The differences between neuronal compositions with patterns of high activity, at the left and right direction of the task, were obtained during decision making about the movement direction, and also at the end of the movement. Distinctions between neuronal compositions with patterns of low activity at this time, on the contrary, diminished. The neuronal compositions with patterns of low activity were much more before the conditioned signal, when the animal did not yet know the task, and at the end of the program when the problem was already solved. The data obtained show that the putamen units control different directions of actions by a multilevel address coding, mainly through reorganizing the neuronal compositions with patterns of different level activity.     

盐胁迫下木麻黄幼苗抗氧化酶活性的变化及Ca2+对它的调控

在单纯NaCl处理下,随着NaCl浓度的加大,木麻黄幼苗的蛋白质含量逐渐升高,超氧化物歧化酶(SOD)活性下降,过氧化物酶(POD)活性则逐渐增加,过氧化氢酶(CAT)活性在低盐下下降,高盐下明显升高.加入适量Ca2 后,SOD活性上升,POD活性和蛋白质含量下降.CAT活性低时加Ca2 ,CAT活性增加;CAT活性高时加Ca2 ,CAT活性则降低.     

The Aetiology of Vascular Discoloration in Cassava Roots after Harvesting: Association with Water Loss from Wounds

When root pieces of cassava, Manihot esculenta Crantz (cv. Yellow Heart or cv. Cuba Sweet), with an area of periderm removed or with a transverse cut uncovered, were held at low humidity and at 22°C, vascular discoloration consistently developed within 2 days. Vascular discoloration was prevented when injured pieces were stored at high humidity or when wounds were covered by a semi-permeable film. When pieces were injured by removal of periderm, at high humidity the respiratory rate was unaltered but at low humidity an increase in respiratory rate occurred after 1 day. When pieces were injured by a transverse cut, at high humidity respiratory rate increased during the first day but decreased thereafter, whereas at low humidity the initial increase was followed by a further increase in respiratory rate after 2 days. It is suggested that vascular discoloration and a respiratory increase may occur in freshly harvested cassava roots as a result of stress produced locally by high rates of water loss at cuts and abrasions.     

Effects of malathion on disease susceptibility in Woodhouse's toads.

Adult male Woodhouse's toads (Bufo woodhousi) developed clinical disease, hepatomegaly, and died at a higher rate when externally exposed once to either a high or low sublethal dose (0.011 or 0.0011 mg malathion/g toad) of field grade malathion and challenged with a sublethal dose of Aeromonas hydrophila injected intraperintoneally (1.1 x 10(4) bacteria/g toad) when compared to toads not exposed to malathion but challenged with A. hydrophila (P < 0.007). Toads exposed to malathion (high or low dose) and challenged with A. hyydrophila had clinical disease, hepatomegaly, and died at a higher rate [9 (90%) of 10] than toads exposed to malathion alone (P < 0.002). Toads exposed to the high and low doses of malathion had a 22% and 17% decrease in brain cholinesterase levels, respectively, when they were compared to nonmalathion exposed toads (P < 0.025, P < 0.006). It appears that field grade malathion applied externally to adult Woodhouse's toads may cause increased disease susceptibility when challenged with a potentially pathogenic bacteria.     

The effects of low pH on egg and alevin survival of kokanee and sockeye salmon, Oncorhynchus nerka

1. The effects of low pH water on embryogenesis and vitellogenesis in kokanee and sockeye salmon (Oncorhynchus nerka) were investigated. Eggs were exposed to low pH from fertilization to 45 days post-median hatch or to an episodic exposure at pH 4.0. Adult kokanee were also exposed to low pH just prior to ovulation and spawning. 2. The most sensitive stages of development during chronic or episodic exposure to low pH were early embryonic development and newly-hatched alevins. 3. Incubation of eggs at low pH caused a lower median survival, delayed hatching, higher alevin mortality and reduced the efficiency of yolk conversion to tissue of yolk-sac alevins. Those effects were more pronounced when the eggs were fertilized at low pH. 4. Exposure of sexually mature kokanee salmon to acidified water reduced egg and alevin survival, delayed embryo hatching and decreased the percent hatch. Those effects were more pronounced when their eggs were incubated at low pH.     

Risks Associated with Predator Immobility,Movement Direction,and Turn Direction Similarly Affect Pursuit‐Deterrent Signaling and Escape by Zebra‐Tailed Lizards (Callisaurus draconoides)

Some prey may signal to deter pursuit by predators. Because deterrence is not needed when risk is low or useful when capture is imminent, most signaling should occur at intermediate risk. Probability of fleeing increases with risk for various risk factors. At low–intermediate risk, more frequent signaling should occur as assessed risk associated with risk factors increases. I examined the effects of three risk factors related to immobility and movement by a predator: standing distance (distance from prey to immobile predator), directions of walking, and turning by the predator. Risk is greater when the predator stands nearer, walks toward prey vs. retreating, and turns toward prey vs. away. In the lizard Callisaurus draconoides, which signals by elevating and waving its tail, signaling was more frequent before fleeing when I stood immobile at the shorter of two distances. All the lizards fled when I walked toward them, regardless of standing distance. Fewer fled when I moved away and only at the shorter standing distance. At the shorter standing distance, signal probability was high and did not differ between movement directions. At the longer standing distance, fewer lizards signaled and only when I moved toward them. Patterns of response of signaling and escape to combinations of standing distance and turn direction were qualitatively identical. When I turned away from lizards, none displayed or fled at the longer standing distance. At the shorter standing distance, probabilities of displaying and fleeing were higher when I turned toward than away from lizards. Standing distance affected signaling interactively with directions of movement and turning in manners readily interpretable from risk. Signaling was affected by risk associated with all factors, being absent or infrequent at both high‐ and low‐risk levels but frequent at intermediate risk, strengthening evidence for pursuit‐deterrent signaling.     

达氏鳇不同发育期胚胎对低温的耐受研究

研究了达氏鳇12个发育期胚胎经过不同低温（2 ℃、3 ℃、5 ℃、7 ℃和8 ℃）处理12 h、24 h、2 d、3 d、6 d、10 d、15 d、20 d和30 d后的孵化率和仔鱼成活率.结果表明,卵黄栓期、隙状胚孔期、神经管闭合期胚胎在2～8 ℃水温下,处理24 h后孵化率为0;卵裂期、囊胚早期、原肠中期胚胎在2～8 ℃水温下,处理3 d后孵化率低于30%;囊胚晚期、原肠早期、眼基期、尾芽期、心跳期和尾达头部期胚胎在5～8 ℃水温下,处理3 d后孵化率、仔鱼成活率超过70%;随低温处理时间延长,胚胎和仔鱼的死亡率增加,处理时间与孵化率、仔鱼成活率呈负相关;囊胚晚期、原肠早期、眼基期胚胎在5 ℃水温下耐受力较强,处理10 d后孵化率、仔鱼成活率超过70%.本研究表明,达氏鳇胚胎发育过程中囊胚晚期、原肠早期和眼基期胚胎可以在某一低温下进行短期保存,其孵化率、仔鱼成活率与常温（16～17 ℃）下没有显著差异.这对于达氏鳇胚胎（受精卵）的长途运输有重要意义.