Physiological costs of combating chemical toxicants: ecological implications.

1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabolically costly. 2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link. 3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.     

Physiological and pharmacological properties of adenosine: therapeutic implications

Adenosine is a nucleoside which has been shown to participate in the regulation of physiological activity in a variety of mammalian tissues, and has been recognized as a homeostatic neuromodulator. It exerts its actions via membrane-bound receptors which have been characterized using biochemical, electrophysiological and radioligand binding techniques. Adenosine has been implicated in the pharmacological actions of several classes of drugs. A number of studies strongly suggest that the nucleoside may regulate cellular activity in many pathological disorders and, in that respect, adenosine derivatives appear as promising candidates for the development of new therapeutic compounds, such as anticonvulsant, anti-ischemic, analgesic and neuroprotective agents.     

Physiological variation in insects: hierarchical levels and implications

Variation, and in particular regular pattern in that variation, forms the foundation for evolutionary physiology. Nonetheless, with the exception of seemingly good fits between the tolerances of animals and the environments they live in, this variation is often not well explored. Here, three examples of different forms of such variation (both large- and small-scale) in a range of physiological traits in insects are explored. In the first example, I show that at global, regional, and local scales, variation in insect upper lethal temperatures is far less variable than variation in lower lethal temperatures, and that upper and lower tolerances are partially decoupled. Second, I demonstrate that variation in upper and lower lethal limits, desiccation resistance and tolerance, and respiration rate are often partitioned at taxonomic levels above that of the species. In other words, there is considerable phylogenetic constraint in the evolution of the responses of insects to the environment. These findings suggest that several ideas regarding insect physiological adaptations might have to be re-examined. They also suggest that approaches using both "raw" and corrected data should be adopted where possible. Finally, I demonstrate that there is considerable intra-individual variation in the characteristics of insect discontinuous gas exchange cycles. This is perhaps well-known to researchers in the field, but the implications thereof for arguments in favour of the adaptive nature of these regular cycles have not been carefully examined. Together, these findings suggest that there is still much to be learned about variation in insect physiological traits.     

Drosophila: sentinels of environmental toxicants

Synthetic insecticides have been used intensively for the past50 years in many parts of the world. Insect populations, bothtarget and nontarget, have responded by evolving resistance.One of the nontarget insects is Drosophila melanogaster, whichis well-suited for genetic analysis and has been particularlywell-studied in both laboratory and field populations. Resistanceto several insecticides, including two for which significantresistance in field populations has not been found, has beengenerated in susceptible laboratory strains following mutagenesis,allowing comprehensive study of the resistance genes. Fieldpopulations of D. melanogaster have evolved resistance to many,but not all, insecticides in use today. Both the genetic andbiochemical mechanisms that underlie resistance in this insectare similar to those in other insects. Therefore, D. melanogastercan be a sentinel organism for long-term release of toxicantsinto the environment. While it remains useful for genetic analysisof resistance, a better understanding of the movement and populationstructures of this insect will be a prerequisite for its sentinelutilization at specific locales.     

Physiological implications of K accumulation in heart muscle

K+-selective microelectrodes in conjugation with the voltage clamp technique were used to examine the voltage and time dependence of K+ efflux and accumulation in cardiac muscle. K+ efflux per action potential is about 10 to 30 pmoles/cm2 per sec. Accumulation of K+ in the paracellular space plays an important role in regulation of action potential duration, so that the [K+]o prior to generation of an action potential determines the duration of following action potential. This regulation is brought about by the shift of inward rectifying K+ current along the voltage axis, so at higher [K+]o there is more outward current at plateau potentials. Monitoring [K+]o after a period of rapid beating provides quantitative data regarding Na-pump activity. The data suggest the Na-pump is electrogenic, making it difficult to assess the extent of K+ accumulation from the measurements of resting potential alone. These studies indicate that changes in [K+]o not only reflect outward membrane currents and Na-pump activity, but also play an important physiological regulatory role in determining the duration of the action potential.     

