Central Exendin‐4 Infusion Reduces Body Weight without Altering Plasma Leptin in (fa/fa) Zucker Rats

Objective: To investigate whether chronic administration of the long‐acting glucagon‐like peptide‐1 receptor agonist exendin‐4 can elicit sustained reductions in food intake and body weight and whether its actions require an intact leptin system. Research Methods and Procedures: Male lean and obese Zucker (fa/fa) rats were infused intracerebroventricularly with exendin‐4 using osmotic minipumps for 8 days. Results: Exendin‐4 reduced body weight in both lean and obese Zucker rats, maximum suppression being reached on Day 5 in obese (8%) and Day 7 in lean (16%) rats. However, epididymal white adipose tissue weight was not reduced, and only in lean rats was there a reduction in plasma leptin concentration. Food intake was maximally suppressed (by 81%) on Day 3 in obese rats but was reduced by only 18% on Day 8. Similarly, in lean rats food intake was maximally reduced (by 93%) on Day 4 of treatment and by 45% on Day 8. Brown adipose tissue temperature was reduced from Days 2 to 4. Plasma corticosterone was elevated by 76% in lean but by only 28% in obese rats. Discussion: Chronic exendin‐4 treatment reduced body weight in both obese and lean Zucker rats by reducing food intake: metabolic rate was apparently suppressed. These effects did not require an intact leptin system. Neither does the absence of an intact leptin system sensitize animals to exendin‐4. Partial tolerance to the anorectic effect of exendin‐4 in lean rats may have been due to elevated plasma corticosterone and depressed plasma leptin levels, but other counter‐regulatory mechanisms seem to play a role in obese Zucker rats.     

盾负泥虫的食性研究

鸣跖草Ｃｏｍｍｅｌｉｎａ ｃｏｍｍｕｎｉｓ Ｌ．是顽固性杂草。质负泥虫Ｌｅｍａ ｓｃｕｔｅｌｌａｒｉｓ １年发生１代,以成虫滞育。用与鸭跖草同科及近缘科、属的植物对其食性进行测定,结果发现其食性单一,只取食鸭跖草,质负泥虫的发生期与鸭跖草的苗期同步,幼虫的喜食与鸭跖草的多分枝特性相吻合,取食营养位与粘液细胞在鸭跖草植株上的分布及细胞的含糖量关系密切。     

生命科学与我国的农业现代化

当前农业的成就显著,但也存在着污染并破坏生态环境、消耗大量矿产能源和资源,以及农产品内在质量常常不佳等问题。在分析国情及上述问题的基础上,提出了我国农业现代化必须要达到的目标为：（１）满足我国人民未来的食物需要;（２）提高农业生产的经济效益;（３）能供应可再生能源和资源,维护及改善生态环境,有利于我国的可持续发展。要达到这些目标,有待生命科学的研究作出重大贡献。农业中的种植业、养殖业和农副产品加工     

昆虫病原斯氏和异小杆线虫对各种非共生微生物的信息反应(英文)

非线虫共生细菌 (Bacillussubtilis ,B .thuringiensis,Pseudomonasfluorescens ,Micromonosporapur purea,Rhizopusdelemar ,Pseudomonasaeruginosa ,Streptomycesvenezuelae ,Streptomycesantibioticus ,Penicilliumcitrnum ,Ganodermalucidum ,Agaricusbisporus,Pleurotusostreatus,Rhizobiumlegumi unosarum和Photobacteriumphosphoreum)的培养液以及其上清液、斜纹夜蛾 (Spodopteralitura)昆虫细胞系用于引诱无菌SteinernemacarpocapsaeA2 4和HeterorhabditisbacteriophoraH0 6发育。上述培养物均未能诱导H .bacteriophoraH0 6发育。虽然P .phosphoreum菌液可致死A2 4线虫 ,但是其上清液可诱导线虫发育。无菌S .carpocapsaeA2 4线虫可利用斜纹夜蛾昆虫细胞繁殖 ,产生下一代感染期线虫。结果进一步说明 ,引诱H .bacteriophoraH0 6发育的化学信息物质比S .carpocapsaeA2 4的专一。     