Physiological and developmental implications of motor unit anatomy

There is increasing evidence that the architectural design and arrangement of the fibers within a motor unit have important physiological and developmental ramifications. Limited data, however, are available to directly address this issue. In the present study the physiological properties of one motor unit in each of seven cat tibialis anterior (TA) muscles were determined. Each of these units then was repetitively stimulated to deplete the glycogen in all muscle fibers within the unit. Subsequently, the length, type of ending, and spatial distribution of fibers sampled from these physiologically and histochemically typed motor units were determined. Four fast fatigable (FF), one fast, fatigue resistant (FR), and two slow (S) motor units (MU) were studied. The samples consisted of all those glycogen-depleted fibers (9-27) contained within a single fascicle or a circumscribed area of each of the motor unit territories. The mean fiber lengths for the two slow motor units were 35.9 and 45.5 mm. The mean fiber lengths for the fast motor unit samples ranged from 8.8 to 48.5 mm. Some fibers of both the fast and slow units reached lengths of 58 mm. Most of the fibers in the slow units extended the entire distance between the proximal and distal musculotendinous planes, had relatively constant cross-sectional areas, and terminated at the tendon as blunt endings. In contrast, the majority of the fibers in the fast units terminated intrafascicularly at one end, and the cross-sectional area decreased progressively along their lengths, that is, showed a tapering pattern for a significant proportion of their lengths. Therefore, the force generated by units that end midfascicularly would appear to be transmitted to connective tissue elements and/or adjacent fibers. All fibers of a fast unit within a fascicle were located at approximately the same proximo-distal location. Thus, developmentally the selection of muscle fibers by a motoneuron would seem to be influenced by their spatial distribution. The architectural complexities of motor units also have clear implications for the mechanical interactions of active and inactive motor units. For example, the tension capabilities of a motor unit may be influenced not only by the spatial arrangement of its own fibers, but also by the level of activation of neighboring motor units.     

Physiological implications of pair-bond status in greylag geese

In group-living vertebrates, reliable social allies play a decisive role in dealing with stressors. For example, support by social allies is known to dampen glucocorticoid responses. It remains unknown, however, how social embedding affects the sympatho-adrenergic axis as indicated by heart rate (HR) in non-human animals. We studied the relationships between HR, pair-bond status and distance from the pair-partner in twenty-five free-ranging greylag geese (Anser anser) in a natural social environment. In three individuals, we investigated HR responses following partner loss. Overall, we found a context- and sex-dependent difference in HR between paired and unpaired individuals, paired males having a lower HR during agonistic encounters, and unpaired females having a lower HR during resting. Also, in paired females HR increased with increasing distance from the partner. Our data suggest that HR is modulated by pair-bond status in greylag geese in a context- and sex-dependent manner, which may be representative for social vertebrates in general. Despite the low sample size, the present study indicates that proper social embedding may optimize an individual's physiological investment in the social domain. This reduces individual energy expenditure and may benefit health and reproductive success.     

Cytophotometric Differentiation Of HIGH Elevation Spruces: Physiological and Ecological Implications

Red and black spruce and their hybrids can be determined by morphological indices; however, the criteria are somewhat subjective and increasingly difficult to use at higher elevations. Although the chromosome number is identical (2n = 24), red spruce has twice as much nuclear DNA (48 pg) than black spruce (24 pg) and thus the species and their hybrids can also be separated by cytophotometry. This is relevant to spruce decline studies because black spruce is much more resistant to high elevation environmental stresses, both natural and anthropogenic. It also has implications for the effect of climatic changes on the composition of high elevation spruce-fir forests because red spruce can outcompete black spruce under more mesic conditions. Four elevation transects sampling spruce on the east and west sides of Mount Washington (New Hampshire) and Camels Hump (Vermont) and a single transect on the southwest side of Whiteface Mountain (New York) were made to investigate the degree of hybridization and introgression between these two species. A positive correlation was found between increased elevation and increased black spruce genes on Mount Washington and Camels Hump. Pure black spruce was found on Mount Washington from 1356 m to 1582 m. No pure black or red spruce was found on Camels Hump although the proportion of red spruce alleles was significantly greater on Camels Hump. All trees sampled at all elevations on Whiteface Mountain were pure red spruce. Thus the proportion of black spruce alleles in high elevation spruce populations decreases from east to west. This closely parallels the increase in spruce decline which increases from east to west.     