干旱胁迫对水稻水分利用效率的影响

通过特殊自然干旱胁迫的方法,研究不同干旱胁迫对水稻的水分利用效率（ＷＵＥ）的影响,在一定供水量时,水稻的ＷＵＥ随供水量的增加而下降,但水稻旱种时,却因供水量过低,干旱胁迫严重,ＷＵＥ值为最低。不同品种的水稻ＷＵＥ存在较大的差异,抗旱性强的品种具有较高ＷＵＥ,因此选用具有较高ＷＵＥ的品种,是水稻节水栽培的关键。     

肉碱的生理功能及其应用前景

概述了Ｌ－肉碱的生理功能,及其机能性食品、饲料添加剂、药品方面的应用。     

Optimal pedalling velocity characteristics during maximal and submaximal cycling in humans

The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance.     

Adaptive Host Preference and the Dynamics of Host–Parasitoid Interactions

Models of two independent host populations and a common parasitoid are investigated. The hosts have density-dependent population growth and only interact indirectly by their effects on parasitoid behavior and population dynamics. The parasitoid is assumed to experience a trade-off in its ability to exploit the two hosts. Three alternative types of parasitoid are investigated: (i) fixed generalists whose consumption rates are those that maximize fitness; (ii) “ideal free” parasitoids, which modify their behavior to maximize their rate of finding unparasitized hosts within a generation; and (iii) “evolving” parasitoids, whose capture rates change between generations based on quantitative genetic determination of the relative attack rates on the two hosts. The primary questions addressed are: (1) Do the different types of adaptive processes stabilize or destabilize the population dynamics? (2) Do the adaptive processes tend to equalize or to magnify differences in host densities? The models show that adaptive behavior and evolution frequently destabilize population dynamics and frequently increase the average difference between host densities.     

Foraging strategies and growth inhibition in five daphnids feeding on mixtures of a toxic cyanobacterium and a green alga

1. Laboratory experiments were used to study the feeding, growth and reproduction of five daphnids in mixtures of a toxic cyanobacterium, Microcystis aeruginosa, and a green alga, Scenedesmus acutus. The mixtures included 0%, 20%, 50%, 80% and 100% Microcystis with a total food concentration of 0.5 mg C L^??1 in each treatment. The feeding rate was measured after 1 and 24 h of acclimatization to the mixtures. 2. Toxic Microcystis inhibited feeding in all the species, but they exhibited an unexpected diversity and complexity in the pattern of feeding inhibition. Daphnia magna exhibited the strongest inhibition of feeding after 1 h of exposure to toxic food, but had substantially recovered after 24 h in the same mixtures. This pattern of inhibition and recovery may balance the benefits of reduced ingestion of toxin with the disadvantage of a reduced energy intake. 3. All five daphnids grew quickly in the Scenedesmus control, whereas growth and reproduction declined with an increasing proportion of the toxic alga in the diet. Daphnia pulicaria showed the least inhibition of growth and reproduction, D. pulex showed the strongest inhibition and the three remaining species exhibited intermediate sensitivity. 4. Estimates of gross growth efficiency (GGE; growth/ingestion) provided a means for discriminating between the effects of feeding inhibition and direct toxicity on zooplankton growth. Daphnia pulex exhibited a sharp decline in GGE, suggesting that growth inhibition was a result of both feeding inhibition and direct toxicity. In contrast, D. magna exhibited a nearly constant GGE, indicating that feeding inhibition accounted for its decline in growth. However, two Daphnia species (i.e. D. pulicaria and D. galeata) exhibited improbable increases in GGE with toxic cyanobacteria, suggesting that their feeding rates were underestimated. Growth assays with sensitive and resistant zooplankton species are proposed for testing the potential impacts toxic cyanobacteria in lakes.