苎麻光合生理生态特性研究

以大田栽培的苎麻植株为材料,用TPS-2便携式光合作用测定系统测定自然条件下生长的苎麻叶片的光合气体交换参数,以及光响应曲线和CO2响应曲线,并通过回归和相关法分析探讨净光合速率与主要生理、生态因子间的关系.结果表明:(1)苎麻叶片的净光合速率(Pn)日变化曲线呈现双峰型,2个光合峰高度接近,其净光合速率具有典型的午休"现象;蒸腾速率(Tr)日变化曲线呈现单峰型,其走势与气孔导度(Gs)日变化一致.(2)苎麻叶片光合作用的光饱和点(LSP)为1 568.5μmol?m-2?s-1,光补偿点(LCP)为54.18μmol?m-2?s-1,表观量子效率(AQY)为0.025 8 mol?mol-1;而其CO2补偿点(CCP)、饱和点(CSP)和羧化效率(CE)分别为49.25、1 746.9μmol?mol-1和0.045;因此,苎麻属于喜光性阳生植物,且对强光有一定的耐受能力.(3)苎麻叶片Pn日变化的主要限制因子是胞间CO2浓度(Ci),主要决定生理因子是气孔导度(Gs).     

Physiological and chemical studies on mould proteins

Summary A series of experiments was done to determine the best conditions for the extraction of protein from mould spores (Penicillium roqueforti). These experiments included studies on the influence of the extraction technique, the nature of the extracting fluid, spores glass: beads: extracting fluid ratio, and the time of extraction.Some work was done in fractionating the extractable nitrogenous substances and proteins of the spores. It was found that the extracted nitrogen could be fractionated into 12% dialysable low molecular weight nitrogen compounds and 88% crude protein, the latter was made up of about 40% albumens and 60% globulins.Visiting Research Professor, on scientific leave from National Research Center, Cairo, U.A.R.; Appointment supported by the International Cooperation Administration under the Visiting Research Scientists Program administered by the National Academy of Sciences of the United States of America. The work also was supported in part by grant E-1201 from the National Institutes of Health.     

Physiological and chemical studies on mould proteins

Summary Studies on the growth and protein content of Penicillium roqueforti as influenced by the various physiological and environmental conditions are reported. These studies included the investigation of the influence exerted by the temperature and hydrogen ion concentration as well as the nature and (or) the concentration of the various nutritive constituents on the total mycelial yield, total nitrogen, soluble nitrogen and protein content of the mycelium. A medium that established the optimum conditions for growth and protein synthesis by the organism was formulated. The protein content of the mycelia was found to be more or less constant and was only decreased when the culture conditions were drastic or on a deficiency of certain nutritive elements.Visiting Research Professor, on scientific leave from National Research Center, Cairo, U.A.R.; Appointment supported by the International Cooperation Administration under the Visiting Research Scientists Program administered by The National Academy of Sciences of the United States of America. The work was also supported in part by grant E-1201 from the National Institutes of Health.     

Retinoblastoma protein: combating algal bloom.

The discovery of a homolog of the retinoblastoma protein (Rb) in a single-celled eukaryote--the alga Chlamydomonas--promises new and surprising insights into Rb's function in cell-cycle regulation.     

Physiological phenomenology of neurally-mediated syncope with management implications

Background

Due to lack of efficacy in recent trials, current guidelines for the treatment of neurally-mediated (vasovagal) syncope do not promote cardiac pacemaker implantation. However, the finding of asystole during head-up tilt –induced (pre)syncope may lead to excessive cardioinhibitory syncope diagnosis and treatment with cardiac pacemakers as blood pressure is often discontinuously measured. Furthermore, physicians may be more inclined to implant cardiac pacemakers in older patients. We hypothesized that true cardioinhibitory syncope in which the decrease in heart rate precedes the fall in blood pressure is a very rare finding which might explain the lack of efficacy of pacemakers in neurally-mediated syncope.

Methods

We studied 173 consecutive patients referred for unexplained syncope (114 women, 59 men, 42±1 years, 17±2 syncopal episodes). All had experienced (pre)syncope during head-up tilt testing followed by additional lower body negative suction. We classified hemodynamic responses according to the modified Vasovagal Syncope International Study (VASIS) classification as mixed response (VASIS I), cardioinhibitory without (VASIS IIa) or with asystole (VASIS IIb), and vasodepressor (VASIS III). Then, we defined the exact temporal relationship between hypotension and bradycardia to identify patients with true cardioinhibitory syncope.

Results

Of the (pre)syncopal events during tilt testing, 63% were classified as VASIS I, 6% as VASIS IIb, 2% as VASIS IIa, and 29% as VASIS III. Cardioinhibitory responses (VASIS class II) progressively decreased from the youngest to the oldest age quartile. With more detailed temporal analysis, blood pressure reduction preceded the heart-rate decrease in all but six individuals (97%) overall and in 10 out of 11 patients with asystole (VASIS IIb).

Conclusions

Hypotension precedes bradycardia onset during head-up tilt-induced (pre)syncope in the vast majority of patients, even in those classified as cardioinhibitory syncope according to the modified VASIS classification. Furthermore, cardioinhibitory syncope becomes less frequent with increasing age.     

Physiological and pathological implications of semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the deamination of primary amines. Such deamination has been shown capable of regulating glucose transport in adipose cells. It has been independently discovered that the primary structure of vascular adhesion protein-1 (VAP-1) is identical to SSAO. VAP-1 regulates leukocyte migration and is related to inflammation. Increased serum SSAO activities have been found in patients with diabetic mellitus, vascular disorders and Alzheimer's disease. The SSAO-catalyzed deamination of endogenous substrates, that is, methylamine and aminoacetone, led to production of toxic formaldehyde and methylglyoxal, hydrogen peroxide and ammonia, respectively. These highly reactive aldehydes have been shown to initiate protein cross-linkage, exacerbate advanced glycation of proteins and cause endothelial injury. Hydrogen peroxide contributes to oxidative stress. 14C-methylamine is converted to 14C-formaldehyde, which then forms labeled long-lasting protein adduct in rodents. Chronic methylamine treatment increased the excretion of malondialdehyde and microalbuminuria, and enhanced the formation of fatty streaks in C57BL/6 mice fed with an atherogenic diet. Treatment with selective SSAO inhibitor reduces atherogenesis in KKAy diabetic mice fed with high-cholesterol diet. Aminoguanidine, which blocks advanced glycation and reduces nephropathy in animals, is in fact more potent at inhibiting SSAO than its effect on glycation. It suggests that SSAO is involved in vascular disorders under certain pathological conditions. Although SSAO has been known for several decades, its physiological and pathological implications are just beginning to be recognized.     

Physiological implications of ultradian oscillations in plant roots

Oscillatory processes are ubiquitous in the Plant Kingdom. Surprisingly, many plant physiologists ignored these as physiologically unimportant unwanted `noise'. Based on the application of the non-invasive ion-selective flux measuring (the MIFE) technique, this paper provides experimental evidence that ultradian oscillations in roots are a widespread phenomenon and reviews some physiological implications of ultradian rhythms in root nutrient acquisition. It is shown that the rhythmical character of root nutrient uptake is a characteristic feature for all measured species (both monocots and dicots; C₃ and C₄ type of photosynthesis). These oscillations were present in all major functional root zones, including root meristem, elongation and mature zone, and root hair region. For the first time, ultradian ion flux oscillations have been reported from the developing root hairs and from vertically grown roots exhibiting circumnutations. Several types of ultradian oscillations were distinguished, including those associated with extension growth of root tissues, more slow oscillations associated with either root circumnutation or nutrient acquisition in the mature zone, and rhythmical fluctuation in nutrient acquisition, associated with root adaptive responses to environmental stresses. Some underlying ionic mechanisms are discussed. Overall, these results show a crucial role of the rhythmical membrane-transport processes in plant–soil environmental interaction.     

Tolerance of switchgrass to extreme soil moisture stress: Ecological implications

Switchgrass (Panicum virgatum L.), a native of eastern and central North America, is a leading candidate as a dedicated biofuel feedstock in the US due to its broad adaptability, rapid growth rate, and ability to grow in low production soils. To begin to characterize the important agronomic and ecological traits related to environmental tolerance of switchgrass, we evaluated fitness under stressful growing conditions. We assessed the germination, establishment, performance, and reproductive potential of four common accessions, both upland and lowland ecotypes, at various levels of soil moisture availability (moisture deficit to flooded) in the greenhouse. Seeds emerged and established (55–90% survival) under all soil moisture conditions (−0.3 MPa to flooded). Transplants of lowland ecotypes performed as well in flooded conditions as in field capacity controls, though flooding reduced performance of upland ecotypes. Drought treatments (−4.0 and −11.0 MPa) reduced tiller length and number, leaf area, and biomass production by up to 80%. However, once established, all plants survived at −4.0 MPa and had the same proportion of tillers in flower as at field capacity. The ability of switchgrass to germinate, establish, and flower in low moisture and flooded conditions, particularly lowland ecotypes, may increase the range of environments suitable for biofuel cultivation, and can serve as a baseline for further ecological studies and genetic improvement.     

Ecological plasticity by morphological design reduces costs of subordination: influence on species distribution

We studied the feeding behaviour of two subordinate tit species (Parus spp.) in two competitive contexts: feeding solitarily versus feeding in the presence of the dominant great tit. Considering ecological plasticity as the within-species component of mean behavioural performance associated with different morphologies in different species, we test the hypothesis that subordinate species with morphological designs allowing a greater ecological plasticity (e.g. blue tit whose hindlimb morphology is modified for greater leg flexion) may gain an advantage against subordinate species with a less plastic design (e.g. crested tit whose hindlimb morphology is modified for aid in leg extension) in a competitive context. Our results demonstrate that the blue tit has greater foraging abilities than the crested tit, as the former is able to modify its feeding behaviour in the presence of the dominant great tit significantly more than the crested tit. In light of these results we propose that some subordinate species can take advantage of their greater ecological plasticity against another less plastic, subordinate species, suggesting that ecological plasticity due to morphological design is a way of reducing costs of subordination as well as a novel, alternative mechanism explaining species distribution.     

Physiological and Ecological Correlates of Preferred Temperature in Fish

Fishes released from constraints of their previous thermal historytend to limit thermal exposure to a narrow range of temperatures.Thermoregulatory behavior (final preferendum) is a stable characteristicof each species studied, suggesting strong regulation by naturalselection. However, the adaptive significance of the final preferendumhas not been documented for most species. Species with widegeographic distributions, such as bluegill sunfish and largemouthbass exhibit constant laboratory final preferenda regardlessof their geographic origin or thermal histories. This apparentevolutionary anomaly of the final preferendum requires furtherstudy. It is no longer adequate to describe responses of fishto thermal gradients, rather falsifiable hypotheses concerningadaptive relations between thermoselection, and physiological,biochemical, life-history and genetic correlates must be developedand tested experimentally.